14642645
BIM-Mediated AKT Phosphorylation Is a Key Modulator of Arsenic Trioxide-Induced Apoptosis in Cisplatin-Sensitive and -Resistant Ovarian Cancer Cells
Background Chemo-resistance to cisplatin-centered cancer therapy is a major obstacle to the effective treatment of human ovarian cancer. Previous reports indicated that arsenic trioxide (ATO) induces cell apoptosis in both drug-sensitive and -resistant ovarian cancer cells. Principal Findings In this study, we determined the molecular mechanism of ATO-induced apoptosis in ovarian cancer cells. Our data demonstrated that ATO induced cell apoptosis by decreasing levels of phosphorylated AKT (p-AKT) and activating caspase-3 and caspase-9. Importantly, BIM played a critical role in ATO-induced apoptosis. The inhibition of BIM expression prevented AKT dephosphorylation and inhibited caspase-3 activation during cell apoptosis. However, surprisingly, gene silencing of AKT or FOXO3A had little effect on BIM expression and phosphorylation. Moreover, the activation of caspase-3 by ATO treatment improved AKT dephosphorylation, not only by cleaving the regulatory A subunit of protein phosphatase 2A (PP2A), but also by increasing its activation. Furthermore, our data indicated that the c-Jun N-terminal kinases (JNK) pathway is involved in the regulation of BIM expression. Conclusions We demonstrated the roles of BIM in ATO-induced apoptosis and the molecular mechanisms of BIM expression regulated by ATO during ovarian cancer cell apoptosis. Our findings suggest that BIM plays an important role in regulating p-AKT by activating caspase-3 and that BIM mediates the level of AKT phosphorylation to determine the threshold for overcoming cisplatin resistance in ovarian cancer cells.
31895029
Current Concepts of Treatment Strategies in Advanced or Recurrent Ovarian Cancer
Ovarian cancer is the fifth most common cause of death from cancer in women. The standard first-line treatment for advanced ovarian cancer is a combination of paclitaxel and carboplatin or carboplatin alone. Sequential single-agent therapy is of particular interest in patients with symptom-free disease progression. Age, performance status and treatment preferences of the respective patient are further decisive factors which should be taken into account when selecting single or combination therapy. Second-line treatment depends, for instance, on the duration of response to first-line platinum therapy, previous treatment regimens used, tolerability, the patient’s performance status and preference of a particular treatment, and cost-effectiveness. If tumor recurrence occurs within 6 months following platinum-based therapy, other agents such as paclitaxel, pegylated liposomal doxorubicin, topotecan or gemcitabine should be used. If the tumor recurs after 6 months, a combination therapy of platinum and paclitaxel has proven to be the most effective. Reasonable options in progressive disease are treatment with platinum, either alone or combined with other agents, especially investigational compounds.
9253403
AKT2 Inhibition of Cisplatin-induced JNK/p38 and Bax Activation by Phosphorylation of ASK1
Cisplatin and its analogues have been widely used for treatment of human cancer. However, most patients eventually develop resistance to treatment through a mechanism that remains obscure. Previously, we found that AKT2 is frequently overexpressed and/or activated in human ovarian and breast cancers. Here we demonstrate that constitutively active AKT2 renders cisplatin-sensitive A2780S ovarian cancer cells resistant to cisplatin, whereas phosphatidylinositol 3-kinase inhibitor or dominant negative AKT2 sensitizes A2780S and cisplatin-resistant A2780CP cells to cisplatin-induced apoptosis through regulation of the ASK1/JNK/p38 pathway. AKT2 interacts with and phosphorylates ASK1 at Ser-83 resulting in inhibition of its kinase activity. Accordingly, activated AKT2 blocked signaling down-stream of ASK1, including activation of JNK and p38 and the conversion of Bax to its active conformation. Expression of nonphosphorylatable ASK1-S83A overrode the AKT2-inhibited JNK/p38 activity and Bax conformational changes, whereas phosphomimic ASK1-S83D inhibited the effects of cisplatin on JNK/p38 and Bax. Cisplatin-induced Bax conformation change was inhibited by inhibitors or dominant negative forms of JNK and p38. In conclusion, our data indicate that AKT2 inhibits cisplatin-induced JNK/p38 and Bax activation through phosphorylation of ASK1 and thus, plays an important role in chemoresistance. Further, regulation of the ASK1/JNK/p38/Bax pathway by AKT2 provides a new mechanism contributing to its antiapoptotic effects.
28317312
High-dose cisplatin therapy in ovarian cancer.
Cisplatin (Platinol) has an important dose-response relationship in ovarian cancer. We have used high-dose cisplatin (40 mg/m2q d X 5) administered in 250 mL 3% saline and 6 L/d of saline hydration in a phase II trial in refractory ovarian cancer patients and together with cyclophosphamide (Cytoxan) (200 mg/m2 qd X 5) in previously untreated advanced ovarian cancer patients. High-dose cisplatin produced a 32% response rate in the phase II trial with a median survival of 12 months for all patients entered in the study and 16 months for responding patients. In previously untreated patients, the preliminary results indicate that intensive treatment with high-dose cisplatin and cyclophosphamide of short duration (3 to 4 months) can produce a high complete remission rate (60%). The dose-limiting toxicity of high-dose cisplatin has been peripheral neuropathy, which limits the number of cycles of high-dose cisplatin that can be administered. Alternative ways to administer higher doses of cisplatin include the use of sodium thiosulfate as a protective agent and the intraperitoneal administration of cisplatin in ovarian cancer patients. These results demonstrate that the cisplatin dose is an important factor in achieving improved results in the treatment of ovarian cancer.
41502815
Arsenic trioxide: new clinical experience with an old medication in hematologic malignancies.
Arsenic trioxide has shown great promise in the treatment of patients with relapsed or refractory acute promyelocytic leukemia (APL). In clinical trials, arsenic trioxide induces complete remission in 87% of patients and molecular remission in 83% of patients. Two-year overall and relapse-free survival estimates are 63% and 49%, respectively. Treatment with arsenic trioxide may be associated with the APL differentiation syndrome, leukocytosis, and electrocardiographic abnormalities. The expanded use of arsenic trioxide in APL for postremission therapy, in conjunction with transplantation, and in patients with newly diagnosed APL is under investigation. The multiple mechanisms of action of arsenic trioxide suggest that it may have antitumor activity in malignancies other than APL and that it may be used in combination with other agents to expand its potential use. This article reviews the clinical use of arsenic trioxide to date and discusses new therapeutic strategies evolving from its diverse biologic activities.
27357070
Arsenic trioxide and cisplatin synergism increase cytotoxicity in human ovarian cancer cells: Therapeutic potential for ovarian cancer
Drug resistance is a major concern in the successful treatment of ovarian cancer. In the present study we report a combinational drug regime using arsenic trioxide (ATO) and cisplatin (CDDP) to increase therapeutic potentiality in ovarian cancer cells. ATO‐mediated growth inhibition and apoptosis in human suspension ovarian cancer COC1 cells were evaluated by MTT assay and annexin V assay using flow cytometry, respectively. cDNA arrays were performed to screen ATO‐mediated gene expression. Treatment of COC1 cells with ATO alone resulted in growth inhibition and apoptosis with a dose‐and time‐dependent fashion; further cDNA arrays showed that 34 genes (23 up‐regulated genes and 11 down‐regulated genes) may strongly associate with the antiproliferative and pro‐apoptotic effects induced by ATO. Furthermore, Chou–Talalay analysis was used to evaluate the combinational effect of ATO and CDDP as well as dose‐reduction index (DRI) in a panel of ovarian cancer cells including CDDP‐sensitive and ‐resistant cell lines. The combination index (CI) analysis indicated that the interaction effect of ATO/CDDP exhibited a wide range of synergism in all the adherent ovarian cancer cells (A2780, IGROV‐1, SKOV‐3, and R182) as well as 0.93 to 0.69 for IC50 to IC90 in suspension COC1 cells where CI < 1, =1, and >1, define synergism, additive effect, and antagonism, respectively. More intriguingly, the combination of ATO and CDDP yielded favorable DRIs ranging from 1.23‐fold to 13.51‐fold dose reduction. These results suggest that ATO and its combination with CDDP present therapeutic potential for ovarian cancer, and deserve further preclinical and clinical studies. (Cancer Sci 2009; 100: 2459–2464)
21805253
Arsenic compounds induce cytotoxicity and apoptosis in cisplatin-sensitive and -resistant gynecological cancer cell lines
Abstract. Purpose: Arsenic compounds have been found to be effective in the treatment of acute promyelocytic leukemia through the downregulation of bcl-2 expression. Resistant ovarian cancer cells often overexpress bcl-2 or p53 proteins or both. We hypothesized that arsenic compounds, such as As2O3 and As2S3, could also be active against gynecological cancers resistant to conventional chemotherapy. Methods: We investigated the effects of these two arsenic compounds in vitro on ovarian cancer cell lines sensitive (OVCAR, GG, JAM) and resistant (CI80-13S) to cisplatin (CDDP) and on human cervical cancer cell lines (HeLa) in comparison with their effects on human fibroblasts (HF). A fluorometric assay based on measurements of fluorescein diacetate (FDA) in cells was used to determine cell viability. Apoptosis was assessed in terms of cell morphology, by flow cytometry and by a DNA fragmentation assay. Results: Treatment of each cell line with the As2O3 or As2S3 led to a marked dose-dependent decrease in cell growth. The IC50 of the two compounds indicated a significantly greater cytotoxic effect against all the cancer cells tested than against the normal HF. At a clinically achievable concentration (2 µM), As2O3 selectively inhibited the growth and induced apoptosis in CI80-13S, OVCAR and HeLa cells but had no significant apoptotic effect on GG or JAM cells or HF. Following treatment with 5 µM As2S3, the CI80-13S, OVCAR and HeLa cells also exhibited growth inhibition and induction of apoptosis. Conclusions: Arsenic compounds (As2O3 and As2S3) can inhibit growth and induce apoptosis in human ovarian and cervical cancer cells at clinically achievable concentrations, indicating that As2O3 and As2S3 could be effective in the treatment of gynecological cancer.
11696307
Arsenic Trioxide inhibits the growth of human ovarian carcinoma cell line.
OBJECTIVE
To determine whether Arsenic Trioxide may be an effective treatment of human ovarian carcinoma, we examined if it induced apoptosis in human ovarian cancer cell line.


METHODS
The human ovarian cell line SKOV3 was exposed to different concentrations of As2O3: 0 (control), 0.1 microM, 1 microM, 5 microM and 10 microM. The effect on cells proliferation and apoptotic parameters was examined.


RESULTS
The most effective inhibitory Arsenic Trioxide concentrations were 5 microM and 10 microM, causing growth inhibition of 79% and 83%, respectively. The maximum inhibitory effect of Arsenic Trioxide on cellular proliferation was seen after 48 h. No morphological or molecular features of apoptosis have been observed. At the same time, there were no typical changes of cellular necrosis.


CONCLUSIONS
The exact mechanism by which Arsenic Trioxide inhibits the growth of ovarian cancer cells is probably not by apoptosis. However, since As2O3 has been shown to inhibit ovarian cancer cellular growth, it should be further elucidated as a possible chemotherapeutic agent of ovarian cancer.
1936809
Arsenic trioxide-mediated cytotoxicity and apoptosis in prostate and ovarian carcinoma cell lines.
We studied the effect of arsenic trioxide (As2O3) on prostate and ovarian carcinoma cell lines. As2O3 has been shown to be effective in leukemia, and acute promyelocytic leukemia in particular, both in vitro and in vivo. As model cell lines, we used DU145 and PC-3 for prostate cancer and MDAH 2774 for ovarian cancer. New modalities of treatment are essential in these kinds of cancers, which produce a high death toll. The 3-(4,5-dimethyl-thiazoyl-2-yl)-2,5-diphenyl-tetrazolium bromide assay was used to evaluate cytotoxicity. Flow cytometric analysis and mono-oligo nucleosome detection-based ELISA were used to determine the apoptosis. Isobologram analysis was used to evaluate synergism and/or the additive effects of As2O3 and conventional chemotherapeutic agents. We clearly demonstrated that As2O3 has significant cytotoxic effect on both prostate and ovarian carcinoma cell lines. The dose range of As2O3 in all three cell lines was approximately 10(-6) M. The mechanism underlying cytotoxicity of As2O3 was shown to be apoptosis. The experiments by butylated hydroxyanisole showed that the cytotoxic effect of As2O3 was not through superoxide generation. There was no synergism, but the additive effects of As2O3 were demonstrated with cisplatin, adriamycin, and etoposide. We strongly suggest that As2O3 alone or in combination with conventional chemotherapeutic agents be evaluated further as a new agent for the treatment of prostate and ovarian cancers.
760741
p53 is a determinant of X-linked inhibitor of apoptosis protein/Akt-mediated chemoresistance in human ovarian cancer cells.
We established previously that X-linked inhibitor of apoptosis protein (Xiap) is a determinant of cisplatin (CDDP) resistance in human ovarian cancer cells and that down-regulation of Xiap sensitizes cells to CDDP in the presence of wild-type p53. Furthermore, Xiap up-regulates the phosphatidylinositol 3'-kinase/Akt pathway by increasing Akt phosphorylation. However, the precise relationships among Xiap, Akt, and p53 in chemoresistance are unknown. Here we show that both Xiap and Akt can modulate CDDP sensitivity individually but that Xiap requires Akt for its full function. Furthermore, dominant-negative Akt sensitizes ovarian cancer cells to CDDP (10 micro M), an effect that is absent in cells expressing mutant p53 or treated with the p53 inhibitor pifithrin-alpha-hydrobromide (30 micro M) but restored by exogenous wild-type p53. CDDP increased p53, decreased Xiap content, and induced apoptosis in OV2008 cells but not in the resistant counterpart (C13*). However, dominant-negative Akt restored all of these characteristics to C13* cells. Expression of a constitutively active Akt2 prevented CDDP-mediated down-regulation of Xiap and apoptosis in A2780s cells. Akt2-mediated chemoresistance could not be reversed by Xiap down-regulation. These results suggest that whereas Xiap, Akt2, and p53 are important mediators of chemoresistance in ovarian cancer cells, Akt2 may be an important regulator of both Xiap and p53 contents after CDDP challenge. Inhibition of Xiap and/or Akt expression/function may be an effective means of overcoming chemoresistance in ovarian cancer cells expressing either endogenous or reconstituted wild-type p53.
25076009
Molecular cloning and identification of a serine/threonine protein kinase of the second-messenger subfamily.
A partial cDNA was isolated that encoded a protein kinase, termed rac (related to the A and C kinases). This cDNA was subsequently used to screen libraries derived from the human cell lines MCF-7 and WI38 and led to the isolation of full-length cDNA clones. DNA sequence analysis identified an open reading frame of 1440 base pairs encoding a protein of 480 amino acids (Mr, 55,716). This result was supported by the synthesis of a Mr 58,000 protein in an in vitro translation system that used RNA transcribed from cloned cDNAs with SP6 RNA polymerase. The predicted protein contains consensus sequences characteristic of a protein kinase catalytic domain and shows 73% and 68% similarity to protein kinase C and the cAMP-dependent protein kinase, respectively. Northern (RNA) analysis revealed a single mRNA transcript of 3.2 kilobases that varied up to 300-fold between different cell lines. Specific antisera directed towards the carboxyl terminal of the rac protein kinase were prepared and used to identify that phosphorylated several substrates in immunoprecipitates prepared with the rac-specific antisera.
18562503
XIAP regulates Akt activity and caspase-3-dependent cleavage during cisplatin-induced apoptosis in human ovarian epithelial cancer cells.
Chemoresistance is a major hurdle for successful cancer therapy. Although multiple mechanisms have been implicated to be involved in cisplatin resistance, recent evidence has suggested that X-linked inhibitor of apoptosis protein (XIAP) may be a key determinant in chemosensitivity in ovarian cancer. Cell fate is determined by a balance between cell survival and apoptotic signaling. Whereas phosphatidylinositol 3-kinase (PI 3-K) and XIAP are believed to be important cell survival factors in human ovarian surface epithelial cancer cells, if and how they interact to confer resistance to chemotherapy is not known. In the present study, we have investigated the role of XIAP in the regulation of the PI 3-K/Akt survival pathway in chemosensitive (A2780-s, OV2008, and OVCAR-3) and resistant (A2780-cp) ovarian cancer cell lines and the nature of this interaction in cell death/survival signaling. Cisplatin decreased XIAP protein levels and induced Akt cleavage and apoptosis in chemosensitive, but not in resistant, ovarian cancer cells. Cisplatin also induced cleavage of caspase-9 and caspase-3, a process blocked by XIAP overexpression. Pretreatment of ovarian cancer cells and their whole cell lysate with tetrapeptide inhibitors of caspases in vitro significantly decreased Akt cleavage induced by cisplatin and exogenous active caspase-3. Adenoviral sense XIAP cDNA expression increased XIAP protein levels and increased Akt phosphorylation, indicative of activation of Akt and, likely, of PI 3-K. This was associated with a decrease in cisplatin-induced apoptosis. In a cell line (OVCAR-3) where basal phosphorylated Akt levels were high, XIAP overexpression failed to increase further the level of this phosphoprotein. XIAP down-regulation induced Akt cleavage and apoptosis, and treatment of whole cell lysate with human recombinant active caspase-3 resulted in a similar pattern of Akt cleavage. In the presence of the PI 3-K inhibitor (LY294002), XIAP overexpression failed to block cisplatin-induced apoptosis and to induce Akt phosphorylation, suggesting that the site of action of XIAP is upstream of Akt in this cell survival pathway. Taken together, the results indicate that XIAP prevents apoptosis through a PI 3-K-dependent inhibition of the caspase cascade. These results demonstrate a novel mechanism by which XIAP regulates apoptosis and the possible involvement of the PI 3-K/Akt survival pathway in XIAP-mediated chemoresistance of ovarian cancer cells.
16634079
Akt-mediated cisplatin resistance in ovarian cancer: modulation of p53 action on caspase-dependent mitochondrial death pathway.
Akt is a determinant of cisplatin [cis-diammine-dichloroplatinum (CDDP)] resistance in ovarian cancer cells, and this may be related to the regulation of p53. Precisely how Akt facilitates CDDP resistance and interacts with p53 is unclear. Apoptotic stimuli induce second mitochondria-derived activator of caspase (Smac) release from mitochondria into the cytosol, where it attenuates inhibitor of apoptosis protein-mediated caspase inhibition. Whereas Smac release is regulated by p53 via the transactivation of proapoptotic Bcl-2 family members, it is unclear whether p53 also facilitates Smac release via its direct mitochondrial activity. Here we show that CDDP induces mitochondrial p53 accumulation, the mitochondrial release of Smac, cytochrome c, and HTR/Omi, and apoptosis in chemosensitive but not in resistant ovarian cancer cells. Smac release was p53 dependent and was required for CDDP-induced apoptosis. Mitochondrial p53 directly induced Smac release. Akt attenuated mitochondrial p53 accumulation and Smac/cytochrome c/Omi release and conferred resistance. Inhibition of Akt facilitated Smac release and sensitized chemoresistant cells to CDDP in a p53-dependent manner. These results suggest that Akt confers resistance, in part, by modulating the direction action of p53 on the caspase-dependent mitochondrial death pathway. Understanding the precise etiology of chemoresistance may improve treatment for ovarian cancer.
14946297
Inhibitors of the Ubiquitin-Proteasome System and the cell death machinery: How many pathways are activated?
Over the past decade, the promising results of UPSIs (UPS inhibitors) in eliciting apoptosis in various cancer cells, and the approval of the first UPSI (Bortezomib/Velcade/PS-341) for the treatment of multiple myeloma have raised interest in assessing the death program activated upon proteasomal blockage. Several reports indicate that UPSIs stimulate apoptosis in malignant cells by operating at multiple levels, possibly by inducing different types of cellular stress. Normally cellular stress signals converge on the core elements of the apoptotic machinery to trigger the cellular demise. In addition to eliciting multiple stresses, UPSIs can directly operate on the core elements of the apoptotic machinery to control their abundance. Alterations in the relative levels of anti and pro-apoptotic factors can render cancer cells more prone to die in response to other anti-cancer treatments. Aim of the present review is to discuss those core elements of the apoptotic machinery that are under the control of the UPS.
14708272
Cisplatin Resistance Inhibition of Glutathione Synthesis Reverses Bcl-2-mediated Updated Version
Cisplatin is a potent cytotoxic agent that functions as a bivalent electrophile, forming both interstrand and intrastrand DNA cross-links. Cisplatin-mediated DNA damage results in cell cycle arrest and initiation of apoptotic cell death. Increased cellular glutathione concentrations have been closely correlated with cisplatin resistance but do not reduce the extent of cisplatin-DNA adduct formation. One hypothesis to explain the ability of glutathione to inhibit cisplatin cytotoxicity is that glutathione, through its antioxidant function, plays a role in apoptotic regulatory pathways. We tested this hypothesis using MCF-7 breast cancer cells transfected with the apoptotic inhibitor Bcl-2. Bcl-2 overexpression in MCF-7 cells was associated with a nearly 3-fold increase in cellular glutathione levels and with increased resistance to cell death after cisplatin exposure. Treatment of MCF-7 lines with buthionine sulfoximine, an inhibitor of glutathione synthesis, normalized glutathione levels in Bcl-2 and control transfectants and completely abrogated Bcl-2-mediated cisplatin resistance without affecting Bcl-2 expression. Bcl-2 overexpression and up-regulation of glutathione were not associated with a change in either cisplatin-DNA adduct formation or repair over time. These results suggest that Bcl-2-mediated cisplatin resistance in MCF-7 cells is dependent on up-regulation of glutathione production, which contributes to cell survival by mechanisms independent of cisplatin inactivation or inhibition of DNA adduct formation. A similar dependence on glutathione for Bcl2-mediated inhibition of cisplatin toxicity was confirmed in a second cell line, the lymphocytic precursor FL5.12. Taken together, these data suggest that apoptotic signaling after genotoxic exposure can be inhibited by the antioxidant activity of glutathione. Inhibition of glutathione synthesis or modulation of glutathione stores in tumors that overexpress Bcl-2 may comprise a novel anticancer strategy.
25655463
Expression of Bcl-xL in ovarian carcinoma is associated with chemoresistance and recurrent disease.
OBJECTIVE
The long-term survival of patients with epithelial ovarian cancer is limited by the emergence of tumor cells that are resistant to chemotherapy. We hypothesized that expression of Bcl-x(L), a homologue of Bcl-2 that confers protection from chemotherapy-induced apoptosis, may be predictive of patients' clinical response to treatment, and that treatment with chemotherapy may result in the selection of tumor cells that overexpress this protein.


METHODS
We determined the expression of Bcl-x(L) in epithelial ovarian cancers from 28 patients at the time of initial staging laparotomy and in recurrent tumors in the same patients following treatment with platinum-based chemotherapy. The data were analyzed to determine whether Bcl-x(L) expression was predictive of clinical outcome. A2780 ovarian cancer cells were stably transfected with Bcl-x(L) or control plasmid. Chemotherapy-induced apoptosis in these cell lines was determined in vitro and in a xenograft model.


RESULTS
Bcl-x(L) expression in primary tumors was associated with a significantly shorter disease-free interval as compared to patients whose tumors did not express Bcl-x(L) (1.6 months as compared to 7.7 months). We found that Bcl-x(L) expression conferred resistance to chemotherapy-induced apoptosis resulting from treatment with cisplatin, paclitaxel, topotecan, and gemcitabine in vitro. In a xenograft model, Bcl-x(L) expressing tumors continued to grow following treatment with cisplatin, paclitaxel, topotecan, and gemcitabine, in contrast to control tumors, which disappeared.


CONCLUSION
These results portray an important role for Bcl-x(L) as a key factor associated with chemotherapy failure in the treatment of ovarian cancer.
43736039
PUMA, a novel proapoptotic gene, is induced by p53.
The p53 tumor-suppressor protein functions as a transcriptional activator, and several p53-inducible genes that play a role in the induction of apoptosis in response to p53 have been described. We have identified a novel gene named PUMA (p53 upregulated modulator of apoptosis) as a target for activation by p53. This gene encodes two BH3 domain-containing proteins (PUMA-alpha and PUMA-beta) that are induced in cells following p53 activation. PUMA-alpha and PUMA-beta show similar activities; they bind to Bcl-2, localize to the mitochondria to induce cytochrome c release, and activate the rapid induction of programmed cell death. Antisense inhibition of PUMA expression reduced the apoptotic response to p53, and PUMA is likely to play a role in mediating p53-induced cell death through the cytochrome c/Apaf-1-dependent pathway.
32271546
Evidence That Ser87 of BimEL Is Phosphorylated by Akt and Regulates BimEL Apoptotic Function*
Bim, the Bcl-2 interacting mediator of cell death, is a member of the BH3-only family of pro-apoptotic proteins. Recent studies have demonstrated that the apoptotic activity of Bim can be regulated through a post-translational mechanism whereby ERK phosphorylation serves as a signal for Bim ubiquitination and proteasomal degradation. In this report, we investigated the signaling pathways leading to Bim phosphorylation in Ba/F3 cells, an interleukin-3 (IL-3)-dependent B-cell line. IL-3 stimulation induced phosphorylation of BimEL, one of the predominant isoforms of Bim expressed in cells, at multiple sites, as evidenced by the formation of at least three to four bands by Western blotting that were sensitive to phosphatase digestion. The appearance of multiple, phosphorylated species of BimEL correlated with Akt, and not ERK, activation. The PI3K inhibitor, LY294002, blocked IL-3-stimulated Akt activity and partially blocked BimEL phosphorylation. In vitro kinase assays showed that recombinant Akt could directly phosphorylate a GST-BimEL fusion protein and identified the Akt phosphorylation site in the BimEL domain as Ser87. Further, we demonstrated that cytokine stimulation promotes BimEL binding to 14-3-3 proteins. Finally, we show that mutation of Ser87 dramatically increases the apoptotic potency of BimEL. We propose that Ser87 of BimEL is an important regulatory site that is targeted by Akt to attenuate the pro-apoptotic function of BimEL, thereby promoting cell survival.
16648832
Bim: a novel member of the Bcl‐2 family that promotes apoptosis
Certain members of the Bcl‐2 family inhibit apoptosis while others facilitate this physiological process of cell death. An expression screen for proteins that bind to Bcl‐2 yielded a small novel protein, denoted Bim, whose only similarity to any known protein is the short (nine amino acid) BH3 motif shared by most Bcl‐2 homologues. Bim provokes apoptosis, and the BH3 region is required for Bcl‐2 binding and for most of its cytotoxicity. Like Bcl‐2, Bim possesses a hydrophobic C‐terminus and localizes to intracytoplasmic membranes. Three Bim isoforms, probably generated by alternative splicing, all induce apoptosis, the shortest being the most potent. Wild‐type Bcl‐2 associates with Bim in vivo and modulates its death function, whereas Bcl‐2 mutants that lack survival function do neither. Significantly, Bcl‐xL and Bcl‐w, the two closest homologues of Bcl‐2, also bind to Bim and inhibit its activity, but more distant viral homologues, adenovirus E1B19K and Epstein–Barr virus BHRF‐1, can do neither. Hence, Bim appears to act as a ‘death ligand’ which can only neutralize certain members of the pro‐survival Bcl‐2 sub‐family.
25788324
The proapoptotic BH3-only protein bim is expressed in hematopoietic, epithelial, neuronal, and germ cells.
Proapoptotic Bcl-2 family members activate cell death by neutralizing their anti-apoptotic relatives, which in turn maintain cell viability by regulating the activation of the cell death effectors, the caspases. Bim belongs to a distinct subgroup of proapoptotic proteins that only resemble other Bcl-2 family members within the short BH3 domain. Gene targeting experiments in mice have shown that Bim is essential for the execution of some but not all apoptotic stimuli, for hematopoietic cell homeostasis, and as a barrier against autoimmunity. There are three Bim isoforms, Bim(S), Bim(L), and Bim(EL), which have different proapoptotic potencies due at least in part to differences in interaction with the dynein motor complex. The expression pattern of Bim was investigated by immunohistochemical staining, immunoprecipitation followed by Western blotting, and in situ hybridization. Bim was found in hematopoietic, epithelial, neuronal, and germ cells. Bim(L) and Bim(EL) were coexpressed at similar levels in many cell types, but Bim(S) was not detected. Microscopic examination revealed a punctate pattern of Bim(L) and Bim(EL) immunostaining, indicating association with cytoplasmic structures. These results are discussed in the context of the phenotype of Bim-deficient mice and the post-translational regulation of Bim's pro-apoptotic activity.
39217074
The proapoptotic activity of the Bcl-2 family member Bim is regulated by interaction with the dynein motor complex.
Bcl-2 family members that have only a single Bcl-2 homology domain, BH3, are potent inducers of apoptosis, and some appear to play a critical role in developmentally programmed cell death. We examined the regulation of the proapoptotic activity of the BH3-only protein Bim. In healthy cells, most Bim molecules were bound to LC8 cytoplasmic dynein light chain and thereby sequestered to the microtubule-associated dynein motor complex. Certain apoptotic stimuli disrupted the interaction between LC8 and the dynein motor complex. This freed Bim to translocate together with LC8 to Bcl-2 and to neutralize its antiapoptotic activity. This process did not require caspase activity and therefore constitutes an initiating event in apoptosis signaling.
13300521
Apoptosis Initiated When BH3 Ligands Engage Multiple Bcl-2 Homologs, Not Bax or Bak
A central issue in the regulation of apoptosis by the Bcl-2 family is whether its BH3-only members initiate apoptosis by directly binding to the essential cell-death mediators Bax and Bak, or whether they can act indirectly, by engaging their pro-survival Bcl-2–like relatives. Contrary to the direct-activation model, we show that Bax and Bak can mediate apoptosis without discernable association with the putative BH3-only activators (Bim, Bid, and Puma), even in cells with no Bim or Bid and reduced Puma. Our results indicate that BH3-only proteins induce apoptosis at least primarily by engaging the multiple pro-survival relatives guarding Bax and Bak.
2776870
Down-regulation of phospho-Akt is a major molecular determinant of bortezomib-induced apoptosis in hepatocellular carcinoma cells.
Bortezomib, a proteasome inhibitor, has been clinically approved for the treatment of myeloma and lymphoma. Here, we report a differential effect of bortezomib on apoptosis in four hepatocellular carcinoma (HCC) cell lines and identify the major molecular event that determines sensitivity. Although bortezomib inhibited proteasome activity to a similar extent in all HCC cell lines, it showed differential effects on their viability: Huh-7 (IC(50) 196 nmol/L), Sk-Hep1 (IC(50) 180 nmol/L), Hep3B (IC(50) 112 nmol/L), and resistant PLC5 (IC(50) >1,000 nmol/L). Bortezomib caused cell cycle arrest at G(2)-M phase in all HCC cells tested whereas apoptotic induction was found only in sensitive cells but not in PLC5 cells. No significant bortezomib-induced NF-kappaB changes were noted in Huh-7 and PLC5. Bortezomib down-regulated phospho-Akt (P-Akt) in a dose- and time-dependent manner in all sensitive HCC cells whereas no alterations of P-Akt were found in PLC5. Down-regulation of Akt1 by small interference RNA overcame the apoptotic resistance to bortezomib in PLC5 cells, but a constitutively activated Akt1 protected Huh-7 cells from bortezomib-induced apoptosis. Furthermore, bortezomib showed suppression of tumor growth with down-regulation of P-Akt in Huh-7 tumors but not in PLC5 tumors. Down-regulation of P-Akt represents a major molecular event of bortezomib-induced apoptosis in HCC cell lines and may be a biomarker for predicting clinical response to HCC treatment. Targeting Akt signaling overcomes drug resistance to bortezomib in HCC cells, which provides a new approach for the combinational therapy of HCC.
40871609
PI3K/Akt and apoptosis: size matters
Recent research has examined Akt and Akt-related serine–threonine kinases in signaling cascades that regulate cell survival and are important in the pathogenesis of degenerative diseases and in cancer. We seek to recapitulate the research that has helped to define the current understanding of the role of the Akt pathway under normal and pathologic conditions, also in view of genetic models of Akt function. In particular, we will evaluate the mechanisms of Akt regulation and the role of Akt substrates in Akt-dependent biologic responses in the decisions of cell death and cell survival. Here, we hope to establish the mechanisms of apoptosis suppression by Akt kinase as a framework for a more general understanding of growth factor-dependent regulation of cell survival.
14506473
Akt Promotes Cell Survival by Phosphorylating and Inhibiting a Forkhead Transcription Factor
Survival factors can suppress apoptosis in a transcription-independent manner by activating the serine/ threonine kinase Akt, which then phosphorylates and inactivates components of the apoptotic machinery, including BAD and Caspase 9. In this study, we demonstrate that Akt also regulates the activity of FKHRL1, a member of the Forkhead family of transcription factors. In the presence of survival factors, Akt phosphorylates FKHRL1, leading to FKHRL1's association with 14-3-3 proteins and FKHRL1's retention in the cytoplasm. Survival factor withdrawal leads to FKHRL1 dephosphorylation, nuclear translocation, and target gene activation. Within the nucleus, FKHRL1 triggers apoptosis most likely by inducing the expression of genes that are critical for cell death, such as the Fas ligand gene.
21386023
Interleukin-3-induced phosphorylation of BAD through the protein kinase Akt.
BAD is a distant member of the Bcl-2 family that promotes cell death. Phosphorylation of BAD prevents this. BAD phosphorylation induced by interleukin-3 (IL-3) was inhibited by specific inhibitors of phosphoinositide 3-kinase (PI 3-kinase). Akt, a survival-promoting serine-threonine protein kinase, was activated by IL-3 in a PI 3-kinase-dependent manner. Active, but not inactive, forms of Akt were found to phosphorylate BAD in vivo and in vitro at the same residues that are phosphorylated in response to IL-3. Thus, the proapoptotic function of BAD is regulated by the PI 3-kinase-Akt pathway.
40630868
Regulation of cell death protease caspase-9 by phosphorylation.
Caspases are intracellular proteases that function as initiators and effectors of apoptosis. The kinase Akt and p21-Ras, an Akt activator, induced phosphorylation of pro-caspase-9 (pro-Casp9) in cells. Cytochrome c-induced proteolytic processing of pro-Casp9 was defective in cytosolic extracts from cells expressing either active Ras or Akt. Akt phosphorylated recombinant Casp9 in vitro on serine-196 and inhibited its protease activity. Mutant pro-Casp9(Ser196Ala) was resistant to Akt-mediated phosphorylation and inhibition in vitro and in cells, resulting in Akt-resistant induction of apoptosis. Thus, caspases can be directly regulated by protein phosphorylation.
9021216
FoxO3a Transcriptional Regulation of Bim Controls Apoptosis in Paclitaxel-treated Breast Cancer Cell Lines*
Paclitaxel is used to treat breast cancers, but the mechanisms by which it induces apoptosis are poorly understood. Consequently, we have studied the role of the FoxO transcription factors in determining cellular response to paclitaxel. Western blotting revealed that in a panel of nine breast cancer cell lines expression of FoxO1a and FoxO3a correlated with the expression of the pro-apoptotic FoxO target Bim, which was associated with paclitaxel-induced apoptosis. In MCF-7 cells, which were paclitaxel-sensitive, the already high basal levels of FoxO3a and Bim protein increased dramatically after drug treatment, as did Bim mRNA, which correlated with apoptosis induction. This was not observed in MDA-231 cells, which expressed low levels of FoxOs and Bim. Gene reporter experiments demonstrated that in MCF-7 cells maximal induction of Bim promoter was dependent on a FoxO binding site, suggesting that FoxO3a is responsible for the transcriptional up-regulation of Bim. Gene silencing experiments showed that small interference RNA (siRNA) specific for FoxO3a reduced the levels of FoxO3a and Bim protein as well as inhibited apoptosis in paclitaxel-treated MCF-7 cells. Furthermore, siRNA specific for Bim reduced the levels of Bim protein and inhibited apoptosis in paclitaxel-treated MCF-7 cells. This is the first demonstration that up-regulation of FoxO3a by paclitaxel can result in increased levels of Bim mRNA and protein, which can be a direct cause of apoptosis in breast cancer cells.
694068
FOXO transcription factors directly activate bim gene expression and promote apoptosis in sympathetic neurons
Developing sympathetic neurons die by apoptosis when deprived of NGF. BIM, a BH3-only member of the BCL-2 family, is induced after NGF withdrawal in these cells and contributes to NGF withdrawal-induced death. Here, we have investigated the involvement of the Forkhead box, class O (FOXO) subfamily of Forkhead transcription factors in the regulation of BIM expression by NGF. We find that overexpression of FOXO transcription factors induces BIM expression and promotes death of sympathetic neurons in a BIM-dependent manner. In addition, we find that FKHRL1 (FOXO3a) directly activates the bim promoter via two conserved FOXO binding sites and that mutation of these sites abolishes bim promoter activation after NGF withdrawal. Finally, we show that FOXO activity contributes to the NGF deprivation-induced death of sympathetic neurons.
9795380
Experimental and theoretical studies on the pharmacodynamics of cisplatin in jurkat cells.
For Jurkat cells in culture exposed to cisplatin (1), we measured the number of platinum adducts on DNA and showed that it is proportional to the AUC, the area under the concentration vs time curve, for cisplatin. The number of platinum-DNA adducts is measured immediately following exposure to drug. The AUC is calculated either as the product of the initial cisplatin concentration and the exposure time or as the integral under the concentration vs time curve for the unreacted dichloro species, which decreases exponentially. We also show that the number of adducts correlates with decreases in respiration, with the amount of DNA fragmentation, and with cell viability, all measured 24 h after exposure to the drug. To study the reactions of cisplatin at concentrations approaching clinical relevance (65 microM), we use two-dimensional [1H15N]HSQC NMR and the 15N-labeled form of the drug, cis-Pt(15NH3)2Cl2, 1. In the absence of cells, 1 reacts with components of the growth medium and also transforms slowly (k(h) = 0.205 h-1 at 37 degrees C) into the chloro-aquo species, cis-[Pt(15NH3)2Cl(H2O)]+ (2), which at the pH of the medium (pH 7.15), is mainly in the deprotonated chloro-hydroxy form, cis-Pt(15NH3)2Cl(OH) (4). The concentration of 2 (4), as measured by HSQC NMR, decreases due to reaction with components of the medium. In the presence of 5 million or more cells, the concentration of 1 decreases with time, but the NMR signal for 2 (4) is not seen because it is rapidly removed from solution by the cells, keeping its concentration very low. These experiments confirm that the species preferentially removed from the medium by cells is 2 (4) and not 1. Our findings are discussed in the context of a kinetic model for platination of nuclear DNA by cisplatin, which includes aquation of cisplatin outside the cell, passage of 2 (4) through the cell membrane, reaction of reactive platinum species (RPS) in the cytosol with thiols, formation of adducts between RPS and accessible sites on genomic DNA, and removal of platinum from DNA by repair. Some of the rate constants involved are measured, but others can only be estimated. Calculations with this model show that little of the platinum reacts with intracellular thiols before reaching the nuclear DNA, indicating that binding to thiols is not important in cisplatin resistance. The model also predicts the circumstances under which the amount of platination of nuclear DNA is proportional to AUC.
206866407
BH3-only proteins Noxa, Bmf, and Bim are necessary for arsenic trioxide-induced cell death in myeloma.
The use of arsenic trioxide (ATO) to treat multiple myeloma (MM) is supported by preclinical studies as well as several phase 2 studies, but the precise mechanism(s) of action of ATO has not been completely elucidated. We used gene expression profiling to determine the regulation of apoptosis-related genes by ATO in 4 MM cell lines and then focused on Bcl-2 family genes. ATO induced up-regulation of 3 proapoptotic BH3-only proteins (Noxa, Bmf, and Puma) and down-regulation of 2 antiapoptotic proteins Mcl-1 and Bcl-X(L). Coimmunoprecipitation demonstrated that Noxa and Puma bind Mcl-1 to release Bak and Bim within 6 hours of ATO addition. Bak and Bim are also released from Bcl-X(L). Silencing of Bmf, Noxa, and Bim significantly protected cells from ATO-induced apoptosis, while Puma silencing had no effect. Consistent with a role for Noxa inhibition of Mcl-1, the Bad-mimetic ABT-737 synergized with ATO in the killing of 2 MM lines. Finally, Noxa expression was enhanced by GSH depletion and inhibited by increasing GSH levels in the cells. Understanding the pattern of BH3-only protein response should aid in the rational design of arsenic-containing regimens.
17945478
Expression of the pro-apoptotic Bcl-2 family member Bim is regulated by the forkhead transcription factor FKHR-L1
Cell death is regulated mainly through an evolutionarily conserved form of cell suicide termed apoptosis [1]. Deregulation of apoptosis has been associated with cancer, autoimmune diseases and degenerative disorders. Many cells, particularly those of the hematopoietic system, have a default program of cell death and survival that is dependent on the constant supply of survival signals. The Bcl-2 family, which has both pro- and anti-apoptotic members, plays a critical role in regulating cell survival [2]. One family member, the Bcl-2 interacting mediator of cell death (Bim), contains only a protein-interaction motif known as the BH3 domain, allowing it to bind pro-survival Bcl-2 molecules, neutralizing their function [3]. Disruption of the bim gene results in resistance to apoptosis following cytokine withdrawal in leukocytes, indicating that regulation of the pro-apoptotic activity of Bim is critical for maintenance of the default apoptotic program [4]. Here, we report that withdrawal of cytokine results in upregulation of Bim expression concomitant with induction of the apoptotic program in lymphocytes. Activation of the forkhead transcription factor FKHR-L1, previously implicated in regulation of apoptosis in T lymphocytes [5], was sufficient to induce Bim expression. We propose a mechanism by which cytokines promote lymphocyte survival by inhibition of FKHR-L1, preventing Bim expression.
23141705
Arsenic trioxide decreases AKT protein in a caspase-dependent manner
Arsenic trioxide (As2O3) is used clinically to treat acute promyelocytic leukemia but is less successful in other malignancies. To identify targets for potential combination therapies, we have begun to characterize signaling pathways leading to As2O3-induced cytotoxicity. Previously, we described the requirement for a reactive oxygen species–mediated, SEK1/c-Jun NH2-terminal kinase (JNK) pathway to induce apoptosis. AKT inhibits several steps in this pathway; therefore, we postulated that As2O3 might decrease its activity. Indeed, As2O3 decreases not only AKT activity but also total AKT protein, and sensitivity to As2O3 correlates with the degree of AKT protein decrease. Decreased AKT expression further correlates with JNK activation and the release of AKT from the JNK-interacting protein 1 scaffold protein known to assemble the mitogen-activated protein kinase cascade. We found that As2O3 regulates AKT protein stability without significant effects on its transcription or translation. We show that As2O3 decreases AKT protein via caspase-mediated degradation, abrogated by caspase-6, caspase-8, caspase-9, and caspase-3 inhibitors but not proteosome inhibitors. Furthermore, As2O3 enhances the ability of a heat shock protein 90 inhibitor to decrease AKT expression and increase growth inhibition. This suggests that As2O3 may be useful in combination therapies that target AKT pathways or in tumors that have constitutively active AKT expression. [Mol Cancer Ther 2008;7(6):1680–7]
230319
SIN1/MIP1 Maintains rictor-mTOR Complex Integrity and Regulates Akt Phosphorylation and Substrate Specificity
Mammalian target of rapamycin (mTOR) controls cell growth and proliferation via the raptor-mTOR (TORC1) and rictor-mTOR (TORC2) protein complexes. Recent biochemical studies suggested that TORC2 is the elusive PDK2 for Akt/PKB Ser473 phosphorylation in the hydrophobic motif. Phosphorylation at Ser473, along with Thr308 of its activation loop, is deemed necessary for Akt function, although the regulatory mechanisms and physiological importance of each phosphorylation site remain to be fully understood. Here, we report that SIN1/MIP1 is an essential TORC2/PDK2 subunit. Genetic ablation of sin1 abolished Akt-Ser473 phosphorylation and disrupted rictor-mTOR interaction but maintained Thr308 phosphorylation. Surprisingly, defective Ser473 phosphorylation affected only a subset of Akt targets in vivo, including FoxO1/3a, while other Akt targets, TSC2 and GSK3, and the TORC1 effectors, S6K and 4E-BP1, were unaffected. Our findings reveal that the SIN1-rictor-mTOR function in Akt-Ser473 phosphorylation is required for TORC2 function in cell survival but is dispensable for TORC1 function.
45837814
Phosphorylation and Regulation of Akt/PKB by the Rictor-mTOR Complex
Deregulation of Akt/protein kinase B (PKB) is implicated in the pathogenesis of cancer and diabetes. Akt/PKB activation requires the phosphorylation of Thr308 in the activation loop by the phosphoinositide-dependent kinase 1 (PDK1) and Ser473 within the carboxyl-terminal hydrophobic motif by an unknown kinase. We show that in Drosophila and human cells the target of rapamycin (TOR) kinase and its associated protein rictor are necessary for Ser473 phosphorylation and that a reduction in rictor or mammalian TOR (mTOR) expression inhibited an Akt/PKB effector. The rictor-mTOR complex directly phosphorylated Akt/PKB on Ser473 in vitro and facilitated Thr308 phosphorylation by PDK1. Rictor-mTOR may serve as a drug target in tumors that have lost the expression of PTEN, a tumor suppressor that opposes Akt/PKB activation.
14414927
TORC-specific phosphorylation of mammalian target of rapamycin (mTOR): phospho-Ser2481 is a marker for intact mTOR signaling complex 2.
The mammalian target of rapamycin (mTOR) serine/threonine kinase is the catalytic component of two evolutionarily conserved signaling complexes. mTOR signaling complex 1 (mTORC1) is a key regulator of growth factor and nutrient signaling. S6 kinase is the best-characterized downstream effector of mTORC1. mTOR signaling complex 2 (mTORC2) has a role in regulating the actin cytoskeleton and activating Akt through S473 phosphorylation. Herein, we show that mTOR is phosphorylated differentially when associated with mTORC1 and mTORC2 and that intact complexes are required for these mTORC-specific mTOR phosphorylations. Specifically, we find that mTORC1 contains mTOR phosphorylated predominantly on S2448, whereas mTORC2 contains mTOR phosphorylated predominantly on S2481. Using S2481 phosphorylation as a marker for mTORC2 sensitivity to rapamycin, we find that mTORC2 formation is in fact rapamycin sensitive in several cancer cell lines in which it had been previously reported that mTORC2 assembly and function were rapamycin insensitive. Thus, phospho-S2481 on mTOR serves as a biomarker for intact mTORC2 and its sensitivity to rapamycin.
748271
JNK-Mediated BIM Phosphorylation Potentiates BAX-Dependent Apoptosis
Trophic factor deprivation (TFD) activates c-Jun N-terminal kinases (JNKs), culminating in coordinate AP1-dependent transactivation of the BH3-only BCL-2 proteins BIM(EL) and HRK, which in turn are critical for BAX-dependent cytochrome c release, caspase activation, and apoptosis. Here, we report that TFD caused not only induction but also phosphorylation of BIM(EL). Mitochondrially localized JNKs but not upstream activators, like mixed-lineage kinases (MLKs) or mitogen-activated protein kinase kinases (MKKs), specifically phosphorylated BIM(EL) at Ser65, potentiating its proapoptotic activity. Inhibition of the JNK pathway attenuated BIM(EL) expression, prevented BIM(EL) phosphorylation, and abrogated TFD-induced apoptosis. Conversely, activation of this pathway promoted BIM(EL) expression and phosphorylation, causing BIM- and BAX-dependent cell death. Thus, JNKs regulate the proapoptotic activity of BIM(EL) during TFD, both transcriptionally and posttranslationally.
25935862
Protein phosphatase 2A-linked and -unlinked caspase-dependent pathways for downregulation of Akt kinase triggered by 4-hydroxynonenal
AbstractWe studied the signal pathways for regulation of serine/threonine protein kinase Akt in Jurkat cells that had been treated with 4-hydroxynonenal (HNE) for caspase-dependent apoptosis induction. Treatment of cells with HNE led to a decrease in the level of Akt activity due to the dephosphorylation at Ser473, a major regulatory phosphorylation site. HNE-mediated dephosphorylation of Akt was prevented by a protein phosphatase 2A (PP2A) inhibitor, okadaic acid, and by a caspase-3 inhibitor, DEVD-CHO. HNE treatment resulted in an increase in the total level of PP2A activity, release of active tyrosine-dephosphorylated PP2A from the cytoskeleton and PP2A-Akt association, which were all dependent on caspase-3 activation. These results suggest that the level of PP2A activity is at least in part determined by its tyrosine phosphorylation, which is dually controlled by okadaic acid-sensitive phosphatases and protein-tyrosine kinases. Possibly underlying the mechanism of caspase-mediated activation of PP2A, HNE treatment resulted in downregulation of the activity of Src kinase, as a representative caspase-sensitive kinase to phosphorylate PP2A at tyrosine. In addition, activated caspase-3 partially cleaved Akt at a late stage of the apoptosis. These results indicate the existence of two distinct caspase-dependent signal pathways for downregulation of Akt that works as a mechanism of positive feedback regulation for HNE-triggered apoptotic signals.
45493758
Regulation of Protein Phosphatase 2A Activity by Caspase-3 during Apoptosis*
Although the available evidence suggests that whereas the caspase family plays a major role in apoptosis, they are not the sole stimulators of death. A random yeast two-hybrid screen of a lymphocyte cDNA library (using caspase-3 as the bait) found an interaction between caspase-3 and the regulatory subunit Aα of protein phosphatase 2A. This protein was found to be a substrate for caspase-3, but not caspase-1, and could compete effectively against either a protein or synthetic peptide substrate. In Jurkat cells induced to undergo apoptosis with anti-Fas antibody, protein phosphatase 2A (PP2A) activity increased 4.5-fold after 6 h. By 12 h, the regulatory Aα subunit could no longer be detected in cell lysates. There was no change in the amount of the catalytic subunit. The effects on PP2A could be prevented by the caspase family inhibitors acetyl-Asp-Glu-Val-Asp (DEVD) aldehyde or Ac-DEVD fluoromethyl ketone. The mitogen-activated protein (MAP) kinase pathway is regulated by PP2A. At 12 h after the addition of anti-Fas antibody, a decrease in the amount of the phosphorylated forms of MAP kinase was observed. Again, this loss of activated MAP kinase could be prevented by the addition of DEVD-cho or DEVD-fmk. These data are consistent with a pathway whereby induction of apoptosis activates caspase-3. This enzyme then cleaves the regulatory Aα subunit of PP2A, increasing its activity. These data show that the activated PP2A will then effect a change in the phosphorylation state of the cell. These data provide a link between the caspases and signal transduction pathways.
16223140
Induction of BIM, a Proapoptotic BH3-Only BCL-2 Family Member, Is Critical for Neuronal Apoptosis
Sympathetic neuronal death induced by nerve growth factor (NGF) deprivation requires the macromolecular synthesis-dependent translocation of BAX from the cytosol to mitochondria and its subsequent integration into the mitochondrial outer membrane, followed by BAX-mediated cytochrome c (cyt c) release. The gene products triggering this process remain unknown. Here, we report that BIM, a member of the BH3-only proapoptotic subfamily of the BCL-2 protein family, is one such molecule. NGF withdrawal induced expression of BIM(EL), an integral mitochondrial membrane protein that functions upstream of (or in parallel with) the BAX/BCL-2 and caspase checkpoints. Bim deletion conferred protection against developmental and induced neuronal apoptosis in both central and peripheral populations, but only transiently, suggesting that BIM--and perhaps other BH3-only proteins--serve partially redundant functions upstream of BAX-mediated cyt c release.
10250592
JNK phosphorylation of Bim-related members of the Bcl2 family induces Bax-dependent apoptosis
The c-Jun NH2-terminal kinase (JNK) is activated when cells are exposed to environmental stress, including UV radiation. Gene disruption studies demonstrate that JNK is essential for UV-stimulated apoptosis mediated by the mitochondrial pathway by a Bax/Bak-dependent mechanism. Here, we demonstrate that JNK phosphorylates two members of the BH3-only subgroup of Bcl2-related proteins (Bim and Bmf) that are normally sequestered by binding to dynein and myosin V motor complexes. Phosphorylation by JNK causes release from the motor complexes. These proapoptotic BH3-only proteins therefore provide a molecular link between the JNK signal transduction pathway and the Bax/Bak-dependent mitochondrial apoptotic machinery.
9121751
Dominant-Negative c-Jun Promotes Neuronal Survival by Reducing BIM Expression and Inhibiting Mitochondrial Cytochrome c Release
Sympathetic neurons require nerve growth factor for survival and die by apoptosis in its absence. Key steps in the death pathway include c-Jun activation, mitochondrial cytochrome c release, and caspase activation. Here, we show that neurons rescued from NGF withdrawal-induced apoptosis by expression of dominant-negative c-Jun do not release cytochrome c from their mitochondria. Furthermore, we find that the mRNA for BIM(EL), a proapoptotic BCL-2 family member, increases in level after NGF withdrawal and that this is reduced by dominant-negative c-Jun. Finally, overexpression of BIM(EL) in neurons induces cytochrome c redistribution and apoptosis in the presence of NGF, and neurons injected with Bim antisense oligonucleotides or isolated from Bim(-/-) knockout mice die more slowly after NGF withdrawal.
13780564
Enhancing the efficacy of cisplatin in ovarian cancer treatment – could arsenic have a role
Ovarian cancer affects more than 200,000 women each year around the world. Most women are not diagnosed until the disease has already metastasized from the ovaries with a resultant poor prognosis. Ovarian cancer is associated with an overall 5 year survival of little more than 50%. The mainstay of front-line therapy is cytoreductive surgery followed by chemotherapy. Traditionally, this has been by the intravenous route only but there is more interest in the delivery of intraperitoneal chemotherapy utilizing the pharmaco-therapeutic advantage of the peritoneal barrier. Despite three large, randomized clinical trials comparing intravenous with intraperitoneal chemotherapy showing improved outcomes for those receiving at least part of their chemotherapy by the intraperitoneal route.Cisplatin has been the most active drug for the treatment of ovarian cancer for the last 4 decades and the prognosis for women with ovarian cancer can be defined by the tumor response to cisplatin. Those whose tumors are innately platinum-resistant at the time of initial treatment have a very poor prognosis. Although the majority of patients with ovarian cancer respond to front-line platinum combination chemotherapy the majority will develop disease that becomes resistant to cisplatin and will ultimately succumb to the disease.Improving the efficacy of cisplatin could have a major impact in the fight against this disease. Arsenite is an exciting agent that not only has inherent single-agent tumoricidal activity against ovarian cancer cell lines but also multiple biochemical interactions that may enhance the cytotoxicity of cisplatin including inhibition of deoxyribose nucleic acid (DNA) repair. In vitro studies suggest that arsenite may enhance the activity of cisplatin in other cell types. Arsenic trioxide is already used clinically to treat acute promyelocytic leukemia demonstrating its safety profile. Further research in ovarian cancer is warranted to define its possible role in this disease.
23374013
Pharmacologic inhibitors of PI3K/Akt potentiate the apoptotic action of the antileukemic drug arsenic trioxide via glutathione depletion and increased peroxide accumulation in myeloid leukemia cells.
Treatment for 14 to 24 hours with low concentrations of arsenic trioxide (As2O3, 1-4 microM) caused apoptosis in U-937 promonocytes and other human myeloid leukemia cell lines (HL-60, NB4). This effect was potentiated by cotreatment with the phosphatidylinositol 3-kinase (PI3K) inhibitors LY294002 and wortmannin, and the Akt inhibitor Akt(i)5. However, the inhibitors did not increase the toxicity of the mitochondria-targeting drug lonidamine, and the DNA-specific drugs camptothecin and cisplatin, when used under similar experimental conditions as As2O3. The potentiation of As2O3-provoked apoptosis involved the increased disruption of mitochondrial transmembrane potential, increased caspase-3 activation and cytochrome c release from mitochondria, increased Bax and Bid activation, and attenuation of 27-kDa heat shock protein (HSP27) expression; the potentiation was prevented by Bcl-2 overexpression. The PI3K/Akt inhibitors decreased the intracellular glutathione content, and caused intracellular oxidation, as measured by peroxide accumulation. Cotreatment with subcytotoxic concentrations of hydrogen peroxide increased apoptosis induction by As2O3. On the other hand, the treatments did not significantly affect glutathione S-transferase pi expression and activity. These results, which indicate that glutathione is a target of PI3K/Akt in myeloid leukemia cells, may partially explain the selective increase of As2O3 toxicity by PI3K/Akt inhibitors, and may provide a rationale to improve the efficacy of these inhibitors as therapeutic agents.
31659372
Akt promotes cisplatin resistance in human ovarian cancer cells through inhibition of p53 phosphorylation and nuclear function
Resistance to cisplatin‐based chemotherapy is a major cause of treatment failure in human ovarian cancer. Wild‐type TP53 status is often, but not always, associated with cisplatin sensitivity, suggesting that additional factors may be involved. Overexpression/activation of the phosphatidylinositol‐3‐kinase/Akt pathway is commonly observed in ovarian cancer, and Akt activation is a determinant of chemoresistance in ovarian cancer cells, an effect that may be due, in part, to its inhibitory actions on p53‐dependent apoptosis. To that end, we examined the role and regulation of p53 in chemosensitive ovarian cancer cells, as well as in their chemoresistant counterparts, and investigated if and how Akt influences this pathway. Cisplatin induced apoptosis in chemosensitive, but not chemoresistant cells, and this was inhibited by downregulation of p53. Cisplatin upregulated PUMA in a p53‐dependent manner, and the presence of PUMA was necessary, but not sufficient for cisplatin‐induced apoptosis. p53 was phosphorylated on numerous N‐terminal residues, including Ser15, Ser20, in response to cisplatin in chemosensitive, but not chemoresistant cells. Furthermore, activation of Akt inhibited the cisplatin‐induced upregulation of PUMA, and suppressed cisplatin‐induced p53 phosphorylation, while inhibition of Akt increased total and phospho‐p53 contents and sensitized p53 wild‐type, chemoresistant cells to cisplatin‐induced apoptosis. Finally, mutation of Ser15 and/or Ser20, but not of Ser37, to alanine significantly attenuated the ability of p53 to facilitate CDDP‐induced apoptosis, and this was independent of PUMA expression. These results support the hypothesis that p53 is a determinant of CDDP sensitivity, and suggest that Akt contributes to chemoresistance, in part, by attenuating p53‐mediated PUMA upregulation and phosphorylation of p53, which are essential, but independent determinants of sensitivity to CDDP‐induced apoptosis. © 2007 Wiley‐Liss, Inc.
25568613
Induction of B-Chronic Lymphocytic Leukemia Cell Apoptosis by Arsenic Trioxide Involves Suppression of the Phosphoinositide 3-Kinase/Akt Survival Pathway via c-jun-NH2 Terminal Kinase Activation and PTEN Upregulation
Purpose: Arsenic trioxide (ATO) induces B-cell chronic lymphocytic leukemia (B-CLL) cell apoptosis in vitro. We sought to study the mechanism involved in this effect and whether ATO is suitable for combination therapies with protein kinase inhibitors. Experimental Design: B-CLL cells were isolated from the peripheral blood of 28 patients. Cell viability studies with ATO alone or in combination with kinase inhibitors were done by flow cytometry, Western blotting, and immunofluorescence analyses. Results: After 48 hours, 3 μmol/L ATO induced apoptosis (average 75%) in all B-CLL samples studied and with minimal effect on normal peripheral blood lymphocytes. Apoptosis entailed Akt and NF-κB inactivation, XIAP downregulation, and PTEN upregulation, thus implying inhibition of the phosphoinositide 3-kinase (PI3K) survival pathway. Indeed, the combination of ATO and PI3K inhibitors increased the apoptotic effect of either agent alone. ATO also induced c-jun-NH2 terminal kinase (JNK) activation, and this was crucial and required for subsequent apoptotic events, as inhibiting JNK activity by either gene silencing or specific inhibitors prevented Akt and NF-κB inactivation, caspase activation, and mitochondrial damage. Moreover, JNK activation was the earliest response to ATO, preceding and determining reactive oxygen species production. Conclusions: We identified the mechanism involved in ATO action on B-CLL cells and show that the combination of low doses of ATO and PI3K inhibitors efficiently induces B-CLL cell death. ATO may therefore constitute an efficient treatment for B-CLL, particularly in combined therapies. Clin Cancer Res; 16(17); 4382–91. ©2010 AACR.
8508641
Mcl-1 is an important determinant of the apoptotic response to the BH3-mimetic molecule HA14-1 in cisplatin-resistant ovarian carcinoma cells
Chemoresistance of ovarian carcinoma has been associated previously to the absence of Bcl-xL expression downregulation in response to cisplatin. Among BH3-mimetic molecules constituting promising anticancer agents able to inhibit the activity of antiapoptotic Bcl-2 family proteins, we evaluated the effect of one of them, HA14-1, on various ovarian carcinoma cell lines. In response to HA14-1, the cisplatin-resistant IGROV1-R10 cell line underwent massive cell death, whereas other cell lines presented a partial response (IGROV1, SKOV3, and A2780) or did not respond to this molecule (OAW42 and OAW42-R). However, the expression of HA14-1 targets (Bcl-2 and Bcl-xL) did not correlate to these different responses. In contrast, cell death was associated with the disappearance of Mcl-1 after exposure to HA14-1. We showed that, in the HA14-1 nonresponsive cell lines (SKOV3 and OAW42), small interfering RNA–mediated Mcl-1 downregulation allowed HA14-1–induced massive apoptosis in the absence of chemotherapy. Furthermore, cisplatin-induced Mcl-1 downregulation was also able to sensitize highly chemoresistant SKOV3 cells to HA14-1. Taken together, these results show that Bcl-xL and Mcl-1 are able to cooperate to protect ovarian carcinoma cells against oncogenic stress or chemotherapy-induced apoptosis and suggest that the development of multitargeted strategies directed against these two antiapoptotic proteins may constitute a major challenge for the therapeutic care of chemoresistant ovarian carcinomas. BH3-mimetic compounds represent promising tools for this purpose either on their own (direct or indirect pan-inhibitors) or in combination with new drugs aiming to inactivate Mcl-1. [Mol Cancer Ther 2009;8(11):3162–70]
205371172
Cysteine 62 of Bax Is Critical for Its Conformational Activation and Its Proapoptotic Activity in Response to H2O2-induced Apoptosis*
Bax is activated and translocated onto mitochondria to mediate cytochrome c release and apoptosis. The molecular mechanisms of Bax activation during apoptosis remain a subject of debate. We addressed the question of whether reactive oxygen species could directly activate Bax for its subsequent translocation and apoptosis. Using the SW480 human colon adenocarcinoma cell line stably expressing Bax fused to GFP, we showed that H2O2 induces Bax conformational change, mitochondrial translocation, and subsequent oligomerization at mitochondria. We found that H2O2-induced Bax activation is dependent on the conserved cysteine residue 62 of Bax. Mutation of cysteine 62, but not cysteine 126, to serine or alanine abolished its activation by H2O2 but not other death stimuli, both in SW480 and Bax-deficient HCT116 cells, whereas wild type Bax sensitizes these cells to apoptosis. Cysteines of Bax could chemically react with H2O2. Mutation of Bax BH3 domain in the presence of cysteine 62 also abolished Bax proapoptotic activity. We conclude that reactive oxygen species could be a direct signal for Bax activation by reacting with cysteine residues. Our results identify a critical role of cysteine 62 in oxidative stress-induced Bax activation and subsequent apoptosis.
22317826
Nicotine Inactivation of the Proapoptotic Function of Bax through Phosphorylation*
Nicotine-induced cell survival is associated with chemoresistance of human lung cancer cells, but our understanding of the intracellular mechanism(s) is fragmentary. Bax is a major proapoptotic member of the Bcl2 family and a molecule required for apoptotic cell death. Growth factor (i.e. granulocyte-macrophage colony-stimulating factor)-induced phosphorylation of Bax has been reported to negatively regulate its proapoptotic function. Because Bax is ubiquitously expressed in both small cell lung cancer and non-small cell lung cancer cells, nicotine may mimic growth factor(s) to regulate the activity of Bax. We found that nicotine potently induces Bax phosphorylation at Ser-184, which results in abrogation of the proapoptotic activity of Bax and increased cell survival. AKT, a known physiological Bax kinase, is activated by nicotine, co-localizes with Bax in the cytoplasm, and can directly phosphorylate Bax in vitro. Treatment of cells with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 or specific depletion of AKT expression by RNA interference can block both nicotine-induced Bax phosphorylation and cell survival. Importantly, nicotine-induced Bax phosphorylation potently blocks stress-induced translocation of Bax from cytosol to mitochondria, impairs Bax insertion into mitochondrial membranes, and reduces the half-life of Bax protein (i.e. from 9-12 h to <6 h). Because knockdown of Bax expression by gene silencing results in prolonged cell survival following treatment with cisplatin in the absence or presence of nicotine, Bax may be an essential component in the nicotine survival signaling pathway. Thus, nicotine-induced survival and chemoresistance of human lung cancer cells may occur in a novel mechanism involving activation of PI3K/AKT that directly phosphorylates and inactivates the proapoptotic function of Bax.