Immune response to p53 is dependent upon p53/HSP70 complexes in breast cancers. Overexpression of the p53 protein, resulting from gene mutations that increase protein stability, has been detected in greater than 25% of primary human breast cancers. In addition, approximately 10% of breast cancer patients have circulating antibodies to the p53 protein. In this study, the anti-p53 humoral response is correlated with the presence and type of mutant p53 protein expressed in the tumor. In a series of 60 breast cancer patients, 0 of 30 tumors with normal, low-level p53 expression induced anti-p53 antibodies, whereas 7 (23%) of 30 tumors with p53 overexpression elicited a specific anti-p53 antibody response. These 7 patients had anti-p53 antibodies that recognized wild-type p53 and a variety of mutant p53 proteins. A comparison of p53 mutations revealed that antibody-negative tumors had mutations exclusively in exons 7 and 8, whereas antibody-positive tumors had mutations primarily in exons 5 and 6. Moreover, all antibody-eliciting tumors contained complexes between p53 and a 70-kDa heat shock protein, whereas none of the antibody-negative tumors contained this complex. This study implicates a 70-kDa heat shock protein in the antigenic presentation of p53.


Selectively amplified expression of an isoform of the vacuolar H(+)-ATPase 56-kilodalton subunit in renal intercalated cells. The intercalated cells of the kidney collecting duct are specialized for physiologically regulated proton transport. In these cells, a vacuolar H(+)-ATPase is expressed at enormous levels in a polarized distribution on the plasma membrane, enabling it to serve in transepithelial H+ transport. In contrast, in most eukaryotic cells, vacuolar H(+)-ATPases reside principally in intracellular compartments to effect vacuolar acidification. To investigate the basis for the selective amplification of the proton pump in intercalated cells, we isolated and sequenced cDNA clones for two isoforms of the approximately 56-kDa subunit of the H(+)-ATPase and examined their expression in various tissues. The predicted amino acid sequence of the isoforms was highly conserved in the internal region but diverged in the amino and carboxyl termini. mRNA hybridization to a cDNA probe for one isoform (the "kidney" isoform) was detected only in kidney cortex and medulla, whereas mRNA hybridization to the other isoform of the approximately 56-kDa subunit and to the H(+)-ATPase 31-kDa subunit was found in the kidney and other tissues. Immunocytochemistry of rat kidney with an antibody specific to the kidney isoform revealed intense staining only in the intercalated cells. Staining was absent from proximal tubule and thick ascending limb, where H(+)-ATPase was detected with a monoclonal antibody to the 31-kDa subunit of the H(+)-ATPase. This example of specific amplification of an isoform of one subunit of the vacuolar H(+)-ATPase being limited to a specific cell type suggests that the selective expression of the kidney isoform of the approximately 56-kDa subunit may confer the capacity for amplification and other specialized functions of the vacuolar H(+)-ATPase in the renal intercalated cell.


Role and regulation of interleukin (IL)-2 receptor alpha and beta chains in IL-2-driven B-cell growth. Substantial proportions of resting B cells constitutively express low levels of IL-2 receptor (IL-2R) alpha and/or beta chains. The expression of these chains is differentially regulated by anti-IgM and IL-2/IL-4. The anti-IgM induces IL-2R alpha chain expression, whereas each of the two cytokines induces IL-2R beta chain expression in a dose-dependent manner. Moreover, IL-2 induces the growth of B cells, when the cells were pretreated with IL-2 or IL-4 for 24 h. The magnitude of this IL-2-driven B-cell growth depends upon the level of IL-2R beta chain expression. Costimulation of the B cells with IL-2 and anti-IgM shifts the dose-response curve, and the cells proliferate at an IL-2 concentration as low as 40 pM. These results indicate that the levels of anti-IgM-induced IL-2R alpha chain and IL-2-induced IL-2R beta chain determine the sensitivity of the cells to IL-2.


Cyclic AMP induces transforming growth factor beta 2 gene expression and growth arrest in the human androgen-independent prostate carcinoma cell line PC-3. The standard therapy for advanced prostate cancer is androgen ablation. Despite transitory responses, hormonally treated patients ultimately relapse with androgen-independent disease that is resistant to further hormonal manipulation and cytotoxic chemotherapy. To develop an additional approach to the treatment of advanced prostate cancer, we have been studying the signal transductions controlling the growth of human androgen-independent prostate carcinoma cell lines. We report here that elevation of intracellular cAMP markedly inhibits the growth of the hormone-refractory cell line PC-3. To examine the mechanism of cAMP action in PC-3 cells, we tested the effect of the cAMP analog dibutyryl cAMP (Bt2-cAMP) on the regulation of the potent negative growth factor transforming growth factor beta (TGF-beta). Bt2-cAMP selectively induced the secretion of TGF-beta 2 and not TGF-beta 1 by PC-3 cells. This TGF-beta 2 was shown to be bioactive by using the CCL-64 mink lung cell assay. TGF-beta 1 was not activated despite being present at 3-fold higher concentrations than TGF-beta 2. Northern analysis showed that Bt2-cAMP induced an increase in the five characteristic TGF-beta 2 transcripts and had no effect on the level of TGF-beta 1 or TGF-beta 3 transcripts. TGF-beta 2 induction was only weakly enhanced by cycloheximide and was completely inhibited by actinomycin D. These data show that Bt2-cAMP induces the expression of active TGF-beta 2 by PC-3 prostate carcinoma cells, suggesting a new approach to the treatment of prostate cancer and a new molecular mechanism of cAMP action.