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Séminaire FSER organisé par Cédric Blanpain (IRIBHM / ULB, Belgique) et John E. Dick (University Health Netword, Toronto, Canada) du 10 au 15 septembre 2018ParticipantsIannis Aifantis, Salvador Aznar-Benitah, Eduard Batlle, Cédric Blanpain, John E. Dick, Peter Dirks, Michaela Frye, Elaine Fuchs, Richard Gilbertson, Margaret A. Goodell, Carla Kim, Barbara Marte (Senior editor, Nature, Londres), Emmanuelle Passegué, Karl Lenhard Rudolph, Frederic de Sauvage, Andreas Trumpp, Doug Winton, Jing YangRésuméCe colloque avait pour but de discuter les avancées qui se sont opérées dans le domaine des cellules souches et leur relation avec l’initiation des cancers, la croissance tumorale, la dissémination métastatique et la réponse aux traitements anti-cancéreux. Il a aussi été question du rôle des cellules souches au cours du vieillissement, de la réparation tissulaire et de l’inflammation ainsi que de la grande plasticité des cellules souches dans les phénomènes de régénération. De nombreuses perspectives thérapeutiques de ces thèmes de recherche ont été présentées. Ce meeting a réuni plusieurs chercheurs parmi les personnalités scientifiques les plus prestigieuses dans le domaine. Les discussions ont été productives et animées avec une excellente ambiance. En conclusion, le meeting des treilles « les cellules souches et le cancer » a été un grand succès.CommunicationsIannis (Ioannis) Aifantis (New York University School of Medicine, USA) – Cell intrinsic and extrinsic regulation of leukemia initiation and progressionIannis Aifantis identified the transcriptional landscape of the bone marrow vascular, perivascular, and osteoblast niche populations at single cell resolution in both homeostasis and stress. These findings refine our understanding of the cellular architecture of the bone marrow niche, reveal a dynamic and heterogeneous molecular landscape that is highly sensitive to stress, and illustrate the utility of single cell transcriptomic data in mechanically evaluating the regulation of hematopoiesis by discrete niche populations.Salvador Aznar-Benitah (IRB Barcelona, Spain) – Adult stem cells in homeostasis, ageing and cancer: interplay between time, diet, and epigeneticsSalvador Aznar Benitah presented evidence that the function of stem cells is under a circadian control. This mechanism prolongs stem cell fitness. They have shown that perturbations in this clock mechanism occur during physiological aging, and result in a significant loss of stem cell function and that loss of cell identity is a hallmark of dermal aging, whereby dermal fibroblasts present adipogenic differentiation that severely impair their function.Eduard Batlle (IRB Barcelona, Spain) – Stems cells and tumor microenvironment in colorectal cancerEduard Batlle discussed how stromal cells help disseminated colorectal tumor cells to evade the attack of the immune system and the design of new therapeutic strategies based on targeting the tumor microenvironment such as TGFBR1 inhibitors combined with check-point blockade that promotes the eradication of metastasis.Cédric Blanpain, organisateur (IRIBHM / ULB, Brussels, Belgium) – Cancer Cell of origin and Tumor heterogeneityCédric Blanpain showed how the chromatin and transcriptional landscape of the cancer cell at the origin of cancers influence tumor heterogeneity and EMT. He then presented evidence that EMT occurs through distinct cell transitional states that present different functions and are located in different niches are and regulated by distinct transcription factors. He finally shows how genetic mutations can stabilize the EMT states associated with metastasis.John E. Dick, organisateur (Princess Margaret Cancer Centre, University Health Network, Toronto, Canada) – Stem Cells play a role in leukaemia from the beginning to the endJohn E. Dick showed that pre-existing LSC survive therapy and cause relapse after therapy. The existence of clonally expanded pre-leukemic hematopoietic stem cells in the diagnosis blood sample of many leukemic samples predicted that it should be possible to identify individuals who are at risk for progressing to acute myeloid leukemia (AML) long before disease develops. They found a signature able to predict with high accuracy individuals who progress to AML, almost 10 years prior to AML development, offering the potential for future prevention trials.Peter Dirks (The Hospital for Sick Children, University of Toronto, Canada) – Mapping functional and molecular properties of brain tumour stem cellsPeter Dirks presented work in mouse and human models of brain cancer that support that quiescent brain tumour stem cells drive tumor growth in childhood and adult brain tumours. Brain tumour stem cells have a limited number of chromatin states that cross cut genetic diversity, suggesting that the abnormal brain tumour genome converges on a more limited number of programs that are essential for the tumorigenic state.Michaela Frye (University of Cambridge, UK) – The regulatory potential of RNA modifications in stem cellsMichaela Frye discussed the importance of RNA modifications in the regulation of gene expression and the modulation of cell fate decisions. Some modifications in transfer RNAs are deposited in response to external cues and adapt global protein synthesis and gene-specific translational accordingly, thereby facilitating development. Aberrant deposition of these modifications can lead to human disease, including cancer.Elaine Fuchs (The Rockefeller University, New York, USA) – Environmental impacts on skin stem cellsElaine Fuchs summarized her lab’s research in which they identified the skin stem cells and their niches, and demonstrated that their interactions with their niches dictate both the molecular properties of each stem cell and its role in tissue regeneration. She showed that the critical genes controlling stem cells and lineage progression are rooted in chromatin dynamics and that stem cells retain epigenetic memory of inflammation that persists over an extended time period, and allows skin stem cells to respond more rapidly upon the next damage.Richard Gilbertson (CRUK, Cambridge Institute, UK) – Mapping cancer origins – a route to preventionRichard Gilbertson demonstrated that different childhood brain tumours arise from specific progenitor cells in the developing nervous system, enabling brain tumours to be classified and treated with much greater precision. By extending this work to whole organism studies, he demonstrated that a combination of stem cell mutagenesis and organ damage determines cancer risk across different tissues.Margaret (Peggy) Goodell (Baylor College of Medicine, Houston, USA) – Stem Cell Competition in HematopoiesisMargaret A. Goodell explored the concept of clonal hematopoiesis, discussing the broader findings in the field and provoking the group to think about different strategies through which a clone may prevail during cell competition. She then described the strategy through which HSCs with DNMT3A mutations prevail, through an advantage of self-renewal. Finally, she described the strategy that HSCs with mutations in PPM1D attain clonal dominance, through resistance to apoptosis in the context of a chemotherapeutic insult.Carla Kim (Children’s Hospital Boston, USA) – Regulation of progenitor cells in the adult lung and in lung cancerCarla Kim discussed how lung organoid culture allowed to uncover molecular mechanisms by which adult lung progenitor cells can be directed to differentiate by their surrounding microenvironment and to model lung diseases and lung cancer. She discussed her data showing that the histone methyltransferase G9a is a suppressor of lung tumor-propagating cells and cancer progression.Emmanuelle Passegué (Columbia Stem Cell Initiative, Columbia University, New York, USA) – Hematopoietic stem cells in stress, disease and agingEmmanuelle Passegué described how aberrant activation of hematopoietic stem cell (HSC) differentiation pathways in leukemia-initiating stem cells (LSC) contribute to disease development. In particular, she described how decreased Notch and increased Wnt activities synergize together to force leukemic SC to overproduce a population of myeloid-biased multipotent progenitors, which in turn drive malignant myeloid burden, and how normalization of these deregulated signalling activity could limit leukemia progression.Karl Lenhard Rudolph (Leibniz Institute on Aging – Fritz Lipmann Institute, Jean, Germany) – Epigenetic stress responses in stem cell agingKL Rudolph talked about his new concept that the epigenome integrates responses to aging-associated, cell intrinsic changes (such as accumulation of molecular damages) as well as to aging-associated, cell extrinsic changes (such as increases in inflammatory signal in aging). Epigenetic alteration in stem cells in turn limit stem cell function in tissue maintenance and select for clonal dominance of altered stem cells. These altered stem cell clones will further aggravate defects in tissue maintenance during aging.Frederic (Fred) de Sauvage (Genentech, San Francisco, USA) – Plasticity of cancer stem cellsFred de Sauvage showed that despite the efficacy of Hedgehog Inhibitors in the treatment of Basal Cell Carcinoma (BCC), residual disease persists in some patients and may contribute to relapse when treatment is discontinued. Profiling experiments of residual tumor cells revealed that residual BCCs required Wnt pathway activation. Accordingly, co-treatment of BCC with vismodegib and a Wnt inhibitor further reduced the residual tumor burden achieving eradication of most tumors.Andreas Trumpp (HI-STEM gGMBH, German Cancer Research Center (DKFZ)) – Metabolism and Therapy ResistanceAndreas Trumpp presented the mechanisms regulating the resistance of pancreatic cancer to chemotherapy. The resistance is caused by up-regulation of CYP3A5 pathway activity, which metabolizes and inactivates these drugs intracellularly. Inhibition or CYP3A5 sensitizes cancer cells to chemotherapy. Two different CYP3A5 inhibitors have been identified and clinical trial testing these inhibitors have been initiated in pancreatic cancer patients.Doug Winton (CRUK, Cambridge Institute, UK) – Impact of Stem cell organisation on somatic mutational burden in intestineDoug Winton presented how the plasticity of intestinal secretory progenitors allows them to act as self-renewing stem cells, in particular during regenerative settings. He then described how somatic mutations allow to visualising clones in human colonic epithelium and discuss how high mutant allele frequencies can be achieved by biased behaviours that may contribute to cancer development.Jing Yang (University of California San Diego, USA) – Epithelial-Mesenchymal Plasticity in Carcinoma MetastasisJing Yang discussed the importance of epithelial-mesenchymal transition (EMT) in carcinoma metastasis. She presented evidence that reversible activation of EMT could promote breast tumor metastasis. Then she discussed how EMT could be regulated by both extracellular matrix cues and epithelial polarity.