Département Relations Extérieures Service Communication Recherche Nancy Dath, T : +32 (0)2 650 92 03, +32 (0) 473 97 22 56 M : [email protected] Nathalie Gobbe, T : +32 (0)2 650 92 06, +32 (0)474 84 23 02 M : [email protected] Press Release Brussels, 8th July 2016 Cancer : the stem cell dynamics Publication in the accelerated article preview of Nature: researchers at the Université libre de Bruxelles, ULB define for the first time the changes in the stem cell dynamics that lead to tumor initiation. One of the key questions in cancer biology is to identify the cancer cell of origin and understand in these cells how oncogene alters their clonal dynamics and changes their proliferation, cell death, balance between renewal and differentiation to induce tumor development. In a study published in Nature, researchers lead by Pr. Cédric Blanpain, MD/PhD, Welbio investigator, and Professor at the Université Libre de Bruxelles, Belgium, in collaboration with Pr. Benjamin D Simons, University of Cambridge,UK, demonstrated that the capacity of oncogene-expressing cells to induce tumor formation depends on the clonal dynamics of the cancer cell of origin. Many cancers arise from tissues maintained by stem and progenitor cells that ultimately give rise to non-dividing terminally differentiated cells. However, little is known about the contribution of stem cells and progenitors to cancer initiation. During tumor initiation, cells targeted by oncogenic mutations undergo a series of molecular changes leading to their clonal expansion and the acquisition of invasive properties. How exactly oncogenic mutations impact on the rate of stem cell and progenitor division, and change the proportion of divisions that result in symmetric and asymmetric cell fate, allowing clonal expansion and tumor progression is poorly understood. In this new study published in Nature, Adriana Sánchez-Danés and colleagues define the clonal dynamics that lead to skin cancer initiation using the basal cell carcinoma, the most frequent tumor in humans, as a model. They used state of the art genetic mouse models to activate the oncogene in stem cells and committed progenitor populations. Specifically, they use a genetic tracing strategy that allowed them to mark the stem cells and committed progenitors that express the oncogene and follow the fate of their progeny over time. Interestingly, they found that only stem cells and not their progenitor cell progeny were competent to initiate tumor formation upon oncogenic activation. “It was particularly exciting to observe that progenitor-derived clones grew in size but eventually became frozen in a pre- tumorigenic state while stem cell-derived clones expanded rapidly leading in time to basal cell carcinoma formation”, comments Adriana Sánchez-Danés, the first author of the study. In collaboration with Pr.Benjamin D Simons, Cavendish Laboratory and the Gurdon Institute, University of Cambridge, UK, they developed a mathematical model of clonal evolution, which defines for the first time, at the single cell resolution, the quantitative dynamics of tumor initiation from the activation of the oncogene to the development of invasive tumours. Interestingly, they found that oncogenic activation in progenitors lead to the generation of pre-tumorigenic lesions that are frozen and cannot progress into invasive tumors. In contrast, oncogene expression in stem cells resulted in a more rapid clonal expansion characterized by an increase in self-renewing divisions combined with a higher resistance to cell death, and leading in turn to the development of clones that progress into invasive tumors. These data demonstrate that targeting stem cells, which reside at the top of the cellular hierarchy in the skin epidermis, was necessary for tumor formation. Altogether, this study provides important insights into the changes in the cellular dynamics that lead to tumor formation and demonstrates that the capacity of oncogene expressing cells to induce tumor formation depends on the specific clonal dynamics of the cancer cell of origin. “This new finding not only demonstrates that the cancer cell of origin matters, but also that stem cells are particularly sensitive to tumor initiation due to their natural ability to selfrenew and their resistance to oncogene mediated cell death. This mode of tumour development suggests that therapy promoting differentiation or apoptosis should be effective in the treatment of basal cell carcinomas, and should lead to tumour regression and prevent tumour relapse.” explains Cédric Blanpain, the senior author of this Nature paper. This work was supported by the FNRS, TELEVIE, a research grant from the Fondation Contre le Cancer, the ULB fondation, Wellcome Trust and Trinity College Cambridge, the foundation Bettencourt Schueller, the foundation Baillet Latour, the European Research Council (ERC). Journalists should credit Nature as the source of stories covered. Adriana Sánchez-Danés*, Edouard Hannezo*, Jean-Christophe Larsimont, Mélanie Liagre, Khalil Kass Youssef, Benjamin D Simons# and Cédric Blanpain#. Defining the clonal dynamics leading to mouse skin tumour initiation Nature, 2016. DOI 10.1038/nature19069 * denotes co-first authors # Corresponding authors Contacts : Cédric Blanpain, MD, PhD Welbio, Interdisciplinary Research Institute (IRIBHM) U-CRC, Université Libre de Bruxelles (ULB) Tél. : 32-2-555 4175 ou 32-2- 555 4190 Email: [email protected] Lab Website: http://blanpainlab.ulb.ac.be/index.htm Benjamin D Simons, PhD Herchel Smith Professor of Physics Head of the Theory of Condensed Matter Physics Group Cavendish Laboratory Tel. +44(0)1223 337253/338738/334095, Fax 337356, Admin. 746651 http://www.tcm.phy.cam.ac.uk/~bds10/ Email: [email protected]