Abstract 285: Antagonistic functions of EMT-inducing transcription factors during melanoma development.
Authors: Caramel Julie , Papadogeorgakis Eftychios , Hill Louise , Browne Gareth J. , Richard Geoffrey , Wierinckx Anne , Saldanha Gerald , Hutchinson Peter , Pringle James H. , Puisieux Alain , Tulchinsky Eugene , Ansieau Stephane 
Published: August 2014

Abstract
Embryonic transcription factors (ETFs) of the Snail, Zeb and Twist families are essential mediators of EMT programs (Epithelial to Mesenchymal Transition) and play central roles in cell determination and cell plasticity. The aberrant expression of ETFs is frequently observed in various cancer types, particularly in carcinomas, and is associated with poor prognosis and high risk of metastasis. We and others have demonstrated that their oncogenic potential relies on their ability to enable escape from oncogene-induced failsafe programs, senescence and apoptosis. Therefore, EMT-resembling processes initiated by ETFs contribute to neoplastic transformation in vitro and accelerate tumor progression in vivo in an epithelial context. We now unveil a completely different scenario in melanoma, a highly metastatic neural crest-derived cancer. Consistent with their role in melanoblasts determination, SNAIL2 and ZEB2 are already expressed in melanocytes and naevi, but their expression is down-regulated in primary melanoma. In contrast, TWIST1 and ZEB1 are aberrantly reactivated in primary and metastatic melanoma. Interestingly, this switch in ETFs expression represents a novel independent factor of poor prognosis in patients with malignant melanoma. We further demonstrate that BRAF activation, the most frequent driving event in melanoma, induces a drastic upregulation of TWIST1 and ZEB1 at the expense of SNAIL2 and ZEB2 in murine and human melanocytes. This reversible switch, orchestrated by the FRA1 transcription factor, is determinant for BRAF-driven melanocyte transformation in vitro and in a xenograft model. As a whole, while TWIST1 and ZEB1 cooperate with oncogenic BRAF to induce neoplastic transformation, SNAIL2 and ZEB2 rather behave as oncosuppressive proteins in melanoma. Gene expression profiles analyses further show that this oncogenic reprogramming of ETFs regulates the expression of the MITF master regulator, with an inhibition of MITF-regulated differentiation program and an activation of TGFβ- and invasion-associated gene expression signatures. Collectively, these data highlight yet unexpected antagonistic properties of ETFs in tumor progression, and place the ETF network as a master regulator of MITF-dependent phenotype switching during melanomagenesis.
Citation Format: Julie Caramel, Eftychios Papadogeorgakis, Louise Hill, Gareth J. Browne, Geoffrey Richard, Anne Wierinckx, Gerald Saldanha, Peter Hutchinson, James H. Pringle, Alain Puisieux, Eugene Tulchinsky, Stephane Ansieau. Antagonistic functions of EMT-inducing transcription factors during melanoma development. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 285. doi:10.1158/1538-7445.AM2013-285