Resumen de Fibroblastic SNAIL1 induces a metastasis-permisive tumor Stroma by regulating fibronectin alternative splicing
SNAIL1 is a transcription factor with roles in repression of epithelial genes and enhancement of mesenchymal genes. As such, it plays a key role in Epithelial-to-mesenchymal transition and in fibroblast activation into myofibroblast. In this thesis, we characterize a novel role in splicing regulation, focusing on the induction of inclusion of the fibronectin extra domain A. This alternatively spliced domain, expressed in pathological situations such as wound healing and cancer, has various roles in inflammatory response, fibroblast activation and tumor cell migration. We show a correlation between SNAIL1 and EDA inclusion among a breast cancer PDX cohort and samples for 5 solid tumor types in advanced stages. Here, we describe a TGFbeta/SNAIL1 dependent recruitment of the splicing factor SRSF1 to the EDA coding RNA, associated to increased inclusion. We focus on the effects of this increase in EDA inclusion in the context of fibronectin fibers assembled into the extracellular matrix. We use genetically modified fibroblasts, expressing specific isoforms of fibronectin, to derive matrices and demonstrate that, like fibroblastic SNAIL1 expression, the presence of fibronectin EDA is required to organize an aligned and stiffer extracellular matrix. The induced mechanical and topological ECM properties enhance tumor cell oriented individual migration, facilitate coordinated collective movement and induce a more efficient invasion. Depletion of the isoform completely prevents metastasis formation in an orthotopic cancer model. We use specific inhibitors to block EDA signaling reducing fibroblastic activation and leading to a restrictive matrix that limits tumor cell invasion. Therefore, our results demonstrate the role of the fibronectin EDA isoform in the conversion of a restrictive tumor stroma to a permissive one and its molecular control by the transcription factor SNAIL1.
