THE ROLE OF MIR199A IN BREAST CANCER PROGRESSION AND METASTASIS

Metastasis remains one of the leading causes of death in cancer patients. The epithelial to mesenchymal transition (EMT) is proposed as a preliminary event underlying the metastatic process, allowing tumor cells to migrate and colonize new tissues and organs. EMT is a trans-differentiation program active during embryonic development that produces mesechymal-like cells from epithelial sheets by loss of cell adhesion and leading to increased cell motility. Dissecting molecular pathways associated to EMT and to its metastasis-promoting potential is essential to develop therapeutic strategies against cancer metastasis. Our group developed a model of mammary carcinogenesis based on the rat cancer stem cell line LA7, that when engrafted at the single cell level in immuno-compromised mice, recapitulates the entire process of tumor development including the EMT process that lead to metastasis formation, through the generation of fibroblast-like cells (LA7-Elongated cells). Using the LA7 system we found miR-199a up regulated during in vivo EMT transition. Ectopic expression of the miR-199a in LA7 induced cell shape modification and changes in marker expression coherent with an epithelial to mesenchymal trans-differentiation, recapitulating the fibroblast-like LA7 counterpart phenotype (LA7-Elongated). These results suggest that miR-199a is an effective inducer of EMT. We demonstrate that the action of miR-199a is directed on adherens junction proteins such as E-Cadherin and β-Catenin, gatekeepers of EMT, through leukocyte antigen-related tyrosine phosphatase (LAR or PTPRF) protein down-regulation. Furthermore, the induction of EMT in LA7 by TGF-β treatment resulted in miR-199a up-regulation through TWIST1 induction, while the down-regulation of miR-199a abrogated the invasion capacity of the LA7-Elongated fibroblast-like cells in 3D cell culture assays. Moreover when injected in NOD/SCID mice, LA7 cells in which we induced modulation of miR-199a were unable to form metastasis, even if their tumor seeding ability was not affected. Taken together our results support that miR-199a is a component of the pathway that commits epithelial cells to the EMT program and an important factor in the metastatic cascade engagement. Research concerning miRs identified using the LA7 model system and their possible use as therapeutic agents is ongoing in our lab and will provide new useful tools for cancer therapy.