Expression of activated M-Ras in a murine mammary epithelial cell line induces epithelial-mesenchymal transition and tumorigenesis

The expression of activated mutants of M-Ras (G22V or Q71L), but not wild-type M-Ras, in a murine mammary epithelial cell line, scp2, resulted in epithelial - mesenchymal transition (EMT) and oncogenic transformation. Cells expressing constitutively active M-Ras continued to grow in the absence of serum and exhibited a loss of the epithelial markers cytokeratin, E-cadherin and beta-catenin, together with a gain of the mesenchymal marker vimentin, a loss of contact inhibition in monolayer growth and a gain of the capacity for anchorage-independent growth. Moreover, unlike the parental cells, they failed to form differentiated mammospheres on Matrigel and instead formed branched networks of cells that grew and invaded the Matrigel. The expression of activated p21 Ras (G12V H-Ras or Q61K N-Ras) also resulted in EMT and tumorigenesis, although there was evidence that expression of higher levels was toxic. Tumors derived from scp2 cells expressing activated M-Ras exhibited activation of Akt and of ERK. The levels of expression of Q71L M-Ras and G12V H-Ras required for tumorigenesis were comparable, although higher levels of the weaker G22V M-Ras mutant were selected for in vivo. These data indicate that the expression of activated mutants of M-Ras was sufficient for oncogenic transformation of a murine mammary epithelial cell line.