The small GTPase N-Ras regulates extracellular matrix synthesis, proliferation and migration in fibroblasts.

ABSTRACT

In addition to their role as oncogenes, Ras GTPases are key regulators of cell function. There is a proven relationship between the signaling pathways of transforming growth factor-ß1 (TGF- ß1) and Ras GTPases. Each of the Ras isoforms (H, N and K) exhibits specific modulatory activity on different cellular pathways. Our purpose has been to study some of the mechanisms involved in the development of renal fibrosis, assessing the individual role of N-Ras in basal and TGF-ß1-mediated extracellular matrix (ECM) synthesis, proliferation, and migration in immortalized N-Ras deficient fibroblasts (N-ras(-/-)). Compared to normal counterparts, fibroblasts deficient for N-Ras exhibited higher basal activity levels of phosphatidylinositol-3-kinase (PI3K)/Akt and MEK/Erk, accompanied by upregulated collagen synthesis and diminished proliferation and migration rates. We found that the absence of N-Ras did not affect TGF-ß1-induced proliferation and migration, which required PI3K/Akt but not Erk1/2 activation. Similar effector pathway dependence was found for fibronectin and collagen type I expression. Our results indicate that N-Ras might contribute to renal fibrosis through the down-regulation of ECM synthesis and up-regulation proliferation and migration modulating Akt activation. N-Ras also regulates TGF-ß1-induced collagen I and fibronectin expression through Erk-independent pathways.