TGF-β-regulated collagen type I accumulation:: role of Src-based signals

Transforming growth factor-beta ( TGF-beta) stimulates myofibroblast transdifferentiation, leading to type I collagen accumulation and fibrosis. We investigated the function of Src in TGF-beta- induced collagen I accumulation. In human mesangial cells, PTyr416 Src ( activated Src) was 3.3- fold higher in TGF-beta- treated cells than in controls. Src activation by TGF-beta was blocked by rottlerin and by a dominant negative mutant of protein kinase C delta ( PKC delta), showing that TGF-beta activates Src by a PKC delta-based mechanism. Pharmacological inhibitors and a dominant negative Src mutant prevented the increase in collagen type I secretion in cells exposed to TGF-beta. Similarly, on- target Src small interference RNA ( siRNA) prevented type I collagen secretion in response to TGF-beta, but off- target siRNA complexes had no effect. It is well established in mesangial cells that upregulation of type I collagen by TGF-beta requires extracellular signal- regulated kinase 1/2 ( ERK1/2), and we found that activation of ERK1/ 2 by TGF-beta requires Src. In conclusion, these results suggest that stimulation of collagen type I secretion by TGF-beta requires a PKC delta-Src-ERK1/2 signaling motif.