FAK Is Required for TGFβ-induced JNK Phosphorylation in Fibroblasts: Implications for Acquisition of a Matrix-remodeling Phenotype

Abstract

Transforming growth factor β (TGFβ) plays a critical role in connective tissue remodeling by fibroblasts during development, tissue repair, and fibrosis. We investigated the molecular pathways in the transmission of TGFβ signals that lead to features of connective tissue remodeling, namely formation of an α-smooth muscle actin (α-SMA) cytoskeleton, matrix contraction, and expression of profibrotic genes. TGFβ causes the activation of focal adhesion kinase (FAK), leading to JNK phosphorylation. TGFβ induces JNK-dependent actin stress fiber formation, matrix contraction, and expression of profibrotic genes in fak+/+, but not fak−/−, fibroblasts. Overexpression of MEKK1, a kinase acting upstream of JNK, rescues TGFβ responsiveness of JNK-dependent transcripts and actin stress fiber formation in FAK-deficient fibroblasts. Thus we propose a FAK-MEKK1-JNK pathway in the transmission of TGFβ signals leading to the control of α-SMA cytoskeleton reorganization, matrix contraction, and profibrotic gene expression and hence to the physiological and pathological effects of TGFβ on connective tissue remodeling by fibroblasts.