CCN2 is necessary for adhesive responses to transforming growth factor-β1 in embryonic fibroblasts

CCN2 is induced by transforming growth factor-beta (TGF beta) in fibroblasts and is overexpressed in connective tissue disease. CCN2 has been proposed to be a downstream mediator of TGF beta action in fibroblasts; however, the role of CCN2 in regulating this process unclear. By using embryonic fibroblasts isolated from ccn2-/- mice, we showed that CCN2 is required for a subset of responses to TGF beta. Affymetrix genome-wide expression profiling revealed that 942 transcripts were induced by TGF beta greater than 2-fold in ccn2-/- fibroblasts, of which 345 were not induced in ccn2-/- fibroblasts, including pro-adhesive and matrix remodeling genes. Whereas TGF beta properly induced a generic Smad3-responsive promoter in ccn2-/- fibroblasts, TGF beta-induced activation of focal adhesion kinase (FAK) and Akt was reduced in ccn2-/- fibroblasts. Emphasizing the importance of FAK and Akt activation in CCN2-dependent transcriptional responses to TGF beta in fibroblasts, CCN2 dependent transcripts were not induced by TGF beta in fak-/- fibroblasts and were reduced by wortmannin in wild-type fibroblasts. Akt1 overexpression in ccn2-/- fibroblasts rescued the TGF beta-induced transcription of CCN2-dependent mRNA. Finally, induction of TGF beta-induced fibroblast adhesion to fibronectin and type I collagen was significantly diminished in ccn2-/- fibroblasts. Thus in embryonic fibroblasts, CCN2 is a necessary cofactor required for TGF beta to activate the adhesive FAK/Akt/phosphatidylinositol 3-kinase cascade, FAK/Akt-dependent genes, and adhesion to matrix.