Hic-5 Mediates TGFβ-Induced Adhesion in Vascular Smooth Muscle Cells by a Nox4-Dependent Mechanism

Objective-Focal adhesions (FAs) link the cytoskeleton to the extracellular matrix and as such play important roles in growth, migration, and contractile properties of vascular smooth muscle cells. Recently, it has been shown that downregulation of Nox4, a transforming growth factor (TGF) beta-inducible, hydrogen peroxide (H2O2)-producing enzyme, affects the number of FAs. However, the effectors downstream of Nox4 that mediate FA regulation are unknown. The FA resident protein H2O2 -inducible clone (Hic)-5 is H2O2 and TGF beta inducible, and a binding partner of the heat shock protein (Hsp) 27. The objective of this study was to elucidate the mechanism, by which Hic-5 and Hsp27 participate in TGF beta-induced, Nox4-mediated vascular smooth muscle cell adhesion and migration. Approach and Results-Through a combination of molecular biology and biochemistry techniques, we found that TGF beta, by a Nox4-dependent mechanism, induces the expression and interaction of Hic-5 and Hsp27, which is essential for Hic-5 localization to FAs. Importantly, we found that Hic-5 expression is required for the TGF beta-mediated increase in FA number, adhesive forces and migration. Mechanistically, Nox4 downregulation impedes Smad (small body size and mothers against decapentaplegic) signaling by TGF beta, and Hsp27 and Hic-5 upregulation by TGF beta is blocked in small body size and mothers against decapentaplegic 4-deficient cells. Conclusions-Hic-5 and Hsp27 are effectors of Nox4 required for TGF beta-stimulated FA formation, adhesion strength and migration in vascular smooth muscle cell.