Endoproteolytic Activation of α v Integrin by Proprotein Convertase PC5 Is Required for Vascular Smooth Muscle Cell Adhesion to Vitronectin and Integrin-Dependent Signaling

Abstract

Background— Integrins play an important role for vascular smooth muscle cell (VSMC) migration during the development of atherosclerosis and restenosis. Integrin α v -subunit consists of disulphide-bound 125-kDa heavy and 25-kDa light chains, which are generated by endoproteolytic cleavage. This type of activation requires the presence of suitable proprotein convertases (PCs). Based on ex vivo and in vitro data, the PC5 isozyme has been suggested to be the major integrin convertase. We have recently demonstrated that PC5 is upregulated during vascular remodeling in rodents, colocalizing with α v in VSMCs. The aim of this study was to investigate the activation of α v by PCs in VSMCs and its consequences for α v -dependent cell functions. Methods and Results— Immunoblotting demonstrated that inhibition of PC activity by the specific pharmacological inhibitor dec-CMK inhibits α v cleavage in VSMCs. These results were confirmed using PC5-specific antisense oligonucleotides. PC5-antisense oligonucleotides and dec-CMK inhibited VSMC adhesion to the α v β 3 /β 5 ligand vitronectin (both P <0.05). Furthermore, PC5-asODNs inhibited VSMC migration on vitronectin-coated wells ( P <0.05). Inhibition of PC activity and consequently α v cleavage inhibited the adhesion-dependent focal adhesion kinase Y397 -autophosphorylation and subsequent Akt activation, whereas phosphorylation of extracellular signal-regulated kinase 1/2 was not affected. In human endarterectomy lesions, PC5 colocalized with α v integrin in VSMCs in the atherosclerotic plaques. Conclusions— The present study demonstrates that α v endoproteolytic activation is necessary for integrin-mediated adhesion and migration as well as signaling and requires PC5 in VSMCs. The colocalization of PC5 and α v in human carotid plaques indicates that PC5 might play a key role for α v activation in vivo.