Caveolin-1 can regulate vascular smooth muscle cell fate by switching platelet-derived growth factor signaling from a proliferative to an apoptotic pathway

Background - Caveolin-1 is a regulator of signaling events originating from plasma membrane microdomains termed caveolae. This study was performed to determine the regulatory role of caveolin-1 on the proliferative events induced by platelet-derived growth factor (PDGF) in vascular smooth muscle cells (VSMCs). Methods and Results - Treatment of VSMCs with PDGF for 24 hours resulted in a loss of caveolin-1 protein expression and plasma membrane-associated caveolae, despite a 3-fold increase in caveolin-1 mRNA. Pretreatment of VSMCs with chloroquine, an inhibitor of lysosomal function, inhibited the PDGF-induced loss of caveolin-1. These studies demonstrated that caveolin-1 was a target of PDGF signaling events. Adenoviral overexpression of caveolin-1 was associated with a switch in PDGF-induced signaling events from a proliferative response to an apoptotic response. This overexpression inhibited PDGF-induced expression of cyclin D1 in the presence of unaffected mitogen-activated protein kinase activation. Conclusions - Taken together, these studies suggest that caveolin-1 is an inhibitor of PDGF proliferative responses and might be capable of transforming PDGF-induced proliferative signals into death signals.