The slingshot family of phosphatases mediates cofilin activation during PDGF‐induced migration in vascular smooth muscle cells

Abstract

Platelet‐derived growth factor (PDGF) is a potent regulator of vascular smooth muscle cell (VSMC) migration. While a variety of signaling mechanisms have been reported during VSMC migration, ultimately the regulation of cell motility is via the actin cytoskeleton. We hypothesized that cofilin, a protein that facilitates actin depolymerization, is a key mediator of PDGF‐induced VSMC migration. In cultured rat aortic VSMCs, protein regulation was determined by immunoblotting with phosphospecific antibodies and migration was quantified using a modified Boyden chamber assay. Cofilin activity is increased by dephosphorylation at ser3, a process balanced by the dual regulation of LIM‐Kinase and the Slingshot family of phosphatases (SSH). Immunoblotting studies confirmed that PDGF increased cofilin activity in a time and dose dependent fashion. Relative to non‐treated control VSMCs, PDGF significantly increased VSMC migration (3.3 ± 0.4 fold), whereas in VSMCs treated with cofilin siRNA, PDGF‐induced migration is virtually eliminated (0.8 ± 0.1). The knockdown of SSH1 expression by siRNA resulted in attenuated PDGF‐induced activity of cofilin (∼80% inhibition) and a significant reduction in PDGF‐induced VSMC migration (4.4 ± 1.5; control vs 1.1 ± 0.7; siSSH1). Thus, these studies demonstrate that VSMC migration following PDGF stimulation is mediated by the SSH1 regulation of cofilin activity.AHA 0330019N