PDGF-induced migration of synthetic vascular smooth muscle cells through c-Src-activated L-type Ca2+ channels with full-length CaV1.2 C-terminus

In atherosclerosis, vascular smooth muscle cells (VSMC) migrate from the media toward the intima of the arteries in response to cytokines, such as platelet-derived growth factor (PDGF). However, molecular mechanism underlying the PDGF-induced migration of VSMCs remains unclear. The migration of rat aorta-derived synthetic VSMCs, A7r5, in response to PDGF was potently inhibited by a Ca(V)1.2 channel inhibitor, nifedipine, and a Src family tyrosine kinase (SFK)/Abl inhibitor, bosutinib, in a less-than-additive manner. PDGF significantly increased Ca(V)1.2 channel currents without altering Ca(V)1.2 protein expression levels in A7r5 cells. This reaction was inhibited by C-terminal Src kinase, a selective inhibitor of SFKs. In contractile VSMCs, the C-terminus of Ca(V)1.2 is proteolytically cleaved into proximal and distal C-termini (PCT and DCT, respectively). Clipped DCT is noncovalently reassociated with PCT to autoinhibit the channel activity. Conversely, in synthetic A7r5 cells, full-length Ca(V)1.2 (Ca(V)1.2FL) is expressed much more abundantly than truncated Ca(V)1.2. In a heterologous expression system, c-Src activated Ca(V)1.2 channels composed of Ca(V)1.2FL but not truncated Ca(V)1.2 (Ca(V)1.2 Delta 1763) or Ca(V)1.2 Delta 1763 plus clipped DCT. Further, c-Src enhanced the coupling efficiency between the voltage-sensing domain and activation gate of Ca(V)1.2FL channels by phosphorylating Tyr1709 and Tyr1758 in PCT. Compared with Ca(V)1.2 Delta 1763, c-Src could more efficiently bind to and phosphorylate Ca(V)1.2FL irrespective of the presence or absence of clipped DCT. Therefore, in atherosclerotic lesions, phenotypic switching of VSMCs may facilitate pro-migratory effects of PDGF on VSMCs by suppressing posttranslational Ca(V)1.2 modifications.