Protein kinase C-δ regulates migration and proliferation of vascular smooth muscle cells through the extracellular signal-regulated kinase 1/2

BackgroundSmooth muscle cell (SMC) migration and proliferation are early and crucial events in the pathogenesis of intimal hyperplasia, the primary cause of restenosis after vascular intervention. We tested the hypothesis that protein kinase C-δ (PKCδ), a ubiquitously expressed intracellular protein kinase, regulates vascular SMC proliferation and migration.MethodsExogenous PKCδ was expressed in cultured SMCs via stable transfection or adenovirus-mediated gene transfer. Conversely, endogenous PKCδ was inhibited by means of targeted gene deletion (gene knock-out). Cell proliferation and migration were determined by 3H-thymidine incorporation and 24-well transwell assay, respectively.ResultsWe isolated and examined three A10 SMC lines in which PKCδ was stably transfected. Compared with cells that were transfected with an empty vector, cells transfected with PKCδ exhibited reduced ability to proliferate. Moreover, PKCδ transfection inhibited SMC migration toward platelet-derived growth factor-BB. Similar inhibitory effects on proliferation and migration were also observed when PKCδ was introduced into primary aortic SMCs via an adenoviral vector. Interestingly, SMCs isolated from PKCδ knockout mice also displayed decreased chemotaxis and proliferation compared with PKCδ+/+ littermates, suggesting a complex yet critical role for PKCδ. We studied the mitogen-activated protein kinase extracellular signal-regulated kinases (ERK) 1/2 as a possible signaling pathway for PKCδ’s inhibitory effect. PKCδ overexpression diminished ERK1/2 activity. Molecular restoration of ERK activation reversed the inhibitory effect of PKCδ on SMC proliferation and migration.ConclusionsWe demonstrate that although normal migration and proliferation is lessened in SMCs deficient in PKCδ, its prolonged activation also diminishes those behaviors. This suggests a dual, critical role for PKCδ in SMC proliferation and migration, and thus intimal hyperplasia and restenosis.

Clinical RelevanceRestenotic or hyperplastic lesions are typified by dedifferentiated vascular smooth muscle cells (VSMC) that demonstrate excessive proliferation and migration. We have previously demonstrated that protein kinase C-δ (PKCδ) is a critical upstream factor leading to VSMC apoptosis. The present study shows that PKCδ, when ectopically expressed in VSMCs, also inhibits proliferation and migration as well as extracellular signal-regulated mitogen-activated protein kinase. Thus, gene transfer of PKCδ is a potential molecular therapeutic strategy to inhibit intimal hyperplasia.