Regulation of vascular smooth muscle migration by mitogen-activated protein kinase and calcium/calmodulin-dependent protein kinase II signaling pathways

Platelet-derived growth factor BE (PDGF BE) activation of the mitogen-activ ated protein kinases (MAPK), ERK1 and ERK2, has been shown to be necessary for mitogen-stimulated proliferation, but its role in regulating cell migra tion and its relationship to other chemotactic signaling events, such as Ca mKII activation, has not been defined. Using a modified Boyden chamber appa ratus, we tested the effects of a selective inhibitor of the upstream activ ator of ERK1/2, MEK1, on PDGF-stimulated rat aortic vascular smooth muscle cells (VSMCs) alone and in combination with KN62, a selective inhibitor of CamKII. The MEK1 inhibitor, PD98059, caused a dose-dependent reduction in E RK2 activity that paralleled a decrease in migration up to 60%, This inhibi tion of migration was, similar to that seen with KN62 and the combined effe cts of both inhibitors were non-additive. Although KN62 did not affect ERK2 activity in response to PDGF, PD98059 markedly inhibited PDGF-stimulated C amKII activity, suggesting that activation of CamKII by PDGF was dependent on ERK activity and that the effects of ERK inhibition on migration may be mediated through its ability to inhibit CamKII activity. To directly test t his, VSMCs were infected with a recombinant adenovirus expressing constitut ively activated CamKII. Infection reversed the inhibitory effects of KN62 o n migration, but had no effect on the inhibition of migration seen with PD9 8059. These results suggest that while MAPK may act upstream of CamKII to c ontrol its activation in response to PDGF, it also regulates migration inde pendently of CamKII activation. (C) 1998 Academic Press.