Smooth muscle cell migration and proliferation are mediated by distinct phases of activation of the intracellular messenger mitogen-activated protein kinase

Purpose: Mitogen-activated protein kinase (MAPK) is a ubiquitous signaling protein that has been associated with cellular proliferation; however, its role in cellular migration has not been established. In this study, we investigate the role of MAPK: in platelet-derived growth factor (PDGF)-induced migration and proliferation of human vascular smooth muscle cells (SMCs). Methods: SMC migration was measured using a microchemotaxis assay (4 hours), and proliferation was assessed using H-3-thymidine uptake and cell counts. PD098059 was used as a specific noncompetitive inhibitor of MAPK activation. Results: Coincubation of SMCs with PD098059 resulted in significant inhibition of PDGF-BB (5 ng/ml)-induced SMC chemotaxis and proliferation. The IC50 for both processes was approximately 10 mu mol/L with complete inhibition at 50 mu mol/L. Stimulation of SMCs with PDGP produced an early peak in MAPK activity followed by a plateau of activity that persisted for 24 hours. We hypothesized that variations in the temporal activation of MAPK might explain the action of this enzyme on these two disparate cellular events. By adding PD098059 at intervals after stimulation of SMCs with PDGP, we demonstrated an association between MAPK activity within the first 15 min minutes and SMC migration, whereas MAPK activity between 1 and 4 hours was associated with SMC proliferation. Conclusions: MP;IR activity is essential for both SMC migration and proliferation, and distinct phases of enzyme activation are required to stimulate these two discrete cellular events. Inhibition of this signaling protein may prove to be a useful method for preventing intimal hyperplasia.