MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVATION IS INVOLVED IN PLATELET-DERIVED GROWTH FACTOR-DIRECTED MIGRATION BY VASCULAR SMOOTH-MUSCLE CELLS

Migration of vascular smooth muscle cells (VSMCs) is a crucial respons e to vascular injury resulting in neointima formation and atherosclero sis. Platelet-derived growth factor (PDGF-BB) functions as a potent ch emoattractant for VSMCs and enhances these pathologies in the vasculat ure. However, little is known about the intracellular pathways that me diate VSMC migration. In the present study, we investigated the role o f mitogen-activated protein kinase (MAPK) activation in this function, since PDGF-BB as well as other growth factors activate this pathway. Using an in-gel kinase assay, we observed that PD 98059, an inhibitor of MEK that activates MAP kinase, inhibited PDGF-BB-induced activation of ERK-1 and ERK-2 in cultured rat aortic smooth muscle cells in a co ncentration-dependent manner. In contrast, PDGF-mediated activation of intracellular calcium release was not affected by PD 98059. The chemo tactic response of both rat aortic smooth muscle cells (RASMCs) and hu man umbilical vein smooth muscle cells (HUSMCs) toward PDGF-BB (10 ng/ mL) was significantly reduced by PD 98059 (10 mu mol/L) to 41.7 +/- 7. 1% in RASMCs (P < .01) and to 47.2 +/- 5.3% in HUSMCs (P < .01). Simil ar inhibition was seen at 30 mu mol/L, less at 1 mu mol/L. To further confirm the specificity of these results implicating the MAPK pathway, an antisense oligodeoxynucleotide (ODN) directed against the initiati on translation site of rat ERK-1 and ERK-2 mRNA was used to suppress M AP kinase synthesis and function in rat VSMCs. Liposomal transfection with 0.4 mu mol/L antisense ODN reduced ERK-1 and ERK-2 protein by 65% (P < .01) after 48 hours. The chemotactic response to PDGF-BB (10 ng/ mL) was reduced by 75% (P < .01) in rat VSMCs transfected with the sam e antisense ODN concentration. Sense and scrambled control ODNs (0.4 m u mol/L) did not affect ERK-1 and ERK-2 protein concentrations or chem otaxis of VSMCs induced by PDGF-BB. These experiments provide the firs t evidence that activation of MAPK is a critical event in PDGF-mediate d signal transduction regulating VSMC migration.