PURIFICATION AND CHARACTERIZATION OF AN AUTOCRINE MIGRATION FACTOR FOR VASCULAR SMOOTH-MUSCLE CELLS (SMC), SMC-DERIVED MIGRATION FACTOR

Migration of medial smooth muscle cells (SMC) into the intima is a key step in intimal thickening of atherosclerotic tissues. We previously reported that cultured SMC secrete a potent migration factor for SMC, named SMC-derived migration factor (SDMF). We purified this factor to homogeneity from 20 liters of serum-free conditioned medium of culture d rat aortic SMC by sequential heparin-Sepharose column, red-Sepharose column, TSK-heparin high performance liquid chromatography (HPLC) col umn, and Superose 6 HPLC column chromatographies. SDMF was found to be a 58-kDa polypeptide by sodium dodecyl sulfate-polyacrylamide gel ele ctrophoresis. Reduction by mercaptoethanol caused only a slight decrea se in its molecular mass to 53 kDa. Preparative isoelectric focusing r evealed that SDMF is a basic protein with a pI of approximately 10. Pu rified SDMF enhanced the migration of rat SMC dose dependently, its ma ximal activity being 4 times that of platelet-derived growth factor-BB . In contrast, SDMF did not enhance the migration of endothelial cells from either human umbilical cord vein or rabbit retinal tissue. SDMF had no effect on the proliferation of SMC. These findings suggest that SDMF enhances SMC migration in vascular walls and that the autocrine system of SMC migration contributes to the formation of intimal thicke ning in atheroma formation.