Increased migration in late G(1) phase in cultured smooth muscle cells

Migration and proliferation of smooth musclecells (SMC) contribute to neointimal formation after arterial injury.However, the relation between migration and proliferation in thesecells is obscure. To discriminate between migration and proliferation, we employed a migration assay of SMC at different phases of the cellcycle. Serum-deprived SMC were synchronized in different phases of thecell cycle by addition of serum for various periods of time. Migrationinduced by platelet-derived growth factor B-chain homodimer was maximalin SMC that were predominantly in the late G₁(G_1b) phase. In addition, in nonsynchronized SMC,65-75% of SMC that had migrated were in the G_1bphase. Phosphorylated myosin light chain was enriched around the cellperiphery in SMC in the G_1b phase compared with SMC in theother cell cycle phases. Interestingly, the Triton X-100-insolublefraction of myosin was remarkably decreased in G_1b-enrichedSMC. These findings suggest that migratory activity of SMC may becoupled with the G_1b phase. The phosphorylation andretention of myosin might explain some of the properties responsible for increased migration.