We conducted a study to investigate whether expression of the contractile proteins in cultured rat mesangial cells (MC) was associated with the cell cycle and protein kinase C (PKC). When growth-arrested MC were stimulated with 100 nM phorbol myristate acetate (PMA) for 24 hours, an increased expression of smooth muscle α-actin and vimentin was detected by immunocytochemistry. A proportion of the S- and G2/M-phase in MC was increased in accordance with the enhanced expression of contractile proteins on flow cytometry. Immunoblot analysis revealed that 100 nM PMA stimulated expression of α-actin and vimentin as a single band. These results indicate that expression of contractile proteins, such as α-actin and vimentin, is dependent on the cell cycle and PKC, suggesting a phenotypic change in which MC assume smooth muscle cell characteristics.
