Insulin activates p38 mitogen-activated protein (MAP) kinase via a MAB kinase kinase (MKK) 3/MKK 6 pathway in vascular smooth muscle cells

Background Induction of stress-activated mitogen-activated protein (MAP) ki nases such as p38 could be important for the development of cardiovascular diseases since p38 MAP kinase activation stimulates apoptosis, cell growth, prostanoid formation and other cellular dysfunctions when induced by oxida nts, hyperosmolarity, or pro-inflammatory cytokines. On the other hand, ins ulin resistance is one of the most important factors promoting atherogenesi s, including cardiovascular diseases, but it is not clear how these differe nt factors transmit their signals intracellularly at the cytosolic and nucl ear levels. In this study, we investigated the effect of insulin on p38 mit ogen-activated protein (MAP) kinase activation in cultured rat vascular smo oth muscle cells (VSMC). Materials and methods VSMC were obtained from the aortas of male Wistar rat s by the media explant technique. After being stimulated by insulin with SB -203580, PD-98059, or GF109203X, the cells were solubilized and the express ions of MAP kinases, MAP kinase kinases and p70 S6 kinase were examined by immunoblot analysis. The amount of DNA synthesis was measured by [H-3]thymi dine incorporation. Results Insulin activated p38 MAP kinase phosphorylation in a dose-dependen t manner, and the phosphorylation was specifically inhibited by SB-203580, a p38 MAP kinase-specific inhibitor, but not by PD-98059, a specific inhibi tor of upstream kinase (MEK), of extracellular signal-regulated kinase (ERK ), or GF209203X, a protein kinase C-specific inhibitor. Insulin also activa ted MAP kinase kinase (MKK) 3/MKK 6 phosphorylation, the upstream kinase of p38 MAP kinase, but neither stress-activated protein kinase (SAPK)/ERK kin ase (SEK1/MKK4) nor SAPK/c-jun NH2-terminal protein kinase. Surprisingly, p hosphorylation of p70S6 kinase and an increase of DNA synthesis by insulin were suppressed dose dependently by SB-203580. Conclusion These results have established that insulin activates the p38 MA P kinase cascade via an MKK 3/6 pathway in rat VSMC, independently of a MEK -ERK cascade, and partly regulates cell growth.