Insulin activates p38 mitogen-activated protein (MAP) kinase via a MAP kinase kinase (MKK) 3/MKK 6 pathway in vascular smooth muscle cells.
BACKGROUND
Induction of stress-activated mitogen-activated protein (MAP) kinases 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 oxidants, hyperosmolarity, or pro-inflammatory cytokines. On the other hand, insulin resistance is one of the most important factors promoting atherogenesis, including cardiovascular diseases, but it is not clear how these different factors transmit their signals intracellularly at the cytosolic and nuclear levels. In this study, we investigated the effect of insulin on p38 mitogen-activated protein (MAP) kinase activation in cultured rat vascular smooth muscle cells (VSMC).


METHODS
VSMC were obtained from the aortas of male Wistar rats by the media explant technique. After being stimulated by insulin with SB-203580, PD-98059, or GF109203X, the cells were solubilized and the expressions of MAP kinases, MAP kinase kinases and p70 S6 kinase were examined by immunoblot analysis. The amount of DNA synthesis was measured by [3H]thymidine incorporation.


RESULTS
Insulin activated p38 MAP kinase phosphorylation in a dose-dependent manner, and the phosphorylation was specifically inhibited by SB-203580, a p38 MAP kinase-specific inhibitor, but not by PD-98059, a specific inhibitor of upstream kinase (MEK), of extracellular signal-regulated kinase (ERK), or GF209203X, a protein kinase C-specific inhibitor. Insulin also activated MAP kinase kinase (MKK) 3/MKK 6 phosphorylation, the upstream kinase of p38 MAP kinase, but neither stress-activated protein kinase (SAPK)/ERK kinase (SEK1/MKK4) nor SAPK/c-jun NH2-terminal protein kinase. Surprisingly, phosphorylation of p70 S6 kinase and an increase of DNA synthesis by insulin were suppressed dose dependently by SB-203580.


CONCLUSIONS
These results have established that insulin activates the p38 MAP kinase cascade via an MKK 3/6 pathway in rat VSMC, independently of a MEK-ERK cascade, and partly regulates cell growth.
Igarashi
M
M
Third Department of Internal Medicine, Yamagata University School of Medicine, Japan. migarasi@med.id.yamagata-u.ac.jp
Yamaguchi
H
H
Hirata
A
A
Daimon
M
M
Tominaga
M
M
Kato
T
T
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D020935:MAP Kinase Signaling System; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D048056:Mitogen-Activated Protein Kinase 9; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D007211:Indoles; D007328:Insulin; D008301:Maleimides; D011725:Pyridines; D004247:DNA; D048056:Mitogen-Activated Protein Kinase 9; D011505:Protein-Tyrosine Kinases; D019893:Ribosomal Protein S6 Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D020929:Mitogen-Activated Protein Kinase Kinases; C070515:bisindolylmaleimide I; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one