High glucose attenuates insulin-induced mitogen-activated protein kinase phosphatase-1 (MKP-1) expression in vascular smooth muscle cells.
The mechanisms for the effect of hyperglycemia on insulin-induced mitogenesis were investigated using rat vascular smooth muscle cells (VSMC). VSMC were preincubated in serum-free medium with low (5 mM) glucose (LG condition) or high (25 mM) glucose (HG condition), and examined for DNA synthesis using bromodeoxyuridine (BrdUrd) incorporation. Mitogen-activated protein kinase (MAPK) activity and MAPK phosphatase (MKP-1) protein expression were detected by Western blot analysis. Phosphatidylinositol 3-kinase (PI-3K) activity was detected by thin layer chromatography. Insulin induced a dose-dependent increase in BrdUrd incorporation (123.3+/-2.6% over basal level with 1 microM insulin) in the LG group and this effect was significantly enhanced (161.6+/-10.4% over basal level) in the HG group. In the LG group, MAPK activity was transient with a peak activation (137.4+/-11.2% over basal level) after 10 min exposure to 100 nM insulin. In the HG group, the MAPK activity was significantly potentiated (two-fold compared to the LG group) and was sustained even after 60 min. Insulin also induced PI-3K activity and MKP-1 expression, both of which were blocked by the PI-3K inhibitor wortmannin. In the HG group, insulin-induced PI-3K and MKP-1 expression was almost abolished. In conclusion, high glucose enhances insulin-induced mitogenesis associated with the potentiation of insulin-stimulated MAPK activity in VSMC. These effects of glucose might in part be due to the attenuation of MKP-1 expression through the blockage of the insulin-PI-3K signal pathway.
Takehara
N
N
The First Department of Medicine, Asahikawa Medical College, 4-5-3 Nishikagura, 078-8510, Asahikawa, Japan.
Kawabe
J
J
Aizawa
Y
Y
Hasebe
N
N
Kikuchi
K
K
D000818:Animals; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D054638:Dual Specificity Phosphatase 1; D005947:Glucose / Q000494:pharmacology*; D017874:Immediate-Early Proteins / Q000096:biosynthesis*; D007328:Insulin; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis*; D051381:Rats; D015398:Signal Transduction
D018797:Cell Cycle Proteins; D017874:Immediate-Early Proteins; D007328:Insulin; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054638:Dual Specificity Phosphatase 1; C517021:Dusp1 protein, rat; D017027:Protein Tyrosine Phosphatases; D005947:Glucose