H-ras induces glucose uptake in brown adipocytes in an insulin- and phosphatidylinositol 3-kinase-independent manner.
Fetal brown adipocytes (parental cells) expressed mainly Glut4 mRNA glucose transporter, the expression of Glut1 mRNA being much lower. At physiological doses, insulin stimulation for 15 min increased 3-fold glucose uptake and doubled the amount of Glut4 protein located at the plasma membrane. Moreover, phosphatidylinositol (PI) 3-kinase activity was induced by the presence of insulin in those cells, glucose uptake being precluded by PI 3-kinase inhibitors such as wortmannin or LY294002. H-raslys12-transformed brown adipocytes showed a 10-fold higher expression of Glut1 mRNA and protein than parental cells, Glut4 gene expression being completely down-regulated. Glucose uptake increased by 10-fold in transformed cells compared to parental cells; this uptake was unaltered in the presence of insulin and/or wortmannin. Transient transfection of parental cells with a dominant form of active Ras increased basal glucose uptake by 5-fold, no further effects being observed in the presence of insulin. However, PI 3-kinase activity (immunoprecipitated with anti-alphap85 subunit of PI 3-kinase) remained unaltered in H-ras permanent and transient transfectants. Our results indicate that activated Ras induces brown adipocyte glucose transport in an insulin-independent manner, this induction not involving PI 3-kinase activation.
Valverde
A M
AM
Faculty of Pharmacy, University Complutense, Madrid, 28040, Spain.
Navarro
P
P
Benito
M
M
Lorenzo
M
M
D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D002001:Adipose Tissue, Brown / Q000166:cytology; D000818:Animals; D002461:Cell Line, Transformed; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D014162:Transfection
D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495679:Slc2a1 protein, rat; C495694:Slc2a4 protein, rat; D019869:Phosphatidylinositol 3-Kinases; D016283:Proto-Oncogene Proteins p21(ras); D005947:Glucose