The tumor suppressor PTEN negatively regulates insulin signaling in 3T3-L1 adipocytes.
PTEN is a tumor suppressor with sequence homology to protein-tyrosine phosphatases and the cytoskeleton protein tensin. PTEN is capable of dephosphorylating phosphatidylinositol 3,4, 5-trisphosphate in vitro and down-regulating its levels in insulin-stimulated 293 cells. To study the role of PTEN in insulin signaling, we overexpressed PTEN in 3T3-L1 adipocytes approximately 30-fold above uninfected or control virus (green fluorescent protein)-infected cells, using an adenovirus gene transfer system. PTEN overexpression inhibited insulin-induced 2-deoxy-glucose uptake by 36%, GLUT4 translocation by 35%, and membrane ruffling by 50%, all of which are phosphatidylinositol 3-kinase-dependent processes, compared with uninfected cells or cells infected with control virus. Microinjection of an anti-PTEN antibody increased basal and insulin stimulated GLUT4 translocation, suggesting that inhibition of endogenous PTEN function led to an increase in intracellular phosphatidylinositol 3,4,5-trisphosphate levels, which stimulates GLUT4 translocation. Further, insulin-induced phosphorylation of downstream targets Akt and p70S6 kinase were also inhibited significantly by overexpression of PTEN, whereas tyrosine phosphorylation of the insulin receptor and IRS-1 or the phosphorylation of mitogen-activated protein kinase were not affected, suggesting that the Ras/mitogen-activated protein kinase pathway remains fully functional. Thus, we conclude that PTEN may regulate phosphatidylinositol 3-kinase-dependent insulin signaling pathways in 3T3-L1 adipocytes.
Nakashima
N
N
Department of Medicine, Division of Endocrinology and Metabolism, University of California, San Diego, La Jolla, California 92093, USA.
Sharma
P M
PM
Imamura
T
T
Bookstein
R
R
Olefsky
J M
JM
D016475:3T3 Cells; D000256:Adenoviridae / Q000235:genetics; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D003847:Deoxyglucose / Q000378:metabolism; D018014:Gene Transfer Techniques; D051275:Glucose Transporter Type 4; D049452:Green Fluorescent Proteins; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D020935:MAP Kinase Signaling System; D051379:Mice; D008856:Microscopy, Fluorescence; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000502:physiology*; D010766:Phosphorylation; D025521:Tumor Suppressor Proteins
D018076:DNA, Complementary; D051275:Glucose Transporter Type 4; D007328:Insulin; D008164:Luminescent Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse; D025521:Tumor Suppressor Proteins; D049452:Green Fluorescent Proteins; D003847:Deoxyglucose; D019869:Phosphatidylinositol 3-Kinases; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human