Phorbol esters stimulate phosphatidylinositol 3,4,5-trisphosphate production in 3T3-L1 adipocytes: implications for stimulation of glucose transport.
The effects of insulin and phorbol 12-myristate 13-acetate (PMA) on the levels of cellular phosphoinositides were investigated in 3T3-L1 adipocytes. Stimulation for 4 min with PMA (1 microM) or insulin (10 nM) increased levels of PtdIns(3,4,5)P3 approx. 2-fold and 6-fold respectively. PMA also had a small effect on the cellular levels of PtdIns4P, whereas insulin had no effect on PtdIns4P levels; levels of PtdIns(4,5)P2 and PtdIns3P were not significantly affected by either agent. Insulin increased the levels of the p85 alpha subunit of phosphoinositide (PI) 3-kinase associated with membranes, whereas PMA decreased levels of membrane-associated p85 alpha. PMA did not increase PI 3-kinase activity in anti-phosphotyrosine or anti-p85 immunoprecipitates. The stimulation of glucose transport by insulin or PMA was blocked by 100 nM wortmannin or 10 ng/ml LY294002, indicating that PI 3-kinase is essential for stimulation by both agents. In summary, these results demonstrate: (1) that PMA and insulin stimulate PtdIns(3,4,5)P3 production by distinct mechanisms in 3T3-L1 adipocytes, and (2) that stimulation of PtdIns(3,4,5)P3 production by PMA is likely to be important in signalling pathways leading from PMA stimulation to end-point responses such as glucose transport.
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B T
BT
Department of Clinical Biochemistry, University of Cambridge, UK.
Siddle
K
K
Shepherd
P R
PR
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D007329:Insulin Antagonists / Q000494:pharmacology; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates / Q000096:biosynthesis*; D010716:Phosphatidylinositols / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D019000:Phosphotyrosine / Q000276:immunology; D011233:Precipitin Tests; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D000077191:Wortmannin
D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D007328:Insulin; D007329:Insulin Antagonists; D009025:Morpholines; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; C060974:phosphatidylinositol 3,4,5-triphosphate; D019000:Phosphotyrosine; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D005947:Glucose; D013755:Tetradecanoylphorbol Acetate; D000077191:Wortmannin