Compartment-specific regulation of phosphoinositide 3-kinase by platelet-derived growth factor and insulin in 3T3-L1 adipocytes.
To understand how the stimulation of phosphoinositide 3-kinase (PI 3-kinase) by different growth factors can activate different subsets of downstream responses, growth-factor regulation of PI 3-kinase activity at different intracellular locations was investigated in 3T3-L1 adipocytes. Insulin caused a large stimulation of glucose transport and stimulated recruitment of transferrin receptors to the plasma membrane (PM) in these cells, whereas platelet-derived growth factor (PDGF)-bb was virtually without effect on these responses. Subcellular fractionation studies after stimulation with PDGF-bb or insulin revealed a differential effect of these growth factors on subcellular localization of PI 3-kinase activity. PDGF was more effective than insulin in stimulating PI 3-kinase activity and recruiting the p85 alpha PI 3-kinase adaptor subunit in the fraction containing the PM. However, in the microsomal fraction insulin significantly increased PI 3-kinase activity and p85 alpha levels, whereas PDGF was almost without effect. In the microsomal membrane fraction the insulin-stimulated recruitment of p85 alpha closely matched the increase PI 3-kinase activity, indicating that insulin stimulation of PI 3-kinase in this fraction is largely due to recruitment of PI 3-kinase enzyme rather than alterations in specific activity. Insulin-stimulated recruitment of p85 alpha to the microsomal membranes was not inhibited by wortmannin, indicating that PI 3-kinase activity was not required for this process. A further level of compartment-specific regulation of PI 3-kinase in response to PDGF was revealed by the finding that tyrosine phosphorylation of the p85 alpha adaptor was restricted to the PM-containing fraction. Insulin had no effect on p85 tyrosine phosphorylation in either fraction. In summary, these results suggest a basis by which insulin and PDGF could both use PI 3-kinase signalling cascades but achieve different signalling outcomes.
Navé
B T
BT
Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, U.K.
Haigh
R J
RJ
Hayward
A C
AC
Siddle
K
K
Shepherd
P R
PR
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000201:enzymology*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002462:Cell Membrane / Q000201:enzymology; D003847:Deoxyglucose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology*; D007329:Insulin Antagonists / Q000494:pharmacology; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011990:Receptors, Transferrin / Q000378:metabolism; D013347:Subcellular Fractions / Q000201:enzymology; D000077191:Wortmannin; D018909:src Homology Domains
D000730:Androstadienes; D051275:Glucose Transporter Type 4; D007328:Insulin; D007329:Insulin Antagonists; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D010982:Platelet-Derived Growth Factor; D011990:Receptors, Transferrin; C495693:Slc2a4 protein, mouse; D019000:Phosphotyrosine; D003847:Deoxyglucose; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D005947:Glucose; D000077191:Wortmannin