Calmodulin antagonists inhibit insulin-stimulated GLUT4 (glucose transporter 4) translocation by preventing the formation of phosphatidylinositol 3,4,5-trisphosphate in 3T3L1 adipocytes.
It has been previously reported that calmodulin plays a regulatory role in the insulin stimulation of glucose transport. To examine the basis for this observation, we examined the effect of a panel of calmodulin antagonists that demonstrated a specific inhibition of insulin-stimulated glucose transporter 4 (GLUT4) but not insulin- or platelet-derived growth factor (PDGF)-stimulated GLUT1 translocation in 3T3L1 adipocytes. These treatments had no effect on insulin receptor autophosphorylation or tyrosine phosphorylation of insulin receptor substrate 1 (IRS1). Furthermore, IRS1 or phosphotyrosine antibody immunoprecipitation of phosphatidylinositol (PI) 3-kinase activity was not affected. Despite the marked insulin and PDGF stimulation of PI 3-kinase activity, there was a near complete inhibition of protein kinase B activation. Using a fusion protein of the Grp1 pleckstrin homology (PH) domain with the enhanced green fluorescent protein, we found that the calmodulin antagonists prevented the insulin stimulation of phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] formation in vivo. Similarly, although PDGF stimulation increased PI 3-kinase activity in in vitro immunoprecipitation assays, there was also no significant formation of PI(3,4,5)P3 in vivo. These data demonstrate that calmodulin antagonists prevent insulin-stimulated GLUT4 translocation by inhibiting the in vivo production of PI(3,4,5)P3 without directly affecting IRS1- or phosphotyrosine-associated PI 3-kinase activity. This phenomenon is similar to that observed for the PDGF stimulation of 3T3L1 adipocytes.
Yang
C
C
Department of Physiology and Biophysics, The University of Iowa, Iowa City 52242, USA.
Watson
R T
RT
Elmendorf
J S
JS
Sacks
D B
DB
Pessin
J E
JE
D016475:3T3 Cells / Q000187:drug effects / Q000378:metabolism; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000187:drug effects / Q000378:metabolism*; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D013449:Sulfonamides / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology
D002147:Calmodulin; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D013449:Sulfonamides; D014268:Trifluoperazine; C526295:Irs1 protein, mouse; C495678:Slc2a1 protein, mouse; C495693:Slc2a4 protein, mouse; C060974:phosphatidylinositol 3,4,5-triphosphate; C017967:W 7; C034700:N-(6-aminohexyl)-1-naphthalenesulfonamide; C033772:N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide