title: Increased p85/55/50 expression and decreased phosphotidylinositol 3-kinase activity in insulin-resistant human skeletal muscle.
abstract: Insulin resistance is predominantly characterized by decreased insulin-stimulated glucose uptake into skeletal muscle. In the current study, we have assessed various aspects of the phosphatidylinositol (PI) 3-kinase pathway in skeletal muscle biopsies obtained from normal, obese nondiabetic, and type 2 diabetic subjects, before and after a 5-h insulin infusion. We found a highly significant inverse correlation between in vivo insulin sensitivity (as measured by the glucose infusion rate) and increased protein expression of p85/55/50, protein kinase C (PKC)-theta activity, levels of pSer307 insulin receptor substrate (IRS)-1 and p-Jun NH2-terminal kinase (JNK)-1, and myosin heavy chain IIx fibers. Increased basal phosphorylation of Ser307 IRS-1 in the obese and type 2 diabetic subjects corresponds with decrease in insulin-stimulated IRS-1 tyrosine phosphorylation, PI 3-kinase activity, and insulin-induced activation of Akt and, more prominently, PKC-zeta/lambda. In summary, increased expression of the PI 3-kinase adaptor subunits p85/55/50, as well as increased activity of the proinflammatory kinases JNK-1, PKC-theta, and, to a lesser extent, inhibitor of kappaB kinase-beta, are associated with increased basal Ser307 IRS-1 phosphorylation and decreased PI 3-kinase activity and may follow a common pathway to attenuate in vivo insulin sensitivity in insulin-resistant subjects. These findings demonstrate interacting mechanisms that can lead to impaired insulin-stimulated PI 3-kinase activity in skeletal muscle from obese and type 2 diabetic subjects.
authors.affiliation: University of California at San Diego, Department of Medicine (0673), 225 Stein Clinical Research Bldg., 9500 Gilman Dr., La Jolla, CA 92093, USA.
authors.forename: Gautam K
authors.initials: GK
authors.lastname: Bandyopadhyay
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Yu
authors.forename: Jachelle
authors.initials: J
authors.lastname: Ofrecio
authors.forename: Jerold M
authors.initials: JM
authors.lastname: Olefsky
mesh_terms: D000328:Adult; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology / Q000473:pathology; D004789:Enzyme Activation; D006019:Glycolysis; D006801:Humans; D007249:Inflammation / Q000201:enzymology; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D007527:Isoenzymes / Q000378:metabolism; D016014:Linear Models; D008875:Middle Aged; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000473:pathology; D009765:Obesity / Q000201:enzymology / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000032:analysis* / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021122:Protein Subunits / Q000032:analysis*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D000099293:Protein Kinase C-lambda; D000099221:Protein Kinase C zeta
chemical_list: D055504:Insulin Receptor Substrate Proteins; D007527:Isoenzymes; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases; D000099293:Protein Kinase C-lambda; D000099221:Protein Kinase C zeta; C526292:IRS1 protein, human; C494918:AKT1 protein, human