title: Adiponectin sensitizes insulin signaling by reducing p70 S6 kinase-mediated serine phosphorylation of IRS-1.
abstract: Adiponectin functions as an insulin sensitizer, and yet the underlying molecular mechanism(s) remains largely unknown. We found that treating C2C12 myotubes with adiponectin or rapamycin enhanced the ability of insulin to stimulate IRS-1 tyrosine phosphorylation and Akt phosphorylation, concurrently with reduced p70 S6 kinase phosphorylation at Thr389 as well as IRS-1 phosphorylation at Ser302 and Ser636/639. Overexpression of dominant-negative AMP kinase (AMPK), but not dominant-negative p38 MAPK, reduced the insulin-sensitizing effect of adiponectin. Rapamycin, but not adiponectin, enhanced insulin-stimulated Akt phosphorylation in HeLa cells, which lack LKB1, and exogenous expression of LKB1 in HeLa cells rescued the insulin-sensitizing effect of adiponectin. Finally, overexpression of wild-type Rheb (Ras homology-enriched in brain) or the TSC2 mutant lacking the AMPK phosphorylation site (TSC2S1345A) inhibited the insulin-sensitizing effect of adiponectin in C2C12 cells. These results indicate that activation of the LKB1/AMPK/TSC1/2 pathway alleviates the p70 S6 kinase-mediated negative regulation of insulin signaling, providing a mechanism by which adiponectin increases insulin sensitivity in cells.
authors.affiliation: Department of Pharmacology, University of Texas Health Science Center, San Antonio, Texas 78229, USA.
authors.forename: Changhua
authors.initials: C
authors.lastname: Wang
authors.forename: Xuming
authors.initials: X
authors.lastname: Mao
authors.forename: Lixin
authors.initials: L
authors.lastname: Wang
authors.forename: Meilian
authors.initials: M
authors.lastname: Liu
authors.forename: Michael D
authors.initials: MD
authors.lastname: Wetzel
authors.forename: Kun-Liang
authors.initials: KL
authors.lastname: Guan
authors.forename: Lily Q
authors.initials: LQ
authors.lastname: Dong
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
mesh_terms: D055372:AMP-Activated Protein Kinases; D052242:Adiponectin / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D008954:Models, Biological; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D052242:Adiponectin; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; C000624651:Tsc1 protein, mouse; C000624654:Tsc2 protein, mouse; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D012694:Serine; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C491654:Stk11 protein, mouse; D048051:p38 Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases