title: Muscle-specific deletion of rictor impairs insulin-stimulated glucose transport and enhances Basal glycogen synthase activity.
abstract: Rictor is an essential component of mTOR (mammalian target of rapamycin) complex 2 (mTORC2), a kinase complex that phosphorylates Akt at Ser473 upon activation of phosphatidylinositol 3-kinase (PI-3 kinase). Since little is known about the role of either rictor or mTORC2 in PI-3 kinase-mediated physiological processes in adult animals, we generated muscle-specific rictor knockout mice. Muscle from male rictor knockout mice exhibited decreased insulin-stimulated glucose uptake, and the mice showed glucose intolerance. In muscle lacking rictor, the phosphorylation of Akt at Ser473 was reduced dramatically in response to insulin. Furthermore, insulin-stimulated phosphorylation of the Akt substrate AS160 at Thr642 was reduced in rictor knockout muscle, indicating a defect in insulin signaling to stimulate glucose transport. However, the phosphorylation of Akt at Thr308 was normal and sufficient to mediate the phosphorylation of glycogen synthase kinase 3 (GSK-3). Basal glycogen synthase activity in muscle lacking rictor was increased to that of insulin-stimulated controls. Consistent with this, we observed a decrease in basal levels of phosphorylated glycogen synthase at a GSK-3/protein phosphatase 1 (PP1)-regulated site in rictor knockout muscle. This change in glycogen synthase phosphorylation was associated with an increase in the catalytic activity of glycogen-associated PP1 but not increased GSK-3 inactivation. Thus, rictor in muscle tissue contributes to glucose homeostasis by positively regulating insulin-stimulated glucose uptake and negatively regulating basal glycogen synthase activity.
authors.affiliation: Department of Pharmacology, University of Virginia Health System, P.O. Box 800735, 1300 Jefferson Park Ave., Charlottesville, VA 22908, USA. al4p@virginia.edu
authors.forename: Anil
authors.initials: A
authors.lastname: Kumar
authors.forename: Thurl E
authors.initials: TE
authors.lastname: Harris
authors.forename: Susanna R
authors.initials: SR
authors.lastname: Keller
authors.forename: Kin M
authors.initials: KM
authors.lastname: Choi
authors.forename: Mark A
authors.initials: MA
authors.lastname: Magnuson
authors.forename: John C
authors.initials: JC
authors.lastname: Lawrence
mesh_terms: D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D000076226:Rapamycin-Insensitive Companion of mTOR Protein
chemical_list: D002352:Carrier Proteins; D020690:GTPase-Activating Proteins; D007328:Insulin; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; C505647:Tbc1d4 protein, mouse; C525637:rictor protein, mouse; D010769:Phosphothreonine; D010768:Phosphoserine; D006003:Glycogen; D006006:Glycogen Synthase; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose