title: Defining the contribution of AMP-activated protein kinase (AMPK) and protein kinase C (PKC) in regulation of glucose uptake by metformin in skeletal muscle cells.
abstract: The importance of AMP-activated protein kinase (AMPK) and protein kinase C (PKC) as effectors of metformin (Met) action on glucose uptake (GU) in skeletal muscle cells was investigated. GU in L6 myotubes was stimulated 2-fold following 16 h of Met treatment and acutely enhanced by insulin in an additive fashion. Insulin-stimulated GU was sensitive to PI3K inhibition, whereas that induced by Met was not. Met and its related biguanide, phenformin, stimulated AMPK activation/phosphorylation to a level comparable with that induced by the AMPK activator, 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide (AICAR). However, the increase in GU elicited by AICAR was significantly lower than that induced by either biguanide. Expression of a constitutively active AMPK mimicked the effects of AICAR on GU, whereas a dominant interfering AMPK or shRNA silencing of AMPK prevented AICAR-stimulated GU and Met-induced AMPK signaling but only repressed biguanide-stimulated GU by ∼20%. Consistent with this, analysis of GU in muscle cells from α1(-/-)/α2(-/-) AMPK-deficient mice revealed a significant retention of Met-stimulated GU, being reduced by ∼35% compared with that of wild type cells. Atypical PKCs (aPKCs) have been implicated in Met-stimulated GU, and in line with this, Met and phenformin induced activation/phosphorylation of aPKC in L6 myotubes. However, although cellular depletion of aPKC (>90%) led to loss in biguanide-induced aPKC phosphorylation, it had no effect on Met-stimulated GU, whereas inhibitors targeting novel/conventional PKCs caused a significant reduction in biguanide-induced GU. Our findings indicate that although Met activates AMPK, a significant component of Met-stimulated GU in muscle cells is mediated via an AMPK-independent mechanism that involves novel/conventional PKCs.
authors.affiliation: Division of Cell Signaling and Immunology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom.
authors.forename: Sophie
authors.initials: S
authors.lastname: Turban
authors.forename: Clare
authors.initials: C
authors.lastname: Stretton
authors.forename: Olivier
authors.initials: O
authors.lastname: Drouin
authors.forename: Charlotte J
authors.initials: CJ
authors.lastname: Green
authors.forename: Maria L
authors.initials: ML
authors.lastname: Watson
authors.forename: Alexander
authors.initials: A
authors.lastname: Gray
authors.forename: Fiona
authors.initials: F
authors.lastname: Ross
authors.forename: Louise
authors.initials: L
authors.lastname: Lantier
authors.forename: Benoit
authors.initials: B
authors.lastname: Viollet
authors.forename: D Grahame
authors.initials: DG
authors.lastname: Hardie
authors.forename: Andre
authors.initials: A
authors.lastname: Marette
authors.forename: Harinder S
authors.initials: HS
authors.lastname: Hundal
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D020536:Enzyme Activators / Q000494:pharmacology; D005947:Glucose / Q000235:genetics / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D018345:Mice, Knockout; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000201:enzymology*; D010629:Phenformin / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D012265:Ribonucleotides / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors
chemical_list: D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide; D020536:Enzyme Activators; D005947:Glucose; D007004:Hypoglycemic Agents; D008687:Metformin; D010629:Phenformin; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D012265:Ribonucleotides; C548179:Prkaa1 protein, mouse; C534978:Prkaa2 protein, mouse; C031143:AICA ribonucleotide