title: Metformin regulates glucose transporter 4 (GLUT4) translocation through AMP-activated protein kinase (AMPK)-mediated Cbl/CAP signaling in 3T3-L1 preadipocyte cells.
abstract: Metformin is a leading oral anti-diabetes mellitus medication and is known to stimulate GLUT4 translocation. However, the mechanism by which metformin acts is still largely unknown. Here, we showed that short time treatment with metformin rapidly increased phosphorylation of Cbl in an AMP-activated protein kinase (AMPK)-dependent fashion in 3T3-L1 preadipocytes. Metformin also increased phosphorylation of Src in an AMPK-dependent manner. Src inhibition blocked metformin-mediated Cbl phosphorylation, suggesting that metformin stimulates AMPK-Src-Cbl axis pathway. In addition, long term treatment with metformin stimulated the expression of Cbl-associated protein (CAP) mRNA and protein. Long term treatment with metformin stimulated phosphorylation of c-Jun N-terminal kinase (JNK) and its downstream molecule c-Jun, which is a critical molecule for CAP transcription. Knockdown of AMPK and JNK blocked metformin-induced expression of CAP, implying that metformin stimulates AMPK-JNK-CAP axis pathway. Moreover, AMPK knockdown attenuated metformin-induced Cbl/CAP multicomplex formation, which is critical for GLUT4 translocation. A colorimetric absorbance assay demonstrated that metformin-induced translocation of GLUT4 was suppressed in CAP or Cbl knockdown cells. Furthermore, the promoter activity of CAP was increased by metformin in an AMPK/JNK-dependent fashion. In summary, these results demonstrate that metformin modulates GLUT4 translocation by regulating Cbl and CAP signals via AMPK.
authors.affiliation: Department of Anatomy, Korea University College of Medicine, Seoul 136-705, Korea.
authors.forename: Jung Ok
authors.initials: JO
authors.lastname: Lee
authors.forename: Soo Kyung
authors.initials: SK
authors.lastname: Lee
authors.forename: Ji Hae
authors.initials: JH
authors.lastname: Kim
authors.forename: Nami
authors.initials: N
authors.lastname: Kim
authors.forename: Ga Young
authors.initials: GY
authors.lastname: You
authors.forename: Ji Wook
authors.initials: JW
authors.lastname: Moon
authors.forename: Su Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Sun Hwa
authors.initials: SH
authors.lastname: Park
authors.forename: Hyeon Soo
authors.initials: HS
authors.lastname: Kim
mesh_terms: D041721:3T3-L1 Cells; D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D003598:Cytoskeletal Proteins; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D008687:Metformin; D050721:Proto-Oncogene Proteins c-cbl; D055372:AMP-Activated Protein Kinases; C493849:Cbl protein, mouse