title: Paraquat-induced oxidative stress represses phosphatidylinositol 3-kinase activities leading to impaired glucose uptake in 3T3-L1 adipocytes.
abstract: Accumulated evidence indicates that oxidative stress causes and/or promotes insulin resistance; however, the mechanism by which this occurs is not fully understood. This study was undertaken to elucidate the molecular mechanism by which oxidative stress induced by paraquat impairs insulin-dependent glucose uptake in 3T3-L1 adipocytes. We confirmed that paraquat-induced oxidative stress decreased glucose transporter 4 (GLUT4) translocation to the cell surface, resulting in repression of insulin-dependent 2-deoxyglucose uptake. Under these conditions, oxidative stress did not affect insulin-dependent tyrosine phosphorylation of insulin receptor, insulin receptor substrate (IRS)-1 and -2, or binding of the phosphatidylinositol 3'-OH kinase (PI 3-kinase) p85 regulatory subunit or p110alpha catalytic subunit to each IRS. In contrast, we found that oxidative stress induced by paraquat inhibited activities of PI 3-kinase bound to IRSs and also inhibited phosphorylation of Akt, the downstream serine/threonine kinase that has been shown to play an essential role in insulin-dependent translocation of GLUT4 to the plasma membrane. Overexpression of active form Akt (myr-Akt) restored inhibition of insulin-dependent glucose uptake by paraquat, indicating that paraquat-induced oxidative stress inhibits insulin signals upstream of Akt. Paraquat treatment with and without insulin treatment decreased the activity of class Ia PI 3-kinases p110alpha and p110beta that are mainly expressed in 3T3-L1 adipocytes. However, paraquat treatment did not repress the activity of the PI 3-kinase p110alpha mutated at Cys(90) in the p85 binding region. These results indicate that the PI 3-kinase p110 is a possible primary target of paraquat-induced oxidative stress to reduce the PI 3-kinase activity and impaired glucose uptake in 3T3-L1 adipocytes.
authors.affiliation: Department of Animal Sciences and Applied Biological Chemistry, Graduate School of Agriculture and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Michihiro
authors.initials: M
authors.lastname: Shibata
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Hakuno
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yamanaka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Okajima
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Fukushima
authors.forename: Takashi
authors.initials: T
authors.lastname: Hasegawa
authors.forename: Tomomi
authors.initials: T
authors.lastname: Ogata
authors.forename: Yuka
authors.initials: Y
authors.lastname: Toyoshima
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Chida
authors.forename: Kumi
authors.initials: K
authors.lastname: Kimura
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Sakoda
authors.forename: Asako
authors.initials: A
authors.lastname: Takenaka
authors.forename: Tomoichiro
authors.initials: T
authors.lastname: Asano
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Takahashi
mesh_terms: D016475:3T3 Cells; D000256:Adenoviridae / Q000235:genetics; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D017931:DNA Primers; D004794:Enzyme Repression; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006801:Humans; D007668:Kidney; D051379:Mice; D018384:Oxidative Stress / Q000187:drug effects*; D010269:Paraquat / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D010957:Plasmids; D013601:T-Lymphocytes / Q000276:immunology; D014162:Transfection
chemical_list: D017931:DNA Primers; D051275:Glucose Transporter Type 4; D019869:Phosphatidylinositol 3-Kinases; D005947:Glucose; D010269:Paraquat