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Tomoyuki Yuasa,
Keiji Uchiyama,
Yuko Ogura,
Masafumi Kimura,
Kiyoshi Teshigawara,
Toshio Hosaka,
Yoshinori Tanaka,
Toshiyuki Obata,
Hiroyuki Sano,
Kazuhiro Kishi,
Yousuke Ebina
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ABSTRACT: Akt substrate of 160kDa (AS160) is a Rab GTPase activating protein (GAP) and was recently identified as a component of the insulin signaling pathway of glucose transporter type 4 (GLUT4) translocation. We and others, previously reported that the activation of Galphaq protein-coupled receptors (GalphaqPCRs) also stimulated GLUT4 translocation and glucose uptake in several cell lines. Here, we report that the activation of GalphaqPCRs also promoted phosphorylation of AS160 by the 5'-AMP activated protein kinase (AMPK). The suppression of AS160 phosphorylation by the siRNA mediated AMPKalpha1 subunit knockdown promoted GLUT4 vesicle retention in intracellular compartments. This suppression did not affect the ratio of non-induced cell surface GLUT4 to Galphaq-induced it. Rat 3Y1 cells lacking AS160 did not show insulin-induced GLUT4 translocation. The cells stably expressing GLUT4 revealed GLUT4 vesicles that were mainly localized in the perinuclear region and less frequently on the cell surface. After expression of exogenous AS160, GLUT4 on the cell surface decreased and GLUT4 vesicles were redistributed throughout the cytoplasm. Although PMA-induced or sodium fluoride-induced GLUT4 translocation was significantly increased in these cells, insulin did not affect GLUT4 translocation. These results suggest that AS160 is a common regulator of insulin- and GalphaqPCR activation-mediated GLUT4 distribution in the cells.
Endocrine Journal 02/2009; 56(3):345-59. · 2.03 Impact Factor
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ABSTRACT: Insulin resistance is a common disorder caused by a wide variety of physiological insults, some of which include poor diet, inflammation, anti-inflammatory steroids, hyperinsulinemia, and dyslipidemia. The common link between these diverse insults and insulin resistance is widely considered to involve impaired insulin signaling, particularly at the level of the insulin receptor substrate (IRS). To test this model, we utilized a heterologous system involving the platelet-derived growth factor (PDGF) pathway that recapitulates many aspects of insulin action independently of IRS. We comprehensively analyzed six models of insulin resistance in three experimental systems and consistently observed defects in both insulin and PDGF action despite a range of insult-specific defects within the IRS-Akt nexus. These findings indicate that while insulin resistance is associated with multiple deficiencies, the most deleterious defects and the origin of insulin resistance occur independently of IRS.
Cell metabolism 06/2008; 7(5):421-33. · 17.35 Impact Factor
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ABSTRACT: APS, a tyrosine kinase adaptor protein with pleckstrin homology and Src homology 2 domains, is rapidly and strongly tyrosine-phosphorylated by insulin receptor kinase upon insulin stimulation. We have previously shown that APS knockout mice have increased insulin sensitivity, and that this enhancement is possibly due to increased insulin-response on adipose tissues. However, the function of APS in insulin signaling has so far been controversial. Here, we report that APS enhanced ligand-dependent multi-ubiquitination of the insulin receptor (IR) in CHO cells overexpressing the IR. APS-mediated ubiquitination of the IR induced enhancement of the IR internalization, but did not affect the IR degradation. This finding shows one of the pleiotropic functions of APS in insulin signaling.
Endocrine Journal 03/2007; 54(1):77-88. · 2.03 Impact Factor
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ABSTRACT: Insulin stimulates the disposal of blood glucose into skeletal muscle and adipose tissues by the translocation of GLUT4 from intracellular pools to the plasma membrane, and consequently the concentration of blood glucose levels decreases rapidly in vivo. Phosphatidylinositol (PI) 3-kinase and Akt play a pivotal role in the stimulation of glucose transport by insulin, but detailed mechanisms are unknown. We and others reported that not only insulin but also platelet-derived growth factor (PDGF) and epidermal growth factor facilitate glucose uptake through GLUT4 translocation by activation of PI 3-kinase and Akt in cultured cells. However, opposite results were also reported. We generated transgenic mice that specifically express the PDGF receptor in skeletal muscle. In these mice, PDGF stimulated glucose transport into skeletal muscle in vitro and in vivo. Thus, PDGF apparently shares with insulin some of the signaling molecules needed for the stimulation of glucose transport. The degree of glucose uptake in vivo reached approximately 60% of that by insulin injection in skeletal muscle, but blood glucose levels were not decreased by PDGF in these mice. Therefore, PDGF-induced disposal of blood glucose into skeletal muscle is insufficient for rapid decrease of blood glucose levels.
Diabetes 12/2004; 53(11):2776-86. · 8.29 Impact Factor
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Yoshiko Kanezaki,
Toshiyuki Obata,
Rie Matsushima,
Asako Minami, Tomoyuki Yuasa,
Kazuhiro Kishi,
Yoshimi Bando,
Hisanori Uehara,
Keisuke Izumi,
Tasuku Mitani,
Mitsuru Matsumoto,
Yukari Takeshita,
Yutaka Nakaya,
Toshio Matsumoto,
Yousuke Ebina
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ABSTRACT: Impaired insulin secretion and insulin resistance are thought to be two major causes of type 2 diabetes mellitus. There are two kinds of diabetic model mice: one is a K(ATP) channel knockout (Kir6.2KO) mouse which is defective in glucose-induced insulin secretion, and the other is a transgenic mouse expressing the tyrosine kinase-deficient (dominant-negative form of) human insulin receptor (hIR(KM)TG), and which has insulin resistance in muscle and fat. However, all of these mice have no evidence of overt diabetes. To determine if the double mutant Kir6.2KO/hIR(KM)TG mice would have diabetes, we generated mutant mice by crossbreeding, which would show both impaired glucose-induced insulin secretion and insulin resistance in muscle and fat. We report here that: 1) blood glucose levels of randomly fed and 6 h fasted double mutant (Kir6.2KO/hIR(KM)TG) mice were comparable with those of wild type mice; 2) in intraperitoneal glucose tolerance test (ipGTT), Kir6.2KO/hIR(KM)TG mice had an impaired glucose tolerance; and 3) during ipGTT, insulin secretion was not induced in either Kir6.2KO/hIR(KM)TG or Kir6.2KO mice, while the hIR(KM)TG mice showed a more prolonged insulin secretion than did wild type mice; 4) hyperinsulinemic euglycemic clamp test revealed that Kir6.2KO, Kir6.2KO/hIR(KM)TG and hIR(KM)TG mice, showed decreased whole-body glucose disposal compared with wild type mice; 5) Kir6.2KO, but not Kir6.2KO/hIR(KM)TG mice had some obesity and hyperleptinemia compared with wild type mice. Thus, the defects in glucose-induced insulin secretion (Kir6.2KO) and an insulin resistance in muscle and fat (hIR(KM)TG) were not sufficient to lead to overt diabetes.
Endocrine Journal 05/2004; 51(2):133-44. · 2.03 Impact Factor
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ABSTRACT: The AMP-activated protein kinase (AMPK) functions as a metabolic sensor that monitors cellular AMP and ATP levels. Platelet-activating factor (PAF) activates endogeneous AMPKα1 in Chinese hamster ovary cells expressing the PAF receptor coupled with both Gi and Gq, but its activity was not inhibited after treatment with islet-activating protein. Norepinephrine and bradykinin also activated AMPKα1 in cells expressing the Gq-coupled α1b-adrenergic receptor and bradykinin receptor, respectively. Stimulations of the Gi-coupled α2A-adrenergic receptor, fMet-Leu-Phe receptor, prostaglandin EP3α receptor, and Gs-coupled β2-adrenergic receptor did not activate AMPKα1. AMPKα1 thus is activated specifically by stimulation of Gq-coupled receptors. Gq-coupled receptors transmit the signal for GLUT4 translocation and glucose uptake through an insulin-independent pathway. However, direct activation of AMPKα1 with treatment of 5-aminoimidazole-4-carboxamide-1-β--ribofuranoside did not trigger GLUT4 translocation nor stimulate glucose uptake in our cells. Thus, activation of AMPKα1 via Gq is not sufficient to trigger GLUT4 translocation or stimulate glucose uptake.
Biochemical and Biophysical Research Communications.
