Caro J F, Raju M S, Caro M, Lynch C J, Poulos J, Exton J H, Thakkar J K
Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
J Cell Biochem. 1994 Mar;54(3):309-19. doi: 10.1002/jcb.240540307.
A novel pathway for physiological "cross-talk" between the insulin receptor and the regulatory Gi-protein has been demonstrated. We tested the hypothesis that a coupling defect between Gi and the insulin receptor is present in the liver of obese patients with and without type II diabetes. Insulin 1 x 10(-9) M (approximately ED50) and 1 x 10(-7) M (Max) inhibited pertussis toxin-catalyzed ADP ribosylation of Gi in human liver plasma membranes from lean and obese nondiabetic patients. However, 1 x 10(-7) M insulin was without effect in membranes from patients with type II diabetes. This coupling defect was not intrinsic to Gi, since Mg2+ and GTP gamma S inhibited pertussis toxin-catalyzed ADP ribosylation in both diabetic and nondiabetic patients. Binding of insulin of the alpha-subunit and activation of the tyrosine kinase intrinsic to the beta-subunit of the insulin receptor are not responsible for the coupling defect. 125I insulin binding is the same in obese patients with or without diabetes. Tyrosine kinase of the insulin receptor is decreased in diabetes. However, a monoclonal antibody to the insulin receptor (MA-20) at equimolar concentrations with insulin equally inhibits pertussis toxin-catalyzed ADP ribosylation of Gi without activating tyrosine kinase or insulin receptor autophosphorylation. Immunodetection of G-proteins suggested that Gi3 alpha was normal in diabetes and Gi1-2 alpha was decreased by 40% in the diabetic group as compared to the obese nondiabetic group but was normal when compared to the lean non diabetic group. We conclude that the novel pathway of insulin signaling involving the regulatory Gi proteins via biochemical mechanisms not directly involving the tyrosine kinase of the insulin receptor is altered in obese type II diabetes and offers a new target for the search of the mechanism(s) of insulin resistance.
胰岛素受体与调节性Gi蛋白之间生理性“串扰”的新途径已得到证实。我们检验了这样一个假设：在伴有或不伴有II型糖尿病的肥胖患者肝脏中，Gi与胰岛素受体之间存在偶联缺陷。1×10⁻⁹M（约为半数有效剂量）和1×10⁻⁷M（最大剂量）的胰岛素可抑制来自瘦型和肥胖非糖尿病患者的人肝细胞膜中百日咳毒素催化的Gi的ADP核糖基化。然而，1×10⁻⁷M胰岛素对II型糖尿病患者的细胞膜没有作用。这种偶联缺陷并非Gi所固有，因为Mg²⁺和GTPγS可抑制糖尿病患者和非糖尿病患者中百日咳毒素催化的ADP核糖基化。胰岛素与α亚基的结合以及胰岛素受体β亚基固有的酪氨酸激酶的激活与这种偶联缺陷无关。有或没有糖尿病的肥胖患者中¹²⁵I胰岛素结合情况相同。糖尿病患者中胰岛素受体的酪氨酸激酶减少。然而，与胰岛素等摩尔浓度的抗胰岛素受体单克隆抗体（MA - 20）同样抑制百日咳毒素催化的Gi的ADP核糖基化，而不激活酪氨酸激酶或胰岛素受体自身磷酸化。G蛋白的免疫检测表明，糖尿病患者中Gi3α正常，与肥胖非糖尿病组相比，糖尿病组中Gi1 - 2α减少40%，但与瘦型非糖尿病组相比则正常。我们得出结论，在肥胖II型糖尿病中，涉及通过不直接涉及胰岛素受体酪氨酸激酶的生化机制的调节性Gi蛋白的胰岛素信号新途径发生了改变，这为寻找胰岛素抵抗机制提供了一个新靶点。
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