Kulas D T, Zhang W R, Goldstein B J, Furlanetto R W, Mooney R A
Department of Pathology, University of Rochester School of Medicine and Dentistry, New York 14642.
J Biol Chem. 1995 Feb 10;270(6):2435-8. doi: 10.1074/jbc.270.6.2435.
Considerable evidence has shown that most physiologic responses to insulin require activation of the intrinsic tyrosine kinase of the insulin receptor. Biochemical studies have also supported the hypothesis that receptor kinase activity can be modulated by cellular protein tyrosine phosphatases (PTPases), which have not yet been identified. To test the hypothesis that the transmembrane PTPase LAR can modulate insulin receptor signaling in vivo, antisense RNA expression was used to specifically suppress LAR protein levels by 63% in the rat hepatoma cell line, McA-RH7777. Hormone-dependent autophosphorylation of the insulin receptor was increased by approximately 150% in the antisense-expressing cells at all insulin concentrations tested. This increase in autophosphorylation was paralleled by a 35% increase in insulin receptor tyrosine kinase activity. Reduced LAR levels did not alter non-hormone-dependent tyrosine phosphorylation nor basal insulin receptor tyrosine phosphorylation and kinase activity. Most significantly, reduced LAR levels resulted in a 350% increase in insulin-dependent phosphatidylinositol 3-kinase activity. These studies provide unique in vivo evidence that LAR is involved in the modulation of insulin receptor signaling in intact cells.
大量证据表明，胰岛素的大多数生理反应需要激活胰岛素受体的内在酪氨酸激酶。生化研究也支持这样的假说，即受体激酶活性可被尚未确定的细胞蛋白酪氨酸磷酸酶（PTPases）调节。为了验证跨膜PTPase LAR可在体内调节胰岛素受体信号传导这一假说，采用反义RNA表达在大鼠肝癌细胞系McA-RH7777中特异性抑制LAR蛋白水平达63%。在所有测试的胰岛素浓度下，反义表达细胞中胰岛素受体的激素依赖性自磷酸化增加了约150%。自磷酸化的这种增加与胰岛素受体酪氨酸激酶活性增加35%相平行。LAR水平降低并未改变非激素依赖性酪氨酸磷酸化，也未改变基础胰岛素受体酪氨酸磷酸化和激酶活性。最显著的是，LAR水平降低导致胰岛素依赖性磷脂酰肌醇3-激酶活性增加350%。这些研究提供了独特的体内证据，表明LAR参与完整细胞中胰岛素受体信号传导的调节。
