Kulas D T, Freund G G, Mooney R A
Department of Pathology, University of Rochester School of Medicine and Dentistry, New York 14642, USA.
J Biol Chem. 1996 Jan 12;271(2):755-60. doi: 10.1074/jbc.271.2.755.
Overexpression of the transmembrane protein-tyrosine phosphatase (PTPase) CD45 in nonhematopoietic cells results in decreased signaling through growth factor receptor tyrosine kinases. Consistent with these data, insulin receptor signaling is increased when the CD45-related PTPase LAR is reduced by antisense suppression in a rat hepatoma cell line. To test whether the hematopoietic cell-specific PTPase CD45 functions in a manner similar to LAR by negatively modulating insulin receptor signaling in hematopoietic cells, the insulin-responsive human multiple myeloma cell line U266 was isolated into two subpopulations that differed in CD45 expression. In CD45 nonexpressing (CD45-) cells, insulin receptor autophosphorylation was increased by 3-fold after insulin treatment when compared to CD45 expressing (CD45+) cells. This increase in receptor autophosphorylation was associated with similar increases in insulin-dependent tyrosine kinase activation. These receptor level effects were paralleled by postreceptor responses. Insulin-dependent tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) and Shc was 3-fold greater in CD45- cells. In addition, insulin-dependent IRS-1/phosphatidylinositol 3-kinase association and MAP kinase activation in CD45- cells were also 3-fold larger. While expression of CD45 was associated with a decrease in the responsiveness of early insulin receptor signaling, interleukin 6-dependent activation of mitogen-activated protein kinase kinase and mitogen-activated protein kinase was equivalent between CD45- and CD45+ cells. These observations indicate that CD45 can function as a negative modulator of growth factor receptor tyrosine kinases in addition to its well-established role as an activator of src family tyrosine kinases.
跨膜蛋白酪氨酸磷酸酶（PTPase）CD45在非造血细胞中的过表达导致通过生长因子受体酪氨酸激酶的信号传导减少。与这些数据一致的是，当大鼠肝癌细胞系中与CD45相关的PTPase LAR通过反义抑制而减少时，胰岛素受体信号传导增强。为了测试造血细胞特异性PTPase CD45是否通过负向调节造血细胞中的胰岛素受体信号传导而以类似于LAR的方式发挥作用，将胰岛素反应性人多发性骨髓瘤细胞系U266分离为两个CD45表达不同的亚群。在不表达CD45（CD45-）的细胞中，与表达CD45（CD45+）的细胞相比，胰岛素处理后胰岛素受体自磷酸化增加了3倍。受体自磷酸化的这种增加与胰岛素依赖性酪氨酸激酶激活的类似增加相关。这些受体水平的效应与受体后反应平行。胰岛素受体底物1（IRS-1）和Shc的胰岛素依赖性酪氨酸磷酸化在CD45-细胞中高3倍。此外，CD45-细胞中胰岛素依赖性IRS-1/磷脂酰肌醇3-激酶结合和MAP激酶激活也大3倍。虽然CD45的表达与早期胰岛素受体信号传导的反应性降低有关，但CD45-细胞和CD45+细胞之间白细胞介素6依赖性丝裂原活化蛋白激酶激酶和丝裂原活化蛋白激酶的激活是等效的。这些观察结果表明，CD45除了作为src家族酪氨酸激酶的激活剂这一已确立的作用外，还可以作为生长因子受体酪氨酸激酶的负调节剂。
