Tiganis T, Kemp B E, Tonks N K
St. Vincent's Institute of Medical Research, Fitzroy, Victoria 3065, Australia.
J Biol Chem. 1999 Sep 24;274(39):27768-75. doi: 10.1074/jbc.274.39.27768.
In this study we have investigated the down-regulation of epidermal growth factor (EGF) receptor signaling by protein-tyrosine phosphatases (PTPs) in COS1 cells. The 45-kDa variant of the PTP TCPTP (TC45) exits the nucleus upon EGF receptor activation and recognizes the EGF receptor as a cellular substrate. We report that TC45 inhibits the EGF-dependent activation of the c-Jun N-terminal kinase, but does not alter the activation of extracellular signal-regulated kinase 2. These data demonstrate that TC45 can regulate selectively mitogen-activated protein kinase signaling pathways emanating from the EGF receptor. In EGF receptor-mediated signaling, the protein kinase PKB/Akt and the mitogen-activated protein kinase c-Jun N-terminal kinase, but not extracellular signal-regulated kinase 2, function downstream of phosphatidylinositol 3-kinase (PI 3-kinase). We have found that TC45 and the TC45-D182A mutant, which is capable of forming stable complexes with TC45 substrates, inhibit almost completely the EGF-dependent activation of PI 3-kinase and PKB/Akt. TC45 and TC45-D182A act upstream of PI 3-kinase, most likely by inhibiting the recruitment of the p85 regulatory subunit of PI 3-kinase by the EGF receptor. Recent studies have indicated that the EGF receptor can be activated in the absence of EGF following integrin ligation. We find that the integrin-mediated activation of PKB/Akt in COS1 cells is abrogated by the specific EGF receptor protein-tyrosine kinase inhibitor tyrphostin AG1478, and that TC45 and TC45-D182A can inhibit activation of PKB/Akt following the attachment of COS1 cells to fibronectin. Thus, TC45 may serve as a negative regulator of growth factor or integrin-induced, EGF receptor-mediated PI 3-kinase signaling.
在本研究中，我们研究了蛋白酪氨酸磷酸酶（PTP）在COS1细胞中对表皮生长因子（EGF）受体信号传导的下调作用。PTP TCPTP（TC45）的45 kDa变体在EGF受体激活后离开细胞核，并将EGF受体识别为细胞底物。我们报告称，TC45抑制c-Jun N端激酶的EGF依赖性激活，但不改变细胞外信号调节激酶2的激活。这些数据表明，TC45可以选择性地调节源自EGF受体的丝裂原活化蛋白激酶信号通路。在EGF受体介导的信号传导中，蛋白激酶PKB/Akt和丝裂原活化蛋白激酶c-Jun N端激酶，而非细胞外信号调节激酶2，在磷脂酰肌醇3激酶（PI 3激酶）的下游发挥作用。我们发现，TC45和能够与TC45底物形成稳定复合物的TC45-D182A突变体几乎完全抑制PI 3激酶和PKB/Akt的EGF依赖性激活。TC45和TC45-D182A在PI 3激酶的上游起作用，很可能是通过抑制EGF受体对PI 3激酶p85调节亚基的募集。最近的研究表明，在整合素连接后，EGF受体可在无EGF的情况下被激活。我们发现，COS1细胞中整合素介导的PKB/Akt激活被特异性EGF受体蛋白酪氨酸激酶抑制剂 tyrphostin AG1478消除，并且TC45和TC45-D182A可以抑制COS1细胞附着于纤连蛋白后PKB/Akt的激活。因此，TC45可能作为生长因子或整合素诱导的、EGF受体介导的PI 3激酶信号传导的负调节因子。
