Okamura Tatsunori, Singh Simendra, Buolamwini John, Haystead Timothy, Friedman Henry, Bigner Darell, Ali-Osman Francis
From the Departments of Surgery, Durham, North Carolina 27710.
Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163.
J Biol Chem. 2009 Jun 19;284(25):16979-16989. doi: 10.1074/jbc.M808153200. Epub 2009 Mar 2.
Epidermal growth factor receptor (EGFR) gene amplification, mutations, and/or aberrant activation are frequent abnormalities in malignant gliomas and other human cancers and have been associated with an aggressive clinical course and a poor therapeutic outcome. Elevated glutathione S-transferase P1 (GSTP1), a major drug-metabolizing and stress response signaling protein, is also associated with drug resistance and poor clinical outcome in gliomas and other cancers. Here, we provide evidence that GSTP1 is a downstream EGFR target and that EGFR binds to and phosphorylates tyrosine residues in the GSTP1 protein in vitro and in vivo. Mass spectrometry and mutagenesis analyses in a cell-free system and in gliomas cells identified Tyr-7 and Tyr-198 as major EGFR-specific phospho-acceptor residues in the GSTP1 protein. The phosphorylation increased GSTP1 enzymatic activity significantly, and computer-based modeling showed a corresponding increase in electronegativity of the GSTP1 active site. In human glioma and breast cancer cells, epidermal growth factor stimulation rapidly increased GSTP1 tyrosine phosphorylation and decreased cisplatin sensitivity. Lapatinib, a clinically active EGFR inhibitor, significantly reversed the epidermal growth factor-induced cisplatin resistance. These data define phosphorylation and activation of GSTP1 by EGFR as a novel, heretofore unrecognized component of the EGFR signaling network and a novel mechanism of tumor drug resistance, particularly in tumors with elevated GSTP1 and/or activated EGFR.
表皮生长因子受体（EGFR）基因扩增、突变和/或异常激活是恶性胶质瘤和其他人类癌症中常见的异常情况，并且与侵袭性临床病程和不良治疗结果相关。谷胱甘肽S-转移酶P1（GSTP1）是一种主要的药物代谢和应激反应信号蛋白，其表达升高也与胶质瘤和其他癌症中的耐药性及不良临床结果相关。在此，我们提供证据表明，GSTP1是EGFR的下游靶点，并且EGFR在体外和体内均能与GSTP1蛋白中的酪氨酸残基结合并使其磷酸化。在无细胞系统和胶质瘤细胞中进行的质谱分析和诱变分析确定，Tyr-7和Tyr-198是GSTP1蛋白中主要的EGFR特异性磷酸化受体残基。磷酸化显著增加了GSTP1的酶活性，基于计算机的建模显示GSTP1活性位点的电负性相应增加。在人胶质瘤和乳腺癌细胞中，表皮生长因子刺激迅速增加了GSTP1的酪氨酸磷酸化并降低了顺铂敏感性。拉帕替尼是一种具有临床活性的EGFR抑制剂，可显著逆转表皮生长因子诱导的顺铂耐药性。这些数据将EGFR对GSTP1的磷酸化和激活定义为EGFR信号网络中一种新的、迄今未被认识的成分，以及肿瘤耐药的一种新机制，特别是在GSTP1升高和/或EGFR激活的肿瘤中。
