Ling Xiaoyang, Ma Guozhen, Sun Tong, Liu Jiaxin, Arlinghaus Ralph B
Department of Molecular Pathology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Cancer Res. 2003 Jan 15;63(2):298-303.
c-Abl tyrosine kinase is under rigorous control because of an unknown cellular inhibitor that maintains c-Abl in a relatively inactive state. Because SH2 domains are positive regulators of the nonreceptor tyrosine kinases, we tested whether this putative inhibitor would bind to an Abl SH2 protein construct and thus activate the c-Abl tyrosine kinase. Expression of a Mr 10,000 Abl SH2 protein in COS-1 and Rat-1 cells activated the tyrosine kinase activity of p145 ABL and induced both morphological transformation and foci formation in Rat-1 cells. Importantly, the R to L mutant of the FLVRES sequence of the Abl SH2 protein also activated the c-Abl tyrosine kinase and induced oncogenic transformation. Addition of the Abl kinase inhibitor STI-571 to ABL SH2-transformed Rat-1 cells inhibited tyrosine phosphorylation of p145 ABL. Overexpression of Bcr has been shown to inhibit the Bcr-Abl oncoprotein, and the endogenous Bcr protein forms a complex with c-Abl in hematopoietic cells and insect cells. Therefore, we determined whether Bcr is the putative c-Abl inhibitor that interacts with the Mr 10,000 Abl SH2 protein. Bcr expression in Rat-1 cells transformed by the Mr 10,000 Abl SH2 protein reduced the activated c-Abl tyrosine kinase activity to near normal levels and reversed the oncogenic effects (morphology changes and foci formation) seen in the Abl SH2-treated cells. We additionally demonstrated that Bcr and the Mr 10,000 Abl SH2 protein are present in a complex. We conclude from these studies that Bcr is a major tyrosine kinase inhibitor of cytoplasmic c-Abl and that procedures that sequester Bcr will release the c-Abl protein from the Bcr/c-Abl complex, which leads to c-Abl oncogenic activation.
c-Abl酪氨酸激酶受到严格调控，原因是存在一种未知的细胞内抑制剂，该抑制剂使c-Abl维持在相对无活性的状态。由于SH2结构域是非受体酪氨酸激酶的正调控因子，我们测试了这种假定的抑制剂是否会与Abl SH2蛋白构建体结合，从而激活c-Abl酪氨酸激酶。在COS-1细胞和大鼠1型（Rat-1）细胞中表达分子量为10,000的Abl SH2蛋白，激活了p145 ABL的酪氨酸激酶活性，并在大鼠1型细胞中诱导了形态转化和集落形成。重要的是，Abl SH2蛋白的FLVRES序列的R到L突变体也激活了c-Abl酪氨酸激酶并诱导了致癌转化。向ABL SH2转化的大鼠1型细胞中添加Abl激酶抑制剂STI-571可抑制p145 ABL的酪氨酸磷酸化。已有研究表明，Bcr的过表达可抑制Bcr-Abl癌蛋白，并且内源性Bcr蛋白在造血细胞和昆虫细胞中与c-Abl形成复合物。因此，我们确定Bcr是否是与分子量为10,000的Abl SH2蛋白相互作用的假定c-Abl抑制剂。在由分子量为10,000的Abl SH2蛋白转化的大鼠1型细胞中表达Bcr，可将激活的c-Abl酪氨酸激酶活性降低至接近正常水平，并逆转在Abl SH2处理的细胞中观察到的致癌作用（形态变化和集落形成）。我们还证明了Bcr和分子量为10,000的Abl SH2蛋白存在于一个复合物中。我们从这些研究中得出结论，Bcr是细胞质c-Abl的主要酪氨酸激酶抑制剂，并且隔离Bcr的过程将使c-Abl蛋白从Bcr/c-Abl复合物中释放出来，从而导致c-Abl致癌激活。
