Karni R, Jove R, Levitzki A
Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Oncogene. 1999 Aug 19;18(33):4654-62. doi: 10.1038/sj.onc.1202835.
Tumors that overexpress HER-2/neu receptor or exhibit enhanced EGFR signaling have been reported to possess constitutively activated Src family kinases, especially pp60c-Src. High levels of pp60c-Src activity have also been reported for cell lines that overexpress the EGFR or the chimeric EGFR-HER-2 receptor. It has therefore been suggested that Src kinases may contribute significantly to the oncogenic phenotype of these cells and to the degree of malignancy of tumors that overexpress EGFR family receptors. In this study we show that the induced expression of c-SRC antisense RNA or the application of a selective Src kinase inhibitor induces growth arrest, programmed cell death and reverses the transformed properties of cells that overexpress EGFR or HER-2 receptors. We show that inhibition of Src kinase expression or activity results in the reduction of Stat3 tyrosine phosphorylation, decline of Bcl-XL expression, and induction of cell death. Using a construct in which the promoter of Bcl-X, which possesses putative Stat3 sites, is tethered to the luciferase reporter gene, we show that inhibition of Src activity or expression induces a decline in Bcl-X expression. We also show that the expression of activated Src induces activation of the Bcl-X promoter. This activation is inhibited by the expression of kinase dead Src or of Stat3beta, the dominant-negative form of Stat3. Taken together, these results support the hypothesis that Src positively regulates the transformed phenotype of cells overexpressing EGFR family kinases. Furthermore, these results also suggest that Src positively regulates Bcl-XL expression via Stat3 activation and thus acts not only as a potent mitogenic signaling element, but also as an anti-apoptotic signaling protein. The combination of both activities probably confers upon activated Src its oncogenic activity. Since Src kinase is activated in many tumors, pp60c-Src kinase inhibitors may prove useful as anti-cancer agents for many types of cancer.
据报道，过表达HER-2/neu受体或表现出增强的表皮生长因子受体（EGFR）信号传导的肿瘤具有组成性激活的Src家族激酶，尤其是pp60c-Src。对于过表达EGFR或嵌合型EGFR-HER-2受体的细胞系，也有报道称其具有高水平的pp60c-Src活性。因此，有人提出Src激酶可能对这些细胞的致癌表型以及过表达EGFR家族受体的肿瘤的恶性程度有显著贡献。在本研究中，我们表明，诱导表达c-SRC反义RNA或应用选择性Src激酶抑制剂可诱导生长停滞、程序性细胞死亡，并逆转过表达EGFR或HER-2受体的细胞的转化特性。我们表明，抑制Src激酶表达或活性会导致信号转导和转录激活因子3（Stat3）酪氨酸磷酸化减少、Bcl-XL表达下降以及细胞死亡诱导。使用一种构建体，其中具有假定Stat3位点的Bcl-X启动子与荧光素酶报告基因相连，我们表明抑制Src活性或表达会导致Bcl-X表达下降。我们还表明，激活的Src的表达会诱导Bcl-X启动子的激活。这种激活被激酶失活的Src或Stat3的显性负性形式Stat3β的表达所抑制。综上所述，这些结果支持了Src正向调节过表达EGFR家族激酶的细胞的转化表型这一假说。此外，这些结果还表明，Src通过激活Stat3正向调节Bcl-XL表达，因此不仅作为一种有效的促有丝分裂信号元件起作用，而且还作为一种抗凋亡信号蛋白起作用。这两种活性的结合可能赋予激活的Src致癌活性。由于Src激酶在许多肿瘤中被激活，pp60c-Src激酶抑制剂可能被证明是许多类型癌症的有用抗癌药物。
