Zhang J, Lahti J M, Bruce A, He L, Parihar K, Fan C, Grenet J, Liu L, Kidd V J, Cormier S, Tang D
Division of Nephrology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
Oncogene. 2006 Sep 14;25(41):5601-11. doi: 10.1038/sj.onc.1209565. Epub 2006 Apr 24.
Bcl-2 can both promote and attenuate tumorigenesis. Although the former function is relatively well characterized, the mechanism of the latter remains elusive. We report here that enforced Bcl-2 expression in MCF7 cells stabilizes p53, induces phosphorylation of p53 serine 15 (p53pSer15) and inhibits MCF7 cell growth. Consistent with p53 Ser15 being a target of ataxia telangiectasia mutated protein(ATM)/ATR (ATM- and rad3-related) in the DNA damage response, Bcl-2 activates ATM by inducing ATM Ser1981 phosphorylation, which is accompanied with the phosphorylaton of two additional ATM substrates, Chk2 Thr68 and H2AX Ser139. Downregulation of ATM using a specific small interference RNA fragment (ATMRNAi) abolished Bcl-2-induced p53pSer15 and Bcl-2-mediated growth inhibition of MCF7 cells. Ectopic expression of a dominant-negative p53 mutant, p53175H, partially rescued this growth inhibition. Taken together, these observations demonstrate the contribution of ATM-p53 function to Bcl-2-mediated inhibition of MCF7 cell growth, indicating an ATM-mediated surveillance system for regulating Bcl-2 overexpression. Consistent with this concept, we found that MCF7 cells express Bcl-2 heterogeneously with 34.5% of cells being Bcl-2 negative. In general, Bcl-2-positive MCF7 cells proliferate slower than those of Bcl-2 negative. Thus, we provide evidence suggesting that activation of ATM suppresses Bcl-2-induced tumorigenesis, and that attenuation of ATM function may be an important event in breast cancer progression.
Bcl-2既能促进肿瘤发生，也能减弱肿瘤发生。虽然其前一种功能已得到较好的表征，但其后一种功能的机制仍不清楚。我们在此报告，在MCF7细胞中强制表达Bcl-2可使p53稳定，诱导p53丝氨酸15（p53pSer15）磷酸化，并抑制MCF7细胞生长。与p53丝氨酸15是DNA损伤反应中共济失调毛细血管扩张突变蛋白（ATM）/ATR（ATM和rad3相关）的靶点一致，Bcl-2通过诱导ATM丝氨酸1981磷酸化激活ATM，同时伴随着另外两个ATM底物Chk2苏氨酸68和H2AX丝氨酸139的磷酸化。使用特异性小干扰RNA片段（ATMRNAi）下调ATM可消除Bcl-2诱导的p53pSer15和Bcl-2介导的MCF7细胞生长抑制。显性负性p53突变体p53175H的异位表达部分挽救了这种生长抑制。综上所述，这些观察结果证明了ATM-p53功能对Bcl-2介导的MCF7细胞生长抑制的作用，表明存在一种ATM介导的监测系统来调节Bcl-2的过表达。与此概念一致，我们发现MCF7细胞中Bcl-2表达不均一，34.5%的细胞Bcl-2呈阴性。一般来说，Bcl-2阳性的MCF7细胞比Bcl-2阴性的细胞增殖慢。因此，我们提供的证据表明，ATM的激活抑制了Bcl-2诱导的肿瘤发生，而ATM功能的减弱可能是乳腺癌进展中的一个重要事件。
