Yan Ying, Spieker Rebecca S, Kim Min, Stoeger Scott M, Cowan Kenneth H
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, USA.
Oncogene. 2005 May 5;24(20):3285-96. doi: 10.1038/sj.onc.1208492.
Germline mutations in the BRCA1 gene are associated with an increased susceptibility to the development of breast and ovarian cancers. Evidence suggests that BRCA1 protein plays a key role in mediating DNA damage-induced checkpoint responses. Several studies have shown that ectopic expression of BRCA1 in human cells can trigger cellular responses similar to those induced by DNA damage, including G2/M cell cycle arrest and apoptosis. While the effects of ectopic BRCA1 expression on the G2/M transition and apoptosis have been extensively studied, the factors that dictate the balance between these two responses remain poorly understood. We have recently shown that ectopic expression of BRCA1 in MCF-7 human breast cancer cells resulted in activation of extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) and G2/M cell cycle arrest. Furthermore, inhibition of BRCA1-induced ERK1/2 activation using mitogen-activated protein kinase kinase 1 and 2 (MEK1/2)-specific inhibitors resulted in increased apoptosis, suggesting a potential role of ERK1/2 kinases in BRCA1-mediated G2/M checkpoint response. In this study, we assessed the role of ERK1/2 kinases in the regulation of BRCA1-mediated G2/M cell cycle arrest. Results indicate that BRCA1-induced G2/M cell cycle arrest and ERK1/2 activation correlate with changes in the level and/or activity of several key regulators of the G2/M checkpoint, including activation of Chk1 and Wee1 kinases, induction of 14-3-3, and down-regulation of Cdc25C. Furthermore, inhibition of ERK1/2 kinases using MEK1/2-specific inhibitors results in a marked attenuation of the BRCA1-induced G2/M arrest. Biochemical studies established that ERK1/2 inhibition abolished the effects of BRCA1 on components of the G2/M checkpoint, including regulation of Cdc25C expression and activation of Wee1 and Chk1 kinases. These results implicate a critical role of ERK1/2 signaling in the regulation of BRCA1 function on controlling the G2/M checkpoint responses.
BRCA1基因的种系突变与乳腺癌和卵巢癌发生易感性增加相关。有证据表明，BRCA1蛋白在介导DNA损伤诱导的检查点反应中起关键作用。多项研究表明，在人类细胞中异位表达BRCA1可触发类似于DNA损伤诱导的细胞反应，包括G2/M期细胞周期停滞和细胞凋亡。虽然异位表达BRCA1对G2/M期转换和细胞凋亡的影响已得到广泛研究，但决定这两种反应之间平衡的因素仍知之甚少。我们最近发现，在MCF-7人乳腺癌细胞中异位表达BRCA1会导致细胞外信号调节蛋白激酶1和2（ERK1/2）激活以及G2/M期细胞周期停滞。此外，使用丝裂原活化蛋白激酶激酶1和2（MEK1/2）特异性抑制剂抑制BRCA1诱导的ERK1/2激活会导致细胞凋亡增加，这表明ERK1/2激酶在BRCA1介导的G2/M检查点反应中具有潜在作用。在本研究中，我们评估了ERK1/2激酶在调节BRCA1介导的G2/M期细胞周期停滞中的作用。结果表明，BRCA1诱导的G2/M期细胞周期停滞和ERK1/2激活与G2/M检查点几个关键调节因子的水平和/或活性变化相关，包括Chk1和Wee1激酶的激活、14-3-3的诱导以及Cdc25C的下调。此外，使用MEK1/2特异性抑制剂抑制ERK1/2激酶会导致BRCA1诱导的G2/M期停滞明显减弱。生化研究证实，ERK1/2抑制消除了BRCA1对G2/M检查点组分的影响，包括对Cdc25C表达的调节以及Wee1和Chk1激酶的激活。这些结果表明ERK1/2信号在调节BRCA1控制G2/M检查点反应的功能中起关键作用。
