BRCA1-induced large-scale chromatin unfolding and allele-specific effects of cancer-predisposing mutations.
BRCA1-induced large-scale chromatin unfolding and allele-specific effects of cancer-predisposing mutations.
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DOI：
10.1083/jcb.200108049
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发表时间：
2001-12-10
影响因子：
7.8
通讯作者：
Li, R
中科院分区：
文献类型：
--
作者：
Ye, Q;Hu, Y F;Zhong, H;Nye, A C;Belmont, A S;Li, R
乳腺癌易感基因BRCA1编码的蛋白质参与多种核功能，包括转录和DNA修复。BRCA1的多功能性提高了这种多肽可能通过一种共同的潜在机制（如染色质重塑）调节各种核过程的可能性。然而，到目前为止，没有直接的证据存在于哺乳动物细胞中的BRCA1介导的变化，无论是局部或大规模的染色质结构。在这里，我们表明，靶向BRCA1的扩增，乳糖操纵子在哺乳动物基因组中的染色体区域的结果在大规模的染色质去凝聚。这种解折叠活性独立地由BRCA 1的反式激活结构域内的三个亚结构域（即激活结构域1）和两个BRCA 1 COOH末端（BRCT）重复序列赋予。此外，我们证明了一个类似的染色质展开活动与E2F1和肿瘤抑制基因p53的反式激活结构域。然而，与E2F1和p53不同，BRCT介导的染色质展开不伴随组蛋白过度乙酰化。BRCA1的癌症易感突变对染色质解折叠显示出等位基因特异性效应：导致蛋白质总截短的5′突变消除了染色质解折叠活性，而基因3′区域的突变显著增强了这种活性。BRCA1的一种新的辅因子（COBRA1）被BRCA1的第一个BRCT重复序列募集到染色体位点，并且其本身足以诱导染色质展开。增强染色质展开的BRCA1突变也增加了其对COBRA1的亲和力和募集。这些结果表明，更高水平的染色质结构的重组是BRCA1介导的核功能的重要调控步骤。
The breast cancer susceptibility gene BRCA1 encodes a protein that has been implicated in multiple nuclear functions, including transcription and DNA repair. The multifunctional nature of BRCA1 has raised the possibility that the polypeptide may regulate various nuclear processes via a common underlying mechanism such as chromatin remodeling. However, to date, no direct evidence exists in mammalian cells for BRCA1-mediated changes in either local or large-scale chromatin structure. Here we show that targeting BRCA1 to an amplified, lac operator–containing chromosome region in the mammalian genome results in large-scale chromatin decondensation. This unfolding activity is independently conferred by three subdomains within the transactivation domain of BRCA1, namely activation domain 1, and the two BRCA1 COOH terminus (BRCT) repeats. In addition, we demonstrate a similar chromatin unfolding activity associated with the transactivation domains of E2F1 and tumor suppressor p53. However, unlike E2F1 and p53, BRCT-mediated chromatin unfolding is not accompanied by histone hyperacetylation. Cancer-predisposing mutations of BRCA1 display an allele-specific effect on chromatin unfolding: 5′ mutations that result in gross truncation of the protein abolish the chromatin unfolding activity, whereas those in the 3′ region of the gene markedly enhance this activity. A novel cofactor of BRCA1 (COBRA1) is recruited to the chromosome site by the first BRCT repeat of BRCA1, and is itself sufficient to induce chromatin unfolding. BRCA1 mutations that enhance chromatin unfolding also increase its affinity for, and recruitment of, COBRA1. These results indicate that reorganization of higher levels of chromatin structure is an important regulated step in BRCA1-mediated nuclear functions.