Mutation of the BRCA1 SQ-cluster results in aberrant mitosis, reduced homologous recombination, and a compensatory increase in non-homologous end joining
Mutation of the BRCA1 SQ-cluster results in aberrant mitosis, reduced homologous recombination, and a compensatory increase in non-homologous end joining
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DOI：
10.18632/oncotarget.4876
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发表时间：
2015-09-29
期刊：
影响因子：
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通讯作者：
Valerie, Kristoffer
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文献类型：
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作者：
Beckta, Jason M.;Dever, Seth M.;Valerie, Kristoffer
乳腺癌易感性 1 (BRCA1) 基因突变是乳腺癌和卵巢癌的催化剂。大多数突变与 BRCA1 N 端和 C 端结构域相关，而 BRCA1 N 端和 C 端结构域与 DNA 双链断裂 (DSB) 修复相关。然而，除了其在调节细胞周期检查点方面的重要性之外，人们对介入丝氨酸-谷氨酰胺 (SQ) 簇在 DNA 损伤反应中的作用知之甚少。我们发现，已知被 ATM 和 ATR 磷酸化的 SQ 簇内关键残基的丝氨酸至丙氨酸的改变会导致同源重组修复 (HRR) 减少和异常有丝分裂。虽然 S1387A BRCA1 突变体（之前显示可消除辐射反应中的 S 期阻滞）仅导致 HRR 适度降低，但 S1387A 与额外的改变 S1423A (BRCA1(2P)) 一起，将 HRR 降低至载体对照水平，类似于也包括 S1457A 和 S1524A (BRCA1(4P)) 的四重突变体。这些效应似乎与 PALB2 无关。此外，我们发现BRCA1(4P)在细胞周期后期促进了延长且挣扎的HRR，并将DSB修复从HRR转移到非同源末端连接，这在面对不可修复的染色体损伤时导致了有丝分裂灾难。总而言之，SQ 簇磷酸化对于在有丝分裂之前有足够的时间完成正常 HRR 并防止细胞过早进入 G1 导致严重染色体畸变至关重要。
Mutations in the breast cancer susceptibility 1 (BRCA1) gene are catalysts for breast and ovarian cancers. Most mutations are associated with the BRCA1 N- and C-terminal domains linked to DNA double-strand break (DSB) repair. However, little is known about the role of the intervening serine-glutamine (SQ) - cluster in the DNA damage response beyond its importance in regulating cell cycle checkpoints. We show that serine-to-alanine alterations at critical residues within the SQ-cluster known to be phosphorylated by ATM and ATR result in reduced homologous recombination repair (HRR) and aberrant mitosis. While a S1387A BRCA1 mutant - previously shown to abrogate S-phase arrest in response to radiation - resulted in only a modest decrease in HRR, S1387A together with an additional alteration, S1423A (BRCA1(2P)), reduced HRR to vector control levels and similar to a quadruple mutant also including S1457A and S1524A (BRCA1(4P)). These effects appeared to be independent of PALB2. Furthermore, we found that BRCA1(4P) promoted a prolonged and struggling HRR late in the cell cycle and shifted DSB repair from HRR to non-homologous end joining which, in the face of irreparable chromosomal damage, resulted in mitotic catastrophe. Altogether, SQ-cluster phosphorylation is critical for allowing adequate time for completing normal HRR prior to mitosis and preventing cells from entering G1 prematurely resulting in gross chromosomal aberrations.