Jeffers L J, Coull B J, Stack S J, Morrison C G
Department of Biochemistry and NCBES, National University of Ireland-Galway, Galway, Ireland.
Oncogene. 2008 Jan 3;27(1):139-44. doi: 10.1038/sj.onc.1210595. Epub 2007 Jun 25.
Microcephalin (MCPH1/BRIT1) forms ionizing radiation-induced nuclear foci (IRIF) and is required for DNA damage-responsive S and G(2)-M-phase checkpoints. MCPH1 contains three BRCT domains. Here we report the cloning of chicken Mcph1 (cMcph1) and functional analysis of its individual BRCT domains. Full-length cMcph1 localized to centrosomes throughout the cell cycle and formed IRIF that colocalized with gamma-H2AX. The tandem C-terminal BRCT2 and BRCT3 domains of cMcph1 were necessary for IRIF formation, while the N-terminal BRCT1 was required for centrosomal localization in irradiated cells. Centrosomal targeting of cMcph1 was independent of ATM, Brca1 or Chk1. cMcph1 formed IRIF in ATM- and Brca1-deficient cells, but not in H2AX-deficient cells. Inability to form cMcph1 IRIF impaired the cellular response to DNA damage. These results suggest that the role of microcephalin in the vertebrate DNA damage response is controlled by interaction of the C-terminal BRCT domains with gamma-H2AX.
小头畸形蛋白（MCPH1/BRIT1）可形成电离辐射诱导的核灶（IRIF），并且是DNA损伤应答性S期和G2-M期检查点所必需的。MCPH1包含三个BRCT结构域。在此我们报告鸡Mcph1（cMcph1）的克隆及其单个BRCT结构域的功能分析。全长cMcph1在整个细胞周期中定位于中心体，并形成与γ-H2AX共定位的IRIF。cMcph1的串联C端BRCT2和BRCT3结构域是IRIF形成所必需的，而N端BRCT1是受照射细胞中中心体定位所必需的。cMcph1的中心体靶向不依赖于ATM、Brca1或Chk1。cMcph1在ATM和Brca1缺陷细胞中形成IRIF，但在H2AX缺陷细胞中不形成。无法形成cMcph1 IRIF会损害细胞对DNA损伤的反应。这些结果表明，小头畸形蛋白在脊椎动物DNA损伤应答中的作用是由C端BRCT结构域与γ-H2AX的相互作用所控制的。
