Fujisawa Hiroshi, Fujimori Akira, Okayasu Ryuichi, Uesaka Mitsuru, Yajima Hirohiko
School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan; Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan; International Open Laboratory, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
Mutat Res. 2015 Jan;771:36-44. doi: 10.1016/j.mrfmmm.2014.12.001. Epub 2014 Dec 11.
Homologous recombination (HR) is a major repair pathway for DNA double strand breaks (DSBs), and end resection, which generates a 3'-single strand DNA tail at the DSB, is an early step in the process. Resection is initiated by the Mre11 nuclease together with CtIP. Here, we describe novel characteristics of CtIP at DSBs. At early times following exposure of human cells to ionizing radiation, CtIP localized to the DSB, became hyperphosphorylated and formed foci in an ATM-dependent manner. At later times, when the initiation of resection had occurred, CtIP foci persist but CtIP is maintained in a hypophosphorylated state, which is dependent on ATM and ATR. Exposure to cycloheximide revealed that CtIP turns over at DSB sites downstream of resection. Our findings provide strong evidence that CtIP is continuously recruited to DSBs downstream of both the initiation and extension step of resection, strongly suggesting that CtIP has functions in addition to promoting the initiation of resection during HR.
同源重组（HR）是DNA双链断裂（DSB）的主要修复途径，而在DSB处产生3'单链DNA尾巴的末端切除是该过程的早期步骤。切除由Mre11核酸酶与CtIP共同启动。在此，我们描述了CtIP在DSB处的新特性。在人类细胞暴露于电离辐射后的早期，CtIP定位于DSB，发生超磷酸化并以依赖ATM的方式形成焦点。在后期，当切除开始时，CtIP焦点持续存在，但CtIP保持在低磷酸化状态，这依赖于ATM和ATR。用放线菌酮处理表明，CtIP在切除下游的DSB位点周转。我们的发现提供了强有力的证据，表明CtIP在切除的起始和延伸步骤下游持续被招募到DSB，强烈提示CtIP除了在HR过程中促进切除起始外还具有其他功能。
