Function of MDC1/53BP1 sensor chaperone in radiation-induced chromatin repair

本研究的目的是阐明MDC 1/53 BP 1传感分子伴侣在检测染色质损伤和修复中的作用。本研究建立了一种检测磷酸化组蛋白H2 AX焦点和MDC 1/53 BP 1传感分子伴侣焦点的方法。照射后即刻，染色体畸变以染色单体型为主，照射后20小时，染色体畸变以染色体型为主。磷酸化组蛋白H2 AX的病灶在照射后立即与染色单体型畸变共定位，而病灶在照射后20小时与染色体型畸变共定位。这些结果表明，病灶可以持续存在或染色体没有可检测的断裂。为了进一步了解MDC 1/53 BP 1传感分子伴侣在DNA/染色质损伤识别的初始过程中的作用，我们构建了携带EGFP-53 BP 1基因的正常人细胞。在照射后15分钟内，检测到EGFP-53 BP 1灶为微小灶，但此后它们生长，并且在照射后30至60分钟，它们形成直径超过2微米的大灶。此外，ATM的抑制剂KU 55933有效地抑制了MDC 1/53 BP 1传感器伴侣的焦点。这清楚地表明，MDC 1/53 BP 1传感器伴侣焦点的形成依赖于ATM功能。

The purpose of this study is to clarify the role of MDC1/53BP1 sensor chaperone on detection of chromatin damage and repair. In this study, a method by which phosphorylated histone H2AX foci and MDC1/53BP1 sensor chaperone foci can be detected was established.After X-irradiation, chromosome aberrations were induced. Immediately after irradiation, most of the chromosome aberration were chromatid-type, in contrast those detected 20 hours after irradiation were chromosome-type. the foci of phosphorylated histone H2AX were colocalized with chromatid-type aberrations immediately after irradiation, whereas the foci were colocalized with chromosome-type aberrations 20 hours after irradiation. These results indicate that the foci could persist or chromosomes without detectable breaks. It suggests that DNA damage checkpoint also senses chromatin damage, which is generated by mis-rejoining DNA double strand breaks.Furthermore, to know the function of MDC1/53BP1 sensor chaperone in the initial process of DNA/chromatin damage recognition, normal human cells harboring EGFP-53BP1 gene was established. Within 15 minutes after irradiation, EGFP-53BP1 foci were detected as tiny foci, but they grew thereafter, and 30 to 60 minutes after irradiation, they formed large foci, whose diameter was over 2 micrometer. Moreover, an inhibitor for ATM, KU55933, efficiently suppressed the foci of MDC1/53BP1 sensor chaperone. It clearly indicates that MDC1/53BP1 sensor chaperone foci formation is dependent on the ATM function.