Clinical Laboratory of Xuanwu Hospital, Capital Medical University, Beijing, 100053, People's Republic of China.
Beijing Institute of Brain Disorders, Capital Medical University, Beijing, 100053, People's Republic of China.
Cell Mol Life Sci. 2019 Jul;76(14):2833-2850. doi: 10.1007/s00018-019-03070-z. Epub 2019 Mar 20.
POLD1, the catalytic subunit of DNA Pol δ, plays an important role in DNA synthesis and DNA damage repair, and POLD1 is downregulated in replicative senescence and mediates cell aging. However, the mechanisms of age-related downregulation of POLD1 expression have not been elucidated. In this study, four potential CpG islands in the POLD1 promoter were found, and the methylation levels of the POLD1 promoter were increased in aging 2BS cells, WI-38 cells and peripheral blood lymphocytes, especially at a single site, CpG 36, in CpG island 3. Then, the transcription factor E2F1 was observed to bind to these sites. The binding affinity of E2F1 for the POLD1 promoter was found to show age-related attenuation and was confirmed to be positively regulated by the E2F1 level and negatively regulated by POLD1 promoter methylation. Moreover, cell senescence characteristics were observed in the cells transfected with shRNA-E2F1 and could contribute to the downregulation of POLD1 induced by the E2F1 decline. Collectively, these results indicated that the attenuation of the binding affinity of E2F1 for the POLD1 promoter, mediated by an age-related decline in E2F1 and increased methylation of CpG island 3, downregulates POLD1 expression in aging.
POLD1 是 DNA 聚合酶 δ 的催化亚基，在 DNA 合成和 DNA 损伤修复中发挥重要作用，并且在复制性衰老和介导细胞衰老中下调。然而，与年龄相关的 POLD1 表达下调的机制尚未阐明。在这项研究中，发现 POLD1 启动子中有四个潜在的 CpG 岛，衰老 2BS 细胞、WI-38 细胞和外周血淋巴细胞中 POLD1 启动子的甲基化水平升高，尤其是在 CpG 岛 3 中的单个位点 CpG36 上。然后观察到转录因子 E2F1 结合到这些位点。发现 E2F1 与 POLD1 启动子的结合亲和力随年龄呈衰减趋势，并且通过 E2F1 水平的正调控和 POLD1 启动子甲基化的负调控来证实。此外，在转染了 shRNA-E2F1 的细胞中观察到细胞衰老特征，这可能导致 E2F1 下降诱导的 POLD1 下调。总之，这些结果表明，E2F1 与 POLD1 启动子结合亲和力的衰减是由 E2F1 随年龄下降和 CpG 岛 3 甲基化增加介导的，从而下调衰老过程中的 POLD1 表达。
