Hosen Md Bayejid, Kawasumi Ryotaro, Hirota Kouji
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo 192-0397, Japan.
Nucleic Acids Res. 2025 Jul 8;53(13). doi: 10.1093/nar/gkaf617.
Chain-terminating nucleoside analogs (CTNAs) are frequently used as antiviral and anticancer agents. CTNAs are incorporated into the end of nascent DNA during DNA synthesis and inhibit subsequent DNA polymerization, thereby restricting the proliferation of viruses and cancer cells. Alovudine, a thymidine analog, exerts chain-termination effects and is used as an antiviral drug. However, the mechanisms underlying cellular tolerance to alovudine have not been fully elucidated. Here, we show that flap endonuclease-1 (Fen1) and p53 binding protein-1 (53BP1) counteractively mitigate the chain-terminating effect of alovudine. We found that the cells deficient in Fen1 (FEN1-/-) showed stronger chain-terminating effects of alovudine with augmented DNA damage than wild-type cells, leading to their alovudine hypersensitivity. Moreover, we found that the Okazaki fragment maturation was critically slowed in FEN1-/- cells when cells were challenged with alovudine. Remarkably, the loss of 53BP1 rescued these phenotypes. We found that 53BP1 formed sub-nuclear foci upon alovudine treatment and these 53BP1 foci were critically increased in FEN1-/- cells, indicating that Fen1 suppresses alovudine-mediated toxic 53BP1 subnuclear foci thereby promoting Okazaki fragment maturation and suppressing DNA damage. In this study, we uncovered the previously unappreciated role of Fen1 in the suppression of toxic action of 53BP1 at alovudine-incorporated Okazaki fragment.
链终止核苷类似物（CTNAs）常被用作抗病毒和抗癌药物。CTNAs在DNA合成过程中掺入新生DNA的末端，抑制后续的DNA聚合，从而限制病毒和癌细胞的增殖。阿洛维啶是一种胸苷类似物，具有链终止作用，用作抗病毒药物。然而，细胞对阿洛维啶耐受性的潜在机制尚未完全阐明。在此，我们表明瓣状核酸内切酶-1（Fen1）和p53结合蛋白-1（53BP1）可对抗性减轻阿洛维啶的链终止作用。我们发现，缺乏Fen1（FEN1-/-）的细胞对阿洛维啶表现出更强的链终止作用，DNA损伤增加，导致其对阿洛维啶超敏。此外，我们发现当用阿洛维啶处理细胞时，冈崎片段成熟在FEN1-/-细胞中严重减慢。值得注意的是，53BP1的缺失挽救了这些表型。我们发现，阿洛维啶处理后53BP1形成亚核灶，且这些53BP1灶在FEN1-/-细胞中显著增加，这表明Fen1抑制阿洛维啶介导的毒性53BP1亚核灶，从而促进冈崎片段成熟并抑制DNA损伤。在本研究中，我们揭示了Fen1在抑制阿洛维啶掺入的冈崎片段处53BP1的毒性作用方面以前未被认识到的作用。
