Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Nucleic Acids Res. 2019 May 7;47(8):4039-4053. doi: 10.1093/nar/gkz058.
FBXW7, a classic tumor suppressor, is a substrate recognition subunit of the Skp1-cullin-F-box (SCF) ubiquitin ligase that targets oncoproteins for ubiquitination and degradation. We recently found that FBXW7 is recruited to DNA damage sites to facilitate nonhomologous end-joining (NHEJ). The detailed underlying molecular mechanism, however, remains elusive. Here we report that the WD40 domain of FBXW7, which is responsible for substrate binding and frequently mutated in human cancers, binds to poly(ADP-ribose) (PAR) immediately following DNA damage and mediates rapid recruitment of FBXW7 to DNA damage sites, whereas ATM-mediated FBXW7 phosphorylation promotes its retention at DNA damage sites. Cancer-associated arginine mutations in the WD40 domain (R465H, R479Q and R505C) abolish both FBXW7 interaction with PAR and recruitment to DNA damage sites, causing inhibition of XRCC4 polyubiquitination and NHEJ. Furthermore, inhibition or silencing of poly(ADP-ribose) polymerase 1 (PARP1) inhibits PAR-mediated recruitment of FBXW7 to the DNA damage sites. Taken together, our study demonstrates that the WD40 domain of FBXW7 is a novel PAR-binding motif that facilitates early recruitment of FBXW7 to DNA damage sites for subsequent NHEJ repair. Abrogation of this ability seen in cancer-derived FBXW7 mutations provides a molecular mechanism for defective DNA repair, eventually leading to genome instability.
FBXW7 是一种经典的肿瘤抑制因子，作为 Skp1-cullin-F-box（SCF）泛素连接酶的底物识别亚基，可靶向癌蛋白进行泛素化和降解。我们最近发现，FBXW7 可募集至 DNA 损伤部位以促进非同源末端连接（NHEJ）。然而，其详细的潜在分子机制仍不清楚。在这里，我们报告 FBXW7 的 WD40 结构域可与多聚 ADP 核糖（PAR）结合，该结构域负责与底物结合，并且在人类癌症中经常发生突变，可在 DNA 损伤后立即与 PAR 结合，并介导 FBXW7 快速募集至 DNA 损伤部位，而 ATM 介导的 FBXW7 磷酸化则促进其在 DNA 损伤部位的保留。WD40 结构域中的癌症相关精氨酸突变（R465H、R479Q 和 R505C）可同时消除 FBXW7 与 PAR 的相互作用和募集至 DNA 损伤部位的能力，导致 XRCC4 多泛素化和 NHEJ 受到抑制。此外，聚 ADP 核糖聚合酶 1（PARP1）的抑制或沉默会抑制 PAR 介导的 FBXW7 向 DNA 损伤部位的募集。综上所述，我们的研究表明，FBXW7 的 WD40 结构域是一种新型的 PAR 结合基序，可促进 FBXW7 早期募集至 DNA 损伤部位，随后进行 NHEJ 修复。在癌症衍生的 FBXW7 突变中观察到这种能力的丧失为 DNA 修复缺陷提供了分子机制，最终导致基因组不稳定。
