FANCJ/BRIP1 is an iron-sulfur (FeS) cluster-binding DNA helicase involved in DNA inter-strand cross-link (ICL) repair and G-quadruplex (G4) metabolism. Mutations in FANCJ are associated with Fanconi anemia and an increased risk for developing breast and ovarian cancer. Several cancer-associated mutations are located in the FeS domain of FANCJ, but how they affect FeS cluster binding and/or FANCJ activity has remained mostly unclear. Here we show that the FeS cluster is indispensable for FANCJ’s ability to unwind DNA substrates in vitro and to provide cellular resistance to agents that induce ICLs. Moreover, we find that FANCJ requires an intact FeS cluster for its ability to unfold G4 structures on the DNA template in a primer extension assay with the lagging-strand DNA polymerase delta. Surprisingly, however, FANCJ variants that are unable to bind an FeS cluster and to unwind DNA in vitro can partially suppress the formation of replisome-associated G4 structures that we observe in a FANCJ knock-out cell line. This may suggest a partially retained cellular activity of FANCJ variants with alterations in the FeS domain. On the other hand, FANCJ knock-out cells expressing FeS cluster-deficient variants display a similar–enhanced–sensitivity towards pyridostatin (PDS) and CX-5461, two agents that stabilise G4 structures, as FANCJ knock-out cells. Mutations in FANCJ that abolish FeS cluster binding may hence be predictive of an increased cellular sensitivity towards G4-stabilising agents.

FANCJ/BRIP1 是一种铁硫 (FeS) 簇结合 DNA 解旋酶，参与 DNA 链间交联 (ICL) 修复和 G-四链体 (G4) 代谢。 FANCJ突变与范可尼贫血以及患乳腺癌和卵巢癌的风险增加有关。一些与癌症相关的突变位于FANCJ的 FeS 结构域中，但它们如何影响 FeS 簇结合和/或 FANCJ 活性仍不清楚。在这里，我们证明 FeS 簇对于 FANCJ在体外解旋 DNA 底物以及为诱导 ICL 的试剂提供细胞抵抗力的能力是不可或缺的。此外，我们发现 FANCJ 需要完整的 FeS 簇才能在使用滞后链 DNA 聚合酶 delta 的引物延伸测定中在 DNA 模板上展开 G4 结构。然而，令人惊讶的是，无法在体外结合 FeS 簇和解旋 DNA 的 FANCJ 变体可以部分抑制我们在FANCJ敲除细胞系中观察到的复制体相关 G4 结构的形成。这可能表明 FANCJ 变体部分保留了 FeS 结构域改变的细胞活性。另一方面，表达 FeS 簇缺陷变体的FANCJ敲除细胞对吡啶他汀 (PDS) 和 CX-5461（两种稳定 G4 结构的药物）表现出与FANCJ敲除细胞相似的增强敏感性。因此， FANCJ中废除 FeS 簇结合的突变可能预示着细胞对 G4 稳定剂的敏感性增加。