BRCA1 缺陷细胞的 IRE1 RNase 增加，可降解多种 microRNA。其中一种 miR-4638-5p 的重建表达导致 BRCA1 缺陷的癌细胞产生合成致死性。我们发现 miR-4638-5p 抑制 TATDN2 的表达，TATDN2 是 TATD 核酸酶家族中一个尚未被充分表征的成员。我们发现人类 TATDN2 对双链发夹 RNA 结构具有 RNA 3' 核酸外切酶和核酸内切酶活性。鉴于 TATDN2 对发夹 RNA 的切割，以及 BRCA1 缺陷细胞难以解析 R 环，我们测试了 TATDN2 是否可以解析 R 环。使用体外生化重建测定，我们发现 TATDN2 与 R 环结合，并以 Mg2 依赖性方式降解 RNA 链，但不降解体外多种形式 R 环的 DNA。 Alphafold-2 预测氨基酸 E593 和 E705 的突变会螯合必需的 Mg2+ 阳离子，从而完全消除了这种 R 环解析活性。耗尽 TATDN2 会增加细胞 R 环、DNA 损伤和染色体不稳定。 TATDN2 缺失导致 R 环增加的情况下复制叉进展不良。值得注意的是，我们发现 TATDN2 对于 BRCA1 缺陷型癌细胞的生存至关重要，但对于同源 BRCA1 丰富的癌细胞来说则不然。因此，我们提出 TATDN2 是治疗 BRCA1 缺陷型癌症的新靶点。© 作者 2023。由牛津大学出版社代表 Nucleic Acids Research 出版。

BRCA1-deficient cells have increased IRE1 RNase, which degrades multiple microRNAs. Reconstituting expression of one of these, miR-4638-5p, resulted in synthetic lethality in BRCA1-deficient cancer cells. We found that miR-4638-5p represses expression of TATDN2, a poorly characterized member of the TATD nuclease family. We discovered that human TATDN2 has RNA 3' exonuclease and endonuclease activity on double-stranded hairpin RNA structures. Given the cleavage of hairpin RNA by TATDN2, and that BRCA1-deficient cells have difficulty resolving R-loops, we tested whether TATDN2 could resolve R-loops. Using in vitro biochemical reconstitution assays, we found TATDN2 bound to R-loops and degraded the RNA strand but not DNA of multiple forms of R-loops in vitro in a Mg2+-dependent manner. Mutations in amino acids E593 and E705 predicted by Alphafold-2 to chelate an essential Mg2+ cation completely abrogated this R-loop resolution activity. Depleting TATDN2 increased cellular R-loops, DNA damage and chromosomal instability. Loss of TATDN2 resulted in poor replication fork progression in the presence of increased R-loops. Significantly, we found that TATDN2 is essential for survival of BRCA1-deficient cancer cells, but much less so for cognate BRCA1-repleted cancer cells. Thus, we propose that TATDN2 is a novel target for therapy of BRCA1-deficient cancers.© The Author(s) 2023. Published by Oxford University Press on behalf of Nucleic Acids Research.