Kim Tae Moon, Son Mi Young, Dodds Sherry, Hu Lingchuan, Luo Guangbin, Hasty Paul
Department of Molecular Medicine and Institute of Biotechnology, The Barshop Center of Aging, University of Texas Health Science Center, San Antonio, TX 78245, USA.
Department of Genetics, Case Western Reserve University, BRB-720, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
Nucleic Acids Res. 2015 Jan;43(2):893-903. doi: 10.1093/nar/gku1334. Epub 2014 Dec 17.
Fanconi anemia (FA) patients exhibit bone marrow failure, developmental defects and cancer. The FA pathway maintains chromosomal stability in concert with replication fork maintenance and DNA double strand break (DSB) repair pathways including RAD51-mediated homologous recombination (HR). RAD51 is a recombinase that maintains replication forks and repairs DSBs, but also rearranges chromosomes. Two RecQ helicases, RECQL5 and Bloom syndrome mutated (BLM) suppress HR through nonredundant mechanisms. Here we test the impact deletion of RECQL5 and BLM has on mouse embryonic stem (ES) cells deleted for FANCB, a member of the FA core complex. We show that RECQL5, but not BLM, conferred resistance to mitomycin C (MMC, an interstrand crosslinker) and camptothecin (CPT, a type 1 topoisomerase inhibitor) in FANCB-defective cells. RECQL5 suppressed, while BLM caused, breaks and radials in FANCB-deleted cells exposed to CPT or MMC, respectively. RECQL5 protected the nascent replication strand from MRE11-mediated degradation and restarted stressed replication forks in a manner additive to FANCB. By contrast BLM restarted, but did not protect, replication forks in a manner epistatic to FANCB. RECQL5 also lowered RAD51 levels in FANCB-deleted cells at stressed replication sites implicating a rearrangement avoidance mechanism. Thus, RECQL5 and BLM impact FANCB-defective cells differently in response to replication stress with relevance to chemotherapeutic regimes.
范可尼贫血（FA）患者表现出骨髓衰竭、发育缺陷和癌症。FA途径与复制叉维持以及包括RAD51介导的同源重组（HR）在内的DNA双链断裂（DSB）修复途径协同维持染色体稳定性。RAD51是一种重组酶，可维持复制叉并修复DSB，但也会重排染色体。两种RecQ解旋酶，RECQL5和布鲁姆综合征突变体（BLM）通过非冗余机制抑制HR。在这里，我们测试了RECQL5和BLM的缺失对缺失FA核心复合物成员FANCB的小鼠胚胎干细胞（ES）的影响。我们发现，在FANCB缺陷细胞中，RECQL5而非BLM赋予了对丝裂霉素C（MMC，一种链间交联剂）和喜树碱（CPT，一种1型拓扑异构酶抑制剂）的抗性。RECQL5抑制，而BLM分别在暴露于CPT或MMC的FANCB缺失细胞中导致断裂和辐射。RECQL5保护新生复制链免受MRE11介导的降解，并以与FANCB相加的方式重新启动应激的复制叉。相比之下，BLM以与FANCB上位的方式重新启动但不保护复制叉。RECQL5还降低了应激复制位点处FANCB缺失细胞中的RAD51水平，这暗示了一种重排避免机制。因此，RECQL5和BLM在对复制应激的反应中对FANCB缺陷细胞的影响不同，这与化疗方案相关。
