Synthetic Lethality during Replication Stress Induced by the Loss of RECQ1 and BLM DNA Helicases

Authors

• KM Conners
• M Hashemian
• C Kinzy
• JL Hall
• C Herr
• R Sharma
• N Ibrahim
• VL Roger

Abstract

RecQ helicases are a highly conserved family of DNA unwinding enzymes that operate with other DNA repair proteins in genome metabolism. Mono-allelic mutations in RECQ1 are associated with many phenotypic abnormalities. RECQ1, like the RecQ helicase BLM, is important for suppression of chromosomal instability. We performed RNAi screens using a pool library of DNA damage response/repair genes and an isogenic pair of CRISPR knockout and wild-type RECQ1 HeLa cell lines. Using low doses of the DNA alkylating agent MMS to stress replication forks in vivo, we identified novel target genes that behaved in a synthetic lethal manner with RECQ1. BLM was synthetic lethal with RECQ1 and was validated using individual RNAis for in vivo depletion and colony formation assays. Under MMS-induced replication stress, co-deficiency of RECQ1 and BLM showed decrease in replication fork speed compared to the WT Hela cells or cells deficient in RECQ1 or BLM. Cells doubly deficient for BLM and RECQ1 displayed increasing DNA damage as evidenced by the percentage of cells with positive γ-H2AX foci. Under hydroxyurea induced stress, cells lacking BLM and RECQ1 experienced reduced ongoing forks. In mouse models, doubly-deficient mice showed increase in fat mass gain and an increase in both Small Pre-B and CD43 (–) cell numbers. The synthetic lethal interaction suggests redundant roles to deal with replication stress with the mouse models and PCS phenotype indicating a more significant impact for deficient individuals. RECQ1 may be a suitable target to overcome tumor resistance by destabilizing forks in rapidly dividing cancer cells.

Scientific Focus Area: Cell Biology

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