HELQ is a dual-function DSB repair enzyme modulated by RPA and RAD51
Authors: Simon J Boulton
David S Rueda
Ondrej Belan
Simon N Powell
Erika Buechelmaier
Aleksandra Vancevska
Roopesh Anand
Artur Kaczmarczyk
Matthew Newton
Tohru Takaki
Journal: Nature (2021)
Discipline: Multidisciplinary
Keywords: DNA double-stranded breaks; HELQ helicase; DSB repair; RAD51; RPA
Affiliations: DSB Repair Metabolism Laboratory, The Francis Crick Institute, London, UK., Memorial Sloan Kettering Cancer Center, New York, NY, USA., Department of Infectious Disease, Faculty of Medicine, Imperial College London, London, UK., Department of Infectious Disease, Faculty of Medicine, Imperial College London, London, UK. ., Memorial Sloan Kettering Cancer Center, New York, NY, USA. ., DSB Repair Metabolism Laboratory, The Francis Crick Institute, London, UK. .

Abstract:  DNA double-stranded breaks (DSBs) are deleterious lesions, and their incorrect repair can drive cancer development1. HELQ is a superfamily 2 helicase with 3' to 5' polarity, and its disruption in mice confers germ cells loss, infertility and increased predisposition to ovarian and pituitary tumours2-4. At the cellular level, defects in HELQ result in hypersensitivity to cisplatin and mitomycin C, and persistence of RAD51 foci after DNA damage3,5. Notably, HELQ binds to RPA and the RAD51-paralogue BCDX2 complex, but the relevance of these interactions and how HELQ functions in DSB repair remains unclear3,5,6. Here we show that HELQ helicase activity and a previously unappreciated DNA strand annealing function are differentially regulated by RPA and RAD51. Using biochemistry analyses and single-molecule imaging, we establish that RAD51 forms a complex with and strongly stimulates HELQ as it translocates during DNA unwinding. By contrast, RPA inhibits DNA unwinding by HELQ but strongly stimulates DNA strand annealing. Mechanistically, we show that HELQ possesses an intrinsic ability to capture RPA-bound DNA strands and then displace RPA to facilitate annealing of complementary sequences. Finally, we show that HELQ deficiency in cells compromises single-strand annealing and microhomology-mediated end-joining pathways and leads to bias towards long-tract gene conversion tracts during homologous recombination. Thus, our results implicate HELQ in multiple arms of DSB repair through co-factor-dependent modulation of intrinsic translocase and DNA strand annealing activities. 

Retracted: No

PubPeer comments:
 Love the basic molecular biology. However, I really think people need to stop using U2OS as a model for DSB repair. It matters that it is ATRX null. , 
 Great work! Yes, U2OS is an immortal cancer cell type which apparently uses alternate telomere lengthening mechanism to maintain telomeres instead of telomerase. Therefore, any claims on signalling pathways in these cells need to verified in normal non-immortal cells. , 
 Thanks for your comments. Indeed, U2OS are ALT (Atrx null) and we share your concerns about the widespread use of these cells for cell cycle and DDR research when used in isolation. Many of the DSB reporter assays used on our study have been established in U2OS and are widely used and validated in the field (work of Maria Jasin, Jeremy Stark, Ralph Scully and many others etc). Our conclusions that HELQ functions in DSB repair is further supported by our and other groups previous work using isogenic Wt and HELQ mouse knockouts (eg. Adelman Nature 2013). In the Adelman study, we observed a clear defect in DSB repair with evidence of defects in HR (ICL, PARPi sensitivity and persistent RAD51 foci). Similar observations were reported by Rick Wood and Niaoko Shima in Nature Comms and NAR, respectively. Our current findings of defects in DSB repair (by HR, SSA and MMEJ) in human cells, were also very nicely corroborated by the recent Nature Comms paper from Marcel Tijsterman s group using C. elegans as a model system. Hence, we believe that our current work in conjunction with the previous published studies of HELQ and the complementary findings of Tijsterman, leave us in little doubt that HELQ performs a conserved function in DSB repair and more specifically SSA, MMEJ and HR. We hope this addresses your point. Happy New Year. , 
 In addition to Simon Boulton s remarks above, we are very well aware of the issues of working with U2OS cells. Lobrich (Molecular Cell 71, 11u201324 July 5, 2018) suggested that ATRX-deficient cells had more short tract events and less long-tract homologous recombination events, although the magnitude of the changes in LTGC STGC are relatively small. In spite of the ATRX status, inactivation of HELQ in U2OS cells still resulted in a significant shift towards LTGC, in spite of the ATRX deficiency, suggesting that we are still able to observe in-vivo effects of manipulating HELQ, in spite of being impaired by the loss of ATRX. We have observed the same effects HELQ-inactivation resulting in impaired SSA and HR in other cell types, as outlined above. Thus, we think our conclusions about the role of HELQ in homologous recombination in-vivo are valid as concluded in the paper. Happy New Year. ,