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Developmental Biology - DNA Repair|
Repairing DNA Breaks in Aging, Cancer and MND
Eukaryotic topoisomerase 1 (TOP1) regulates DNA topology to ensure efficient DNA replication and transcription. TOP1 is also a major driver of endogenous genome instability, particularly when its catalytic intermediate—a covalent TOP1-DNA adduct known as a TOP1 cleavage complex (TOP1cc)—is stabilised. TOP1ccs are highly cytotoxic and a failure to resolve them underlies the pathology of neurological disorders; but, it is also exploited in cancer therapy where TOP1ccs are the target of widely used frontline anti-cancer drugs. A critical enzyme for TOP1cc resolution is the tyrosyl-DNA phosphodiesterase (TDP1), which hydrolyses the bond that links a tyrosine in the active site of TOP1 to a 3’ phosphate group on a single-stranded (ss)DNA break. However, TDP1 can only process small peptide fragments from ssDNA ends, raising the question of how the ~90 kDa TOP1 protein is processed upstream of TDP1. Here we find that TEX264 fulfils this role by forming a complex with the p97 ATPase and the SPRTN metalloprotease. We show that TEX264 recognises both unmodified and SUMO1-modifed TOP1 and initiates TOP1cc repair by recruiting p97 and SPRTN. TEX264 localises to the nuclear periphery, associates with DNA replication forks, and counteracts TOP1ccs during DNA replication. Altogether, our study elucidates the existence of a specialised repair complex required for upstream proteolysis of TOP1ccs and their subsequent resolution.
John Fielden, Katherine Wiseman, Ignacio Torrecilla, Shudong Li, Samuel Hume, Shih-Chieh Chiang, Annamaria Ruggiano, Abhay Narayan Singh, Raimundo Freire, Sylvana Hassanieh, Enric Domingo, Iolanda Vendrell, Roman Fischer, Benedikt M. Kessler, Timothy S. Maughan, Sherif F. El-Khamisy and Kristijan Ramadan.
The authors thank Paul Elliott for generating the homology-based structural models and for helpful discussions. This work was supported by the Medical Research Council programme grant (MC_EX_MR/K022830/1) to K.R. J.F. is supported by a CRUK DPhil studentship. K.W. was supported by an MRC studentship and A.R. is supported by a European Molecular Biology Organization (EMBO) long-term fellowship (ALTF 1109-2017). E.D. is supported by the S:CORT consortium which is funded by a grant from the MRC and CRUK. S.F.E. is funded by a Wellcome Trust Investigator award (103844) and a Lister Institute Fellowship.
Conflicts of Interest
The authors declare the following competing interests. K.R., J.F., and T.S.M., are inventors of, and Oxford Innovation Ltd. are holders of a patent application for the use of SPRTN as a cancer biomarker. The remaining authors declare no competiting interests.
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TOP1 regulates DNA topology to ensure efficient DNA replication and transcription.
It is also a major driver of endogenous genome instability. The authors
hold a patent application for the use of SPRTN as a cancer biomarker.