Editors' ChoiceDNA Repair

NLS protects DNA damage protein

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Sci. Signal.  11 Apr 2017:
Vol. 10, Issue 474, eaan4046
DOI: 10.1126/scisignal.aan4046

A single motif targets a protein to the nucleus and directs its deubiquitylation, promoting high-fidelity DNA damage repair.

Double-strand breaks (DSBs) in DNA can be repaired by nonhomologous end-joining (NHEJ), which is fast, but extremely error-prone, or homologous recombination (HR), which is slower but more accurate. The proteins involved in the two types of repair mechanism are frequently antagonistic. Ring finger protein 169 (RNF169) prevents the accumulation of 53BP1 and RAP80, proteins involved in NHEJ, on chromatin at DSBs, thus promoting repair by HR. An et al. found that the nuclear localization signal (NLS) of RNF169 interacted with ubiquitin-specific protease 7 (USP7), a DNA damage–regulated deubiquitylating protein with antiapoptotic properties, to mediate its function in DNA repair. Purified recombinant RNF169 coimmunoprecipitated with USP7. Structural analysis revealed that the ubiquitin-like (UBL) domain of USP7 bound to a specific domain of RNF169, the KxxxK motif, which was predicted to be an NLS based on the chemistry of the surrounding residues. Indeed, substituting residues in the KxxxK motif impaired both its nuclear localization ability and the interaction with USP7 in HEK 239T cells. Knocking down USP7 with siRNA, generating catalytically inactive mutants of USP7, or pharmacologically inhibiting its deubiquitylase activity all reduced the amount of RNF169 in the cell and increased RNF169 turnover, suggesting that USP7 deubiquitylates RNF169 to protect it from proteolytic degradation. When USP7 activity was reduced, RNF169 failed to accumulate at radiation-induced foci in cells, and high-fidelity, HR-mediated repair was reduced. Because the homologous and nonhomologous DNA damage repair mechanisms are regulated differently in different cell types and errors in this differential regulation are involved in both the development of various cancers and resistance to treatment, identification of the dual-functionality motif in RNF169 suggests a target for fine-tuning this regulation.

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