A ubiquitin-dependent signalling axis specific for ALKBH-mediated DNA dealkylation repair

A signalling mechanism in human cells for sensing DNA damage induced by alkylation involves ubiquitin-dependent recruitment of the alkylation repair complex ASCC to the vicinity of the damage and co-localization with transcription and splicing factors. Ubiquitin drives DNA alkylation repair The upstream signalling pathway that initiates the repair of alkylation damage in DNA is not well understood. Nima Mosammaparast and colleagues have found that the activating signal cointegrator complex (ASCC) is recruited to the vicinity of alkylation damage, co-localizing the transcription and splicing factors. The recruitment of ASCC depends on the ability of ASCC2 protein to bind K63-linked polyubiquitin chains made by the E3 ligase RNF113A, although the polyubiquitinated target remains unclear. Individuals with X-linked trichothiodystrophy carry a mutation in RNF113A, and these results clarify the underlying basis of their hypersensitivity to alkylating agents. DNA repair is essential to prevent the cytotoxic or mutagenic effects of various types of DNA lesions, which are sensed by distinct pathways to recruit repair factors specific to the damage type. Although biochemical mechanisms for repairing several forms of genomic insults are well understood, the upstream signalling pathways that trigger repair are established for only certain types of damage, such as double-stranded breaks and interstrand crosslinks 1 , 2 , 3 . Understanding the upstream signalling events that mediate recognition and repair of DNA alkylation damage is particularly important, since alkylation chemotherapy is one of the most widely used systemic modalities for cancer treatment and because environmental chemicals may trigger DNA alkylation 4 , 5 , 6 . Here we demonstrate that human cells have a previously unrecognized signalling mechanism for sensing damage induced by alkylation. We find that the alkylation repair complex ASCC (activating signal cointegrator complex) 7 relocalizes to distinct nuclear foci specifically upon exposure of cells to alkylating agents. These foci associate with alkylated nucleotides, and coincide spatially with elongating RNA polymerase II and splicing components. Proper recruitment of the repair complex requires recognition of K63-linked polyubiquitin by the CUE (coupling of ubiquitin conjugation to ER degradation) domain of the subunit ASCC2. Loss of this subunit impedes alkylation adduct repair kinetics and increases sensitivity to alkylating agents, but not oth