Transcription-coupled nucleotide excision repair protects against genomic instability and cell death induced by the liver toxin methyleugenol.

Methyleugenol (ME) is a hepatotoxic phenylpropene naturally present in various herbs and spices. Following dietary exposure, ME undergoes metabolic activation in the liver, resulting in the formation of DNA adducts and liver damage. Although ME is a suspected human liver carcinogen, it is still unknown which DNA repair pathway removes the ME-induced DNA adducts. Here, we studied the relevance of nucleotide excision repair (NER) using various genetically engineered cell models. Our data show a crucial role for transcription-coupled (TC)-NER rather than global genome (GG)-NER, revealing that ME-induced DNA damage triggers detrimental transcription stress. Mechanistically, ME-derived DNA adducts stall RNA polymerase II (RNAPII), resulting in the chromatin release and cytoplasmic export of its active subunit RPB1, followed by proteasomal degradation to allow for repair and transcription recovery. Blocking of RNAPII by ME-derived DNA lesions promotes CSB immobilization and recruitment of CSA and UVSSA. The triggered canonical TC-NER pathway removes the ME-induced DNA lesions, preserves genome integrity and promotes cell survival. At high DNA adduct levels or in cells with deficient TC-NER, persistent transcription stress provokes genomic instability, induces apoptotic cell death and strongly reduces long-term cell survival. In contrast to that, GG-NER-compromised cells are not sensitized to ME-triggered cytotoxicity. Taken together, the canonical TC-NER pathway is crucial for the repair of DNA adducts induced by ME and likely also structurally related phenylpropenes. These findings are particularly important for Cockayne syndrome patients with defective TC-NER.