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Recruitment of KMT2C/MLL3 to DNA Damage Sites Mediates DNA Damage Responses and Regulates PARP Inhibitor Sensitivity in Cancer.

ABSTRACT: When recruited to promoters, histone 3 lysine 4 (H3K4) methyltransferases KMT2 (KMT2A-D) activate transcription by opening chromatin through H3K4 methylation. Here, we report that KMT2 mutations occur frequently in non-small cell lung cancer (NSCLC) and are associated with high mutation loads and poor survival. KMT2C regulated DNA damage responses (DDR) through direct recruitment to DNA damage sites by Ago2 and small noncoding DNA damage response RNA, where it mediates H3K4 methylation, chromatin relaxation, secondary recruitment of DDR factors, and amplification of DDR signals along chromatin. Furthermore, by disrupting homologous recombination (HR)-mediated DNA repair, KMT2C/D mutations sensitized NSCLC to Poly(ADP-ribose) polymerase inhibitors (PARPi), whose efficacy is unclear in NSCLC due to low BRCA1/2 mutation rates. These results demonstrate a novel, transcription-independent role of KMT2C in DDR and identify high-frequency KMT2C/D mutations as much-needed biomarkers for PARPi therapies in NSCLC and other cancers with infrequent BRCA1/2 mutations. SIGNIFICANCE: This study uncovers a critical role for KMT2C in DDR via direct recruitment to DNA damage sites, identifying high-frequency KMT2C/D mutations as biomarkers for response to PARP inhibition in cancer.

SUBMITTER: Chang A

PROVIDER: S-EPMC8260460 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Human DNA polymerase ? (Pol ?) is involved in various DNA damage responses in addition to its central role in DNA replication. The Pol ?4 holoenzyme consists of four subunits, p125, p50, p68 and p12. It has been established that the p12 subunit is rapidly degraded in response to DNA damage by UV leading to the in vivo conversion of Pol ?4 to Pol ?3, a trimeric form lacking the p12 subunit. We provide the first analysis of the time-dependent recruitment of the individual Pol ? subunits to sites of DNA damage produced by UV irradiation through 5 ?m polycarbonate filters by immunofluorescence microscopy and laser scanning cytometry (LSC). Quantitative analysis demonstrates that the recruitments of the three large subunits was near complete by 2 h and did not change significantly up to 4 h after UV exposure. However, the recruitment of p12 was incomplete even at 4 h, with about 70% of the Pol ? lacking the p12 subunit. ChIP analysis of Pol ? after global UV irradiation further demonstrates that only p125, p50 and p68 were present. Thus, Pol ?3 is the predominant form of Pol ? at sites of UV damage as a result of p12 degradation. Using LSC, we have further confirmed that Pol ? was recruited to CPD damage sites in all phases of the cell cycle. Collectively, our results show that Pol ? at the DNA damage site is the Pol ? trimer lacking p12 regardless of the cell cycle phase.

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