Wee1 epigenetically modulates H2B mono‐ubiquitination at K120 lysine and DNA double‐strand break repair through phosphorylation of H2BY37‐dependent manner in small‐cell lung cancer

BACKGROUND: DNA damage repair is a crucial mechanism highly related to therapy resistance for various therapeutic strategies. Our previous results have shown that the degree of drug resistance in small‐cell lung cancer (SCLC) cell lines was proportional to both the transcription and expression levels of Wee1, indicating that Wee1, an evolutionarily highly conserved kinase, plays a vital role in the therapeutic resistance of SCLC. In the present study, we aim to determine the nonclassical mechanism of Wee1 on DNA repair regulation. METHODS: Western blot was conducted to determine the mono‐ubiquitination level of H2Bub. Comet assay was used to evaluate the degree of DNA damage. Immunofluorescence was conducted to determine the DNA repair markers. Co‐immunoprecipitation was utilized to assess the potential interactions with H2BY37ph. MTT assays were used to evaluate the survival rates of SCLC cells. RESULTS: Overexpression of Wee1 increases the level of H2BK120ub and alleviates ionizing radiation (IR)‐induced DNA damage in SCLC cells. Moreover, H2BK120ub is a crucial molecule in Wee1‐mediated double‐strain break (DSB) repair in SCLC cells. Mechanisms study indicated that H2BY37ph is involved in Wee1‐mediated H2BK120ub through interaction with the E3 ubiquitin ligase RNF20–RNF40 complex and upregulates its phosphorylation, mutation of H2BY37 phosphorylation sites attenuated DSB repair and enhanced the sensitivity of IR‐induced SCLC cell death. CONCLUSION: H2BY37ph produces crosstalk with H2BK120ub in an E3 ubiquitin ligase‐dependent manner, promoting Wee1‐mediated DSB repair in SCLC cells. This study clarifies the nonclassical mechanism of Wee1 regulation of DSB repair, which provides a theoretical basis for the clinical understanding of the regulatory network of Wee1 and its use as a target for overcoming multiple types of therapeutic resistance.