HSF1 and YTHDC1 enhance DNA repair under heat stress by promoting repair-associated gene expression.

External stressors, particularly heat stress, induce DNA damage and genomic instability in cells. However, the mechanisms by which cells rapidly respond to such DNA damage remain largely unknown. In this study, we found that heat shock factor 1 (HSF1), the major transcription factor in the heat shock response, activated several non-homologous end joining (NHEJ) pathway-associated genes, particularly NHEJ1, through puncta formation, thereby maintaining the stability of NHEJ pathway and alleviating the repair burden of DNA double-strand breaks caused by heat stress. Furthermore, N6-methyladenosine (m6A) RNA modification and its reader YTH domain-containing protein 1 (YTHDC1) contributed to this process by promoting the splicing of NHEJ1. Knockdown of HSF1 or YTHDC1 increased nuclear intensity of phosphorylation of histone variant H2AX at Ser-139 (γH2AX) in heat-stressed cells, whereas NHEJ1 overexpression rescued this effect. Moreover, HSF1 or YTHDC1 overexpression increased NHEJ repair efficiency in heat-stressed cells, supporting the existence of an HSF1/YTHDC1-NHEJ1-DNA double-strand repair axis. Our findings reveal a mechanism by which cells repair DNA damage during the heat shock response, providing new insights into how cells maintain genomic stability under external stress conditions.