RNA helicase DDX5 alleviates UVB-induced skin DNA damage through RBM15/METTL14-mediated m⁶A modification

Ultraviolet (UV) radiation-induced DNA damage is a major driver of skin carcinogenesis and premature aging. Understanding the mechanisms of DNA damage repair is crucial for preventing these skin disorders. Proteomic profiling revealed a significant downregulation of RNA helicase DDX5 in the UVB-irradiated cells, which strongly correlated with nucleotide excision repair and mRNA metabolic processes. Although DDX5 has been implicated in cell cycle regulation and helicase-dependent facilitation of DNA repair, its specific function and underlying mechanisms in mitigating UV-triggered DNA damage remain unclear. Consistent with proteomic data, western blotting analysis confirmed that UVB radiation could cause the upregulation of DDX5 both in vitro and in vivo. To further confirm the effects of DDX5, DDX5 expression was modulated in UVB-irradiated HaCaT cells by siRNA transfection and lipofection, and in mice by AAV transduction. Functional assays demonstrated that DDX5 overexpression robustly reversed UVB-triggered apoptosis, DNA damage, γH₂AX focus formation, and the production of cyclobutane pyrimidine dimers, whereas DDX5 knockdown exacerbated these effects. Co-immunoprecipitation revealed direct interactions between DDX5 and methyltransferase complex subunits, including RBM15 and METTL14. MeRIP-seq and MeRIP-qPCR further revealed that DDX5 overexpression elevated m⁶A modification on mRNAs encoding key DNA repair factors (LIG1, RFC2, and RAD51), which was accompanied by markedly increased mRNA and protein levels of these repair mediators. Consistently, inhibiting m⁶A methylation with cycloleucine or knocking down RBM15/METTL14 abolished the protective effects of DDX5 and reversed the DDX5-mediated upregulation of repair factor expression. Collectively, these findings illustrated that DDX5 interacts with RBM15/METTL14 to promote m⁶A modification of DNA repair factor mRNAs, thereby enhancing their expression and facilitating the repair of UV-induced DNA damage.