DPP9 modulates RPA1 stability and temozolomide sensitivity through RFWD3 Nuclear localization in glioma

Temozolomide resistance is a major barrier to effective glioma treatment and is frequently associated with enhanced DNA damage repair capacity. Although DPP9 has been linked to tumor development in several malignancies, whether it contributes to glioma therapeutic resistance has not been explored. Transcriptomic datasets, glioma specimens, and genetic gain- and loss-of-function approaches were employed to characterize DPP9 expression and function. RNA sequencing, co-immunoprecipitation, subcellular fractionation, and ubiquitination analyses were conducted to define the molecular basis of DPP9-mediated effects. Higher DPP9 expression was observed in glioma specimens and coincided with shorter patient survival. DPP9 depletion inhibited glioma growth and enhanced TMZ sensitivity in both cultured cells and xenograft tumors. Functional experiments support a role for altered RFWD3 localization in the association between DPP9 depletion and reduced RPA1 stability. Loss of DPP9 promoted RFWD3 redistribution to the cytoplasm, resulting in increased RPA1 ubiquitination and degradation. The reduction in RPA1 was accompanied by elevated replication stress, increased accumulation of DNA damage markers, and enhanced sensitivity to TMZ-induced genotoxic stress. Restoration of RPA1 expression attenuated these defects, indicating that RPA1 mediates a substantial portion of the cellular consequences associated with DPP9 loss. DPP9 contributes to glioma resistance to TMZ by sustaining RPA1-dependent DNA damage responses through regulation of the RFWD3-RPA1 axis. These results identify DPP9 as an important determinant of genome maintenance in glioma cells and nominate DPP9 as a candidate target for further investigation in TMZ-resistant glioma.