Abstract

Temozolomide (TMZ) resistance remains a major obstacle in glioblastoma (GBM) therapy. Here, we identified E2F6 as a critical driver of TMZ resistance in GBM. E2F6 expression was significantly elevated in glioma tissues and correlated with advanced tumor grade, recurrence, and poor prognosis. Functionally, E2F6 depletion sensitized GBM cells to TMZ, suppressing proliferation and promoting apoptosis both in vitro and in vivo. Mechanistically, E2F6 directly bound to the SH3GL2 promoter and transcriptionally repressed its expression. SH3GL2 acted as a key downstream effector of E2F6, as SH3GL2 silencing abolished the chemosensitizing effects induced by E2F6 knockdown. Further investigation revealed that SH3GL2 promoted HMGB1 secretion through BAR domain-mediated interaction with CHMP4B and SH3 domain-dependent binding to HMGB1. Enhanced HMGB1 secretion reduced intracellular HMGB1 retention, impaired DNA damage repair, and increased TMZ-induced DNA damage. In addition, extracellular HMGB1 promoted M1 macrophage polarization, thereby enhancing anti-tumor immune responses. Collectively, our findings identify the E2F6/SH3GL2/HMGB1 axis as a previously unrecognized mechanism linking DNA repair and tumor immune regulation during TMZ resistance, and suggest that targeting this pathway may represent a promising therapeutic strategy for GBM. Highly expressed E2F6 in glioma cells directly binds to the SH3GL2 promoter and transcriptionally represses its expression. As a key effector molecule, SH3GL2 binds to CHMP4B via its BAR domain and to HMGB1 via its SH3 domain, promoting the exosomal export of HMGB1 protein upon TMZ stimulation. This process, on one hand, reduces intracellular HMGB1 levels, thereby impairing DNA damage repair capacity, and on the other hand, induces the polarization of tumor-associated macrophages toward the M1 phenotype, enhancing anti-tumor immunity.