BARD1 phase separation orchestrates a repair hub by enriching XRCC5 to drive chemoresistance in glioma.

Temozolomide (TMZ) resistance is a major challenge in glioblastoma (GBM). The role of BRCA1-associated RING domain protein 1 (BARD1), a DNA damage response protein, in GBM and its potential link to liquid-liquid phase separation (LLPS) remain unclear. Bioinformatics analysis of TCGA, CGGA, and GEO datasets revealed that high BARD1 expression correlates with poor prognosis in GBM. Functional studies demonstrated that BARD1 knockdown inhibited glioma cell proliferation, migration, and invasion. We discovered that BARD1 undergoes LLPS via its intrinsically disordered region (IDR, aa 113-425). Upon TMZ-induced DNA damage, BARD1 forms nuclear condensates that recruit X-ray repair cross-complementing protein 5 (XRCC5) to damage sites, promoting repair and driving TMZ resistance. Disrupting this phase separation capability impaired DNA repair. Through structure-based virtual screening, our results suggest that Ziprasidone and Apomorphine may disrupt the BARD1-XRCC5 interaction. Combining either compound with TMZ enhanced cytotoxicity in vitro and suppressed tumor growth in vivo. Our findings unveil a novel LLPS-mediated mechanism by which BARD1 confers TMZ resistance in GBM, positioning it as a prognostic marker and a therapeutic target. Targeting the BARD1-XRCC5 axis presents a promising strategy to overcome chemoresistance.