ZUP1 promotes DNA repair and immune evasion to drive olaparib resistance in triple-negative breast cancer

Introduction: Olaparib resistance limits its therapeutic efficacy in triple-negative breast Cancer (TNBC). Exploring the mechanisms underlying olaparib resistance and developing combination strategies are of great clinical significance for improving the long-term therapeutic benefit in TNBC.

Objectives: This study aimed to determine whether ZUP1 is associated with olaparib resistance in TNBC patients and to elucidate the underlying mechanisms involved.

Methods: We established an olaparib-resistant TNBC cell model and integrated transcriptomic profiling with public datasets to DUBs linked to resistance. Candidate function was assessed by drug sensitivity assay, clonogenic assay, Apoptosis assay, HR/NHEJ reporter assays and comet assays. Mechanistic studies used co-immunoprecipitation, chromatin fractionation, and PARylation assays. In vitro co-culture assays and flow cytometry analysis were used to evaluated immune infiltration. High-throughput virtual screening (HTVS), biolayer interferometry (BLI), and deubiquitination assays nominated small molecule inhibitors and assessed therapeutic synergy with olaparib.

Results: We identified ZUP1, a recently uncovered Deubiquitinase, as significantly upregulated in TNBC patients who did not respond to olaparib. Mechanistically, ZUP1 stabilized PARP1 by removing its polyubiquitin chains at lysine 425, resulting in increased PARylation and enhanced chromatin retention of SSRP1 and SPT16, thereby promoting DNA repair. ZUP1 deficiency significantly increased olaparib-induced DNA damage, facilitates cytosolic dsDNA release to activate STING signalling, and enhanced CD8⁺T cell infiltration into tumors. High-throughput virtual screening identified procyanidin C1 as a potential ZUP1 inhibitor. Combination treatment with procyanidin C1 and olaparib significantly suppressed tumor growth in olaparib -resistant TNBC models.

Conclusion: ZUP1 facilitates olaparib resistance in TNBC by stabilizing PARP1 and enhancing DNA damage repair. Pharmacological inhibition of ZUP1 with procyanidin C1 represents a promising therapeutic strategy to overcome olaparib resistance in TNBC.

PARP1; Triple-negative breast cancer; ZUP1; olaparib; resistance.