RAD6B is a major mediator of triple negative breast cancer cisplatin resistance: Regulation of translesion synthesis/Fanconi anemia crosstalk and BRCA1 independence

BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR BASIS OF DISEASE

卷:1866

Article

Haynes, Brittany^1,2  Gajan, Ambikai^1,2  Nangia-Makker, Pratima^1,2  Shekhar, Malathy P.^1,2,3 

[1] Karmanos Canc Inst, 421 E Canfield Ave, Detroit, MI 48201 USA

[2] Wayne State Univ, Sch Med, Dept Oncol, 421 E Canfield Ave, Detroit, MI 48201 USA

[3] Wayne State Univ, Sch Med, Dept Pathol, 421 E Canfield Ave, Detroit, MI 48201 USA

关键词: Triple negative breast cancer;    BRCA1;    FANCD2;    POL eta;    H2AX;    Cisplatin;    Ubiquitination;    Small molecule inhibitor;    Homologous recombination;    Replication restart;   

DOI  :  10.1016/j.bbadis.2019.165561

来源: Elsevier

【 摘 要 】

Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype with few therapy options besides chemotherapy. Although platinum-based drugs have shown initial activity in BRCA1-mutated TNBCs, chemoresistance remains a challenge. Here we show that RAD6B (UBE2B), a principal mediator of translesion synthesis (TLS), is overexpressed in BRCA1 wild-type and mutant TNBCs, and RAD6B overexpression correlates with poor survival. Pretreatment with a RAD6-selective inhibitor, SMI#9, enhanced cisplatin chemosensitivity of BRCA1 wild-type and mutant TNBCs. SMI#9 attenuated cisplatin-induced PCNA monoubiquitination (TLS marker), FANCD2 (Fanconi anemia (FA) activation marker), and TLS polymerase POL eta. SMI#9-induced decreases in gamma H2AX levels were associated with concomitant inhibition of H2AX monoubiquitination, suggesting a key role for RAD6 in modulating cisplatin-induced gamma H2AX via H2AX monoubiquitination. Concordantly, SMI#9 inhibited gamma H2AX, POL eta and FANCD2 foci formation. RAD51 foci formation was unaffected by SMI#9, however, its recruitment to double-strand breaks was inhibited. Using the DR-GFP-based assay, we showed that RAD6B silencing or SMI#9 treatment impairs homologous recombination (HR) in HR-proficient cells. DNA fiber assays confirmed that restart of cisplatin-stalled replicating forks is inhibited by SMI#9 in both BRCA1 wild-type and mutant TNBC cells. Consistent with the in vitro data, SMI#9 and cisplatin combination treatment inhibited BRCA1 wild-type and mutant TNBC growth as compared to controls. These RAD6B activities are unaffected by BRCA1 status of TNBCs suggesting that the RAD6B function in TLS/FA crosstalk could occur in HR-dependent and independent modes. Collectively, these data implicate RAD6 as an important therapeutic target for TNBCs irrespective of their BRCA1 status.

【 授权许可】

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