BRCA1 and HSP90 cooperate in homologous and non-homologous DNA double-strand-break repair and G2/M checkpoint activation

Abstract

Expression of functional breast cancer susceptibility gene 1 (BRCA1) in human breast and ovarian cancers is associated with resistance to platinum-based chemotherapeutics and poly(ADP ribose) polymerase (PARP) inhibitors. BRCA1 is a nuclear tumor suppressor that is critical for resolving double-strand DNA breaks (DSBs) and interstrand crosslinks (ICLs) by homologous recombination (HR). In vitro, animal and human clinical data have demonstrated that BRCA1-deficient cancers are highly sensitive to ICL-inducing chemotherapeutic agents, are amenable to synthetic lethal approaches that exploit defects in DSB/ ICL repair, and may be associated with improved survival. Conversely, high or restored expression of BRCA1 in breast and ovarian cancer is associated with therapeutic resistance and poor prognosis. There has been much interest in identifying agents that interfere with BRCA1-dependent DSB/ICL repair to restore or enhance sensitivity to cancer therapeutics. We demonstrate that the heat-shock protein 90 (HSP90) inhibitor 17-allylamino-17-demethoxygeldanamycin [17-AAG (Tanespimycin)], currently in Phase II/III clinical evaluation for several cancers, induces BRCA1 ubiquitination and proteasomal degradation, resulting in compromised repair of ionizing radiation-and platinum-induced DNA damage. We show that loss of HSP90 function abolishes BRCA1-dependent DSB repair and that BRCA1-deficient cells are hypersensitive to 17-AAG due to impaired Gap 2/Mitosis (G2/M) checkpoint activation and resultant mitotic catastrophe. In summary, we document an upstream HSP90-dependent regulatory point in the Fanconi anemia/BRCA DSB/ICL repair pathway, illuminate the role of BRCA1 in regulating damage-associated checkpoint and repair responses to HSP90 inhibitors, and identify BRCA1 as a clinically relevant target for enhancing sensitivity in refractory and/or resistant malignancies. chemosensitivity | DNA repair I nherited mutations in the breast cancer susceptibility gene 1 (BRCA1) predispose the development of breast, ovarian, and other malignancies (1-5). BRCA1 is a nuclear tumor suppressor critical for repair of double-strand DNA breaks (DSBs) and interstrand crosslinks (ICLs) by homologous recombination (HR) (6). BRCA1 is phosphorylated by ataxia telangiectasia mutated (ATM), ataxia telangiectasia and Rad3 related (ATR), and checkpoint kinase 2 (CHK2) kinases in response to DNA damage and recruits and organizes multiple distinct protein complexes that recognize and repair damaged DNA and activate cell cycle checkpoints (7,8). In vitro and in vivo studies have shown that tumor cells expressing high levels of BRCA1 are resistant to both ionizing radiation (IR) and several classes of chemotherapeutic agents, and that ablation of BRCA1 expression can restore sensitivity to these agents (9, 10). Indeed, cancers arising in BRCA1 mutation carriers are relatively hypersensitive to platinum-based therapies, and high BRCA1 mRNA expression in sporadic cancers is a biomarker for poor response to these same agents (11-13).DSB-repair-deficient...

Strong antitumor synergy between DNA crosslinking and HSP90 inhibition causes massive premitotic DNA fragmentation in ovarian cancer cells

“…Homologous recombination repair of double-stranded DNA breaks, as well as non-homologous end joining, are impaired by HSP90 inhibitors, enhancing radiosensitivity of tumor cells. [34][35][36][37] Moreover, HSP90 inhibitors interfere with DNA damage signaling by degrading ATR, Chk1 and Rad51. [38][39][40] Table S1) in the presence of 20 μM zVAD.…”

Characterization ofLGALS3(galectin-3) as a player in DNA damage response

“…43 In response to IR, HSP90 is phosphorylated by DNA-PK, ATR, and ATM kinases, and co-localizes with γH2AX at DNA damage sites. Importantly, cells lacking HSP90 exhibited an impaired maintenance of γH2AX foci, as well as the treatment with HSP90 inhibitors that led to a reduction of BRCA1 protein levels, associated to ubiquitin-proteasome pathway.…”

HSP90 Inhibition Enhances the Anti-Tumor Efficacy of Combination Chemo Immunotherapy Targeting DNA Repair Proteins

“…Since members of the DNA-RP family of proteins have been previously suggested to represent HSP90 clients [13][14][15][16][17], we next analyzed whether expression of DNA-RP by TMZ-conditioned B16 (murine) and MEL526 (human) cells was sensitive to treatment with the HSP90i STA9090 in vitro. As shown in (Figure 2&Table S4), we found that TMZ-induced DNA-RP expression was downregulated after co-culture with STA9090 when compared with β-actin protein controls.…”

“…In the melanoma setting, DNA-RP (such as ATR, MRN complex proteins (MRE11, Rad50, NBN), Rad51, PRKDC) are transcriptionally over expressed in a disease stage-associated manner in association with chemotherapy-resistance and poor overall survival [11][12][13][14][15][16][17][18]. Notably, tumor cell (over) expression of DNA-RP may also be posttranslationally stabilized via the action of heat shock protein-90 HSP90; [11,[13][14][15][16][17]19], a molecular chaperone that is highlyabundant in the cancer proteome [20]. HSP90 forms the core of a super-chaperone machine consisting of HSP70, HSP40, HIP and HOP, which extends the molecular lifespan of a growing list of client proteins, including signaling protein kinases, transcription factors, DNA-RP and other cytosolic or nuclear proteins in their functionally mature and active conformations [19].…”