BRCA1/ATF1-Mediated Transactivation is Involved in Resistance to PARP Inhibitors and Cisplatin

Abstract

Homologous recombination (HR)-deficient cells are sensitive to PARP inhibitors through a synthetic lethal effect. We previously developed an HR activity assay named Assay of Site-Specific HR Activity (ASHRA). Here, we evaluated the HR activity of 30 missense variants of BRCA1 by ASHRA and found that several BRCA1 variants showed intermediate HR activity, which was not clearly discerned by our previous analyses using a conventional method. HR activity measured by ASHRA was significantly correlated with sensitivity to olaparib. However, cells expressing the severely HR-deficient BRCA1-C61G variant were resistant to olaparib, and resistance was dependent on high expression of activating transcription factor 1 (ATF1), which binds to BRCA1 and activates the transcription of target genes to regulate cell proliferation. The BRCA1-C61G variant bound to ATF1 and stimulated ATF1-mediated transactivation similar to wild-type BRCA1. High expression of ATF1 conferred resistance to olaparib and cisplatin activating BRCA1/ATF1-mediated transcription without affecting HR activity in BRCA2-knockdown or RAD51-knockdown cells, but not in BRCA1-knockdown cells. These results suggest that ASHRA is a useful method to evaluate HR activity in cells and to predict the sensitivity to PARP inhibitors. The expression level of ATF1 might be an important biomarker of the effect of PARP inhibitors and platinum agents on HR-deficient tumors with the BRCA1-C61G variant or alteration of non-BRCA1 HR factors such as BRCA2 and RAD51. Significance: ASHRA could evaluate HR activity in cells and predict the sensitivity to PARP inhibitors. High expression level of ATF1 may predict the resistance of BRCAness tumors with alterations of non-BRCA1 HR factors to PARP inhibitors and platinum agents.

BRCA1 transports the DNA damage signal for CDDP‐induced centrosome amplification through the centrosomal Aurora A

“…Finally, we identified three patient-derived variants, which reduced the interaction of BRCA1 with Aurora A (Figure 7E). The N132K variant, which moderately decreases homologous recombination activity, 53 The present data suggest that, in response to nuclear DNA damage, BRCA1 is phosphorylated by ATM in the nucleus, moves to the cytoplasm, localizes to the centrosome, and promotes the centrosomal localization of Aurora A, which phosphorylates PLK1. Activated PLK1 causes premature centriole disengagement and centriole overduplication, leading to DDICA (Figure 8).…”

“…Finally, we identified three patient‐derived variants, which reduced the interaction of BRCA1 with Aurora A (Figure 7E ). The N132K variant, which moderately decreases homologous recombination activity, 53 reduced the CDDP‐induced centrosomal localization of BRCA1 and Aurora A, whereas V191I reduced that of only Aurora A (Figure 7F,G ). The Y105C variant, which induced a mild reduction of the BRCA1–Aurora A association compared with N132K and V191I, did not affect the CDDP‐induced centrosomal localization of BRCA1 and Aurora A.…”

DNA repair function scores for 2172 variants in the BRCA1 amino-terminus

“…The effects of missense variants on BRCA1 have been tested in a number of studies by analyzing one variant at a time in the HDR assay-the singleton assay [8,13,[28][29][30][31][32]. For the current study, we have analyzed 18 different variants in the singleton assay (Fig 6A) in addition to variants in the BRCA1 amino-terminus that have been previously published [8,12,17,33].…”

“…In the case of BRCA1, previous studies have suggested that its function in homology directed repair of DNA double-strand breaks is key to its tumor suppressor activity [3,[8][9][10][11]. Cells with a loss of BRCA1 function in homology directed repair assays exhibit heightened sensitivity to DNA-damaging agents and PARP inhibitors [12][13][14][15]. The use of multiplexed approaches to analyze many hundreds to thousands of variants at once [3,8,9,12,16] enable the analysis of many variants that are rare in the population.…”

Bevacizumab increases the sensitivity of olaparib to homologous recombination-proficient ovarian cancer by suppressing CRY1 via PI3K/AKT pathway

“…The effect of the inhibition of the VEGF pathway on HR activity was evaluated using ASHRA to elucidate the mechanism of sensitization to olaparib by the inhibition of the VEGF pathway. ASHRA can quantify cellular HR activity, and the measured activity in ASHRA correlates linearly with sensitivity to PARP inhibitors 23 . The treatment with the addition of bevacizumab or cediranib signi cantly suppressed the HR activity in OVISE cells (Fig.…”