Functional characterization of EMSY gene amplification in human cancers

Abstract

The 11q13-q14 locus is frequently amplified in human cancers, with a complex structure harbouring multiple potential oncogenic drivers. The EMSY gene has been proposed as a driver of the third core of the 11q13-q14 amplicon. This gene encodes a protein reported to be a BRCA2-binding partner, which when over-expressed would lead to impairment of BRCA2 functions and could constitute a mechanism for BRCA2 inactivation in non-hereditary breast and ovarian cancers. We hypothesized that if EMSY amplification abrogates BRCA2 functions, cells harbouring this aberration would be unable to elicit competent homologous recombination DNA repair and, therefore, may have increased sensitivity to genotoxic therapies and potent PARP inhibitors. Microarray-based comparative genomic hybridization of cell lines from distinct tumour sites, including breast, ovary, pancreas, oesophagus, lung and the oral cavity, led to the identification of 10 cell lines with EMSY amplification and 18 without. EMSY amplification was shown to correlate with EMSY mRNA levels, although not all cell lines harbouring EMSY amplification displayed EMSY mRNA or protein over-expression. RNA interference-mediated silencing of EMSY did not lead to a reduction in cell viability in tumour models harbouring EMSY amplification. Cell lines with and without EMSY amplification displayed a similar ability to elicit RAD51 foci in response to DNA damaging agents, and similar sensitivity to cisplatin and olaparib. Taken together, this suggests that EMSY is unlikely to be a driver of the 11q13-q14 amplicon and does not have a dominant role in modulating the response to agents targeting cells with defective homologous recombination.

Preclinical evaluation of the PARP inhibitor BMN-673 for the treatment of ovarian clear cell cancer

“…We first assessed the ability of OCCC cells to elicit RAD51 foci formation in the presence of ionising radiation-induced DNA DSBs (Figure 1A–1C). As expected, SUM149 and CAPAN1 cells were unable to elicit RAD51 foci following exposure to DNA damaging agents, given that they harbour deleterious BRCA1 and BRCA2 mutations, respectively (Figure 1A and 1B) [14, 15, 41]. Although none of the OCCC cells completely lacked the ability to elicit RAD51 foci, KOC-7c, TOV-21G, KK, RMG-1, and SMOV-2 cells had significantly lower proportions of RAD51-positive nuclei in response to ionising radiation than HR competent cancer cells (i.e.…”

“…The inability of cancer cells to elicit RAD51 foci in the presence of DNA DSBs was used as a surrogate for dysfunctional HR as previously described [14, 15, 41]. We first assessed the ability of OCCC cells to elicit RAD51 foci formation in the presence of ionising radiation-induced DNA DSBs (Figure 1A–1C).…”

Predictors and Modulators of Synthetic Lethality: An Update on PARP Inhibitors and Personalized Medicine

“…It was suggested that because EMSY amplification could mimic a BRCA2 mutated state [148], it could account for BRCAness in sporadic breast and ovarian cancers with intact BRCA2 [122] and possibly predict hypersensitivity to PARP inhibitors. However, it was recently shown that cells with an amplified EMSY had the same RAD51 foci formation efficacy, as well as sensitivity to PARP inhibitors, as cells without EMSY amplification [149]. Taken together, these results underscore the importance of triangulating BRCAness through a variety of biomarkers in order to detect opportunities for synergism, avoid conflation of various cytotoxic mechanisms, and customize treatment.…”

Breast: Ductal carcinoma

“…Coamplification of CCND1 and EMSY was shown to be associated with an adverse outcome in ER-positive tamoxifen-treated breast cancers (Brown et al, 2010). On the other hand, a recent study suggested that EMSY is unlikely to be a driver of the 11q13-q14 amplicon and does not have a dominant role in modulating the response to agents targeting cells with defective homologous recombination (Wilkerson et al, 2011).…”