EMSY is a recently identified gene that maps to chromosome 11q13.5 and is amplified and overexpressed in a subset of sporadic cases of poor prognosis breast and ovarian carcinomas. At a molecular level, this finding is of interest because EMSY has been found to interact directly with BRCA2 and thereby repress the ability of BRCA2 to promote double strand break repair. Here we report the results of experiments designed to test the hypothesis that EMSY overexpression can elicit the same genetic instability phenotype associated with the loss of BRCA2. We first constructed a lentiviral vector containing an EF1α-promoted cassette containing the first half of a full-length EMSY cDNA that included the 5’-BRCA2 interacting domain as well as GFP downstream of an IRES element. Concentrated VSV-packaged virus preparations containing this vector were then used to infect a near-diploid H-tert-immortalized human breast epithelial cell line (48, XX, +20,+20). Subsequent analysis of FACS-selected GFP+ cells showed these remained GFP+ for more than 10 passages and maintained increased levels of 5’-EMSY mRNA expression (70 to 300-fold above control cells transduced with GFP only). Cytogenetic analyses showed a significant reproducible polyclonal increase in structural chromosomal abnormalities in the EMSY-transduced cells within 5 passages by comparison to GFP-transduced controls (39/150 vs 19/150, p=0.003, data pooled from 3 different experiments). These included 55 unique structural abnormalities in the EMSY-transduced cells vs. 20 in the controls (p<0.001). In contrast, the same cells showed no difference in numerical chromosomal abnormalities. Cells with structural abnormalities continued to accumulate in the EMSY-transduced cultures but remained unchanged in the controls (63/150 vs. 22/150 affected cells at passage 10, p<0.001; including 112 vs. 25 unique structural abnormalities, p<0.001). In addition, as reported for BRCA2 null cells, exposure of the EMSY-transduced cells for 24 hours to the DNA crosslinking agent, Mitomycin-C (0.4 μM), enhanced their chromosomal instability and caused the formation of dicentric chromosomes whereas neither of these effects were obtained with the control cells. These results directly implicate EMSY in the genesis of sporadic breast and ovarian cancer through effects on pathways affected by BRCA2 deletion.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]