DOWN-REGULATION OF BRCA1 AND BRCA2 IN HUMAN OVARIAN-CANCER CELLS EXPOSED TO ADRIAMYCIN AND ULTRAVIOLET-RADIATION

Germ-line mutations of the BRCA1 and BRCA2 genes predispose women to d evelop cancers of the breast and ovary, but the biologic functions of these genes remains unclear. We have investigated the responses of the BRCA1 and BRCA2 gene products to cytotoxic agents in 3 human ovarian cancer cell lines: SK-OV-3 (which contains a p53 deletion mutation), C AOV-3 (which over-expresses a mutant p53) and PA-I (which expresses wi ld-type p53). In screening studies, we determined the effects of 7 dif ferent agents on BRCA1 and BRCA2 expression. We found that Adriamycin (ADR) and ultraviolet (UV)radiation significantly down-regulated BRCA1 and BRCA2 mRNA expression in SK-OV-3 cells. On the other hand, campto thecin, nitrogen mustard, taxol, vincristine and etoposide had no effe ct on BRCA1 or BRCA2 mRNA levels at doses that yielded degrees of cyto toxicity similar to or greater than ADR. The down-regulation of BRCA1 and BRCA2 mRNAs was dose and time dependent; significant down-regulati on was first observed at 8-16 hr after exposure to ADR. BRCA1 protein levels were also down-regulated following treatment of SK-OV-3 cells w ith ADR. Similar results were observed in CAOV-3 and PA- I cells treat ed with ADR, and this finding could not be directly attributed to ADR- induced changes in the cell cycle distribution. The ADR doses required for significant decreases of BRCA1 and BRCA2 were about 10-15, 5-10 a nd 2 mu M, respectively, for SK-OV-3, CAOV-3 and PA-I; the IC50 doses for loss of cell viability (determined by Trypan blue dye exclusion) w ere 23, 14 and 0.4 mu M, respectively. Thus, at equitoxic doses of ADR , PA-I cells were more resistant to down-regulation of BRCA1 and BRCA2 than SK-OV-3 or CAOV-3. Our findings suggest that I) BRCA1 and BRCA2. expression in human ovarian cancer cell lines is selectively down-reg ulated by 2 DNA-damaging agents (ADR and UV radiation); 2) these respo nses are not due to non-specific cytotoxicity; and 3) the BRCA1 and BR CA2 responses may be dependent, in part, on the p53 functional status of the cells. We speculate that the downregulation of BRCA1 and BRCA2 may be part of a cellular survival response activated by certain forms of DNA damage. Int.J Cancer 77:600-609, 1998. (C) 1998 Wiley-Liss, In c.