Interferon induced increases in c-myc expression in a human breast carcinoma cell line

Previous studies from our laboratory have indicated that interferon-gamma inhibits the growth of a human breast carcinoma cell line, MDA 468. We measured steady state levels of c-myc mRNA to determine if the antiproliferative effect of IFN-gamma was mediated by changes in the expression of this proto-oncogene. C-myc message levels increased after 24 hours of IFN treatment, peaked at 48 hours, but remained elevated through 96 hours of treatment. The increase in c-myc mRNA was observed with as little as 10 U/ml of IFN-gamma. The stability of mRNA was enhanced in interferon treated cells. These data suggest that IFN-gamma increased expression of c-myc mRNA, but decreased cell growth, and point out the complexities of the relationship of the expression of this protooncogene to cell growth.