Inhibition of interferon-gamma antiviral and antiproliferative activities by ras oncogene expression

In this study, we evaluated the effect of ras oncogene activation on cell response to interferons (IFNs). For this purpose, we treated NIH 3T3 murine fibroblasts transformed by transfection with K-, Ha-, or N-ras oncogenes, either mutated or amplified, for 24 hours with IFN-gamma or IFN-alpha. We evaluated cell response by measuring virus replication, [3H]thymidine incorporation, 2',5'-oligoadenylate synthetase activation, and class I antigen induction. Transformed cells were much less responsive to IFN-gamma antiviral and antiproliferative activities than normal NIH 3T3 cells. Similarly, the induction of 2',5'-oligoadenylate synthetase following IFN-gamma treatment was completely depressed in transformed cells. Only class I antigens, measured at the cell surface and mRNA levels, appeared partially inducible by IFN-gamma in ras-transformed cells. When the same cell lines were treated with IFN-alpha, we observed full response. Because both normal and ras-transformed NIH 3T3 cells were able to bind [125I]IFN-gamma with comparable Kd values (8.3 X 10(-11) M vs. 3 X 10(-11) M, respectively), these findings suggest that ras oncogenes may differentially impair IFN-gamma activities by affecting activation of IFN-inducible genes downstream from the receptor binding event.