Cellular commitment to oncogene-induced transformation or apoptosis is dependent on the transcription factor IRF-1

The transcriptional activator interferon regulatory factor 1 (IRF-1) and its antagonistic repressor IRF-2 are regulators of the interferon (IFN) system and of cell growth. Here we report that embryonic fibroblasts (EFs) from mice with a null mutation in the IRF-1 gene ( IRF-1 −/− mice) can be transformed by expression of an activated c-Ha- ras oncogene. This property is not observed in EFs from wild-type or IRF-2 −/− mice but is still observed in EFs from mice deficient in both genes. The transformed phenotype of ras-expressing IRF-1 −/− EFs could be suppressed by the expression of the IRF-1 cDNA. Thus, IRF-1 functions as a tumor suppressor. Furthermore, expression of the c-Ha- ras oncogene causes wild-type but not IRF-1 −/− EFs to undergo apoptosis when combined with a block to cell proliferation or treated by anticancer drugs or ionizing radiation. Hence, IRF-1 may be a critical determinant of oncogene-induced cell transformation or apoptosis.