Differential regulation of a cellular gene by human interferon-gamma and interferon-alpha.

Two cDNA clones complementary to interferon (IFN)-gamma inducible mRNAs in human cells were isolated, and one of these, C5-4, was used for studying the regulation of its cognate mRNA by IFNs. C5-4 cDNA hybridized to a 2.2-kilobase mRNA that coded for a 42,000 Mr polypeptide in vitro. This mRNA was induced by HuIFN-gamma as well as by HuIFN-alpha 2 but in different manners: (i) IFN-gamma induced this mRNA greater than 100-fold and this induction was sustained for at least 48 h, whereas IFN-alpha 2 induced it approximately 10-fold but only transiently. (ii) Cells that were pretreated with IFN-alpha 2 (18h) became refractory to induction by IFN-alpha 2 but responded normally to IFN-gamma. (iii) Cycloheximide (50 micrograms/ml) and anisomycin (10 micron or higher) inhibited the induction by IFN-gamma but not by IFN-alpha 2, suggesting the requirement for some newly synthesized, presumably IFN-gamma-induced, protein factor(s) in IFN-gamma-mediated but not in IFN-alpha 2-mediated induction. Interestingly, this inhibition by cycloheximide of the IFN-gamma-mediated induction was overcome by 24 h, whereas a sustained inhibition was obtained with anisomycin. Our results suggest that this release from cycloheximide-mediated inhibition was apparently due to a leakiness in its inhibitory action on protein biosynthesis. As analyzed by nuclear runoff transcription, IFN-gamma induced the transcription of C5-4-specific RNA within 2 h and it was inhibited by cycloheximide, indicating that the newly synthesized protein mediator(s) required plays a role in the transcriptional activation of the C5-4 gene by IFN-gamma. Southern blot analysis indicated that the C5-4 gene is present in a single copy in the genome. The results demonstrate that IFN-gamma and IFN-alpha induced the expression of a common gene through different mechanisms and suggest the involvement of an intermediary mechanism in IFN-gamma-mediated transcriptional activation of certain cellular genes.