IFN-GAMMA INDUCES A P91 STAT1-ALPHA-RELATED TRANSCRIPTION FACTOR WITHDISTINCT ACTIVATION AND BINDING-PROPERTIES/

The 5' flanking region of the mig gene, a member of the chemokine fami ly of small m.w. chemoattractant and growth regulatory factors, contai ns an IFN-gamma-responsive enhancer, gamma RE-1, consisting of an exte nded imperfect palindrome. In this report we show that a novel factor, gamma RF-1, which binds to the gamma RE-1 element, is rapidly activat ed in a variety of primary cell types and tumor cell lines treated wit h IFN-gamma. Our data indicate that gamma RF-1 is present in a latent form in unstimulated cells and its DNA-binding activity is dependent u pon tyrosine phosphorylation. UV cross-linking studies revealed that g amma RF-1 consists of at least two proteins of approximately 95 and 13 0 kDa, which interact with the gamma RE-1 element. A comparison of gam ma RF-1 and GAF, an IFN-gamma-activated transcription factor containin g the p91/Stat1 alpha protein (Stat, signal transducer and activator o f transcription), showed that these two factors exhibited differences in electrophoretic mobility, responsiveness to IFN-alpha, and kinetics of activation. Using anti-Stat Ab, however, we found that one or more subunits of gamma RF-1 are antigenically related to p91/Stat1 alpha. Our results indicate, therefore, that gamma RF-1 and GAF are distinct IFN-gamma-responsive transcription factors and probably contain closel y related members of the Stat protein family.