IL-10-induced factors belonging to the p91 family of proteins bind to IFN-gamma-responsive promoter elements.

Expression of the gene encoding the high affinity IgG receptor (Fc gamma RI) is stimulated by IFN-gamma through a promoter element designated gamma-IFN activation site (GAS). This sequence binds a transcription factor designated gamma-IFN activation factor (GAF). GAF-GAS complexes contain an IFN-regulated 91-kDa protein (p91). In mouse peritoneal macrophages, IL-4 and IL-10 influenced both basal and IFN-gamma-induced expression of Fc gamma RI in opposite ways: IL-10 was stimulatory and IL-4 repressed Fc gamma RI expression. IL-4 or IL-10 did not affect the activation of GAF by IFN-gamma, but both activated the binding of latent, receptor-activated factors (RAFTs) to the Fc gamma RI GAS. RAFTs-IL-4 and -IL-10 migrated similarly in electrophoretic mobility shift assays but could be distinguished through their specificities for different GAS sequences and their reactivity with anti-p91 antisera. These experiments also revealed two distinct RAFTs-IL-10 to be members of the p91 family of proteins. The data suggest GAS-related elements to integrate signals from IFN-gamma-, IL-4- and IL-10-activated signaling paths.