Time-dependent recruitment of GAF, ISGF3 and IRF1 complexes to GAS, ISRE and composite genes shapes IFNa and IFNg activated transcriptional responses and explains functional overlap [RNA-seq]

Although the core type I and type II IFN signaling pathways are distinct, their expression profiles show considerable overlap and are difficult to discern. Using a genome-wide RNAseq-ChIPseq integrative approach, our results identify a novel class of IFN-I and IFN-II responsive genes that use ISRE and GAS composite sites to recruit STAT1 and STAT2-containing ISGF3 and GAF-like complexes and IRF1 for optimal expression. Moreover, they support the existence of an analogous transcriptional regulatory mechanism of IFNα and IFNγ inducible genes, in which STAT1 and STAT2-containing ISGF3 and GAF-like complexes and IRF1 are recruited to individual or combined ISRE and GAS composite sites in an IFN- and time-dependent manner. In addition, we present proof for the involvement of an ISRE and GAS composite-dependent regulatory system in IFN-activated positive feedback regulation of the STAT1, STAT2, IRF9 and IRF1 genes and long-term response to IFNs, which depends on phosphorylation and expression of ISGF3, IRF1 and GAF-like components. These findings provide further insight in the existence of a novel intracellular amplifier circuit that offer an explanation for the existing molecular and functional overlap between IFN-I and IFN-II activated ISG expression. Comparative gene expression profiling analysis of RNA-seq data for the human hepatocellular carcinoma cell lines – Huh7.5 WT, Huh7.5 IRF9KO, Huh7.5 STAT1KO, Huh7.5 STAT2KO, Huh7.5 IRF1KO and Huh7.5 IRF9/IRF1 dKO treated with IFN alpha and IFN gamma