Recruitment of Stat4 to the Human Interferon-α/β Receptor Requires Activated Stat2

Pre-assembly of STAT4 with the human IFN-α/β receptor-2 subunit is mediated by the STAT4 N-domain

“…Here, IFN-α/β-induced STAT4 tyrosine phosphorylation was found to be dependent upon the presence of human STAT2 (Farrar et al, 2000b). Unlike other STAT family members, STAT2 is highly divergent between mouse and human, and this dissimilarity is particularly striking within the COOH-terminal transactivation domain (Farrar et al, 2000a;Park et al, 1999;Paulson et al, 1999).…”

“…Further, receptor specificity for STAT activation is constrained in part by the affinity of each STAT SH2 domain for specific amino acids adjacent to each tyrosine motif within receptor cytoplasmic domains (Greenlund et al, 1995;Krishnan et al, 1998;Yan et al, 1996). As neither the IFNAR1 nor R2 subunits are well conserved between mice and humans, the paradigm of direct STAT recruitment was the basis of previous studies that determined the ability of STAT4 to interact directly with phosphorylated tyrosine residues within the receptor COOH-termini (Farrar et al, 2000b). Here, STAT4 was unable to interact directly with any of the phosphorylated tyrosine residues within either the human IFNAR1 or R2 subunits.…”

“…1B). We previously demonstrated that none of the phosphorylated tyrosine residues within either the human IFNAR1 or IFNAR2 subunits could interact with the SH2 domain of STAT4 (Farrar et al, 2000b), thus eliminating the hypothesis that STAT4 was recruited to the human IFNAR based solely on a linear SH2/phosphotyrosine interaction. However, we have now reexamined how the IFNAR cytoplasmic domains contribute to IFN-α/β-dependent STAT4 activation based on recent findings implicating the STAT N-terminal domain (amino acids 1-130) in receptor-proximal tyrosine phosphorylation.…”

“…Fusion protein enrichments were routinely monitored by SDS-PAGE followed by silver staining (data not shown). Cell lysates, prepared from murine STAT4-transfected human 2fTGH cells (Farrar et al, 2000b), were incubated with equimolar quantities of purified fusion proteins bound to glutathione-Sepharose. Enriched GST was incapable of interacting with STAT4 ( Fig.…”

“…However, unlike IL-12, the effects of IFN-α/β on STAT4 activation, Th1 development, and acute IFN-γ secretion are not well conserved when comparing mouse and human CD4 + T cells. In human CD4 + T cells, IFN-α/ β promotes STAT4 activation (Cho et al, 1996;Farrar et al, 2000b;Rogge et al, 1998) and can drive acute IFN-γ secretion in response to IFN-α/β + IL-18 stimulation (Brinkmann et al, 1993;Matikainen et al, 2001;Parronchi et al, 1992;Sareneva et al, 2000;Sareneva et al, 1998). In murine CD4 + T cells, IFN-α/β is inefficient at promoting STAT4 activation (Berenson et al, 2004;Farrar and Murphy, 2000;Farrar et al, 2000a;Farrar et al, 2000b;Persky et al, 2005;Rogge et al, 1998;Szabo et al, 1997), and as a consequence, murine CD4 + T cells fail to differentiate to Th1 cells and do not secrete IFN-γ in response to IFN-α/ β + IL-18 in vitro (Berenson et al, 2004;Persky et al, 2005;Rogge et al, 1998;Wenner et al, 1996).…”