Phosphorylation of the Stat1 Transactivation Domain Is Required for Full-Fledged IFN-γ-Dependent Innate Immunity

Abstract

Stat1 is phosphorylated on serine 727 within its transactivating domain (TAD) in response to interferons or other immunological signals. We generated gene-targeted mutant mice expressing a serine727-alanine mutant of Stat1. These animals showed increased mortality upon infection with Listeria monocytogenes and impaired clearance of the bacteria from spleen and liver. The Stat1S727A mice were more resistant to the LPS-induced septic shock syndrome, suggesting that Stat1 serine phosphorylation promotes inflammatory responses. Expression of IFN-gamma-induced genes was strongly reduced in macrophages expressing Stat1(S727A). While mutation of Stat1 at S727 did not reduce its binding to chromatin, association with the coactivator CBP and histone acetylation at the interferon-responsive GBP promoter was strongly reduced, suggesting defective recruitment of histone acetylases as the mechanism underlying IFN-gamma hyporesponsiveness. Our data demonstrate that the increase in transcription factor activity caused by Stat serine phosphorylation contributes to macrophage activation and to IFN-gamma-dependent immune responses in vivo.

Serine-phosphorylated STAT1 is a prosurvival factor in Wilms' tumor pathogenesis

“…We observed serine-phosphorylated STAT1 in the developing rat kidney, and it may have a role in kidney development, for example, to promote progenitor cell survival before tissue vascularization. Although STAT1-deficient mice or mice expressing constitutively inactive STAT1-S727A mutant do not have a kidney phenotype (Kaplan et al, 1998;Varinou et al, 2003), probably because activated STAT3 can replace STAT1 to drive the transcription of certain genes (Qing and Stark, 2004), it may be more revealing to evaluate the renal response to overexpression of constitutively active STAT1 during metanephric differentiation or carcinogenesis.…”

Role of PKCδ in IFN-γ-inducible CIITA gene expression☆

“…These studies support the notion that pStat1(ser727) is less critical for IRF-1 expression by stimulation of IFN-γ. However, other studies have reported that IRF-1 expression requires pSTAT1(ser727) (Kovarik et al, 2001;Ramsauer et al, 2002;Varinou et al, 2003). Although the sources of discrepancy between two types of results are not clear at the moment, in all studies, IRF-1 expression was induced by IFN-γ in the absence of serine phosphorylation of Stat1, albeit at a low level.…”

“…Although the sources of discrepancy between two types of results are not clear at the moment, in all studies, IRF-1 expression was induced by IFN-γ in the absence of serine phosphorylation of Stat1, albeit at a low level. Notably, Varinou et al showed that the expression of several IFN-γ inducible genes including IRF-1 was down-regulated in macrophages that were prepared from the mice expressing only a serine 727-alanine mutant of Stat1 (Stat1S727A) (Varinou et al, 2003). However, the IRF-1 levels in mutant mice after IFN-γ stimulation were still higher than the basal levels, implying that tyrosine phosphorylated Stat1 can activate IRF-1 expression.…”

SENP1 regulates IFN-γ−STAT1 signaling through STAT3−SOCS3 negative feedback loop

“…Among them, STAT1 is activated by IFN-γ (Levy and Darnell, 2002;Ramana et al, 2002;Varinou et al, 2003) during M1 macrophage activation. As a downstream target of cytokine or growth factor receptors, STAT3 always induces expressions of genes (Il10, Tgfb1, Mrc1) associated with M2-like macrophage phenotype to counteract inflammation induced by STAT1 (Hong et al, 2002;Qing and Stark, 2004;Regis et al, 2008).…”

“…IFN-γ binds to its cell-surface receptor, triggers receptor-associated JAK1 and JAK2 auto-phosphorylation, and followed by phosphorylation of an IFNγR1 tyrosine residue, which serves as a docking site predominantly for STAT1 (Darnell et al, 1994;Sakatsume et al, 1995;Bach et al, 1996;Kaplan et al, 1996;Bach et al, 1997;Pestka et al, 2004;Platanias, 2005;Stark and Darnell, 2012). IFNγR1-recruited STAT1 is phosphorylated on tyrosine 701 by JAK, dimerizes, and then translocates to the nucleus where it can bind to a regulatory DNA element termed gamma-activated sequence (GAS), which is important for regulating gene expression (Levy and Darnell, 2002;Varinou et al, 2003;Qing and Stark, 2004;Stark and Darnell, 2012). Major mechanisms that are responsible for negative regulation of IFN-γ signaling in cells include STAT dephosphorylation by tyrosine phosphatases and JAK catalytic inhibition by suppressor of cytokine signaling 1 (SOCS1) protein (David et al, 1993;Alexander et al, 1999;Marine et al, 1999;Chen et al, 2000;Kinjyo et al, 2002;ten Hoeve et al, 2002).…”