CCAAT/Enhancer-binding Protein-β Regulates Interferon-induced Transcription through a Novel Element

Abstract

We have described previously a novel interferon (IFN)-responsive cis-acting enhancer element called ␥-IFN-activated transcriptional element (GATE). GATE is distinct from the known IFN-stimulated elements and binds to novel transacting factors. To identify the ␥-IFNresponsive transacting factors that interact with GATE, we have screened a cDNA expression library derived from IFN-␥-stimulated murine macrophage cell line and isolated three different cDNAs. Among these is a gene coding for the pleiotropic transcription factor, CCAAT/ enhancer-binding protein-␤ (C/EBP-␤). We report here that the gene for C/EBP-␤ binds to GATE and induces gene expression. A mutant C/EBP-␤ interferes with the IFN-␥-stimulated transcription of the ISGF3␥ (p48) promoter. Other members of the C/EBP family do not cause these effects. Interestingly, the expression of C/EBP-␤, not the other members of its family, is induced by IFN-␥. These studies thus identify a novel role for C/EBP-␤ in the IFN-signaling pathways.

Expression regulation of zebrafish interferon regulatory factor 9 by promoter analysis

“…In mammals, IFNc-induced IRF9 protein expression requires de novo protein synthesis, which results in the discovery of GATE motif-dependent induction of mouse IRF9 (Xiao et al, 1997a). A serial of studies revealed the underlying mechanism: initially, IFNc treatment induces the synthesis of two kinds of transcription factors, C/EBP-b and GBF1, possibly through JAK-STAT signaling pathway; subsequently, the produced transcription factors are activated by IFNc treatment, translocate to nucleus and bind to the GATE motif triggering IRF9 expression (Hu et al, 2002;Kalvakolanu and Roy, 2005;Meng et al, 2005;Roy et al, 2000;Xiao et al, 2001). Therefore, the signaling transduction involved is likely different between GAS-dependent and GATE-dependent induction of zebrafish IRF9 gene by zebrafish IFNc2.…”

“…The expression property of mouse IRF9 correlates with the complexity of its promoter structure, which includes multiple potential regulatory elements including NF-jB, GAS, GATE (IFN-gamma-activated transcriptional element), and Myc/Max elements (Rani et al, 2010). GATE motif is first characterized in mouse IRF9 promoter as a binding site of CAAAT/enhancer binding protein-b (C/EBP-b) (Roy et al, 2000;Xiao et al, 1997aXiao et al, , 2001) and GATE-binding factor 1 (GBF1) (Hu et al, 2002;Meng et al, 2005) in response to IFNc treatment. Both C/EBP-b and GBF1 binding to GATE site significantly promotes IRF9 gene transcription (Meng et al, 2005).…”

MEKK1 plays a critical role in activating the transcription factor C/EBP-β-dependent gene expression in response to IFN-γ

“…In this construct a 74-bp element of murine p48 gene promoter, encompassing GATE, was cloned upstream of the simian virus 40 (SV40) early promoter driving luciferase. Mutagenesis of the GATE sequence in this construct caused a loss of IFN-␥ response and C͞EBP-␤ binding (8). The GATE-Luc and GATE-Mu constructs contained a single copy of wild-type and mutant GATE, respectively, cloned upstream of simian virus 40 minimal promoter in pGL3 promoter vector (7).…”

Stat1-independent regulation of gene expression in response to IFN-γ

“…The specificity of EGR-1 DNA binding activity was demonstrated by competition with wild-type but not mutant unlabeled probes (data not shown). Recent studies have revealed that C͞EBP-␤, a member of the CCAAT family of transcription factors, is induced by IFN-␥ in different tissues (7). Western analysis revealed that C͞EBP-␤ is induced by IFN-␥ in Stat1-null fibroblasts.…”

“…About a third of the genes induced by IFN-␥ in Stat1-null fibroblasts also are induced by IFN-␥ in wild-type cells. These include the transcription factors EGR-1, C͞EBP-␤, and LRG-21 (7,25,26), the cytoplasmic regulatory proteins SOCS-2 and SOCS-3 (27), the stress-response proteins metallothionein and PGHS-2 (28,29), osteopontin (30), and the secreted autocrine factor HB-EGF (29). Several genes are suppressed by IFN-␥ in Stat1-null fibroblasts (see Table 2, which is published as supplemental data on the PNAS web site, www.pnas.org).…”