Activation of Oas1a gene expression by type I IFN requires both STAT1 and STAT2 while only STAT2 is required for Oas1b activation

Abstract

The murine 2′-5′ oligoadenylate synthetase 1a (Oas1a) and Oas1b genes are type 1 IFN responsive genes. Oas1a is an active synthetase with broad antiviral activity mediated through RNase L. Oas1b is inactive but can inhibit Oas1a synthetase activity and mediate a flavivirus-specific antiviral activity through an unknown RNase L-independent mechanism. Analysis of promoter elements regulating gene transcription confirmed that an IFN-stimulated response element (ISRE) is required for IFN beta-activation but neither the overlapping IRF binding site present in both promoters nor the adjacent Oas1b NF-kappa B site is required. Mutation of the overlapping STAT site negatively affected IFN beta-induction of Oas1a but not of Oas1b. Also, IFN beta induction of Oas1a was STAT1- and STAT2-dependent, while induction of Oas1b was STAT1-independent but STAT2-dependent. The two promoters differ at a single nucleotide in the STAT site. The data indicate that these two duplicated genes can be differentially regulated by IFN beta.

Type 1 IFN-independent activation of a subset of interferon stimulated genes in West Nile virus Eg101-infected mouse cells

“…3A, B and C). Consistent with previous observations (Ousman et al, 2005; Pulit-Penaloza et al, 2012), no upregulation of Oas1a after stimulation with IFN beta was observed in either tSTAT1−/− or tSTAT2−/− MEFs (Fig. 3A), while Oas1b (Fig.…”

“…The Oas1a and Oas1b promoters each contain a canonical ISRE (Pulit-Penaloza et al, 2012), Irf7 contains an inverted ISRE (Ning et al, 2005; Schmid et al, 2010) and the Irf1 promoter has a GAS element instead of an ISRE which is upregulated in IFN-stimulated cells by a STAT1 dimer (Pine et al, 1994). STAT1 and STAT2 occupancy on the Oas1a, Oas1b and Irf7 promoters and STAT1 occupancy on the Irf1 promoter in vivo was analyzed with a chromatin immunoprecipitation (ChIP) assay done as described in Materials and Methods using tC3H/He MEFs that were mock-infected, infected with WNV Eg101 (MOI of 5) for 7, 16 or 24 h or treated with 1000 U/ml of murine IFN beta for 30 m. Briefly, in vivo crosslinked DNA-protein complexes were immunoprecipitated using anti-STAT1, anti-STAT2 or a nonspecific IgG antibody.…”

“…Confluent tC3H/He monolayers were mock-infected, infected with WNV Eg101 at a MOI 5 for 7, 16 or 24 h or treated with 1000 U/ml of murine IFN beta for 3 h. The ChIP assay was done as previously described (Pulit-Penaloza et al, 2012). Isolated DNA was analyzed by real-time PCR using probes and primers designed to span the proximal Oas1a and Oas1b promoters.…”

“…Oas1b was also reported to inhibit in vitro Oas1a synthetase activity in a dose-dependent manner (Elbahesh et al, 2011). IFN beta activation of Oas1a expression was shown to be STAT1- and STAT2-dependent while that of Oas1b was STAT1-independent and STAT2-dependent indicating that these two duplicated genes are differentially regulated by IFN beta (Pulit-Penaloza et al, 2012). WNV Eg101 infection in MEFs was previously reported to activate IFN-beta expression, induce STAT1 Tyr701 phosphorylation and upregulate the expression of Oas1a, Oas1b as well as other ISGs including Irf7 and Irf1(Scherbik et al, 2006; Scherbik et al, 2007).…”

STAT2-dependent induction of RNA adenosine deaminase ADAR1 by type I interferon differs between mouse and human cells in the requirement for STAT1

“…Induction of mouse Oas1b and IRF7 by type I IFNs likewise has been described to be STAT1-independent. IFNβ induction of the Oas1b gene in Stat1(Δ1-124) −/− MEFs is STAT1-independent but STAT2-dependent (Pulit-Penaloza et al, 2012), and induction of IRF7 following lymphocytic choriomeningitis virus (LCMV) infection or IFNα treatment is STAT2- and IRF9-dependent but independent of STAT1 based on Stat1(Δ1-124) −/− knockout (Ousman et al, 2005). LCMV also has been seen to evade the mouse immune system through a type I IFN-mediated response that is STAT1-independent but STAT2-dependent (Hahm et al, 2005).…”