2′-5′-Oligoadenylate Synthetase-Like Protein Inhibits Respiratory Syncytial Virus Replication and Is Targeted by the Viral Nonstructural Protein 1

Abstract

2=-5=-Oligoadenylate synthetase-like protein (OASL) is an interferon-inducible antiviral protein.Here we describe differential inhibitory activities of human OASL and the two mouse OASL homologs against respiratory syncytial virus (RSV) replication. Interestingly, nonstructural protein 1 (NS1) of RSV promoted proteasome-dependent degradation of specific OASL isoforms. We conclude that OASL acts as a cellular antiviral protein and that RSV NS1 suppresses this function to evade cellular innate immunity and allow virus growth. C ellular innate immunity against virus infection is primarily mediated by type I interferons (IFNs). In turn, the IFNs exert their pleiotropic effects through the induction of a variety of IFNstimulated genes (ISGs) (1-4). Although the general antiviral roles of several ISGs have been demonstrated, the roles of individual ISGs and their effect on specific viruses have remained largely unidentified (5-9). On the other hand, the coevolution of the host and the virus has resulted in viral strategies to evade the host IFN response by targeting ISGs and other IFN pathway proteins (10). Oligoadenylate synthetases (OAS) are a family of ISGs characterized by their ability to synthesize 2=-5=-oligoadenylate (2-5A), which induces RNA degradation by activating RNase L (11, 12). Human oligoadenylate synthetase-like protein (OASL) is related to the OAS family by its N-terminal OAS-like domain but is devoid of 2-5A synthetase activity. Additionally, OASL contains two tandem ubiquitin-like (UBL) domains in the C terminus, which are absent in any of the other members of the OAS family (12-15). OASL is directly and rapidly induced by virus infection via interferon regulatory factor 3 (IRF3) as well as by IFN signaling (1,12,16,17). Unlike in humans, two OASL isoforms have been identified in the mouse, Oasl1 and Oasl2. We have recently described the (18), were grown in monolayers on coverslips and infected with RSV Long at a multiplicity of infection of 3. At 18 h postinfection, cells were fixed and immunostained with mouse anti-RSV nucleoprotein (N) antibody (Abnova clone B023), followed by Alex Fluor 610-conjugated donkey anti-mouse IgG (Life Technologies). Images were captured in a Nikon AIRSI spectral confocal microscope system. (B) (Top) The same cell lines were infected as described above, and the total cell lysates were analyzed by immunoblotting using the same primary antibody described above and horseradish peroxidase (HRP)-conjugated secondary antibody, followed by ECL (enhanced chemiluminescence) detection. Actin is the loading control. (Bottom) Total RNA isolated from parallel cultures was subjected to quantitative reverse transcription-PCR (qRT-PCR), as described previously (38). The primers, synthesized by Integrated DNA Technologies (Coralville, IA), were as follows. RSV N gene, forward 5=-TGCAGGGCAAGTGATGTTAC-3=, and reverse, 5=-TTCCATTTCTGCTTGCACAC-3=; actin, forward, 5=-AGAAAATCTGGCACCACACC-3=, and reverse, 5=-GGGGTGTTGAAGGTCTCAAA-3=. A portion of the PCR sample was analyzed on 1.5% agarose...

Unique nonstructural proteins of Pneumonia Virus of Mice (PVM) promote degradation of interferon (IFN) pathway components and IFN-stimulated gene proteins

“…We also show for the first time that the NS proteins of PVM promote degradation of selected murine ISGs, the most distal arm of the type I IFN pathway. Recent studies, including ours, have shown that at least two ISGs can act as antivirals against RSV; they are viperin and OASL323336. We also showed that RSV NS1 could degrade OASL, allowing better RSV growth33.…”

“…Recent studies, including ours, have shown that at least two ISGs can act as antivirals against RSV; they are viperin and OASL323336. We also showed that RSV NS1 could degrade OASL, allowing better RSV growth33. It is reasonable to assume that the NS proteins of both viruses are capable of inhibiting or degrading many more members of the ISG family that need to be identified.…”

“…It is currently unknown which ISG(s) can inhibit PVM; however, we have observed that RSV NS1 protein promotes degradation of OASL (2′-5′-Oligoadenylate Synthetase Like), an ISG that is antagonistic to RSV replication3233, suggesting that the IFN suppressors of a virus may have evolved to counteract specific host functions that directly inhibit the virus. Since we established a degradative assay for the PVM NS proteins, we moved on to determine if an ISG is also targeted by these proteins.…”

“…This is particularly evident for the NS proteins that promote the ubiquitination of multiple yet selective substrates. RSV NS1, for example, recruits EloC, Cul2, and an Rbx subunit, all of which were essential for NS1-mediated ubiquitination and subsequent degradation of STAT29; however, it was later shown that RSV NS1 can also cause degradation of OASL, a major cellular ISG33, even though STAT2 and OASL are highly dissimilar in sequence.…”

Molecular Cloning and Identification of the 2′–5′ Oligoadenylate Synthetase 2 Gene in Chinese Domestic Pigs Through Bioinformatics Analysis, and Determination of Its Antiviral Activity Against Porcine Reproductive and Respiratory Syndrome Virus Infection

“…Further studies are required to determine its effect on other RNA or DNA viruses. It has previously been reported that viruses may evade innate immunity by inhibiting OAS expression through self-encoded structural or non-structural proteins [41][42][43][44][45]. Whether such mechanism exists in PRRSV, and which protein is specific to this virus, remain to be determined.…”