RNase L activity does not contribute to host RNA degradation induced by herpes simplex virus infection

Abstract

In early herpes simplex virus (HSV) infection, the virion host shutoff (vhs) protein mediates the degradation of mRNA and subsequent shutoff of host protein synthesis. It is unclear whether vhs acts alone or in concert with virus-induced cellular factors for this activity. This paper examines whether RNase L, a virally induced endoribonuclease, contributes to HSV-induced mRNA decay. Results showed that RNA degradation was comparable in wild-type and RNase L 2/2 cells, demonstrating that HSV-mediated RNA degradation is independent of RNase L activity. Furthermore, the data show that HSV-1 does not significantly induce RNase L activity in murine embryo fibroblasts.During herpes simplex virus (HSV) infection, the product of the UL41 gene, known as the virion host shutoff (vhs) protein, causes the rapid shutoff of macromolecular synthesis. This 58 kDa phosphoprotein, packaged within the tegument of the virus, can exert its effect immediately upon infection (Fenwick & Clark, 1982;Read et al., 1993). Viruses lacking vhs do not cause rapid RNA destabilization (Fenwick & Everett, 1990;Read & Frenkel, 1983;Read et al., 1993;Smibert et al., 1992), exhibit only modest growth reductions in growth in tissue culture (Read & Frenkel, 1983), but are profoundly attenuated in vivo (Strelow & Leib, 1995. vhs non-specifically induces the destabilization of cytoplasmic cellular and viral mRNAs leading to the preferential translation of viral messages and efficient, sequential transition between the viral gene kinetic classes (Kwong & Frenkel, 1987Kwong et al., 1988;Oroskar & Read, 1989;Read & Frenkel, 1983). Both tRNAs and rRNAs are resistant to vhs-mediated degradation and there is a preferential degradation of mRNA at regions of translation initiation through the interaction of vhs with the cellular translation factor eIF4H (Feng et al., 2001). Several non-mutually exclusive models have been proposed for the mechanism of action of vhs. First, that the vhs protein is a messenger ribonuclease (RNase) itself; second, that it is part of a ribonuclease complex requiring activation by some additional cellular targeting protein; or third that it activates a latent cellular mRNase or modifies mRNA rendering it susceptible to cellular RNase activity (Lu et al., 2001;Zelus et al., 1996). vhs is part of an integral ribonuclease component and it functions in the absence of other HSV proteins (Doherty et al., 1996; Jones et al., 1995). Cellular factors, however, are required for vhs-mediated degradation activity in vitro and in yeast (Elgadi & Smiley, 1999;Lu et al., 2001;Zelus et al., 1996). These studies support the idea that vhs is the only HSV protein necessary to cause shutoff but that a host cell component is likely involved in this nuclease complex.Mammalian cells contain multiple RNases with little or no apparent specificity for any type of RNA. RNase L, a ubiquitous 29-,59-oligoadenylate (2-5A)-dependent endoribonuclease, is present at low levels in an inactive form (Silverman, 1997). When activated, it mediates both the antiviral and...

Varicella-zoster virus does not significantly induce the cell defence mechanism mediated by the 2-5A/RNase L pathway during its replication cycle

“…However, we demonstrated that the RNase L pathway is only modestly activated during the time course of the VZV infection. The rRNA cleavage assay showed almost no 28S and 18S rRNA cleavage, indicating that VZV is a poor inducer of RNase L in vitro, as is also the case for HSV-1 [7,20]. In VZV-infected, IFN-treated cells, minor rRNA cleavage products were observed to a greater extent than in nontreated cells.…”

“…Until recently, it was unclear whether the vhs protein acts alone or as a part of a ribonuclease complex, or whether it activates a latent cellular RNase such as RNase L. Smith et al [20] demonstrated that RNase L does not contribute to host RNA degradation mediated by the HSV vhs protein. We have reported that VZV does not cause a rapid shutoff like HSV but a delayed vhs effect during its replication cycle [21].…”

Suppression of Proinflammatory Cytokine Expression by Herpes Simplex Virus Type 1

“…However, since the stability of ␤-actin mRNA was not differentially affected by infection with wt HSV-1 versus in1814, RNase L appears not to be a likely candidate. Moreover, a recent study demonstrated that HSV-1 does not activate RNase L and that mRNA degradation in HSV-infected cells is independent of RNase L (41). The HSV tegument protein UL41 (or VHS), which promotes mRNA degradation, has previously been shown to decrease accumulation of some virus-induced cellular mRNAs (44), although the majority of cellular genes induced by HSV-1 infection are not affected by UL41 (45).…”

Viral Encounters with 2′,5′-Oligoadenylate Synthetase and RNase L during the Interferon Antiviral Response

“…Furthermore, only low levels of RNase L-mediated rRNA cleavage products were observed, despite the fact that RNase L is typically highly activated by similar levels of 2-5A in IFN-treated EMCV-infected cells. RNase L also has little or no effect on host RNA degradation mediated by VHS, the HSV-1 virion host shutoff protein, in MEFs (111). A possible explanation for the relative inactivity of RNase L in HSV-infected cells emerged from analysis of the types of 2-5A species produced.…”