HSV-2 inhibits type-I interferon signaling via multiple complementary and compensatory STAT2-associated mechanisms

Abstract

Type-1 interferon (IFN)-mediated responses are a crucial first line of defense against viral infections and are critical for generating both innate and adaptive immunity. Therefore, viruses have necessarily evolved mechanisms to impede the IFN response. HSV-2 was found to completely abolish type-1 IFN-mediated signaling via multiple STAT2-associated mechanisms. Although the extent and kinetics of this inactivation were indistinguishable between the various cell-lines examined, there were distinct differences in the mechanisms HSV-2 employed to subvert IFN-signaling amongst the cell-lines. These mechanistic differences could be segregated into two categories dependent on the phase of the HSV replicative cycle that was responsible for this inhibition: 1) early phase-inhibited cells which exhibited abrogation of IFN-signaling prior to viral DNA replication; 2) late phase-inhibited cells where early phase inhibition mechanisms were not functional, but viral functions expressed following DNA replication compensated for their ineffectiveness. In early phase-inhibited cells, HSV-2 infection targeted STAT2 protein for proteosomal degradation and prevented de novo expression of STAT2 by degrading its mRNA. In contrast, HSV-2 infected late phase-inhibited cells exhibited no apparent changes in STAT2 transcript or protein levels. However, in these cells STAT2 was not activated by phosphorylation and failed to translocate to the cell nucleus, thereby preventing transactivation of antiviral genes. In primary human fibroblasts, HSV-2 failed to fully degrade STAT2 and therefore, both early and late phase mechanisms functioned cooperatively to subvert IFN-mediated antiviral gene expression. Taken together, these results indicate the importance that HSV-2 has assigned to STAT2, investing significant genomic currency throughout its replicative lifecycle for continuous targeted destruction and inhibition of this protein.

Development and evaluation of a host-targeted antiviral that abrogates herpes simplex virus replication through modulation of arginine-associated metabolic pathways

“…After 2h adsorption at 4°C, virus was removed and cells w ere overlaid with pre-warmed medium or medium containing 2-fold serial dilutions of peg-ArgI (from 10,000-19.5ng/ml). Virus was allowed to penetrate for 2h at 37°C after which ext racellular virus was inactivated by low-pH treatment (Kadeppagari et al, 2012; Sanchez et al, 2012). Cells were subsequently washed twice with complete media and overlaid with media containing peg-ArgI.…”

Recent advances in understanding viral evasion of type I interferon

“…78 HSV-2 causes the selective loss of STAT2 transcripts and proteins in some cell types, whereas in others, STAT2 levels remain constant but its phosphorylation and nuclear translocation are inhibited. 79 The papain-like protease from SARS-CoV has a complex mechanism of interference: it is a de-ubiquitinating enzyme that up-regulates the expression of ubiquitin-conjugating enzyme E2-25k, leading to the ubiquitin-dependent proteasomal degradation of extracellular signal-regulated kinase (ERK) 1, which interferes with ERK1-mediated STAT1 phosphorylation. 80 Interestingly, adenovirus stabilizes tyrosine-phosphorylated, activated STAT1, sequestering it at viral replication centres, potentially through binding with viral DNA.…”

Viral evasion mechanisms of early antiviral responses involving regulation of ubiquitin pathways

“…Recently, the UBR4 member of the N-recognin family of E3 ligases was found to be required for DENV-mediated STAT2 degradation and efficient DENV replication [44]. Other viruses that target STAT factors required for IFN signaling to degradation by ubiquitination include hepatitis C virus (HCV), which targets STAT3 [45], and herpes simplex virus type 2 (HSV-2) and HCMV, which target STAT2 [46,47]. In addition, the V protein encoded by the paramyxoviruses simian virus 5 (SV5) and type 2 human parainfluenza virus (HPIV2) target STAT1 and STAT2 for Ub-dependent degradation, respectively, whereas mumps virus V protein targets both STAT1 and STAT3 [48].…”