The ribonucleotide reductase R1 subunits of herpes simplex virus types 1 and 2 protect cells against TNFα- and FasL-induced apoptosis by interacting with caspase-8

Abstract

We previously reported that HSV-2 R1, the R1 subunit (ICP10; UL39) of herpes simplex virus type-2 ribonucleotide reductase, protects cells against apoptosis induced by the death receptor (DR) ligands tumor necrosis factor-alpha-(TNFa) and Fas ligand (FasL) by interrupting DR-mediated signaling at, or upstream of, caspase-8 activation. Further investigation of the molecular mechanism underlying HSV-2 R1 protection showed that extracellularregulated kinase 1/2 (ERK1/2), phosphatidylinositol 3-kinase (PI3-K)/Akt, NF-jB and JNK survival pathways do not play a major role in this antiapoptotic function. Interaction studies revealed that HSV-2 R1 interacted constitutively with caspase-8. The HSV-2 R1 deletion mutant R1(1-834)-GFP and Epstein-Barr virus (EBV) R1, which did not protect against apoptosis induced by DR ligands, did not interact with caspase-8, indicating that interaction is required for protection. HSV-2 R1 impaired caspase-8 activation induced by caspase-8 over-expression, suggesting that interaction between the two proteins prevents caspase-8 dimerization/activation. HSV-2 R1 bound to caspase-8 directly through its prodomain but did not interact with either its caspase domain or Fas-associated death domain protein (FADD). Interaction between HSV-2 R1 and caspase-8 disrupted FADD-caspase-8 binding. We further demonstrated that individually expressed HSV-1 R1 (ICP6) shares, with HSV-2 R1, the ability to bind caspase-8 and to protect cells against DR-induced apoptosis. Finally, as the long-lived Fas protein remained stable during the early period of infection, experiments with the HSV-1 UL39 deletion mutant ICP6D showed that HSV-1 R1 could be essential for the protection of HSV-1-infected cells against FasL.Keywords FasL Á ICP6 Á ICP10 Á Viral inhibitor of apoptosis Á Caspase-8Electronic supplementary material The online version of this article

Direct activation of RIP3/MLKL-dependent necrosis by herpes simplex virus 1 (HSV-1) protein ICP6 triggers host antiviral defense

“…S6D), consistent with the previous observation that ICP6 is dispensable for virus multiplication in dividing cells (30). It has been demonstrated that ICP6 constitutively interacts with caspase-8 and RIP1 through its reductase domain and functions in an antiapoptotic role in death triggered by TNF-α, FasL, or TLR3 (31,32). Although the N-terminal RHIM sequence of ICP6 was shown to be dispensable for the interaction with RIP1 and caspase-8, we have found that it is essential for the interaction with RIP3 (Fig.…”

The Ribonucleotide Reductase R1 Subunits of Herpes Simplex Virus 1 and 2 Protect Cells against Poly(I · C)-Induced Apoptosis

“…In light of previous reports showing the key role of caspase 8 activation in poly(I ⅐ C)-induced apoptosis (29,72), the present study was undertaken to validate the hypothesis that HSV R1s could prevent poly(I ⅐ C)-induced apoptosis by virtue of their ability to inhibit caspase 8 activation (15). Our demonstration that HSV R1s impair the apoptotic host defense mechanism triggered by dsRNA adds a new facet to the ability of HSVs to manipulate antiviral responses.…”

“…HSVs encode different cell death suppressors, several of them conferring resistance to apoptosis elicited by the process of viral replication itself and/or by extrinsic stimuli linked to immune effector cell cytotoxicity or activation of death receptors (25). Among the viral genes involved in the control of apoptosis, UL39, which encodes the R1 subunit of HSV ribonucleotide reductase (HSV R1), protects epithelial cells from apoptosis induced by the death receptor ligands tumor necrosis factor alpha (TNF-␣) and Fas ligand (FasL) (15,44). Double-stranded RNA (dsRNA), one of the major viral products involved in the cellular sensing of viral invasion, triggers both IFN and apoptosis responses (17,29).…”

“…In addition to being the catalytic subunit for ribonucleotide reduction, HSV R1 possesses several non-ribonucleotide reductase-related activities, including (i) chaperone activity similar to that of small heat shock proteins (8), (ii) the ability to stimulate translation in quiescent cells by promoting eIF4F translation complex assembly (71), and (iii) antiapoptotic properties (23,44). The extensively studied role of HSV type 1 (HSV-1) R1 and HSV-2 R1 in the antiapoptotic response extends from the impairment of apoptosis induced by the mitochondrial pathway through activation of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 and the phosphatidylinositol-3-kinase/Akt axes by HSV-2 R1 (23) to the protection of epithelial cells by both HSV R1s from TNF-␣-and FasL-induced apoptosis through constitutive interaction with caspase 8 (15,44).…”

Inhibition of Bim Enhances Replication of Varicella-Zoster Virus and Delays Plaque Formation in Virus-Infected Cells

“…Herpes simplex virus 1 (HSV-1) and HSV-2 encode a number of proteins that inhibit apoptosis (9,10), including protein kinase US3 (11,12), glycoprotein J (gJ) (13), and latency-associated transcript (LAT) (14). In addition, HSV mutants deleted for ICP4, ICP27, UL39, and gD undergo apoptosis in a cell-type-specific manner (15)(16)(17)(18)(19).…”