The γ ₁ 34.5 protein of herpes simplex virus 1 complexes with protein phosphatase 1α to dephosphorylate the α subunit of the eukaryotic translation initiation factor 2 and preclude the shutoff of protein synthesis by double-stranded RNA-activated protein kinase

Abstract

In human cells infected with herpes simplex virus 1 the double-stranded RNA-dependent protein kinase (PKR) is activated but phosphorylation of the ␣ subunit of eukaryotic translation initiation factor 2 (eIF-2) and total shutoff of protein synthesis is observed only in cells infected with ␥ 1 z34.5 ؊ mutants. The carboxyl-terminal 64 aa of ␥ 1 34.5 protein are homologous to the corresponding domain of MyD116, the murine growth arrest and DNA damage gene 34 (GADD34) protein and the two domains are functionally interchangeable in infected cells. This report shows that (i) the carboxyl terminus of MyD116 interacts with protein phosphatase 1␣ in yeast, and both MyD116 and ␥ 1 34.5 interact with protein phosphatase 1␣ in vitro; (ii) protein synthesis in infected cells is strongly inhibited by okadaic acid, a phosphatase 1 inhibitor; and (iii) the ␣ subunit in purified eIF-2 phosphorylated in vitro is specifically dephosphorylated by S10 fractions of wild-type infected cells at a rate 3000 times that of mock-infected cells, whereas the eIF-2␣-P phosphatase activity of ␥ 1 34.5 ؊ virus infected cells is lower than that of mock-infected cells. The eIF-2␣-P phosphatase activities are sensitive to inhibitor 2. In contrast to eIF-2␣-P phosphatase activity, extracts of mock-infected cells exhibit a 2-fold higher phosphatase activity on [ 32 P]phosphorylase than extracts of infected cells. These results indicate that in infected cells, ␥ 1 34.5 interacts with and redirects phosphatase to dephosphorylate eIF-2␣ to enable continued protein synthesis despite the presence of activated PKR. The GADD34 protein may have a similar function in eukaryotic cells. The proposed mechanism for maintenance of protein synthesis in the face of double-stranded RNA accumulation is different from that described for viruses examined to date.

Binding and Nuclear Relocalization of Protein Kinase R by Human Cytomegalovirus TRS1

“…Several viruses block activation of PKR by sequestering dsRNA or by interfering with PKR dimerization or enzymatic activity (26,27,32,64,65,72). The herpes simplex virus ␥34.5 gene product blocks the effects of PKR by cooperating with cellular protein phosphatase 1␣ to dephosphorylate eIF2␣-phosphate (37). To our knowledge, our results represent the first description of a viral gene product that may inhibit PKR activity by affecting its subcellular localization.…”

ICP34.5 deleted herpes simplex virus with enhanced oncolytic, immune stimulating, and anti-tumour properties

“…The adenovirus E1B region is required for virus replication in cells with a functional p53 pathway, but is dispensable in most tumour cells where the p53 or related pathways are disrupted (eg see reference 18). The HSV ICP34.5 gene counteracts the interferon-induced PKR-mediated block to virus replication, 19,20 which is usually disabled in tumour cells. ONYX-O15 has been tested in a variety of clinical situations with maximal success following repeated administration at high dose in head and neck cancer patients [21][22][23] or intra-hepatic artery infusion into liver cancer patients, 24 both combined with chemotherapy.…”

Impact of novel oncolytic virus HF10 on cellular components of the tumor microenviroment in patients with recurrent breast cancer

“…39 HSV 1 can reduce apoptosis via the ICP 34.5 gene product, which modifies the protein kinase R pathway, blocking the apoptotic mechanism in normal cells. [39][40][41][42] The effects of oncolytic herpes viruses on apoptosis are controversial: apoptosis is elevated upon viral treatment in some studies, 43,44 but reduced in others. 45,46 Some have argued that induction of premature apoptosis is not a desirable feature of oncolytic viral treatment; 47 instead, reducing or delaying apoptosis may enhance viral penetration of the tumor, another determinant of the potency of an oncolytic virus.…”