ICP34.5 influences herpes simplex virus type 1 maturation and egress from infected cells in vitro

Abstract

We have previously demonstrated that efficient replication of mutant herpes simplex virus which fails to synthesize the polypeptide ICP34.5 is cell type and cell state dependent. ICP34.5 negative viruses do not grow in stationary state mouse embryo fibroblast 3T6 cells whereas the growth kinetics in BHK cells are indistinguishable from those of wild-type. We now demonstrate that this defect is not due to an inability of mutant virus to adsorb to 3T6 cells but rather to an inability to spread from the initially infected cells. Electron microscopic studies with wild-type HSV in both BHK and 3T6 cells revealed virus particles equally distributed between nucleus and cytoplasm, and additionally in the extracellular matrix. In BHK cells infected with the ICP34.5 negative mutant 1716, virus is likewise distributed between nucleus and cytoplasm but in 50 % of the infected cells there is marked delamination and swelling of the nuclear membrane. In addition there is evidence of a significant number of particles trapped between the nuclear lamellae. When 1716 is used to infect 3T6 cells, over 90% of the virus particles are confined to the nuclei and the number of infected cells remains constant between 24 and 48 h with no increase in the proportion of extracellular virus. Failure to express ICP34.5 appears therefore to result in a defect in virus maturation and egress from the nuclei of infected cells. Egress of HSV from the nuclei to the extracellular space is thought to occur via two pathways. We postulate that lack of expression of ICP34.5 results in one of these pathways being blocked. In BHK cells this leads to overloading of the alternative pathway with a buildup of particles in the nuclear lamellae and associated endoplasmic reticulum. In stationary state 3T6 cells, it appears that there is no functional alternative pathway. We conclude that ICP34.5 exerts an effect on HSV maturation by controlling the passage of virus through infected cells.

Myeloid differentiation (MyD) primary response genes in hematopoiesis

“…Both the g(1)34.5 gene of HSV and MyD116/ GADD34 were reported to interact, via their conserved C-terminal domains, with proliferating cell nuclear antigen (PCNA) (Brown et al, 1997), an important player in DNA replication and DNA repair. The signi®cance of this interaction remains to be determined.…”

p32 Is a Novel Target for Viral Protein ICP34.5 of Herpes Simplex Virus Type 1 and Facilitates Viral Nuclear Egress

“…Previous studies suggest that nuclear egress involves HSV-1 ICP34.5 (23,24), which is an essential protein in viral pathogenesis (25)(26)(27). HSV-1 ICP34.5 consists of 263 amino acids with an amino-terminal domain, a linker Ala-Thr-Pro repeat, and a carboxyl-terminal domain.…”

Selective in vitro replication of herpes simplex virus type 1 (HSV-1) ICP34.5 null mutants in primary human CNS tumours - evaluation of a potentially effective clinical therapy

“…Variations in expression of proteins which are functionally homologous to ICP34.5 could account for the differences observed in 1716 growth or alternatively the cellular proteins could be totally unrelated. As the cells were infected at high multiplicities of infection, where all cells in the culture would be expected to be infected, a difference in a 1 2 3 4 5 6 CNS U_W Umapy m. HSV-1 EA McKe et a X 751 individual cellular metabolism or protein expression would seem a more likely explanation than a defect in maturation and virus egress preventing further rounds of replication as previously shown in 3T6 (Brown 1994b).…”