Viral glycoprotein synthesis under conditions of glucosamine block in cells transformed by avian sarcoma viruses

The effects of 2-deoxyglucose and tunicamycin on the biosynthesis of the murine mammary tumor virus proteins, and on the assembly and release of the virus

The role of glycosylation in the biosynthesis, processing, and shedding of the murine mammary tumor virus (MuMTV) glycoproteins and in virus production was investigated in a clonal mammary tumor cell line, GR-3A, using two inhibitors of protein glycosylation, 2-deoxyglucose (2-DG) and tunicamycin (TM). It was found that both 2-DG and TM completely inhibited the synthesis of the MuMTV envelope precursor polyprotein, Pr70env, and, as a consequence, the synthesis of the viral glycoproteins gp52 and gp36. By contrast, the synthesis of Pr73gag, the polyprotein precursor of the internal structural proteins of the virus, was only inhibited by 10-15% by 2-DG and TM. Although 2-DG and TM blocked the synthesis of Pr70env, a new polypeptide, related to gp52 and gp36, with a mol wt of 60,000 (P60env) was found to be synthesized in the treated cells. The P60env molecules appeared to be degraded intracellularly since they were not found to (1) undergo site-specific cleavage; (2) accumulate inside the cell or on the cell surface; (3) be secreted into the culture medium; and (4) be incorporated into the virions produced during the drug treatment. In spite of the lack of gp52 and gp36 synthesis in the presence of TM and 2-DG, mature MuMTV particles containing the characteristic surface projections known to be composed of gp52 and gp36 continued to be assembled and released at a reduced rate for at least 30 hr. In addition, the buoyant density and the polypeptide composition of the particles were found to be identical to virions produced by untreated cells. Thus, the virions assembled and released during 2-DG and TM treatment were not defective. Our investigations into the origin of gp52 and gp36 in these particles revealed that both molecules were synthesized prior to 2-DG and TM treatment and continued to be incorporated, along with the newly synthesized viral core proteins, into budding virions during the drug treatment. Furthermore, we found that gp52 and P75env (an aberrant form of Pr70env) that were not incorporated into virions continued to be shed normally from the cell during drug treatment. In conclusion, our results suggest that MuMTV assembly is not dependent on the synchronized synthesis of the viral core and envelope polypeptides, and that the assembled virions contain the correct ratio of these polypeptides, even when their ratio in the cell varies.

Selective inhibition of herpes simplex virus glycoprotein synthesis by a benz-amidinohydrazone derivative

1H-benz[f]indene-1.3(2H)dione-bis-amidinohydrazone (benzhydrazone) inhibited incorporation of 14C-glucosamine, 14C-fucose and 14C-mannose into glycoproteins of HEp-2 cells infected with various strains of herpes simplex virus 1 (HSV-1) and impaired RNA and protein synthesis to a low extent. These biochemical effects are very similar to those induced by glycosylation inhibitors such as tunicamycin, D-glucosamine and 2-deoxy-D-glucose. In contrast to these inhibitors, benzhydrazone reduced HSV glycoprotein synthesis selectively since it did not significantly modify i) the saccharide uptake into glycoproteins of uninfected and of Sindbis virus-infected cells, ii) viral growth and cell fusion in paramyxovirus-infected cells, two activities which depend on viral glycoprotein synthesis. Benzhydrazone had only minor effects on the overall metabolism of uninfected cells, since it did not alter cell growth rate, and amino acid, uridine, and hexose incorporations were about 80% those of untreated cells.

Effects of inhibitors of lipid synthesis on the replication of Rous sarcoma virus. A specific effect of cerulenin on the processing of major non-glycosylated viral structural proteins

The effects of two inhibitors of lipid biosynthesis on the replication of Rous sarcoma virus Prague C strain in chick embryo fibroblasts have been examined in media containing delipidated serum. 25-Hydroxycholestetate into sterols, had no effect on the formation of infectious virions or on the synthesis and processing of intracellular virion proteins. Cerulenin strongly inhibited [1(-14C)]acetate incorporation into fatty acids and partially inhibited its incorporation into sterols in chick embryo cells. Rous sarcoma virus production as measured by focus formation and by the production of [35S]methionine-labeled virions was strongly inhibited within 5 h after cerulenin addition to infected cultures. Examinatin of extracts of these cells revealed the accumulation of the 76 000 dalton precursor (Pr76) of the major non-glycosylated virion structural proteins, p27, p19, p15 and p12. The failure to process the 76 000 dalton precursor was coincident in time with the decrease in viron production. Neither whole serum nor mixtures of fatty acids plus cholesterol were able to reverse the effects of cerulenin.

Persistent parainfluenza type 1 (6/94) infection of brain cells in tissue culture

A state of persistent infection with parainfluenza type 1 virus (6/94 strain) was established in cultures of human and bovine brain cells. Following primary infection of human brain cells, viral cytopathic effect (CPE) and hemadsorption (HAD) depended on the multiplicity of infection. After persistent infection was established the virus rapidly became cell-associated; no CPE occurred and no viral antigen was detectable by HAD, immunofluorescence (FA), or immunoprecipitation. Infectious virus could be recovered only by fusion or cocultivation. This was in marked contrast with infected bovine brain cells, where, following primary infection, little or no CPE occurred. A productive infection rapidly evolved and persisted without CPE, but with 100 per cent HAD and FA positive cells.

A fucose-deficient glycoprotein precursor to Rauscher leukemia virus gp69/71

Rauscher leukemia virus glycoprotein gp69/71 is synthesized in virus-infected cells by way of a 90,000 dalton glycoprotein precursor, termed Pr2a+b. This precursor could be labeled with radioactive glucosamine and methionine but not with fucose; whereas gp69/71 could be detected by labeling with radioactive glucosamine, fucose, or a mixture of amino acids but seemed to be deficient in methionine relative to Pr2a+b. Pr2a+b and gp69/71, were specifically precipitated by an antiserum prepared against phosphocellulose purified Rauscher gp69/71. Other virus-specific precursors, in addition to Pr2a+b, could be precipitated by antiserum prepared against detergent disrupted virus. Neither Pr2a+b nor gp69/71 was precipitated from cell extracts by antisera to Rauscher p30. Tryptic maps of Pr2a+b and gp69/71 showed that these glycoproteins share many tryptic peptides. Pulse-chase experiments with 14C-labeled amino acids indicated that gp69/71 was not radio-labeled during the pulse-labeling period but slowly appeared during the chase incubations. Pr2a+b, however, was rapidly labeled and tended to disappear during long chases. Furthermore, two nonglycosylated viral proteins, termed p15E and p12E, are structurally related to Pr2a+b. Viral p15E and p12E contained the same methionine-containing tryptic peptide fraction as Pr2a+b as determined by ion-exchange chromatography. These results provide evidence that Pr2a+b is a precursor to gp69/71 and establish a structural and possible precursor-product relationship between Pr2a+b, p15E, and p12E.

In vivo antiviral activity of D-glucosamine

Intraperitoneal treatments with D-glucosamine, an inhibitor of the glycosylation of the viral envelope, decreased the growth rate of tumors induced in quails or in chicks by Rous sarcoma virus and increased the survival of mice inoculated with human influenza virus.