Use of antiviral-antiferritin hybrid antibody for localization of viral antigen in plasma membrane

Mapping regions of the matrix protein of vesicular stomatitis virus which bind to ribonucleocapsids, liposomes, and monoclonal antibodies

The matrix (M) protein of vesicular stomatitis virus (VSV) appears to function as a bridge between the ribonucleocapsid (RNP) core and the envelope in assembly of the virion. Two such properties would necessitate at least one site for interaction with the nucleocapsid and one with the envelope. In this study M protein was found to mediate the in vitro binding to RNP cores of phospholipid vesicles, representing membrane structures. The M protein could bind initially to either the vesicles or the RNP cores to promote RNP-vesicle association. A trypsin-resistant fragment (MT) of M protein, missing the initial 43 amino acids from its amino terminus, reconstituted with acidic phospholipid vesicles with the same binding efficiency as did whole M protein, suggesting that the carboxy-terminal 81% retained those regions of the M protein which interact with a lipid bilayer. The MT protein, however, was considerably less efficient than intact M protein as an inhibitor of in vitro virus transcription; almost 2.5-fold more MT protein than intact M protein was required for 50% inhibition of VSV transcription, indicating that a site for interaction with the RNP core may have been lost. A monoclonal antibody which is able to reverse the in vitro inhibition of transcription by M protein did not react by immunoblotting with MT protein. Partial tryptic digests of the M protein probed with this monoclonal antibody indicated that epitope 1 lies between amino acid residues 18 and 43. This region appears to be a site that promotes interaction of the M protein with the RNP core of VSV. Monoclonal antibodies to epitopes 2 and 3, which exhibit some overlap in binding to M protein but do not reverse transcription inhibition, were mapped by cleavage with N-chlorosuccinimide at regions in a carboxy direction from epitope 1.

Antibody-induced modulation of proteins in vesicular stomatitis virus-infected fibroblasts

When vesicular stomatitis virus-infected baby hamster kidney cells were treated with rabbit anti-vesicular stomatitis virus serum, there was a loss of the viral glycoprotein G into acid-soluble products. This degradation occurred within minutes at 37 degrees C and required the presence of G protein at the cell surface. The degree of degradation depended on antiserum concentration. The antiserum, also, prevented maturation of extracellular virions and induced partial degradation of the intracellular viral proteins, without affecting host proteins. The degradation could not be prevented by the presence of lysosomotropic agents, protease inhibitors, colchicine, or cytochalasin B. Similar kinetics and specificity of degradation was obtained with cells infected with vesicular stomatitis virus mutants that were less cytopathic. These results characterize a model system for studying the parameters and consequences of antigenic modulation as well as for studying the fate of viral antigens during persistent infections.

Antibody-induced modulation of proteins in vesicular stomatitis virus-infected fibroblasts

When vesicular stomatitis virus-infected baby hamster kidney cells were treated with rabbit anti-vesicular stomatitis virus serum, there was a loss of the viral glycoprotein G into acid-soluble products. This degradation occurred within minutes at 37 degrees C and required the presence of G protein at the cell surface. The degree of degradation depended on antiserum concentration. The antiserum, also, prevented maturation of extracellular virions and induced partial degradation of the intracellular viral proteins, without affecting host proteins. The degradation could not be prevented by the presence of lysosomotropic agents, protease inhibitors, colchicine, or cytochalasin B. Similar kinetics and specificity of degradation was obtained with cells infected with vesicular stomatitis virus mutants that were less cytopathic. These results characterize a model system for studying the parameters and consequences of antigenic modulation as well as for studying the fate of viral antigens during persistent infections.

Assembly of vesicular stomatitis virus: distribution of the glycoprotein on the surface of infected cells

This study demonstrates that the glycoprotein of vesicular stomatitis virus clusters in the plasma membrane of infected Chinese hamster lung cells during morphogenesis and suggests that viral nucleocapsids are required for this clustering. A mutant virus (ts E-1) which is temperature sensitive for the synthesis of viral nucleocapsids but not viral membrane proteins was used. The surface distribution of the viral glycoprotein in cells infected by this virus was determined by a specific indirect immunoferritin stain. Early in infection at permissive temperatures, the glycoprotein was randomly distributed on membrane ghosts. Later, clusters of ferritin the size and shape of virus particles were seen. In contrast, ghosts prepared from virus-infected cells maintained at a restrictive temperature always had a random distribution of viral glycoprotein.

Virus-induced alterations in insulin release in hamster islets of Langerhans

After the inoculation of Golden Syrian hamsters with the TC-83 vaccine strain of Venezuelan encephalitis (VE) virus, a sustained diminution in glucose-stimulated insulin release and glucose intolerance of shorter duration develops. To understand better the mechanism of this defect in insulin release, we examined insulin secretion in response to several test agents in isolated perifused islets from control and 24-d post-VE virus-infected hamsters. 50 islets were used in all perifusion experiments, and data were expressed as total insulin released as well as peak response for each test agent during a 30-min perifusion period from control and VE-infected islets. After perifusion with 20 mM glucose, a 45% diminution of insulin release was noted in VE-infected islets in comparison with control islets, which in turn was similar to in vivo findings. However, following 1-mM tolbutamide stimulation, insulin release was similar in control and VE-infected islets. In separate studies, 1 mM tolbutamide, 10 mM theophilline, 1 mM dibutyryl cyclic (c)AMP, and 1 mM 8-bromo-cAMP resulted in statistically similar insulin-release curves in control and VE-infected islets. Additional experiments assessing [5-3H]glucose use in control and infected islets after 20 min of perifusion with 20 mM glucose revealed virtually identical values (239 +/- 30-control; and 222 +/- 27-VE-infected islets). Morphological and morphometric evaluation of VE-infected islets (21 d following virus inoculation) showed no changes in islet volume density, beta cell density, and beta cell granulation. Thus, VE virus induces a defect in glucose-stimulated insulin release from hamster beta cells that can be corrected by cAMP analogues and does not alter islet glucose use.

Virus-induced decrease of insulin receptors in cultured human cells

Viral infections may produce abnormalities in carbohydrate metabolism in normal subjects and profound changes in glucose homeostasis in insulin-dependent diabetics. Using an in vitro radio-receptor assay with 125I-labeled insulin and human-amnion (WISH) cells, the effect of viral infections on insulin receptors was examined. Both herpes simplex virus and vesicular stomatitis virus produced a 50% decrease in insulin binding. There was no evidence that this decrease was due to degradation of insulin. On quantitative analysis, this decrease in binding was found to be the result of a decrease in receptor concentration with no change in receptor affinity. The decrease in receptors occurred between 4 and 12 h, at the time viral antigens were being inserted into the plasma membrane of infected cells. Because the t 1/2 of insulin receptors in uninfected cells was between 14 and 24 h, the decrease in insulin receptors cannot be explained solely by virus-induced shut-off of macromolecular synthesis. Moreover, viruses such as encephalomyocarditis that do not insert new antigens into the plasma membrane, did not cause changes in the number of insulin receptors. The most likely explanation is that virus-induced changes in the plasma membrane altered or displaced insulin receptors. It is concluded that the insulin receptor assay is a sensitive and quantitative method for studying the effect of viral infections on cell membranes. These data also suggest that abnormalities in glucose metabolism associated with some viral infections may be due, in part, to changes in the concentration of insulin receptors.

Morphogenesis of vesicular stomatitis virus: electron microscope observations with freeze-fracture techniques

The morphogenesis of vesicular stomatitis virus was examined using freeze-fracture techniques, and the results obtained were compared with those from previously published experiments carried out with influenza viruses and togaviruses. The process of conversion of the host cell plasma membrane into the vesicular stomatitis virus envelope was accompanied by a loss of the intramembranal particles abundant in cell membranes. Frequently a dense accumulation of intramembranal particles could be seen at the base of the developing virion, suggesting that these structures might play some role in the generation of viral envelope. In addition to the viral structures that were seen to develop in the classical fashion, with their long axis perpendicular to the cell surface, structures were also found that suggested the initiation of a process similar to budding, with the long axis of the viral capsid parallel to the plasma membrane. In this situation, as in the "perpendicular" process, intramembranal particles were excluded from the viral structure, and an accumulation of these particles could be seen adjacent to the developing viral membrane.

In vitro tritium labeling of anti-sendai virus antibody

Anti-Sendai virus immunoglobulin G was tritium labeled in vitro by the borohydride exchange method. Tritium was incorporated into the antibody at 28.5 muCi per mg of protein, with little detectable loss of antiviral activity.

Cytoplasmic compartmentalization of the protein and ribonucleic acid species of vesicular stomatitis virus

The cytoplasmic sites of synthesis in L cells of the protein and ribonucleic acid species of vesicular stomatitis virus were studied by polyacrylamide gel electrophoresis after fractionation of membrane and other cytoplasmic components by the Caliguiri-Tamm technique. The viral spike protein (glycoprotein G) was found primarily associated with a smooth membrane fraction which is rich in plasma membrane; the G protein was also present in fractions containing rough endoplasmic reticulum. The nonglycosylated envelope protein S (also called M) was found in the smooth membrane fractions but was more abundant in endoplasmic reticulum-enriched fractions. Longer labeling resulted in detection of nucleoprotein N, as well as other minor nucleocapsid proteins L and NS(1), in the cellular membrane fractions. The N protein appeared to be made in membrane-free cytoplasm along with progeny ribonucleic acid and later became associated with membrane containing G and S viral proteins.

Entry of vesicular stomatitis virus into L cells

Early stages of the entry of vesicular stomatitis (VS) virus into L cells were followed by electron microscopy with the aid of ferritin antibody labeling. Cells which were infected at 0 C and incubated for 10 min at 37 C were reacted first with antiviral-antiferritin hybrid antibody and then with ferritin or fluorescein-labeled apoferritin. Extensive ferritin labeling of the cell surface was detected by both electron and fluorescence microscopy. The labeled regions of the cell surface were continuous with and indistinguishable from the rest of the host cell membrane, suggesting incorporation of viral antigens into the cell surface during viral penetration. Fusion of parental viral membrane with host cell membrane was further demonstrated by examining the localization of (3)H-labeled viral structural proteins in cells infected at 0 C and incubated for short periods at 37 C. Viral nucleoprotein was found in a soluble fraction of the cells which was derived primarily from the cytoplasm, whereas a particulate fraction from the cells was enriched in viral envelope proteins. Cytoplasmic membrane was isolated from these cells, and this membrane contained viral envelope proteins. These results suggest that penetration by VS virus occurs by fusion of the viral and cellular membranes followed by release of nucleo-protein into the cytoplasm.

Temperature-sensitive mutants of vesicular stomatitis virus: synthesis of virus-specific proteins

Viral proteins synthesized in L cells infected with temperature-sensitive (ts) mutants of vesicular stomatitis (VS) virus at permissive (31 C) and nonpermissive (39 C) temperatures were compared by polyacrylamide gel electrophoresis. Mutant ts 5, deficient in synthesis of viral ribonucleic acid (RNA(-)), failed to synthesize any of the five identifiable viral proteins at 39 C. Each of three RNA(+) mutants, representing three separate complementation groups, showed distinctive patterns of viral protein synthesis at nonpermissive temperature. Equivalent amounts of (3)H-amino acids were incorporated into the five viral proteins made in cells infected with RNA(+) mutant ts 45 at 31 and 39 C. Complete virions of ts 45 could be identified by electron microscopy of infected cells incubated at the nonpermissive temperature; the defect in ts 45 appeared to be due in part to greater thermolability of virions as compared with the wild-type. RNA(+) mutant ts 23 was deficient in synthesis of viral envelope protein S and failed to make detectable virions at the nonpermissive temperature. Infection of cells at 39 C with the third RNA(+) mutant, ts 52, resulted in synthesis of all five viral proteins, but the peak of radioactivity representing the viral membrane glycoprotein migrated more rapidly on gels than coelectrophoresed authentic virion (14)C-glycoprotein or viral (3)H-glycoprotein extracted from cells infected at 31 C. These data and results of experiments on incorporation of radioactive glucosamine suggest that the primary defect in mutant ts 52 at nonpermissive temperature is failure of glycosylation of the viral glycoprotein. The viral structural proteins made in cells infected with ts 52 at the nonpermissive temperature did not assemble into sedimentable components as they did at permissive temperature; this observation indicates failure of insertion of the nonglycosylated protein (G') into cell membrane. In support of this hypothesis was the finding that antiviral-antiferritin hybrid antibody did not detect VS viral antigen on the plasma membrane of L cells infected at 39 C with ts 52. In contrast, VS viral antigen localized in plasma membrane of L cells infected at 39 C with mutants ts 23 and ts 45 was readily detected by electron microscopy and fluorescence microscopy.