A host-induced modification of hemagglutinating virus of Japan (HVJ, Sendai virus) in its hemolytic and cytopathic activity

Evidence of proteolytic activation of Sendai virus in mouse lung

A device was made to analyze the pneumotropism of Sendai virus in mouse. Minced lung blocks were prepared from the mouse intranasally infected with Sendai virus for 2 hours and cultured in a CO2 incubator. This culture system provided a suitable in vitro model of Sendai virus infection in mice in terms of the distribution of the viral antigens and histopathological findings. The progeny virus recovered from the lung culture was already activated and was accompanied by the cleavage of F glycoprotein into F1 and F2. This fact demonstrates that the activating mechanism is reversed in the lung culture as found in vivo infection of mouse lung. The viral activation and the cleavage of F glycoprotein were simultaneously inhibited by tosyllysylchloromethylketone, leupeptin, soybean trypsin inhibitor and antipain, but not by tosylamidophenylethylchloromethyl-ketone, chymostatin, pepstatin, iodoacetamide, phenylmethylsulfonylfluoride and p-chloromercuribenzoate. These results show that the activating enzyme of Sendai virus found in the lung culture was similar to trypsin. The existence of the activating enzyme may support the replication of Sendai virus in mouse lung in multiple-step and also result in the lung pathology.

Pneumotropism of Sendai virus in relation to protease-mediated activation in mouse lungs

The pneumotropism of Sendai virus in mice was studied in relation to the activation and replication of the virus in the lung. Inactive Sendai virus grown in LLC-MK(2) cells, which possessed an uncleaved precursor glycoprotein, F, and was noninfectious to tissue culture cells, neither grew nor caused pathological changes in the lung of mice. When trypsin treatment was made which cleaved F into F(1) and F(2) subunits, the virus became activated so that it could initiate replication in the bronchial epithelium of the lung. In this case, the progeny virus was produced in the activated form and multiple-cycle replication occurred successively. A parallel relationship was found between the degree of the viral replication and that of clinical signs of the respiratory disease, body weight loss, and histopathological changes in the lung. A protease mutant, TR-2, which was able to be activated only by chymotrypsin but not by trypsin, could also initiate replication in the bronchial epithelium, when activated by chymotrypsin before inoculation into mice. The progeny virus, however, remained inactive, and the replication was limited to a single cycle, which resulted in the limited lung lesion. The overall results suggest that some activating mechanism for the progeny virus of wild-type Sendai virus exists in the lung of mice and the principle (activator) responsible for this phenomenon has a character similar to trypsin. The possible location of the activator is discussed.

Neuroblastoma cell membranes: specificity for cell fusion mediated by a temperature-sensitive mutant of vesicular stomatitis virus

Temperature-sensitive mutant G31 of vesicular stomatitis virus induces mouse neuroblastoma N-18 cells to fuse during infections that are nonpermissive for virus replication, but BHK-21 cells do not undergo the viral glycoprotein-mediated cell fusion. The viral glycoprotein was expressed at the cell surface of both N-18 and BHK-21 cells; therefore, the host cell specificity did not stem from an absence of the viral glycoprotein at the surface of BHK-21 cells. Cell fusion readily occurred between infected and uninfected N-18 cells in mixed cultures, demonstrating that the viral glycoprotein was interacting with an uninfected cell for the initial cell-cell interaction of the cell fusion. Mixing infected BHK-21 cells with uninfected N-18 cells resulted in cell fusion initiated by BHK-21 cell-synthesized viral glycoprotein, but 88% of the nuclei in polykaryocytes were N-18 nuclei. The N-18 cell fusion specificity was readily apparent when infected N-18 cells were mixed with uninfected BHK-21 cells; 98% of the nuclei in polykaryocytes were N-18 nuclei. Similar results also were obtained with mixed cultures of N-18 cells and primary astroglial cells. Thus, the viral glycoprotein synthesized in any of the cell types could initiate cell fusion, but the properties of plasma membranes of neuroblastoma cells appeared to be much more suitable for cell-cell fusion.

Trypsin action on the growth of Sendai virus in tissue culture cells. V. An activating enzyme for Sendai virus in the chorioallantoic fluid of the embryonated chicken egg

A trypsin-like protease which is responsible for activation of Sendai virus was found in the chorioallantoic fluid (CAF) of embryonated chicken eggs. Treatment of the inactive form of Sendai virus, grown in LLC-MK2 cells, with CAF enhanced both hemolytic activity and infectivity for the cells. Soybean trypsin inhibitor restrained the enhancing activity of CAF. These results indicate that CAF contains a trypsin-like protease which activates the inactive form of Sendai virus. The activation was strongly inhibited by phenylmethylsulfonylfluoride, ethylenediaminetetraacetate, antipain, and leupeptin but not by tosyllysylchloromethylketone, suggesting that the activating enzyme in CAF is a protease similar to but not identical with trypsin. The inactive form of the virion was produced in ovo when the seed virus was inoculated along with antipain or leupeptin. In deembryonated chicken eggs in which CAF was substituted for a culture medium, multiple cycle growth occurred, but not when soybean trypsin inhibitor was present. These observations indicate that some activating enzyme, possibly the same one as found in CAF, was secreted from the chorioallantoic membrane.

Restitution of hemagglutinating activity to spikeless particles of HVJ (Sendai virus) by glycoprotein components of Newcastle disease virus

Spikeless particles of HVJ (Sendai virus) lacking in hemagglutinating (HA) activity were obtained by enzymatic digestion of virions with trypsin followed by centrifugation through a sucrose gradient. When they were mixed with glycoprotein components of Newcastle disease virus (NDV) obtained by treatment of purified virions with deoxycholate (DOC), the mixture showed hemagglutination reaction, which was inhibited by anti-NDV serum, but not by anti-HVJ serum. Sedimentation profile of the HA active agents was then examined by centrifugation of the mixture of spikeless particles of HVJ (labeled with 3H-uridine) and glycoproteins of NDV (labeled with 14C-amino acid mixture). The results showed that the peak of HA activity had both of the radioactivities, and that the sedimentation rate of the HA was faster than that of spikeless HVJ but slower than that of intact HVJ. Electron micrographs of such HA active structures showed that they were morphologically closely similar to intact virion of HVJ, although they had neither hemolytic activity nor infectivity. The mixture of spikeless HVJ and glycoproteins of HVJ or NDV which were removed from virions by proteolytic enzymes, on the other hand, did not show any detectable hemagglutinating activity.

Trypsin action on the growth of Sendai virus in tissue culture cells. 3. Structural difference of Sendai viruses grown in eggs and tissue culture cells

Polypeptides of egg-borne Sendai virus (egg Sendai), which is biologically active on the basis of criteria of the infectivity for L cells and of hemolytic and cell fusion activities, were compared by polyacrylamide gel electrophoresis with those of L cell-borne (L Sendai) and HeLa cell-borne Sendai (HeLa Sendai) viruses, which are judged biologically inactive by the above criteria. Densitometer profiles on the stained gels of egg Sendai resolved six polypeptides (virion protein [VP] 1 to VP6), in which VP2 and VP4 were identified as glycoproteins by PAS stain. Comparative electropherograms of both L Sendai and HeLa Sendai revealed that there were significantly larger amounts in the VP2 region of these viruses but VP4 was present only in greatly reduced amounts as compared to egg Sendai. It was also found that VP2 of L Sendai and HeLa Sendai consisted of two components, VP2a and VP2b, but the one of egg Sendai consisted of only VP2a. A mild trypsin treatment which converts both L Sendai and HeLa Sendai to a biologically active form selectively removed VP2b from these viruses and increased concomitantly the amounts of materials in the VP4 region. The same treatment of egg Sendai affected neither its biological activities nor its electropherogram. Consequently, gross polypeptide profiles on the stained gels of L Sendai and HeLa Sendai after trypsin treatment became favorably comparable to that of egg Sendai. Electrophoresis of labeled L Sendai and HeLa Sendai with a (3)H-amino acids mixture and (14)C-glucosamine resolved at least three glycoproteins, GP1, GP2, and GP3, each corresponding to VP2a, VP2b, and VP4, respectively. The trypsin treatment of these viruses removed almost all the radioactivity of GP2 and simultaneously increased the radioactive counts of GP3 and raised small amounts of rapidly moving heterogeneous glycoprotein, GP4. A possible relationship between the biological modification and the above characteristic polypeptide patterns of Sendai virus was discussed.

Trypsin action on the growth of Sendai virus in tissue culture cells. II. Restoration of the hemolytic activity if L cell-borne Sendai virus by trypsin

Sendai virus grown in L cells (L Sendai) caused little hemolysis, whereas the one grown in fertile eggs (egg Sendai) induced distinct hemolysis. Enzymatic treatment with trypsin at low concentrations markedly enhanced the hemolytic activity of L Sendai but not that of egg Sendai. Both sonic treatment and freezing and thawing greatly enhanced the hemolytic activity of egg Sendai, but they gave little enhancing effect on that of L Sendai which could, however, be greatly increased by successive treatment with trypsin. Dose response and kinetic experiments on the trypsin effect have suggested that a similarity exists in the inhibitory mechanism of infectivity for L cells and hemolytic activity of L Sendai. Treatment of L cells with trypsin at later stages of infection released a highly hemolytic L Sendai from those cells. The present study, by reference to the density centrifugation studies in a previous report (4), has shown that a variation in infectivity for L cells and in the hemolytic activity of L Sendai is a type of host-controlled modification distinguishable from the density variation.

Virus-erythrocyte interactions

This chapter summarizes the experimental evidence bearing on the nature of virus-erythrocyte reactions characteristic of several taxonomic groups.. Such evidence is culled from (1) the study of conditions necessary for hemagglutination; (2) the examination of specific factors affecting either the cell or the virion to enhance, alter, or abolish the reaction; and (3) the direct physicochemical analysis of cells, viruses, and “receptor analogs.” The hemadsorption phenomenon also provides evidence for virus-erythrocyte interactions, which is based on the attachment of erythrocytes to infected cells in culture having hemagglutinin at their surfaces. This phenomenon reflects the interaction between erythrocytes and viral envelope components. The major virus groups that react with erythrocytes include myxoviruses, paramyxoviruses, pseudomyxoviruses, adenoviruses, arboviruses, reoviruses, enteroviruses, and miscellaneous hemagglutinating viruse (rubella virus, coronaviruses, rhabdoviruses, and oncogenic viruses). The agglutination of erythrocytes by the direct action of viral particles was first described in connection with myxoviruses. This led directly to the discovery of viral neuraminidase—a property unique to myxoviruses and paramyxoviruses. A number of viruses unrelated to myxoviruses have since been shown to agglutinate erythrocytes of various species. The visible result of viral hemagglutination is the “pattern” formed at the bottom of a test tube or well plate by lattices of red cells lightly conjoined by viral hemagglutinin. Hemagglutination serves as a useful direct means of titering intact viral particles or hemagglutinating subunits.

Trypsin action on the growth of Sendai virus in tissue culture cells. I. Restoration of the infectivity for L cells by direct action of tyrpsin on L cell-borne Sendai virus

Sendai virus grown in fertile eggs (egg Sendai) infects L cells in which the synthesis of L Sendai (grown in L cells) occurs by the one-step mechanism. L Sendai is not infectious for L cells when tested by the tube titration method although it is infectious for chick embryos. When L cells infected with egg Sendai were dispersed by trypsin and plated on a monolayer culture of L cells, the viral agents spread to the adjacent recipient cells in which the synthesis of L Sendai occurred. The newly infected L cells became infectious for L cells again by trypsin treatment. Kinetic experiments suggested that the target of trypsin is the mature virus, of L Sendai nature, just budding from the L-cell surface. By using an immunofluorescent cell-counting technique, recovery of the infectivity of L Sendai for L cells due to a direct enzymatic action of trypsin was demonstrated. Under the optimal condition, the infectivity increased 1,000-fold for L cells and 10-fold for chick embryos, and both the titers could favorably be compared. No increasing effect of trypsin was observed on the infectivity of egg Sendai. Density centrifugation studies revealed a difference between egg Sendai and L Sendai in the density. Trypsin treatment which induced the maximal enhancement of L Sendai infectivity did not affect both the densities, showing that variations of Sendai virus in the infectivity for L cells and in the density are independent types of host-controlled modification.