Early molecular events in the interaction of enveloped viruses with cells. I. A fluorescence and radioactivity study

Effect of modification of HEp 2 cell membrane lipidic phase on susceptibility to infection from herpes simplex virus

We have verified the consequences of alterations of the lipidic phase of HEp 2 cell membranes on susceptibility to infection from Herpes simplex virus, and have related these results to modification in membrane fluidity. This was carried out by treating HEp 2 cells with saturated and unsaturated fatty acids with chain lengths from eight to 18 carbon atoms. The results show that HEp 2 cells treated with saturated fatty acids with eight and ten carbon atoms have both increased membrane fluidity and increased susceptibility to Herpes simplex virus infection while both parameters were reduced when HEp 2 cells were treated with saturated fatty acids having 14 and 18 carbon atoms. Fatty acids with 16 carbon atoms, however, show an increase in membrane fluidity which has no significant correlation to infection susceptibility. As to unsaturated acids, those with eight carbon atoms, 2-octenoic acid (trans-8: 1[2]) and 2-octynoic acid (8:::1[2]), increase the susceptibility to infection and fluidity while low concentrations of monounsaturated acids with 14 and 18 carbon atoms, myristoleic acid (cis-14:1[9]) and oleic acid (cis-18:1[9]), reduce both the susceptibility to infection and the fluidity of the membrane.

Low pH fusion of mouse liver nuclei with liposomes bearing covalently bound lysozyme

Lysozyme covalently bound to liposomes induces the fusion of liposomes with isolated mouse liver nuclei. The fusion behavior is very similar to the case of erythrocyte ghosts (Arvinte, T., Hildenbrand, K., Wahl, P. and Nicolau, C. (1986) Proc. Natl. Acad. Sci. USA 83, 962-966). Kinetic studies showed that membrane lipid mixing was completed within 15 min, as indicated from the resonance energy transfer (RET) measurements. For the resonance energy transfer kinetic measurements the liposomes contained L-alpha-dipalmitoylphosphatidylethanolamine (DPPE), labeled at the free amino group with the energy donor 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) or with the energy acceptor tetramethylrhodamine. The lipid mixing at equilibrium was studied by the fluorescence recovery after photobleaching technique (FRAP). Liposomes (with/without lysozyme) containing Rh-labeled DPPE in their membranes were incubated with nuclei at 37 degrees C, pH 5.2, for 30 min. After washing of nuclei by three centrifugations, 60-70% of the initial amount of labeled DPPE was associated with the nuclei in the case of liposomes bearing lysozyme and only 7-10% in the case of liposomes without lysozyme. For the nuclei incubated with liposomes having lysozyme, about 70% of the total Rh-labeled lipids present in the nuclei diffused in the nuclear membrane(s) (lateral diffusion constant of D = (1.4 +/- 0.5) X 10(-9) cm2/s). By encapsulating fluorescein isothiocyanate-labeled dextran of 150 kDa molecular mass into the liposomes and using a microfluorimetric method, it was shown that after the fusion a part of the liposome contents is found in the nuclei interior. In this lysozyme-induced fusion process between liposomes and nuclei or erythrocyte ghosts, the binding of lysozyme to the glycoconjugates contained in the biomembranes at acidic pH seems to be the determining step which explains the high fusogenic property of the liposomes bearing lysozyme.

Interaction of polyunsaturated fatty acids with animal cells and enveloped viruses

Essential unsaturated fatty acids such as oleic, linoleic, or arachidonic were incorporated into the phospholipids of animal cells and induced in them a change in the fluidity of their membranes. Exposure of enveloped viruses such as arbo-, myxo-, paramyxo-, or herpesviruses to micromolar concentrations of these fatty acids (which are not toxic to animal cells) caused rapid loss of infectivity of these viruses. Naked viruses such as encephalomyocarditis virus, polio virus or simian virus 40 were not affected by incubation with linoleic acid. The loss of infectivity was attributed to a disruption of the lipoprotein envelope of these virions, as observed in an electron microscope.

Unsaturated free fatty acids inactivate animal enveloped viruses

Unsaturated free fatty acids such as oleic, arachidonic or linoleic at concentrations of 5-25 microgram/ml inactivate enveloped viruses such as herpes, influenza, Sendai, Sindbis within minutes of contact. At these concentrations the fatty acids are inocuous to animal host cells in vitro. Naked viruses, such as polio, SV40 or EMC are not affected by these acids. Saturated stearic acid does not inactivate any viruses at concentrations tested. Though the mode of action of unsaturated fatty acids is not understood, electronmicrographs of enveloped viruses treated by them indicate that the inactivation is associated with disintegration of the virus envelope.

Early molecular events during the interaction of enveloped riboviruses with cells. II. A kinetic study

A kinetic model was constructed and partly solved to describe the migration of the fluorescence label 1,6-diphenylhexatriene (DPH) in both directions when enveloped viruses, labelled with DPH in their envelopes are in contact with unlabelled cells or cell labelled in their membranes are in contact with unlabelled enveloped viruses. The central assumption is that two types of receptor sites exist on the cell surface, i.e., physical adsorption sites (P-sites), available to all the viruses studied in these papers and binding sites (B-sites) available only to the viruses which penetrate into the specific cells. The differential equations for the label migration, for different values of the ratio number of viruses number of sites were numerically solved, assuming different fractions of P- and B-sites. The equations also describe, appropriately the mechanism of rapid label migration in the system and substantiate the magnitude "time of residence" of the nonpenetrating viruses adsorbed on the cell surface. The resulting curves match satisfactorily those for the label release by the viruses and account well for the steady state values of the kinetics of label migration in the virus-cell system.