Saturable attachment sites for polyhedron-derived baculovirus on insect cells and evidence for entry via direct membrane fusion.
This research provides the first evidence for specific receptor binding of polyhedron-derived baculovirus (PDV) to host cells and to lepidopteran brush border membrane vesicles (BBMV) and demonstration of entry via a nonendocytotic pathway involving direct membrane fusion. The technique of fluorescence-activated cell sorting analysis was used to investigate the specificity of binding between the PDV phenotype of Lymantria dispar nuclear polyhedrosis virus (LdNPV) and host membranes. Fluorescein isothiocyanate-labeled PDV was found to bind in a saturable manner to the gypsy moth cell line IPLB-LdEIta and to L. dispar BBMV. The IPLB-LdEIta cell line was found to possess approximately 10(6) PDV-specific receptor sites per cell. Excess levels of unlabeled PDV were highly efficient in competing with fluorescein isothiocyanate-labeled PDV for limited receptor sites, further supporting the specificity of the interaction. Major reductions in virus binding (as high as 70%) after protease treatment of cells indicated that a protein receptor is involved. A fluorescence dequenching assay of membrane fusion with octadecyl rhodamine B (R18)-labeled PDV was used to identify PDV fusion to host cells and BBMV. Direct membrane fusion of PDV occurred at 27 degrees C to both target membranes as well as at 4 degrees C at approximately 55% of the levels achieved at 27 degrees C. Viral fusion to BBMV occurred throughout the pH range of 4 to 11, with dramatically increased fusion levels (threefold) under the alkaline conditions normal for lepidopteran larval midguts. Treatment of cells with chloroquine, a lysosomotropic agent, did not significantly affect PDV fusion to cells or infectivity in tissue culture assays.
Horton
H M
HM
Department of Microbiology, University of Massachusetts, Amherst 01003.
Burand
J P
JP
D000818:Animals; D016367:Baculoviridae / Q000254:growth & development* / Q000378:metabolism; D001665:Binding Sites; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology; D004705:Endocytosis; D005976:Glutaral / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007313:Insecta; D007700:Kinetics; D008561:Membrane Fusion; D008871:Microvilli / Q000382:microbiology; D011991:Receptors, Virus / Q000378:metabolism*
D011991:Receptors, Virus; D002738:Chloroquine; D005976:Glutaral