title: Endocytosis is a critical step in entry of subgroup B avian leukosis viruses.
abstract: The avian leukosis virus (ALV) entry mechanism is controversial, with evidence for and against a low-pH requirement for viral fusion. To further address this question, we tested the entry of human immunodeficiency virus type 1 (HIV-1) pseudotyped with the envelope protein of subgroup B ALV (ALV-B) in the presence of three different lysosomotropic agents. These lysosomotropic agents were able to block the entry of wild-type and pseudotyped ALV-B in two different cell lines, strongly suggesting that ALV-B requires a low-pH step for entry. ALV-B and pH-dependent Semliki Forest virus (SFV) entered cells with slower uptake kinetics than HIV-1, which is pH independent. These slow uptake rates support the theory that ALV-B utilizes endocytic pathways to enter cells. Using immunofluorescence and electron microscopy analysis, we visualized the colocalization of virus particles with the endosomal marker transferrin and demonstrated virus particles in clathrin-coated vesicles and endosome-like structures. Surprisingly, a low-pH treatment did not overcome the inhibition of ALV-B entry by lysosomotropic agents. This indicates that, in contrast to SFV, ALV-B is unable to fuse at the cellular surface, even at a low pH. Taken together, our findings suggest that endocytosis and a subsequent low-pH step are critical for successful ALV-B infection.
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: Felipe
authors.initials: F
authors.lastname: Diaz-Griffero
authors.forename: Steven Ari
authors.initials: SA
authors.lastname: Hoschander
authors.forename: Jürgen
authors.initials: J
authors.lastname: Brojatsch
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001354:Avian Leukosis Virus / Q000145:classification / Q000502:physiology* / Q000648:ultrastructure; D002642:Chick Embryo; D002738:Chloroquine / Q000494:pharmacology; D004705:Endocytosis; D011992:Endosomes / Q000821:virology; D005347:Fibroblasts / Q000821:virology; D015497:HIV-1 / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D014771:Virion / Q000502:physiology
chemical_list: D000643:Ammonium Chloride; D002738:Chloroquine