title: Fragments of Target Cells are Internalized into Retroviral Envelope Protein-Expressing Cells during Cell-Cell Fusion by Endocytosis.
abstract: Retroviruses enter into host cells by fusion between viral and host cell membranes. Retroviral envelope glycoprotein (Env) induces the membrane fusion, and also mediates cell-cell fusion. There are two types of cell-cell fusions induced by the Env protein. Fusion-from-within is induced by fusion between viral fusogenic Env protein-expressing cells and susceptible cells, and virions induce fusion-from-without by fusion between adjacent cells. Although entry of ecotropic murine leukemia virus (E-MLV) requires host cell endocytosis, the involvement of endocytosis in cell fusion is unclear. By fluorescent microscopic analysis of the fusion-from-within, we found that fragments of target cells are internalized into Env-expressing cells. Treatment of the Env-expressing cells with an endocytosis inhibitor more significantly inhibited the cell fusion than that of the target cells, indicating that endocytosis in Env-expressing cells is required for the cell fusion. The endocytosis inhibitor also attenuated the fusion-from-without. Electron microscopic analysis suggested that the membrane fusion resulting in fusion-from-within initiates in endocytic membrane dents. This study shows that two types of the viral cell fusion both require endocytosis, and provides the cascade of fusion-from-within.
authors.affiliation: Division of Cytokine Signaling, Graduate School of Biomedical Sciences, Nagasaki UniversityNagasaki, Japan; Department of Clinical Medicine, Institute of Tropical Medicine, Nagasaki UniversityNagasaki, Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Izumida
authors.affiliation: Division of Cytokine Signaling, Graduate School of Biomedical Sciences, Nagasaki UniversityNagasaki, Japan; Department of AIDS Research, Institute of Tropical Medicine, Nagasaki UniversityNagasaki, Japan.
authors.forename: Haruka
authors.initials: H
authors.lastname: Kamiyama
authors.affiliation: Central Electron Microscope Laboratory, Nagasaki University School of Medicine Nagasaki, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Suematsu
authors.affiliation: Division of Cytokine Signaling, Graduate School of Biomedical Sciences, Nagasaki University Nagasaki, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Honda
authors.affiliation: Division of Cytokine Signaling, Graduate School of Biomedical Sciences, Nagasaki University Nagasaki, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Koizumi
authors.affiliation: Division of Cytokine Signaling, Graduate School of Biomedical Sciences, Nagasaki University Nagasaki, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Yasui
authors.affiliation: Division of Cytokine Signaling, Graduate School of Biomedical Sciences, Nagasaki University Nagasaki, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Hayashi
authors.affiliation: Department of Clinical Medicine, Institute of Tropical Medicine, Nagasaki University Nagasaki, Japan.
authors.forename: Koya
authors.initials: K
authors.lastname: Ariyoshi
authors.affiliation: Division of Cytokine Signaling, Graduate School of Biomedical Sciences, Nagasaki UniversityNagasaki, Japan; Department of AIDS Research, Institute of Tropical Medicine, Nagasaki UniversityNagasaki, Japan.
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Kubo
keywords: cell-cell fusion; endocytosis; envelope; human immunodeficiency virus; murine leukemia virus; retrovirus
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