pH regulation in early endosomes and interferon-inducible transmembrane proteins control avian retrovirus fusion.
Enveloped viruses infect host cells by fusing their membranes with those of the host cell, a process mediated by viral glycoproteins upon binding to cognate host receptors or entering into acidic intracellular compartments. Whereas the effect of receptor density on viral infection has been well studied, the role of cell type-specific factors/processes, such as pH regulation, has not been characterized in sufficient detail. Here, we examined the effects of cell-extrinsic factors (buffer environment) and cell-intrinsic factors (interferon-inducible transmembrane proteins, IFITMs), on the pH regulation in early endosomes and on the efficiency of acid-dependent fusion of the avian sarcoma and leukosis virus (ASLV), with endosomes. First, we found that a modest elevation of external pH can raise the pH in early endosomes in a cell type-dependent manner and thereby delay the acid-induced fusion of endocytosed ASLV. Second, we observed a cell type-dependent delay between the low pH-dependent and temperature-dependent steps of viral fusion, consistent with the delayed enlargement of the fusion pore. Third, ectopic expression of IFITMs, known to potently block influenza virus fusion with late compartments, was found to only partially inhibit ASLV fusion with early endosomes. Interestingly, IFITM expression promoted virus uptake and the acidification of endosomal compartments, resulting in an accelerated fusion rate when driven by the glycosylphosphatidylinositol-anchored, but not by the transmembrane isoform of the ASLV receptor. Collectively, these results highlight the role of cell-extrinsic and cell-intrinsic factors in regulating the efficiency and kinetics of virus entry and fusion with target cells.
From the Division of Pediatric Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30322 and.
Tanay M
TM
Desai
From the Division of Pediatric Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30322 and.
Mariana
M
Marin
From the Division of Pediatric Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30322 and.
Caleb
C
Mason
From the Division of Pediatric Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30322 and gmeliki@emory.edu.|the Children's Healthcare of Atlanta, Atlanta, Georgia 300322.
Gregory B
GB
Melikyan
D000072283:A549 Cells; D000143:Acids / Q000737:chemistry; D000818:Animals; D001358:Avian Sarcoma Viruses / Q000502:physiology*; D002460:Cell Line; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011991:Receptors, Virus / Q000378:metabolism; D013696:Temperature; D022161:Transport Vesicles / Q000378:metabolism; D053586:Virus Internalization
D000143:Acids; C080082:IFITM3 protein, human; D008565:Membrane Proteins; D020033:Protein Isoforms; D016601:RNA-Binding Proteins; D011991:Receptors, Virus
endocytosis; fusion protein; pH regulation; viral protein; virus entry