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Unformatted text preview: Distinct Cellular Interactions of Secreted and Transmembrane Ebola Virus Glycoproteins Zhi-yong Yang, Rafael Delgado, Ling Xu, Robert F. Todd, Elizabeth G. Nabel, Anthony Sanchez, Gary J. Nabel* The mechanisms by which Ebola virus evades detection and infects cells to cause hemorrhagic fever have not been defined, though its glycoprotein, synthesized in either a secreted or transmembrane form, is likely involved. Here the secreted glycoprotein was found to interact with neutrophils through CD16b, the neutrophil-specific form of the Fc g receptor III, whereas the transmembrane glycoprotein was found to interact with endothelial cells but not neutrophils. A murine retroviral vector pseudotyped with the transmembrane glycoprotein preferentially infected endothelial cells. Thus, the secreted glycoprotein inhibits early neutrophil activation, which likely affects the host response to infection, whereas binding of the transmembrane glycoprotein to endothelial cells may contribute to the hemorrhagic symptoms of this disease. E bola virus has been identified as the cause of several highly lethal outbreaks of hemorrhagic fever. Infection typically be- gins with flu- like symptoms, which often progress rapidly to fatal complications of hemorrhage, fever, and hypotensive shock ( 14 ). The negative- stranded genome of Ebola virus contains seven structural and regulatory proteins ( 5 ), but despite its rel- ative simplicity, the molecular basis for Ebola virus pathogenicity is unknown. Among the viral gene products, the glyco- protein is found in two forms: a secreted form, 50 to 70 kD ( 6 ), synthesized in large amounts early in the course of infection, and an alternative transmembrane form, which arises from RNA editing to encode a 120- to 150- kD glycoprotein that is in- corporated into the virion ( 6, 7 ). The first 295 amino acids of both proteins are iden- tical in the Zaire strain, but secreted gly- coprotein (sGP) contains an additional 69 and the transmembrane glycoprotein (GP) another 381 COOH- terminal amino acid residues ( 6 ). The specific cellular targets of these related gene products and their roles in the pathogenesis of Ebola infec- tion have not been characterized. To determine the specificity of Ebola virus glycoproteins, we transfected expres- sion vectors encoding either sGP, GP, or a plasmid control ( 8 ) into human 293 cells, and cell culture supernatants were used as a source of relevant recombinant glyco- proteins. Binding of sGP was determined by immunofluorescence analysis after in- cubation of the relevant supernatants with normal or transformed human cell lines. No binding was detected to several hema- topoietic lineages, including lymphocytes or monocytes (Fig. 1A), transformed Jur- kat or CEM T leukemias, or the HL- 60 myelomonocytic or U- 937 promonocytic leukemia cells ( 9 ). In contrast, sGP bound to granulocytic cells, as evidenced by flu- orescence- activated cell sorting (FACS) analysis of this subset of peripheral blood...
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This note was uploaded on 07/12/2011 for the course BIO 620 taught by Professor Hardy during the Spring '11 term at University of Florida.
- Spring '11