Frey, S; Günther, S; Stegmann, T; Marsh, M; Pelchen-Matthews, A; Stephens, P; Ortlepp, S; (1995) Temperature dependence of cell-cell fusion induced by the envelope glycoprotein of human immunodeficiency virus type 1. Journal of Virology , 69 (3) 1462 - 1472.
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We investigated cell-cell fusion induced by the envelope glycoprotein of human immunodeficiency virus type 1 strain IIIB expressed on the surface of CHO cells. These cells formed syncytia when incubated together with CD4- positive human lymphoblastoid SupT1 cells or HeLa-CD4 cells but not when incubated with CD4-negative cell lines. A new assay for binding and fusion was developed by using fluorescent phospholipid analogs that were produced in SupT1 cells by metabolic incorporation of BODIPY-labeled fatty acids. Fusion occurred as early as 10 min after mixing of labeled SupT1 cells with unlabeled CHO-gp160 cells at 37°C. When both the fluorescence assay and formation of syncytia were used, fusion of SupT1 and HeLa-CD4 cells with CHO- gp160 cells was observed only at temperatures above 25°C, confirming recent observations (Y.-K. Fu, T. K. Hart, Z. L. Jonak, and P. J. Bugelski, J. Virol. 67:3818-3825, 1993). This temperature dependence was not observed with influenza virus-induced cell-cell fusion, which was quantitatively similar at both 20 and 37°C, indicating that cell-cell fusion in general is not temperature dependent in this range. gp120-CD4-specific cell-cell binding was found over the entire 0 to 37°C range but increased markedly above 25°C. The enhanced binding and fusion were reduced by cytochalasins B and D. Binding of soluble gp120 to CD4-expressing cells was equivalent at 37 and 16°C. Together, these data indicate that during gp120-gp41-induced syncytium formation, initial cell-cell binding is followed by a cytoskeleton-dependent increase in the number of gp120-CD4 complexes, leading to an increase in the avidity of cell-cell binding. The increased number of gp120-CD4 complexes is required for fusion, which suggests that the formation of a fusion complex consisting of multiple CD4 and gp120-gp41 molecules is a step in the fusion mechanism.
|Title:||Temperature dependence of cell-cell fusion induced by the envelope glycoprotein of human immunodeficiency virus type 1|
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