Cellular distribution of tetherin. (A) Confocal analysis of HeLa cells showing the distribution of endogenous tetherin, detected with a specific antiserum. Cells that were fixed but not permeablized (left panel) allowed visualization of tetherin at the cell surface, while permeabilized cells revealed tetherin concentrated in a perinuclear compartment that was visible in ~50% of cells. This intracellular pool co-localized with a marker for the TGN (TGN-46), as shown by the PDM analysis in the upper right corner of the merged image, where positive co-localization is pseudocolored in orange. Scale bars represent 10 μM. (B) 293A cells were co-transfected with 10 μg HIV-1-pack and 100 ng of expression plasmids for either untagged tetherin or EGFP-tagged tetherin. Cell lysates were analyzed by Western blotting, using antibodies against GFP and tetherin. (C) Cell lysates and pelleted supernatant fractions (VLPs) from same experiment as (B) were probed for HIV-1 p24 expression. Both tetherin constructs inhibited VLP release. (D) HeLa and 293A cells were transfected with either 100 ng or 300 ng of the EGFP-tetherin plasmid. With 300 ng, a punctate pattern of EGFP fluorescence was observed throughout the cells; with 100 ng, the protein could only be detected using an anti-GFP antibody, that revealed an intense surface rim and a fainter PNC in both types of cells. Cells were fixed and permeabilized before staining. Scale bars represent 10 μM. (E) The intracellular concentration of EGFP-tetherin in transiently transfected HeLa cells (100 ng plasmid) was analyzed by confocal microscopy using anti-GFP antibody and specific markers for the TGN (TGN46) and recycling endosomes (endocytosed transferrin). The degree of co-localization was calculated using Pearson's coefficients. Mean +/- SEM is shown for 20 individual cells analyzed.