CCR5-CD4 association is not affected by Brefeldin A treatment. CHO-K1 cells were transfected with the plasmids coding for CD4-Luc and HA-CCR5-YFP or HA-CCR5ΔCter-YFP at concentrations yielding submaximal BRET (indicated by an asterisk in Figure 2E). Fourteen hours before BRET analysis, cells were subjected or not to a brefeldin A (BFA) treatment (see “BRET assays”). (A) BFA-treated and untreated cells were stained for the Golgi marker Giantin; DAPI (4,6 diamidino-2-phenylindole) was added to label nuclei. Scale bar, 10 μM. (B) FACS analysis of CCR5 cell-surface expression in cells treated or not with BFA. The gray filled histogram is the isotypic control, the dotted open histogram corresponding to the specific signal. (C) BRET analysis of CD4-CCR5 (wild-type and truncated) interaction in CHO-K1 cells after BFA treatment. Procedure and BRET controls were as in Figure 2E.