Overexpression of an F-box-deficient β-TrCP abolishes Vpu-mediated depletion of CD4, but not of endogenous CD317. HeLaP4 cells were transfected with expression constructs for Vpu and either HA-tagged β-TrCP1 wt or β-TrCP1ΔF. Two days later, cells were processed for microscopic analysis to (A) visualize and (B) quantify the expression of either CD4 or endogenous CD317 (both in red) in relation to HA-β-TrCP1 wt or the HA-β-TrCP1ΔF mutant (cells co-expressing HA-tagged β-TrCPs and Vpu are labelled by a green asterisk; this fluorescent channel is not depicted). The quantification in (B) depicts the percentage of cells that displayed markedly reduced levels of CD4 (upper panel) or CD317 (lower panel) in cells co-expressing Vpu together with either HA-tagged HA-β-TrCP1 wt or HA-β-TrCP1ΔF relative to untransfected neighbouring cells. The arithmetic means ± SEM of three independent experiments are shown. Scale bar: 10 μm. Student's t-test: ** p = 0.0021, n.s. = not significant.