The HIV-1 Vpu protein promotes the degradation of the CD4 receptor by recruiting an SCF like ubiquitination complex that promotes CD4 degradation. Vpu links beta-TrCP to CD4 at the ER membrane through interactions with beta-TrCP and the cytoplasmic tail of CD4. The SKP1 component of the SCF complex is then recruited to the Vpu:beta-TrCP:CD4 promoting ubiquitination and subsequent proteasome-mediated degradation of CD4 (reviewed in Li et al., 2005). Vpu has also been shown to also increases progeny virus secretion from infected cells. Although the precise role of Vpu in this process is not yet known, it may affect ion conductive membrane pore formation and/or interference with TASK-1, an acid-sensitive K+ channel that inhibits virion release in some cells (see references in Li et al., 2005).