Silencing of both β-TrCP1 and HOS (β-TrCP2) Is Required To Suppress Human Immunodeficiency Virus Type 1 Vpu-Mediated CD4 Down-Modulation

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Abstract
The human immunodeficiency virus type 1 (HIV-1) Vpu protein interacts with CD4 within the endoplasmic reticula of infected cells and targets CD4 for degradation through interaction with β-TrCP1. Mammals possess a homologue of β-TrCP1, HOS, which is also named β-TrCP2. We show by coimmunoprecipitation experiments that β-TrCP2 binds Vpu and is able to induce CD4 down-modulation as efficiently as β-TrCP1. In two different cell lines, HeLa CD4+ and Jurkat, Vpu-mediated CD4 down-modulation could not be reversed through the individual silencing of endogenous β-TrCP1 or β-TrCP2 but instead required the two genes to be silenced simultaneously.