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J Virol. Feb 1996; 70(2): 809–819.
PMCID: PMC189883

The two biological activities of human immunodeficiency virus type 1 Vpu protein involve two separable structural domains.


The human immunodeficiency virus type 1 (HIV-1) Vpu protein is an integral membrane phosphoprotein that induces CD4 degradation in the endoplasmic reticulum and enhances virus release from the cell surface. CD4 degradation is specific, requires phosphorylation of Vpu, and involves the interaction between Vpu and the CD4 cytoplasmic domain. In contrast, regulation of virus release is less specific and not restricted to HIV-1 and may be mechanistically-distinct from CD4 degradation. We show here that a mutant of Vpu, Vpu35, lacking most of its cytoplasmic domain has residual biological activity for virus release but is unable to induce CD4 degradation. This finding suggests that the N terminus of Vpu encoding the transmembrane (TM) anchor represents an active domain important for the regulation of virus release but not CD4 degradation. To better define the functions of Vpu's TM anchor and cytoplasmic domain, we designed a mutant, VpuRD, containing a scrambled TM sequence with a conserved amino acid composition and alpha-helical structure. The resulting protein was integrated normally into membranes, was able to form homo-oligomers, and exhibited expression levels, protein stability, and subcellular localization similar to those of wild-type Vpu. Moreover, VpuRD was capable of binding to CD4 and to induce CD4 degradation with wild-type efficiency, confirming proper membrane topology and indicating that the alteration of the Vpu TM domain did not interfere with this function of Vpu. However, VpuRD was unable to enhance the release of virus particles from infected or transfected cells, and virus encoding VpuRD had replication characteristics in T cells indistinguishable from those of a Vpu-deficient HIV-1 isolate. Mutation of the phosphorylation sites in VpuRD resulted in a protein which was unable to perform either function of Vpu. The results of our experiments suggest that the two biological activities of Vpu operate via two distinct molecular mechanisms and involve two different structural domains of the Vpu protein.

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Selected References

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  • Adachi A, Gendelman HE, Koenig S, Folks T, Willey R, Rabson A, Martin MA. Production of acquired immunodeficiency syndrome-associated retrovirus in human and nonhuman cells transfected with an infectious molecular clone. J Virol. 1986 Aug;59(2):284–291. [PMC free article] [PubMed]
  • Anderson SJ, Lenburg M, Landau NR, Garcia JV. The cytoplasmic domain of CD4 is sufficient for its down-regulation from the cell surface by human immunodeficiency virus type 1 Nef. J Virol. 1994 May;68(5):3092–3101. [PMC free article] [PubMed]
  • Bour S, Boulerice F, Wainberg MA. Inhibition of gp160 and CD4 maturation in U937 cells after both defective and productive infections by human immunodeficiency virus type 1. J Virol. 1991 Dec;65(12):6387–6396. [PMC free article] [PubMed]
  • Bour S, Schubert U, Strebel K. The human immunodeficiency virus type 1 Vpu protein specifically binds to the cytoplasmic domain of CD4: implications for the mechanism of degradation. J Virol. 1995 Mar;69(3):1510–1520. [PMC free article] [PubMed]
  • Buonocore L, Rose JK. Prevention of HIV-1 glycoprotein transport by soluble CD4 retained in the endoplasmic reticulum. Nature. 1990 Jun 14;345(6276):625–628. [PubMed]
  • Chen MY, Maldarelli F, Karczewski MK, Willey RL, Strebel K. Human immunodeficiency virus type 1 Vpu protein induces degradation of CD4 in vitro: the cytoplasmic domain of CD4 contributes to Vpu sensitivity. J Virol. 1993 Jul;67(7):3877–3884. [PMC free article] [PubMed]
  • Cohen EA, Terwilliger EF, Sodroski JG, Haseltine WA. Identification of a protein encoded by the vpu gene of HIV-1. Nature. 1988 Aug 11;334(6182):532–534. [PubMed]
  • Crise B, Buonocore L, Rose JK. CD4 is retained in the endoplasmic reticulum by the human immunodeficiency virus type 1 glycoprotein precursor. J Virol. 1990 Nov;64(11):5585–5593. [PMC free article] [PubMed]
  • Deen KC, McDougal JS, Inacker R, Folena-Wasserman G, Arthos J, Rosenberg J, Maddon PJ, Axel R, Sweet RW. A soluble form of CD4 (T4) protein inhibits AIDS virus infection. Nature. 1988 Jan 7;331(6151):82–84. [PubMed]
  • Folks T, Benn S, Rabson A, Theodore T, Hoggan MD, Martin M, Lightfoote M, Sell K. Characterization of a continuous T-cell line susceptible to the cytopathic effects of the acquired immunodeficiency syndrome (AIDS)-associated retrovirus. Proc Natl Acad Sci U S A. 1985 Jul;82(13):4539–4543. [PMC free article] [PubMed]
  • Friborg J, Ladha A, Göttlinger H, Haseltine WA, Cohen EA. Functional analysis of the phosphorylation sites on the human immunodeficiency virus type 1 Vpu protein. J Acquir Immune Defic Syndr Hum Retrovirol. 1995 Jan 1;8(1):10–22. [PubMed]
  • Gorman CM, Merlino GT, Willingham MC, Pastan I, Howard BH. The Rous sarcoma virus long terminal repeat is a strong promoter when introduced into a variety of eukaryotic cells by DNA-mediated transfection. Proc Natl Acad Sci U S A. 1982 Nov;79(22):6777–6781. [PMC free article] [PubMed]
  • Göttlinger HG, Dorfman T, Cohen EA, Haseltine WA. Vpu protein of human immunodeficiency virus type 1 enhances the release of capsids produced by gag gene constructs of widely divergent retroviruses. Proc Natl Acad Sci U S A. 1993 Aug 1;90(15):7381–7385. [PMC free article] [PubMed]
  • Graham FL, van der Eb AJ. A new technique for the assay of infectivity of human adenovirus 5 DNA. Virology. 1973 Apr;52(2):456–467. [PubMed]
  • Hoxie JA, Alpers JD, Rackowski JL, Huebner K, Haggarty BS, Cedarbaum AJ, Reed JC. Alterations in T4 (CD4) protein and mRNA synthesis in cells infected with HIV. Science. 1986 Nov 28;234(4780):1123–1127. [PubMed]
  • Huet T, Cheynier R, Meyerhans A, Roelants G, Wain-Hobson S. Genetic organization of a chimpanzee lentivirus related to HIV-1. Nature. 1990 May 24;345(6273):356–359. [PubMed]
  • Jabbar MA, Nayak DP. Intracellular interaction of human immunodeficiency virus type 1 (ARV-2) envelope glycoprotein gp160 with CD4 blocks the movement and maturation of CD4 to the plasma membrane. J Virol. 1990 Dec;64(12):6297–6304. [PMC free article] [PubMed]
  • Klimkait T, Strebel K, Hoggan MD, Martin MA, Orenstein JM. The human immunodeficiency virus type 1-specific protein vpu is required for efficient virus maturation and release. J Virol. 1990 Feb;64(2):621–629. [PMC free article] [PubMed]
  • Laemmli UK. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature. 1970 Aug 15;227(5259):680–685. [PubMed]
  • Lenburg ME, Landau NR. Vpu-induced degradation of CD4: requirement for specific amino acid residues in the cytoplasmic domain of CD4. J Virol. 1993 Dec;67(12):7238–7245. [PMC free article] [PubMed]
  • Maldarelli F, Chen MY, Willey RL, Strebel K. Human immunodeficiency virus type 1 Vpu protein is an oligomeric type I integral membrane protein. J Virol. 1993 Aug;67(8):5056–5061. [PMC free article] [PubMed]
  • Schubert U, Clouse KA, Strebel K. Augmentation of virus secretion by the human immunodeficiency virus type 1 Vpu protein is cell type independent and occurs in cultured human primary macrophages and lymphocytes. J Virol. 1995 Dec;69(12):7699–7711. [PMC free article] [PubMed]
  • Schubert U, Henklein P, Boldyreff B, Wingender E, Strebel K, Porstmann T. The human immunodeficiency virus type 1 encoded Vpu protein is phosphorylated by casein kinase-2 (CK-2) at positions Ser52 and Ser56 within a predicted alpha-helix-turn-alpha-helix-motif. J Mol Biol. 1994 Feb 11;236(1):16–25. [PubMed]
  • Schubert U, Schneider T, Henklein P, Hoffmann K, Berthold E, Hauser H, Pauli G, Porstmann T. Human-immunodeficiency-virus-type-1-encoded Vpu protein is phosphorylated by casein kinase II. Eur J Biochem. 1992 Mar 1;204(2):875–883. [PubMed]
  • Schubert U, Strebel K. Differential activities of the human immunodeficiency virus type 1-encoded Vpu protein are regulated by phosphorylation and occur in different cellular compartments. J Virol. 1994 Apr;68(4):2260–2271. [PMC free article] [PubMed]
  • Strebel K, Klimkait T, Martin MA. A novel gene of HIV-1, vpu, and its 16-kilodalton product. Science. 1988 Sep 2;241(4870):1221–1223. [PubMed]
  • Strebel K, Klimkait T, Maldarelli F, Martin MA. Molecular and biochemical analyses of human immunodeficiency virus type 1 vpu protein. J Virol. 1989 Sep;63(9):3784–3791. [PMC free article] [PubMed]
  • Terwilliger EF, Cohen EA, Lu YC, Sodroski JG, Haseltine WA. Functional role of human immunodeficiency virus type 1 vpu. Proc Natl Acad Sci U S A. 1989 Jul;86(13):5163–5167. [PMC free article] [PubMed]
  • Vincent MJ, Raja NU, Jabbar MA. Human immunodeficiency virus type 1 Vpu protein induces degradation of chimeric envelope glycoproteins bearing the cytoplasmic and anchor domains of CD4: role of the cytoplasmic domain in Vpu-induced degradation in the endoplasmic reticulum. J Virol. 1993 Sep;67(9):5538–5549. [PMC free article] [PubMed]
  • Willey RL, Buckler-White A, Strebel K. Sequences present in the cytoplasmic domain of CD4 are necessary and sufficient to confer sensitivity to the human immunodeficiency virus type 1 Vpu protein. J Virol. 1994 Feb;68(2):1207–1212. [PMC free article] [PubMed]
  • Willey RL, Maldarelli F, Martin MA, Strebel K. Human immunodeficiency virus type 1 Vpu protein regulates the formation of intracellular gp160-CD4 complexes. J Virol. 1992 Jan;66(1):226–234. [PMC free article] [PubMed]
  • Willey RL, Maldarelli F, Martin MA, Strebel K. Human immunodeficiency virus type 1 Vpu protein induces rapid degradation of CD4. J Virol. 1992 Dec;66(12):7193–7200. [PMC free article] [PubMed]
  • Willey RL, Smith DH, Lasky LA, Theodore TS, Earl PL, Moss B, Capon DJ, Martin MA. In vitro mutagenesis identifies a region within the envelope gene of the human immunodeficiency virus that is critical for infectivity. J Virol. 1988 Jan;62(1):139–147. [PMC free article] [PubMed]
  • Wray V, Federau T, Henklein P, Klabunde S, Kunert O, Schomburg D, Schubert U. Solution structure of the hydrophilic region of HIV-1 encoded virus protein U (Vpu) by CD and 1H NMR spectroscopy. Int J Pept Protein Res. 1995 Jan;45(1):35–43. [PubMed]
  • Yagi MJ. Cultivation and characterization of BALB-cfC3H mammary tumor cell lines. J Natl Cancer Inst. 1973 Dec;51(6):1849–1860. [PubMed]
  • Yao XJ, Garzon S, Boisvert F, Haseltine WA, Cohen EA. The effect of vpu on HIV-1-induced syncytia formation. J Acquir Immune Defic Syndr. 1993 Feb;6(2):135–141. [PubMed]
  • Yao XJ, Göttlinger H, Haseltine WA, Cohen EA. Envelope glycoprotein and CD4 independence of vpu-facilitated human immunodeficiency virus type 1 capsid export. J Virol. 1992 Aug;66(8):5119–5126. [PMC free article] [PubMed]

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