Disease relevance of vpu

• METHODS: HIV-1 accessory genes vif, vpu and nef were modified to express under the control of a single promoter with cellular proteolytic cleavage sites between the coding sequences (VVN-P) [1].
• Previously, only lentiviruses infecting humans (human immunodeficiency virus type 1 [HIV-1]) and chimpanzees (SIVcpz) were known to have a vpu gene; more recently, this has also been found in SIVgsn from Cercopithecus nictitans [2].
• A retroviral vector was constructed that induces long-term expression of human immunodeficiency virus type 1 (HIV-1) rev, vpu and env genes [3].
• Consistent with these quantitative differences, Nef inhibited superinfection more efficiently than Vpu and Env [4].
• The human immunodeficiency virus type 1 (HIV-1) vpu gene encodes a small integral membrane phosphoprotein with two established functions: degradation of the viral coreceptor CD4 in the endoplasmic reticulum (ER) and augmentation of virus particle release from the plasma membrane of HIV-1-infected cells [5].

High impact information on vpu

• In contrast, vif and rev are closer to HIV-1 group M, and vpu is highly divergent [6].
• When expressed in vitro, the 81-amino acid vpu protein reacted with about one-third of the serum samples from AIDS patients that were tested, indicating that the vpu open reading frame is expressed in vivo as well [7].
• These data suggest that the vpu gene product is required for efficient virus replication and may have a role in assembly or maturation of progeny virions [7].
• Introduction of a frame-shift mutation into the vpu open reading frame did not significantly interfere with expression of the major viral proteins in a transient expression system [7].
• Consequently, efficient expression of the Vif, Vpr, Vpu, and Env proteins from these RNAs is dependent on Rev. These results exclude a mechanism whereby the sole function of Rev is simply to export RNAs from nucleus to cytoplasm [8].

Chemical compound and disease context of vpu

• Human immunodeficiency virus type 1 (HIV-1) Vpu is phosphorylated at two serine residues (Ser52 and Ser56) present within the acidic dodecapeptide region of the 54-aa cytoplasmic domain [9].
• This increased expression of gp120 at the cell surface may explain the more rapid onset of syncytium formation observed in cell transfected with vpu mutant proviruses [10].
• In this report, we have mutated the two phosphorylated serine residues of the HIV-1 Vpu to glycine residues and have reconstructed a SHIV expressing this nonphosphorylated Vpu (SHIV(S52,56G)) [11].
• Expression of vpu in Escherichia coli cells increases membrane permeability to a number of molecules such as 2-nitrophenyl beta-D-galactopyranoside, uridine, the impermeable translation inhibitor hygromycin B, and lysozyme [12].
• Examination of SHIVM2-infected cells treated with 50 microM rimantadine revealed numerous viral particles associated with the cell plasma membrane and within intracytoplasmic vesicles, which is similar to HIV-1 mutants lacking a functional vpu [13].

Biological context of vpu

• We found that simultaneous mutations in both vpu and nef severely impaired virus replication [14].
• Using a pathogenic variant of SHIV-4 known as SHIV(KU-1bMC33), we reported that a mutant of this virus with the majority of the vpu deleted was still capable of causing profound CD4(+) T cell loss and neuroAIDS in pig-tailed macaques (McCormick-Davis et al., 2000, Virology 272, 112-116) [15].
• Especially, in the 5'tat/rev-vpu tree, they branched before the root of HIV-1 group M. These findings suggest that these Congolese SIVcpz genomes are mosaic, probably due to a recombinational event in the recent past, and it provides evidence for a rather recently occurring cross-species transmission between humans and chimpanzees [16].
• Our studies have further revealed that phosphorylation of either of the two phosphoacceptor sites is not sufficient to generate a functional Vpu protein [9].
• Taken together, these observations suggest that DeltavpuSHIV(KU-1bMC33) has a low pathogenic phenotype in macaques but that individual pig-tailed macaques can select for additional mutations within the Env and Nef which can compensate for the lack of an intact Vpu and ultimately increase its pathogenicity [15].

Anatomical context of vpu

• None of the transgenic mice that expressed vif, tat, rev, or vpu in podocytes, even with the FVB/N genetic background, developed podocyte injury [17].
• A molecular clone of simian-human immunodeficiency virus (DeltavpuSHIV(KU-1bMC33)) with a truncated, non-membrane-bound vpu results in rapid CD4(+) T cell loss and neuro-AIDS in pig-tailed macaques [18].
• The membrane traffic of human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins has been investigated in COS-1 cells transiently expressing the HIV-1 env, vpu, and rev genes [19].
• Histological examination of tissues from this macaque revealed a thymus with severe atrophy that was similar to that of a previously reported macaque inoculated with a SHIV lacking vpu (Virology 293, 2002, 252) [11].
• HIV-1 Vpu interacts with CD4 in the endoplasmic reticulum and triggers CD4 degradation, presumably by proteasomes [20].

Associations of vpu with chemical compounds

• No major changes in the topology of this membrane-associated amphipathic helix were observed upon phosphorylation of serine residues 52 and 56, although this modification regulates biological function of Vpu [21].
• Sequence analysis revealed no reversion of the glycine residues in the vpu sequences isolated from this macaque [11].
• Phosphorylation of both Ser52 and Ser56 was demonstrated by in vitro phosphorylation using three 54-residue peptides comprising the entire hydrophilic part of Vpu and containing single serine to asparagine transitions in either position 52 or 56 [22].
• In this study, Vpu-induced degradation of CD4 in the ER was investigated by quantitative immunoprecipitation of CD4 following cotransfection of COS-7 cells with CD4 and Vpu expressors in the presence of brefeldin A, a drug that blocks protein transport from the ER to the Golgi complex [23].
• This indicates that important effects of vpu may have been lost in some experimental systems because of the particular viruses used, and further suggests the involvement of a determinant in the transmembrane glycoprotein of the virus in the action of vpu [24].

Regulatory relationships of vpu

• This group contains nine bicistronic mRNAs producing Env and Vpu and three mRNAs expressing only the first exon of tat [25].

Other interactions of vpu

• Vif, Vpu and Nef as a fusion protein with proteolytic cleavage sites (VVN-P) is able to induce a significant level of cellular immune responses [1].
• Various viral proteins have been implicated in direct modulation like the regulatory proteins Tat, Nef and Vpu, but also the envelope proteins gp 120 and gp41 [26].
• Northern and Southern blot analyses revealed no apparent deletion in the proviral DNA and mRNA prepared from these clones, except in the case of type I and II clones isolated from M10/vpu- which contained large deletions in the mRNAs for gag and gag-pol proteins [27].

Analytical, diagnostic and therapeutic context of vpu

• Flow cytometry analysis indicates that the relative amounts of envelope glycoprotein gp120 expressed at the surface of cells transfected with these vpu mutant proviruses was two- to threefold greater than that observed on cells transfected with a vpu+ provirus [10].
• To investigate the subcellular location of Ubp, and to see whether Vpu affects the intracellular distribution of Gag, we carried out immunofluorescence localization in conjunction with confocal microscopy [28].
• The Vpu and CD4 cytoplasmic domains were found, by using a two-hybrid assay in yeast, to interact in the absence of their membrane anchor domains [29].
• Monoclonal and polyclonal antibodies directed against two different epitopes of Vpu were used for immunoprecipitation of Vpu from HIV-1-infected cells and for detection of Vpu in Western blot analyses [30].
• Presence of Intact vpu and nef genes in nonpathogenic SHIV is essential for acquisition of pathogenicity of this virus by serial passage in macaques [31].

References