Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0019693 (HIV)
 170,526 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

While Ricinus communis agglutinin 1 (RCA-1) can be used as a specific marker to study the development and differentiation of microglial cells in human embryogenesis, little is known about the structural heterogeneity and nature of RCA-1+ cells. To analyse the structural peculiarities of RCA-1+ cells, we have used primary dissociated cultures of human embryonic brain. These have been used as models for investigating many of the aspects of central nervous system (CNS) HIV infection. We have shown that primary dissociated cultures from human embryos as young as 10 weeks gestation contain RCA-1+ cells. The RCA-1+ cells exist in two forms, those without (type I) and those with (type II) processes. The former have a poorly developed ultrastructure, while the latter have well developed ultrastructural features, such as rough endoplasmic reticulum with short cisternae, abundant ribosomes, mitochondria, lysosomes and vacuoles. Furthermore, some of these cells with processes have well developed cytoskeletal features. In this paper, the classification of RCA-1+ cells of embryonic human brain is considered and their morphology compared to microglia identified in rodent CNS.
 ...
PMID:Ultrastructural identification of Ricinus communis agglutinin-1 positive cells in primary dissociated cell cultures of human embryonic brain. 773 77

The HIV-1-encoded Vpu protein induces a rapid and specific degradation of CD4 molecules in the endoplasmic reticulum (ER). 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. In order to precisely define the sequence(s) or structural element(s) in the CD4 cytoplasmic domain necessary for Vpu-induced degradation, a panel of deletion and substitution mutants in the cytoplasmic domain of CD4 was generated and analyzed. In agreement with previous reports, our deletion analysis indicates that a region encompassing amino acids 411 to 419 (KRLLSEKKT) in the cytoplasmic domain of CD4 was required to confer Vpu sensitivity. However, six specific substitution mutations within this region did not confer CD4 resistance to Vpu, suggesting that neither the amino acid sequence nor the charge of the amino acids in this region was critical to Vpu-induced CD4 degradation. A dileucine motif that is important for internalization of CD4 and Nef-induced CD4 down-regulation was also not required for Vpu-induced CD4 degradation. Interestingly, two substitution mutants (CD4EMKL and CD4MK407,11PP) located in a more proximal cytoplasmic region of CD4 abolished Vpu-induced CD4 degradation. Computer-assisted analysis of the substitution and deletion mutants conferring CD4 resistance to Vpu-induced degradation indicated that these mutations disrupted a putative alpha-helix formed in the proximal cytoplasmic region of CD4. Taken together, these studies strongly suggest that a structural element in the proximal cytoplasmic region of CD4 contributes to Vpu sensitivity.
 ...
PMID:Degradation of CD4 induced by human immunodeficiency virus type 1 Vpu protein: a predicted alpha-helix structure in the proximal cytoplasmic region of CD4 contributes to Vpu sensitivity. 777 93

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. Analysis of oligosaccharide processing revealed that the majority of gp160 remained fully endo-H sensitive throughout a 21-h chase period, and hence cleavage of gp160 to gp120-gp41 took place prior to the creation of hybrid and complex oligosaccharides on gp120. Immunofluorescence microscopy demonstrated that in the absence of CD4 both gp160 and Vpu are targeted to the Golgi apparatus, that can be stained with wheat germ agglutinin or antibodies to the human KDEL receptor. In contrast, gp160 complexed with CD4 was retained in the ER and thus failed to reach the cis-Golgi compartment. Although gp160-bound CD4 has its own half life of 4 h 35 min in the endoplasmic reticulum (ER), co-expression of Vpu accelerated the turnover of CD4 by 5.5-fold and thereby enabled gp160 to be translocated out of the ER to the cis-Golgi compartment. We concluded that Vpu prevents the formation of stable CD4-gp160 complexes in the ER and thus indirectly allows gp160 to accumulate in the Golgi apparatus, where it is selectively retained to produce gp120-gp41.
 ...
PMID:Intracellular membrane traffic of human immunodeficiency virus type 1 envelope glycoproteins: vpu liberates Golgi-targeted gp160 from CD4-dependent retention in the endoplasmic reticulum. 796 87

A combination of saturation and site-directed mutagenesis was utilized to disrupt the alpha 2 domain disulfide bridge of HLA-A*0201. Mutation of cysteine 101 to a serine (C101S) or of cysteine 164 to alanine (C164A) decreased the rate of maturation of the heavy chain, the total amount of mature heavy chain within the cell, and the level of surface expression. Cells expressing these genes and loaded with a synthetic peptide derived from the influenza A matrix protein (58-66) were recognized poorly by HLA-A*0201-restricted, peptide-specific CTLs. Cells expressing mutant HLA-A*0201 loaded with a synthetic peptide derived from the HIV-1 pol protein (476-484) were not recognized by pol IV-9-specific CTLs. Mutant C164A cells infected with influenza virus were partially recognized by influenza matrix peptide-specific CTLs, while C101S cells were not lysed. Surprisingly, endogenous peptide loading of cells expressing mutant HLA-A*0201 using a minigene coding for either the influenza A matrix peptide 58-66, or HIV-1 pol peptide 476-484, resulted in efficient CTL recognition. This suggests different structural constraints for peptide binding in the endoplasmic reticulum during biosynthesis and for binding to exported molecules on the cells surface.
 ...
PMID:Mutation of the alpha 2 domain disulfide bridge of the class I molecule HLA-A*0201. Effect on maturation and peptide presentation. 807 Nov 1

The Vpu protein of HIV-1 induces degradation of CD4 in the endoplasmic reticulum. Previous studies have elucidated the role of the CD4 cytoplasmic domain in the Vpu-induced degradation process, and the minimal Vpu responsive element mapped to a small region in the CD4 tail. In the present study, we have carried out both biochemical and biological experiments to analyze the role of the CD4 anchor domain in the Vpu-induced degradation process. We generated chimeric proteins that possessed the ecto-anchor domains of gp160 and the cytoplasmic domain of CD4. The chimeric envelope glycoproteins were functionally active in the fusion of HeLa CD4+ cells, with the exception of those having the arginine to isoleucine (R to I) substitution in the gp160 anchor domain. Coexpression studies revealed that these chimeric glycoproteins were stable and functionally active in the presence of Vpu, as opposed to those having the anchor-cytoplasmic domains of CD4. The half-life of Vpu-sensitive chimeric glycoproteins was calculated to be approximately 60-90 min, whereas Vpu-resistant envelope glycoproteins exhibited relatively longer half-lives in the presence of Vpu. Taken together, these studies strongly suggest that the CD4 anchor domain appears to provide critical sequence or structural elements through which the Vpu protein could access CD4 or glycoproteins bearing the Vpu responsive element for degradation in the endoplasmic reticulum.
 ...
PMID:Vpu-mediated proteolysis of gp160/CD4 chimeric envelope glycoproteins in the endoplasmic reticulum: requirement of both the anchor and cytoplasmic domains of CD4. 809 66

In vivo infection of human T cell lymphocytes by HIV-1 is mediated by the specific binding of the HIV-1 envelope glycoprotein gp120 to the T cell CD4 receptor. One of the post-infection events observed in vivo is the progressive loss of CD4+ T cells. One possible mechanism is the production of infected T cells which are lacking in surface expression of the CD4 receptor protein. We have analysed this possibility utilizing the two HIV-1 chronically-infected CD4- cell lines, 8E5 and ACH-2, both of which are derived from a CD4+ parental strain (A3.01) after HIV-1 infection. In each cell (8E5 and ACH-2) the loss of CD4 surface expression was found to occur by different mechanisms. In ACH-2 cells, neither CD4 protein nor the 3 kb CD4 RNA transcript could be detected. However, treatment of ACH-2 cells with cycloheximide elicited production of the 3 kb transcript suggesting the possibility for a repressor protein(s) to act at the level of transcription and/or stability of the 3 kb mRNA. In contrast, in 8E5 cells the level of the 3 kb CD4 RNA was comparable with that found in the CD4+ A3.01 parental strain. Analysis of the 8E5 strain revealed the presence of a CD4- gp160 bimolecular protein complex sequestered internally in the rough endoplasmic reticulum (RER). Finally, the protein tyrosine kinase p56lck, normally associated with the cellular membrane, appeared to be linked to the RER and bound to the CD4- gp160 proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Transcriptional and post-transcriptional mechanisms are involved in the absence of CD4 surface expression in two HIV-1 chronically infected T cell lines. 810 73

The human immunodeficiency virus type 1 (HIV-1) encoded Vpu is a small integral membrane phosphoprotein that functions in the enhancement of viral particle release and has more recently been shown to cause degradation of CD4 at the endoplasmic reticulum. We have demonstrated earlier that Vpu is phosphorylated by the ubiquitous casein kinase-2 (CK-2) in HIV-1 infected cells. The phosphoacceptor sites targeted by CK-2 in Vpu, however, have not been demonstrated and it was unclear whether Vpu was phosphorylated at one or more of its four serine residues. In this study we characterized the CK-2 phosphoacceptor sites in Vpu using recombinant CK-2 for in vitro phosphorylation of recombinant Vpu protein as well as synthetic peptides of Vpu. 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. The Km values of CK-2 to these peptides were established, revealing a preferential phosphorylation of Ser56. The Km values are: Ser56 = 31 microM; Ser 52 = 156 microM; wild type = 27 microM. In addition, we studied phosphorylation of Vpu by endogenous CK-2 following in vitro translation in rabbit reticulocyte lysate of wild-type Vpu or a mutant, Vpum2/6, carrying serine to asparagine changes at amino acid positions 52 and 56. The in vivo phosphorylation of Vpu was studied in transiently transfected human embryonic kidney (293) cells. In this system, the mutant Vpum2/6 was not phosphorylated, indicating that the seryl residues of Vpu at amino acid positions 52 and 56, but not those at positions 23 and 61, are phosphorylated by CK-2. The two CK-2 phosphorylation sites are conserved in all known Vpu sequences and represent the consensus Ser52GlyAsn(Glu/Asp)Ser(Glu/Asp)Gly(Glu/Asp)59. Prediction of the secondary structure revealed a conserved alpha-helix-turn-alpha-helix motif for the hydrophilic C-terminal part of Vpu. A structural model for Vpu is proposed in which the membrane anchor precedes a region comprising two amphipathic alpha-helices of opposed polarity, joined by a strongly acidic turn that protrudes into the cytoplasm and contains the CK-2 phosphorylation sites. Possible functional and structural homologies of Vpu to the membrane channel-forming M2 protein of influenza A viruses are discussed.
 ...
PMID: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. 810 1

The human immunodeficiency virus type 1 (HIV-1)-specific Vpu is an 81-amino-acid amphipathic integral membrane protein with at least two different biological functions: (i) enhancement of virus particle release from the plasma membrane of HIV-1-infected cells and (ii) degradation of the virus receptor CD4 in the endoplasmic reticulum (ER). We have previously found that Vpu is phosphorylated in infected cells at two seryl residues in positions 52 and 56 by the ubiquitous casein kinase 2. To study the role of Vpu phosphorylation on its biological activity, a mutant of the vpu gene lacking both phosphoacceptor sites was introduced into the infectious molecular clone of HIV-1, pNL4-3, as well as subgenomic Vpu expression vectors. This mutation did not affect the expression level or the stability of Vpu but had a significant effect on its biological activity in infected T cells as well as transfected HeLa cells. Despite the presence of comparable amounts of wild-type and nonphosphorylated Vpu, decay of CD4 was observed only in the presence of phosphorylated wild-type Vpu. Nonphosphorylated Vpu was unable to induce degradation of CD4 even if the proteins were artificially retained in the ER. In contrast, Vpu-mediated enhancement of virus secretion was only partially dependent on Vpu phosphorylation. Enhancement of particle release by wild-type Vpu was efficiently blocked when Vpu was artificially retained in the ER, suggesting that the two biological functions of Vpu are independent, occur at different sites within a cell, and exhibit different sensitivity to phosphorylation.
 ...
PMID:Differential activities of the human immunodeficiency virus type 1-encoded Vpu protein are regulated by phosphorylation and occur in different cellular compartments. 813 11

The human immunodeficiency virus type-1 (HIV-1) encoded Vpu protein facilitates the release of budding virions from the surface of infected cells and delays the rate of syncytium formation of the virus. Furthermore, Vpu induces rapid degradation of nascent CD4 molecules that are retained in the endoplasmic reticulum by the formation of gp160-CD4 complexes. Currently, little is known of the precise mechanism(s) by which Vpu function. Whether or not these different events are related remain unclear. In this report, we describe our recent structure/function studies on vpu suggesting that the protein may have independent biological activities during the HIV-1 infection.
 ...
PMID:Mutational analysis of the HIV-1 Vpu protein. 815 84

CD8+ cytolytic T lymphocytes (CTL) identify virally infected cells by recognizing processed viral antigen in association with class I major histocompatibility complex (MHC) molecules on infected cells. Processing begins in the cytosol with the generation of peptides, possibly by a protease complex with MHC-encoded subunits, known as the proteasome. Transport of the resulting cytosolic peptides into the endoplasmic reticulum for association with class I molecules is essential and probably involves a heterodimer of the MHC-encoded proteins, Tap-1 and Tap-2. The site of processing of viral envelope proteins is uncertain. These proteins are not present in the cytosol because of cotranslational translocation into the endoplasmic reticulum. We show here that the HIV-1 envelope (env) protein is processed in infected cells by a novel Tap-1/Tap-2-independent pathway that seems to be localized to the endoplasmic reticulum.
 ...
PMID:Transporter-independent processing of HIV-1 envelope protein for recognition by CD8+ T cells. 832 Dec 86


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>