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

HIV-1 Vpu is a small transmembrane phosphoprotein of 16 kDa which performs critical roles in CD4 proteolysis and virus release. Previous studies have demonstrated that Vpu-induced degradation of CD4 occurs in the endoplasmic reticulum (ER), and that the proteolytic process is sequence specific requiring both the transmembrane and cytoplasmic domains of CD4. In the present study, we investigated the effects of Vpu expression on the intracellular membrane trafficking pathway of mammalian cells. In singly transfected cells, the HIV envelope glycoproteins and vesicular stomatitis virus glycoprotein (VSV G) were properly transported to the cell surface undergoing oligosaccharide modifications characteristic of their movement through the Golgi complex. In contrast, the cell surface delivery of glycoproteins was severely impeded in cells expressing Vpu. Biochemical analyses revealed that Vpu expression blocked the transfer of proteins from the ER-Golgi complex to the plasma membrane in a dose- and protein-dependent manner. Soluble gp120 exhibited extreme transport defects in the presence of Vpu, whereas transmembrane proteins (e.g., gp160, VSV) responded only moderately to wild-type Vpu. To gain insight into Vpu-mediated transport inhibition, we performed mutational analysis of the CK-2 phosphorylation sites (serines at 52 and 56) in the Vpu protein. CK-2 phosphorylation of Vpu has been shown to regulate the activity of the protein in reactions that involve the proteolysis of CD4 in the ER. We demonstrate here that the phosphorylation mutant is defective in both sequence-specific degradation of VRE-containing substrates and the transport inhibition of gp120 and VSV-G in the secretory pathway. Thus, these experiments have revealed that Vpu-mediated proteolysis and transport inhibition are mechanistically coupled requiring the same structural elements of the Vpu protein in both processes. We propose that the primary effect of Vpu expression is to impede the secretion process and then access glycoproteins bearing the VRE for Vpu-mediated proteolysis in the ER of mammalian cells.
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PMID:The human immunodeficiency virus type 1 Vpu protein: a potential regulator of proteolysis and protein transport in the mammalian secretory pathway. 749 87

A cDNA encoding a double-stranded-RNA (dsRNA)-binding protein was isolated by screening a HeLa cell cDNA expression library for proteins that bind the HIV-1 Rev-responsive-element RNA. The cDNA encoded a protein that was identical to TRBP, the previously reported cellular protein that binds the transactivation response element (TAR) RNA of human immunodeficiency virus type 1. TRBP inhibited phosphorylation of the interferon-induced ribosome-associated protein kinase PKR and of the eukaryotic translation initiation factor eIF-2 alpha in a transient-expression system in which the translation of a reporter gene was inhibited by the localized activation of PKR. TRBP expression in HeLa cells complemented the growth and protein-synthesis defect of a vaccinia virus mutant lacking the expression of the dsRNA-binding protein E3L. These results implicate TRBP as a cellular regulatory protein that binds RNAs containing specific secondary structure(s) to mediate the inhibition of PKR activation and stimulate translation in a localized manner.
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PMID:TAR RNA-binding protein is an inhibitor of the interferon-induced protein kinase PKR. 751 77

The TAR sequence at the 5'-termini of all HIV-1 mRNA species forms a stable structure that is responsible for both transcriptional and translational regulation of HIV-1. Previously we and others reported that purified TAR RNA synthesized by in vitro transcription could activate two interferon-induced enzymes, the protein kinase (PKR) and 2-5A-synthetase. Because the PKR- and 2-5A-systems block protein synthesis initiation and induce RNA decay, respectively, these findings suggested mechanisms for the control of HIV-1 replication by the interferon system. To determine if contaminating dsRNA from in vitro transcription reactions was responsible for this effect, as suggested by Gunnery et al. 1990, (Proc., Natl. Acad. Sci. USA 87, 8687), we have reexamined these findings using chemically synthesized TAR (nucleotides +1 to +57). TAR RNA is shown here to have an intrinsic ability to activate PKR and 2-5A-synthetase. In contrast, a mutant form of TAR designed to have a disrupted secondary structure did not stimulate either enzyme. Chemically synthesized TAR mimicked other dsRNA species in its ability to activate and inhibit PKR at low and high RNA concentrations, respectively. HIV-1 TAT protein inhibited activation of PKR by HIV-1 TAR RNA suggesting an escape mechanism for the virus.
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PMID:HIV-1 TAR RNA has an intrinsic ability to activate interferon-inducible enzymes. 752 41

This review describes the structure and function of the double-stranded RNA-dependent protein kinase (PKR) and its interaction with RNA activators and inhibitors. The abilities of small virally-encoded RNAs such as VAI RNA of adenovirus, the Epstein-Barr virus encoded (EBER) RNAs and the Tat-responsive region RNA of HIV-1 to bind to and regulate PKR are reviewed, and the physiological implications of such regulation for the control of viral replication and cell growth are discussed. The potential effects on the activity of PKR of other proteins that bind double-stranded RNA and/or small viral and cellular RNAs are also considered.
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PMID:Regulation of the interferon-inducible eIF-2 alpha protein kinase by small RNAs. 753 82

Calcium depletion from the endoplasmic reticulum inhibits protein synthesis and correlates with increased phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2 alpha) by a mechanism that does not require ongoing protein synthesis. To elucidate whether protein synthesis inhibition requires eIF-2 alpha phosphorylation and whether eIF-2 alpha phosphorylation is mediated by the double-stranded RNA-dependent protein kinase (PKR), we studied protein synthesis in response to calcium depletion mediated by calcium ionophore A23187 in cell lines overexpressing wild-type eIF-2 alpha, a mutant eIF-2 alpha (S51A) that is resistant to phosphorylation, or a dominant negative mutant PKR (K296P in catalytic subdomain II). Expression of either mutant eIF-2 alpha or mutant PKR partially protected NIH3T3 cells from inhibition of protein synthesis upon A23187 treatment. In contrast, overexpression of wild-type PKR increased sensitivity to protein synthesis inhibition mediated by A23187 treatment. In a COS-1 monkey cell transient transfection system, increased eIF-2 alpha phosphorylation in response to A23187 treatment was inhibited by expression of the dominant negative PKR mutant. Overexpression of the PKR regulatory RNA binding domain, independent of the PKR catalytic domain, was sufficient to inhibit increased phosphorylation of eIF-2 alpha upon A23187 treatment. In addition, overexpression of the HIV TAR RNA binding protein also inhibited eIF-2 alpha phosphorylation upon A23187 treatment. Taken together, our data show that calcium depletion activates PKR to phosphorylate eIF-2 alpha, and this activation is likely mediated through the PKR RNA binding domain.
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PMID:Calcium depletion from the endoplasmic reticulum activates the double-stranded RNA-dependent protein kinase (PKR) to inhibit protein synthesis. 762 70

Active nuclear import of protein is controlled by nuclear localization signals (NLSs), but nuclear export is not understood well. Nuclear trafficking of the catalytic (C) subunit of cAMP-dependent protein kinase (cAPK) is critical for regulation of gene expression. The heat-stable inhibitor (PKl) of cAPK contains a nuclear export signal (NES) that triggers rapid, active net extrusion of the C-PKl complex from the nucleus. This NES (residues 35-49), fused or conjugated to heterologous proteins, was sufficient for rapid nuclear export. Hydrophobic residues were critical. The NES is a slightly weaker signal than the SV40 NLS. A sequence containing only residues 37-46, LALKLAGLDI, is also sufficient for nuclear export. This is an example of a protein-based NES having no obvious association with RNA. A similar sequence, LQLPPLERLTL, from Rev, an RNA-binding protein of HIV-1, also is an NES.
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PMID:Identification of a signal for rapid export of proteins from the nucleus. 763 36

Pentosan polysulfate, a polyanionic mucopolysaccharide, which has been shown to exert inhibitory effects on human immunodeficiency virus (HIV-I) replication, inhibited the activities of protein tyrosine kinases from lymphocytes (Jurkat cells) and rat lung in a concentration dependent manner. In addition, the autophosphorylation of p56lck, a lymphocyte associated protein tyrosine kinase from Jurkat cells was also inhibited by pentosan polysulfate (100 micrograms/ml). Furthermore, the activities of protein serine/threonine kinases such as Ca2+, phospholipid-dependent protein kinase (protein kinase C) from human platelets and the catalytic subunit of cAMP-dependent protein kinase from skeletal muscle were also inhibited by this mucopolysaccharide. However, the activity of phosphorylase kinase was not altered. The inhibition of rat lung protein tyrosine kinase was rapid and competitive with respect to ATP with an apparent Ki value of 5-20 micrograms/ml. These results suggest that the ability of pentosan polysulfate to inhibit various protein serine/threonine and tyrosine kinases may be one of the mechanisms by which this compound exerts its inhibitory effect of HIV-I replication.
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PMID:Pentosan polysulfate, a potent anti HIV and anti tumor agent, inhibits protein serine/threonine and tyrosine kinases. 768 45

B-HIV1, an oligoclone of immortalized cells derived from human peripheral B lymphocytes infected in vitro with the TIIIB isolate of HIV-1, produces low levels of replication-competent HIV when propagated in 1% serum, but increases production > or = 5-fold after phorbol myristate acetate (PMA) exposure. Electron microscopy reveals budding of mature virions from the plasma membrane, without concentration in endocytotic spaces. The PMA effect is specific for protein kinase activation, occurring upon exposure of B-HIV1 to those congeners capable of upregulating calcium and phospholipid dependent protein kinase C and susceptible to inhibition by the protein kinase antagonists H-7 and staurosporine. Induction could also be effected by another viral activator, 5-azacytidine, which acts via an alternate mechanism, and blocked by high doses of interferon-alpha but not the anti-viral nucleoside analog zidovudine (AZT). B-HIV1 may provide a model system for study of the regulation of chronic HIV infection in cells of B lymphocyte lineage.
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PMID:A model system for regulation of chronic HIV-1 infection in peripheral B lymphocytes. 769 May

Nucleolar protein B23 is a putative ribosome assembly factor with a high affinity for peptides containing nuclear localization signals (NLSs). The interactions of various NLS-containing peptides with two B23 isoforms (B23.1 and B23.2) were examined using equilibrium dialysis and Scatchard analyses. The KD for protein B23 binding to a peptide containing the SV40 T-antigen NLS sequence was approximately 1 microM with a stoichiometry of 1:1 (peptide:protein). No significant differences were seen between the two B23 isoforms in their affinities for any of the peptides tested. Binding by a reverse sequence SV40 T-NLS peptide showed a nonlinear Scatchard plot: this peptide was unable displace the correct sequence peptide, suggesting that the reverse sequence peptide binds to a different site on the protein. A peptide containing the sequence required for nucleolar localization of the HIV-1 Rev protein had an affinity for B23 approximately 10-fold greater than that of the SV40 T-NLS. However, with a sequence sufficient only for Rev location in the nucleoplasm, the affinity for B23 was diminished to a level between that of the longer Rev sequence and the SV40 T-NLS. In competition binding assays, the Rev NLS peptide was able to displace the SV40 T NLS, indicating that both peptides bind to the same site on protein B23. There was no detectable binding to protein B23 by a peptide containing the bipartite NLS of nucleoplasmin. Phosphorylation of protein B23 by casein kinase II enhanced its affinity for the SV40 T- and Rev-derived peptides approximately 2-fold.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Interaction of nucleolar protein B23 with peptides related to nuclear localization signals. 779 16

Efficient replication of human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) requires the virus transactivator proteins known as Tat. In order to understand the molecular mechanisms involved in Tat transactivation, it is essential to identify the cellular target(s) of the Tat activation domain. Using an in vitro kinase assay, we previously identified a cellular protein kinase activity, Tat-associated kinase (TAK), that specifically binds to the activation domains of Tat proteins. Here it is demonstrated that TAK fulfills the genetic criteria established for a Tat cofactor. TAK binds in vitro to the activation domains of the Tat proteins of HIV-1 and HIV-2 and the distantly related lentivirus equine infectious anemia virus but not to mutant Tat proteins that contain nonfunctional activation domains. In addition, it is shown that TAK is sensitive to dichloro-1-beta-D-ribofuranosylbenzimidazole, a nucleoside analog that inhibits a limited number of kinases and is known to inhibit Tat transactivation in vivo and in vitro. We have further identified an in vitro substrate of TAK, the carboxyl-terminal domain of the large subunit of RNA polymerase II. Phosphorylation of the carboxyl-terminal domain has been proposed to trigger the transition from initiation to active elongation and also to influence later stages during elongation. Taken together, these results imply that TAK is a very promising candidate for a cellular factor that mediates Tat transactivation.
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PMID:Lentivirus Tat proteins specifically associate with a cellular protein kinase, TAK, that hyperphosphorylates the carboxyl-terminal domain of the large subunit of RNA polymerase II: candidate for a Tat cofactor. 785 96


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