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The Journal of Biological Chemistry May 2019Human immunodeficiency virus-1 (HIV-1) Tat is degraded in the host cell both by proteasomal and lysosomal pathways, but the specific molecules that engage with Tat from...
Human immunodeficiency virus-1 (HIV-1) Tat is degraded in the host cell both by proteasomal and lysosomal pathways, but the specific molecules that engage with Tat from these pathways are not known. Because E3 ubiquitin ligases are the primary determinants of substrate specificity within the ubiquitin-dependent proteasomal degradation of proteins, we first sought to identify the E3 ligase associated with Tat degradation. Based on the intrinsic disordered nature of Tat protein, we focused our attention on host cell E3 ubiquitin ligase CHIP (C terminus of HSP70-binding protein). Co-transfection of Tat with a CHIP-expressing plasmid decreased the levels of Tat protein in a dose-dependent manner, without affecting the corresponding mRNA levels. Additionally, the rate of Tat protein degradation as measured by cycloheximide (CHX) chase assay was increased in the presence of CHIP. A CHIP mutant lacking the U-box domain, which is responsible for protein ubiquitination (CHIPΔU-box), was unable to degrade Tat protein. Furthermore, CHIP promoted ubiquitination of Tat by both WT as well as Lys-48-ubiquitin, which has only a single lysine residue at position 48. CHIP transfection in HIV-1 reporter TZM-bl cells resulted in decreased Tat-dependent HIV-1 long-terminal repeat (LTR) promoter transactivation as well as HIV-1 virion production. CHIP knockdown in HEK-293T cells using CRISPR-Cas9 led to higher virion production and enhanced Tat-mediated HIV-1 LTR promoter transactivation, along with stabilization of Tat protein. Together, these results suggest a novel role of host cell E3 ubiquitin ligase protein CHIP in regulating HIV-1 replication through ubiquitin-dependent degradation of its regulatory protein Tat.
Topics: Gene Knockdown Techniques; Gene Products, tat; HEK293 Cells; HIV-1; Humans; Proteasome Endopeptidase Complex; Proteolysis; Ubiquitin; Ubiquitin-Protein Ligases; Virion; Virus Replication
PubMed: 30885946
DOI: 10.1074/jbc.RA118.007257 -
Retrovirology May 2009The human immunodeficiency virus type 1 (HIV-1) trans-activator of transcription protein Tat is an important factor in viral pathogenesis. In addition to its function as... (Review)
Review
The human immunodeficiency virus type 1 (HIV-1) trans-activator of transcription protein Tat is an important factor in viral pathogenesis. In addition to its function as the key trans-activator of viral transcription, Tat is also secreted by the infected cell and taken up by neighboring cells where it has an effect both on infected and uninfected cells. In this review we will focus on the relationship between the structure of the Tat protein and its function as a secreted factor. To this end we will summarize some of the exogenous functions of Tat that have been implicated in HIV-1 pathogenesis and the impact of structural variations and viral subtype variants of Tat on those functions. Finally, since in some patients the presence of Tat-specific antibodies or CTL frequencies are associated with slow or non-progression to AIDS, we will also discuss the role of Tat as a potential vaccine candidate, the advances made in this field, and the importance of using a Tat protein capable of eliciting a protective or therapeutic immune response to viral challenge.
Topics: AIDS Vaccines; HIV-1; Humans; tat Gene Products, Human Immunodeficiency Virus
PubMed: 19467159
DOI: 10.1186/1742-4690-6-50 -
Neuropharmacology Oct 2016Depression and psychostimulant abuse are common comorbidities among humans with immunodeficiency virus (HIV) disease. The HIV regulatory protein TAT is one of multiple...
Depression and psychostimulant abuse are common comorbidities among humans with immunodeficiency virus (HIV) disease. The HIV regulatory protein TAT is one of multiple HIV-related proteins associated with HIV-induced neurotoxicity. TAT-induced dysfunction of dopamine and serotonin systems in corticolimbic brain areas may result in impaired reward function, thus, contributing to depressive symptoms and psychostimulant abuse. Transgenic mice with doxycycline-induced TAT protein expression in the brain (TAT+, TAT- control) show neuropathology resembling brain abnormalities in HIV+ humans. We evaluated brain reward function in response to TAT expression, nicotine and methamphetamine administration in TAT+ and TAT- mice using the intracranial self-stimulation procedure. We evaluated the brain dopamine and serotonin systems with high-performance liquid chromatography. The effects of TAT expression on delay-dependent working memory in TAT+ and TAT- mice using the operant delayed nonmatch-to-position task were also assessed. During doxycycline administration, reward thresholds were elevated by 20% in TAT+ mice compared with TAT- mice. After the termination of doxycycline treatment, thresholds of TAT+ mice remained significantly higher than those of TAT- mice and this was associated with changes in mesolimbic serotonin and dopamine levels. TAT+ mice showed a greater methamphetamine-induced threshold lowering compared with TAT- mice. TAT expression did not alter delay-dependent working memory. These results indicate that TAT expression in mice leads to reward deficits, a core symptom of depression, and a greater sensitivity to methamphetamine-induced reward enhancement. Our findings suggest that the TAT protein may contribute to increased depressive-like symptoms and continued methamphetamine use in HIV-positive individuals.
Topics: Animals; Central Nervous System Stimulants; Dose-Response Relationship, Drug; Gene Expression; Gene Products, tat; HIV-1; Male; Memory; Mice; Mice, Inbred C57BL; Mice, Transgenic; Reaction Time; Reward; Time Factors
PubMed: 27316905
DOI: 10.1016/j.neuropharm.2016.06.011 -
Proceedings of the National Academy of... Oct 1998The HIV-1 Tat protein is a potent chemoattractant for monocytes. We observed that Tat shows conserved amino acids corresponding to critical sequences of the chemokines,...
The HIV-1 Tat protein is a potent chemoattractant for monocytes. We observed that Tat shows conserved amino acids corresponding to critical sequences of the chemokines, a family of molecules known for their potent ability to attract monocytes. Synthetic Tat and a peptide (CysL24-51) encompassing the "chemokine-like" region of Tat induced a rapid and transient Ca2+ influx in monocytes and macrophages, analogous to beta-chemokines. Both monocyte migration and Ca2+ mobilization were pertussis toxin sensitive and cholera toxin insensitive. Cross-desensitization studies indicated that Tat shares receptors with MCP-1, MCP-3, and eotaxin. Tat was able to displace binding of beta-chemokines from the beta-chemokine receptors CCR2 and CCR3, but not CCR1, CCR4, and CCR5. Direct receptor binding experiments with the CysL24-51 peptide confirmed binding to cells transfected with CCR2 and CCR3. HIV-1 Tat appears to mimic beta-chemokine features, which may serve to locally recruit chemokine receptor-expressing monocytes/macrophages toward HIV producing cells and facilitate activation and infection.
Topics: Amino Acid Sequence; Calcium; Cells, Cultured; Chemokines; Chemotaxis, Leukocyte; Flow Cytometry; Gene Products, tat; HIV-1; Humans; Macrophages; Molecular Sequence Data; Monocytes; Peptide Fragments; Sequence Alignment; Sequence Homology, Amino Acid; Signal Transduction; T-Lymphocytes; tat Gene Products, Human Immunodeficiency Virus
PubMed: 9789057
DOI: 10.1073/pnas.95.22.13153 -
Protein Science : a Publication of the... Dec 1992
Review
Topics: Amino Acid Sequence; Bacterial Proteins; Base Sequence; Chemoreceptor Cells; Escherichia coli Proteins; Gene Products, tat; HIV; Membrane Proteins; Molecular Sequence Data; Nucleic Acid Conformation; Protein Conformation; RNA, Messenger; RNA, Viral; Receptors, Cell Surface; tat Gene Products, Human Immunodeficiency Virus
PubMed: 1304886
DOI: 10.1002/pro.5560011202 -
International Journal of Molecular... Aug 2020HIV transactivator protein (Tat) plays a pivotal role in viral replication through modulation of cellular transcription factors and transactivation of viral genomic...
HIV transactivator protein (Tat) plays a pivotal role in viral replication through modulation of cellular transcription factors and transactivation of viral genomic transcription. The effect of HIV-1 Tat on reverse transcription has long been described in the literature, however, that of HIV-2 is understudied. Sequence homology between Tat proteins of HIV-1 and 2 is estimated to be less than 30%, and the main difference lies within their N-terminal region. Here, we describe Y44A-inactivating mutation of HIV-2 Tat, studying its effect on capsid production, reverse transcription, and the efficiency of proviral transcription. Investigation of the mutation was performed using sequence- and structure-based in silico analysis and in vitro experiments. Our results indicate that the Y44A mutant HIV-2 Tat inhibited the activity and expression of RT (reverse transcriptase), in addition to diminishing Tat-dependent LTR (long terminal repeat) transactivation. These findings highlight the functional importance of the acidic domain of HIV-2 Tat in the regulation of reverse transcription and transactivation of the integrated provirions.
Topics: HIV Long Terminal Repeat; HIV-2; Mutation, Missense; Protein Domains; Reverse Transcription; Virus Replication; tat Gene Products, Human Immunodeficiency Virus
PubMed: 32824587
DOI: 10.3390/ijms21165907 -
The Journal of Biological Chemistry Apr 1997Human immunodeficiency virus type 1 (HIV-1) Tat protein is released from infected cells. Extracellular Tat enters the cell where it stimulates the transcriptional... (Comparative Study)
Comparative Study
Human immunodeficiency virus type 1 (HIV-1) Tat protein is released from infected cells. Extracellular Tat enters the cell where it stimulates the transcriptional activity of HIV-long terminal repeat (LTR) and of endogenous genes. Heparin modulates the angiogenic (Albini, A., Benelli, R., Presta, M., Rusnati, M., Ziche, M., Rubartelli, A., Paglialunga, G., Bussolino, F., and Noonan, D. (1996) Oncogene 12, 289-297) and transcriptional (Mann, D. A., and Frankel, A. D. (1991) EMBO J. 10, 1733-1739) activity of extracellular Tat. Here we demonstrate that heparin binds specifically to recombinant HIV-1 Tat produced as glutathione S-transferase (GST) fusion protein and immobilized on glutathione-agarose beads. Heparin and heparan sulfate (HS), but not dermatan sulfate, chondroitin sulfates A and C, hyaluronic acid, and K5 polysaccharide, competed with 3H-labeled heparin for binding to immobilized GST-Tat and inhibited HIV-LTR transactivation induced by extracellular GST-Tat. Selective 2-O-, 6-O-, total-O-desulfation, or N-desulfation/N-acetylation dramatically reduced the capacity of heparin to bind GST-Tat. Totally-O-desulfated and 2-O-desulfated heparins also showed a reduced capacity to inhibit the transactivating activity of GST-Tat. Very low molecular weight heparins showed a significant decrease in their capacity to bind GST-Tat and to inhibit its LTR transactivating activity when compared with conventional 13.6-kDa heparin. However, when 3.0-kDa heparin was affinity chromatographed on immobilized GST-Tat to isolate binding and non-binding subfractions, the Tat-bound fraction was >/=1,000 times more potent than the unbound fraction in inhibiting the transactivating activity of GST-Tat. The results demonstrate that Tat interacts in a size-dependent manner with heparin/HS and that high affinity Tat-heparin interaction requires at least some 2-O-, 6-O-, and N-positions to be sulfated. The Tat binding activity of the glycosaminoglycans tested correlates with their capacity to affect the transactivating activity of extracellular Tat, indicating the possibility to design specific heparin/HS-like structures with Tat-antagonist activity.
Topics: Binding Sites; Gene Products, tat; Glycosaminoglycans; HIV Long Terminal Repeat; HIV-1; Heparin; Heparitin Sulfate; Protein Binding; Recombinant Fusion Proteins; Structure-Activity Relationship; Sulfuric Acid Esters; Transcriptional Activation; tat Gene Products, Human Immunodeficiency Virus
PubMed: 9111037
DOI: 10.1074/jbc.272.17.11313 -
ENeuro 2020Despite the success of antiretroviral therapy in suppressing viral load, nearly half of the 37 million people infected with HIV experience cognitive and motor...
Despite the success of antiretroviral therapy in suppressing viral load, nearly half of the 37 million people infected with HIV experience cognitive and motor impairments, collectively classified as HIV-associated neurocognitive disorders (HAND). In the CNS, HIV-infected microglia release neurotoxic agents that act indirectly to elicit excitotoxic synaptic injury. HIV trans-activator of transcription (Tat) protein is one such neurotoxin that is thought to play a major role in the neuropathogenesis of HAND. The endocannabinoid (eCB) system provides on-demand neuroprotection against excitotoxicity, and exogenous cannabinoids attenuate neurotoxicity in animal models of HAND. Whether this neuroprotective system is altered in the presence of HIV is unknown. Here, we examined the effects of Tat on the eCB system in rat primary hippocampal cultures. Using whole-cell patch-clamp electrophysiology, we measured changes in retrograde eCB signaling following exposure to Tat. Treatment with Tat significantly reduced the magnitude of depolarization-induced suppression of excitation (DSE) in a graded manner over the course of 48 h. Interestingly, Tat did not alter this form of short-term synaptic plasticity at inhibitory terminals. The Tat-induced decrease in eCB signaling resulted from impaired CB receptor (CBR)-mediated presynaptic inhibition of glutamate release. This novel loss-of-function was particularly dramatic for low-efficacy agonists such as the eCB 2-arachidonoylglycerol (2-AG) and Δ-tetrahydrocannabinol (Δ-THC), the main psychoactive ingredient in marijuana. Our observation that HIV Tat decreases CBR function suggests that eCB-mediated neuroprotection may be reduced ; this effect of Tat may contribute to synaptodendritic injury in HAND.
Topics: Animals; Endocannabinoids; HIV Infections; Neuronal Plasticity; Rats; Receptor, Cannabinoid, CB1; Synapses; tat Gene Products, Human Immunodeficiency Virus
PubMed: 32471847
DOI: 10.1523/ENEURO.0119-20.2020 -
Retrovirology Feb 2005HIV infection and progression to AIDS is characterized by the depletion of T cells, which could be due, in part, to apoptosis mediated by the extra-cellular HIV-encoded...
BACKGROUND
HIV infection and progression to AIDS is characterized by the depletion of T cells, which could be due, in part, to apoptosis mediated by the extra-cellular HIV-encoded Tat protein as a consequence of Tat binding to tubulin. Microtubules are tubulin polymers that are essential for cell structure and division. Molecules that target microtubules induce apoptosis and are potent anti-cancer drugs. We studied the effect on tubulin polymerization of three Tat variants: Tat HxB2 and Tat Eli from patients who are rapid progressors (RP) and Tat Oyi from highly exposed but persistently seronegative (HEPS) patients. We compared the effect on tubulin polymerization of these Tat variants and peptides corresponding to different parts of the Tat sequence, with paclitaxel, an anti-cancer drug that targets microtubules.
RESULTS
We show that Tat, and specifically, residues 38-72, directly enhance tubulin polymerization. We demonstrate that Tat could also directly trigger the mitochondrial pathway to induce T cell apoptosis, as shown in vitro by the release of cytochrome c from isolated mitochondria.
CONCLUSIONS
These results show that Tat directly acts on microtubule polymerization and provide insights into the mechanism of T cell apoptosis mediated by extra-cellular Tat.
Topics: Animals; Antineoplastic Agents, Phytogenic; Apoptosis; Cell Line, Tumor; Cytochromes c; Gene Products, tat; HIV-1; Humans; Jurkat Cells; Microtubules; Mitochondria; Paclitaxel; Polymers; T-Lymphocytes; Tubulin; tat Gene Products, Human Immunodeficiency Virus
PubMed: 15691386
DOI: 10.1186/1742-4690-2-5 -
Viruses Nov 2023Tat, the trans-activator of transcription, is a multifunctional HIV-1 protein that can induce chronic inflammation and the development of somatic diseases in...
Tat, the trans-activator of transcription, is a multifunctional HIV-1 protein that can induce chronic inflammation and the development of somatic diseases in HIV-infected patients. Natural polymorphisms in Tat can impact the propagation of the inflammatory signal. Currently, Tat is considered an object for creating new therapeutic agents. Therefore, the identification of Tat protein features in various HIV-1 variants is a relevant task. The purpose of the study was to characterize the genetic variations of Tat-A6 in virus variants circulating in the Moscow Region. The authors analyzed 252 clinical samples from people living with HIV (PLWH) with different stages of HIV infection. Nested PCR for two fragments (, ) with subsequent sequencing, subtyping, and statistical analysis was conducted. The authors received 252 sequences for and 189 for HIV-1 sub-subtype A6 was identified in 250 samples. The received results indicated the features of Tat1-A6 in variants of viruses circulating in the Moscow Region. In PLWH with different stages of HIV infection, C31S in Tat1-A6 was detected with different occurrence rates. It was demonstrated that Tat2-A6, instead of a functional significant RGD motif, had a QRD motif. Herewith, G79R in Tat2-A6 was defined as characteristic amino acid substitution for sub-subtype A6. Tat2-A6 in variants of viruses circulating in the Moscow Region demonstrated high conservatism.
Topics: Humans; Gene Products, tat; Moscow; HIV-1; HIV Infections; Russia; tat Gene Products, Human Immunodeficiency Virus
PubMed: 38005889
DOI: 10.3390/v15112212