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)

TAK/P-TEFb is an elongation factor for RNA polymerase II-directed transcription that is thought to function by phosphorylating the C-terminal domain of the largest subunit of RNA polymerase II. TAK/P-TEFb is composed of Cdk9 and cyclin T and serves as the cellular cofactor for the human immunodeficiency virus transactivator Tat protein. In this study, we examined the subcellular distribution of Cdk9 and cyclin T1 using high resolution immunofluorescence microscopy and found that Cdk9 and cyclin T1 localized throughout the non-nucleolar nucleoplasm, with increased signal present at numerous foci. Both Cdk9 and cyclin T1 showed only limited colocalization with different phosphorylated forms of RNA polymerase II. However, significant colocalization with antibodies to several splicing factors that identify nuclear 'speckles' was observed for Cdk9 and especially for cyclin T1. The pattern of Cdk9 and cyclin T1 distribution was altered in cells treated with transcription inhibitors. Transient expression of cyclin T1 deletion mutants indicated that a region in the central portion of cyclin T1 is important for accumulation at speckles. Furthermore, cyclin T1 proteins that accumulated at speckles were capable of recruiting Cdk9 and the HIV Tat protein to this compartment in overexpression experiments. These results suggest that cyclin T1 functions to recruit its binding partners to nuclear speckles and raises the possibility that nuclear speckles are a site of TAK/P-TEFb function.
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PMID:The Cdk9 and cyclin T subunits of TAK/P-TEFb localize to splicing factor-rich nuclear speckle regions. 1128 25

Progress in developing a small animal model of human immunodeficiency virus type 1 (HIV-1) disease would greatly facilitate studies of transmission, pathogenesis, host immune responses, and antiviral strategies. In this study, we have explored the potential of rats as a susceptible host. In a single replication cycle, rat cell lines Rat2 and Nb2 produced infectious virus at levels 10- to 60-fold lower than those produced by human cells. Rat-derived cells supported substantial levels of early HIV-1 gene expression, which was further enhanced by overexpression of human cyclin T1. Rat cells displayed quantitative, qualitative, and cell-type-specific limitations in the late phase of the HIV-1 replication cycle including relative expression levels of HIV-1 Gag proteins, intracellular Gag processing, and viral egress. Nb2 cells were rendered permissive to HIV-1 R5 viruses by coexpression of human CD4 and CCR5, indicating that the major restriction on HIV-1 replication was at the level of cellular entry. We also found that primary rat lymphocytes, macrophages, and microglia expressed considerable levels of early HIV-1 gene products following infection with pseudotyped HIV-1. Importantly, primary rat macrophages and microglia, but not lymphocytes, also expressed substantial levels of HIV-1 p24 CA and produced infectious virions. Collectively, these results identify the rat as a promising candidate for a transgenic small animal model of HIV-1 infection and highlight pertinent cell-type-specific restrictions that are features of this species.
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PMID:Susceptibility of rat-derived cells to replication by human immunodeficiency virus type 1. 1148 51

SIVsm, the simian immunodeficiency virus that naturally infects sooty mangabeys in West Africa, is the closest lentiviral relative of human immunodeficiency virus type 2 (HIV-2). To determine the genetic characteristics of SIVsm in its natural host, we sequenced the full-length genome of SIVsmSL92b, a primary isolate obtained from a pet sooty mangabey in Sierra Leone. SIVsmSL92b proved to be the most divergent member of the HIV-2/SIVsm lineage found thus far, having as much as 35% nucleotide divergence from other HIV-2 genomes. A phylogenetic association between SIVsmSL92b and HIV-2 PA subtype E, which had been previously revealed by the analysis of partial gag sequences, was extended to the pol gene. SIVsmSL92b showed several divergent features, including a short Tat protein of 104 residues and an atypical TAR structure. Specifically, only one of the duplicate TAR elements contained the conserved hexanucleotide loop sequence CUGGGX important for Tat-cyclin T1 binding. These features suggested that the mechanism of SIVsmSL92b Tat and TAR interaction differed from that described for HIV-2. Taken together, these findings indicated that the structural diversity within the HIV-2/SIVsm lineage was greater than previously appreciated.
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PMID:A divergent simian immunodeficiency virus from sooty mangabey with an atypical Tat-TAR structure. 1152 85

Regulation of HIV-1 gene expression by the viral Tat transactivator is a critical step in the viral life cycle. Tat acts as a highly unusual transcription factor that interacts with a stem-loop RNA structure (TAR) found at the 5' end of all viral transcripts. There, it induces a modification of chromatin at the HIV-1 long terminal repeat (LTR) promoter and stimulates the recruitment of elongation-competent RNA polymerase II complexes capable of processive transcription. Increase of transcriptional elongation is the consequence of the interaction of Tat with cyclin T1, the cyclin component of CDK9, which phosphorylates the carboxy-terminal domain of RNA polymerase II to enhance its processivity. Tat-induced transcriptional activation of the LTR promoter is concomitant with recruitment of the transcriptional coactivators p300 and the highly homologue cAMP-responsive transcription factor binding protein (CBP). These large proteins act at the level of transcriptional initiation by bridging the basal transcription machinery with specific transcriptional activators. Furthermore, p300/CBP are histone acetyl-transferases capable of modulating the interaction of nucleosomes with DNA and with chromatin remodeling complexes. Besides histones, Tat itself is a substrate for the enzymatic activity of p300/CBP and of the associated factor P/CAF, suggesting a regulatory role of acetylation on the protein itself. Devising a unifying model for LTR activation that includes activities of Tat at the levels of both transcriptional initiation and transcriptional elongation is a challenging task at this moment. Nevertheless, protein localization studies indicate that both cyclin T1 and p300/CBP co-localize in specific subnuclear compartments, thus suggesting participation of both proteins in the formation of multimolecular complexes governing coordinated steps of transcriptional activation.
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PMID:Multiple modes of transcriptional regulation by the HIV-1 Tat transactivator. 1154 19

Tat stimulates human immunodeficiency virus, type 1 (HIV-1), transcription elongation by recruitment of the human transcription elongation factor P-TEFb, consisting of CDK9 and cyclin T1, to the TAR RNA structure. It has been demonstrated further that CDK9 phosphorylation is required for high affinity binding of Tat/P-TEFb to the TAR RNA structure and that the state of P-TEFb phosphorylation may regulate Tat transactivation. We now demonstrate that CDK9 phosphorylation is uniquely regulated in the HIV-1 preinitiation and elongation complexes. The presence of TFIIH in the HIV-1 preinitiation complex inhibits CDK9 phosphorylation. As TFIIH is released from the elongation complex between +14 and +36, CDK9 phosphorylation is observed. In contrast to the activity in the "soluble" complex, phosphorylation of CDK9 is increased by the presence of Tat in the transcription complexes. Consistent with these observations, we have demonstrated that purified TFIIH directly inhibits CDK9 autophosphorylation. By using recombinant TFIIH subcomplexes, our results suggest that the XPB subunit of TFIIH is responsible for this inhibition of CDK9 phosphorylation. Interestingly, our results further suggest that the phosphorylated form of CDK9 is the active kinase for RNA polymerase II carboxyl-terminal domain phosphorylation.
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PMID:TFIIH inhibits CDK9 phosphorylation during human immunodeficiency virus type 1 transcription. 1157 68

Combinations of cytokines are known to reactivate transcription and replication of latent human immunodeficiency virus type 1 (HIV-1) proviruses in resting CD4(+) T lymphocytes isolated from infected individuals. Transcription of the HIV-1 provirus by RNA polymerase II is strongly stimulated by the viral Tat protein. Tat function is mediated by a cellular protein kinase known as TAK (cyclin T1/P-TEFb) that is composed of Cdk9 and cyclin T1. We have found that treatment of peripheral blood lymphocytes and purified resting CD4(+) T lymphocytes with the combination of interleukin-2 (IL-2), IL-6, and tumor necrosis factor alpha resulted in an increase in Cdk9 and cyclin T1 protein levels and an increase in TAK enzymatic activity. The cytokine induction of TAK in resting CD4(+) T lymphocytes did not appear to require proliferation of lymphocytes. These results suggest that induction of TAK by cytokines secreted in the microenvironment of lymphoid tissue may be involved in the reactivation of HIV-1 in CD4(+) T lymphocytes harboring a latent provirus.
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PMID:Induction of TAK (cyclin T1/P-TEFb) in purified resting CD4(+) T lymphocytes by combination of cytokines. 1168 14

We report that p160 nuclear receptor coactivators potentiate the transactivating activity of Tat, the most potent virally encoded transactivator of HIV-1. One of the p160 proteins (GRIP1) is tethered to the HIV-1 long terminal repeat (LTR) through kappaB-responsive elements, most likely via NF-kappaB, with which it also associates through its coactivator motifs (LXXLL motifs, "NR boxes"). Indeed, the Tat-stimulated kappaB-defective HIV-1 LTR had a markedly impaired response to GRIP1, whereas NR box-defective GRIP1 proteins lost part of their Tat coactivator effect on the HIV-1 LTR. Through its N-terminal basic helix-loop-helix and C-terminal domains, GRIP1 binds to the N-terminal region of Tat and to the host cell protein cyclin T1, respectively, which is normally complexed with CDK9 as P-TEFb. Thus, NF-kappaB is crucial for tethering p160 coactivator molecules to the HIV-1 LTR, allowing full activation of this promoter by Tat. Interestingly, cotransfection of Tat, GRIP1, and cyclin T1 enhanced not only the activity of the HIV-1 LTR, but also the glucocorticoid receptor-mediated stimulation of the mouse mammary tumor virus (MMTV) promoter, suggesting that Tat can also attract the P-TEFb complex to the MMTV LTR through GRIP1. Thus, it appears that the coactivator complexes of the HIV-1 and MMTV LTRs both include p160 coactivators and use similar coactivator and elongation complexes for their transcription. Tat may function as an adaptor molecule, efficiently stimulating the processes of transcription initiation and elongation through potentiation of the coupling of p160 coactivators and the P-TEFb complex.
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PMID:Nuclear receptor coactivator p160 proteins enhance the HIV-1 long terminal repeat promoter by bridging promoter-bound factors and the Tat-P-TEFb complex. 1170 62

The human positive transcription elongation factor P-TEFb, consisting of a CDK9/cyclin T1 heterodimer, functions as both a general and an HIV-1 Tat-specific transcription factor. P-TEFb activates transcription by phosphorylating RNA polymerase (Pol) II, leading to the formation of processive elongation complexes. As a Tat cofactor, P-TEFb stimulates HIV-1 transcription by interacting with Tat and the transactivating responsive (TAR) RNA structure located at the 5' end of the nascent viral transcript. Here we identified 7SK, an abundant and evolutionarily conserved small nuclear RNA (snRNA) of unknown function, as a specific P-TEFb-associated factor. 7SK inhibits general and HIV-1 Tat-specific transcriptional activities of P-TEFb in vivo and in vitro by inhibiting the kinase activity of CDK9 and preventing recruitment of P-TEFb to the HIV-1 promoter. 7SK is efficiently dissociated from P-TEFb by treatment of cells with ultraviolet irradiation and actinomycin D. As these two agents have been shown to significantly enhance HIV-1 transcription and phosphorylation of Pol II (refs 6,7,8), our data provide a mechanistic explanation for their stimulatory effects. The 7SK/P-TEFb interaction may serve as a principal control point for the induction of cellular and HIV-1 viral gene expression during stress-related responses. Our studies demonstrate the involvement of an snRNA in controlling the activity of a Cdk-cyclin kinase.
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PMID:The 7SK small nuclear RNA inhibits the CDK9/cyclin T1 kinase to control transcription. 1171 32

In addition to its stimulatory effect on transcription of the HIV-1 LTR, the early protein of HIV-1, Tat, exhibits detrimental effects on the CNS by deregulating the expression of several cytokines and immunomodulators including TNFalpha. Activation of the viral promoter by Tat requires several cellular proteins including cyclin T1 and its partner, cdk9, which upon association with the TAR sequence of the LTR, forms a complex that enhances the activity of RNA polymerase II. Here, we examined the involvement of cyclin T1/cdk9 in Tat-mediated transcriptional activation of the TNFalpha promoter which has no TAR sequence. Results from transfection of human astrocytic cells revealed that both cyclin T1 and cdk9 stimulate the basal promoter activity of TNFalpha, although the level of such activation is decreased in the presence of Tat. Ectopic expression of Puralpha, a brain-derived regulatory protein which binds to Tat, enhanced the basal level of TNFalpha transcription, yet exerted a negative effect on the level of Tat activation of the TNFalpha promoter. The antagonistic effect of Puralpha and Tat upon the TNFalpha promoter was diminished in the presence of cyclin T1 and cdk9, suggesting cooperativity of Puralpha with cyclin T1 and cdk9 in Tat activation of the TNFalpha promoter. Results from protein-protein binding studies showed the interaction of Puralpha with both cyclin T1 and cdk9 through distinct domains of Puralpha which are in juxtaposition with each other. Interestingly, the site for cyclin T1 binding within Puralpha is adjacent to the region which is important for Tat/Puralpha association. In light of these observations, we propose a model which ascribes a bridging role for Puralpha in assembling Tat, cyclin T1, and cdk9 around the promoter region of TAR-negative genes such as TNFalpha, which is responsive to Tat activation.
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PMID:Functional interaction between cyclin T1/cdk9 and Puralpha determines the level of TNFalpha promoter activation by Tat in glial cells. 1173 Sep 34

Murine cells do not support efficient assembly and release of human immunodeficiency virus type 1 (HIV-1) virions. HIV-1-infected mouse cells that express transfected human cyclin T1 synthesize abundant Gag precursor polyprotein, but inefficiently assemble and release virions. This assembly defect may result from a failure of the Gag polyprotein precursor to target to the cell membrane. Plasma membrane targeting of the precursor is mediated by the amino-terminal region of polyprotein. To compensate for the assembly block, we substituted the murine leukemia virus matrix coding sequences into an infectious HIV-1 clone. Transfection of murine fibroblasts expressing cyclin T1 with the chimeric proviruses resulted in viruses that were efficiently assembled and released. Chimeric viruses, in which the cytoplasmic tail of the transmembrane subunit, gp41, was truncated to prevent potential interference between the envelope glycoprotein and the heterologous matrix, could infect human and murine cells. They failed to further replicate in the murine cells, but replicated with delayed kinetics in human MT-4 cells. These findings may be useful for establishing a murine model for HIV-1 replication.
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PMID:Chimeric human immunodeficiency virus type 1 containing murine leukemia virus matrix assembles in murine cells. 1173 11


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