Distinct transcriptional pathways of TAR-dependent and TAR-independent human immunodeficiency virus type-1 transactivation by Tat

Association between HIV Serostatus and premalignant cervical lesions among women attending a cervical cancer screening clinic at a tertiary care facility in southwestern Uganda: a comparative cross-sectional study

BACKGROUND

Uganda has approximately 1.2 million people aged 15-64 years living with human immunodeficiency virus (HIV). Previous studies have shown a higher prevalence of premalignant cervical lesions among HIV-positive women than among HIV-negative women. Additionally, HIV-infected women are more likely to have human papilloma virus (HPV) infection progress to cancer than women not infected with HIV. We determined the prevalence of premalignant cervical lesions and their association with HIV infection among women attending a cervical cancer screening clinic at Mbarara Regional Referral Hospital (MRRH) in southwestern Uganda.

METHODS

We conducted a comparative cross-sectional study of 210 women aged 22-65 years living with HIV and 210 women not living with HIV who were systematically enrolled from March 2022 to May 2022. Participants were subjected to a structured interviewer-administered questionnaire to obtain their demographic and clinical data. Additionally, Papanicolaou smears were obtained for microscopy to observe premalignant cervical lesions. Multivariate logistic regression was performed to determine the association between HIV status and premalignant cervical lesions.

RESULTS

The overall prevalence of premalignant cervical lesions in the study population was 17% (n = 72; 95% C.I: 14.1-21.4), with 23% (n = 47; 95% C.I: 17.8-29.5) in women living with HIV and 12% (n = 25; 95% C.I: 8.2-17.1) in women not living with HIV (p < 0.003). The most common premalignant cervical lesions identified were low-grade squamous intraepithelial lesions (LSIL) in both women living with HIV (74.5%; n = 35) and women not living with HIV (80%; n = 20). HIV infection was significantly associated with premalignant lesions (aOR: 2.37, 95% CI: 1.27-4.42; p = 0.007).

CONCLUSION

Premalignant cervical lesions, particularly LSILs, were more common in HIV-positive women than in HIV-negative women, highlighting the need to strengthen the integration of cervical cancer prevention strategies into HIV care programs.

Bcl-2 Antagonist Obatoclax Reactivates Latent HIV-1 via the NF-κB Pathway and Induces Latent Reservoir Cell Apoptosis in Latently Infected Cells

The implementation of combined antiretroviral therapy (cART) has rendered HIV-1 infection clinically manageable and efficiently improves the quality of life for patients with AIDS. However, the persistence of a latent HIV-1 reservoir is a major obstacle to achieving a cure for AIDS. A "shock and kill" strategy aims to reactivate latent HIV and then kill it by the immune system or cART drugs. To date, none of the LRA candidates has yet demonstrated effectiveness in achieving a promising functional cure. Interestingly, the phosphorylation and activation of antiapoptotic Bcl-2 protein induce resistance to apoptosis during HIV-1 infection and the reactivation of HIV-1 latency in central memory CD4+ T cells from HIV-1-positive patients. Therefore, a Bcl-2 antagonist might be an effective LRA candidate for HIV-1 cure. In this study, we reported that a pan-Bcl-2 antagonist obatoclax induces HIV-1 reactivation in latently infected cell lines in vitro and in PBMCs/CD4+ T cells of HIV-infected individuals ex vivo. Obatoclax promotes HIV-1 transcriptional initiation and elongation by regulating the NF-κB pathway. Obatoclax activates caspase 8 and does not induce the phosphorylation of the antiapoptotic protein Bcl-2 in latent HIV-1 infected cell lines. More importantly, it preferentially induces apoptosis in latently infected cells. In addition, obatoclax exhibited potent anti-HIV-1 activity on target cells. The abilities to reactivate latent HIV-1 reservoirs, inhibit HIV-1 infection, and induce HIV-1 latent cell apoptosis make obatoclax worth investigating for development as an ideal LRA for use in the "shock and kill" approach.

Human Immunodeficiency Virus Type-1 (HIV-1) Transcriptional Regulation, Latency and Therapy in the Central Nervous System

The central nervous system (CNS) is highly compartmentalized and serves as a specific site of human immunodeficiency virus (HIV) infection. Therefore, an understanding of the cellular populations that are infected by HIV or that harbor latent HIV proviruses is imperative in the attempts to address cure strategies, taking into account that HIV infection and latency in the CNS may differ considerably from those in the periphery. HIV replication in the CNS is reported to persist despite prolonged combination antiretroviral therapy due to the inability of the current antiretroviral drugs to penetrate and cross the blood–brain barrier. Consequently, as a result of sustained HIV replication in the CNS even in the face of combination antiretroviral therapy, there is a high incidence of HIV-associated neurocognitive disorders (HAND). This article, therefore, provides a comprehensive review of HIV transcriptional regulation, latency, and therapy in the CNS.

Genetic variation and function of the HIV-1 Tat protein

Human immunodeficiency virus type 1 (HIV-1) encodes a transactivator of transcription (Tat) protein, which has several functions that promote viral replication, pathogenesis, and disease. Amino acid variation within Tat has been observed to alter the functional properties of Tat and, depending on the HIV-1 subtype, may produce Tat phenotypes differing from viruses' representative of each subtype and commonly used in in vivo and in vitro experimentation. The molecular properties of Tat allow for distinctive functional activities to be determined such as the subcellular localization and other intracellular and extracellular functional aspects of this important viral protein influenced by variation within the Tat sequence. Once Tat has been transported into the nucleus and becomes engaged in transactivation of the long terminal repeat (LTR), various Tat variants may differ in their capacity to activate viral transcription. Post-translational modification patterns based on these amino acid variations may alter interactions between Tat and host factors, which may positively or negatively affect this process. In addition, the ability of HIV-1 to utilize or not utilize the transactivation response (TAR) element within the LTR, based on genetic variation and cellular phenotype, adds a layer of complexity to the processes that govern Tat-mediated proviral DNA-driven transcription and replication. In contrast, cytoplasmic or extracellular localization of Tat may cause pathogenic effects in the form of altered cell activation, apoptosis, or neurotoxicity. Tat variants have been shown to differentially induce these processes, which may have implications for long-term HIV-1-infected patient care in the antiretroviral therapy era. Future studies concerning genetic variation of Tat with respect to function should focus on variants derived from HIV-1-infected individuals to efficiently guide Tat-targeted therapies and elucidate mechanisms of pathogenesis within the global patient population.

Cellular RelB interacts with the transactivator Tat and enhance HIV-1 expression

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) Tat protein plays an essential role in HIV-1 gene transcription. Tat transactivates HIV-1 long terminal repeat (LTR)-directed gene expression through direct interactions with the transactivation-responsive region (TAR) element and other cis elements in the LTR. The TAR-independent Tat-mediated LTR transactivation is modulated by several host factors, but the mechanism is not fully understood.

RESULTS

Here, we report that Tat interacts with the Rel homology domain of RelB through its core region. Furthermore, RelB significantly increases Tat-mediated transcription of the HIV-1 LTR and viral gene expression, which is independent of the TAR. Both Tat and RelB are recruited to the HIV-1 promoter, of which RelB facilitates the recruitment of Tat to the viral LTR. The NF-κB elements are key to the accumulation of Tat and RelB on the LTR. Knockout of RelB reduces the accumulation of RNA polymerase II on the LTR, and decreases HIV-1 gene transcription. Together, our data suggest that RelB contributes to HIV-1 transactivation.

CONCLUSIONS

Our results demonstrate that RelB interacts with Tat and enhances TAR-independent activation of HIV-1 LTR promoter, which adds new insights into the multi-layered mechanisms of Tat in regulating the gene expression of HIV-1.

Tat predominantly associates with host promoter elements in HIV-1-infected T-cells - regulatory basis of transcriptional repression of c-Rel

HIV-1 Tat is a multifunctional regulatory protein that, in addition to its primary function of transactivating viral transcription, also tends to modulate cellular gene expression, for which the molecular mechanism remains to be clarified. We have reported earlier nuclear factor kappa B (NFκB) enhancer binding activity of Tat and proposed this DNA binding activity as a possible molecular basis for Tat-mediated regulation of cellular gene expression in infected cells. In the present study, we analyzed the genome-wide occupancy of Tat protein on host cell chromatin in HIV-1-infected T-cells to investigate a potential role of Tat on cellular gene expression. The results obtained identify a spectrum of binding sites of Tat protein on the chromatin and reveal that Tat is also recruited on a number of cellular gene promoters in HIV-1-infected T-cells, indicating its possible involvement in the regulation of gene expression of such cellular genes. Tat was identified as a repressor of one such validated gene, c-Rel, because it downregulates the expression of c-Rel in both Tat expressing and HIV-1-infected T-cells. The results also show that Tat downregulates c-Rel promoter activity by interacting with specific NFκB sites on the c-Rel promoter, thus providing a molecular basis of Tat-mediated regulation of cellular gene expression. Thus, in the present study, we have not only identified recruitment sites of Tat on the chromatin in HIV-1-infected T-cells, but also report for the first time that c-Rel is downregulated in HIV-1-infected cells specifically by interaction of Tat with NFκB binding sites on the promoter.

The presence of HIV-1 Tat protein second exon delays fas protein-mediated apoptosis in CD4+ T lymphocytes: a potential mechanism for persistent viral production

HIV-1 replication is efficiently controlled by the regulator protein Tat (101 amino acids) and codified by two exons, although the first exon (1-72 amino acids) is sufficient for this process. Tat can be released to the extracellular medium, acting as a soluble pro-apoptotic factor in neighboring cells. However, HIV-1-infected CD4(+) T lymphocytes show a higher resistance to apoptosis. We observed that the intracellular expression of Tat delayed FasL-mediated apoptosis in both peripheral blood lymphocytes and Jurkat cells, as it is an essential pathway to control T cell homeostasis during immune activation. Jurkat-Tat cells showed impairment in the activation of caspase-8, deficient release of mitochondrial cytochrome c, and delayed activation of both caspase-9 and -3. This protection was due to a profound deregulation of proteins that stabilized the mitochondrial membrane integrity, such as heat shock proteins, prohibitin, or nucleophosmin, as well as to the up-regulation of NF-κB-dependent anti-apoptotic proteins, such as BCL2, c-FLIPS, XIAP, and C-IAP2. These effects were observed in Jurkat expressing full-length Tat (Jurkat-Tat101) but not in Jurkat expressing the first exon of Tat (Jurkat-Tat72), proving that the second exon, and particularly the NF-κB-related motif ESKKKVE, was necessary for Tat-mediated protection against FasL apoptosis. Accordingly, the protection exerted by Tat was independent of its function as a regulator of both viral transcription and elongation. Moreover, these data proved that HIV-1 could have developed strategies to delay FasL-mediated apoptosis in infected CD4(+) T lymphocytes through the expression of Tat, thus favoring the persistent replication of HIV-1 in infected T cells.

Transition step during assembly of HIV Tat:P-TEFb transcription complexes and transfer to TAR RNA

Transcription factors regulate eukaryotic RNA polymerase II (Pol II) activity by assembling and remodeling complexes at multiple steps in the transcription cycle. In HIV, we previously proposed a two-step model where the viral Tat protein first preassembles at the promoter with an inactive P-TEFb:7SK snRNP complex and later transfers P-TEFb to TAR on the nascent transcript, displacing the inhibitory snRNP and resulting in Pol II phosphorylation and stimulation of elongation. It is unknown how the Tat:P-TEFb complex transitions to TAR to activate the P-TEFb kinase. Here, we show that P-TEFb artificially recruited to the nascent transcript is not competent for transcription but rather remains inactive due to its assembly with the 7SK snRNP. Tat supplied in trans is able to displace the kinase inhibitor Hexim1 from the snRNP and activate P-TEFb, thereby uncoupling Tat requirements for kinase activation and TAR binding. By combining comprehensive mutagenesis of Tat with multiple cell-based reporter assays that probe the activity of Tat in different arrangements, we genetically defined a transition step in which preassembled Tat:P-TEFb complexes switch to TAR. We propose that a conserved network of residues in Tat has evolved to control this transition and thereby switch the host elongation machinery to viral transcription.

The HIV-1 Tat protein has a versatile role in activating viral transcription

It is generally acknowledged that the Tat protein has a pivotal role in HIV-1 replication because it stimulates transcription from the viral long terminal repeat (LTR) promoter by binding to the TAR hairpin in the nascent RNA transcript. However, a multitude of additional Tat functions have been suggested. The importance of these functions is difficult to assess in replication studies with Tat-mutated HIV-1 variants because of the dominant negative effect on viral gene expression. We therefore used an HIV-1 construct that does not depend on the Tat-TAR interaction for transcription to reevaluate whether or not Tat has a second essential function in HIV-1 replication. This HIV-rtTA variant uses the incorporated Tet-On gene expression system for activation of transcription and replicates efficiently upon complete TAR deletion. Here we demonstrated that Tat inactivation does nevertheless severely inhibit replication. Upon long-term culturing, the Tat-minus HIV-rtTA variant acquired mutations in the U3 region that improved promoter activity and reestablished replication. We showed that in the absence of a functional TAR, Tat remains important for viral transcription via Sp1 sequence elements in the U3 promoter region. Substitution of these U3 sequences with nonrelated promoter elements created a virus that replicates efficiently without Tat in SupT1 T cells. These results indicate that Tat has a versatile role in transcription via TAR and U3 elements. The results also imply that Tat has no other essential function in viral replication in cultured T cells.

Cross-interaction between JC virus agnoprotein and human immunodeficiency virus type 1 (HIV-1) Tat modulates transcription of the HIV-1 long terminal repeat in glial cells

The human polyomavirus JC virus (JCV) is the causative agent of the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML), which is commonly seen in AIDS patients. The bicistronic viral RNA, which is transcribed at the late phase of infection, is responsible for expressing the viral capsid proteins and a small regulatory protein, agnoprotein. Immunohistochemical analysis of brain tissue from subjects with AIDS/PML revealed colocalization of the human immunodeficiency virus type 1 (HIV-1) transactivator, Tat, and JCV agnoprotein in nucleus and cytoplasm of "bizarre" astrocytes. In accord with this observation, we detected the copresence of agnoprotein and Tat in human astrocytes upon infection with JCV and HIV-1 or in astrocytic cells expressing these proteins after transfection. Interestingly, results from infection of human astrocytes with HIV-1 and JCV showed a decrease in the level of HIV-1 replication in cells that are coinfected with JCV. Conversely, a slight increase in the level of JCV replication was observed in the presence of HIV-1. The copresence of JCV and HIV-1 in astrocytes prompted us to investigate the possible cross-interaction of agnoprotein with Tat and its impact on HIV-1 gene transcription. Our results demonstrate that agnoprotein through its N-terminal domain associates with Tat and the interaction causes the suppression of Tat-mediated enhancement of HIV-1 promoter activity in these cells. Results from RNA and protein binding assays showed that agnoprotein can inhibit the association of Tat with its target RNA sequence, TAR, and with cyclin T1. Furthermore, agnoprotein is able to interfere with cross-interaction of Tat with the p65 subunit of NF-kappaB and Sp1, whose functions are critical for Tat activation of the long terminal repeat. These observations unravel a new pathway for the molecular interaction of these two viruses in biologically relevant cells in the brains of AIDS/PML patients.

HIV-1 Tat directly binds to NFkappaB enhancer sequence: role in viral and cellular gene expression

HIV-1 Tat protein reprograms cellular gene expression of infected as well as uninfected cells apart from its primary function of transactivating HIV-1 long terminal repeat (LTR) promoter by binding to a nascent RNA stem-loop structure known as the transactivator response region (TAR). Tat also induces chromatin remodeling of proviral LTR-mediated gene expression by recruiting histone acetyl transferases to the chromatin, which results in histone acetylation. Furthermore several studies have shown convincing evidence that Tat can transactivate HIV-1 gene expression in the absence of TAR, the molecular mechanism of which remains to be elucidated. Here we show a direct interaction of Tat with nuclear factor kappa B (NFkappaB) enhancer, a global regulatory sequence for many cellular genes both in vitro and in vivo. This interaction not only provides a novel molecular basis to explain TAR-independent transactivation in HIV-1, but also points toward the potential mechanism of Tat- mediated modulation of cellular genes.

Multiple effects of HIV-1 trans-activator protein on the pathogenesis of HIV-1 infection

The HIV-1 trans-activator (Tat) protein is proposed as an important factor in the complex HIV-induced pathogenesis of AIDS. In this paper, multiple effects of this viral protein are described. Originally discovered as an intracellular activator of HIV-1 transcription, Tat was found to regulate viral reverse transcription as well. Trans-activator was found to be secreted by HIV-infected cells and taken up by neighbouring cells. In this way, Tat is able to affect both infected and uninfected cells. Intracellularly, Tat can deregulate the expression of several heterologous cellular and viral genes. Extracellular Tat can contribute to the spreading of HIV-1 and immunosuppression of uninfected cells. Finally, there is evidence that exogenous Tat is involved in AIDS-associated pathologies such as Kaposi's sarcoma and HIV-associated dementia. These capacities together accelerate the progression towards AIDS and make Tat an interesting candidate as a constituent of an anti-AIDS vaccine.

Identification of a novel protein from glial cells based on its ability to interact with NF-?B subunitsr

Nuclear factor kappaB (NF-kappaB) represents a family of inducible DNA-binding transcription factors whose activity is critical for expression of the HIV-1 genome in a broad range of cells. In addition to its interaction with the kappaB DNA sequence, the association of NF-kappaB subunits with other cellular proteins plays an important role in stimulation of HIV-1 gene transcription in astrocytic cells. Here, we utilized a yeast two-hybrid system to screen a cDNA library from a human astrocytic cell line and were able to isolate a partial cDNA belonging to a gene with an open reading frame of 1,871 amino acid residues which binds to both the p50 and p65 subunits of NF-kappaB. This gene, named NF-kappaB-binding protein (NFBP) is located on chromosome 10q24.2-25.1 and hybridized to a single transcript of nearly 6 kb in size. It is localized to the nucleus, specifically the nucleolus of cells. Extensive computer analysis was performed with the sequence of the full length NFBP and significant homology was found between NFBP, and yeast and mouse proteins. A discussion of the potential roles of NFBP in normal and viral infected cells is included.

Intracellular human immunodeficiency virus Tat expression in astrocytes promotes astrocyte survival but induces potent neurotoxicity at distant sites via axonal transport

The human immunodeficiency virus (HIV)-Tat protein has been implicated in the neuropathogenesis of HIV infection. However, its role in modulating astroglial-neuronal relationships is poorly understood. Astrocyte infection with HIV has been associated with rapid progression of dementia. We thus initially transfected astrocytes with HIV proviral DNA and confirmed Tat production in these cells. Subsequently, using stably Tat-producing asytocyte cell lines, we observed that Tat promoted astrocyte survival by causing a prominent antioxidant effect and resistance to cell injury in these cells. Tat was released extracellularly where it could be taken up by other cells. Tat remained functionally active following uptake and caused long terminal repeat (LTR) transactivation in lymphocytic and astrocytic cell lines. Tat released from astrocytes caused mitochondrial dysfunction, trimming of neurites, and cell death in neurons. Tat neurotoxicity was attenuated by anti-Tat antibodies, kynurenate or heparan sulfate. The neurotoxic effects of Tat were caused at concentrations lower than that needed to cause LTR transactivation. When Tat-expressing cells were injected into the rat dentate gyrus, Tat was taken up by granule cells and transported along neuronal pathways to the CA3 region where it caused glial cell activation and neurotoxicity. The arginine-rich domain of Tat was essential for both the LTR transactivation and the neurotoxic properties of Tat. Thus HIV-Tat is a potent neurotoxin that may act at distant sites while at the same time it assures its production by preventing cell death in astrocytes where it is produced.

The Tat protein of human immunodeficiency virus type 1 (HIV-1) can promote placement of tRNA primer onto viral RNA and suppress later DNA polymerization in HIV-1 reverse transcription

Human immunodeficiency virus type-1 Tat has been proposed to play a role in the regulation of reverse transcription. We previously demonstrated that wild-type Tat can augment viral infectivity by suppressing the reverse transcriptase (RT) reaction at late stages of the viral life cycle in order to prevent the premature synthesis of potentially deleterious viral DNA products. Here we have performed a detailed analysis of the cell-free reverse transcription reaction to elucidate the mechanism(s) whereby Tat can affect this process. Our results show that Tat can suppress nonspecific DNA elongation while moderately affecting the specific initiation stage of reverse transcription. In addition, Tat has an RNA-annealing activity and can promote the placement of tRNA onto viral RNA. This points to a functional homology between Tat and the viral nucleocapsid (NC) protein that is known to be directly involved in this process. Experiments using a series of mutant Tat proteins revealed that the cysteine-rich and core domains of Tat are responsible for suppression of DNA elongation, while each of the cysteine-rich, core, and basic domains, as well as a glutamine-rich region in the C-terminal domain, are important for the placement of tRNA onto the viral RNA genome. These results suggest that Tat can play at least two different roles in the RT reaction, i.e., suppression of DNA polymerization and placement of tRNA onto viral RNA. We believe that the first of these activities of Tat may contribute to the overall efficiency of reverse transcription of the viral genome during a new round of infection as well as to enhanced production of infectious viral particles. We hypothesize that the second activity, illustrating functional homology between Tat and NC, suggests a potential role for NC in the displacement of Tat during viral maturation.

Postmodern cancer: the role of human immunodeficiency virus in uterine cervical cancer

The association between cervical cancer and human papillomavirus (HPV) is well known, but its association with human immunodeficiency virus (HIV) is controversial. Coinfection with HPV and HIV is to be expected and recent epidemiological data from Africa show that cervical cancer is the most common AIDS defining neoplasm in women. Unlike other AIDS defining neoplasms, the occurrence of cervical cancer is not dependent on immune compromise. HIV alters the natural history of HPV infection, with decreased regression rates and more rapid progression to high grade and invasive lesions, which are refractory to treatment, requiring more stringent intervention and monitoring. The more aggressive behaviour is mirrored by a different molecular pathway. HIV associated cervical cancers are thought to progress through the microsatellite instability pathway, whereas HIV negative ones progress through loss of heterozygosity. Interaction is probably via viral proteins, with HIV proteins enhancing effectiveness of HPV proteins, and perhaps contributing to cell cycle disruption. Dysregulation of the cellular and humoral arms of the local and systemic immune systems may ensure disease progression. Furthermore, HPV infection may predispose to HIV infection and facilitate its progression.

Role for human immunodeficiency virus type 1 Tat protein in suppression of viral reverse transcriptase activity during late stages of viral replication

We have examined the role of the human immunodeficiency virus type 1 (HIV-1) Tat protein in the regulation of reverse transcription. We show that a two-exon but not a one-exon form of Tat markedly suppressed cell-free reverse transcriptase (RT) activity. Conversely, viruses expressing two-exon Tat (pNL43 and pNL101) showed rapid replication kinetics and more efficient endogenous RT activity compared with viruses expressing one-exon Tat (pM1ex). The pM1ex virions, as well as pM1ex-infected cells, also contained higher levels of viral DNA than did either the pNL43 or pNL101 viruses, indicating that reverse transcription might have continued during later stages of viral replication in the absence of the second Tat exon. Moreover, degradation of viral genomic RNA was more apparent in the pM1ex virions. Accordingly, we propose that the two-exon Tat may help augment viral infectivity by suppressing the reverse transcription reaction during late stages of viral synthesis and by preventing the synthesis of potentially deleterious viral DNA products.

Human GLI-2 is a tat activation response element-independent Tat cofactor

Zinc finger-containing GLI proteins are involved in the development of Caenorhabditis elegans, Xenopus, Drosophila, zebrafish, mice, and humans. In this study, we show that an isoform of human GLI-2 strongly synergizes with the Tat transactivating proteins of human immunodeficiency virus types 1 and 2 (HIV-1 and -2) and markedly stimulates viral replication. GLI-2 also synergizes with the previously described Tat cofactor cyclin T1 to stimulate Tat function. Surprisingly, GLI-2/Tat synergy is not dependent on either a typical GLI DNA binding site or an intact Tat activation response element but does require an intact TATA box. Thus, GLI-2/Tat synergy results from a mechanism of action which is novel both for a GLI protein and for a Tat cofactor. These findings link the GLI family of transcriptional and developmental regulatory proteins to Tat function and HIV replication.

Human immunodeficiency virus infection in vitro activates naturally integrated human papillomavirus type 18 and induces synthesis of the L1 capsid protein

Human papillomavirus (HPV) infections are prevalent in human immunodeficiency virus (HIV)-positive individuals. To highlight the effect of HIV on HPV expression, HPV-18-positive HIV-permissive HeLa-T4 cells were either infected with HIV-1 or treated with Tat or with the cytokines IL-1alpha, IL-1beta, IL-6 and TNF-alpha. The presence of HPV-18 E1 (early) and L1 (late) transcripts was then determined by dot-blot or Northern blot hybridization with E1 and L1 or with genomic HPV-18 DNA probes, respectively. Protein extracts from parallel cultures were challenged by Western blotting with an antiserum raised against an L1-beta-galactosidase hybrid protein. Results indicated that HeLa-T4 cells constitutively express E1 and L1 transcripts. When cells were infected with HIV, the amounts of E1 and L1 RNAs increased with time, followed by the de novo appearance of L1 protein. E1 and L1 transcripts were also increased, in a dose-dependent manner, by treatment of uninfected cultures with Tat or with IL-6, but were not affected by IL-1alpha, IL-1beta and TNF- alpha. Neither Tat nor IL-6 could induce L1 translation. These findings raise the hypothesis that the increase of HPV shedding and of HPV-associated diseases in HIV-infected individuals could be due in part to a direct or cytokine-mediated action of HIV, in addition to the HIV-induced immunodeficiency.

Activation of Bcl-2 promoter-directed gene expression by the human immunodeficiency virus type-1 Tat protein

Human immunodeficiency virus type 1 (HIV-1) Tat transcriptionally activates expression from a number of viral and cellular promoters. Recent studies demonstrate the ability of Tat to differentially modulate cellular responses to apoptotic signaling. The antiapoptotic effects of Tat appear to correlate with increased expression of Bcl-2, a cellular protein that enhances cellular survival. Here, endogenous expression of HIV-1 Tat in HeLa and Jurkat cells elevates levels of Bcl-2. Transient expression assays performed in HeLa cells demonstrate that Tat directly or indirectly enhances Bcl-2 promoter-directed gene expression by more than 10-fold. Analyses of Tat mutants demonstrate that two noncontiguous regions in the N- and C-termini of Tat mediate maximal transactivation of the Bcl-2 promoter. The requirement for C-terminal sequences contrasts with transactivation of the HIV-1 long terminal repeat in which the N-terminal 57 amino acids are required but downstream residues are not. Bcl-2 promoter analyses suggest that sequences required for Tat responsiveness are located upstream of P1 and between the P1 and P2 promoter units. Results from these studies reveal effects of HIV-1 Tat on Bcl-2 expression and provide a putative mechanism by which endogenously expressed Tat affects cellular survival through the up-regulation of Bcl-2.

Diminished production of human immunodeficiency virus type 1 in astrocytes results from inefficient translation of gag, env, and nef mRNAs despite efficient expression of Tat and Rev

Astrocytes infected with human immunodeficiency virus type 1 (HIV-1) produce only minimal quantities of virus. The molecular events that limit acute-phase HIV-1 infection of astrocytes were examined after inducing acute-phase replication by transfection with the pNL4-3 proviral plasmid. The levels of HIV-1 mRNA were similarly high in both astrocytes and HeLa cells, but astrocytes produced approximately 50-fold less supernatant p24 than HeLa cells. We found that diminished HIV-1 production in astrocytes resulted from inefficient translation of gag, env, and nef mRNAs that were efficiently transported to the cytoplasm. Tat- or Rev-dependent reporter constructs showed no defect in Tat or Rev function in astrocytes compared with HeLa cells. HIV-1 mRNAs were correctly spliced, but only Rev and Tat proteins were efficiently translated from their native mRNAs. Pulse-chase labelling and immunoblot experiments revealed no defect in protein processing, but levels of Gag, Env, or Nef protein expressed were dramatically reduced in astrocytes compared to HeLa cells. These results demonstrate that inefficient translation of HIV-1 structural proteins underlies the restricted infection of astrocytes. The efficient expression of functional Tat and Rev by astrocytes may contribute to HIV-1 neuropathogenesis.

Regulation of TNFalpha and TGFbeta-1 gene transcription by HIV-1 Tat in CNS cells

Tat is a transcription transactivator produced by the human immunodeficiency virus type 1 (HIV-1) at the early phase of infection and plays a critical role in the expression and replication of the viral genome. This 86 amino acid protein, which can be secreted from the infected cells, has the ability to enter uninfected cells and exert its activity upon the responsive genes. Earlier results indicated that in addition to the HIV-1 promoter, Tat has the capacity to induce transcription of a variety of cellular genes. In this study, we demonstrate that exposure of cells from the central nervous system (U-87MG and SK-N-MC) and the lymphoid T cells (Jurkat) to highly purified Tat increases transcriptional activity of the reporter constructs containing the promoters from the transforming growth factor beta-1 (TGFbeta-1), the tumor necrosis factor alpha (TNFalpha), and the HIV-1 LTR. In addition, Tat treatment results in increased levels of TGFbeta-1 and TNFalpha mRNAs in these cells. Activation of the TGFbeta-1 and TNFalpha promoter constructs by Tat in U-87MG and SK-N-MC cells required amino acid residues 2 to 36 which spans the acidic and the cysteine-rich domains of Tat. In both CNS and lymphoid cells, the level of endogenous TGFbeta-1 mRNA was increased by mutant Tat protein containing amino acids 1 to 48 but not with a mutant Tat protein with a deletion between residues 2 to 36. TNFalpha mRNA level was increased by mutant Tat spanning residues 1 to 48 in U-87MG cells, but not in SK-N-MC and Jurkat cells. These observations suggest that activation of cellular and viral genes by Tat in various cells may be mediated by different pathways as evidenced by the requirements of the different regions of Tat. Activation of the TGFbeta-1 and TNFalpha promoters by wild-type Tat was severely affected by the mutant peptides spanning residues 2 to 36 and 1 to 48 suggesting that both truncated Tat peptides may function as dominant negative mutants over TNFalpha and TGFbeta-1 gene transcription. The importance of these findings in Tat-induced regulation of viral and cellular genes in various cell types is discussed.

Repression of tumor necrosis factor-beta expression by the human immunodeficiency virus type-1 tat protein in central nervous system-derived glial cells

HIV-1 Tat is a potent transactivator that stimulates expression from the HIV-1 LTR, from certain cellular gene promoters and from several heterologous viral promoters. Previous reports show that HIV-1 Tat transactivates tumor necrosis factor-beta (TNF-beta) promoter-directed gene expression in lymphocytic and monocytic cell lines and further demonstrate that a 'TAR-like structure' downstream of the TNF-beta promoter is essential for Tat activity. The ability of Tat to activate TNF-beta may have profound effects as TNF has been shown to be a potent activator of HIV-1 gene expression and an important immunomodulatory and growth regulatory factor. The studies presented herein demonstrate a novel finding where HIV-1 Tat specifically represses (> 10-fold) TNF-beta promoter-directed gene expression in central nervous system-derived glial cells. Amino acid residues 2 to 36 of HIV-1 Tat are required for TNF-beta repression. Tat repression of TNF-beta, a factor which upregulates HIV-1 gene expression, suggests a novel mechanism whereby HIV-1 is able to establish latent infection of glial cells that present no detectable virions and/or viral antigens.