TAR and Sp1-independent transactivation of HIV long terminal repeat by the Tat protein in the presence of human cytomegalovirus IE1/IE2

Human cytomegalovirus IE1 protein elicits a type II interferon-like host cell response that depends on activated STAT1 but not interferon-γ

Human cytomegalovirus (hCMV) is a highly prevalent pathogen that, upon primary infection, establishes life-long persistence in all infected individuals. Acute hCMV infections cause a variety of diseases in humans with developmental or acquired immune deficits. In addition, persistent hCMV infection may contribute to various chronic disease conditions even in immunologically normal people. The pathogenesis of hCMV disease has been frequently linked to inflammatory host immune responses triggered by virus-infected cells. Moreover, hCMV infection activates numerous host genes many of which encode pro-inflammatory proteins. However, little is known about the relative contributions of individual viral gene products to these changes in cellular transcription. We systematically analyzed the effects of the hCMV 72-kDa immediate-early 1 (IE1) protein, a major transcriptional activator and antagonist of type I interferon (IFN) signaling, on the human transcriptome. Following expression under conditions closely mimicking the situation during productive infection, IE1 elicits a global type II IFN-like host cell response. This response is dominated by the selective up-regulation of immune stimulatory genes normally controlled by IFN-γ and includes the synthesis and secretion of pro-inflammatory chemokines. IE1-mediated induction of IFN-stimulated genes strictly depends on tyrosine-phosphorylated signal transducer and activator of transcription 1 (STAT1) and correlates with the nuclear accumulation and sequence-specific binding of STAT1 to IFN-γ-responsive promoters. However, neither synthesis nor secretion of IFN-γ or other IFNs seems to be required for the IE1-dependent effects on cellular gene expression. Our results demonstrate that a single hCMV protein can trigger a pro-inflammatory host transcriptional response via an unexpected STAT1-dependent but IFN-independent mechanism and identify IE1 as a candidate determinant of hCMV pathogenicity.

Transcription through the HIV-1 nucleosomes: effects of the PBAF complex in Tat activated transcription

The SWI/SNF complex remodels nucleosomes, allowing RNA Polymerase II access to the HIV-1 proviral DNA. It has not been determined which SWI/SNF complex (BAF or PBAF) remodels nucleosomes at the transcription start site. These complexes differ in only three subunits and determining which subunit(s) is required could explain the regulation of Tat activated transcription. We show that PBAF is required for chromatin remodeling at the nuc-1 start site and transcriptional elongation. We find that Baf200 is required to ensure activation at the LTR level and for viral production. Interestingly, the BAF complex was observed on the LTR whereas PBAF was present on both LTR and Env regions. We found that Tat activated transcription facilitates removal of histones H2A and H2B at the LTR, and that the FACT complex may be responsible for their removal. Finally, the BAF complex may play an important role in regulating splicing of the HIV-1 genome.

Retroviral proteomics and interactomes: intricate balances of cell survival and viral replication

Overall changes in the host cellular proteome upon retroviral infection intensify from the initial entry of the virus to the incorporation of viral DNA into the host genome, and finally to the consistent latent state of infection. The host cell reacts to both the entry of viral elements and the manipulation of host cellular machinery, resulting in a cascade of signaling events and pathway activation. Cell type- and tissue-specific responses are also characteristic of infection and can be classified based on the differential expression of genes and proteins between normal and disease states. The characterization of differentially expressed proteins upon infection is also critical in identifying potential biomarkers within infected bodily fluids. Biomarkers can be used to monitor the progression of infection, track the effectiveness of specific treatments and characterize the mechanisms of disease pathogenesis. Standard proteomic approaches have been applied to monitor the changes in global protein expression and localization in infected cells, tissues and fluids. Here we report on recent investigations into the characterization of proteomes in response to retroviral infection.

Lysine methylation of HIV-1 Tat regulates transcriptional activity of the viral LTR

Background

The rate of transcription of the HIV-1 viral genome is mediated by the interaction of the viral protein Tat with the LTR and other transcriptional machinery. These specific interactions can be affected by the state of post-translational modifications on Tat. Previously, we have shown that Tat can be phosphorylated and acetylated in vivo resulting in an increase in the rate of transcription. In the present study, we investigated whether Tat could be methylated on lysine residues, specifically on lysine 50 and 51, and whether this modification resulted in a decrease of viral transcription from the LTR.

Results

We analyzed the association of Tat with histone methyltransferases of the SUV39-family of SET domain containing proteins in vitro. Tat was found to associate with both SETDB1 and SETDB2, two enzymes which exhibit methyltransferase activity. siRNA against SETDB1 transfected into cell systems with both transient and integrated LTR reporter genes resulted in an increase in transcription of the HIV-LTR in the presence of suboptimal levels of Tat. In vitro methylation assays with Tat peptides containing point mutations at lysines 50 and 51 showed an increased incorporation of methyl groups on lysine 51, however, both residues indicated susceptibility for methylation.

Conclusion

The association of Tat with histone methyltransferases and the ability for Tat to be methylated suggests an interesting mechanism of transcriptional regulation through the recruitment of chromatin remodeling proteins to the HIV-1 promoter.

Effect of transcription peptide inhibitors on HIV-1 replication

HIV-1 manipulates cellular machineries such as cyclin dependent kinases (cdks) and their cyclin elements, to stimulate virus production and maintain latent infection. Specifically, the HIV-1 viral protein Tat increases viral transcription by binding to the TAR promoter element. This binding event is mediated by the phosphorylation of Pol II by complexes such as cdk9/Cyclin T and cdk2/Cyclin E. Recent studies have shown that a Tat 41/44 peptide derivative prevents the loading of cdk2 onto the HIV-1 promoter, inhibiting gene expression and replication. Here we show that Tat peptide analogs computationally designed to dock at the cyclin binding site of cdk2 have the ability to bind to cdk2 and inhibit the association of cdk2 with the HIV promoter. Specifically, the peptide LAALS dissociated the complex and decreased kinase activity in vitro. We also describe our novel small animal model which utilizes humanized Rag2(-/-)gamma(c)(-/-) mice. This small peptide inhibitor induces a decrease in HIV-1 viral transcription in vitro and minimizes viral loads in vivo.

Effect of SWI/SNF chromatin remodeling complex on HIV-1 Tat activated transcription

Background

Human immunodeficiency virus type 1 (HIV-1) is the etiologic agent of acquired immunodeficiency virus (AIDS). Following entry into the host cell, the viral RNA is reverse transcribed into DNA and subsequently integrated into the host genome as a chromatin template. The integrated proviral DNA, along with the specific chromatinized environment in which integration takes place allows for the coordinated regulation of viral transcription and replication. While the specific roles of and interplay between viral and host proteins have not been fully elucidated, numerous reports indicate that HIV-1 retains the ability for self-regulation via the pleiotropic effects of its viral proteins. Though viral transcription is fully dependent upon host cellular factors and the state of host activation, recent findings indicate a complex interplay between viral proteins and host transcription regulatory machineries including histone deacetylases (HDACs), histone acetyltransferases (HATs), cyclin dependent kinases (CDKs), and histone methyltransferases (HMTs).

Results

Here, we describe the effect of Tat activated transcription at the G₁/S border of the cell cycle and analyze the interaction of modified Tat with the chromatin remodeling complex, SWI/SNF. HIV-1 LTR DNA reconstituted into nucleosomes can be activated in vitro using various Tat expressing extracts. Optimally activated transcription was observed at the G₁/S border of the cell cycle both in vitro and in vivo, where chromatin remodeling complex, SWI/SNF, was present on the immobilized LTR DNA. Using a number of in vitro binding as well as in vivo chromatin immunoprecipitation (ChIP) assays, we detected the presence of both BRG1 and acetylated Tat in the same complex. Finally, we demonstrate that activated transcription resulted in partial or complete removal of the nucleosome from the start site of the LTR as evidenced by a restriction enzyme accessibility assay.

Conclusion

We propose a model where unmodified Tat is involved in binding to the CBP/p300 and cdk9/cyclin T₁ complexes facilitating transcription initiation. Acetylated Tat dissociates from the TAR RNA structure and recruits bromodomain-binding chromatin modifying complexes such as p/CAF and SWI/SNF to possibly facilitate transcription elongation.

Reciprocal transactivation between HIV-1 and other human viruses

A variety of rare clinical syndromes are seen with strikingly increased prevalence in HIV-1-infected individuals, many with underlying viral etiologies. The emergence of these diseases in AIDS reflects a reduction in the ability of the immune system to mount an adequate defense against viruses in general due to the damage inflicted to the immune system by HIV-1 infection. However, in many cases, it has been found that HIV-1 can enhance the level of expression and hence the life cycle of other viruses independently of immunosuppression through specific interactions with the viruses. This can occur either directly by HIV-1 proteins such as Tat enhancing the activity of heterologous viral promoters, and/or indirectly by HIV-1 inducing the expression of cytokines and activation of their downstream signaling that eventually promotes the multiplication of the other virus. In a reciprocal manner, the effects of other viruses can enhance the pathogenicity of HIV-1 infection in individuals with AIDS through stimulation of the HIV-1 promoter activity and genome expression. The purpose of this review is to examine the cross-interactions between these viruses and HIV-1.

Interactions between human immunodeficiency virus and herpes viruses within the oral mucosa

There is evidence from clinical case reports and epidemiological studies that human immunodeficiency virus (HIV) can be transmitted through oral sex. Herpes viruses that appear in the oral mucosa might influence the oral replication of HIV. A review of data suggesting that interactions occur between HIV and herpes viruses indicates that such interactions might operate in the oral mucosa. Defining the mechanisms by which herpes viruses interact with HIV in the oral mucosa should permit intervention measures to be targeted more precisely.

The HIV RNA Levels of Plasma and Ocular Fluids in AIDS Patients with Ophthalmic Infections

The aim of the present study was to evaluate the impact of highly active antiretroviral therapy (HAART) on HIV viral load of plasma and intraocular fluids in AIDS patients with ophthalmic opportunistic infections. We further compared the treatment effect of HAART on these patients. From June 1997 to July 2003, we examined and followed up the ophthalmic conditions of 49 patients receiving HAART with ophthalmic diseases during this period. The method of reverse-transcriptase polymerase chain reaction was used to detect and monitor HIV load in plasma and/or aqueous humor of AIDS patients. Before HAART, the HIV levels in the plasma and aqueous humor in 8 AIDS patients with ophthalmic opportunistic infections were significantly higher than those in 6 patients with HIV-related retinopathy (p < 0.05). Compared to the eye findings and clinical improvement, HIV loads of aqueous humor in 10 of 14 AIDS patients (6 with HIV-related retinopathy, 5 with cytomegalovirus retinitis, 2 with toxoplasmic retinitis and 1 with cryptococcal chorioretinitis) declined to undetectable levels (< 400 copies/ml) after 4-8 months of HAART. HIV virus levels in the plasma of AIDS patients were significantly decreased, and the CD4 counts of these patients were significantly increased (Wilcoxon test) after initiation of HAART.

Conditional expression of IFN-alpha and IFN-gamma activated by HBV as genetic therapy for hepatitis B

Chronic infection with hepatitis B virus (HBV) has potentially devastating consequences and is very difficult to treat. Therapy with recombinant interferons (IFN), especially IFN-alpha, may be effective. The blood IFN-alpha levels that are needed to maintain therapeutic IFN-alpha levels in the liver, however, often cause severe side effects. Gene delivery to the liver may provide a solution. Using a long-term expression construct could provide the desired levels of IFN locally without the need to maintain potentially problematic blood levels. Recombinant, Tag-deleted SV40-derived vectors transduce hepatocytes efficiently and provide permanent transgene expression. We designed an expression construct that was effective against HBV and whose activity was limited to HBV-infected cells. To do this, we exploited the ability of HBV X protein to activate NF-kappaB and, via NF-kappaB, to activate promoter activity of HIV long terminal repeat (LTR) in hepatocytes. Using HIVLTR as a conditional promoter upstream of human and murine IFN-alpha and IFN-gamma cDNAs, rSV40 vectors were used to test the responsiveness of IFN to HBV and the ability of these IFNs to inhibit HBV transcripts and protein production and to activate IFN signaling in neighboring untransduced cells. We found that in hepatocyte cell lines and in primary hepatocytes, HBV activated the promoter activity of the HIVLTR via NF-kappaB. When whole HBV genome was delivered to cells by transfection to simulate HBV infection, IFN expression was activated, IFNs were produced and secreted, and they protected cells from HBV. Levels of IFN proteins that were secreted in this context were comparable to targeted blood levels needed to control chronic hepatitis viral infection. Further, IFNs that were elicited and secreted in this manner were able to activate IFN-induced signaling pathways in neighboring, untransduced cells and so were likely to provide protection even to cells that the rSV40 vector did not transduce. Gene delivery using such rSV40 vectors expressing IFNs conditionally in response to HBV may be an attractive therapeutic option for the treatment of chronic hepatitis B.

Exploiting hepatitis C virus activation of NFkappaB to deliver HCV-responsive expression of interferons alpha and gamma

Chronic infection with hepatitis C virus (HCV) may lead to liver failure and hepatocellular carcinoma. Current treatment for HCV includes high systemic doses of interferonalpha (IFNalpha), which is effective in less than half of patients and may have severe side effects. We designed conditional IFNalpha and IFNgamma expression constructs to be triggered by HCV-induced activation of NFkappaB, and delivered these using highly efficient recombinant Tag-deleted SV40-derived vectors. NFkappaB activates the HIV-1NL4-3 long terminal repeat (HIVLTR) as a promoter, which accounts for the conditional transgene expression. Human hepatocyte lines and primary rat hepatocytes (PRH) were transduced with SV[HIVLTR](IFN) vectors, and transfected with HCV cDNA. Production of human and murine IFNalpha and IFNgamma in cytosol and culture supernatants was measured. HCV activated the HIVLTR to produce and secrete IFNs, and did so largely through the NFkappaB binding sites of the HIVLTR. Levels of IFNs secreted, and the magnitude of induction in response to HCV, were greater in hepatocyte lines than in primary cultured hepatocytes. However, even in the latter, supernatant IFNalpha concentrations achieved by this approach were similar to therapeutic serum concentrations sought in systemic IFNalpha-treated patients. In coculture studies, secreted IFNalpha activated its cognate response elements in untransduced cells, suggesting that its potential inhibitory effects on HCV may not be limited to transduced cells. Although HCV replication in culture is difficult to assess, HCV-induced IFNalpha production demonstrably reduced HCV transcription. Conditional expression of IFNs within the liver may represent an attractive approach to therapy of severe chronic HCV infection that could avoid the side effects of systemic treatment regimens.

Synergism between HIV and other viruses in the mouth

The HIV family replicate in and are shed from the mouth. Oral sexual practices potentially contribute to the overall extent of HIV transmission, particularly if high-risk practices are not restricted. Herpesviruses and papillomaviruses that appear in the oral cavity can determine oral HIV replication. The mechanisms probably include heterologous transactivation, enhanced expression of HIV receptors and co-receptors in target cells, release of cytokines and chemokines, and production of superantigens. Oral diseases peculiar to, or more common in, the HIV-infected patient further predispose to heightened oral HIV replication and trafficking. Defining the mechanisms by which oral viruses interact with HIV in the co-infected host should permit intervention measures against oral HIV transmission to be more precisely targeted.

SUMO-1 modification of human cytomegalovirus IE1/IE72

Human cytomegalovirus (HCMV) immediate-early protein IE1/IE72 is involved in undermining many cellular processes including cell cycle regulation, apoptosis, nuclear architecture, and gene expression. The multifunctional nature of IE72 suggests that posttranslational modifications may modulate its activities. IE72 is a phosphoprotein and has intrinsic kinase activity (S. Pajovic, E. L. Wong, A. R. Black, and J. C. Azizkhan, Mol. Cell. Biol. 17:6459-6464, 1997). We now demonstrate that IE72 is covalently conjugated to the small ubiquitin-like modifier (SUMO-1). SUMO-1 is an 11.5-kDa protein that is conjugated to multiple proteins and has been reported to exhibit multiple effects, including modulation of protein stability, subcellular localization, and gene expression. A covalently modified protein migrating at approximately 92 kDa, which is stabilized by a SUMO-1 hydrolase inhibitor, is revealed by Western blotting with anti-IE72 of lysates from cells infected with HCMV or cells expressing IE72. SUMO modification of IE72 was confirmed by immunoprecipitation with anti-IE72 and anti-SUMO-1 followed by Western blotting with anti-SUMO-1 and anti-IE72, respectively. Lysine 450 is within a sumoylation consensus site (I,V,L)KXE; changing lysine 450 to arginine by point mutation abolishes SUMO-1 modification of IE72. Inhibition of protein phosphatase 1 and 2A, which increases the phosphorylation of IE72, suppresses the formation of SUMO-1-IE72 conjugates. Both wild-type IE72 and IE72(K450R) localize to nuclear PML oncogenic domains and disrupt them. Studies of protein stability, transactivation, and complementation of IE72-deficient HCMV (CR208) have revealed no significant differences between wild-type IE72 and IE72(K450R).

The hepatitis B virus X protein induces HIV-1 replication and transcription in synergy with T-cell activation signals: functional roles of NF-kappaB/NF-AT and SP1-binding sites in the HIV-1 long terminal repeat promoter

Co-infection with hepatitis B virus (HBV) and human immunodeficiency virus type-1 (HIV-1) is relatively common. However, the impact of this co-infection on the clinical outcome of HIV infection has not been elucidated. We herein demonstrate that the HBV X protein (HBx) superinduces ongoing HIV-1 replication and HIV-1 long terminal repeat (LTR) transcription by synergizing with Tat protein and with T-cell activation signals. Although HBx cooperated with mitogenic stimuli in the induction of reporter plasmids harboring the HIV-1 kappaB enhancer, in both a NF-kappaB-dependent manner and a NF-AT-dependent manner, deletion of this element from the LTR did not affect the HBx-mediated up-regulation in the presence of Tat and/or mitogens. In contrast, mutation of the proximal LTR Sp1-binding sites abolished the HBx-mediated synergistic activation, but only when it was accompanied by deletion of the kappaB enhancer. When HBx was targeted to the nucleus, its ability to synergize with cellular activation stimuli was maintained. Furthermore, mutations of HBx affecting its interaction with the basal transcription machinery abrogated the synergistic activation by HBx, suggesting that this protein exerts its function by acting as a nuclear co-activator. These results indicate that HBx could contribute to a faster progression to AIDS in HBV-HIV co-infected individuals.

Cytomegalovirus (CMV) DNA load is an independent predictor of CMV disease and survival in advanced AIDS

The impact of cytomegalovirus (CMV) on human immunodeficiency virus type 1 (HIV-1) disease progression has been controversial. In this study, we sought to determine if CMV viral load is independent of HIV-1 viral load in predicting CMV disease and survival. Our findings indicate that in patients with advanced AIDS, CMV DNA load is an independent marker of CMV disease and survival and is more predictive than HIV-1 RNA load. Moreover, patients who respond to preemptive therapy with oral ganciclovir, with resulting undetectable levels of CMV DNA, in their plasma, have a significantly lower risk of developing CMV disease and higher rates of survival, despite stable or increasing HIV-1 RNA loads. These data provide support for CMV as an independent risk factor for mortality in persons with advanced AIDS and further suggest that effective preemptive therapy for CMV can improve patient survival rates.

Transcriptional activation of HIV by Mycobacterium tuberculosis in human monocytes

Recently it has been shown that infection with Mycobacterium tuberculosis increases the replication of HIV in mononuclear cells. The objective of this study was to investigate the mechanism(s) of up-regulation of HIV in primary human monocytes. Monocytes from healthy subjects were infected with HIV in vitro and then cultured with purified protein derivative (PPD) of M. tuberculosis. Culture supernatants were assessed for HIV p24 and cytokines. HIV expression was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). PPD induced HIV-infected monocytes to increased expression of HIV RNA and production of HIV p24. This effect correlated with production of tumour necrosis factor-alpha (TNF-alpha) in monocyte cultures. However, neutralizing antibody to TNF-alpha only partly abrogated the PPD-induced HIV p24 in these cultures. Also, PPD and culture filtrate of M. tuberculosis induced HIV mRNA expression. Further, using an adenovirus infection system containing an HIV long-terminal repeat (LTR) reporter plasmid, we showed that M. tuberculosis and its PPD induced HIV LTR. Therefore, the effect of M. tuberculosis and its PPD on HIV replication in monocytes is primarily one of transcriptional activation.

Human cytomegalovirus product UL44 downregulates the transactivation of HIV-1 long terminal repeat

OBJECTIVE

Human cytomegalovirus (HCMV) is often isolated from HIV-1-infected patients and the two viruses can infect the same cell type giving rise to direct bidirectional interactions. Whereas the long terminal repeat (LTR) transactivation ability of HCMV immediate early gene (IE1/IE2) is well documented, no information is available on the possible role of other HCMV proteins. In this study, the activity of ppUL44, an early DNA-binding protein, on HIV LTR transactivation was investigated.

METHODS

HIV LTR transactivation by ppUL44 in presence or absence of HIV-1 Tat and HCMV IE1/IE2 was determined in J-Jhan and U973 cells through transient transfection experiments with a series of different expression vectors. Some experiments were also performed on U373-MG astrocytoma cells permanently transfected with UL44 or with another HCMV gene used as a control (UL55).

RESULTS

The basal transactivation activity of the HIV LTR was not influenced by the presence of ppUL44. On the contrary, the transactivation observed in the presence of Tat, IE1/IE2 or both factors in synergy was strongly downregulated by ppUL44 in a dose-dependent manner. Deletion constructs of ppUL44 demonstrated that the region of the molecule responsible for the inhibition of the LTR is located within the last 114 amino acids at the carboxyl-terminal region.

CONCLUSIONS

The results obtained indicate that within the last 114 amino acids of ppUL44 there is a domain that has a negative effect on the ability of HIV-1 LTR to be activated by both its autologous transactivator Tat and the heterologous transactivator HCMV IE1/IE2 functioning individually or synergistically.