Human immunodeficiency virus type 1 tat gene enhances human cytomegalovirus gene expression and viral replication

Relationship Between Opacity of Cytomegalovirus Retinitis Lesion Borders and Severity of Immunodeficiency Among People With AIDS

Purpose

To evaluate risk factors for severity of cytomegalovirus (CMV) retinitis lesion whitening (opacity), using a standardized scoring system.

Methods

We performed a cross-sectional, observational investigation of all individuals with newly diagnosed AIDS-related CMV retinitis in three randomized clinical trials and one prospective observational study. Opacity was scored by masked readers, using a prospectively defined ordinal 6-point scale. Demographic factors, laboratory data (CD4+, CD8+ T-lymphocyte counts, human immunodeficiency virus [HIV] blood levels), and lesion characteristics (location, size) were compared to the highest opacity score assigned to either eye. Among eyes with active lesions (scores ≥3), factors associated with severe opacity (scores 5, 6) were identified.

Results

There were 299 participants (401 eyes with CMV retinitis). In one or more comparisons, increased opacity was associated with lower CD4+ and lower CD8+ T-lymphocyte counts, higher HIV blood level, lack of antiretroviral therapy, male sex, race/ethnicity, and bilateral disease. In eyes with active disease, severe opacity was associated with lower CD4+ T-lymphocyte count, higher HIV blood level, older age, Karnofsky score, lesion size, and bilateral disease. No relationship was identified between opacity and lesion location.

Conclusions

Lesion border opacity (resulting from CMV activity) reflects level of immune function; as immunodeficiency becomes worse, CMV activity (and opacity) increases. The positive relationship between opacity and HIV blood level may reflect both immunodeficiency and increased CMV activity caused by transactivation of CMV by HIV. Scoring of opacity may be a useful, standard measure for continued study of CMV retinitis across different settings and populations. (Clinicaltrials.gov number for the HPMPC CMV Retinitis Trial: NCT00000142; Clinicaltrials.gov number for the Monoclonal Antibody CMV Retinitis Trial: NCT00000135; Clinicaltrials.gov number for the Ganciclovir-Cidofovir CMV Retinitis Trial: NCT0000014; Clinicaltrials.gov number for the Longitudinal Study of the Ocular Complications of AIDS: NCT00000168.).

Activation of early gene transcription in polyomavirus BK by human immunodeficiency virus type 1 Tat

Polyomavirus BK (BKV) is a serious problem for immunocompromised patients, where latent virus can enter into the lytic cycle causing cytolytic destruction of host cells. BKV infects >80% of the population worldwide during childhood and then remains in a latent state in the kidney. In the context of immunosuppression in kidney transplant patients, reactivation of the viral early promoter (BKV(E)) results in production of T antigen, enabling virus replication and transition from latency to the lytic phase, causing polyomavirus-associated nephropathy. Reactivation of BKV can also cause complications such as nephritis, atypical retinitis and haemorrhagic cystitis in AIDS patients. Here, the effects of human immunodeficiency virus type 1 (HIV-1) proteins Tat and Vpr on BKV transcription were investigated and it was demonstrated that Tat dramatically stimulated BKV(E). Site-directed mutagenesis analysis of potential Tat-responsive transcriptional motifs complemented by an electrophoretic mobility shift assay (EMSA) showed that Tat activated BKV(E) by inducing binding of the NF-kappaB p65 subunit to a kappaB motif near the 3' end of BKV(E). In addition, a sequence within the 5' UTR of BKV(E) transcripts (BKV(E)-TAR) was identified that is identical to the HIV-1 transactivation response (TAR) element. The BKV(E)-TAR sequence bound TAT in RNA EMSA assays and deletion of the BKV(E)-TAR sequence eliminated Tat transactivation of BKV(E) transcription. Thus, Tat positively affected BKV(E) transcription by a dual mechanism and this may be important in diseases involving BKV reactivation in AIDS patients.

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.

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.

Cytotoxic T-lymphocyte responses to cytomegalovirus in normal and simian immunodeficiency virus-infected rhesus macaques

Disseminated cytomegalovirus (CMV) infection is a frequent occurrence in human immunodeficiency virus-infected humans and in simian immunodeficiency virus (SIV)-infected rhesus macaques. Rhesus macaques are a suitable animal model with which to study in vivo interactions between CMV and AIDS-associated retroviruses. Since cytotoxic T lymphocytes (CTL) play a major role in control of viral infections, we have characterized CMV-specific CTL responses in SIV-infected and uninfected rhesus macaques. Autologous fibroblasts infected with rhesus CMV were used to stimulate freshly isolated peripheral blood mononuclear cells from CMV-seropositive animals. Following in vitro stimulation, specific CTL activity against CMV-infected autologous fibroblasts was detected in CMV-seropositive but not in CMV-seronegative normal macaques. CMV-specific CTL activity comparable to that in normal animals was also detected in two CMV-seropositive macaques infected with a live attenuated SIV strain (SIVdelta3) and in two of three macaques infected with pathogenic SIV strains. The CMV-specific CTL response was class I major histocompatibility complex restricted and mediated by CD8+ cells. An early CMV protein(s) was the dominant target recognized by bulk CTL, although the pattern of CTL recognition of CMV proteins varied among animals. Analysis of CMV-specific CTL responses in macaques should serve as a valuable model for CMV immunopathogenesis and will facilitate prospective in vivo studies of immune interactions between CMV and SIV in AIDS.

Enhanced HIV-1 replication in V beta 12 T cells due to human cytomegalovirus in monocytes: evidence for a putative herpesvirus superantigen

HIV-1 replicates more efficiently in cultured IL-2-dependent CD4 T cells expressing V beta 12 T cell receptors (TCRs) rather than other TCRs (Laurence et al., 1992). A viral reservoir is frequently established in V beta 12 T cells in HIV-1-infected patients. Here we show that cytomegalovirus (CMV) is responsible for V beta 12-selective HIV-1 replication that is indistinguishable from the effect of known superantigens (SAGs). This effect is dependent on direct contact of T cells with CMV-infected monocytes. CMV infection, but not ie1 or ie2 transfection, reproduces this effect in a monocytoid cell line (U937). In HIV-infected patients, the presence of CMV antibodies correlates with an HIV-1 viral load preferentially skewed to the V beta 12 subset. Together, these data suggest that a CMV gene product is responsible for a SAG-driven V beta 12-selective HIV-1 reservoir in vivo.

HIV Tat represses transcription through Sp1-like elements in the basal promoter

MHC class I genes are potently repressed by HIV Tat, which transactivates the HIV LTR. Tat represses class I transcription by binding to complexes associated with a novel promoter element, consisting of Sp1-like DNA binding sites. Transcription by other Sp1-dependent promoters, such as MDR1 and the minimal SV40 promoters, is also repressed by Tat, whereas the human beta-actin promoter is neither activated by Sp1 nor repressed by Tat. Tat repression can be overcome by a strong enhancer element. Thus, the SV40 72 bp enhancer element confers protection from Tat-mediated repression on both the minimal SV40 promoter and the class I promoter. Surprisingly, Tat can activate the class I promoter in the presence of both the HIV TAR element and a strong upstream enhancer. These data demonstrate that Tat differentially affects Sp1-responsive promoters, depending on promoter architecture.

Changes in cellular proteins associated with the expression of human immunodeficiency virus type 1 trans-activator protein Tat

Earlier studies have revealed a distinct class of regulatory proteins known as trans-activator proteins in diverse biological systems. These proteins have been shown to act on both homologous and heterologous promoter targets. Activation of heterologous targets is speculated to be an integral part of virus-induced pathogenesis. To verify this hypothesis, stable Tat-producing human rhabdomyosarcoma (RD) cell lines were generated. These cell lines produced significant levels of functional Tat, as measured by transfection with the reporter plasmid pLTR-CAT. Tat-producing cells, although morphologically similar to the control, exhibited a slower growth rate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the cellular proteins from control (tat-) and tat+ cells revealed increased quantities of 34- and 40-kD proteins along with the appearance of a new 74-kD protein in tat+ cells. Subsequent two-dimensional gel analysis revealed several additional differences. Tat+ cell lines produced two proteins of M(r) 19.5 and 44 kD anew, while proteins with M(r) 14.5, 42, and 52.5 kD were in greater abundance. Interestingly, a 26-kD protein that was originally present in the G418+/tat- (control) sample disappeared in the presence of Tat. These data support a possible modulator role for Tat in cellular gene expression.