Stimulation of the human immunodeficiency virus type 1 enhancer by the human T-cell leukemia virus type I tax gene product involves the action of inducible cellular proteins

Therapeutic advances for the management of adult T cell leukemia: Where do we stand?

Adult T cell leukemia (ATL) is an aggressive blood malignancy secondary to chronic infection with the human T cell leukemia virus type I (HTLV-1) retrovirus. ATL encompasses four subtypes (acute, lymphoma, chronic, and smoldering), which exhibit different clinical characteristics and respond differently to various treatment strategies. Yet, all four subtypes are characterized by a dismal long-term prognosis and a low survival rate. While antiretroviral therapy improves overall survival outcomes in smoldering and chronic subtypes, survival remains poor in lymphoma subtypes despite their good response to intensive chemotherapy. Nonetheless, acute ATL remains the most aggressive form associated with profound immunosuppression, chemo-resistance and dismal prognosis. Targeted therapies such as monoclonal antibodies, epigenetic therapies, and arsenic/IFN, emerged as promising therapeutic approaches in ATL. Allogeneic hematopoietic cell transplantation is the only potentially curative modality, alas applicable to only a small percentage of patients. The recent findings demonstrating the expression of the viral oncoprotein Tax in primary ATL cells from patients with acute or chronic ATL, albeit at low levels, and their dependence on continuous Tax expression for their survival, position ATL as a virus-addicted leukemia and validates the rationale of anti-viral treatment strategies. This review provides a comprehensive overview on conventional, anti-viral and targeted therapies of ATL, with emphasis on Tax-targeted therapied in the pre-clinical and clinical settings.

Co-Infection and Cancer: Host–Pathogen Interaction between Dendritic Cells and HIV-1, HTLV-1, and Other Oncogenic Viruses

Dendritic cells (DCs) function as a link between innate and adaptive immune responses. Retroviruses HIV-1 and HTLV-1 modulate DCs to their advantage and utilize them to propagate infection. Coinfection of HTLV-1 and HIV-1 has implications for cancer malignancies. Both viruses initially infect DCs and propagate the infection to CD4+ T cells through cell-to-cell transmission using mechanisms including the formation of virologic synapses, viral biofilms, and conduits. These retroviruses are both neurotrophic with neurovirulence determinants. The neuropathogenesis of HIV-1 and HTLV-1 results in neurodegenerative diseases such as HIV-associated neurocognitive disorders (HAND) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Infected DCs are known to traffic to the brain (CNS) and periphery (PNS, lymphatics) to induce neurodegeneration in HAND and HAM/TSP patients. Elevated levels of neuroinflammation have been correlated with cognitive decline and impairment of motor control performance. Current vaccinations and therapeutics for HIV-1 and HTLV-1 are assessed and can be applied to patients with HIV-1-associated cancers and adult T cell leukemia/lymphoma (ATL). These diseases caused by co-infections can result in both neurodegeneration and cancer. There are associations with cancer malignancies and HIV-1 and HTLV-1 as well as other human oncogenic viruses (EBV, HBV, HCV, HDV, and HPV). This review contains current knowledge on DC sensing of HIV-1 and HTLV-1 including DC-SIGN, Tat, Tax, and current viral therapies. An overview of DC interaction with oncogenic viruses including EBV, Hepatitis viruses, and HPV is also provided. Vaccines and therapeutics targeting host–pathogen interactions can provide a solution to co-infections, neurodegeneration, and cancer.

Interplay between innate immunity and the viral oncoproteins Tax and HBZ in the pathogenesis and therapeutic response of HTLV-1 associated adult T cell leukemia

The Human T-cell Leukemia virus type 1 (HTLV-1) causes an array of pathologies, the most aggressive of which is adult T-cell leukemia (ATL), a fatal blood malignancy with dismal prognosis. The progression of these diseases is partly ascribed to the failure of the immune system in controlling the spread of virally infected cells. HTLV-1 infected subjects, whether asymptomatic carriers or symptomatic patients are prone to opportunistic infections. An increasing body of literature emphasizes the interplay between HTLV-1, its associated pathologies, and the pivotal role of the host innate and adoptive immune system, in shaping the progression of HTLV-1 associated diseases and their response to therapy. In this review, we will describe the modalities adopted by the malignant ATL cells to subvert the host innate immune response with emphasis on the role of the two viral oncoproteins Tax and HBZ in this process. We will also provide a comprehensive overview on the function of innate immunity in the therapeutic response to chemotherapy, anti-viral or targeted therapies in the pre-clinical and clinical settings.

Tax Induces the Recruitment of NF-κB to Unintegrated HIV-1 DNA To Rescue Viral Gene Expression and Replication

We previously reported that the normally essential step of integration of the HIV-1 proviral DNA intermediate into the host cell genome becomes dispensable in T cells that express the human T cell leukemia virus 1 (HTLV-1) Tax protein, a known activator of cellular NF-κB. The rescue of integrase (IN)-deficient HIV-1 replication by Tax results from the strong activation of transcription from the long terminal repeat (LTR) promoter on episomal HIV-1 DNA, an effect that is closely correlated with the recruitment of activating epigenetic marks, such as H3Ac, and depletion of repressive epigenetic marks, such as H3K9me3, from chromatinized unintegrated proviruses. In addition, activation of transcription from unintegrated HIV-1 DNA coincides with the recruitment of NF-κB to the two NF-κB binding sites found in the HIV-1 LTR enhancer. Here, we report that the recruitment of NF-κB to unintegrated viral DNA precedes, and is a prerequisite for, Tax-induced changes in epigenetic marks, so that an IN^- HIV-1 mutant lacking both LTR NF-κB sites is entirely nonresponsive to Tax and fails to undergo the epigenetic changes listed above. Interestingly, we found that induction of Tax expression at 24 h postinfection, when unintegrated HIV-1 DNA is already fully repressed by inhibitory chromatin modifications, is able to effectively reverse the epigenetic silencing of that DNA and rescue viral gene expression. Finally, we report that heterologous promoters introduced into IN-deficient HIV-1-based vectors are transcriptionally active even in the absence of Tax and do not increase their activity when the HIV-1 promoter and enhancer, located in the LTR U3 region, are deleted, as has been recently proposed. IMPORTANCE Integrase-deficient expression vectors based on HIV-1 are becoming increasingly popular as tools for gene therapy in vivo due to their inability to cause insertional mutagenesis. However, many IN^- lentiviral vectors are able to achieve only low levels of gene expression, and methods to increase this low level have not been extensively explored. Here, we analyzed how the HTLV-1 Tax protein is able to rescue the replication of IN^- HIV-1 in T cells, and we describe IN^- lentiviral vectors, lacking any inserted origin of replication, that are able to express a heterologous gene effectively.

Reversal of Epigenetic Silencing Allows Robust HIV-1 Replication in the Absence of Integrase Function

While retroviral DNA is synthesized normally after infection by integrase-deficient viruses, the resultant episomal DNA is then epigenetically silenced. Here, we show that expression of the Tax transcription factor encoded by a second human retrovirus, HTLV-1, prevents or reverses the epigenetic silencing of unintegrated HIV-1 DNA and instead induces the addition of activating epigenetic marks and the recruitment of NF-κB/Rel proteins to the HIV-1 LTR promoter. Moreover, in the presence of Tax, the HIV-1 DNA circles that form in the absence of integrase function are not only efficiently transcribed but also support a spreading, pathogenic integrase-deficient (IN⁻) HIV-1 infection. Thus, retroviruses have the potential to replicate without integration, as is indeed seen with HBV. Moreover, these data suggest that integrase inhibitors may be less effective in the treatment of HIV-1 infections in individuals who are also coinfected with HTLV-1.

Integration of the proviral DNA intermediate into the host cell genome normally represents an essential step in the retroviral life cycle. While the reason(s) for this requirement remains unclear, it is known that unintegrated proviral DNA is epigenetically silenced. Here, we demonstrate that human immunodeficiency virus 1 (HIV-1) mutants lacking a functional integrase (IN) can mount a robust, spreading infection in cells expressing the Tax transcription factor encoded by human T-cell leukemia virus 1 (HTLV-1). In these cells, HIV-1 forms episomal DNA circles, analogous to hepatitis B virus (HBV) covalently closed circular DNAs (cccDNAs), that are transcriptionally active and fully capable of supporting viral replication. In the presence of Tax, induced NF-κB proteins are recruited to the long terminal repeat (LTR) promoters present on unintegrated HIV-1 DNA, and this recruitment in turn correlates with the loss of inhibitory epigenetic marks and the acquisition of activating marks on histones bound to viral DNA. Therefore, HIV-1 is capable of replication in the absence of integrase function if the epigenetic silencing of unintegrated viral DNA can be prevented or reversed.

Neurological Aspects of HIV-1/HTLV-1 and HIV-1/HTLV-2 Coinfection

Simultaneous infection by human immunodeficiency viruses (HIV) and human T-lymphotropic viruses (HTLV) are not uncommon since they have similar means of transmission and are simultaneously endemic in many populations. Besides causing severe immune dysfunction, these viruses are neuropathogenic and can cause neurological diseases through direct and indirect mechanisms. Many pieces of evidence at present show that coinfection may alter the natural history of general and, more specifically, neurological disorders through different mechanisms. In this review, we summarize the current evidence on the influence of coinfection on the progression and outcome of neurological complications of HTLV-1/2 and HIV-1.

40 years of the human T-cell leukemia virus: past, present, and future

It has been nearly 40 years since human T-cell leukemia virus-1 (HTLV-1), the first oncogenic retrovirus in humans and the first demonstrable cause of cancer by an infectious agent, was discovered. Studies indicate that HTLV-1 is arguably one of the most carcinogenic agents to humans. In addition, HTLV-1 causes a diverse array of diseases, including myelopathy and immunodeficiency, which cause morbidity and mortality to many people in the world, including the indigenous population in Australia, a fact that was emphasized only recently. HTLV-1 can be transmitted by infected lymphocytes, from mother to child via breast feeding, by sex, by blood transfusion, and by organ transplant. Therefore, the prevention of HTLV-1 infection is possible but such action has been taken in only a limited part of the world. However, until now it has not been listed by the World Health Organization as a sexually transmitted organism nor, oddly, recognized as an oncogenic virus by the recent list of the National Cancer Institute/National Institutes of Health. Such underestimation of HTLV-1 by health agencies has led to a remarkable lack of funding supporting research and development of treatments and vaccines, causing HTLV-1 to remain a global threat. Nonetheless, there are emerging novel therapeutic and prevention strategies which will help people who have diseases caused by HTLV-1. In this review, we present a brief historic overview of the key events in HTLV-1 research, including its pivotal role in generating ideas of a retrovirus cause of AIDS and in several essential technologies applicable to the discovery of HIV and the unraveling of its genes and their function. This is followed by the status of HTLV-1 research and the preventive and therapeutic developments of today. We also discuss pending issues and remaining challenges to enable the eradication of HTLV-1 in the future.

HTLV-1/-2 and HIV-1 co-infections: retroviral interference on host immune status

The human retroviruses HIV-1 and HTLV-1/HTLV-2 share similar routes of transmission but cause significantly different diseases. In this review we have outlined the immune mediated mechanisms by which HTLVs affect HIV-1 disease in co-infected hosts. During co-infection with HIV-1, HTLV-2 modulates the cellular microenvironment favoring its own viability and inhibiting HIV-1 progression. This is achieved when the HTLV-2 proviral load is higher than that of HIV-1, and thanks to the ability of HTLV-2 to: (i) up-regulate viral suppressive CCL3L1 chemokine expression; (ii) overcome HIV-1 capacity to activate the JAK/STAT pathway; (iii) reduce the activation of T and NK cells; (iv) modulate the host miRNA profiles. These alterations of immune functions have been mainly attributed to the effects of the HTLV-2 regulatory protein Tax and suggest that HTLV-2 exerts a protective role against HIV-1 infection. Contrary to HIV-1/HTLV-2, the effect of HIV-1/HTLV-1 co-infection on immunological and pathological conditions is still controversial. There is evidence that indicates a worsening of HIV-1 infection, while other evidence does not show clinically relevant effects in HIV-positive people. Possible differences on innate immune mechanisms and a particularly impact on NK cells are becoming evident. The differences between the two HIV-1/HTLV-1 and HIV-1/HTLV-2 co-infections are highlighted and further discussed.

Interleukin-2 inhibits HIV-1 replication in some human T cell lymphotrophic virus-1-infected cell lines via the induction and incorporation of APOBEC3G into the virion

IL-2 has been used in culture of primary T cells to maintain cell proliferation. We have previously reported that IL-27 inhibits HIV-1 replication in primary T cells in the presence of IL-2. To gain a better understanding of the mechanisms involved in this inhibitory effect, we attempted to investigate in detail the effects of IL-27 and IL-2 using several cell lines. Unexpectedly, IL-27 did not inhibit HIV-1 in T cell lines, whereas IL-2 inhibited HIV-1 replication in the human T cell lymphotrophic virus (HTLV)-1-transformed T cell lines, MT-2, MT-4, SLB-1, and ATL-2. No effects were seen in HTLV-1-negative cell lines. Utilizing MT-2 cells, we demonstrated that IL-2 treatment inhibited HIV-1 syncytia-inducing ability and dose-dependently decreased supernatant p24 antigen levels by >90%. Using real time PCR and Western blot analysis, we observed that IL-2 treatment induced the host restriction factor, APOBEC3G with accumulation into the lower molecular mass active form as characterized by FPLC. Further analysis revealed that the virus recovered from IL-2-treated MT-2 cells had impaired replication competency. This was found to be due to incorporation of APOBEC3G into the virion despite the presence of Vif. These findings demonstrate a novel role for IL-2 in regulating production of infectious HIV-1 virions in HTLV-1-infected cells through the induction of APOBEC3G.

Human T-cell lymphotropic virus: a model of NF-κB-associated tumorigenesis

Human T-cell lymphotropic virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia/lymphoma (ATL), whereas the highly related HTLV-2 is not associated with ATL or other cancers. In addition to ATL leukemogenesis, studies of the HTLV viruses also provide an exceptional model for understanding basic pathogenic mechanisms of virus-host interactions and human oncogenesis. Accumulating evidence suggests that the viral regulatory protein Tax and host inflammatory transcription factor NF-κB are largely responsible for the different pathogenic potentials of HTLV-1 and HTLV-2. Here, we discuss the molecular mechanisms of HTLV-1 oncogenic pathogenesis with a focus on the interplay between the Tax oncoprotein and NF-κB pro-oncogenic signaling. We also outline some of the most intriguing and outstanding questions in the fields of HTLV and NF-κB. Answers to those questions will greatly advance our understanding of ATL leukemogenesis and other NF-κB-associated tumorigenesis and will help us design personalized cancer therapies.

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.

A transcription inhibitor, actinomycin D, enhances HIV-1 replication through an interleukin-6-dependent pathway

We previously demonstrated that Actinomycin D (ActD) enhanced HIV-1 replication in the MT-2 cell, a human T-cell leukemia virus type-1-infected cell line. The MT-2 cell is known to produce multiple cytokines spontaneously. In this study, we investigated the impact of ActD on the cytokine production from MT-2 cells and HIV-1 replication in a latently infected cell line, U1. MT-2 cells were pulse-treated with 0 or 200 nM of ActD, and culture supernatants were collected 3 days after incubation. Supernatants from untreated cells (Sup0) induced HIV-1 replication by 150-fold in U1 cells. Culture supernatants from ActD-treated cells (Sup200) enhanced HIV-1 replication by 1200-fold. A combination of a sequential chromatographic approach and mass spectrometric analysis identified that the HIV-inducing factors in Sup200 were interleukin (IL)-6 and tumor necrosis factor (TNF)-beta. Quantitative analysis revealed that ActD treatment increased the concentration of IL-6 in Sup200 by 600% compared with that in Sup0 but decreased the amount of TNFbeta in Sup200 by 85%. Northern blot analysis showed that ActD treatment increased IL-6 transcripts; however, no change was seen in TNFbeta transcripts. These results suggest that ActD induces replication of HIV-1 through modulation of cytokine production.

Comparative biology of human T-cell lymphotropic virus type 1 (HTLV-1) and HTLV-2

HTLV-1 and HTLV-2 are highly related complex retroviruses that have been studied intensely for nearly three decades because of their association with neoplasia, neuropathology, and/or their capacity to transform primary human T lymphocytes. The study of HTLV also represents an attractive model that has allowed investigators to dissect the mechanism of various cellular processes, several of which may be critical steps in HTLV-mediated pathogenesis. Both HTLV-1 and HTLV-2 can efficiently immortalize and transform T lymphocytes in cell culture and persist in infected individuals or experimental animals. However, the clinical manifestations of these two viruses differ significantly. HTLV-1 is associated with adult T-cell leukemia (ATL) and a variety of immune-mediated disorders including the chronic neurological disease termed HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). In contrast, HTLV-2 is much less pathogenic with reports of only a few cases of variant hairy cell leukemia and neurological disease associated with infection. The limited number of individuals shown to harbor HTLV-2 in association with specific diseases has, to date, precluded convincing epidemiological demonstration of a definitive etiologic role of HTLV-2 in human disease. Therefore, it has become clear that comparative studies designed to elucidate the mechanisms by which HTLV-1 and HTLV-2 determine distinct outcomes are likely to provide fundamental insights into the initiation of multistep leukemogenesis.

Establishment of a biological assay system for human retroviral protease activity

In order to obtain indicator cell lines that are exquisitely susceptible to human T-lymphotropic virus type 1 (HTLV-1), luciferase gene driven by HTLV-1 long terminal repeat (LTR) was transfected into lymphocytic H9 cells with neo gene, and cell lines were selected by G418. A cell line (H9/K30luc) was found to produce an extremely high level of luciferase only when co-cultured with HTLV-1 producer MT-2 cells. Both in the absence and presence of a reverse transcriptase (RT) inhibitor azidothymidine, H9/K30luc cells generated similarly high luciferase activity upon co-cultivation with MT-2 cells. To develop an equivalent system for human immunodeficiency virus type 1 (HIV-1), H9/NL432 cells, which are stably infected with HIV-1 and producing a low level of the virus-like MT-2 cells for HTLV-1, were generated. Together with the indicator cell line H9/H1luc for HIV-1 already reported, antiviral effects of some agents on HTLV-1 and HIV-1 could be readily and sensitively evaluated by similar methods. In fact, by using our system, an HIV-1 protease inhibitor, saquinavir, was demonstrated to be highly effective against HIV-1 but not against HTLV-1.

Actinomycin D induces high-level resistance to thymidine analogs in replication of human immunodeficiency virus type 1 by interfering with host cell thymidine kinase expression

Actinomycin D (ActD) is a transcription inhibitor and has been used in the treatment of certain forms of cancer. ActD has been reported to be a potential inhibitor of human immunodeficiency virus type 1 (HIV-1) replication due to its ability to inhibit reverse transcription. In contrast to what was expected, low concentrations of ActD (1 to 10 nM) upregulated HIV-1 replication 8- to 10-fold in MT-2 cells and had no effect on HIV-2 replication or on HIV-1 replication in MT-4, Jurkat, or peripheral blood mononuclear cells. The upregulation of HIV-1 replication was associated with an increase in HIV-1 transcription and a decrease in CD4 and CXCR4 expression. To further evaluate the effects of ActD on emergence of drug resistance in HIV-1 replication, a series of drug resistance assays were performed. Of interest, treatment of MT-2 cells with ActD also led to a high level of resistance to thymidine analogs (>1,000-fold increase in resistance to zidovudine and >250-fold to stavudine) but not to other nucleoside reverse transcriptases (RT), nonnucleoside RT, or protease inhibitors. This resistance appeared to be due to a suppression of host cell thymidine kinase-1 (TK-1) expression. These results indicate that ActD leads to a novel form of thymidine analog resistance by suppressing host cell TK-1 expression. These results suggest that administration of combination drugs to HIV-1-infected patients may induce resistance to antiretroviral compounds via a modification of cellular factors.

HTLV-1 Tax-associated hTid-1, a human DnaJ protein, is a repressor of Ikappa B kinase beta subunit

hTid-1, a human DnaJ protein, is a novel cellular target for HTLV-1 Tax. Here, we show that hTid-1 represses NF-kappaB activity induced by Tax as well as other activators such as tumor necrosis factor alpha (TNFalpha) and Bcl10. hTid-1 specifically suppresses serine phosphorylation of IkappaBalpha by activated IkappaB kinase beta (IKKbeta), but the activities of other serine kinases including p38, ERK2, and JNK1 are not affected. The suppressive activity of hTid-1 on IKKbeta requires a functional J domain that mediates association with heat shock proteins and results in prolonging the half-life of the NF-kappaB inhibitors IkappaBalpha and IkappaBbeta. Collectively, our data suggest that hTid-1, in association with heat shock proteins, exerts a negative regulatory effect on the NF-kappaB activity induced by various extracellular and intracellular activators including HTLV-1 Tax.

Contribution of immune activation to the pathogenesis and transmission of human immunodeficiency virus type 1 infection

The life cycle of human immunodeficiency virus type 1 (HIV-1) is intricately related to the activation state of the host cells supporting viral replication. Although cellular activation is essential to mount an effective host immune response to invading pathogens, paradoxically the marked systemic immune activation that accompanies HIV-1 infection in vivo may play an important role in sustaining phenomenal rates of HIV-1 replication in infected persons. Moreover, by inducing CD4+ cell loss by apoptosis, immune activation may further be central to the increased rate of CD4+ cell turnover and eventual development of CD4+ lymphocytopenia. In addition to HIV-1-induced immune activation, exogenous immune stimuli such as opportunistic infections may further impact the rate of HIV-1 replication systemically or at localized anatomical sites. Such stimuli may also lead to genotypic and phenotypic changes in the virus pool. Together, these various immunological effects on the biology of HIV-1 may potentially enhance disease progression in HIV-infected persons and may ultimately outweigh the beneficial aspects of antiviral immune responses. This may be particularly important for those living in developing countries, where there is little or no access to antiretroviral drugs and where frequent exposure to pathogenic organisms sustains a chronically heightened state of immune activation. Moreover, immune activation associated with sexually transmitted diseases, chorioamnionitis, and mastitis may have important local effects on HIV-1 replication that may increase the risk of sexual or mother-to-child transmission of HIV-1. The aim of this paper is to provide a broad review of the interrelationship between immune activation and the immunopathogenesis, transmission, progression, and treatment of HIV-1 infection in vivo.

Quantification of HTLV type I and HIV type I DNA load in coinfected patients: HIV type 1 infection does not alter HTLV type I proviral amount in the peripheral blood compartment

Several reports suggest that HTLV-I/HIV coinfection may be associated with an increased risk of HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). In HTLV-I-monoinfected patients, the occurrence of HAM/TSP is associated with high peripheral blood HTLV-I proviral load. Using a real-time quantitative PCR assay, we assessed the proviral DNA load in peripheral blood mononuclear cells (PBMCs) from 15 asymptomatic HTLV-I-monoinfected patients, 15 HTLV-I-monoinfected patients with HAM/TSP, and 25 HTLV-I/HIV-1 coinfected patients, including 4 with HAM/TSP. We also measured HIV-1 proviral DNA load in PBMCs from the coinfected patients. The median HTLV-I proviral loads were 6,800 and 4,100 copies per 10(6) PBMCs in the asymptomatic monoinfected and coinfected groups, and 58,800 and 43,300 copies per 10(6) PBMCs in the monoinfected and coinfected patients with HAM/TSP, respectively. The difference between HTLV-I proviral loads in HAM/TSP and asymptomatic monoinfected patients was statistically significant (p < 0.0001), but there was no difference between the HTLV-I-monoinfected and HTLV-I/HIV-1-coinfected groups. There was no correlation between HTLV-I and HIV-1 proviral load. HTLV-I proviral load did not correlate with the CD4+ T lymphocyte count. Among patients with no HTLV-I disease, the median copy number of HTLV-I per 10(6) circulating CD4+ T cells was 114,000 in the coinfected group and 16,700 in the monoinfected group, but the difference was not significant (p = 0.089). These data do not confirm the hypothesis in which HIV-1 coinfection would increase HTLV-I proviral burden in the PBMCs. However, depletion of the CD4+ T cell subset, the main target of HTLV-I, could be counterbalanced by an up-regulation of HTLV-I replication or by greater resistance of HTLV-I-infected cells to HIV-1-induced destruction.

Rel induces interferon regulatory factor 4 (IRF-4) expression in lymphocytes: modulation of interferon-regulated gene expression by rel/nuclear factor kappaB

In lymphocytes, the Rel transcription factor is essential in establishing a pattern of gene expression that promotes cell proliferation, survival, and differentiation. Here we show that mitogen-induced expression of interferon (IFN) regulatory factor 4 (IRF-4), a lymphoid-specific member of the IFN family of transcription factors, is Rel dependent. Consistent with IRF-4 functioning as a repressor of IFN-induced gene expression, the absence of IRF-4 expression in c-rel(-/-) B cells coincided with a greater sensitivity of these cells to the antiproliferative activity of IFNs. In turn, enforced expression of an IRF-4 transgene restored IFN modulated c-rel(-/-) B cell proliferation to that of wild-type cells. This cross-regulation between two different signaling pathways represents a novel mechanism that Rel/nuclear factor kappaB can repress the transcription of IFN-regulated genes in a cell type-specific manner.

Deletion of the GPG motif in the HIV type 1 V3 loop does not abrogate infection in all cells

The three amino acids glycine, proline, and glycine (GPG) constitute a conserved motif at the center of the V3 loop of HIV-1 surface glycoprotein 120. It has been indicated that deletion of this GPG motif is lethal for viral infectivity and abrogates the ability of the virus to form syncytia. In the present work, we studied the effects of GPG deletion on viral infectivity, cell tropism, syncytium formation, and initiation of apoptosis by constructing a mutant provirus based on the infectious clone pBRu-2. Successful infection and replication of GPG-deleted virus were detected in MT-2 cells, although the mutant virus showed lower infectivity. Infection could also be observed in the C8166, C91-PL, Molt-3, and THP-1 cell lines, and in PBMC-derived dendritic cells (DCs), but not in CEM-SS, HUT78, H9, Jurkat, and U937 cell lines or in PBMCs. Mutant virus also induced syncytia and apoptosis in the MT-2 cells. An intact GPG motif is probably necessary for unimpaired induction of fusion in some HIV-1-permissive cells. However, once the virus enters the cells, the GPG sequence does not seem to be indispensable for syncytium formation or apoptosis induction in MT-2 cells. Our data also imply that cell surface molecules other than CD4 and CXCR4 may be involved in entry of the GPG-deleted virus.

Differential patterns of interaction between HIV type 1 and HTLV type I in monocyte-derived macrophages cultured in vitro: implications for in vivo coinfection with HIV type 1 and HTLV type I

The interaction between human immunodeficiency virus type 1 (HIV-1) and human T cell leukemia-lymphoma virus type I (HTLV-I) has generated substantial interest. However, there is disagreement on the in vivo consequences of the double infection. We investigated the interactions between HIV-1 and HTLV-I in monocyte-derived macrophages cultured in vitro. For study, the T cell-tropic strain IIIB and the macrophagetropic strain Ada-M of HIV-1 were used. The HTLV-I was prepared from the supernatants of the virus-producing MT-2 cell line. We found that coinfection of macrophages with T cell-tropic HIV-1 and HTLV-I significantly enhanced HIV-1 replication, whereas double infection of the cells with macrophage-tropic HIV-1 and HTLV-I resulted in marked upregulation of HTLV-I production. Stimulatory interactions between HIV-1 and HTLV-I were mediated by their trans-acting proteins. Results of study on nuclear translocation of proviral DNA showed that the tax gene product of HTLV-I was able to facilitate the nuclear import of the reverse-transcribed HIV-1(IIIB) DNA. In contrast, the HIV-1 Tat protein did not increase the intranuclear trafficking of HTLV-I DNA, which suggests another mechanism for HTLV-I enhancement by the tat gene product. In conclusion, this study provides possible mechanisms whereby coinfection of an individual with HIV-1 and HTLV-I may influence the clinical outcome of double infection.

Human T-cell leukemia retrovirus-Tax protein is a repressor of nuclear receptor signaling

The Tax oncoprotein promotes cellular transformation and is associated with the pathogenesis of adult T-cell leukemia. Tax expression activates transcription via the cAMP enhancer binding protein/activating transcription factor (CREB/ATF) and NF-kappaB pathways. In contrast to its positive action, here we demonstrate that Tax is a potent repressor of steroid and retinoid receptor transcription. The Tax protein becomes localized in the promyelocytic (PML) oncogenic domain, and unexpectedly, expression of the PML protein reverses Tax-induced repression. These results suggest that PML and Tax may act in opposing manners to influence nuclear receptor transcription and human T-cell leukemia retrovirus pathogenesis.

Coinfection with HTLV-I and HIV: increase in HTLV-I-related outcomes but not accelerated HIV disease progression?

Human T-lymphotropic virus type I (HTLV-I) and HTLV-II have been postulated to accelerate disease progression in patients coinfected with HIV. However, recent evidence suggests that HTLV-II has no effect on HIV disease progression. In addition, it has recently been reported that HIV viral load was not increased in subjects coinfected with HTLV-I, suggesting that the biologic basis for the hypothesis does not exist. Several recent studies in Brazil, however, suggest that coinfection with HTLV-I and HIV has substantial medical consequences. For example, coinfection was associated with a higher CD4 lymphocytes count following adjustment for HIV viral load or HIV clinical stage. In addition, coinfected subjects have a high prevalence of clinical significant myelopathy. The effect of other putative viruses as cofactors in HIV disease progression is also discussed.

Factors secreted by human T lymphotropic virus type I (HTLV-I)-infected cells can enhance or inhibit replication of HIV-1 in HTLV-I-uninfected cells: implications for in vivo coinfection with HTLV-I and HIV-1

It remains controversial whether human T lymphotropic virus type I (HTLV-I) coinfection leads to more rapid progression of human immunodeficiency virus (HIV) disease in dually infected individuals. To investigate whether HTLV-I infection of certain cells can modulate HIV-1 infection of surrounding cells, primary CD4(+) T cells were treated with cell-free supernatants from HTLV-I-infected MT-2 cell cultures. The primary CD4+ T cells became resistant to macrophage (M)-tropic HIV-1 but highly susceptible to T cell (T)-tropic HIV-1. The CC chemokines RANTES (regulated on activation, normal T cell expressed and secreted), macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta in the MT-2 cell supernatants were identified as the major suppressive factors for M-tropic HIV-1 as well as the enhancers of T-tropic HIV-1 infection, whereas soluble Tax protein increased susceptibility to both M- and T-tropic HIV-1. The effect of Tax or CC chemokines on T-tropic HIV-1 was mediated, at least in part, by increasing HIV Env-mediated fusogenicity. Our data suggest that the net effect of HTLV-I coinfection in HIV-infected individuals favors the transition from M- to T-tropic HIV phenotype, which is generally indicative of progressive HIV disease.

Activation of BLV transcription by NF-kappa B and Tax

Bovine leukemia virus (BLV) is the causative agent of bovine leukosis, a naturally occurring fatal disease in cattle. BLV transcription is regulated by cellular transcription factors and the virally encoded oncoprotein Tax. In this report, we investigated the functional role of the putative NF-kappa B binding site recently identified in the BLV promoter. Our studies indicate that the kappa B binding motif acts as a functional enhancer in the presence of the cellular NF-kappa B proteins. Furthermore, the kappa B site together with a single 21-bp repeat confers strong activation of BLV transcription in the presence the NF-kappa B proteins and Tax. These results suggest that cellular NF-kappa B may be involved in the regulation of BLV transcription and activation of the virus from latency.

Mutational analysis of human T-cell leukemia virus type 2 Tax

A mutational analysis of human T-cell leukemia virus type 2 (HTLV-2) Tax (Tax-2) was performed to identify regions within Tax-2 important for activation of promoters through the CREB/ATF or NF-kappaB/Rel signaling pathway. Tax-2 mutations within the putative zinc-binding region as well as mutations at the carboxy terminus disrupted CREB/ATF transactivation. A single mutation within the central proline-rich region of Tax-2 disrupted the transactivation of the NF-kappaB/Rel pathway. Surprisingly, this mutation, which is thought to be in a separate activation domain, was suppressed by mutations within or around the putative zinc-binding region, suggesting an interaction between these two regions. These analyses indicate that the functional regions or domains important for transactivation through the CREB/ATF or NF-kappaB/Rel signaling pathway are similar, but not identical, in Tax-1 and Tax-2. Identification of these distinct Tax-2 mutants should facilitate comparative biological studies of HTLV-1 and HTLV-2 and ultimately lead to the determination of the functional importance of Tax trans-acting capacities in T-lymphocyte transformation by HTLV.

The human T-cell leukemia virus type 1 transactivator protein Tax colocalizes in unique nuclear structures with NF-kappaB proteins

The Tax protein of human T-cell leukemia virus type 1 (HTLV-1) is a potent activator of viral transcription. Tax also activates the expression of specific cellular genes involved in the control of T-lymphocyte growth via effects on cellular transcription factors, including members of the NF-kappaB/cRel family. Immunocytochemistry and electron microscopy were used to characterize the intracellular localization of Tax and identify cellular factors which are the potential targets for its transcriptional activity. These studies indicated that Tax localizes in discrete nuclear foci in T lymphocytes transformed by HTLV-1 and in cells transduced with Tax expression vectors. The Tax-containing foci are complex nuclear structures comprising a central core in which Tax colocalizes with splicing factor Sm. In addition to splicing factors Sm and SC-35, the Tax-containing nuclear structures also contain transcriptional components, including the largest subunit of RNA polymerase II and cyclin-dependent kinase CDK8. The inclusion of the two subunits of NF-kappaB, p50 and RelA, and the presence of the mRNA from a gene specifically activated by Tax through NF-kappaB binding sites suggest that these unique nuclear structures participate in Tax-mediated activation of gene expression via the NF-kappaB pathway.

Transrepression of lck gene expression by human T-cell leukemia virus type 1-encoded p40tax

To understand the mechanism of p56lck protein downregulation observed in human T cells infected by human T-cell leukemia virus type 1 (HTLV-1), we have investigated the ability of the 3' end of the HTLV-1 genome as well as that of the tax and rex genes to modulate p56lck protein expression and p56lck mRNA synthesis. By using Jurkat T cells stably transfected with constructs that expressed either the 3' end of the HTLV-1 genome (JK C11-pMTEX), the tax gene (JK52-Tax) or the rex gene (JK9-Rex), we found that the expression of p40tax (Tax) was sufficient to modulate p56lck protein expression. Similarly, we found that the expression of the mRNA which encoded p56lck was repressed in Jurkat T cells which expressed Tax. This downregulation was shown to be proportional to the amount of tax mRNA found in the transfected cells, as evidenced by experiments that used cells (JPX-9) stably transfected with a tax gene driven by a cadmium-inducible promoter. Furthermore, cadmium induction of Tax in JPX-9 cells transiently transfected with a construct containing the chloramphenicol acetyltransferase (CAT) gene under control of the lck distal promoter (lck DP-CAT) resulted in the downregulation of CAT gene expression. In contrast, cadmium induction of Tax in JPX-9 cells transiently transfected with a CAT construct driven by a lck DP with a deletion extending from position -259 to -253 (a sequence corresponding to a putative E-Box) did not modulate CAT gene expression, suggesting that the effect of Tax on p56lck is mediated through an E-Box binding protein.

Molecular biology of human immunodeficiency virus type-1

Tremendous progress has been made in our understanding of the multiplication and pathogenesis of the human immunodeficiency virus, the causative agent of acquired immunodeficiency syndrome (AIDS). To block virus multiplication several targets in the life cycle of the virus have already been identified for which antiviral drugs can be developed and gene therapy can be envisaged as a possible treatment or cure of AIDS. The combination of several therapies might be needed for effective treatment. Prevention of HIV infections through effective vaccines still awaits novel, unconventional strategies.

The tax gene of human T-cell leukemia virus type 2 is essential for transformation of human T lymphocytes

The mechanism of human T-cell leukemia virus (HTLV)-mediated transformation and induction of malignancy is unknown; however, several studies have implicated the viral gene product, Tax. Conclusive evidence for the role of Tax in the HTLV malignant process has been impeded by the inability to mutate tax in the context of an infectious virus and dissociate viral replication from cellular transformation. To circumvent this problem we constructed a mutant of HTLV type 2 (HTLV-2) that replicates by a Tax-independent mechanism. For these studies, the Tax response element in the viral long terminal repeat was replaced with the cytomegalovirus immediate-early promoter enhancer (C-enh). Transcription of the chimeric HTLV-2 (HTLVC-enh) was efficiently directed by this heterologous promoter. Also, the chimeric virus transformed primary human T lymphocytes with an efficiency similar to that of wild-type HTLV-2. A tax-knockout virus, termed HTLVC-enhDeltaTax, was constructed to directly assess the importance of Tax in cellular transformation. Transfection and infection studies indicated that HTLVC-enhDeltaTax was replication competent; however, HTLVC-enhDeltaTax failed to transform primary human T lymphocytes. We conclude that Tax is essential for HTLV-mediated transformation of human T lymphocytes. Furthermore, this chimeric HTLV, that replicates in the absence of Tax, should facilitate studies to determine the precise mechanism of T-lymphocyte transformation by HTLV.

Human T-cell leukemia virus type I tax masks c-Myc function through a cAMP-dependent pathway

Human T-cell leukemia virus type I Tax is a pleiotropic gene regulator that functions through CREB/ATF- and NF-kappaB-mediated pathways. In most contexts, Tax is a potent gene activator. Here, we describe an unexpected finding of Myc repression by Tax. In cells that overexpress human T-cell leukemia virus type I Tax, the detection of c-Myc protein in the nucleus by a monoclonal antibody was masked. Tax prevented immunological visualization of a Myc epitope contained within amino acids 45-104, resulting in interference with Myc function in transcription and in anchorage-independent cell growth. Tax did not affect steady-state protein levels since detection of c-Myc with other antibodies was unperturbed. Four observations suggest that this Tax-Myc interaction is mediated through CREB/ATF signal transduction. 1) Tax point mutants, selectively defective for activation of CREB/ATF but not NF-kappaB, failed to mask c-Myc; 2) masking of Myc was abolished when Tax-expressing cells were treated with protein kinase inhibitor H-9; 3) Tax-specific shielding of Myc is absent in cells (B1R) that are genetically defective for cAMP signaling; and 4) forskolin treatment of cells mimicked Tax in masking the Myc epitope. Considered collectively, these findings suggest a regulation of Myc function at the level of localized protein conformation.

Transcriptional activation of RNA polymerase III-dependent genes by the human T-cell leukemia virus type 1 tax protein

The human T-cell leukemia virus-encoded tax protein is a potent activator of many viral and cellular genes transcribed by RNA polymerase II. We find that both chromatin and cell extracts derived from human T-cell leukemia virus type 1-infected human T lymphocytes support higher levels of 5S rRNA and tRNA gene transcription than chromatin or extracts from uninfected T lymphocytes. The viral protein Tax was likely responsible for this higher level of class II gene transcription, as purified Tax was found to stimulate both genes when added to the uninfected cell extract or in reconstituted systems. Both limiting-component transcription assays and DNA binding assays identified the class III gene transcription factor TFIIIB as the principle target of Tax activity. Surprisingly, we find that Tax increases the effective concentration of active TFIIIB molecules. These data suggest that Tax stimulates RNA polymerase III-dependent gene expression by accelerating the rate and/or extent of transcription initiation complex assembly.

Selective infection of human T-lymphotropic virus type 1 (HTLV-1)-infected cells by chimeric human immunodeficiency viruses containing HTLV-1 tax response elements in the long terminal repeat

Previous studies have suggested that the human immunodeficiency virus long terminal repeat (HIV LTR) enhancer/promoter sequences contribute to the replication ability of HIV in different T-cell lines; mutation of these sequences can alter HIV tropism. We have utilized site-specific mutagenesis to generate variants of HIV that exhibit specific tropism for human T-lymphotropic virus type 1 (HTLV-1) Tax-expressing CD4+ T cells. The wild-type HIV LTR NF-kappa B and Sp1 sites in an infectious molecular clone of HIV type 1 were replaced with sequences derived from the 21-bp Tax response elements (TRE) from the HTLV-1 LTR to generate TRE-containing chimeric HIVs (TRE-HIVs). The TRE-HIVs exhibit selective replication and cell killing in HTLV-infected human CD4+ T cells, but not in HTLV-negative T cells. Transient transfections suggested that Tax-TRE interactions could account for the observed replication specificity. The TRE-containing HIV LTRs were synergistically activated by the HIV Tat and HTLV-1 Tax transactivators. These results demonstrate that it is possible to specifically target HIV replication and cytotoxicity to HTLV-1+, CD4+ human T cells, on the basis of Tax-TRE interactions, and provide a model for the development of specific, cytotoxic, retroviral gene therapy vectors for HTLV-1-infected cells based on alterations of the LTR transcriptional regulatory elements. They also suggest that HIV Tat can cooperate with heterologous transcriptional activators, such as Tax, which act through upstream binding sites without directly binding to DNA.

Human T-cell leukemia virus type II infection among high risk groups and its influence on HIV-1 disease progression

The prevalence and the risk factors of the human T-cell leukemia virus type I/II (HTLV-I/II) infection were evaluated among 552 individuals at high risk for HIV-1. HTLV infections showed a low (1.6%) prevalence, were restricted to intravenous drug addicts and were due to HTLV-II alone. Moreover, in order to weigh the influence of HTLV-II on the natural history of HIV-1 infection, the clinical outcome of HIV-1 disease was compared between subjects with and without HTLV-II coinfection. Our findings showed that HTLV-II does not adversely affect the outcome of HIV-1 infection. Infact, a slower disease progression has been recorded in some HTLV-II coinfected subjects.

Persistence of attenuated rev genes in a human immunodeficiency virus type 1-infected asymptomatic individual

With the goal of examining the functional diversity of human immunodeficiency virus type 1 (HIV-1) env genes within the peripheral blood mononuclear cells of an asymptomatic individual, we substituted four complete env genes into the replication-competent NL4-3 provirus. Despite encoding full-length open reading frames for gp120 and gp41 and the second coding exon of tat and rev, each chimera was replication defective. Site-directed mutagenesis of codon 78 in the Rev activation domain (from a hitherto unique Ile to the subtype B consensus Leu) partially restored infectivity for two of three chimeras tested. Similarly, mutagenesis of rev codon 78 of NL4-3 from Leu to Ile partially attenuated this virus. Ile-78 was found in all 13 clones examined from samples taken from this asymptomatic subject 4.5 years after infection, including 9 from peripheral blood mononuclear cells and 4 from a virus isolate, as well as 4 additional clones each from peripheral blood mononuclear cells sampled 37 and 51 months later. We next examined conservation of the Rev activation domain within and among long-term survivors (LTS) and patients with AIDS, as well as T-cell-line-adapted strains of HIV-1. Putative attenuating mutations were found in a minority of sequences from all five LTS and two of four patients with AIDS. Of the 11 T-cell-line-adapted viruses examined, none had these changes. Among and within LTS virus population had marginally higher levels of diversity in Rev than in Env; patients with AIDS had similar levels of diversity in the two reading frames; and T-cell-line-adapted viruses had higher levels of diversity in Env. These results are consistent with the hypothesis that asymptomatic individuals harbor attenuated variants of HIV-1 which correlate with and contribute to their lack of disease progression.

Coupling of a signal response domain in I kappa B alpha to multiple pathways for NF-kappa B activation

The eukaryotic transcription factor NF-kappa B plays a central role in the induced expression of human immunodeficiency virus type 1 and in many aspects of the genetic program mediating normal T-cell activation and growth. The nuclear activity of NF-kappa B is tightly regulated from the cytoplasmic compartment by an inhibitory subunit called I kappa B alpha. This cytoplasmic inhibitor is rapidly phosphorylated and degraded in response to a diverse set of NF-kappa B-inducing agents, including T-cell mitogens, proinflammatory cytokines, and viral transactivators such as the Tax protein of human T-cell leukemia virus type 1. To explore these I kappa B alpha-dependent mechanisms for NF-kappa B induction, we identified novel mutants of I kappa B alpha that uncouple its inhibitory and signal-transducing functions in human T lymphocytes. Specifically, removal of the N-terminal 36 amino acids of I kappa B alpha failed to disrupt its ability to form latent complexes with NF-kappa B in the cytoplasm. However, this deletion mutation prevented the induced phosphorylation, degradative loss, and functional release of I kappa B alpha from NF-kappa B in Tax-expressing cells. Alanine substitutions introduced at two serine residues positioned within this N-terminal regulatory region of I kappa B alpha also yielded constitutive repressors that escaped from Tax-induced turnover and that potently inhibited immune activation pathways for NF-kappa B induction, including those initiated from antigen and cytokine receptors. In contrast, introduction of a phosphoserine mimetic at these sites rectified this functional defect, a finding consistent with a causal linkage between the phosphorylation status and proteolytic stability of this cytoplasmic inhibitor. Together, these in vivo studies define a critical signal response domain in I kappa B alpha that coordinately controls the biologic activities of I kappa B alpha and NF-kappa B in response to viral and immune stimuli.

Kinetic analysis of human T-cell leukemia virus type I Tax-mediated activation of NF-kappa B

The human T-cell leukemia virus type I (HTLV-I) Tax protein induces the expression of cellular genes, at least in part, by activating the endogenous NF-kappa B transcription factors. Induced expression of cellular genes is thought to be important for transformation of T cells to continued growth, a prelude to the establishment of adult T-cell leukemia. However, neither underlying mechanisms nor kinetics of the Tax-mediated activation of NF-kappa B are understood. We have analyzed a permanently transfected Jurkat T-cell line in which the expression of Tax is entirely dependent on addition of heavy metals. The initial NF-kappa B binding activity seen after induction of Tax is due almost exclusively to p50/p65 heterodimers. At later times, NF-kappa B complexes containing c-Rel and/or p52 accumulate. The early activation of p50/p65 complexes is a posttranslational event, since neither mRNA nor protein levels of NF-kappa B subunits had increased at that time. We demonstrate for the first time a Tax-induced proteolytic degradation of the NF-kappa B inhibitor, I kappa B-alpha, which may trigger the initial nuclear translocation of NF-kappa B. As nuclear NF-kappa B rapidly and potently stimulates resynthesis of I kappa B-alpha, the steady-state level of I kappa B-alpha does not significantly change. Thus, the dramatic Tax-induced increase in the I kappa B-alpha turnover may continually weaken inhibition and activate NF-kappa B. Additional, distinct actions of Tax may contribute further to the high levels of NF-kappa B activity seen.

Kinetic analysis of human T-cell leukemia virus type I Tax-mediated activation of NF-kappa B

The human T-cell leukemia virus type I (HTLV-I) Tax protein induces the expression of cellular genes, at least in part, by activating the endogenous NF-kappa B transcription factors. Induced expression of cellular genes is thought to be important for transformation of T cells to continued growth, a prelude to the establishment of adult T-cell leukemia. However, neither underlying mechanisms nor kinetics of the Tax-mediated activation of NF-kappa B are understood. We have analyzed a permanently transfected Jurkat T-cell line in which the expression of Tax is entirely dependent on addition of heavy metals. The initial NF-kappa B binding activity seen after induction of Tax is due almost exclusively to p50/p65 heterodimers. At later times, NF-kappa B complexes containing c-Rel and/or p52 accumulate. The early activation of p50/p65 complexes is a posttranslational event, since neither mRNA nor protein levels of NF-kappa B subunits had increased at that time. We demonstrate for the first time a Tax-induced proteolytic degradation of the NF-kappa B inhibitor, I kappa B-alpha, which may trigger the initial nuclear translocation of NF-kappa B. As nuclear NF-kappa B rapidly and potently stimulates resynthesis of I kappa B-alpha, the steady-state level of I kappa B-alpha does not significantly change. Thus, the dramatic Tax-induced increase in the I kappa B-alpha turnover may continually weaken inhibition and activate NF-kappa B. Additional, distinct actions of Tax may contribute further to the high levels of NF-kappa B activity seen.

Cutaneous disease resembling mycosis fungoides in HIV-infected patients whose skin and blood cells also harbor proviral HTLV type I

Two homosexual HIV-infected patients with lymphocyte counts of < 50 presented with intense pruritus, hyperpigmentation, and skin lesions clinically suggestive of the cutaneous T cell lymphoma, mycosis fungoides. On light microscopy, the skin biopsies were difficult to interpret because of the sparseness of the lymphocytic infiltrates. However, electron microscopy revealed typical Sézary cells in the peripheral blood and skin. Cultures of blood mononuclear cells of one of the patients generated HTLV-I-like particles. Although both patients lacked antibodies to HTLV, their blood and skin specimens proved to harbor tax and pol HTLV-I proviral sequences as shown by the polymerase chain reaction and Southern blot analysis. Dual infection with HIV and HTLV should be considered in the diagnostic work-up of patients at risk, even in the absence of demonstrable antibodies. Dual infections could result in clinical manifestations and evolution of disease not anticipated in patients who harbor only one of these retroviruses.

HTLV-I and HTLV-II infections among HIV-1 seropositive patients in Sao Paulo, Brazil

To estimate the presence of, and the risk factors for HTLV-I and HTLV-II infections among HIV-1 infected subjects in Sao Paulo, Brazil, a serosurvey was performed in 471 HIV-1 infected patients, including 216 intravenous drug addicts (IVDA), 229 homosexual/bisexual men, and 26 with other risk factors. Serum samples were screened for HTLV seroreactivity by ELISA; reactive samples were analyzed by Western Blot (WB), using whole HTLV-I lysate as antigen. To confirm and discriminate HTLV-I and HTLV-II infections, sera presenting any bands on WB were further analyzed by a WB containing recombinant HTLV-I and HTLV-II proteins (WB 2.3), and by enzyme immunoassays using synthetic peptides specific for envelope proteins (Synth-EIA). In 22 cases, cell samples were available for polymerase chain reaction (PCR) studies. On WB, 114 sera were reactive and, of these, 37 and 25 were concordantly positive on both WB 2.3 and Synth-EIA procedures for HTLV-I and HTLV-II specific antibodies, respectively; 37 specimens were negative on both assays, and 15 gave discordant or indeterminate results. PCR findings confirmed concordant results obtained in the discriminatory serological assays. The prevalence rates of HTLV-I and HTLV-II infections were 15.3% and 11.1% in IVDA, and 0.9% and 0.4% in homosexual/bisexual men, respectively. No case of HTLV-I/HTLV-II co-infection was found.

Human T-cell leukemia virus type I Tax associates with and is negatively regulated by the NF-kappa B2 p100 gene product: implications for viral latency

Human T-cell leukemia virus type I (HTLV-I) is the etiologic agent of the adult T-cell leukemia, an aggressive and often fatal malignancy of activated human CD4 T cells. HTLV-I encodes an essential 40-kDa protein termed Tax that not only transactivates the long terminal repeat of this retrovirus but also induces an array of cellular genes. Tax-mediated transformation of T cells likely involves the deregulated expression of various cellular genes that normally regulate lymphocyte growth produced by altered activity of various endogenous host transcription factors. In particular, Tax is capable of modulating the expression or activity of various host transcription factors, including members of the NF-kappa B/Rel and CREB/ATF families, as well as the cellular factors HEB-1 and p67SRF. An additional distinguishing characteristic of HTLV-I infection is the profound state of viral latency that is present in circulating primary leukemic T cells. In this study, we demonstrate that HTLV-I Tax can physically associate with p100, the product of the Rel-related NF-kappa B2 gene, both in transfected cells and in HTLV-I-infected leukemic T-cell lines. Furthermore, the physical interaction of Tax with p100 leads to the inhibition of Tax-induced activation of the HTLV-I and human immunodeficiency virus type 1 long terminal repeats, reflecting p100-mediated cytoplasmic sequestration of the normally nuclearly expressed Tax protein. In contrast, a mutant of Tax that selectively fails to activate nuclear NF-kappa B expression does not associate with p100. Together, these results suggest that the cytoplasmic interplay of Tax and p100 may play an important role in the initiation and maintenance of HTLV-1 latency observed in adult T-cell leukemia.

Human T-cell leukemia virus type I Tax associates with and is negatively regulated by the NF-kappa B2 p100 gene product: implications for viral latency

Human T-cell leukemia virus type I (HTLV-I) is the etiologic agent of the adult T-cell leukemia, an aggressive and often fatal malignancy of activated human CD4 T cells. HTLV-I encodes an essential 40-kDa protein termed Tax that not only transactivates the long terminal repeat of this retrovirus but also induces an array of cellular genes. Tax-mediated transformation of T cells likely involves the deregulated expression of various cellular genes that normally regulate lymphocyte growth produced by altered activity of various endogenous host transcription factors. In particular, Tax is capable of modulating the expression or activity of various host transcription factors, including members of the NF-kappa B/Rel and CREB/ATF families, as well as the cellular factors HEB-1 and p67SRF. An additional distinguishing characteristic of HTLV-I infection is the profound state of viral latency that is present in circulating primary leukemic T cells. In this study, we demonstrate that HTLV-I Tax can physically associate with p100, the product of the Rel-related NF-kappa B2 gene, both in transfected cells and in HTLV-I-infected leukemic T-cell lines. Furthermore, the physical interaction of Tax with p100 leads to the inhibition of Tax-induced activation of the HTLV-I and human immunodeficiency virus type 1 long terminal repeats, reflecting p100-mediated cytoplasmic sequestration of the normally nuclearly expressed Tax protein. In contrast, a mutant of Tax that selectively fails to activate nuclear NF-kappa B expression does not associate with p100. Together, these results suggest that the cytoplasmic interplay of Tax and p100 may play an important role in the initiation and maintenance of HTLV-1 latency observed in adult T-cell leukemia.

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.

Pleiotropic effect of the human T-cell leukemia virus Tax protein on the DNA binding activity of eukaryotic transcription factors

The Tax protein, encoded by the human T-cell leukemia virus type I, is a potent activator of viral and cellular gene transcription. Tax does not bind DNA directly but appears to trans-activate through an interaction with host-cell transcription factors that recognize sequences within the promoters of Tax-responsive genes. Cellular transcriptional activators implicated in mediating Tax trans-activation include members of the activating transcription factor/cAMP response element binding protein (ATF/CREB) family of proteins, serum response factor, Fos-Jun, and NF-kappa B. Recent evidence suggests that Tax may stimulate human T-cell leukemia virus type I transcription, at least in part, through enhanced binding of ATF/CREB proteins to their recognition elements within the Tax-responsive 21-bp repeats of the viral promoter. In this report, we demonstrate that Tax also enhances the site-specific DNA binding activity of serum response factor and Fos-Jun and modestly enhances the binding of the NF-kappa B subunits, p50 and p65. We also show that Tax increases the DNA binding activity of the eukaryotic transcription factors ATF-1, Sp1, and GAL4. These results are consistent with the finding that Tax is highly pleiotropic and suggest that Tax trans-activation may involve enhancement in the DNA binding activity of target transcriptional regulatory proteins. In addition, we show that the mechanism of Tax-enhanced DNA binding activity does not involve an alteration in the redox state of the target protein.

Interaction between NF-kappa B- and serum response factor-binding elements activates an interleukin-2 receptor alpha-chain enhancer specifically in T lymphocytes

We find that a short enhancer element containing the NF-kappa B binding site from the interleukin-2 receptor alpha-chain gene (IL-2R alpha) is preferentially activated in T cells. The IL-2R alpha enhancer binds NF-kappa B poorly and is only weakly activated by the NF-kappa B site alone. Serum response factor (SRF) binds to a site adjacent to the NF-kappa B site in the IL-2R enhancer, and both sites together have strong transcriptional activity specifically in T cells. Surprisingly, the levels of SRF constitutively expressed in T cells are consistently higher than in other cell types. Overexpression of SRF in B cells causes the IL-2R enhancer to function as well as it does in T cells, suggesting that the high level of SRF binding in T cells is functionally important.

Interaction between NF-kappa B- and serum response factor-binding elements activates an interleukin-2 receptor alpha-chain enhancer specifically in T lymphocytes

We find that a short enhancer element containing the NF-kappa B binding site from the interleukin-2 receptor alpha-chain gene (IL-2R alpha) is preferentially activated in T cells. The IL-2R alpha enhancer binds NF-kappa B poorly and is only weakly activated by the NF-kappa B site alone. Serum response factor (SRF) binds to a site adjacent to the NF-kappa B site in the IL-2R enhancer, and both sites together have strong transcriptional activity specifically in T cells. Surprisingly, the levels of SRF constitutively expressed in T cells are consistently higher than in other cell types. Overexpression of SRF in B cells causes the IL-2R enhancer to function as well as it does in T cells, suggesting that the high level of SRF binding in T cells is functionally important.