Activation of T cell-derived lymphokine genes in T cells and fibroblasts: effects of human T cell leukemia virus type I p40x protein and bovine papilloma virus encoded E2 protein

Human T-cell Lymphotropic Viruses: Review and Prospects for Antiviral Therapy

The human T-cell lymphotropic viruses types I and II (HTLV-I, II) pose challenges to researchers and clinicians who seek to unveil mechanisms of viral transformation and pathogenesis. HTLV-I infection in humans is associated with a wide array of primary and secondary diseases ranging from mild immunosuppression to adult T-cell leukaemia/lymphoma and HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a neurological degenerative syndrome. As retroviruses, HTLV-I and II share similar replicative cycles with human immunodeficiency virus (HIV), the causative agent of acquired immunodeficiency syndrome. However, in contrast to HIV-I which destroys CD4+ T cells, HTLV-I and II can preferentially transform a CD4+ T-cell subset to an unrestricted growth state.

HTLV-I and II, along with simian T-lymphotropic virus (STLV) and bovine leukaemia virus (BLV), form a phylogenetic group which is distinct from ungulate, non-human primate and human lentiviruses such as visna, simian immunodeficiency virus (SIV), and human immunodeficiency viruses types 1 and 2. The proviral genome of HTLV-I is flanked at the 5′ and 3′ ends by long terminal repeats (LTR) and is further subdivided into structural gag and env genes, a pro gene encoding an aspartyl protease, a pol gene which encodes reverse transcriptase and endonuclease, and the regulatory gene elements tax and rex. Regions within the LTR contain recognition sites for cellular proteins and the tax gene product that collectively promote viral expression. Tax-mediated activation of cellular genes involved in growth and differentiation is suspected to play a dominant role in the leukaemogenic process associated with HTLV-I infection. Differential rex-regulated splicing of viral message gives rise to transcripts encoding the polyprotein precursor gag-pro-pol (unspliced), envelope (single spliced), or tax/rex (doubly spliced). The 100nm HTLV virion contains an electron-dense core surrounding a divalent-single stranded DNA genome. This core is in turn enclosed by concentric shells of matrix protein and an outer lipid bilayer, the latter acquired as the virus buds from the surface of the infected cell. Envelope glycoproteins associated with the outside of this lipid bilayer can interact with viral receptors on cells and mediate virus entry. Antiviral strategies have been directed at inhibiting viral entry into cells (sulphated and non-sulphated polysaccharides, vaccines), blocking of viral replication (AZT, suramin), intracellular immunization (transdominant repression of rex), and elimination of virus infected cells (IL-2 receptor-directed toxins). Serological screening of the blood supply and curtailing breast feeding of children by HTLV-I + mothers have likely had a major impact in preventing HTLV-I infection.

Transformation studies with a human T-cell leukemia virus type 1 molecular clone

In in vitro studies human T-cell leukemia virus type 1 (HTLV-1) may be produced by stable or transient transfection of target cells with an infectious molecular clone. Studies using primary human T cells, the natural targets of HTLV-1 infection, are hampered by difficulty in achieving significant infection with cell-free virus and a poor efficiency of transfection of primary cells. A method is described for the generation of stable cell lines expressing HTLV-1 from an infectious proviral clone. The stably transfected cells can be irradiated and cocultured with human peripheral blood mononuclear cells (PBMC) resulting in infected primary cells. These cells become immortalized, IL-2 dependent lines, which contain integrated copies of provirus and express a full spectrum of viral proteins. Analysis of cellular markers indicates that immortalized cell lines consist of CD3+/CD4+ T cells, matching the most common adult T-cell leukemia (ATL) cell phenotype. The method described has great utility in the study of the replication and transformation capacity of HTLV and HTLV mutant viruses in their natural targets, primary human T lymphocytes.

Functional activities of the human T-cell leukemia virus type I Tax oncoprotein: cellular signaling through NF-kappa B

Human T-cell leukemia virus type I (HTLV-I) is the etiological agent for adult T-cell leukemia (ATL), as well as for tropical spastic paraparesis (TSP) and HTLV-I associate myelopathy (HAM). A biological understanding of the involvement of HTLV-I and in ATL has focused significantly on the workings of the virally-encoded 40 kDa phospho-oncoprotein, Tax. Tax is a transcriptional activator. Its ability to modulate the expression and function of many cellular genes has been reasoned to be a major contributory mechanism explaining HTLV-I-mediated transformation of cells. In activating cellular gene expression, Tax impinges upon several cellular signal-transduction pathways, including those for CREB/ATF and NF-kappa B. In this paper, we review aspects of Tax's transcriptional potential with particular focus on recent evidence linking Tax to IKK (I kappa B-kinase)-complex and MAP3Ks (mitogen-activated protein kinase kinase kinases).

Human T-lymphotropic virus type 1 infection

Human T-cell lymphotropic virus type-1 (HTLV-1) is aetiologically associated with adult T-cell leukaemia/lymphoma (ATL). HTLV-1 infection can also lead to various non-malignant diseases, for example, HTLV-1 associated myelopathy/tropical spastic paraparesis and HTLV-1 uveitis. HTLV-1 is endemic in southern Japan and the Caribbean. HTLV-1 infection is mainly transmitted by either breast-feeding, sexual intercourse or blood transfusions. Primary prevention of HTLV-1 in endemic areas by screening of blood and by refraining from breast-feeding have been successful. The incidence of ATL is rather low among HTLV-1 carriers (<5%). The precise mechanism of development of ATL remains unknown. It is a multiple-step process which does not require viral expression in the later stages of leukaemogenesis. Many samples have mutations of the tumour suppressor genes, p53 and/or p16(INK4A). Four subtypes of ATL have been identified, each having distinctive clinical features. Monoclonal integration of HTLV-1 proviral DNA into tumour cells is found in each of the subtypes. At present, no effective therapy for ATL exists.

Identification of poly(ADP-ribose) polymerase as a transcriptional coactivator of the human T-cell leukemia virus type 1 Tax protein

Human T-cell leukemia virus type 1 (HTLV-1) encodes a transcriptional activator, Tax, whose activity is believed to contribute significantly to cellular transformation. Tax stimulates transcription from the proviral promoter as well as from promoters for a variety of cellular genes. The mechanism through which Tax communicates to the general transcription factors and RNA polymerase II has not been completely determined. We investigated whether Tax could function directly through the general transcription factors and RNA polymerase II or if other intermediary factors or coactivators were required. Our results show that a system consisting of purified recombinant TFIIA, TFIIB, TFIIE, TFIIF, CREB, and Tax, along with highly purified RNA polymerase II, affinity-purified epitope-tagged TFIID, and semipurified TFIIH, supports basal transcription of the HTLV-1 promoter but is not responsive to Tax. Two additional activities were required for Tax to stimulate transcription. We demonstrate that one of these activities is poly(ADP-ribose) polymerase (PARP), a molecule that has been previously identified to be the transcriptional coactivator PC1. PARP functions as a coactivator in our assays at molar concentrations approximately equal to those of the DNA and equal to or less than those of the transcription factors in the assay. We further demonstrate that PARP stimulates Tax-activated transcription in vivo, demonstrating that this biochemical approach has functionally identified a novel target for the retroviral transcriptional activator Tax.

Persistent activation of NF-kappaB by the tax transforming protein of HTLV-1: hijacking cellular IkappaB kinases

Biochemical coupling of transcription factor NF-kappaB to antigen and co-stimulatory receptors is required for the temporal control of T-cell proliferation. In contrast to its transitory activation during normal growth-signal transduction, NF-kappaB is constitutively deployed in T-cells transformed by the type 1 human T-cell leukemia virus (HTLV-1). This viral/host interaction is mediated by the HTLV-1-encoded Tax protein, which has potent oncogenic properties. As reviewed here, Tax activates NF-kappaB primarily via a pathway leading to the chronic phosphorylation and degradation of IkappaBalpha, a cytoplasmic inhibitor of NF-kappaB. To access this pathway, Tax associates stably with a cytokine-inducible IkappaB kinase (IKK), which contains both catalytic (IKKalpha and IKKbeta) and noncatalytic (IKKgamma) subunits. Unlike their transiently induced counterparts in cytokine-treated cells, Tax-associated forms of IKKalpha and IKKbeta are persistently activated in HTLV-1-infected T cells. Acquisition of the deregulated IKK phenotype is contingent on the presence of IKKgamma, which functions as a molecular adaptor in the assembly of pathologic Tax/IkappaB kinase complexes. These findings highlight a key mechanistic role for IKK in the Tax/NF-kappaB signaling axis and define new intracellular targets for the therapeutic control of HTLV-1-associated disease.

Pathological roles of interleukin-15 in adult T-cell leukemia

Interleukin-15 (IL-15) is a 14-kDa glycoprotein belonging to the same four helix bundle-cytokine family as IL-2. Although the biological activity of IL-15 in vitro has been studied extensively, its physiological role is still obscure. The receptors for IL-15 and IL-2 consist of three subunits, an unique alpha chain and shared beta and gamma chains. Since beta and gamma chains transduce the signals from the receptors, both cytokines share similar biologic functions, although IL-15 and IL-2 do not have sequence homology. The alpha chains function to increase binding affinity for each cytokines. Adult T-cell leukemia (ATL) cells constitutively express the IL-2 receptor (IL-2R) alpha and expression is believed to be essential in the early stages of disease development. We have recently shown that ATL cells also express the complete form of IL-15R including the alpha chain, and that ATL cells proliferate in response to exogenous IL-15. Since the mRNA of IL-15 is ubiquitous and is detected in many tissues and cells, it is possible that IL-15R stimulation is involved in the development and progression of ATL. Here, we review recent studies on IL-15 and IL-15R and their association with ATL and other lymphoproliferative disorders.

Establishment of a seronegative human T-cell leukemia virus type 1 (HTLV-1) carrier state in rats inoculated with a syngeneic HTLV-1-immortalized T-cell line preferentially expressing Tax

Human T-cell leukemia virus type 1 (HTLV-1) causes T-cell malignancies in a small percentage of the population infected with the virus after a long carrier state. In the present study, we established a seronegative HTLV-1 carrier state in rats inoculated with a newly established HTLV-1-infected rat T cell line, FPM1. FPM1 originated from rat thymocytes cocultured with a human HTLV-1 producer, MT-2 cells, and expressed rat CD4, CD5, CD25, and HTLV-1 Tax. However, FPM1 scarcely expressed other major HTLV-1 structural proteins and failed to induce typical antibody responses against HTLV-1 in inoculated rats. In contrast, control rats inoculated with MT-2 cells generated significant levels of anti-HTLV-1 antibodies. HTLV-1 proviruses were detected in peripheral blood cells of syngeneic rats inoculated with FPM1 for more than 1 year. Analysis of the flanking region of HTLV-1 provirus integrated into host cells suggested that FPM1 cells remained in these animals over a relatively long period of time. However, a similar seronegative HTLV-1 carrier state was induced in the rats inoculated with mitomycin C-treated FPM1 cells and also in FPM1-inoculated allogeneic rats, suggesting that FPM1 could also transmit HTLV-1 into host cells in vivo. Our findings indicated that (i) HTLV-1-immortalized T cells which preferentially express HTLV-1 Tax persisted in vivo but failed to induce any diseases in immunocompetent syngeneic rats and that (ii) suboptimal levels of HTLV-1 for antibody responses allowed the establishment of persistent HTLV-1 infection.

Involvement of NF-AT in type I human T-cell leukemia virus Tax-mediated Fas ligand promoter transactivation

Human T-cell leukemia virus type I (HTLV-I)-infected T-cells constitutively express surface Fas ligand (FasL), which may serve as a mechanism of viral pathogenesis. HTLV-I induces transcription of FasL gene through the viral transactivator Tax, although the underlying molecular mechanism remains unclear. In the present study, we have analyzed both the cis-activating element and transactivating factors involved in Tax activation of the FasL promoter. We show that the 486-base pair upstream region of the human FasL gene is sufficient for Tax-mediated transactivation in Jurkat T-cells. Interestingly, a palindromic DNA sequence (GGAAACTTCC) covering the consensus NF-ATp binding site (GGAAA), is required for Tax activation of FasL promoter. The involvement of NF-AT in this transactivation event is suggested by the finding that Tax fails to activate the FasL promoter in a Jurkat T-cell line defective in capacitative calcium entry, a signaling mechanism involved in NF-AT activation. Furthermore, activation of FasL promoter by Tax is largely attenuated in the nonlymphoid F9 embryonal and COS kidney cells deficient in NF-ATp expression. DNA-protein interaction assays reveal that the NF-AT-like motif in the FasL promoter is bound by both NF-ATp and NF-AT4 in Jurkat T-cells expressing Tax. The binding of NF-ATp, although not NF-AT4, to this enhancer also occurs along with HTLV-I-mediated infection of human peripheral blood T-cells. Furthermore, exogenously transfected NF-ATp binds to the NF-AT-like enhancer and participates in Tax-mediated FasL promoter transactivation. These results suggest an important role for proteins of the NF-AT family in HTLV-I Tax-mediated FasL gene transactivation.

Characterization of mRNA expression of IkappaB alpha and NF-kappaB subfamilies in primary adult T-cell leukemia cells

Tax protein of HTLV-1 activates the transcriptional capacity of the NF-kappaB family, resulting in up-regulation of various genes, which are linked to phenotypic alterations of HTLV-1-infected T cells. To understand NF-kappaB regulation in HTLV-1-infected leukemic cells in vivo, we analyzed expression of NF-kappaB and IkappaB alpha in primary cells isolated from ATL patients. Using competitive polymerase chain reaction, we observed an elevated expression of IkappaB alpha mRNA in all four ATL cases tested. In contrast to the elevated mRNA levels, the levels of IkappaB alpha protein were remarkably reduced in some of these cases, suggesting destabilization of IkappaB alpha protein. On the other hand, mRNA expression of p50/p105 and p65, subfamilies of NF-kappaB, was enhanced in primary cells isolated from some ATL patients. Furthermore, the expression patterns of NF-kappaB subfamily were variable among patients and also different from those in T cells isolated from uninfected individuals. Although the number of cases analyzed was limited, we can conclude from these observations that activation of NF-kappaB is restricted to a few subfamilies in vivo. These findings in vivo are strikingly different from those in HTLV-1-infected T cell lines in vitro, in which Tax is responsible for NF-kappaB activation. It is therefore suggested that the elevation of NF-kappaB expression in leukemic cells of ATL patients might not be supported mainly by the viral protein Tax.

Transactivation of the interleukin-1 alpha promoter by human T-cell leukemia virus

The expression of interleukin-1 alpha (IL-1 alpha) appears to be tightly regulated, as the levels of constitutive expression in normal cells is extremely low. In contrast to normal hematopoietic cells, human T-cell leukemia virus type I (HTLV-I)-infected T-cell lines constitutively produce high levels of IL-1 alpha mRNA and secret this cytokine into the culture medium. IL-1-alpha mRNA is also expressed in fresh leukemic cells of adult T-cell leukemia/lymphoma (ATLL) patients. HTLV-I-induced IL-1 alpha might explain some symptoms observed in ATLL. In this regard, molecular dissection of the IL-1 alpha gene transcriptional regulation is of primary importance. In this review, the transcriptional regulation of IL-1 alpha gene expression and the possible role of the NF-kappaB pathway are discussed in the light of our current understanding of IL-1 alpha gene regulation by HTLV-I and HTLV-II Tax proteins, which are viral transcriptional transactivators.

Triple synergism of human T-lymphotropic virus type 1-encoded tax, GATA-binding protein, and AP-1 is required for constitutive expression of the interleukin-5 gene in adult T-cell leukemia cells

Accumulated evidence demonstrates that adult T-cell leukemia (ATL) is frequently associated with eosinophilia, and human T-lymphotropic virus type 1 (HTLV-1)-infected cells frequently express interleukin-5 (IL-5). However, the molecular mechanism of constitutive IL-5 expression in HTLV-1-infected cells remains unclear. To clarify the mechanism of aberrant IL-5 expression in HTLV-1-infected cells, we investigated the response of the human IL-5 promoter to the HTLV-1-encoded protein Tax. Cotransfection experiments using Jurkat cells revealed that Tax is incapable of activating the IL-5 promoter by itself but that it synergistically transactivates the promoter with GATA-binding protein (GATA-4) and 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulation. By introducing a series of mutations within the IL-5 promoter, we found that conserved lymphokine element 0 (CLE0) is responsible for mediating the signal induced by Tax-TPA. A deletion construct of the promoter indicated that the -75 GATA element and CLE0 are sufficient to mediate synergistic activation of the IL-5 promoter. Electrophoretic mobility shift assays using Jurkat cell nuclear extracts demonstrated that TPA induces a transcription factor to bind CLE0, and an experiment using JPX-9 cell nuclear extracts showed that Tax enhances this binding activity. An antibody supershift experiment revealed that this band consists of c-Jun and JunD. However, among the Jun family members, only c-Jun is able to cooperate with Tax and GATA-4 to activate the IL-5 promoter. We have determined the minimum factors required for IL-5 gene activation by reconstituting the IL-5 promoter activity in F9 cells. This is the first report to demonstrate the functional involvement of Tax protein in IL-5 gene regulation and to suggest the functional triple synergism among Tax, GATA-4, and AP-1, which disrupts regulated control of the gene and leads to constitutive expression of the IL-5 gene.

Increased expression of interleukin-2 receptor alpha on peripheral blood mononuclear cells in HTLV-I tax/rex mRNA-positive asymptomatic carriers

Using the double-nested reverse transcription-polymerase chain reaction, we assayed human T-cell leukemia virus type I (HTLV-I) tax/rex-encoded mRNA in the peripheral blood mononuclear cells (PBMCs) of asymptomatic carriers as an index of the expression of HTLV-I in vivo in relation to the proviral DNA level. HTLV-I tax/rex mRNA was detected in only 1 (3.3%) of 30 samples with medium or lower proviral DNA levels, but it was detected in 11 (39.3%) of 28 samples with high HTLV-I proviral DNA levels, estimated as equal to or more than the proviral DNA of 10 ng of HUT102 (i.e., HUT102 cells were used as positive controls). The mean number of interleukin-2 receptor alpha (IL-2R alpha)-positive cells as a percentage of the total number of PBMCs was higher (13.2%) in the tax/rex mRNA-positive carriers with high proviral DNA levels than in the carriers who were mRNA negative (8.4%) (p = 0.004, Wilcoxon test). These results suggest that virus activation as indicated by the presence of tax/rex mRNA in asymptomatic carriers with high proviral DNA levels is associated with an elevation of the IL-2R alpha-positive cells in vivo.

Variable Immortalizing Potential and Frequent Virus Latency in Blood-Derived T-Cell Clones Infected With Human T-Cell Leukemia Virus Type I

Human T-cell leukemia virus type I (HTLV-I)-infected T cells expanded in vitro by single-cell cloning provide a unique system for investigating virus-cell interactions in nonimmortalized T cells. By analysis of clones generated randomly from the blood of virus carriers, we confirm that CD4 T cells are the major reservoir of HTLV-I in vivo and show that most infected cells contain a single integrated provirus. Contrary to the situation in HTLV-I immortalized cell lines, the HTLV-I provirus was found to be transcriptionally silent in a high proportion of randomly generated T-cell clones and could not be reactivated by mitogenic stimulation. The spontaneous proliferation previously documented in HTLV-I–infected T-cell clones was not observed in silently infected cells, and therefore correlates directly with the expression of tax and other viral genes. The only cytokine mRNA found to be significantly elevated in the virus-producing clones was interleukin-6; however, receptor-blocking experiments argue against a role for IL-6 in the virus-induced cell proliferation. We observed a striking variation in the ability of individual HTLV-I–producing clones to immortalize fresh peripheral blood lymphocytes. This ability did not correlate with the levels of viral mRNA expression, gag p24 production, spontaneous proliferation, or tax-transactivation, possibly suggesting a role for host cell factors as determinants of viral infectivity or immortalization. Studies to elucidate the basis of this phenotypic heterogeneity should enhance our understanding of viral spread and pathogenesis.

High levels of the DNA-binding activity of E2F in adult T-cell leukemia and human T-cell leukemia virus type I-infected cells: possible enhancement of DNA-binding of E2F by the human T-cell leukemia virus I transactivating protein, Tax

Transcription factor E2F binds to cellular promoters of certain growth- and cell cycle-controlling genes and forms distinct heteromeric complexes with other nuclear proteins. It has therefore been proposed that E2F is involved in cellular proliferation control. Human T-cell leukemia virus type I (HTLV-I) is an etiological agent of adult T-cell leukemia (ATL). We show here by mobility-shift assay that E2F-containing DNA-binding complexes were detected in HTLV-I-infected T-cell lines and leukemic cells obtained from ATL patients but not in an uninfected T-cell line, Jurkat, and normal peripheral blood mononuclear cells. The Tax protein, encoded by HTLV-I, is a potent transcription activator of viral and several cellular genes. We demonstrate that expression of Tax can induce the E2F-containing DNA-binding complexes in Jurkat T cells. Thus, Tax, through enhancement of the DNA-binding activity of E2F, may be capable of regulating cellular gene expression implicated in the proliferation and transformation of T cells in ATL. This activity may be relevant to the mechanisms whereby HTLV-I which does not contain oncogenes induces neoplasia.

ATL and HTLV-I: in vivo cell growth of ATL cells

The mechanism of leukemogenesis or neoplastic cell growth in adult T cell leukemia (ATL) still remains unclear, although Tax of human T cell leukemia/lymphoma virus type I (HTLV-I), the etiologic virus, has been reported to affect the expression of various cellular genes which encode molecules involved in cell growth or cell death. We have studied the cell growth of HTLV-I-infected human T cells in severe combined immunodeficiency (SCID) mice and found that fresh leukemic cells or cell lines derived from leukemic cell clones but not HTLV-I-infected cell lines of nonleukemic cell origin showed tumorigenicity, and neither HTLV-I nor IL-2 expression was needed for cell growth in vivo, indicating that accumulating changes in addition to the initial events induced by HTLV-I infection were required for the development of ATL. The interaction between ATL cells and vascular endothelial cells appears to be one of the important factors which determine the pattern of organ infiltration by leukemic cells. E-selectin and its ligand are one of the major cell adhesion pathways between ATL cells and human umbilical vein endothelial cells (HUVEC). Another pathway that had not been identified was studied using newly developed monoclonal antibodies capable of blocking cell adhesion. The molecules which directly mediate adhesion between ATL cells and HUVEC were determined to be OX40 and gp34, a member of the tumor necrosis factor receptor (TNF-R) family and TNF family, respectively. The OX40/gp34 system may play a key role in the trafficking and homing of not only ATL cells but also activated normal T cells.

Cytokine production by endothelial cells infected with human T cell lymphotropic virus type I

OBJECTIVE

To investigate the ability of human T cell lymphotropic virus type I (HTLV-I) to infect endothelial cells and induce cytokine production by these cells.

METHODS

Human umbilical vein endothelial cells (HUVEC) were cocultured with HTLV-I infected T cell line (MT-2 cells) or uninfected T cell line (CEM cells).

RESULTS

Following coculture with MT-2 cells, endothelial cells expressed HTLV-I specific core antigens. Endothelial cells cocultured with MT-2 cells produced significant amounts of several cytokines, including interleukin (IL)-1 alpha, IL-6, granulocyte colony stimulating factor (G-CSF), and granulocyte/macrophage colony stimulating factor (GM-CSF), compared with endothelial cells cocultured with CEM cells. Coculturing of endothelial cells with MT-2 and CEM cells failed to produce detectable amounts of IL-1 beta and tumour necrosis factor alpha (TNF-alpha). The production of cytokines by endothelial cells cocultured with MT-2 cells was more persistent than that by endothelial cells cocultured with CEM cells after several passages. Furthermore, the production was blocked by cocultivation of endothelial cells and MT-2 cells using the Millicell system. Finally, after cocultivation of endothelial cells and MT-2 cells, endothelial cells positive for HTLV-I antigen were stained by anti-GM-CSF antibody.

CONCLUSIONS

HTLV-I can infect endothelial cells, resulting in their active production of several cytokines, such as IL-1 alpha, IL-6, G-CSF, and GM-CSF. These findings strongly suggest that the excess production of these cytokines by HTLV-I infected endothelial cells may be involved in the pathogenesis of HTLV-I associated inflammatory diseases.

DNA triplex formation selectively inhibits granulocyte-macrophage colony-stimulating factor gene expression in human T cells

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hemopoietic growth factor that is expressed in activated T cells, fibroblasts, macrophages, and endothelial cells. Although GM-CSF does not appear to be essential for normal hemopoiesis, overexpression of GM-CSF has been implicated in the pathogenesis of some diseases such as myeloid leukemia and chronic inflammation. An NF-kappaB/Rel binding site within the GM-CSF promoter, termed the kappaB element appears to be important for controlling expression in reporter gene assays in response to a number of stimuli in T cells. We investigated oligonucleotide-directed triple helix formation across this regulatory sequence as a potential tool to inhibit GM-CSF gene transcription. A 15-base oligonucleotide, GM3, was targeted to a purine-rich region in the GM-CSF proximal promoter, which overlaps the kappaB element. Gel mobility shift assays and DNase I footprinting demonstrated that GM3 formed a sequence-specific collinear triplex with its double-stranded DNA target. Triplex formation by GM3 blocked recombinant and nuclear NF-kappaB proteins binding to the GM-CSF element. GM3 also caused selective inhibition of the human T-cell lymphotrophic virus-1 Tax transactivator-induced luciferase activity from a reporter construct driven by the GM-CSF promoter in Jurkat T cells. Finally, GM3 greatly reduced the concentration of endogenous GM-CSF mRNA induced by different stimuli in Jurkat T cells but did not affect interleukin 3 mRNA levels in the same cells. We conclude that the kappaB element in the GM-CSF promoter plays a central role in the transcriptional activation of the endogenous GM-CSF gene. Colinear triplex formation acts as a selective transcriptional repressor of the GM-CSF gene and may have potential therapeutic application in cases of undesirable overexpression of this protein.

Costimulation of cytokine gene expression in T cells by the human T leukemia/lymphotropic virus type 1 trans activator Tax

Many cell signals such as CD28 and CD4 binding can costimulate cytokine gene expression in activated T cells. We have found that the human T leukemia/lymphotropic virus type 1 viral protein Tax can also strongly costimulate expression of interleukin-2 (IL-2), IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA in T cells activated with the phorbol ester phorbol myristate acetate (PMA) and calcium ionophore, which can mimic activation through the antigen specific T-cell receptor. Reporter constructs also showed strong synergy between both stimuli and showed that Tax and the PMA-Ca2+ ionophore act through different regions of the IL-2 and GM-CSF genes. Furthermore, the Tax-responsive regions (TxRR) from both GM-CSF and IL-2 respond to costimulation through the CD28 surface receptor. The GM-CSF and IL-2 TxRRs showed significantly higher levels of NF-kappaB/rel binding, following induction by Tax, compared with that of the PMA-Ca2+ ionophore with only Tax capable of inducing c-Rel binding to a Consensus kappaB element within the GM-CSF TxRR. Tax protein mutants, however, showed that a pathway(s) other than NF-kappaB/rel induction could also cooperate with the PMA-Ca2+ ionophore to activate the GM-CSF and IL-2 genes. This high-level costimulation by Tax, through multiple pathways, may be important in the early stages of leukemia and in the nervous system disorder tropical spastic paraparesis.

Features of the cytokines secreted by adult T cell leukemia (ATL) cells

Adult T cell leukemia (ATL) cells show a mature helper-inducer T cell phenotype and are thought to secrete many kinds of cytokines in vivo, complicating the clinical features in these patients. In an attempt to specify the cytokines produced by ATL cells, we measured the cytokine concentration in the culture supernatants of three ATL cell lines, all of which were confirmed to be true peripheral blood ATL cell in origin. All these cell lines showed the same cytokine production profile, secreting IL1-alpha, IL1-beta, LD78(MIP-l alpha), TNF-alpha, IFN-gamma, and GM-CSF, but not secreting IL-1 alpha, IL-1 beta, IL-1 receptor antagonist (IL-1 Ra), IL-4, IFN-alpha, and G-CSF irrespective of the stimulatory agents used. Such limited cytokine production may indicate the specific origin of ATL cells within the helper-inducer T cell subtypes. Moreover, these results explain some of the unusual clinical features of ATL patients.

A novel interferon regulatory factor family transcription factor, ICSAT/Pip/LSIRF, that negatively regulates the activity of interferon-regulated genes

We have isolated a novel cDNA clone encoding interferon (IFN) consensus sequence-binding protein in adult T-cell leukemia cell line or activated T cells (ICSAT); this protein is the human homolog of the recently cloned Pip/LSIRF. ICSAT is structurally most closely related to the previously cloned ICSBP, a member of the IFN regulatory factor (IRF) family of proteins that binds to interferon consensus sequences (ICSs) found in many promoters of the IFN-regulated genes. Among T-cell lines investigated, ICSAT was abundantly expressed in human T-cell leukemia virus type 1 (HTLV-1)-infected T cells. When the HTLV-1 tax gene was expressed or phorbol myristake acetate-A23187 stimulation was used, ICSAT expression was induced in Jurkat cells which otherwise do not express ICSAT. When the binding of ICSAT to four different ICSs was tested, the relative differences in binding affinities for those ICSs were determined. To study the functional role of ICSAT, we performed cotransfection experiments with the human embryonal carcinoma cell line N-Tera2. ICSAT was demonstrated to possess repressive function over the gene activation induced by IFN stimulation or by IRF-1 cotransfection. Such repressive function is similar to that seen in IRF-2 or ICSBP. However, we have found that ICSAT has a different repressive effect from that of IRF-2 or ICSBP in some IFN-responsive reporter constructs. These results suggest that a novel mechanism of gene regulation by "differential repression" is used by multiple members of repressor proteins with different repressive effects on the IFN-responsive genes.

HTLV-I-induced T-cell activation

Infection by the human T-cell lymphotropic virus type I (HTLV-I) causes T-cell activation by at least two separate mechanisms. One mechanism involves activation of the T cells harboring the virus and is exemplified by in vivo infected nonimmortalized T-cell clones that display a prolonged state of activation. This HTLV-I-induced T-cell activation is inhibited by rapamycin, a drug that inhibits p70 S6-kinase and blocks cell cycle in G1, but is not inhibited by FK506 or cyclosporin A, both of which inhibit interleukin-2 (IL-2) production. The phenotype of this pathway is consistent with an hyperactive IL-2R pathway or CD28 pathway, indicating that HTLV-I may contribute a costimulatory signal to the infected T cell. As a separate mechanism, HTLV-I-infected T cells can induce activation of uninfected T cells via T-T-cell interaction mediated by the LFA-3-CD2 pathway. This may induce IL-2 production from the uninfected T cells, leading to a more generalized activation of the immune system that potentially could provide a basis for some of the diseases associated with HTLV-I. Moreover, this THTLV-I-T-cell interaction could explain the spontaneous proliferation observed in patients with HTLV-I-associated myelopathy/tropical spastic paraparesis.

Transgenic mouse models for HTLV-I infection

Human T-cell leukemia virus type I (HTLV-I) was the first human retrovirus isolated and is responsible for at least one form of human leukemia. The pathogenic mechanism(s) whereby HTLV transforms T lymphocytes in vivo is(are) obscure due to its long-term latency and the lack of practical representative animal models. The tax gene of HTLV-I has been implicated in this transformation process because of its ability to transactivate several cellular genes associated with T-cell replication and activation. Here, transgenic mouse models are discussed that express the Tax protein of HTLV-I and provide insights into its role in the cellular transformation process.

HTLV-1 oncoprotein Tax deregulates transcription of cellular genes through multiple mechanisms

Infection of a human retrovirus HTLV-1 induces adult T cell leukemia and a neurological disease, HAM/TSP. Regulatory protein Tax of HTLV-1 is thought to contribute to the pathogenesis. We have studied the mechanism of transcriptional activation induced by Tax protein and identified two independent mechanisms: (a) binding to the enhancer-binding proteins, CREB, CREM, NF-kappa B and SRF, resulting in the activation of these factors through indirect binding to each specific DNA sequence, and (b) binding to I kappa B protein resulting in the suppression of the negative regulator I kappa B, which binds to NF-kappa B. In addition to these factors, a new protein GLI/THP is also involved in the transactivation. On the basis of these mechanisms, gene regulations in vitro and in vivo in HTLV-1-infected cells are discussed.

The amino terminus of Tax is required for interaction with the cyclic AMP response element binding protein

Tax of human T-cell leukemia virus type 1 was analyzed for interaction with the cyclic AMP response element binding protein (CREB) in vitro with and without Tax response element DNA. Mutations in the carboxy terminus of Tax (L296G and L320G) did not affect binding to CREB and led to supershifts. In contrast, mutants with changes in the amino-terminal cysteine-rich region lost the ability to bind to CREB. The S10A mutant protein bound moderately. Thus, the amino terminus of Tax is essential for Tax-CREB interaction.

Of the GATA-binding proteins, only GATA-4 selectively regulates the human interleukin-5 gene promoter in interleukin-5-producing cells which express multiple GATA-binding proteins

Interleukin-5 (IL-5) is produced by T lymphocytes and known to support B-cell growth and eosinophilic differentiation of the progenitor cells. Using ATL-16T cells which express IL-5 mRNA, we have identified a region within the human IL-5 gene promoter that regulates IL-5 gene transcription. This cis-acting sequence contains the core binding motif, (A/T)GATA(A/G), for GATA-binding family proteins and thus suggests the involvement of this family members. In this report, we describe the cloning of human GATA-4 (hGATA-4) and show that hGATA-4 selectively interacts with the -70 GATA site within the IL-5 proximal promoter region. By promoter deletion and mutation analyses, we established this region as a positive regulatory element. Cotransfection experiments revealed that both hGATA-4 and phorbol-12-myristate-13-acetate (PMA)-A23187 stimulation are necessary for IL-5 promoter activation. The requirement for another regulatory element called CLE0, which lies downstream of the -70 GATA site, was also demonstrated. ATL-16T cells express mRNAs of three GATA-binding proteins, hGATA-2, hGATA-3, and hGATA-4, and each of them has a potential to bind to the consensus (A/T)GATA(G/A) motif. However, using ATL-16T nuclear extract, we demonstrated that GATA-4 is the only GATA-binding protein that forms a specific DNA-protein complex with the -70 GATA site. An electrophoretic mobility shift assay with extracts of COS cells expressing GATA-binding proteins showed that GATA-4 has the highest binding affinity for the -70 GATA site among the three GATA-binding proteins. When the transactivation abilities were compared among the three, GATA-4 showed the highest activity. These results demonstrate the selective role of GATA-4 in the transcriptional regulation of the IL-5 gene in a circumstance where multiple members of the GATA-binding proteins are expressed.

Increased number of circulating HTLV-1 infected cells in peripheral blood mononuclear cells of HTLV-1 uveitis patients: a quantitative polymerase chain reaction study

AIMS

This study aimed to characterise the status of viral infection in patients with HTLV-1 uveitis (HU) by quantifying the circulating HTLV-1 infected cells in the peripheral blood.

METHODS

Genomic DNA samples of peripheral blood mononuclear cells (PBMC) were obtained from 25 patients with HU, 14 patients with tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM), and 21 asymptomatic carriers of HTLV-1. Quantitative polymerase chain reaction (PCR) of the gag region of HTLV-1 provirus DNA was performed on these DNA samples. To confirm the PCR, genomic Southern blot hybridisation was performed to identify integrated HTLV-1 provirus. This procedure detected a few percent of HTLV-1 infected cells in the PBMC.

RESULTS

Most of the HU patients had a significantly increased number of circulating HTLV-1 infected cells (mean (SD) 3.84% (4.45%) of the PBMC), whereas the percentage of infected cells in most asymptomatic carriers was less than 1% (0.54% (1.11%)). Most of the TSP/HAM patients also had a relatively high percentage (11.63% (7.67%)). The differences among these three groups were highly significant by the Mann-Whitney U test.

CONCLUSION

The results suggested that the increase in the number of HTLV-1 infected cells is one base for the development of inflammatory HU lesions, as it is for TSP/HAM.

Transactivation of human T-cell leukemia virus type 1 by herpes simplex virus type 1

HTLV-1 transcription depends upon activation by the HTLV-1 tax gene product. In addition, various substances and cellular transcription factors are also known to activate the HTLV-1 long terminal repeat (LTR)-mediated transcription in the absence of Tax. In this work we demonstrate that infection of either Jurkat or 293 cell lines with herpes simplex I (HSV-1), a widespread infectious virus of humans, activates HTLV-1 LTR-mediated gene expression. Further investigation revealed that each of the immediate-early (IE) gene products--ICPO, ICP4, and ICP27--of HSV-1 transactivates the HTLV-1 LTR-mediated gene expression in the absence of Tax. The HSV-1 activation is additive to Tax activation in its presence in the cell. Three 21 base repeats upstream of the TATA box are known as the TAX responsive elements (TRE). Recombinant HTLV-1 minimal promoter composed of the HTLV-1 TATA box fused to a synthetic 21 base TRE is responsive to Tax but not to HSV-1 activation. It thus can be concluded that HSV-1 IE gene products and Tax transactivates HTLV-1 LTR mediated gene expression through different transcription complexes. The results presented in this work may point to one possible way for the transition of HTLV-1 from a quiescent to an actively replicating stage.

Clonal expansion of CD8+ cytotoxic T lymphocytes against human T cell lymphotropic virus type I (HTLV-I) genome products in HTLV-I-associated myelopathy/tropical spastic paraparesis patients

Short-term culture of peripheral blood mononuclear cells (PBMC) derived from patients with human T cell lymphotropic virus type I-associated myelopathy (HAM)/tropical spastic paraparesis resulted in dominance by DR+ activated CD8+ T cells. Variations in the T cell receptor (TCR) V alpha and V beta chains in these cells were analyzed, and in all 10 patients examined, 2-3 V gene families were dominant in both TCR V alpha and V beta. In five patients we examined, cultured lymphocytes contained cytotoxic lymphocytes for p40tax (patients HAM2, 3, 7, and 8) or env protein (patient HAM4) of human T lymphotropic virus type I. In patients HAM2 and HAM8, cultured lymphocytes contained a large proportion of V beta 8+ CD8+ and/or V beta 12+ CD8+ cells. The sequence of V beta 8+ and V beta 12+ cDNA revealed that they were oligoclonal with identical or similar sequences in each patient. Elimination experiments with monoclonal antibodies for TCR V beta 8 and V beta 12 showed that they were CD8+ cytotoxic T lymphocytes (CTL) for p40tax. In addition, flow cytometry and sequencing analysis of uncultured PBMC revealed that in HAM2, V beta 8+ CTL and their precursors account for 7% and V beta 12+ CTL and their precursors account for 18% of total CD8+ cells. This indicates the presence of two markedly expanded clones in vivo. No common dominant TCR V alpha or V beta were observed among 10 HAM patients analyzed.

Regulation of interleukin-5 and granulocyte-macrophage colony-stimulating factor expression

This review concerns the regulation of expression of the two main eosinophil differentiating factors, interleukin-5 (IL-5) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The latter, GM-CSF, is expressed in a wide variety of differentiated and non-differentiated cell types: T cells, monocytes, macrophages, fibroblasts, and endothelial cells. On the other hand, IL-5 is only expressed by a limited number of fully differentiated cells: eosinophils, mast cells, and a subset of T cells. Activation of GM-CSF in T cells and non-T cells occurs by different mechanisms, regulated both transcriptionally and post-transcriptionally. The transcriptional activation of GM-CSF via protein kinase C pathway and via viral transactivating proteins involves different regulatory elements of its promoter. Although one of these cis acting elements is common to IL-5, the activation of IL-5 apparently proceeds via different mechanism(s).

Expression of human T-cell leukaemia virus type I and associated antigens, and interleukin-2 and receptor in lymph nodes of adult T-cell leukaemia/lymphoma

To examine the relationship between the expression of human T-cell leukaemia virus type (HTLV-I) mRNA and associated antigens and clinicopathological features, we studied 31 lymph nodes of patients with adult T-cell leukaemia/lymphoma (ATLL) and related diseases, using in situ hybridization and immunohistochemistry. We classified the patients into four types on the basis of their clinicopathological features (HTLV-I associated lymphadenitis, incipient ATLL, ATLL with complete HTLV-I provirus, and ATLL with defective HTLV-I provirus. The expression of HTLV-I mRNA was detected in all 3 patients with incipient ATLL, in 5 of 10 patients with defective-provirus ATLL, in 5 of 11 patients with complete-provirus ATLL, and 3 of 7 with HTLV-I associated lymphadenitis, but the amounts were very small; approximately 1 in 10000-200000 lymph node cells express the viral genomes. This suggests that expression of viral genomes may not be important for immortalization, but it is important that to note the capacity for HTLV-I infection is preserved in each group of non-neoplastic and neoplastic states. HTLV-I mRNA was detected only in lymphocytes and/or lymphoma cells, but the HTLV-I associated antigens (env, gag and pX) were found in histiocytes and endothelial cells, as well as in lymphocytes and/or lymphoma cells. Anti-interleukin 2 receptor (IL-2R) antibody reacted with the giant cells of incipient ATLL and with the transformed lymphocytes and immunoblast-like cells of the HTLV-I-associated lymphadenitis but not with the lymphocytes in the background. Of the typical ATLL, IL-2R was found in both lymphoma cells and giant cells. IL-2 was rarely detected.

Signals and nuclear factors that regulate the expression of interleukin-4 and interleukin-5 genes in helper T cells

Mouse thymoma line EL-4 cells produce cytokines such as interleukin (IL)-2, IL-3, IL-4, IL-10, and granulocyte-macrophage colony-stimulating factor in response to phorbol 12-myristate 13-acetate (PMA). EL-4 cells also produce low levels of IL-5 when stimulated by PMA alone; however, cAMP greatly augments PMA-dependent IL-5 production. A transient transfection assay revealed that two signals, PMA and cAMP, are required for optimal activation of the IL-5 promoter. In contrast, cAMP almost completely inhibited the PMA-dependent activation of the endogenous IL-2 gene, as well as the transfected IL-2 promoter. These results indicate that the IL-5 gene is positively regulated by cAMP in a manner opposite to that for the IL-2 gene. One of the nuclear factors (NFs) that regulates the response of the IL-5 promoter to cAMP and PMA has properties similar to NF for activated t cell. The P sequence of the IL-4 gene, defined as a responsive element for PMA and calcium ionophore (A23187), shares sequence similarity with the NF kappa B and the NF-activated T cell binding sites. We attempted to determine whether NF(P), a nuclear factor specific for the P sequence, is related to NF-kappa B and nuclear factor for activated T cell (NF-AT). In electromobility shift assays both NF-kappa B (P65 or P65/P50 heterodimer) and NF-AT bound to the P sequence. However, sequence specificity of NF-AT was more similar to that of NF(P), and only a small amount of P65 was detected in NF(P). These results indicate that a component or components of NF-AT have the potential to reconstitute NF(P), whereas NF-kappa B alone does not account for NF(P) in Jurkat crude extract. Taken together, these results suggest that NF-AT-like factors are involved in the regulation of IL-4 and IL-5 genes.

A patient with primary hypoparathyroidism developing hypercalcemia associated with adult T-cell leukemia/lymphoma

A 38-year-old woman was admitted to our hospital with symptoms and signs of hypocalcemia in 1977 and a diagnosis of primary hypoparathyroidism was made with a positive Ellsworth Howard test. She was then lost to follow up until 1992 when she returned this time with symptoms and signs of hypercalcemia. An inguinal lymph node was biopsied showing non-Hodgkin's lymphoma, diffuse pleomorphic type and monoclonal integration of proviral human T-cell lymphotropic virus-1 DNA was detected in lymph node cells indicating ATLL. Serum parathyroid hormone-related peptide (PTHrP) was slightly elevated and the tumor cells were positively stained with anti-PTHrP serum. Combination chemotherapy with vincristine, adriamycin, cyclophosphamide and prednisolone was given to the patient with disappearance of the lymphadenopathy and subsequent normalization of PTHrP levels. Interestingly, the signs and symptoms of hypocalcemia reappeared after the treatment requiring replacement therapy with calcium and vitamin D.

Novel interactions between human T-cell leukemia virus type I Tax and activating transcription factor 3 at a cyclic AMP-responsive element

Human proenkephalin gene transcription is transactivated by human T-cell leukemia virus type I (HTLV-I) Tax in human Jurkat T lymphocytes. This transactivation was further enhanced in Jurkat cells treated with concanavalin A, cyclic AMP, or 12-O-tetradecanoylphorbol-13-acetate. Deletion and cis-element transfer analyses of the human proenkephalin promoter identified a cyclic AMP-responsive AP-1 element (-92 to -86) as both necessary and sufficient to confer Tax-dependent transactivation. Different AP-1 or cyclic AMP-responsive element-binding protein (CREB)/activating transcription factor (ATF) proteins which bind this element were expressed in murine teratocarcinoma F9 cells to identify those capable of mediating Tax-dependent transactivation of human proenkephalin gene transcription. Although CREB, c-Fos, c-Jun, and JunD did not have significant effects, JunB inhibited the Tax-dependent transactivation. In contrast, ATF3 dramatically induced Tax-dependent transactivation, which was further enhanced by protein kinase A. Electrophoretic mobility shift assays with recombinant fusion proteins expressed and purified from bacteria indicate that the DNA-binding activity of ATF3 is also dramatically enhanced by Tax. Chimeric fusion proteins consisting of the DNA-binding domain of the yeast transcription factor Gal4 and the amino-terminal domain (residues 1 to 66) of ATF3 were able to mediate Tax-dependent transactivation of a Gal4-responsive promoter, which suggests a direct involvement of this region of ATF3. Recombinant fusion proteins of glutathione S-transferase with either the amino- or carboxy-terminal (residues 139 to 181) domain of ATF3 were able to specifically interact with Tax. Furthermore, specific antisera directed against Tax coimmunoprecipitated ATF3 only in the presence of Tax.

Novel interactions between human T-cell leukemia virus type I Tax and activating transcription factor 3 at a cyclic AMP-responsive element

Human proenkephalin gene transcription is transactivated by human T-cell leukemia virus type I (HTLV-I) Tax in human Jurkat T lymphocytes. This transactivation was further enhanced in Jurkat cells treated with concanavalin A, cyclic AMP, or 12-O-tetradecanoylphorbol-13-acetate. Deletion and cis-element transfer analyses of the human proenkephalin promoter identified a cyclic AMP-responsive AP-1 element (-92 to -86) as both necessary and sufficient to confer Tax-dependent transactivation. Different AP-1 or cyclic AMP-responsive element-binding protein (CREB)/activating transcription factor (ATF) proteins which bind this element were expressed in murine teratocarcinoma F9 cells to identify those capable of mediating Tax-dependent transactivation of human proenkephalin gene transcription. Although CREB, c-Fos, c-Jun, and JunD did not have significant effects, JunB inhibited the Tax-dependent transactivation. In contrast, ATF3 dramatically induced Tax-dependent transactivation, which was further enhanced by protein kinase A. Electrophoretic mobility shift assays with recombinant fusion proteins expressed and purified from bacteria indicate that the DNA-binding activity of ATF3 is also dramatically enhanced by Tax. Chimeric fusion proteins consisting of the DNA-binding domain of the yeast transcription factor Gal4 and the amino-terminal domain (residues 1 to 66) of ATF3 were able to mediate Tax-dependent transactivation of a Gal4-responsive promoter, which suggests a direct involvement of this region of ATF3. Recombinant fusion proteins of glutathione S-transferase with either the amino- or carboxy-terminal (residues 139 to 181) domain of ATF3 were able to specifically interact with Tax. Furthermore, specific antisera directed against Tax coimmunoprecipitated ATF3 only in the presence of Tax.

Calcineurin potentiates activation of the granulocyte-macrophage colony-stimulating factor gene in T cells: involvement of the conserved lymphokine element 0

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-2 (IL-2) are produced by stimulation with phorbol-12-myristate acetate (PMA) and calcium ionophore (A23187) in human T cell leukemia Jurkat cells. The expression of GM-CSF and IL-2 is inhibited by immunosuppressive drugs such as cyclosporin A (CsA) and FK506. Earlier studies on the IL-2 gene expression showed that overexpression of calcineurin (CN), a Ca2+/calmodulin-dependent protein phosphatase, can stimulate transcription from the IL-2 promoter through the NF-AT-binding site. In this study, we obtained evidence that transfection of the cDNAs for CN A (catalytic) and CN B (regulatory) subunits also augments transcription from the GM-CSF promoter and recovers the transcription inhibited by CsA. The constitutively active type of the CN A subunit, which lacks the auto-inhibitory and calmodulin-binding domains, acts in synergy with PMA to activate transcription from the GM-CSF promoter. We also found that the active CN partially replaces calcium ionophore in synergy with PMA to induce expression of endogenous GM-CSF and IL-2. By multimerizing the regulatory elements of the GM-CSF promoter, we found that one of the target sites for the CN action is the conserved lymphokine element 0 (CLE0), located at positions between -54 and -40. Mobility shift assays showed that the CLE0 sequence has an AP1-binding site and is associated with an NF-AT-like factor, termed NF-CLE0 gamma. NF-CLE0 gamma binding is induced by PMA/A23187 and is inhibited by treatment with CsA. These results suggest that CN is involved in the coordinated induction of the GM-CSF and IL-2 genes and that the CLE0 sequence of the GM-CSF gene is a functional analogue of the NF-AT-binding site in the IL-2 promoter, which mediates signals downstream of T cell activation.

A new regulatory element that augments the Tax-dependent enhancer of human T-cell leukemia virus type 1 and cloning of cDNAs encoding its binding proteins

The Tax protein of human T-cell leukemia virus type 1 (HTLV-1) trans activates the 21-bp enhancer of HTLV-1. A sequence of more than two copies of the 21-bp enhancer is efficiently activated by Tax, but one copy is not activated extensively. Another sequence (TRE-2, positions -163 to -117) adjacent to the 21-bp enhancer in the long terminal repeat of HTLV-1 can enhance a single copy of the 21-bp enhancer activity in trans activation by Tax. This sequence contains motifs related to the Ets- and NF-kappa B-binding sequences, but mutations at these sites indicated that neither is responsive to cooperation with the 21-bp enhancer. A deletion mutation of TRE-2 identified 25 bases at positions -158 to -134 (TRE-2S) as an essential sequence, and TRE-2S was sufficient to give maximum cooperation with one copy of the 21-bp enhancer in trans activation by Tax protein. Using TRE-2S as a probe, we screened a cDNA library of HUT102 cells by the Southwestern (DNA-protein) procedure and isolated two cDNA clones, THP-1 and -2. These two clones encode TRE-2S-binding proteins, and they differ by only an extra 17 amino acids in THP-2. Both THP proteins contain five zinc finger motifs which are strikingly similar to those of the GLI family, an amplified gene product in glyoma cells. The binding site of THP-1 and -2 was GAACCACCCA in TRE-2S, which is highly homologous to the GLI-binding site. These results suggest that binding of THP to TRE-2S may be involved in cooperation with one copy of the 21-bp enhancer in responding to Tax trans activation.

A human T lymphotropic virus type I (HTLV-I) long terminal repeat-directed antisense c-myc construct with an Epstein-Barr virus replicon vector inhibits cell growth in a HTLV-I-transformed human T cell line

A panel of EB virus replicon-based vectors was constructed to examine the relative utility of four distinct eukaryotic promoters for high-level gene expression in a HTLV-I-transformed human T cell line, HUT102. We found that HTLV-I LTR, which is trans-activated by the viral tax protein, was most suited for EBV vector-based stable gene expression in it. We prepared a HTLV-I LTR-directed antisense c-myc construct with an EBV vector. This antisense plasmid suppressed c-myc expression and inhibited growth of HUT102 cells in vitro with unaltered expression of tax. Non-specific plasmid toxicity was excluded by showing that the antisense construct had little effect on growth and c-myc expression of HTLV-I-negative Jurkat T cells, in which the viral LTR is expected to be less active. Our results indicate that c-myc may play an important role in the deregulated growth of HTLV-I-transformed T cells.

GD2 ganglioside on human T-lymphotropic virus type I-infected T cells: possible activation of beta-1,4-N-acetylgalactosaminyltransferase gene by p40tax

Ganglioside expression on adult T-cell leukemia (ATL) and human T-cell lymphotropic virus type I (HTLV-I)-infected cells was determined by using a panel of monoclonal antibodies. ATL lines and HTLV-I-infected cells specifically expressed GD2. Leukemia cells from ATL patients generally expressed low levels of GD2 but the percentage of GD2+ cells increased up to 40-70% after in vitro culture in the presence of interleukin 2 for about a week. No other type of leukemia cells and normal peripheral T cells expressed GD2 during in vitro culture under the same conditions. The appearance of GD2 in the cultured ATL cells corresponded with the expression of p40tax, a product of the HTLV-I gene. Peripheral lymphocytes infected with a p40tax-expressing retroviral vector expressed high levels of GD2 in comparison with control lymphocytes containing the neomycin-resistance gene alone. The apparently increased levels of beta-1,4-N-acetylgalactosaminyltransferase (GM2/GD2 synthase) mRNA in these cells were demonstrated by reverse transcription-polymerase chain reaction analysis. Concordance between mRNA expression for the HTLV-I tax1/rex1 genes and the beta-1,4-N-acetylgalactosaminyltransferase gene was also observed in uncultured ATL cells. These results suggest that high GD2 expression was due to neosynthesis from precursor GD3 by increased expression of this enzyme induced by p40tax in vitro and in vivo.

Proliferative response of Tax1-transduced primary human T cells to anti-CD3 antibody stimulation by an interleukin-2-independent pathway

The growth properties of human T-cell leukemia virus Tax1-transduced primary human T cells derived from peripheral blood lymphocytes were compared with those of the same subset of T cells transduced with a control vector. Tax1-transduced T cells exhibited slightly elevated responsiveness to externally added interleukin-2 (IL-2) and a markedly higher proliferative response to stimulation with anti-CD3 antibody. The proliferation after anti-CD3 antibody stimulation was mainly via an IL-2-independent pathway. Therefore, some other mechanism than the previously proposed IL-2 autocrine model seems to be involved in the process of deregulation of T-cell proliferation by Tax1. Moreover, Tax1-transduced T cells have continued to proliferate in medium containing IL-2 long after control T cells ceased to grow, and so they are considered to be immortalized.

The trans-activator tax of human T-cell leukemia virus type 1 (HTLV-1) interacts with cAMP-responsive element (CRE) binding and CRE modulator proteins that bind to the 21-base-pair enhancer of HTLV-1

The trans-activator protein Tax of human T-cell leukemia virus type 1 (HTLV-1) activates the viral 21-base-pair (bp) enhancer in the long terminal repeat and has been suggested to associate indirectly with the enhancer DNA. To demonstrate this, we used DNA-affinity precipitation assay and detected the Tax protein in 21-bp DNA-protein complexes isolated from HTLV-1-infected cells. To identify cellular components in the complexes, we tested various 21-bp DNA-binding proteins by gel electrophoretic mobility-shift assay. Each binding protein gave a shifted band of each 21-bp DNA-protein complex, and exogenously added Tax protein further shifted these bands of cAMP-responsive element (CRE) binding protein (CREB) and CRE modulator but did not shift other bands. Anti-Tax antibodies blocked formation of the complex, indicating complex formations of [Tax-CREB(or CRE modulator)-21-bp DNA]. The formations of these complexes paralleled the functional activities of Tax mutants. Furthermore, the Tax-CREB complex was detected in a nuclear extract of HTLV-1-infected cells, and the Tax-CREB-21-bp-DNA complex was demonstrated as a major component of Tax complexes containing the 21-bp DNA probe. These observations indicate that Tax protein binds to CREB and CRE modulator and the complexes then bind to the 21-bp enhancer, suggesting that the complex binding to the enhancer mediates trans-activation of transcription.

Human interleukin-9: a new cytokine in hematopoiesis

IL-9 was first identified in the mouse system as a T cell growth factor while human IL-9 was isolated based on its activity on a human myeloid leukemic cell line. The high sequence homology between mouse and human IL-9 plus the preliminary biological analysis have predicted a wide spectrum of in vitro biological activities for this cytokine. Despite the high sequence homology between mouse and human IL-9, many biological activities, however, have not been demonstrated in both species. In vivo studies therefore become essential to understand the physiological role of IL-9. Increasing evidence have also suggested the possible role of IL-9 in the pathogenesis of HD and LCAL. Detailed analysis of IL-9 expression, autocrine growth and clinical outcome of HD patients will be required to make any speculation on the role of this cytokine in the disease states.

Induction of cytokines in glial cells by trans activator of human T-cell lymphotropic virus type I

Human T-cell lymphotropic virus type I (HTLV-I), the cause of adult T-cell leukemia, is also associated with the neurological disease, TSP/HAM (tropical spastic paraparesis/HTLV-I associated myelopathy). The HTLV-I genome encodes a protein, Tax, that trans activates viral and cellular gene transcription. To understand the mechanisms for the production of cytokines by HTLV-I in nervous tissue, we examined their expression in glial cells which carried the Tax-expressing vector. We demonstrated that Tax expression enhanced the production by glial cells of interleukin (IL)-1, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) and transforming growth factor (TGF) beta. We suggest that the excessive production of cytokines in nervous tissue may play a role in pathogenesis of TSP/HAM. Glial cells that carry the tax gene may provide a model useful for in vitro study of the mechanism of production of cytokines in the nervous system.