T-cell activation signals and human T-cell leukemia virus type I-encoded p40x protein activate the mouse granulocyte-macrophage colony-stimulating factor gene through a common DNA element

Activation of T cells by an antigen, a mitogen, or a combination of a phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA]) and a calcium ionophore (A23187) leads to induction of a set of lymphokine genes. Treatment of human T-cell leukemia line Jurkat by a mitogen or p40x, a transactivator protein encoded by human T-cell leukemia virus type I, activates many transfected lymphokine genes in a transient transfection assay. To study the mechanism of lymphokine gene induction, we examined the effects of mitogen stimulation and p40x on the gene for the mouse granulocyte-macrophage colony-stimulating factor (GM-CSF) in Jurkat cells. Deletion and mutation analyses showed that the 5'-flanking region of the gene for the GM-CSF is composed of two types of regulatory elements. One sequence, located at positions -95 to -73, determines response to stimulation by either TPA-A23187 or p40x. This region contains conserved lymphokine element 2, which appears in the gene for interleukin 3 (IL-3) and is followed by a GC-rich stretch. This GC-rich stretch alone specifies inducible response to p40x but not to TPA-A23187. Another sequence, located at positions -113 to -96 upstream of a TATA-like sequence, mediates inducible response to p40x but not to TPA-A23187. This sequence includes conserved lymphokine element 1, which appears in several lymphokine-cytokine genes, such as those for IL-3, G-CSF, and IL-2. We previously showed that the simian virus 40 early region promoter was also induced by a mitogen or p40x in Jurkat cells. Deletion analysis showed that the minimum region require for stimulation by both signals are identical. These results, which indicate that p40(x) stimulates transcription of the gene for the GM-CSF or the simian virus 40 early region promoter through the same DNA element or an overlapping DNA element required for induction by a mitogen, lend further support to the notion that p40(x) can exert its function by activating a component(s) of the T-cell signal transduction pathway which is activated by an antigen or a mitogen.

Two cis-acting elements responsible for posttranscriptional trans-regulation of gene expression of human T-cell leukemia virus type I

The pX sequence of human T-cell leukemia virus type I codes for two nuclear proteins, p40tax and p27rex, and a cytoplasmic protein, p21x-III.p40tax activates transcription from the long terminal repeat (LTR), whereas p27rex modulates posttranscriptional processing to accumulate gag and env mRNAs that retain intron sequences. In this paper, we identify two cis-acting sequence elements needed for regulation by p27rex: a 5' splice signal and a specific sequence in the 3' LTR. These two sequence elements are sufficient for regulation by p27rex; expression of a cellular gene (metallothionein I) became sensitive to rex regulation when the LTR was inserted at the 3' end of this gene. The requirement for these two elements suggests an unusual regulatory mechanism of RNA processing in the nucleus.

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

The effects of p40x, a product of an human T cell leukemia virus type I, on the activation of lymphokine genes were examined. The mouse GM-CSF and IL-3 genes were activated by cotransfection with a pX containing plasmid both in Jurkat and CV1 cells. Mouse GM-CSF gene was also activated by phytohaemagglutinin A (PHA)/phorbol myristate acetate (PMA) or PMA/calcium ionophore A23187 stimulation. The 5'-flanking region of the mouse GM-CSF gene which is required for activation by pX or mitogen was mapped within 226 bp upstream from the transcription initiation site. Action of pX was not restricted to T cells. pX activated exogenously added GM-CSF, IL-2, IL-3 and IL-4 genes in fibroblasts. Activation of the GM-CSF gene in fibroblasts appears to require the same regulatory region as in T cells. Similar results were obtained using bovine papilloma virus encoded E2 protein. We propose that pX or E2 protein, both in T cells and fibroblasts, activates cellular component(s) in the signal transduction pathway which results in the activation of lymphokine genes in the absence of extracellular stimuli.

Cell-line specific activation of SV40 transcriptional enhancer by p40tax of HTLV-1

A transcriptional trans-activator p40tax of HTLV-1 was reported to activate HTLV-1 enhancer, but not SV40 or Rous sarcoma virus enhancer. However, in certain cell lines, we found that SV40 enhancer was activated by p40tax. These cell lines were mostly T cells, where the SV40 enhancer showed only low activity without p40tax. Since p40tax-mediated activation of the LTR is not cell line-specific, the activation of enhancers by p40tax depends on the combination of enhancer and cell type used for the test. Thus, apparent activation by p40tax depends on variable cellular components involved in transcriptional regulation.

Post-transcriptional regulator (rex) of HTLV-1 initiates expression of viral structural proteins but suppresses expression of regulatory proteins

Gene expression of human T-cell leukemia virus type 1 (HTLV-1) is regulated by two trans-acting factors encoded by the pX region, p40tax and p27tax.p40tax is a transcriptional activator and p27rex is a post-transcriptional regulator. Using full-length viral DNA, we studied the regulatory effects of rex on HTLV-1 gene expression. p27rex is required for expression of both gag and env proteins, increasing the level of their mRNAs. The effect was dependent on the dose of p27rex expression plasmid. In parallel, increased doses of p27rex suppressed the expression of fully spliced pX mRNA, which encodes the regulatory proteins. These two effects of p27rex operated at the post-transcriptional level and were independent of transcriptional regulation. Lowering the level of pX mRNA down-regulates transcription of the proviral genome. These observations demonstrate that rex is a positive post-transcriptional regulator for gag, pol and env protein expression, and acts at the same time as an indirect negative regulator of viral transcription.

Polyclonal integration of HTLV-I proviral DNA in lymphocytes from HTLV-I seropositive individuals: an intermediate state between the healthy carrier state and smouldering ATL

We have studied 15 individuals (aged 14-74 years) with antibodies to HTLV-I in their serum and random integration of HTLV-I proviral DNA in their peripheral blood lymphocytes. All but one of these patients suffered from a variety of non-specific complaints which did not correspond to those of adult T-cell leukemia (ATL). All of them were born in Kyushu and Okinawa which are endemic areas for HTLV-I infection; 25% of their family members were also seropositive for HTLV-I. The only haematological abnormality in these patients was the presence of few atypical lymphoid cells in the peripheral blood. The CD4/CD8 ratios were normal but the proportion of Tac positive cells was slightly higher than normal. These individuals with polyclonal integration of HTLV-I proviral DNA seem to represent an intermediate state between smouldering ATL (monoclonal integration) and healthy HTLV-I carriers (with antibodies but no detectable HTLV-I proviral DNA). Patients with this intermediate state of HTLV-I infection may be at risk to progress to ATL. The natural history of HTLV-I infection in humans leading to the development of ATL is reviewed in the light of these new findings.

SR alpha promoter: an efficient and versatile mammalian cDNA expression system composed of the simian virus 40 early promoter and the R-U5 segment of human T-cell leukemia virus type 1 long terminal repeat

We developed a novel promoter system, designated SR alpha, which is composed of the simian virus 40 (SV40) early promoter and the R segment and part of the U5 sequence (R-U5') of the long terminal repeat of human T-cell leukemia virus type 1. The R-U5' sequence stimulated chloramphenicol acetyltransferase (CAT) gene expression only when placed immediately downstream of the SV40 early promoter in the sense orientation. The SR alpha expression system was 1 or 2 orders of magnitude more active than the SV40 early promoter in a wide variety of cell types, including fibroblasts and lymphoid cells, and was capable of promoting a high level of expression of various lymphokine cDNAs. These features of the SR alpha promoter were incorporated into the pcD-cDNA expression cloning vector originally developed by Okayama and Berg.

Monoclonal integration of HTLV-I proviral DNA in patients with strongyloidiasis

The relationship between strongyloidiasis and HTLV-I was investigated in Okinawa, an area where both conditions are endemic. Thirty-six patients with strongyloidiasis were seropositive for HTLV-I and suffered from several related clinical complications. Fourteen of these patients (39%) were shown to have monoclonal integration of HTLV-I proviral DNA in their blood lymphocytes, a condition designated as "smouldering" adult T-cell leukaemia (ATL). Monoclonal integration of proviral DNA correlated with an increased CD4/CD8 ratio and the presence of abnormal lymphocytes in the peripheral blood, and with a trend for greater severity of the parasitic infection. Although the immunodeficiency caused by HTLV-I could predispose to hyperinfestation by Strongyloides, it is also possible that both the parasitic and the retroviral infestations are important co-factors leading to the development of ATL.

Transcriptional (p40x) and post-transcriptional (p27x-III) regulators are required for the expression and replication of human T-cell leukemia virus type I genes

The pX sequence of human T-cell leukemia virus type I codes for three products: p40x, p27x-III, and p21x-III. p40x is a transcriptional trans-activator that activates not only the viral long terminal repeat but also cellular genes for interleukin 2 and its receptor. p27x-III and p21x-III are not required for transcriptional activation, and their functions were unknown. Cotransfection experiments with defective human T-cell leukemia virus type I proviruses and various pX expression plasmids revealed that p27x-III, in addition to p40x, was required for gag gene expression. Furthermore, it was shown that p27x-III induced accumulation of a high level of unspliced viral gag mRNA. These results indicate that p27x-III is a post-transcriptional modulator of viral RNA whose transcription has been fully activated by p40x.

Evidence for aberrant activation of the interleukin-2 autocrine loop by HTLV-1-encoded p40x and T3/Ti complex triggering

In this study we provide evidence that distinct DNA sequences within the 5'-flanking regions of the genes for interleukin-2 (IL-2) and its receptor (IL-2R) are involved in human T-cell-specific activation of transcription by p40x, a product of human T cell leukemia virus type I (HTLV-1). The same DNA sequences appear to be responsible for induction of the genes in a T cell line, Jurkat, by mitogens. Although the IL-2 gene sequences are activated by p40x with much lower efficiency than the IL-2R gene sequences, they are synergistically activated by the p40x expression and subsequent extracellular stimulation by Concanavalin-A or anti-T3. We propose a model for two-step activation of the IL-2 autocrine loop in ATL development.

The second pX product p27 chi-III of HTLV-1 is required for gag gene expression

The human T-cell leukemia virus type-1 (HTLV-1) contains a unique pX region, which encodes the gene products p40 chi, p27 chi-III and p21 chi-III. p40 chi is required for transcriptional trans-activation, whereas p27 chi-III and p21 chi-III have no such function. Transfection of pX expression plasmids containing different combinations for the three gene products into cells integrated with HTLV-1 proviruses defective in pX expression revealed that both p40 chi and p27 chi-III are required for expression of the gag protein and accumulation of gag mRNA. These observations suggest that the pX product p40 chi activates transcription and p27 chi-III controls the level of gag mRNA by post-transcriptional modulation.

Mechanism of the gene expression of HTLV-I and its association with ATL

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL) and a trans-acting viral function was proposed to be involved in ATL development because of the non-specific provirus integration in leukemic cells and the frequent immortalization of helper T-cells by in vitro infection. An extra sequence "pX" in the HTLV-1 genome codes for three proteins, p40x-, p27x- and p21x-, and the p40x- is trans-activator of transcription from the viral LTR. A sequence of 21 bp repeats in the LTR was found to be an enhancer and respond to the trans-activation by p40x-. The transient expression of p40x- also activates a cellular gene for interleukin 2 receptor (IL-2R) in helper T-cell lines. This induction of IL-2R may explain the mechanism of preferential growth of HTLV-1 infected cells and may be an early event of ATL development. For practical purposes, the env gene fragments was expressed in E. coli as fusion proteins with beta-galactosidase. Using these fusion proteins, a diagnostic system detecting anti-env antibodies was developed. Immunization of monkeys with these envelope-fusion proteins protected the monkeys from the viral infection, suggesting possible usage of envelope proteins as vaccine.

A single species of pX mRNA of human T-cell leukemia virus type I encodes trans-activator p40x and two other phosphoproteins

Human T-cell leukemia virus type I (HTLV-I) contains the pX sequence which codes for the trans-activator of the long terminal repeat (LTR) and is thus postulated to be associated with leukemogenesis in adult T-cell leukemia. Overlapping open reading frames (ORF) in the pX sequence were recently found to code for p27x-III and p21x-III by ORF III, in addition to p40x coded for by ORF IV. The mechanism of expression of these newly identified proteins and their possible association with trans-activation were studied. On transfection of an expression plasmid that contains a cDNA sequence of the pX mRNA, products from both ORFs III and IV were detected in the cells. The RNA was synthesized in vitro from the cDNA clone by SP6 RNA polymerase and translated in a rabbit reticulocyte lysate. As translation products, two proteins, p27x-III and p21x-III, were detected in addition to p40x. Elimination of the first and second ATG codons in ORF III resulted in loss of the ability to code for p27x-III and p21x-III, respectively, which indicated that the translations from these two ATG codons were independent. A mutant that lacked both ATG codons was fully active in trans-activation of chloramphenicol acetyltransferase gene expression directed by the LTR. These results indicate that a 2.1-kilobase pX mRNA of HTLV-I independently encodes three proteins, p40x, p27x-III, and p21x-III, by different ORFs and that the last two proteins are not involved in trans-activation of the unintegrated LTR.

Induction of interleukin 2 receptor gene expression by p40x encoded by human T-cell leukemia virus type 1

Human T-cell leukemia virus type 1 (HTLV-1) is an etiologic agent of adult T-cell leukemia (ATL). A viral product, p40x, encoded by the pX sequence of HTLV-1 is a trans-acting transcriptional activator of the long terminal repeat (LTR) and has been suspected of involvement in leukemogenesis, activating the cellular genes. The cellular interleukin-2 (IL-2) and its receptor (IL-2R), the latter of which is expressed on ATL leukemic cells, were shown to be transiently induced by transfection of plasmid pMTPX expressing pX in two T-cell lines, Jurkat and HSB-2, but not in other human T- or B-cell lines. The cell type specificity of IL-2R induction by pX expression was the same as that by phytohaemagglutinin/phorbol ester activation, indicating the requirement for some specific cellular factors or a certain state of cellular differentiation. Induction of IL-2 and IL-2R at mRNA level was also demonstrated in transfected cells. Transfections with mutants of pMTPX in which the open reading frames for p40x, p27x-III and p21x-III were inactivated indicated that p40x alone was sufficient for induction of the IL-2R in inducible cells. This induction of the IL-2R by p40x of HTLV-1 may contribute to preferential proliferation of HTLV-1 infected cells at an early stage of ATL development and eventually increase the number of putative target cells for malignant transformation.

Nucleotide sequence of the protease-coding region in an infectious DNA of simian retrovirus (STLV) of the HTLV-I family

A provirus clone of simian T-cell leukemia virus isolated from a pigtailed monkey (PT-STLV), which is 90% homologous to HTLV-I, was shown to be biologically active in transfection assay. In transfected cells, gp61env, Pr55gag, and the mature gag proteins p24, p21, and p15 were detected, and type C particles were produced. The virus could be transmitted from the transfectants to recipient cells by cocultivation. In this biologically active provirus clone, a coding frame, possibly for protease, was identified between the gag and pol genes. The corrected sequence of the protease region of HTLV-I was also found to have a single open reading frame overlapping the gag and pol genes, although it has an amber codon in the middle of the frame. Thus, a single coding frame, which is different from those of gag and pol, is common to proteases of the HTLV family including HTLV-I.

A transcriptional enhancer sequence of HTLV-I is responsible for trans-activation mediated by p40 chi HTLV-I

Human T-cell leukemia virus type I (HTLV-I) contains a unique sequence pX that is located between env and the 3' long terminal repeat (LTR) and codes for three pX proteins, p40 chi, pp27 chi-III and pp21 chi-III. One of these proteins, p40 chi, was previously shown to activate transcription from the LTR in a trans-acting manner, which suggested that it activated some cellular genes involved in leukemogenesis. In this study, the sequences in the LTR responsible for this trans-activation were analyzed. Construction of deletion mutants of the LTR in pLTR-CAT and measurement of their activities in trans-activated expression of the CAT gene showed that sequences upstream of the TATA box were responsible for the trans-activation mediated by p40 chi. The active unit was identified as an enhancer sequence containing direct repeats by inserting it into an enhancer-minus SV40 promoter. Thus, it was concluded that an enhancer sequence in HTLV-I LTR is responsible, at least in part, for transcriptional trans-activation mediated by the viral product p40 chi.

Direct evidence that p40x of human T-cell leukemia virus type I is a trans-acting transcriptional activator

Human T-cell leukemia virus type I has a unique sequence, pX, between the env gene and the 3'LTR (long terminal repeat). This sequence codes for p40x, which was proposed to trans-activate transcription from the LTR. Recently, we identified novel pX proteins coded by frame III, which mostly overlaps frame IV (x-lor, coding for p40x), in a region also overlapped by frame II. To determine which product is responsible for the trans-acting function, we constructed an active provirus clone, pMTPX, that contained a genomic fragment of the env, pX and 3'LTR, and introduced site-directed mutations into the active site. The effects of various deletions and point mutations that distinguished each of the overlapping open reading frames (ORFs), II, III and IV, on trans-activation of pLTR-CAT were treated by co-transfection assays. The results showed that only mutations which affected p40x expression resulted in loss of activity for transcriptional activation. These findings clearly indicate that p40x coded by frame IV is responsible for the transcriptional activation of the LTR. This conclusion was confirmed by studies on expression of cDNA of pX mRNA.

Human T-cell leukemia virus type I is a member of the African subtype of simian viruses (STLV)

The nucleotide sequences of the long terminal repeat (LTR) of simian retroviruses (STLV), which are closely related to human T-cell leukemia virus type I (HTLV-I) were found to be of at least two subgroups: an Asian subtype in macaques and an African subtype in African green monkeys and chimpanzee. The nucleotide sequence of HTLV-I was found to be included within the divergence among STLV, but showed closer homology (95%) to African subtype STLV than to Asian subtype STLV (90%).

Lymphoma type adult T-cell leukemia--a clinicopathologic study of HTLV related T-cell type malignant lymphoma

The clinical and pathological features of T-cell type malignant lymphoma related to human T-cell leukemia virus (HTLV) were investigated in eight patients presenting lymphadenopathy. Biopsy of lymph nodes showed an histology of diffuse non-Hodgkin's lymphoma. All patients were positive for anti-ATLA antibody and HTLV proviral DNA in the lymph node cells. Most patients showed pronounced hypercalcemia and high serum levels of lactic dehydrogenase. All patients died between 3 and 17 months (mean 8 months) after the onset of disease. HTLV-related malignant lymphoma should be added to the spectrum of ATL, being classified as a lymphoma type ATL.

The p40x of human T-cell leukemia virus type I is a trans-acting activator of viral gene transcription

Human T-cell leukemia virus type I has a unique sequence pX and the product p40x was proposed to be a specific trans-acting transcriptional activator of expression of the viral gene. Recently, a second pX protein p27x-III in addition to p40x was identified; these two proteins are encoded by overlapping frames III and IV (x-lor). For determination of which product is the trans-acting activator, site-directed mutations were introduced into the pX sequence which was placed under the metallothionein promoter. On cotransfection with pLTR-CAT (a plasmid containing the LTR of HTLV-I and chloramphenicol acetyltransferase gene), only the mutations that affected p40x expression inactivated the transcriptional activation from the LTR.

Association of the pX gene product of human T-cell leukemia virus type-I with nucleus

Human T-cell leukemia virus type I (HTLV-I) contains a unique gene pX coding for p40 chi, and this protein was suggested to activate the transcription from the LTR of HTLV. By a similar mechanism, this viral function might be involved in immortalization of T-cells and leukemogenesis in adult T-cell leukemia induced by HTLV-I. In this communication, a part of the p40 chi was found to be tightly associated with nuclei in infected cell lines by subcellular fractionation and immunofluorescence staining.

p27x-III and p21x-III, proteins encoded by the pX sequence of human T-cell leukemia virus type I

Human T-cell leukemia virus type I (HTLV-I) is an etiological agent of adult T-cell leukemia and has a unique sequence, pX, that contains four possible open reading frames, I-IV. p40x was previously identified as the gene product of frame IV (x-lor) and was suggested to mediate transcriptional trans-activation of the viral long terminal repeats. We have identified two pX gene products, p27x-III and p21x-III, encoded by frame III, which mostly overlapped frame IV. These proteins were detected with rabbit antiserum against the synthetic peptide predicted from the 3' end of frame III. p27x-III is phosphorylated in cultured cells, and the phosphoprotein (pp27x-III) is localized in nuclei; some pp27x-III was tightly bound to nuclear components. p27x-III was detected in a number of cell lines that express other viral antigens, including a cell line previously reported to express only p40x as a viral protein. The function(s) of p27x-III and p21x-III is not known, but the tight binding of pp27x-III to nuclear components suggests that it is associated with regulation of viral gene expression.