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Biomedical subjects

M Seiki

Publications and source records attributed to M Seiki.

At least 199 records · Page 11Linked to original sources
PubMed1987

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.

Cell Line↗
PubMed1987

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.

Cell Line↗
PubMed1986

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.

Cell Line↗
PubMed1986

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.

Animals↗
PubMed1986

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%).

Animals↗
PubMed1986

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.

Amnion↗
PubMed1986

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.

Acetyltransferases↗
PubMed1986

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.

Cell Line↗
PubMed1986

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.

Deltaretrovirus↗
PubMed1986

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.

Animals↗
PubMed1985

Sequence homology of the simian retrovirus genome with human T-cell leukemia virus type I.

A retrovirus highly related to human T-cell leukemia virus type I (HTLV-I) was isolated from a T-cell line established from a seropositive pig-tailed monkey and the provirus genome was molecularly cloned using HTLV-I as a probe. The monkey virus (STLV) had the genomic structure of the LTR-gag-pol-env-pX-LTR. Analysis of the env-pX-LTR region revealed the 90% homology of the nucleotide sequence with that of HTLV-I in each region. This high homology of the sequence indicates that STLV is a member of the HTLV family, but apparently different from HTLV-I. This suggests that the possibility of recent interspecies transmission from monkeys to humans in the endemic area is very small. From its similarity to HTLV, STLV should be useful as an animal model in studies on natural HTLV infection and leukemogenesis of HTLV in humans.

Animals↗
PubMed1985

Expression of the pX gene of HTLV-I: general splicing mechanism in the HTLV family.

Human T-cell leukemia virus type I (HTLV-I) is an etiological agent of adult T-cell leukemia. A viral gene pX encodes for p40X and it has been proposed that this protein trans-activates the viral long terminal repeat and possibly some cellular genes; this activation may be associated with T-cell transformation. The mechanism of pX gene expression and the primary structure of p40X are now reported. Two-step splicing generates the 2.1-kilobase pX mRNA; the initiator methionine for env becomes part of the pX protein. These splicing signals are conserved among all members of the HTLV family except for the acquired immune deficiency syndrome-associated viruses.

Animals↗
PubMed1985

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.

Cell Fractionation↗