Prostaglandin D2 receptor of mastocytoma P-815 cells--possible regulation by phosphorylation and dephosphorylation

The 3H-labeled prostaglandin D2 [( 3H]PGD2) binding protein in the membrane fraction of mastocytoma P-815 cells was characterized. The specific binding of [3H]PGD2 to the cells or the membranes reached a maximum at pH 5.6, and was saturable, displaceable and of high affinity when incubated at 0 or 37 degrees C. The Bmax values for [3H]PGD2 binding in the two preparations at pH 5.6 were much higher at 0 degrees C than at 37 degrees C, whereas the Kd values were almost equal (85.3 nM for the cells and 80.5 nM for the membranes, respectively). High specific [3H]PGD2 binding activity in the mildly acid-treated cells was still observed when the external pH was raised from 5.6 to 7.2. Furthermore, specific [3H]PGD2 binding to the membranes (at 0 degrees C, pH 5.6) increased on addition of phosphatase inhibitors (NaF and molybdate) in the presence of 10 microM ATP, but practically disappeared on pretreatment of the membranes with phosphatase. On incubation of the membrane with [gamma-32P]ATP and molybdate, the stimulated incorporation of the [32P]phosphate into several peptides, including ones having an Mr of around 100,000-120,000, was observed. These results suggest that [3H]PGD2 binding in the mastocytoma P-815 cell membrane is controlled through phosphorylation-dephosphorylation of the receptor itself.

Molecular mechanisms of regulation of HTLV-1 gene expression and its association with leukemogenesis

Human T-cell leukemia virus type 1 (HTLV-1) has two trans-acting regulator genes, tax and rex, in the pX region. The tax gene is a trans-acting transcriptional activator of the long terminal repeat (LTR) and also of the cellular gene for IL-2R alpha. The latter seems to explain initiation of abnormal growth of HTLV-1 infected cells. The rex gene is a posttranscriptional regulator accumulating gag and env mRNA and also indirectly suppressing the transcription. The regulation requires two cis-acting elements, the LTR sequence at the 3' terminus and 5' splice signal, suggesting a novel mechanism of RNA processing in the nucleus. These two trans-activator genes are essential for efficient replication of HTLV-1 and also explain its poor replication competence and tendency to be latent in vivo.

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.

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.

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 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.

A new approach to high sensitivity differential hybridization

We describe a new approach to differential hybridization, designed to identify cDNA clones representing rare mRNA species. Duplicate filters carrying a library of cDNA from phorbolmyristate acetate (PMA)-induced EL-4 cells in lambda gt11 were hybridized with high concentrations of unlabeled, cloned, single-stranded cDNA from induced and control EL-4 cells, respectively. Plaques binding single-stranded cDNA were revealed by a second round of hybridization with 35S-labeled DNA complementary to the vector moiety of the single-stranded cDNA. Plaques corresponding to PMA-induced mRNAs occurring at a level of about 1 part in 15,000 were isolated. We believe the method is at least ten times more sensitive than conventional differential hybridization.

Antigenic cross-reaction between the alpha types of human and mouse interferon

Cross-neutralization of the alpha and beta types of human and mouse interferons was tested using antibodies directed against the heterologous types of interferons. The alpha type of mouse interferon (MuIFN-alpha) prepared from L cells was found to be completely neutralizable by high-titered antibody against human alpha-type interferon (HuIFN-alpha), although the titers were much lower than those obtained in neutralization reactions with the homologous interferon. MuIFN-alpha from virus-induced lymphocytes, as well as non-glycosylated MuIFN-alpha from L cells, reacted similarly. The cross-reaction was also observed by the binding of anti-HuIFN-alpha antibody to a column of immobilized MuIFN-alpha. The binding experiment indicated that only a small fraction of the anti-HuIFN-alpha antibody population is heterologous reactive. Reciprocally, HuIFN-alpha from L cells, again with relatively low antibody titers, and the antibody responsible for the heterologous reaction was shown to be the anti-MuIFN-alpha and not anti-MuIFN-beta type. It is concluded that the alpha types of human and mouse interferon bear an antigenic homology. On the other hand, no significant antigenic cross-reactivity has been detected between the beta types of human and mouse interferons.

Antigenic relationships among various interferon species

Mouse L-cell interferon consists of two antigenically distinct species, F (22 to 24K) and S(32 to 40K). Various type I mouse interferons, regardless of lymphoid or nonlymphoid origin, likewise consist of two species, whose antigenicities are indistinguishable from the two L-cell interferons. Interferon F was found to be completely neutralizable by an antiserum against human leukocyte interferon, suggesting a structural similarity between the important species of human and mouse interferons.

Nonglycosylated mouse L cell interferon produced by the action of tunicamycin

The effect of tunicamycin, a specific inhibitor of protein glycosylation, on interferon production by L cells induced by Newcastle disease virus was studied. The interferon yields in the presence of tunicamycin ranged from 20 to 100% of control in various experiments. The two molecular species of normal L cell interferon with 40,000 and 24,000 daltons were completely eliminated, and a new species of a smaller size (18,000 daltons) was produced. Radiolabeling of interferon with [35S]methionine and [3H]glucosamine added to the induced cultures, as studied by immunoprecipitation and polyacrylamide gel electrophoresis, indicated that the two species of control interferon were both glycoproteins but tunicamycin interferon contained little or no sugar. In support of this was the loss of binding to lectin from Wistaria floribunda. A change in physical property of the molecule due to the absence of sugar was found in decreased heat stability in the presence of sodium dodecyl sulfate, although in its absence no significant difference from control interferon was observed. These results indicate that tunicamycin is an effective agent in producing nonglycosylated but fully active interferon molecules; the sugar moiety appears to be unnecessary for the antiviral activity and for secretion from cells.