A stochastic model for circadian rhythms from coupled ultradian oscillators.

Background: Circadian rhythms with varying components exist in organisms ranging from humans to cyanobacteria. A simple evolutionarily plausible mechanism for the origin of such a variety of circadian oscillators, proposed in earlier work, involves the non-disruptive coupling of pre-existing ultradian transcriptional-translational oscillators (TTOs), producing "beats," in individual cells. However, like other TTO models of circadian rhythms, it is important to establish that the inherent stochasticity of the protein binding and unbinding does not invalidate the finding of clear oscillations with circadian period.

A model for generating circadian rhythm by coupling ultradian oscillators.

Background: Organisms ranging from humans to cyanobacteria undergo circadian rhythm, that is, variations in behavior that cycle over a period about 24 hours in length. A fundamental property of circadian rhythm is that it is free-running, and continues with a period close to 24 hours in the absence of light cycles or other external cues. Regulatory networks involving feedback inhibition and feedforward stimulation of mRNA transcription and translation are thought to be critical for many circadian mechanisms, and genes coding for essential components of circadian rhythm have been identified in several organisms.

Interactions of a transcriptional activator in the env gene of the mouse mammary tumor virus with activation-dependent, T cell-specific transacting factors.

The mouse mammary tumor virus env gene contains a transcriptional activator (META) that can control transcription of the adjacent long terminal repeat region. Transcriptional control by META parallels that of several lymphokine genes, being specific to T cells, dependent on their activation, and inhibited by the immunosuppressive drug cyclosporine (CsA). DNase I footprinting indicated that nuclear factors from activated T lymphocytes bound a promoter-proximal site, META(P), and a promoter-distal site, META(D+), within the 400-base pair META region.

A binding factor for interleukin 2 mRNA.

Jurkat cells, a human T lymphocyte line that can be induced to synthesize and secrete interleukin 2, contain a factor that binds interleukin 2 mRNA. Binding can be demonstrated by formation of a complex detectable by gel electrophoresis. The binding is sequence specific and occurs in the 3'-non-coding region, within 160 nt of the end of the coding region, at or near a site on the mRNA that is rich in A and U residues.

A novel immunosuppressive factor in bovine colostrum blocks activation of the interleukin 2 gene enhancer at the NFAT site.

A factor in bovine colostrum (colostrum inhibitory factor, CIF) inhibits interleukin 2 (IL2) production in activated T helper cells by blocking the accumulation of IL2 mRNA. To determine whether CIF blocks at the level of IL2 transcription, we introduced reporter plasmids into the human T leukemia cell line Jurkat by transient transfection. These contained the luciferase gene under the control of either the human IL2 upstream enhancer region (segments -326 to +45) or three repeats of the NFAT element contained within it (segments -255 to -285).

A novel immunosuppressive factor in human colostrum.

Human colostrum contains a factor that inhibits the induction of interleukin 2 (IL2) in T lymphocyte cell lines (colostrum inhibitory factor, CIF). In PMA-stimulated EL4.E1 cells, inhibition is the result of blocking the accumulation of IL2 mRNA.

Induction of a proteoglycan core protein mRNA in mouse T lymphocytes.

The mouse T lymphocyte cell line EL4.E1 synthesizes a proteoglycan core protein (PGCP) mRNA which is identical to serglycin mRNA found in mouse bone marrow-derived mast cells and a mouse mastocytoma cell line. PGCP mRNA was strongly induced in EL4.

An RNasin-resistant ribonuclease selective for interleukin 2 mRNA.

Interleukin 2 (IL2) mRNA has a short half-life in the cytoplasm of T lymphocytes, relative to most mRNA. We have discovered a candidate ribonuclease to account for the rapid turnover of IL2 mRNA in the cytosol of the human T lymphocyte cell line Jurkat. In partially purified form, this RNase is about 7 times as active on IL2 as on beta-globin mRNA.

An activation-dependent, T-lymphocyte-specific transcriptional activator in the mouse mammary tumor virus env gene.

Transcription of the complete mouse mammary tumor virus (MMTV) proviral genome in mouse cells is controlled by a strong promoter in its long terminal repeat. In the mouse T lymphoma EL4, there is a second, activation-dependent transcriptional initiation site within the envelope (env) gene, from which a short mRNA is generated, encoding the open reading frame of the long terminal repeat. We now report the isolation of a segment of the MMTV env gene (called META, for MMTV env transcriptional activator) which has the expected transcription-activating properties seen in EL4.

Human colostrum contains an activity that inhibits the production of IL-2.

The effect of human colostrum on T cell immune function was investigated. Colostrum inhibited the proliferation of human T cells activated by allogeneic, concanavalin A (Con A) or phytohaemagglutinin (PHA) stimulation. Colostrum also inhibited the production of IL-2 by Con A-activated human peripheral blood T cells and by Con A-activated Jurkat cells, a human T lymphoma line.

Synovial cell secretion of IL-2 in vitro, a limiting dilution analysis.

Limiting dilution analysis (LDA) was used to analyze the defect of production of IL-2 by synovial fluid cells in rheumatoid arthritis (RA). LDA is a relatively simple means of separating T-cell function from the potential effects of accessory-cells, suppressor factors and adsorption. The number of precursor cells for interleukin-2 (IL-2) secretion was determined among peripheral blood cells (PBL) from healthy control individuals, and in PBL and synovial fluid (SF) mononuclear cells from patients with rheumatoid arthritis (RA).

IL-4 potentiates the IL-2-dependent proliferation of mouse cytotoxic T cells.

In addition to the regulation of B lymphocyte growth and differentiation, the cytokine IL-4 (BSF-1) exerts effects on T lymphocytes and other bone marrow-derived lineages. We show here that recombinant mouse IL-4 synergizes with low levels of IL-2 to increase the yield of cytotoxic activity in a primary MLR, and the proliferation of both cloned IL-2-dependent CTL lines and cells obtained from a primary MLR. IL-4 did not induce the proliferation of any of several cloned CTL cell lines on its own.

Development of precytotoxic T cells in cyclosporine-suppressed mixed lymphocyte reactions.

Cyclosporine (CsA) blocked the generation of cytolytic activity in a primary MLR of mouse spleen cells. As expected from the known mechanism of action of this drug, it also blocked the accumulation of IL-2 during the MLR. Addition of human rIL-2 did not overcome the inhibition of CTL generation, even when it was added daily to keep its level similar to that produced in a normal MLR.

Deletion of carboxy-terminal residues of murine granulocyte-macrophage colony-stimulating factor results in a loss of biologic activity and altered glycosylation.

A deletion mutant of murine granulocyte-macrophage colony-stimulating factor (GM-CSF) which differs in primary structure from native GM-CSF in the carboxy-terminal 11 amino acids was prepared. Four amino acid residues are mutated and the seven terminal residues including Cys-118 are deleted. Supernatants from COS-1 cells transfected with this deletion mutant (GM-CSF(del] showed a 3000-fold decrease in the ability to stimulate bone marrow stem cells to proliferate and differentiate into granulocytes and macrophages in vitro.

Transcriptional regulation of two cytotoxic T lymphocyte-specific serine protease genes.

The expression of two serine proteases is induced by antigenic stimulation in cytotoxic T lymphocytes. Using nuclear run-on analysis the increase in steady state mRNA level has been shown to correspond to transcriptional activation. However, the two genes appear to be sequentially rather than coordinately induced.

Cyclosporine blocks the activation of antigen-dependent cytotoxic T lymphocytes directly by an IL-2-independent mechanism.

The immunosuppressive drug Cyclosporin A (cyclosporine) inhibits the reactivation of quiescent Ag-dependent CTL in the presence of IL-2. Both proliferation and the regeneration of cytotoxicity are inhibited. The cytotoxic cells that are inhibited are Ag dependent for activation, whereas derived, Ag-independent, but still IL-2-dependent, cytotoxic cells are insensitive to cyclosporine.

The role of IL-5 in IgA B cell differentiation.

IL-5 enhances secretion of IgA by B cells. The stage of B cell differentiation at which IL-5 enhances IgA secretion and the mechanism by which it exerts this effect are unknown. We examined these issues by separating Peyer's patch (PP) B cells into membrane IgA (mIgA)-positive and mIgA-negative cells with panning or cell sorting.

Mechanisms regulating the level of IL-2 mRNA in T lymphocytes.

IL-2 mRNA has a t1/2 of 1 to 2 h in T lymphocyte cell lines and in activated human PBL. Human Jurkat cells show a rapid increase of IL-2 mRNA on induction of IL-2 synthesis, followed by an equally rapid decline 4 to 6 h later. The decline occurs despite a high rate of synthesis, and appears to be due to an enhanced rate of IL-2 mRNA degradation.

Cloning of cDNA for the bovine IL-2 receptor (bovine Tac antigen).

We have cloned the Tac analog of the bovine IL-2 receptor (IL-2R) cDNA. Using mouse and human cDNA probes, we isolated five bovine IL-2R clones from a lambda gt11 bovine long-term lymphocyte cDNA library. Three of the clones had inserts of 2600 base pairs (bp), the same size as the bovine IL-2R mRNA visualized on Northern blots.

Phorbol diester-inducible, cyclosporine-suppressible transcription from a novel promoter within the mouse mammary tumor virus env gene.

The mouse T-cell lymphoma cell line EL4.E1 constitutively synthesizes mouse mammary tumor virus (MMTV) transcripts encoding either the entire proviral genome or segments of it. In addition to these conventional mRNAs, however, an mRNA of about 1 kilobase accumulates after induction of these cells with phorbol myristate acetate (PMA).

A molecular-genetic analysis of cytotoxic T lymphocyte function.

Two genes that are specifically expressed in T cells with cytolytic activity were isolated from a CTL cDNA library by differential screening. Both appear to encode serine proteases, thus suggesting a cascade mechanism, similar to complement, in activated CTL. Both CTL-specific proteases have a number of unusual structural features that suggest that they will have novel substrate specificities.

A serine protease (CCP1) is sequestered in the cytoplasmic granules of cytotoxic T lymphocytes.

Based upon the use of a new predictive algorithm, three peptides were synthesized that correspond to likely antigenic sites of the cytotoxic T cell-specific protease cytotoxic cell protein 1 (CCP1). Antibodies raised against these peptides, under reducing conditions, bound to a single protein of m.w.