Induction and decay of human fibroblast interferon mRNA

Ligand-induced IFNGR1 down-regulation calibrates myeloid cell IFNγ responsiveness

The type II IFN (IFNγ) enhances antimicrobial activity yet also drives expression of genes that amplify inflammatory responses. Hence, excessive IFNγ stimulation can be pathogenic. Here, we describe a previously unappreciated mechanism whereby IFNγ itself dampens myeloid cell activation. Staining of monocytes from Listeria monocytogenes-infected mice provided evidence of type I IFN-independent reductions in IFNGR1. IFNγ was subsequently found to reduce surface IFNGR1 on cultured murine myeloid cells and human CD14+ peripheral blood mononuclear cells. IFNγ-driven reductions in IFNGR1 were not explained by ligand-induced receptor internalization. Rather, IFNγ reduced macrophage Ifngr1 transcription by altering chromatin structure at putative Ifngr1 enhancer sites. This is a distinct mechanism from that used by type I IFNs. Ligand-induced reductions in IFNGR1 altered myeloid cell sensitivity to IFNγ, blunting activation of STAT1 and 3. Our data, thus, reveal a mechanism by which IFNGR1 abundance and myeloid cell sensitivity to IFNγ can be modulated in the absence of type I IFNs. Multiple mechanisms, thus, exist to calibrate macrophage IFNGR1 abundance, likely permitting the fine tuning of macrophage activation and inflammation.

Basal interferon signaling and therapeutic use of interferons in controlling peste des petits ruminants virus infection

Peste des petits ruminants virus (PPRV) is a morbillivirus which causes severe disease in ruminants. Since interferons (IFNs) serve as the important defense line against viral infection, we have investigated the roles of types I and III IFNs in PPRV infection in vitro. Upon PPRV infection, IFN-λ3 was strongly induced, while IFN-β and IFN-λ2 were moderately induced at transcriptional level in human embryonic kidney 293 T (HEK293T) cells. Although the transcription of type I and III IFNs were triggered, the production of functional IFN products was not detected. Importantly, the replication of PPRV was strongly inhibited in HEK293T cells treated by the exogenous IFNs (IFN-α-2b, IFN-β and IFN-λ3). Consistently, these IFNs significantly activate a panel of IFN-stimulated genes (ISGs). The inhibition of JAK-STAT pathway by JAK I inhibitor can abrogate the anti-PPRV activity of IFNs. Thus, our study shall contribute to better understanding of the complex PPRV-host interactions and provide rationale for therapeutic development of IFN-based treatment against PPRV infection.

Control of the induction of type I interferon by Peste des petits ruminants virus

Peste des petits ruminants virus (PPRV) is a morbillivirus that produces clinical disease in goats and sheep. We have studied the induction of interferon-β (IFN-β) following infection of cultured cells with wild-type and vaccine strains of PPRV, and the effects of such infection with PPRV on the induction of IFN-β through both MDA-5 and RIG-I mediated pathways. Using both reporter assays and direct measurement of IFN-β mRNA, we have found that PPRV infection induces IFN-β only weakly and transiently, and the virus can actively block the induction of IFN-β. We have also generated mutant PPRV that lack expression of either of the viral accessory proteins (V&C) to characterize the role of these proteins in IFN-β induction during virus infection. Both PPRV_ΔV and PPRV_ΔC were defective in growth in cell culture, although in different ways. While the PPRV V protein bound to MDA-5 and, to a lesser extent, RIG-I, and over-expression of the V protein inhibited both IFN-β induction pathways, PPRV lacking V protein expression can still block IFN-β induction. In contrast, PPRV C bound to neither MDA-5 nor RIG-I, but PPRV lacking C protein expression lost the ability to block both MDA-5 and RIG-I mediated activation of IFN-β. These results shed new light on the inhibition of the induction of IFN-β by PPRV.

Differential Effects of IFN-β on the Survival and Growth of Human Vascular Smooth Muscle and Endothelial Cells

It has been documented that interferon (IFN)-β is effective against the genesis of atherosclerosis or hyperplastic arterial disease in animal model. The main mechanism of the efficacy was antiproliferative action on the growth of vascular smooth muscle cells (SMC). To understand more about the mechanisms that are responsible for the efficacy, we examined minutely the effects of IFN-β on the apoptosis and growth of vascular SMC and endothelial cells (EC). IFN-β enhanced SMC apoptosis in serum starved medium. Conversely, EC apoptosis induced by serum and growth factor deprivation was inhibited by IFN-β. The induction of SMC apoptosis and anti-apoptotic effect on EC linked to the expression of pro-apoptotic bax mRNA and caspase-3 activities. Anti-apoptotic bcl-2 mRNA was also up-regulated in EC. IFN-β inhibited SMC growth in a dose dependent manner. However, the growth of EC was rather enhanced by a low dose of IFNs. The antiproliferative effect on SMC associated with the activation of p21 and increase of G0/G1 arrested cells. The growth stimulation on EC was considered to link with increase of S and G2/M phase cells. SMC produced IFN-β in response to various stimulants. However, IFN-β was not induced in EC. These suggested that endogenous IFN-β from SMC may act on EC and affect to EC functions. In this study, it was clarified that IFN-β enhances SMC apoptosis and inhibits the EC apoptosis, and stimulates the EC growth. These effects were considered to contribute to a cure against hyperplastic arterial diseases as the mechanisms in the efficacy of IFN-β.

A possible role of autogenous IFN-beta for cytokine productions in human fibroblasts

It has been already known that human diploid fibroblasts are able to produce not only high levels of IFN-beta but also various kinds of cytokines by poly rI: poly rC, and some inflammatory cytokines are induced by IFN-beta gene activation. We also obtained similar results. However, in our system, cytokine productions were extremely enhanced by treating the cells with a low dose of type 1 IFN and the priming effects on cytokine productions were blocked by cycloheximide similar to those on IFN-beta productions. Most of cytokines were produced later than IFN-beta and synthesis patterns of their mRNA showed the same phenomena. We made clear that cytokine productions by poly rI: poly rC are mediated by secreted IFN-beta at a protein level using a monoclonal antibody against human IFN-beta. Further, it was shown that intra-cellular IFN-beta which is not secreted might also participate in cytokine productions. Meanwhile, IL-1beta induced various kinds of cytokines in human fibroblasts and production time courses of these cytokines were similar to those of poly rI: poly rC induced cytokines. Although secreted IFN-beta was not detected in IL-1beta stimulated culture, expression of IFN-beta mRNA was augmented. These results showed that priming effects of type 1 IFN on cytokine productions by poly rI: poly rC might not be the direct action, but successive IFN-beta production might be essential in the production processes of other cytokines. Further, it was suggested that inducible IFN-beta might also take part in IL-1beta-induced cytokine productions.

The interferons: 50 years after their discovery, there is much more to learn

The interferons (IFNs) and their receptors represent a subset of the class 2 alpha-helical cytokines that have been in chordates for millions of years. This brief review focuses on the discovery and purification of interferons, cloning of human IFN-alpha and IFN-beta, interferon receptors, activities and therapeutic uses of interferons, and the side effects of interferons.

Post-transcriptional control of the interferon system

The interferon (IFN) system is a well-controlled network of signaling, transcriptional, and post-transcriptional processes that orchestrate host defense against microbes. The IFN response comprises a multi-array of IFN-stimulated gene products that mediate a variety of biological processes designed to control infection and regulate specific immune responses. In this review, we focus on post-transcriptional mechanisms of gene regulation that occur during the course of IFN induction and during the response of cells to IFN. Post-transcriptional mechanisms involve different levels of regulation such as mRNA stability, alternative splicing, and translation. Such controls offer a fine tuning mechanism for efficient and rapid response and as a negative feedback control in IFN biosynthesis and response.

Interferon: The pathways of discovery

This historical account covers 50 years of seminal research work on interferon done since its discovery in 1957. Topics related to molecular structure, production and action of interferons are considered from the viewpoint of how our insights have expanded and deepened within the context of evolving tools and general knowledge in cellular and molecular biology. Lines of thought that linked each discovery to the next are expounded.

Transformation of revertant murine cells by 5-azacytidine results in rapid inhibition of lysyl oxidase expression

Lysyl oxidase (LO) is synthesized intracellularly as a proenzyme that is secreted and then processed extracellularly to a mature form. LO is expressed in NIH3T3 cells, but only very low levels are observed after NIH 3T3 is transformed by c-H-ras or one of several other oncogenes. LO functions as a tumor suppressor. Treatment of ras-transformed cells with interferon-alpha with or without retinoic acid results in their persistent reversion to a non-transformed state that is dependent on the restoration of LO expression. When such revertant cells are treated with 5-azacytidine (5-azaC), they undergo rapid morphological retransformation. Within one passage after addition of 5-azaC, there was a down regulation of LO mRNA and proenzyme protein. These data suggest a direct relationship between the transformed state and LO expression.

Interferons, interferon-like cytokines, and their receptors

Recombinant interferon-alpha (IFN-alpha) was approved by regulatory agencies in many countries in 1986. As the first biotherapeutic approved, IFN-alpha paved the way for the development of many other cytokines and growth factors. Nevertheless, understanding the functions of the multitude of human IFNs and IFN-like cytokines has just touched the surface. This review summarizes the history of the purification of human IFNs and the key aspects of our current state of knowledge of human IFN genes, proteins, and receptors. All the known IFNs and IFN-like cytokines are described [IFN-alpha, IFN-beta, IFN-epsilon, IFN-kappa, IFN-omega, IFN-delta, IFN-tau, IFN-gamma, limitin, interleukin-28A (IL-28A), IL-28B, and IL-29] as well as their receptors and signal transduction pathways. The biological activities and clinical applications of the proteins are discussed. An extensive section on the evolution of these molecules provides some new insights into the development of these proteins as major elements of innate immunity. The overall structure of the IFNs is put into perspective in relation to their receptors and functions.

Increased interleukin-10 mRNA stability in melanoma cells is associated with decreased levels of A + U-rich element binding factor AUF1

Abnormal production of interleukin-10 (IL-10) is observed in some pathologic conditions. For example, compared with normal melanocytes, IL-10 expression is elevated in melanoma cells. IL-10 overexpression could inhibit both immune surveillance and tumor rejection. We investigated a potential posttranscriptional mechanism for IL-10 overexpression in melanoma cells. In normal melanocytes, the half-life of IL-10 mRNA is 7 min, whereas in the melanoma cell line MNT1, the half-life is 75 min. This 10-fold difference could account, at least in part, for IL-10 overexpression in MNT1 cells. Examination of the 3'-untranslated region (3'-UTR) of IL-10 mRNA revealed a suspected A + U-rich element (ARE) that might target the mRNA for rapid degradation. Transfection experiments confirmed that these sequences promote rapid degradation when inserted into a normally stable mRNA, indicating ARE functionality. As AREs act via their interactions with ARE-binding proteins, we examined cytoplasmic proteins from normal melanocytes and MNT1 cells for IL-10 ARE-binding activity. Compared with cytoplasmic extracts of normal melanocytes, cytoplasmic extracts of MNT1 cells possess substantially less ARE-binding activity, consistent with the extended half-life of IL-10 mRNA in MNT1 cells. Finally, we find that the ARE-binding protein AUF1 comprises the major ARE-binding activity in cytoplasmic extracts of normal melanocytes. By contrast, AUF1 is not detectable in cytoplasmic extracts of MNT1 cells but appears restricted to the nuclear fraction. Together, these data suggest a mechanism whereby reduced cytoplasmic levels of AUF1 in MNT1 melanoma cells may lead to IL-10 overexpression, with deleterious consequences for tumor surveillance and rejection.

Suppression of the induction of alpha, beta, and lambda interferons by the NS1 and NS2 proteins of human respiratory syncytial virus in human epithelial cells and macrophages [corrected]

Wild-type human respiratory syncytial virus (HRSV) is a poor inducer of alpha/beta interferons (IFN-alpha/beta). However, recombinant HRSV lacking the NS1 and NS2 genes (Delta NS1/2) induced high levels of IFN-alpha and -beta in human pulmonary epithelial cells (A549) as well as in macrophages derived from primary human peripheral blood monocytes. Results with NS1 and NS2 single- and double-gene-deletion viruses indicated that the two proteins function independently as well as coordinately to achieve the full inhibitory effect, with NS1 having a greater independent role. The relative contributions of the individual NS proteins were the converse of that recently described for bovine RSV (J. F. Valarcher, J. Furze, S. Wyld, R. Cook, K. K. Conzelmann, and G. Taylor, J. Virol. 77:8426-8439, 2003). This pattern of inhibition by HRSV NS1 and NS2 also extended to the newly described antiviral cytokines IFN-lambda 1, -2 and -3.

Interferon-kappa, a novel type I interferon expressed in human keratinocytes

High throughput cDNA sequencing has led to the identification of interferon-kappa, a novel subclass of type I interferon that displays approximately 30% homology to other family members. Interferon-kappa consists of 207 amino acids, including a 27-amino acid signal peptide and a series of cysteines conserved in type I interferons. The gene encoding interferon-kappa is located on the short arm of chromosome 9 adjacent to the type I interferon gene cluster and is selectively expressed in epidermal keratinocytes. Expression of interferon-kappa is significantly enhanced in keratinocytes upon viral infection, upon exposure to double-stranded RNA, or upon treatment with either interferon-gamma or interferon-beta. Administration of interferon-kappa recombinant protein imparts cellular protection against viral infection in a species-specific manner. Interferon-kappa activates the interferon-stimulated response element signaling pathway and a panel of genes similar to those regulated by other type I interferons including anti-viral mediators and transcriptional regulators. An antibody that neutralizes the type I interferon receptor completely blocks interferon-kappa signaling, demonstrating that interferon-kappa utilizes the same receptor as other type I interferons. Interferon-kappa therefore defines a novel subclass of type I interferon that is expressed in keratinocytes and expands the repertoire of known proteins mediating host defense.

Role of type I IFNs in the in vitro attenuation of live, temperature-sensitive vaccine strains of human respiratory syncytial virus

The contributions of type I interferons (IFNs) to the in vitro attenuation of three temperature-sensitive (Ts) subgroup A and one subgroup B deletion mutant RSV strains were evaluated. The ability of these vaccine viruses to induce IFNs at their permissive and restrictive temperatures and their sensitivity to the antiviral effects of exogenous I IFNs were tested in human lung epithelial A549 cells. Our results show that the highly attenuated and immunogenic subgroup A vaccine strain Ts1C produced higher levels of IFN-beta than its parent RSS-2 or two related strains, Ts1A and Ts1B, at their permissive temperature. Growth of RSV-infected A549 cultures at restrictive temperatures or prior UV inactivation of the virus abolished the observed induction of IFN-beta, suggesting a strict requirement of viral replication for cellular IFN induction. The enhanced induction of IFN-beta by the highly immunogenic Ts1C at permissive temperature may be an advantageous characteristic of a live intranasal vaccine candidate. The subgroup B strain RSV B1 and its mutant cp-52 (with SH and G gene deletions) both induced similar but low levels of IFN-beta. Hence the observed overattenuation of cp-52 in human infants is probably not due to enhanced IFN induction during its replication in the host. The ability of cp-52, which does not express the SH and G proteins, to induce IFN-beta levels similar to those of its parent strain suggests that these viral proteins may not have a role in the induction of IFN-beta in the host. In addition, both subgroup A and B mutants and their respective parent strains were similarly resistant to the antiviral effects of exogenous IFN-alpha or -beta. Therefore, increased sensitivity of the mutants to IFNs does not seem to contribute to their attenuation.

The human interferon alpha species and receptors

Interferon (IFN) was approved by the U.S. Food and Drug Administration on June 5, 1986. As the first biotherapeutic approved, IFN-alpha paved the way for development of many other cytokines and growth factors. Nevertheless, we have just touched the surface of understanding the multitude of human IFNs. This paper reviews the history of the purification of human leukocyte IFN and key aspects of our current state of knowledge of human interferon alpha genes, proteins, and receptors.

Superinduction of interleukin-6 mRNA in lung epithelial H292 cells depends on transiently increased C/EBP activity and durable increased mRNA stability

Restriction of eukaryotic protein synthesis affects the regulation of some transiently expressed gene transcripts resulting in their superinduction. We determined the transcriptional and post-transcriptional processes implicated in IL-6 mRNA superinduction in a human lung-derived epithelial cell line H292, and their kinetics in the absence and presence of an exogenous stimulus, tumor necrosis factor-alpha (TNF-alpha). Cycloheximide (CHI) at 10 microg/ml, which inhibited protein synthesis for 80%, caused a 80-fold induction of IL-6 mRNA level which was due predominantly to a stabilization of IL-6 mRNA (20-fold) early on. Employing transient transfection protocols we noted a small positive effect of CHI on transcription, mediated by the proximal and the distal C/EBP sites of the IL-6 promoter and paralleled by an increased C/EBP DNA-binding activity, similar to that found for exposure to TNF-alpha alone. TNF-alpha and CHI synergized on IL-6 mRNA expression (200-fold increase) which was due to an increased transcription, corresponding to a further increased C/EBP DNA-binding activity. However, the effect of CHI on IL-6 gene transcription was transient, in support of the need for ongoing protein synthesis for C/EBP activity. These findings indicate that IL-6 mRNA superinduction, at least in H292 cells, is regulated predominantly by modulating the repressive system that ensures a rapid degradation of IL-6 mRNA.

Enhanced AP-1 and NF-kappaB activities and stability of interleukin 8 (IL-8) transcripts are implicated in IL-8 mRNA superinduction in lung epithelial H292 cells

Inhibition of protein synthesis may result in superinduction of short-lived transcripts and has been attributed variably to stabilization of transcripts and/or increased gene transcription. Little is known about the kinetics of these processes and relevant transcriptional elements have not been identified. In this study, we describe superinduction of interleukin 8 (IL-8) mRNA, an important inflammatory mediator, in lung epithelial-like H292 cells and identify the underlying molecular mechanisms and their kinetics. Cycloheximide (CHI, 10 microg/ml), an inhibitor of protein synthesis, maximally increased IL-8 mRNA levels 30-fold in H292 cells. Tumour necrosis factor alpha (TNF-alpha), which induced IL-8 mRNA 3-fold, synergized with CHI causing a 150-fold increase at 6 h. CHI early on increased the stability of IL-8 mRNA (from 40 min in cells cultured with medium to more than 4 h with CHI). CHI also increased transcription as shown by transfection with IL-8 promoter constructs. Truncated and mutated constructs identified NF-kappaB and AP-1 binding sites as primary cis-acting elements in IL-8 gene transcription and IL-8 mRNA superinduction. Electrophoretic mobility shift assays indicated that CHI increased NF-kappaB and prolonged AP-1 DNA-binding activities and that the synergism of TNF-alpha and CHI on IL-8 mRNA expression was paralleled by a further increase of AP-1 DNA-binding activity. This synergism was still noticed when 4 h elapsed between the addition of CHI and that of TNF-alpha. Taken together, our results indicate that CHI interferes with both post-transcriptional and transcriptional repressive mechanisms of IL-8 mRNA expression.

Platelet-derived growth factor B-chain gene expression in mesangial cells: effect of phorbol ester on gene transcription and mRNA stability

We have investigated the effect of phorbol 12-myristate 13-acetate (PMA) on platelet-derived growth factor (PDGF) B-chain gene transcription as well as on mRNA stability in cultured human mesangial cells. Addition of actinomycin to cells stimulated with PMA decreases steady state levels of PDGF-B chain mRNA analysed by solution hybridization assay. PDGF-B chain gene transcription was also assayed directly by measuring elongation of transcripts in isolated nuclei followed by hybridization of labeled RNA transcripts to a cDNA encoding for PDGF-B chain. Our data show that PMA induces PDGF-B chain gene transcription by approximately 2-fold. alpha-Amanitin, an RNA polymerase II inhibitor, blocked transcription by more than 70%. In addition, we determined the effect of PMA on the halflife of PDGF-B chain mRNA directly by pulse chase method. In human mesangial cells, the PDGF-B chain mRNA exhibited halflife of approximately 105 min. In the presence of PMA, the halflife of PDGF-B chain mRNA was reduced to approximately 72 min. These studies indicate that regulation of PDGF-B chain gene by PMA in human mesangial cells involves a coordinate effort at the level of transcription and mRNA stability.

The hemispheric functional expression of the thyrotropin-releasing-hormone receptor is not determined by the receptors' physical distribution

The thyrotropin-releasing-hormone receptor (TRH-R) is a member of a family of the G-protein-coupled receptors that share structural similarities and exert their physiological action via the inositol lipid signal-transduction pathway. The TRH-R when expressed in Xenopus oocytes exhibits marked preference of the response (increased chloride conductance) for the animal hemisphere. Whereas the rat TRH-R functional distribution was strongly asymmetric (animal/vegetal ratio = 9.5), the mouse TRH-R exhibited a significantly lower ratio (3.9). Truncation of the last 59 amino acids of the C-terminal region of the mouse TRH-R did not lead to any changes in the functional hemispheric distribution. Despite the polarization of response, receptor number was similar on both hemispheres. Moreover, the apparent half-life of the functional expression of the TRH-R was approx. 4 h on both hemispheres when the expression was inhibited by a specific antisense oligonucleotide. Inhibition of total protein synthesis with cycloheximide affected hemispheric responses mediated by each of the three TRH-Rs tested in a qualitatively different way. These results suggest that an additional, rapidly degraded, protein modulates the functional hemispheric expression of the TRH-Rs.

Constitutive production of alpha and beta interferons in mutant human cell lines

Alpha and beta interferons control expression of a selectable marker in the human hypoxanthine phosphoribosyltransferase-negative cell line 2fTGH, in which transcription of gpt is regulated by the upstream region of an interferon-responsive human gene. Selection of mutagenized 2fTGH cells in hypoxanthine-aminopterin-thymidine medium yielded mutants in one recessive (C1) and two dominant (C2 and C3) complementation groups. The mutants constitutively expressed low levels of beta interferon (C1), alpha interferon (C2), or both (C3).

Suppressin: an endogenous negative regulator of immune cell activation

We have recently identified a new suppressor molecule we named suppressin (SPN) that has all the characteristics of a global negative regulator of the immune system. SPN is a unique 63-kD monomeric polypeptide with a pI of 8.1 that is produced and secreted under basal conditions by murine splenocytes, human peripheral mononuclear cells, and hormone-secreting pituitary cells. The biological actions of SPN in vitro include the inhibition of mitogen-induced proliferation and immunoglobulin synthesis of lymphocytes and the suppression of interleukin-2-dependent CTLL-2 cell proliferation. In addition, SPN enhances natural killer cell activity by eliciting interferon-alpha and -beta synthesis and secretion. SPN effects are reversible, nontoxic, and require the continuous presence of exogenous SPN. T lymphocytes stimulated with concanavalin A or phytohemagglutinin are more sensitive to SPN (90% inhibition) than are lipopolysaccharide-stimulated B cells (60% inhibition). SPN arrests lymphocytes in the G0/G1 phase of the cell cycle after reduction of their RNA, protein and DNA synthesis, suggesting that SPN inhibits the processes required for G0 transition to G1. SPN is found intracellularly in all unstimulated lymphocyte subsets, monocytes, and in phytohemagglutinin-activated T lymphocytes immunopositive for the low affinity interleukin-2 receptor. These results suggest that SPN may be a major negative regulator of cell proliferation in the immune system. All SPN-producing cell types are also sensitive to SPN. Collectively, the results of these experiments provide the foundations for a model in which SPN regulates lymphocyte proliferation in an autocrine and/or paracrine manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet-derived growth factor (PDGF) BB homodimer regulates PDGF A- and PDGF B-chain gene transcription in human mesangial cells

Mesangial cells express platelet-derived growth factor (PDGF) A- and B-chain mRNA and release PDGF. Several polypeptide growth factors, including PDGF itself, induce PDGF A- and B- chain mRNA abundance. To understand the molecular mechanisms associated with the changes in mRNA abundance, we measured the effects of PDGF BB homodimer on PDGF A- and B-chain gene transcription in cultured mesangial cells. The data demonstrate 2- and 4-fold increases in PDGF A-chain gene transcription in response to PDGF BB homodimer at 5 and 24 h time points respectively. PDGF B-chain gene transcription was also induced approximately 3-fold at 2, 5 and 24 h time points in response to treatment with PDGF BB homodimer. The effect of PDGF BB on the half-life of PDGF A- as well as PDGF B-chain mRNA was measured directly by the pulse-chase method. There was no effect on PDGF A-chain mRNA half-life whereas PDGF B-chain mRNA half-life was increased 1.5-fold. These studies indicate that, in human mesangial cells, the increase in the levels of PDGF A- and B-chain mRNA in response to PDGF- receptor(s) activation is mediated at the level of gene transcription. In addition, the regulation of PDGF B- but not PDGF A-chain gene involves increased mRNA stability. Mesangial cells are a useful model for studying molecular mechanisms of PDGF- gene regulation in non-transformed human cells.

Human natural interferon-alpha producing cells

Interferons (IFNs) are critical components of the host immune system, serving as antiviral agents, immunomodulators and inhibitors of cell growth. Among peripheral blood mononuclear cells, the primary IFN-alpha-producing cell is a light density, HLA-DR+ cell negative for cell surface markers typical for T cells, B cells, monocytes, natural-killer or progenitor cells and has been tentatively termed the 'natural IFN-producing cell' or NIPC. Although present in very low frequency (approximately 1:1000 among peripheral blood mononuclear cells), the NIPC are very potent, with an individual cell able to produce 1-2 IU of IFN. In this review, the characteristics, phenotype, regulation and relationship of NIPC to human disease are discussed.

Kinetics of the functional loss of different muscarinic receptor isoforms in Xenopus oocytes

Native Xenopus oocytes express two isoforms of muscarinic receptors that mediate qualitatively different physiological responses. Oocytes of the majority of donors (common) express M3-like receptors (M3Rs) at comparable densities at both the animal and vegetal hemispheres of the cell. Rare (variant) donors possess oocytes that express mainly M1-like receptors (M1Rs), localized predominantly at the animal hemisphere. We have investigated the apparent degradation of these two isoforms and its relationship to their hemispheric distribution. Cycloheximide (CHX) caused a time-dependent decrease in receptor-mediated responses and [3H]quinuclidinyl benzylate (QNB) binding in oocytes from both types of donors. The t1/2 values ranged between 3 and 7 h. Removal of CHX resulted in rapid recovery of the response. This implied rapid degradation and turnover of both types of receptors. The loss of M1Rs was more than that of M3Rs. Moreover, the decrease was more rapid and more extensive on the animal hemisphere in both types of donors. Injection of oocytes expressing either receptor isoform with specific antisense oligonucleotides complementary to either m1 or m3 muscarinic receptors (from mouse) showed receptor loss at approximately the same rate as that calculated from experiments with CHX. Furthermore, oocytes of variant donors express M1Rs exclusively on the animal hemisphere, while the residual activity found on the vegetal hemisphere of the cell was mediated by M3Rs. Inhibition of putative receptor glycosylation with tunicamycin caused a rapid decrease in receptor-mediated responses and radioligand binding on M1Rs, but had virtually no effect on M3Rs. The expression of cloned m1 muscarinic receptors, however, was not affected by tunicamycin, suggesting that glycosylation is not a general prerequisite for the functional expression of muscarinic receptors.

Effects of actinomycin D and cycloheximide on transcript levels of IGF-I, actin, and albumin in hepatocyte primary cultures treated with growth hormone and insulin

The stability of several RNA transcripts in cultured hepatocytes is known to increase when serum is omitted from the culture medium. In order to investigate possible mechanisms for this phenomenon, we examined the effects of actinomycin D and cycloheximide on the levels of actin, albumin, and insulin-like growth factor I transcripts in primary cultures incubated in serum-free medium. The levels of IGF-I and albumin transcripts per culture increased for the first 4 hours following addition of actinomycin D and then declined. The levels of actin transcripts and total RNA per culture declined immediately following actinomycin D addition in a manner consistent with exponential decay. IGF-I and albumin transcript levels were relatively unaffected by cycloheximide, while actin transcript levels increased 7-fold over 7 hours. The half-lives of actin transcripts and total RNA were calculated to be 4.6 to 7.7 hours and 11 to 19 hours, respectively, with no statistically significant correlation with hormone treatment. The data suggest that the stability of albumin and IGF-I transcripts, but not actin transcripts, is controlled in part by an actinomycin D-sensitive process.

Newly synthesized RNA: simultaneous measurement in intact cells of transcription rates and RNA stability of insulin-like growth factor I, actin, and albumin in growth hormone-stimulated hepatocytes

The levels of several RNA transcripts in cultured hepatocytes are regulated by transcriptional and post-transcriptional mechanisms and are affected by growth hormone and insulin. We assessed the effects of these hormones on transcription rates and the stability of insulin-like growth factor I, actin, and albumin transcripts in intact cells of primary cultures of rat hepatocytes by analyzing thiol-labeled, newly synthesized RNA isolated by mercurated agarose affinity chromatography. The application of this concept to the measurement of transcript stability is presented in detail. The data indicate that growth hormone stimulates the transcription rates of insulin-like growth factor I, actin, and albumin genes. The stability of all three transcripts, particularly albumin, appears to be lower in growth hormone-containing medium than it is in insulin-containing medium. The experiments indicate that the rates of transcription and/or degradation of albumin mRNA are influenced by hormonal treatment. However, the cells maintain roughly constant albumin transcript levels independent of hormone treatment by compensatory changes in the rates of transcription and degradation.

Direct induction of interferon-gamma- and interferon-alpha/beta-inducible genes by double-stranded RNA

Using Northern analysis, we here show that the inducibility by double-stranded (ds) RNA of interferon-alpha/beta-inducible genes is not restricted to a few genes but extends to all the genes known to be stimulated by IFN type I in fibroblasts. Moreover, we show that some genes, preferentially regulated by IFN-gamma, are also activated by dsRNA. We present a series of arguments demonstrating that the induction by dsRNA is not mediated by IFN. In addition to the fact that this induction occurs in the presence of cycloheximide and/or anti-IFN-alpha/beta antibodies in fibroblasts, we observed that, in IFN-resistant Daudi cells, ISG15 and IP-10 genes which are not induced by IFN-beta, are still inducible by dsRNA. dsRNA is also still active on 2-5 AS and ISG15 genes in cells carrying homozygous deletions of IFN alpha/beta genes. Actinomycin D experiments and nuclear in vitro elongation assays reveal that the induction by dsRNA involves, as its early step, a transcriptional event. This induction was found not to require protein synthesis, suggesting that activation of preexisting cellular factors is involved. The opposite inducibility by dsRNA of IFN-beta and 2',5'-oligoadenylate (2-5A) synthetase genes in serum-deprived fibroblasts indicates that pathways of induction by dsRNA of these two genes are not identical. Inhibition by 2-aminopurine of the induction of IFN-inducible mRNAs by IFN-beta or dsRNA suggests the participation of a protein kinase in their mechanism of action.

Epstein-Barr virus-encoded nuclear antigen 2 activates the viral latent membrane protein promoter by modulating the activity of a negative regulatory element

Previous studies suggest that the Epstein-Barr virus nuclear antigen EBNA2 participates in the regulation of the expression of the viral latent membrane protein (LMP). We have used reporter plasmids containing DNA fragments of the 5' flanking region of the LMP gene in cotransfection experiments to analyze the effect of EBNA2 on the activity of the LMP promoter. The results show that the LMP promoter is controlled by positive and negative transcription elements in a DNA fragment that contains the LMP transcription initiation site and 634 base pairs of upstream sequences. The promoter is activated by EBNA2. The region between position -54 and +40 relative to the mRNA cap site contains a positive transcription element that is constitutively active in DG75 cells and independent of EBNA2. The -106 to -54 region contains a negative regulatory element that prevents adjacent positive elements from functioning in the absence of EBNA2. Regulatory sequences between -324 and -144 participate in maintaining a high level of transcription of the LMP promoter after induction with EBNA2. The regulatory elements in the -634 to -54 promoter region have the characteristics of an inducible enhancer, including orientation independence and ability to regulate a heterologous promoter.

Induction of Na(+)-K(+)-ATPase and its subunit mRNAs by serum in a rat liver cell line

Addition of serum to confluent Clone 9 cells increased the protein, RNA, and DNA content per plate of cells; the increments became manifest within 3-6 h and were sustained for the 48-h duration of study. After the addition of serum, Na(+)-K(+)-ATPase activity was stimulated 1.25- and 1.45-fold at 6 and 12 h, respectively. In cells preincubated in the absence of serum for 24 h, addition of serum increased the abundances of Na(+)-K(+)-ATPase subunit mRNAs, mRNA alpha 1 and mRNA beta, coordinately by approximately 2- and 2.7-fold at 3 h, an effect that preceded the stimulation of Na(+)-K(+)-ATPase activity. The serum-induced increments in subunit mRNA abundances were further enhanced by the combined presence of serum and cycloheximide; mRNA alpha 1 and mRNA beta abundances were also augmented by cycloheximide alone (approximately 2.5- and 9.2-fold at 6 h, respectively). In cells incubated in the absence of serum, the half-lives of mRNA alpha 1 and mRNA beta, estimated from decrements in their abundances after the addition of actinomycin D, were 12 and 10 h, respectively. These data demonstrate that serum enhances Na(+)-K(+)-ATPase subunit mRNA abundance and enzyme activity in Clone 9 cells. Comparison of the estimated half-lives of Na(+)-K(+)-ATPase subunit mRNAs with the observed increments in their abundances at 3 h suggests that the serum-induced increases in mRNA alpha 1 and mRNA beta abundances are in large part due to enhanced synthesis of these mRNAs.

Postinduction turnoff of beta-interferon gene expression

Viral induction of the human beta-interferon (IFN-beta) gene leads to a transient accumulation of high levels of IFN-beta mRNA. Previous studies have shown that the increase in IFN-beta mRNA levels after induction is due to an increase in the rate of IFN-beta gene transcription. In this paper, we show that the rapid postinduction decrease in the level of IFN-beta mRNA is due to a combination of transcriptional repression and rapid turnover of the mRNA. This transcriptional repression can be blocked with cycloheximide, suggesting that the synthesis of a virus-inducible repressor is necessary for the postinduction turnoff of the IFN-beta gene. Analysis of the sequence requirements for IFN-beta mRNA instability revealed two regions capable of destabilizing a heterologous mRNA. One destabilizer is an AU-rich sequence in the 3' untranslated region, and the other is located 5' to the translation stop codon.

Hormonal regulation of stability of glutamine synthetase mRNA in cultured 3T3-L1 adipocytes

In 3T3-L1 adipocytes, glutamine synthetase (GS; EC 6.3.1.2) is subject to regulation by dexamethasone, insulin and dibutyryl cyclic AMP (Bt2cAMP). Dexamethasone increases GS-mRNA content and GS-gene transcription, whereas insulin and Bt2cAMP prevent these increases. The effects of these modulators on the control of GS-mRNA stability were investigated. We report here that GS mRNA has a half-life of about 110 min. Bt2cAMP increases GS-mRNA degradation by greater than 2-fold (half-life 50 min), whereas insulin or dexamethasone have little effect on GS-mRNA stability. Down-regulation of GS-gene expression by Bt2cAMP will involve a co-ordinate response at the level of gene transcription and mRNA stability. However, the molecular mechanisms by which insulin and dexamethasone regulate GS-gene expression in cultured adipocytes remains to be elucidated.

Postinduction turnoff of beta-interferon gene expression

Viral induction of the human beta-interferon (IFN-beta) gene leads to a transient accumulation of high levels of IFN-beta mRNA. Previous studies have shown that the increase in IFN-beta mRNA levels after induction is due to an increase in the rate of IFN-beta gene transcription. In this paper, we show that the rapid postinduction decrease in the level of IFN-beta mRNA is due to a combination of transcriptional repression and rapid turnover of the mRNA. This transcriptional repression can be blocked with cycloheximide, suggesting that the synthesis of a virus-inducible repressor is necessary for the postinduction turnoff of the IFN-beta gene. Analysis of the sequence requirements for IFN-beta mRNA instability revealed two regions capable of destabilizing a heterologous mRNA. One destabilizer is an AU-rich sequence in the 3' untranslated region, and the other is located 5' to the translation stop codon.

Thyroid hormone induction of Na(+)-K(+)-ATPase and its mRNAs in a rat liver cell line

The expression of mRNAs encoding the alpha- and beta-subunits of Na(+)-K(+)-ATPase (Na(+)-K+ pump) was examined in a rat liver cell line, Clone 9, in various thyroidal states. Northern blot analysis of total RNA isolated from cells incubated in hypothyroid serum-containing medium revealed the expression of mRNAs encoding Na(+)-K(+)-ATPase alpha 1-(mRNA alpha 1) and beta- (mRNA beta) subunits; mRNAs encoding the alpha 2- and alpha 3-subunits were undetectable. There was a discrepancy in the abundance of mRNA alpha 1 relative to mRNA beta such that mRNA alpha 1 exceeded the sum of the multiple mRNA beta bands by approximately 35-fold. 3,3',5-Triiodothyronine (T3) produced a coordinate augmentation of mRNA alpha 1 and mRNA beta contents that was demonstrable within 2 h and preceded the stimulation of Na(+)-K(+)-ATPase activity. After incubation of cells with T3 for 48 h, Na(+)-K(+)-ATPase activity was stimulated by 1.32-fold, whereas mRNA alpha 1 and mRNA beta abundances were increased 1.46- and 2.87-fold, respectively. Treatment of cells for 6 h with 10 micrograms/ml cycloheximide, a concentration sufficient to inhibit protein synthesis by 95%, elicited a 3.5- and 5.1-fold increase in mRNA alpha 1 and mRNA beta content, respectively. Cycloheximide abrogated the stimulatory effect of T3 on mRNA beta abundance, whereas the T3-induced increase in mRNA alpha 1 content was not prevented.(ABSTRACT TRUNCATED AT 250 WORDS)

An assessment of the effects of swainsonine on survival of mice injected with B16-F10 melanoma cells

Systemic administration of swainsonine, an indolizidine alkaloid, inhibits the experimental metastasis of B16-F10 murine melanoma cells. This activity can be attributed primarily to swainsonine-mediated enhancement of host natural killer cell activity. As one next step towards investigating the potential therapeutic utility of this drug, its efficacy in enhancing host survival in the same B16-F10 model system has been assessed. In studies employing intravenously injected tumor cells, pretreatment of mice with swainsonine-containing drinking water provided a reproducible protective effect for the host. This prolongation of survival was substantially enhanced when swainsonine was administered in combination with either of two other immunomodulators, polyinosinic: cytidylic acid (poly-IC) or interleukin-2. In studies in which combinations of these agents were administered after intravenous injection of tumor cells, or after subcutaneous implantation, a greatly reduced effect on host survival was observed. However, when used in combination with cyclophosphamide (to block the effects of suppressor T cells), swainsonine did increase mean survival time. The implications of these results for the use of swainsonine in treatment of metastatic or localized disease, together with its potential mechanism(s) of action, are discussed.

Control of beta-interferon expression in murine embryonal carcinoma F9 cells

Murine embryonal carcinoma F9 cells, a tissue culture model for early embryonic development, do not produce interferon (IFN) in response to poly(I-C), as determined by an antiviral assay. RNase protection analyses were used to examine total RNA extracted from the cells for the presence of beta-IFN RNA. Whereas F9 cells differentiated in vitro with retinoic acid produced a biologically active protein as well as beta-IFN RNA in response to poly(I-C), undifferentiated F9 cells produced no detectable beta-IFN RNA even in the presence of cycloheximide, an IFN-superinducing agent. These results show that undifferentiated embryonal carcinoma cells do not accumulate beta-IFN RNA in response to an IFN-inducing agent, suggesting a transcriptional regulatory mechanism. However, this control mechanism is altered upon differentiation, since the gene can be transcriptionally activated in retinoic acid-differentiated cells.

Beta interferon subtype 1 induction by tumor necrosis factor

Tumor necrosis factor (TNF) induces an antiviral state in various cell lines. This antiviral state is quite similar to that established by interferon (IFN), e.g., TNF treatment of HEp-2 cells induces 2',5'-oligoadenylate synthetase activity. Both antiviral activity and synthetase induction are greatly reduced when TNF treatment occurs in the presence of a beta interferon subtype 1 (IFN-beta 1)-neutralizing antiserum. However, no one has yet directly demonstrated IFN-beta 1 induction, either as an antiviral activity in supernatants from TNF-treated cells or as IFN-specific mRNA by Northern (RNA) blot analysis. We have adopted a recently described in vitro DNA amplification protocol for the detection of specific RNAs. By applying this method to RNA from HEp-2 cells, we could demonstrate increased levels of IFN-beta 1-specific transcripts after TNF treatment. Dose response and kinetics of IFN-beta 1 induction coincided with the TNF-induced antiviral state. Nuclear run-on analysis showed enhanced transcriptional activity of the IFN-beta 1 gene in TNF-treated cells. Our data substantiate a role of IFN-beta 1 as mediator of the biological activity of TNF in HEp-2 cells.

Activators of protein kinase C enhance accumulation of interferon-beta mRNA in murine cell lines

Murine C127 fibroblasts carrying an expression vector for a human interferon gene (HuIFN-beta, under the control of a constitutive promoter) can be induced to produce murine (Mu) IFN by double-stranded (ds) RNA or virus infection. Fibroblasts treated with the protein kinase C activators 1-oleyl-2-acetylglycerol (OAG) or phorbol-12-myristate-13-acetate (PMA) secrete greater amounts of MuIFN than untreated cells, but the same amount of HuIFN-beta. Accordingly, the level of MuIFN-beta mRNA increases in the presence of protein kinase C activators whereas that of HuIFN-beta mRNA is unchanged. In time course experiments after induction with dsRNA, accumulation of MuIFN-beta mRNA is observed within 30 min in the presence of OAG, when this mRNA cannot be detected in control cells. The protein kinase C activators increase accumulation of MuIFN-beta mRNA, even in the presence of the inhibitor of protein synthesis cycloheximide. A similar increase in MuIFN-beta mRNA is observed in C243 fibroblasts treated with phorbol-12-myristate-13-acetate, but not in parental C127 cells. These findings suggest that protein kinase C does not promote synthesis of regulatory factors controlling transcription of IFN mRNA, but that it may be directly or indirectly involved in activation of such factors in some murine cell lines.

Control of beta-interferon expression in murine embryonal carcinoma F9 cells

Murine embryonal carcinoma F9 cells, a tissue culture model for early embryonic development, do not produce interferon (IFN) in response to poly(I-C), as determined by an antiviral assay. RNase protection analyses were used to examine total RNA extracted from the cells for the presence of beta-IFN RNA. Whereas F9 cells differentiated in vitro with retinoic acid produced a biologically active protein as well as beta-IFN RNA in response to poly(I-C), undifferentiated F9 cells produced no detectable beta-IFN RNA even in the presence of cycloheximide, an IFN-superinducing agent. These results show that undifferentiated embryonal carcinoma cells do not accumulate beta-IFN RNA in response to an IFN-inducing agent, suggesting a transcriptional regulatory mechanism. However, this control mechanism is altered upon differentiation, since the gene can be transcriptionally activated in retinoic acid-differentiated cells.

Evidence for a novel signal transduction pathway activated by platelet-derived growth factor and by double-stranded RNA

Platelet-derived growth factor (PDGF) and the synthetic double-stranded RNA poly(I).poly(C) [poly(I.C)] stimulate transcription of the JE gene in BALB/c-3T3 fibroblasts. The response of JE to poly(I.C) does not appear to be channeled through any known component of the PDGF receptor signal transduction apparatus. In addition, JE sequences upstream of the transcription start site are devoid of previously identified poly(I.C)-responsive elements, such as those found in the beta-interferon gene. These data suggest that a novel signal transduction pathway regulates the JE response to PDGF and double-stranded RNA. The c-myc and c-fos proto-oncogenes also respond to this pathway but with poor efficiency. However, this pathway operates very efficiently on other PDGF-inducible genes that encode the secretory proteins KC and M-CSF.

Beta interferon subtype 1 induction by tumor necrosis factor

Tumor necrosis factor (TNF) induces an antiviral state in various cell lines. This antiviral state is quite similar to that established by interferon (IFN), e.g., TNF treatment of HEp-2 cells induces 2',5'-oligoadenylate synthetase activity. Both antiviral activity and synthetase induction are greatly reduced when TNF treatment occurs in the presence of a beta interferon subtype 1 (IFN-beta 1)-neutralizing antiserum. However, no one has yet directly demonstrated IFN-beta 1 induction, either as an antiviral activity in supernatants from TNF-treated cells or as IFN-specific mRNA by Northern (RNA) blot analysis. We have adopted a recently described in vitro DNA amplification protocol for the detection of specific RNAs. By applying this method to RNA from HEp-2 cells, we could demonstrate increased levels of IFN-beta 1-specific transcripts after TNF treatment. Dose response and kinetics of IFN-beta 1 induction coincided with the TNF-induced antiviral state. Nuclear run-on analysis showed enhanced transcriptional activity of the IFN-beta 1 gene in TNF-treated cells. Our data substantiate a role of IFN-beta 1 as mediator of the biological activity of TNF in HEp-2 cells.

Evidence for a novel signal transduction pathway activated by platelet-derived growth factor and by double-stranded RNA

Platelet-derived growth factor (PDGF) and the synthetic double-stranded RNA poly(I).poly(C) [poly(I.C)] stimulate transcription of the JE gene in BALB/c-3T3 fibroblasts. The response of JE to poly(I.C) does not appear to be channeled through any known component of the PDGF receptor signal transduction apparatus. In addition, JE sequences upstream of the transcription start site are devoid of previously identified poly(I.C)-responsive elements, such as those found in the beta-interferon gene. These data suggest that a novel signal transduction pathway regulates the JE response to PDGF and double-stranded RNA. The c-myc and c-fos proto-oncogenes also respond to this pathway but with poor efficiency. However, this pathway operates very efficiently on other PDGF-inducible genes that encode the secretory proteins KC and M-CSF.

Cellular localization of induced human interferon-beta mRNA by non-radioactive in situ hybridization

Induced interferon-beta (IFN-beta) mRNA was localized in human FS-4 fibroblasts by in situ hybridization using biotinylated probes. The hybridization sites were detected by incubation with a nick-translated genomic DNA probe (1.8 kb) via streptavidin-colloidal gold followed by silver contrast enhancement. The positive signals were observed by reflection-contrast light microscopy. IFN-beta mRNA was transiently induced by poly r(I): r(C) in fibroblasts 2-4 h after induction. Induction in the presence of cycloheximide and actinomycin D (superinduction conditions) exhibited an enhanced level of IFN-beta mRNA with a maximum at 4-8 h. The kinetics of the IFN-beta mRNA expression in the cytoplasm as revealed by in situ hybridization proved to be compatible with the results of Northern blotting experiments of total cellular RNA.

Alternative mechanisms for gene activation induced by poly(rI).poly(rC) and Newcastle disease virus

After poly(rI).poly(rC) induction of FS-4 fibroblasts, both human interferon-beta (IFN-beta) mRNA and an additional induced RNA class (12S RNA) hybridize to a genomic cosmid clone containing the human IFN-beta gene as well as 35 kbp of flanking sequences. However, this coinduced 12S RNA does not originate from regions in the neighborhood of the IFN-beta gene, but hybridizes to the genomic cosmid clone via repetitive Alu-family sequences. While IFN-beta mRNA rapidly decays after reaching a maximum 2-4 h after induction, this 12S RNA is stably maintained in the fibroblast cell for more than 16 h. Contrary to IFN-beta mRNA, the level of the 12S RNA is not further elevated by superinduction conditions (cycloheximide treatment) during poly(rI).poly(rC) induction. However, subsequent to treatment with the weaker viral inducer Newcastle disease virus (NDV) both IFN-beta and the 12S RNA transcripts are induced to a higher level in the presence of cycloheximide. Cell-free translation of hybrid-selected 12S RNA leads to detection of an induced protein of 14 kDa. cDNA cloning reveals that the 12S RNA contains part of an Alu-family sequence in the 5'-untranslated region. The 12S RNA is probably not an RNA polymerase III transcript and codes for a protein of 9 kDa (as monitored by in vitro cell-free translation). This discrepancy in molecular mass can be attributed to a retarded migration of the protein in SDS/PAGE.