Complexity of the primary genetic response to mitogenic activation of human T cells

Mechanisms of Immunotoxicity: Stressors and Evaluators

The immune system defends the body against certain tumor cells and against foreign agents such as fungi, parasites, bacteria, and viruses. One of its main roles is to distinguish endogenous components from non-self-components. An unproperly functioning immune system is prone to primary immune deficiencies caused by either primary immune deficiencies such as genetic defects or secondary immune deficiencies such as physical, chemical, and in some instances, psychological stressors. In the manuscript, we will provide a brief overview of the immune system and immunotoxicology. We will also describe the biochemical mechanisms of immunotoxicants and how to evaluate immunotoxicity.

T lymphocyte activation gene identification by coregulated expression on DNA microarrays

High-capacity methods for assessing gene function have become increasingly important because of the increasing number of newly identified genes emerging from large-scale genome sequencing and cDNA cloning efforts. We investigated the use of DNA microarrays to identify uncharacterized genes specifically involved in human T cell activation. Activation of human peripheral blood T lymphocytes induced significant changes in hundreds of transcripts, but most of these were not unique to T cell activation. Variation of experimental parameters and analysis techniques allowed better enrichment for gene expression changes unique to T cell activation. Best results were achieved by identification of genes that were most highly coregulated with the T-cell-specific transcript interleukin 2 (IL2) in a "compendium" of experiments involving both T cells and other cell types. Among the genes most highly coregulated with IL2 were many genes known to function during T cell activation, together with ESTs of unknown function. Four of these ESTs were extended to novel full-length clones encoding T-cell-regulated proteins with predicted functions in GTP metabolism, cell organization, and signal transduction.

Adenovirus-mediated expression of a mutant IkappaB kinase 2 inhibits the response of endothelial cells to inflammatory stimuli

In a variety of cell types, the transcription factor nuclear factor kappaB (NF-kappaB) functions as a mediator of stress and immune responses. In endothelial cells (ECs), it controls the expression of genes encoding, eg, cytokines, cell adhesion molecules, and procoagulatory proteins. This study investigates the effect of NF-kappaB suppression on several pathophysiologic functions of ECs, including inflammation, coagulation, and angiogenesis. A recombinant adenovirus was generated for expression of a dominant negative (dn) mutant of IkappaB kinase 2 (IKK2), a kinase that acts as an upstream activator of NF-kappaB. dnIKK2 inhibited NF-kappaB, resulting in strongly reduced nuclear translocation and DNA binding activity of the transcription factor and lack of expression of several proinflammatory markers, including E-selectin, intercellular adhesion molecule 1, vascular cell adhesion molecule 1, and interleukin-8. Concomitantly, inhibition of leukocyte binding to dnIKK2-expressing ECs could be demonstrated in a cell adhesion assay. Furthermore, expression of tissue factor as well as the ability to form capillary tubes in a matrigel assay was impaired in dnIKK2-expressing ECs. These data demonstrate that NF-kappaB is of central importance not only for the inflammatory response but also for a number of other EC functions. Therefore, this transcription factor as well as its upstream regulatory signaling molecules may represent favorable targets for therapeutic interference.

Genomic-scale analysis of gene expression in resting and activated T cells

Recent advances in gene array technology and isolation of lymphocytes now allow comprehensive analysis of gene expression in many different types of T cells. So far only a few sets of results have been published. However it is already clear that these analyses provide accurate measurements of gene expression in T cells. This technology offers the first opportunity to examine global and subtle changes in gene expression in response to specific stimuli.

Granulysin: a novel antimicrobial peptide of cytolytic T lymphocytes and natural killer cells

Granulysin is a novel antimicrobial protein produced by human cytolytic T lymphocytes and natural killer cells. It is active against a broad range of microbes, including Gram-positive and Gram-negative bacteria, fungi, and parasites. The fact that it kills Mycobacterium tuberculosis is particularly important, since the current vaccine (Bacille Calmette-Guerin, BCG) is of limited efficacy and antibiotic resistance is increasing. Although functionally related to other antibacterial peptides, defensins and magainins, granulysin is structurally distinct. Like porcine NK lysin and amoebapores made by Entamoeba histolytica, granulysin is related to saposins, small lipid-associated proteins present in the central nervous system. The identification of this novel molecule indicates a broader and perhaps more significant role for T lymphocytes in both innate and acquired antimicrobial defenses.

Human T-cell lymphotrophic virus type-I tax gene induces secretion of human macrophage inflammatory protein-1alpha

Human T-cell lymphotropic virus I (HTLV-I) encodes for a 40-kDa protein, Tax, which is important for the immortalization of T cells. Tax has been shown to transactivate several cellular genes. In this study, we show that MIP-1alpha is selectively expressed and secreted in the tax transfected Jurkat cell line upon mitogen stimulation. Expression of MIP-1alpha-R mRNA in these cells suggests an autocrine role for this chemokine in HTLV-I infected T-cells. Induced MIP-1alpha expression and secretion in PMA/PHA stimulated tax transfected cells correlate with the noninduction of MNP-1 transcription factor, which is intimately involved in downmodulating the MIP-1alpha gene.

The EWS/TEC fusion protein encoded by the t(9;22) chromosomal translocation in human chondrosarcomas is a highly potent transcriptional activator

The EWS/TEC gene fusion generated by the t(9;22) chromosomal translocation found in extraskeletal myxoid chondrosarcomas encodes a fusion protein containing the amino-terminal domain of the EWS protein fused to the whole coding sequence of the orphan nuclear receptor TEC. We have compared the DNA-binding and transcriptional activation properties of various TEC isoforms and the corresponding EWS/TEC fusion proteins. Band-shift experiments show that the full-length TEC receptor can efficiently bind the NGFI-B Response Element (NBRE), whereas an isoform lacking the entire carboxyl-terminal domain of the receptor binds much less efficiently the NBRE. Addition of the amino-terminal domain of EWS to either isoforms does not alter significantly their DNA-binding properties to the NBRE. Co-transfection experiments of COS cells and human chondrocytes indicate that whereas TEC moderately activates transcription from a NBRE-containing promoter, the corresponding EWS/TEC fusion protein is a highly potent transcriptional activator of the same promoter, being approximately 270-fold more active than the native receptor. EWS/TEC may thus exert its oncogenic potential in chrondrosarcomas by activating the transcription of target genes involved in cell proliferation.

The transcription factor early growth response 1 (Egr-1) advances differentiation of pre-B and immature B cells

In mature B lymphocytes, the zinc finger transcription factor early growth response 1 (Egr-1) is one of the many immediate-early genes induced upon B cell antigen receptor engagement. However, its role during earlier stages of lymphopoiesis has remained unclear. By examining bone marrow B cell subsets, we found Egr-1 transcripts in pro/pre-B and immature B lymphocytes, and Egr-1 protein in pro/pre-B-I cells cultivated on stroma cells in the presence of interleukin (IL)-7. In recombinase-activating gene (RAG)-2-deficient mice overexpressing an Egr-1 transgene in the B lymphocyte lineage, pro/pre-B-I cells could differentiate past a developmental block at the B220(low) BP-1(-) stage to the stage of B220(low) BP-1(+) pre-B-I cells, but not further to the B220(low) BP-1(+) CD25(+) stage of pre-B-II cells. Therefore, during early B lymphopoiesis progression from the B220(low) BP-1(-) IL-2R- pro/pre-B-I stage to the B220(low) BP-1(+) IL-2R+ pre-B-II stage seems to occur in at least two distinct steps, and the first step to the stage of B220(low) BP-1(+) pre-B-I cells can be promoted by the overexpression of Egr-1 alone. Wild-type mice expressing an Egr-1 transgene had increased proportions of mature immunoglobulin (Ig)M+ B220(high) and decreased proportions of immature IgM+ B220(low) bone marrow B cells. Since transgenic and control precursor B cells show comparable proliferation patterns, overexpression of Egr-1 seems also to promote entry into the mature B cell stage. Analysis of changes in the expression pattern of potential Egr-1 target genes revealed that Egr-1 enhances the expression of the aminopeptidase BP-1/6C3 in pre-B and immature B cells and upregulates expression of the orphan nuclear receptor nur77 in IgM+ B cells.

Intracellular expression in pig cells of anti-alpha1,3galactosyltransferase single-chain FV antibodies reduces Gal alpha1,3Gal expression and inhibits cytotoxicity mediated by anti-Gal xenoantibodies

BACKGROUND

The carbohydrate structure Gal alpha1,3Gal expressed on pig cells is the major antigen recognized by xenoreactive natural antibodies in the higher primates. In xenotransplantation, natural antibodies binding to that structure initiate hyperacute rejection, and the anti-Gal alpha1,3Gal antibodies that are elicited probably take part in later phases of vascularized graft rejection. This epitope also appears to be involved in innate cellular responses. Inactivation of alpha1,3 galactosyltransferase in transgenic pigs would certainly lead to the success of xenotransplantation, but gene knockout in pigs is not feasible yet.

METHODS

As a novel strategy to inhibit alpha1,3 galactosylation, we generated recombinant single-chain Fv (ScFv) antibodies directed against pig alpha1,3-galactosyltransferase and evaluated the effect of their intracellular expression on enzyme activity and Gal alpha1,3Gal expression.

RESULTS

After in vitro transfection in pig cells, the scFv antibody anti-pig alpha1,3-galactosyltransferase reduced the amount or function of enzyme by up to 70% as evidenced by immunofluorescence and measurement of cell-associated activity. Consequently, Gal alpha1,3Gal on cell membranes was reduced to the same extent. This led to a profound (more than 90%) reduction in the cytotoxicity involving anti-Gal antibodies and complement.

CONCLUSION

Although not sufficient to knock out the overall human anti-pig natural xenoreactivity, intracellular expression of the scFv antibody anti-alpha1,3-galactosyltransferase in pig cells significantly decreases the amount of Gal alpha1,3Gal and could be important to protect cells from elicited antibodies as well as from innate effectors.

The early growth response protein (EGR-1) regulates interleukin-2 transcription by synergistic interaction with the nuclear factor of activated T cells

The early growth response-1 gene (EGR-1) is induced by a wide range of stimuli in diverse cell types; however, EGR-1-regulated genes display a highly restricted pattern of expression. Recently, an overlapping Sp1.EGR-1 binding site has been identified within the interleukin-2 (IL-2) gene promoter directly upstream of the binding site for the nuclear factor of activated T cells (NFAT). We used transfection assays to study how the abundantly and constitutively expressed Sp1 protein and the immediate early EGR-1 zinc finger protein regulate IL-2 gene expression. Here, we identify EGR-1 as an important activator of the IL-2 gene. In Jurkat T cells, EGR-1 but not Sp1 acts as a potent coactivator for IL-2 transcription, and in combination with NFATc, EGR-1 increases transcription of an IL-2 reporter construct 200-fold. Electrophoretic mobility shift assays reveal that recombinant EGR-1 and NFATc bind independently to their target sites within the IL-2 promoter, and the presence of both sites on the same DNA molecule is required for EGR-1.NFATc.DNA complex formation. The transcriptional synergy observed here for EGR-1 and NFATc explains how the abundant nuclear factor EGR-1 contributes to the expression of restrictively expressed genes.

Induction of mitogen-inducible nuclear orphan receptor by interleukin 1 in human synovial and gingival fibroblasts

High levels of interleukin 1 (IL-1) found in inflammatory diseases such as rheumatoid arthritis and periodontitis act on the local fibroblasts, resulting in an altered phenotype characterized by hyperplasia and the production of inflammatory mediators and destructive enzymes. The goal of this study was to identify genes induced as an early response to IL-1 in synovial and gingival fibroblasts which might play a regulatory role in the cascade of events leading to their activation. Using the technique of mRNA differential display, we have identified the mitogen-inducible nuclear orphan receptor (MINOR) as a gene up-regulated by IL-1 in human synovial and gingival fibroblasts. The rapid induction of both mRNA and DNA binding activity suggests that MINOR may play an important early role in regulating the response of fibroblasts to inflammation.

Four classes of salicylate-induced tobacco genes

We have identified and characterized fragments of 15 salicylic acid (SA) early response genes. The kinetics of induction and response to cycloheximide (CHX) treatment allowed classification of genes into four groups. Classes I-III are characterized by immediate-early responses, showing increased accumulation of mRNA within 30 min of SA treatment. Moreover, CHX did not block induction of these genes, indicating that latent cellular factors mediate the SA response. Class IV genes were induced more slowly, but still within 2 to 3 h of SA treatment, and required protein synthesis for expression. Although identified in this study as SA-responsive genes, several could also be induced by other compounds. Two genes were characterized in more detail, including isolation of cDNA sequences and additional analysis of gene expression. Sequence analysis revealed that the class I gene, C18-1, is the previously identified ethylene response element binding protein 1 (EREBP1), an ethylene-induced transcription factor for basic pathogenesis-related (PR) genes, whereas the class III gene, G8-1, is a novel sequence. G8-1 was found to be strongly induced only by SA and its active analogs and was exquisitely sensitive to low SA concentrations. These and other genes were found to be activated at early times following tobacco mosaic virus infection of resistant tobacco genotypes.

Biochemical characterization of MIP-1 alpha nuclear protein

A family of hematopoietic specific transcription factors, MIP-1 alpha nuclear protein (MNP) family, has recently been identified. They are intimately involved in regulating the transcription of the huMIP-1 alpha gene in monocytes, T-cells, and transformed B-cells. One member of the family (MNP-1) is essential for promoter activity in monocytes and B-cells, while another (MNP-2) is required for full promotor activity in T-cells. A third member of the family (MNP-3) is expressed in PMA induced HL60 cells and probably has a role in monocyte differentiation. In this communication we demonstrate by two techniques that MNP-1 and MNP-2 are distinct but related factors, and we present further evidence to show that MNP-1 acts as a heterodimer.

Mechanism of action of rapamycin: new insights into the regulation of G1-phase progression in eukaryotic cells

The immunosuppressant drug, rapamycin (RAP), is a potent inhibitor of IL-2-dependent T-cell proliferation. The antiproliferative effect of RAP is mediated through the formation of an active complex with its cytosolic receptor protein, FKBP12. The molecular target of the FKBP12.RAP complex is a putative lipid kinase termed the mammalian Target Of Rapamycin (mTOR). This review will discuss recent findings suggesting that mTOR is a novel regulator of G1- to S-phase progression in eukaryotic cells.

Biological responses to electromagnetic fields

Electrification in developed countries has progressively increased the mean level of extremely low-frequency electromagnetic fields (ELF-EMFs) to which populations are exposed; these humanmade fields are substantially above the naturally occurring ambient electric and magnetic fields of approximately 10(-4) Vm(-1) and approximately 10(-13) T, respectively. Several epidemiological studies have concluded that ELF-EMFs may be linked to an increased risk of cancer, particularly childhood leukemia. These observations have been reinforced by cellular studies reporting EMF-induced effects on biological systems, most notably on the activity of components of the pathways that regulate cell proliferation. However, the limited number of attempts to directly replicate these experimental findings have been almost uniformly unsuccessful, and no EMF-induced biological response has yet been replicated in independent laboratories. Many of the most well-defined effects have come from gene expression studies; several attempts have been made recently to repeat these key findings. This review analyses these studies and summarizes other reports of major cellular responses to EMFs and the published attempts at replication. The opening sections discuss quantitative aspects of exposure to EMFs and the incidence of cancers that have been correlated with such fields. The concluding section considers the problems that confront research in this area and suggests feasible strategies.

p53 transactivation of the HIV-1 long terminal repeat is blocked by PD 144795, a calcineurin-inhibitor with anti-HIV properties

Previous reports have indicated that benzothiophenes exhibit broad anti-inflammatory properties and inhibit human immunodeficiency virus-type 1 (HIV-1) replication. We show that the immunosuppressant cyclosporin A (CsA) and benzothiophene-2-carboxamide, 5-methoxy-3-(1-methyl ethoxy)-1-oxide (PD 144795) block the induction of p53 and NF-kappaB binding to the HIV-1 long terminal repeat (LTR) by the T cell receptor activator phytohemagglutinin. CsA and PD 144795 also inhibit the induction by phytohemagglutinin of the transcription mediated by an HIV-1 LTR fragment containing the p53 and NF-kappaB sites. These effects of PD 144795 on HIV-1 transcription correlate with its ability to inhibit the phosphatase activity of calcineurin and are similar to those previously described for CsA. Moreover, a constitutive active form of calcineurin is able to induce expression from the HIV-1 LTR in a p53- and NF-kappaB-dependent manner and PD 144795 is able to block this induction. These results demonstrate that the DNA binding of p53 to the HIV-1 LTR can be modulated by calcineurin and provide a framework to understand the anti-HIV properties of benzothiophene derivatives.

Identification and categorization of inducible mast cell genes in a subtraction library

Mast cells play an important role in allergic inflammation by releasing inducible proinflammatory cytokines. While many inducible genes have been identified, we hypothesized that a significant number remain to be identified. We thus constructed an activation-specific mast cell subtraction library to establish a profile of induced genes in mast cells following allergic stimulation. To date, we have sequenced 150 cDNA clones. Among them, we have isolated 22 known genes whose expression has not been reported in mast cells, and an additional 26 cDNA clones which do not have significant homology to known genes in the Genbank database. We next selected 10 cDNA clones with strong signals by differential plaque hybridization. Of these cDNA clones, five genes were induced in mast cells upon Fc epsilon RI-mediated stimulation. They are cofilin, annexinVI, interferon (IFN)-beta, serglycin, and a novel inducible mast cell (IMC) gene, IMC-415. Characterization and relevant studies of this novel gene and other inducible known genes in mast cells will provide insight into the functions of mast cells in mammalian biology.

Coordinate expression and distinct DNA-binding characteristics of the four EGR-zinc finger proteins in Jurkat T lymphocytes

The Early Growth Response Genes (EGR-1 to AT133/EGR-4) encode a family of proteins that are composed of three homologous consecutive zinc fingers of the Cys2-His2 type and different flanking sequence. Upon growth stimulation of resting cells the four EGR-genes are simultaneously transcribed. We have analyzed the expression of the four EGR-proteins in Jurkat T cells and show by Western blot analysis that the four EGR-proteins are coordinately induced upon treatment with a combination of PHA and PMA. As the individual proteins are reported to bind to identical target sequences, we have analyzed the DNA-binding of the native proteins. Using nuclear extract in which we have demonstrated expression of all four EGR-proteins, only EGR-1, but no other member of this protein family is found to bind to the EGR-consensus site (GCG GGG GCG). In addition, DNA-binding of both native EGR-1 and of recombinant EGR-1 and AT133/EGR-4 proteins expressed in insect cells was analyzed. This comparison revealed distinct binding properties of recombinant EGR-1 and AT133/EGR-4 to oligonucleotides that include the EGR-consensus sites. The distinct binding affinities suggest that in vivo EGR-proteins bind to different target sequences and that each EGR-protein regulates distinct target genes. This is underlined by demonstrating that EGR-1 but not AT133/EGR-4 binds to a related G-rich promoter element with the sequence GGG GTG GGG. This G-rich sequence serves as an overlapping binding site for the two zinc finger proteins EGR-1 and Sp1. As similar overlapping binding sites for EGR-1 and Sp1 have been identified in several human and mouse gene promoters, we raise the question whether the Sp1 binding sites described in a large number of eukaryotic gene promoters also represent binding sites for EGR-1.

The human zinc finger protein EGR-4 acts as autoregulatory transcriptional repressor

The human EGR-4 (AT133) gene represents one member of a family of four related zinc finger proteins, that are simultaneously and coordinately induced in resting cells upon growth stimulation. In order to characterise the function of the EGR-4 zinc finger protein, we have expressed the protein in the eukaryotic baculovirus system. The recombinant EGR-4 protein has a molecular mass of 78 kDa, as demonstrated by SDS-PAGE and Western blotting. DNA binding studies revealed that the EGR-4 protein binds to the EGR consensus motif GCGTGGGCG, but not to the G-rich regulatory ZIP-element of the human IL-2 gene, that is a binding site for EGR-1. EGR-4 functions as transcriptional repressor. Overexpression of EGR-4 mediates repression of a minimal c-fos promoter through a threefold EGR consensus site. Furthermore the EGR-4 protein displays autoregulatory activities. This protein downregulates expression of its own gene promoter in a dose dependent manner. A G-rich region in the EGR-4 promoter, located at position -106 to -82, could be identified as binding site for the recombinant EGR-4 protein. A comparison of the two related zinc finger proteins EGR-4 and EGR-1 revealed for each protein distinct and specific DNA binding- and transcriptional regulatory activities.

Serum- and polypeptide growth factor-inducible gene expression in mouse fibroblasts

Complex cellular processes such as proliferation, differentiation, and apoptosis are regulated in part by extracellular signaling molecules: for example, polypeptide growth factors, cytokines, and peptide hormones. Many polypeptide growth factors exert their mitogenic effects by binding to specific cell surface receptor protein tyrosine kinases. This interaction triggers numerous biochemical responses, including changes in phospholipid metabolism, the activation of a protein phosphorylation cascade, and the enhanced expression of specific immediate-early, delayed-early, or late response genes. In this review, I summarize the major findings obtained from studies investigating the effects of serum or individual polypeptide growth factors on gene expression in murine fibroblasts. Several experimental approaches, including differential hybridization screening of cDNA libraries and differential display, have been employed to identify mRNA species that are expressed at elevated levels in serum- or polypeptide growth factor-stimulated cells. These studies have demonstrated that serum- and growth factor-inducible genes encode a diverse family of proteins, including DNA-binding transcription factors, cytoskeletal and extracellular matrix proteins, metabolic enzymes, secreted chemokines, and serine-threonine kinases. Some of these gene products act as effectors of specific cell cycle functions (e.g., enzymes involved in nucleotide and DNA synthesis), others are required to successfully convert a metabolically inactive cell to a metabolically active cell that will eventually increase in size and then divide (e.g., glucose-metabolizing enzymes), and some actually function as positive or negative regulators of cell cycle progression. In conclusion, research conducted during the past 15 years on serum- and growth factor-regulated gene expression in murine fibroblasts has provided significant insight into mitogenic signal transduction and cell growth control.

Ras activation leads to cell proliferation or apoptotic cell death upon interleukin-2 stimulation or lymphokine deprivation, respectively

Lymphokine-dependent cells undergo apoptosis upon lymphokine withdrawal. We describe that lymphokine deprivation of the interleukin (IL)-2- or IL-4-dependent mouse T cell line TS1 alpha beta induces Ras activation which plays a role in programmed cell death, since blocking Ras activity reduces the induction of apoptosis. Induction of apoptosis by lymphokine deprivation can be prevented by expression of the Bcl-2 protein. Rescue from cell death by IL-2 also promotes Ras activation, but, in contrast to lymphokine withdrawal, stimulates Bcl-2 expression. IL-4-induced cell survival is Ras- and Bcl-2 independent. These results are compatible with a model in which cell proliferation requires the simultaneous induction of at least two pathways which act in combination to prevent cell death.

Modulation of macrophage inflammatory protein-1alpha and its receptors in human B-cell lines derived from patients with acquired immunodeficiency syndrome and Burkitt's lymphoma

Macrophage inflammatory protein-1 alpha (MIP-1alpha) is a member of the -C-C- family of low-molecular weight chemokines. MIP-1alpha is involved in the homeostatic control of stem cell proliferation, in inducing chemotaxis, and also in inflammatory responses in mature cell types. In order to observe modulations of MIP-1alpha secretion and expression along with MIP-1alpha receptor (MIP-1alpha-R) expression for a possible autocrine role in AIDS associated B-cell lines, we studied a wide panel of human B-cell lines. Previous work by us has shown that HIV-1 tat down modulates MIP-1alpha by inducing a novel transcription factor MNP. Our data in this report suggest that HIV down modulates MIP-1alpha as a mechanism to evade suppression by this chemokine in human B-cells. Furthermore, our results strongly suggest MIP-1alpha autocrine loops in a majority of tumor B-cells as evident by MIP-1alpha-R expression, and also secretion of MIP-1alpha.

An RGD containing peptide from HIV-1 Tat-(65-80) modulates protooncogene expression in human bronchoalveolar carcinoma cell line, A549

Tat (transactivator of transcription) is essential for HIV-1 replication in vivo and in vitro. Tat-(65-80), an RGD containing domain, has been shown to regulate proliferative function of a variety of cell lines, including a human adenocarcinoma cell line, A549. The exact cellular and molecular mechanisms by which these effects are mediated, remain unknown. To evaluate the hypothesis that Tat-(65-80) modulates the expression of immediate early genes (IEG) c-jun, c-myc, c-fos and the tumor suppressor gene p53, serum starved A549 cells were incubated with Tat-(65-80) or heat-inactivated Tat-(65-80) at 10 ng/ml. Total cellular RNA was isolated from the cells at various time points (0-24 hours). In each case, 5 micrograms of RNA was reverse transcribed in 20 microliters of reaction volume. Equal amounts of cDNA were subjected to polymerase chain reaction (PCR) and analyzed by electrophoresis. The photographic negatives of the ethidium bromide stained gels were quantitated by densitometric scanning and normalized to corresponding beta-actin PCR products. Treatment with Tat-(65-80) showed a twofold induction of c-jun at 0.5 h. Peak expression occurred at 60 minutes and remained above baseline at 24 hours (h). c-myc was increased at 0.5 h, reached a twofold increase at 2 h and remained above baseline at 24 h. c-fos increased seven fold at 0.5 h and declined subsequently to baseline at 8 h. p-53 gene was reduced fivefold at 0.5 h and remained downregulated thereafter. These results show that Tat-(65-80) can modulate growth related genes in human lung epithelial cells.

Porcine alpha1,3-galactosyltransferase: tissue-specific and regulated expression of splicing isoforms

Expression of the Gal alpha1,3 Gal epitope on membrane glycolipids and glycoproteins is known to vary widely from one tissue to another. In the course of studying the mechanisms underlying this variability, we have isolated from pig cDNA four sequences corresponding to four isoforms of alpha1,3-galactosyltransferase (alpha1,3GT), the Golgi enzyme that links galactose in alpha1,3 on the galactose residue of N-acetyllactosamine. The isoforms differ from each other in the alternative presence of two nucleotide stretches of 36 and 63 base pairs in a segment encoding the stem region of the protein. Stable expression experiments show that all four isoenzymes can confer alpha-galactosyltransferase activity to HeLa cells, and that they are all located within the Golgi compartment, indicating that variations in length in the stem region do not affect enzyme activity or cellular localization. Analysis of RNA from different pig organs and cells shows quantitative differences between tissues in levels of alpha1,3GT, as well as qualitative differences, the four isoforms being unequally represented in different tissues.

Induction of the early growth response (Egr) family of transcription factors during thymic selection

There is little known about the regulation of gene expression during TCR-mediated differentiation of immature CD4+8+ (double positive) thymocytes into mature T cells. Using the DPK CD4+8+ thymocyte precursor cell line, we demonstrate that the early growth response-1 gene (Erg-1), encoding a zinc finger transcription factor, is rapidly upregulated after TCR stimulation. We also report that Egr-1 is expressed by a subset of normal double positive thymocytes in the thymic cortex, as well by a majority of medullary single positive thymocytes. Expression of Egr-1 is dramatically reduced in the thymus of major histocompatibility complex knockout mice, but can be induced by anti-CD3 antibody stimulation of isolated thymocytes from these animals. These and other data suggest that high level expression of Egr-1 in the thymus is a consequence of selection. A similar pattern of expression is found for family members Egr-2 and Egr-3. Using the DPK cell line, we also demonstrate that expression of Egr-1, 2, and 3 is dependent upon ras activation, as is the initiation of differentiation to a single positive cell. In contrast, the calcineurin inhibitor cyclosporin A, which inhibits DPK cell differentiation as well as positive selection, inhibits expression of Egr-2 and Egr-3, but not Egr-1. The identification of the Egr family in this context represents the first report of a link between the two known signaling pathways involved in positive selection and downstream transcriptional regulators.

Direct activation of the stress-activated protein kinase (SAPK) and extracellular signal-regulated protein kinase (ERK) pathways by an inducible mitogen-activated protein Kinase/ERK kinase kinase 3 (MEKK) derivative

The extracellular signal-regulated kinase (ERK) pathway, the stress-activated protein kinase (SAPK) pathway, and the p38 pathway are three major mitogen-activated protein kinase (MAPK) cascades known to participate in the regulation of cellular responses to a variety of extracellular signals. Upstream regulatory components of these kinase cascades, the MAPK/ERK kinase kinases (MEKK), have been described in several systems. We have isolated a cDNA encoding human MEKK3. Transfected MEKK3 has the ability to activate both SAPK and ERK pathways, but does not induce p38 activity, in agreement with a previous report on murine MEKK3 (Blank, J. L., Gerwins, P., Elliott, E. M., Sather, S., and Johnson, G. L. (1996) J. Biol. Chem. 271, 5361-5368). We now demonstrate that MEKK3 activates SEK and MEK, the known kinases targeting SAPK and ERK, respectively. Utilizing an estrogen ligand-activated MEKK3 derivative, we furthermore demonstrate that MEKK3 regulates the SAPK and the ERK pathway directly. Consistent with the fact that several SAPK-inducing agents activate the transcription factor NFkappaB, we now show that MEKK3 also enhances transcription from an NFkappaB-dependent reporter gene in cotransfection assays. The ability of MEKK3 to simultaneously activate the SAPK and ERK pathways is remarkable, given that they have divergent roles in cellular homeostasis.

Gem, a GTP-binding protein from mitogen-stimulated T cells, is induced in endothelial cells upon activation by inflammatory cytokines

Using differential screening of cytokine-activated versus resting porcine aortic endothelial cells (PAEC), we have isolated a member of the family of Ras/GTP-binding proteins. The cDNA encodes a 34-kilodalton protein showing 97% homology to Gem, a gene recently isolated from activated T cells, likely representing its porcine homologue. The amino acid sequence differs from the Ras consensus by the absence of a C-terminal isoprenylation site and a glycine to glutamic acid substitution in the third GTP-binding domain. We report here, that pigGem mRNA is strongly inducible in PAEC upon activation by either IL-1 alpha, TNF alpha or lipopolysaccharide (LPS). Low constitutive expression is found in several organs. Epitope-tagged pigGem transfected into endothelial cells (EC) localizes to the cytoplasm and to the inner side of the plasma membrane. Structural features of Gem and its inducibility apparently restricted to T cells and endothelial cells, together with Rad, a GTPase overexpressed in skeletal muscle cells of type II diabetic individuals, define a new branch within the superfamily of GTP-binding proteins.

Identification by subtractive hybridization of a spectrum of novel and unexpected genes associated with in vitro differentiation of human cytotrophoblast cells

We have previously demonstrated that epidermal growth factor (EGF), colony stimulating factor-1 (CSF-I), and granulocyte-monocyte colony stimulating factor (GMCSF) stimulate, while transforming growth factor beta 1 (TGF beta 1) inhibits, cytotrophoblast differentiation. To identify genes mediating EGF induced differentiation, we constructed a subtracted cDNA library between undifferentiated cytotrophoblast and differentiating cytotrophoblast. We identified six novel genes and four known syncytial products alpha-human chorionic gonadotrophin (alpha hCG) pregnancy-specific beta 1-glycoprotein, 3 beta-hydroxysteroid dehydrogenase, and plasminogen activator inhibitor type 1 whose mRNAs increased during differentiation. Ten other genes were identified whose mRNAs increased during differentiation. Five of these (keratin 19, calcreticulin, heat shock protein 27, serum and glucocorticoid-regulated kinase and adrenomedullin) were not previously reported to be expressed in placenta. Five other genes known to be expressed in placenta were identified. keratin 8, fibronectin, mitochondrial ATP synthase, 1119, and cytosolic copper-zinc superoxide dismutase (SOD-1). Several of these genes may have regulatory functions in trophoblast differentiation.

The mitogen-activated protein kinase phosphatases PAC1, MKP-1, and MKP-2 have unique substrate specificities and reduced activity in vivo toward the ERK2 sevenmaker mutation

Mitogen-activated protein (MAP) kinases can be grouped into three structural families, ERK, JNK, and p38, which are thought to carry out unique functions within cells. We demonstrate that ERK, JNK, and p38 are activated by distinct combinations of stimuli in T cells that simulate full or partial activation through the T cell receptor. These kinases are regulated by reversible phosphorylation on Tyr and Thr, and the dual specific phosphatases PAC1 and MKP-1 previously have been implicated in the in vivo inactivation of ERK or of ERK and JNK, respectively. Here we characterize a new MAP kinase phosphatase, MKP-2, that is induced in human peripheral blood T cells with phorbol 12-myristate 13-acetate and is expressed in a variety of nonhematopoietic tissues as well. We show that the in vivo substrate specificities of individual phosphatases are unique. PAC1, MKP-2, and MKP-1 recognize ERK and p38, ERK and JNK, and ERK, p38, and JNK, respectively. Thus, individual MAP kinase phosphatases can differentially regulate the potential for cross-talk between the various MAP kinase pathways. A hyperactive allele of ERK2 (D319N), analogous to the Drosophila sevenmaker gain-of-function mutation, has significantly reduced sensitivity to all three MAP kinase phosphatases in vivo.

A regulatory element in the human interleukin 2 gene promoter is a binding site for the zinc finger proteins Sp1 and EGR-1

Activation of the interleukin 2 (IL-2) gene after antigen recognition is a critical event for T cell proliferation and effector function. Prior studies have identified several transcription factors that contribute to the activity of the IL-2 promoter in stimulated T lymphocytes. Here we describe a novel regulatory element within the IL-2 promoter located immediately upstream of the nuclear factor of activated T cell (NFAT) domain. This region (termed the zinc finger protein binding region (ZIP)) serves as binding site for two differently regulated zinc finger proteins: the constitutively expressed transcription factor Sp1 and the inducible early growth response protein EGR-1. In unstimulated cells which do not secrete IL-2, only Sp1 binds to this region, while in stimulated IL-2 secreting cells the inducible EGR-1 protein recognizes this element. In Jurkat T cells, the ZIP site serves as an activator for IL-2 gene expression, and a combination of ZIP and NFAT binding sites is required for maximal IL-2 promoter activity. These results suggest a critical role of the ZIP site for IL-2 promoter activity.

Analysis of growth factor stimulated nucleocytoplasmic protein transport using two-dimensional gel electrophoresis

The rapid activation of gene expression by growth factors frequently involves the nucleocytoplasmic redistribution of proteins which regulate the transcription of discrete sets of genes. In particular, it has become apparent that protein kinases and transcription factors including protein kinase A, mitogen activated protein kinase, protein kinase C, NF-kappa B and Stat91, can rapidly migrate from the cytosol to the nucleus in response to a wide variety of extracellular stimuli. Furthermore, it is assumed that these proteins represent important components of the signal transduction pathways which operate between the plasma membrane and the nucleus. Here two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) has been used to detect proteins which undergo rapid growth factor stimulated nucleocytoplasmic redistribution. Epidermal growth factor and insulin influenced the association of 15 individual protein spots with the nucleus. Estimates of the abundance of these proteins revealed that they represented approximately 1/1000 to 1/5000 of total nuclear protein. To permit identification by microsequencing, five of the protein spots have been recovered from multiple 2-D PAGE gels and concentrated by one-dimensional elution-concentration gel electrophoresis. The data obtained demonstrate that 2-D PAGE can be used to: (i) analyse putative regulators of growth factor activated gene transcription, and (ii) purify sufficient amounts of these proteins to facilitate identification by microsequence analysis.

Rapid activation of the Stat3 transcription complex in liver regeneration

Liver regeneration in response to partial hepatectomy is a physiological growth response observed in the intact animal. Understanding the early signals that trigger liver regeneration is of vital importance to understand the liver's response to injury. It has been observed that several growth factors and cytokines, including epidermal growth factor (EGF) and interleukin-6 (IL-6), can activate members of the signal transducers and activators of transcription (Stat) family of transcription factors resulting in tyrosine phosphorylation of these factors, nuclear translocation, and an active DNA binding transcriptional complex. Because Stat3 participates in the regulation of primary growth response genes, we wondered if it is induced in the early phase of liver regeneration. We found that Stat3 DNA-binding activity is increased in the remnant liver within 30 minutes of partial hepatectomy and peaks at more than 30-fold at 3 hours. This induction is not observed after sham surgery. The induction of Stat3 appears to be part of the initial response of the remnant liver to partial hepatectomy, because it occurs in the presence of cycloheximide-mediated protein synthesis blockade. Activation of Stat3 is unusual, because it extends beyond the immediate-early time period and remains near peak level at 5 hours posthepatectomy. Although insulin-treated H35 cells activate many of the same immediate-early genes as regenerating liver, Stat3 is not induced in these cells. Because Stat factors are known to be inactivated by protein tyrosine phosphatases (PTPase), we showed that a PTPase is able to eliminate the DNA binding of hepatic Stat3.(ABSTRACT TRUNCATED AT 250 WORDS)

The dual specificity phosphatase PAC-1 is transcriptionally induced in the rat brain following transient forebrain ischemia

PAC-1 mRNA has previously been found only in activated T-cells in vitro and in vivo. The gene encodes a dual specificity protein phosphatase that regulates MAP kinase activity. Here, I describe that PAC-1 mRNA is induced also in neurons in the rat brain following 30 min of forebrain ischemia. At 6, 12 and 24 h after ischemia, PAC-1 mRNA was found most prominently in hippocampal cells which are resistant to 30 min of forebrain ischemia, but not in the selectively vulnerable CA1 sector. At later time points and in control animals no PAC-1 mRNA could be detected in any brain region. The protein-tyrosine/threonine phosphatase PAC-1, therefore, may be involved in adaptational responses of hippocampal cells resistant to ischemic injury.

JNK is involved in signal integration during costimulation of T lymphocytes

T lymphocyte activation and interleukin-2 (IL-2) production require at least two signals, generated by phorbol ester (TPA) and Ca2+ ionophore or costimulation of the T cell receptor (TCR) and the CD28 auxiliary receptor. We investigated how these stimuli affect mitogen activated protein (MAP) kinases. Full activation of the MAP kinases that phosphorylate the Jun activation domain, JNK1 and JNK2, required costimulation of T cells with either TPA and Ca2+ ionophore or antibodies to TCR and CD28. Alone, each stimulus resulted in little or no activation. Similar to its effect on IL-2 induction, cyclosporin A (CsA) inhibited the synergistic activation of JNK, and a competitive inhibitor of Jun phosphorylation by JNK inhibited IL-2 promoter activation. By contrast, the MAP kinases ERK1 and ERK2 were fully activated by TPA or TCR stimulation and were not affected by Ca2+, CD28, or CsA. Hence, integration of signals that lead to T cell activation occurs at the level of JNK activation.

Immediate early transcription activation by salicylic acid via the cauliflower mosaic virus as-1 element

Transgenic tobacco plants carrying a number of regulatory sequences derived from the cauliflower mosaic virus 35S promoter were tested for their response to treatment with salicylic acid (SA), an endogenous signal involved in plant defense responses. beta-Glucuronidase (GUS) gene fusions with the full-length (-343 to +8) 35S promoter or the -90 truncation were found to be induced by SA. Time course experiments revealed that, in the continuous presence of SA, the -90 promoter construct (-90 35S-GUS) displayed rapid and transient induction kinetics, with maximum RNA levels at 1 to 4 hr, which declined to low levels by 24 hr. Induction was still apparent in the presence of the protein synthesis inhibitor cycloheximide (CHX). Moreover, mRNA levels continued to accumulate over 24 hr rather than to decline. By contrast, mRNA from the endogenous pathogenesis-related protein-1a (PR-1a) gene began to accumulate at later times during SA treatment and steadily increased through 24 hr; transcription of this gene was almost completely blocked by the presence of CHX. Further dissection of the region from -90 and -46 of the 35S promoter revealed that the SA-responsive element corresponds to the previously characterized activation sequence-1 (as-1). These results represent a definitive analysis of immediate early responses to SA, relative to the late induction of PR genes, and potentially elucidate the early events of SA signal transduction during the plant defense response.

Immediate early transcription activation by salicylic acid via the cauliflower mosaic virus as-1 element

Transgenic tobacco plants carrying a number of regulatory sequences derived from the cauliflower mosaic virus 35S promoter were tested for their response to treatment with salicylic acid (SA), an endogenous signal involved in plant defense responses. beta-Glucuronidase (GUS) gene fusions with the full-length (-343 to +8) 35S promoter or the -90 truncation were found to be induced by SA. Time course experiments revealed that, in the continuous presence of SA, the -90 promoter construct (-90 35S-GUS) displayed rapid and transient induction kinetics, with maximum RNA levels at 1 to 4 hr, which declined to low levels by 24 hr. Induction was still apparent in the presence of the protein synthesis inhibitor cycloheximide (CHX). Moreover, mRNA levels continued to accumulate over 24 hr rather than to decline. By contrast, mRNA from the endogenous pathogenesis-related protein-1a (PR-1a) gene began to accumulate at later times during SA treatment and steadily increased through 24 hr; transcription of this gene was almost completely blocked by the presence of CHX. Further dissection of the region from -90 and -46 of the 35S promoter revealed that the SA-responsive element corresponds to the previously characterized activation sequence-1 (as-1). These results represent a definitive analysis of immediate early responses to SA, relative to the late induction of PR genes, and potentially elucidate the early events of SA signal transduction during the plant defense response.

Structure and localization of the IGFBP-1 gene and its expression during liver regeneration

Insulin-like growth factor-binding protein-1s are important modulators of the insulin-like growth factors that may have both positive and negative effects on the ability of insulin-like growth factors to stimulate cell growth. The IGFBP-1 gene is one of the most highly induced immediate-early genes after partial hepatectomy. The IGFBP-1 gene is also expressed at a high level during fetal liver development and in response to nutritional changes and diabetes. Therefore it may have important roles in liver growth and metabolism. To begin to examine the regulation of this gene, we cloned and sequenced the entire mouse IGFBP-1 gene. Its structure is highly similar to that of the human gene, and, in addition to the exonic regions, the two genes are highly conserved in specific regions in the promoter and first intron. Analysis of this conservation allows us to predict important regulatory sites that define the tissue specific and insulin-mediated regulation of the gene and identify potential sites that might be important for the transcriptional induction during liver regeneration. The mouse gene is located on mouse chromosome 11; it is found at the boundary between regions in the mouse genome homologous to human chromosomes 22 and 7. We found IGFBP-1 mRNA in both parenchymal and nonparenchymal RNA after partial hepatectomy. Using in situ hybridization of IGFBP-1 mRNA in regenerating rat liver tissue, we demonstrated IGFBP-1 transcripts in several cell types. We found that IGFBP-1 gene induction after partial hepatectomy is paralleled by protein expression.(ABSTRACT TRUNCATED AT 250 WORDS)

A human gene encoding a putative basic helix-loop-helix phosphoprotein whose mRNA increases rapidly in cycloheximide-treated blood mononuclear cells

G0S8 is a member of a set of putative G0/G1 switch regulatory genes (G0S genes) selected by screening cDNA libraries prepared from blood mononuclear cells cultured for 2 hr with lectin and cycloheximide. Comparison of a full-length cDNA sequence with the corresponding genomic sequence reveals an open reading frame of 211 amino acids, distributed across 5 exons. The 24-kD protein has a basic domain preceding a potential helix-loop-helix domain which contains a QTK motif found about 60 amino acids from the carboxyl terminus in the loop region of several helix-loop-helix proteins. There are potential phosphorylation sites for protein kinase C, creatine kinase II, and protein tyrosine kinases and regions of sequence similarity to helix-loop-helix proteins, tyrosine phosphatases, and RNA and DNA polymerases. The genomic sequence contains a CpG island, suggesting expression in the germ line. Potential binding sites for transcription factors are present in the 5' flank and introns; these include Zif268/NGFI-A/EGR1/G0S30, NGFI-B, Ap1, and factors that react with retroviral long terminal repeats (LTRs). There are several potential interferon response elements and a serum response element in the 3' flank overlapping a region of similarity to a cytomegalovirus immediate-early gene enhancer. Many of these motifs are found in immediate-early G0/G1 switch genes; however, we were unable to demonstrate an increase in G0S8 mRNA in response to lectin alone. Sequence similarities are noted between G0S8 and a variety of genes involved in the immune system, in the regulation of retroviruses, and in the cell cycle.

Identification of serum-inducible genes: different patterns of gene regulation during G0-->S and G1-->S progression

We have identified, by differential cDNA library screening, 15 serum inducible genes in the human diploid fibroblast cell line WI-38. The genes fall into two classes that are distinguished by their dependence on protein synthesis for the induction by serum, i.e., primary and secondary genes. While 11 of these genes encode known proteins, 4 other genes have not been described to date. The former genes encode proteins of diverse functions, including the monocyte-derived neutrophil chemotactic factor (MONAP), calmodulin, tropomyosin, tenascin, collagenase, plasminogen activator inhibitor-2a, the ‘sperm-specific’ cleavage signal-1 protein, metallothionein IIa and the mitochondrial chaperonin hsp-60. Interestingly, one of the unknown genes contains a large open reading frame for a polypeptide that is highly homologous to a previously unidentified long open reading frame in the opposite strand of the gene coding for the transcription factor HTF-4. We also studied the regulation of these serum-induced genes during cell cycle progression in normally cycling WI-38 and HL-60 cells separated by counterflow elutriation as well as in serum-stimulated HL-60 cells. Our results clearly show that, in contrast to the prevailing opinion, the expression of most genes induced after mitogen stimulation is not subject to a significant regulation in normally proliferating cells. This supports the hypothesis that the progression into S from either G0 or G1 are distinct processes with specific patterns of gene expression.

Detection of distinct sets of newly synthesized polypeptides in supernatants of TCR-triggered T cell clones. Implication for the search for new lymphokines

Using metabolic radiolabelling of proteins, which are newly synthesized during TCR-triggered T cell activation we were able to visualize distinct patterns of secreted polypeptides (with molecular weights ranging from 6 to 44 kDa) in supernatants of different T helper-1, T helper-2 and cytotoxic T cell clones. Most of these detected proteins are secreted in response to TCR-crosslinking (or to combined action of PMA and A231287), in an extracellular Ca(2+)-dependent manner and their appearance in supernatants was completely blocked by the addition of RNA synthesis or protein synthesis inhibitors or EGTA. Cyclosporin A (CsA) blocks secretion of several detected polypeptides, but does not affect TCR-triggered synthesis and secretion of others reflecting the existence of TCR-triggered, CsA-insensitive protein synthesis and secretion pathway. The insensitivity of secretion of several easily detectable polypeptides to inhibition by CsA offers a promising approach to further define the CsA-resistant and calcineurin-independent molecular pathways of TCR-triggered T cell activation. Several lymphokines (e.g., interferon-gamma, tumor necrosis factor, interleukin-4 and interleukin-10) are identified among the visualized set of secreted polypeptides. Since other, yet unidentified, secreted polypeptides in the same set of secreted proteins share important properties with known lymphokines it seems promising to use described approach in search for new lymphokines.