Identification of a zinc finger protein that inhibits IL-2 gene expression

Transcriptional control and the role of silencers in transcriptional regulation in eukaryotes

Mechanisms controlling transcription and its regulation are fundamental to our understanding of molecular biology and, ultimately, cellular biology. Our knowledge of transcription initiation and integral factors such as RNA polymerase is considerable, and more recently our understanding of the involvement of enhancers and complexes such as holoenzyme and mediator has increased dramatically. However, an understanding of transcriptional repression is also essential for a complete understanding of promoter structure and the regulation of gene expression. Transcriptional repression in eukaryotes is achieved through 'silencers', of which there are two types, namely 'silencer elements' and 'negative regulatory elements' (NREs). Silencer elements are classical, position-independent elements that direct an active repression mechanism, and NREs are position-dependent elements that direct a passive repression mechanism. In addition, 'repressors' are DNA-binding trasncription factors that interact directly with silencers. A review of the recent literature reveals that it is the silencer itself and its context within a given promoter, rather than the interacting repressor, that determines the mechanism of repression. Silencers form an intrinsic part of many eukaryotic promoters and, consequently, knowledge of their interactive role with enchancers and other transcriptional elements is essential for our understanding of gene regulation in eukaryotes.

DeltaEF1, a zinc finger and homeodomain transcription factor, is required for skeleton patterning in multiple lineages

DeltaEF1 is a DNA binding protein containing a homeodomain and two zinc finger clusters, and is regarded as a vertebrate homologue of zfh-1 (zinc finger homeodomain-containing factor-1) in Drosophila. In the developing embryo, deltaEF1 is expressed in the notochord, somites, limb, neural crest derivatives and a few restricted sites of the brain and spinal cord. To elucidate the regulatory function of deltaEF1 in mouse embryogenesis, we generated deltaEF1 null mutant (deltaEF1null(lacZ)) mice. The deltaEF1null(lacZ) homozygotes developed to term, but never survived postnatally. In addition to severe T cell deficiency of the thymus, the deltaEF1null(lacZ) homozygotes exhibited skeletal defects of various lineages. (1) Craniofacial abnormalities of neural crest origin: cleft palate, hyperplasia of Meckel's cartilage, dysplasia of nasal septum and shortened mandible. (2) Limb defects: shortening and broadening of long bones, fusion of carpal/tarsal bone and fusion of joints. (3) Fusion of ribs. (4) Sternum defects: split and asymmetric ossification pattern of the sternebrae associated with irregular sternocostal junctions. (5) Hypoplasia of intervertebral discs. These results indicate that deltaEF1 has an essential role in regulating development of these skeletal structures. Since the skeletal defects were not observed in deltaEF1deltaC727 mice, deltaEF1 bears distinct regulatory activities which are dependent on different domains of the molecule.

Involvement of negative cofactor NC2 in active repression by zinc finger-homeodomain transcription factor AREB6

The transcription factor AREB6 contains a homeodomain flanked by two clusters of Krüppel type C2H2 zinc fingers. AREB6 binds to the E-box consensus sequence, CACCTGT, through either the N- or the C-terminal zinc finger cluster. To gain insights into the molecular mechanism by which AREB6 activates and represses gene expression, we analyzed the domain structure of AREB6 in the context of a heterologous DNA-binding domain by transient-transfection assays. The C-terminal region spanning amino acids 1011 to 1124 was identified as a conventional acidic activation domain. The region containing amino acids 754 to 901, which was identified as a repression domain, consists of 40% hydrophobic amino acids displaying no sequence similarities to other known repression domains. This region repressed transcription in vitro in a HeLa nuclear extract but not in reconstituted transcription systems consisting of transcription factor IID (TFIID), TFIIB, TFIIE, TFIIH/F, and RNA polymerase II. The addition of recombinant negative cofactor NC2 (NC2alpha/DRAP1 and NC2beta/Dr1) to the reconstituted transcription system restored the activity of the AREB6 repression domain. We further demonstrated interactions between the AREB6 repression domain and NC2alpha in yeast two-hybrid assay. Our findings suggest a mechanism of transcriptional repression that is mediated by the general cofactor NC2.

T cell clonal anergy

Recent experiments have elucidated two molecular mechanisms that may account for the failure of anergic T cell clones to initiate IL-2 gene transcription following TCR stimulation. First, a block has been identified in the ERK and JNK mitogen-activated protein kinase pathways; the block results from a failure to activate p21ras. It leads to reduced induction of c-Fos and JunB proteins and to a failure to form and phosphorylate the activator protein (AP)-1 heterodimers required for IL-2 gene transcriptional activation. Second, repressor molecules (Nil-2-a and a molecule related to AP-1) have been characterized that dominantly inhibit IL-2 gene transcription.

Impairment of T cell development in deltaEF1 mutant mice

Using the method of gene targeting in mouse embryonic stem cells, regulatory function of deltaEF1, a zinc finger and homeodomain-containing transcription factor, was investigated in vivo by generating the deltaEF1 mutant mice. The mutated allele of deltaEF1 produced a truncated form of the deltaEF1 protein lacking a zinc finger cluster proximal to COOH terminus. The homozygous deltaEF1 mutant mice had poorly developed thymi with no distinction of cortex and medulla. Analysis of the mutant thymocyte showed reduction of the total cell number by two orders of magnitude accompanying the impaired thymocyte development. The early stage intrathymic c-kit+ T precursor cells were largely depleted. The following thymocyte development also seemed to be affected as assessed by the distorted composition of CD4- or CD8-expressing cells. The mutant thymocyte showed elevated alpha4 integrin expression, which might be related to the T cell defect in the mutant mice. In the peripheral lymph node tissue of the mutant mice, the CD4-CD8+ single positive cells were significantly reduced relative to CD4+CD8-single positive cells. In contrast to T cells, other hematopoietic lineages appeared to be normal. The data indicated that deltaEF1 is involved in regulation of T cell development at multiple stages.

Constitutive binding of the transcription factor interleukin-2 (IL-2) enhancer binding factor to the IL-2 promoter

A positive regulatory element in the interleukin-2 (IL-2) promoter, designated the antigen receptor response element-2, is essential for the induction of IL-2 gene expression upon the binding of an inducible multiprotein complex of proteins known as nuclear factor of activated T cells. In the current study, we demonstrated that the winged-helix transcription factor IL-2 enhancer binding factor (ILF) is constitutively expressed in both resting and activated Jurkat cells and binds to two adjacent sequence motifs immediately downstream of the binding site for NFAT. One of these elements has a high degree of homology with consensus binding sites for a variety of winged-helix DNA binding proteins, and the second site functions to modulate ILF binding. Mutagenesis of each of the two sequence elements required for ILF binding decreased IL-2 promoter activity when assayed in transfection assays. Although ILF bound constitutively to the IL-2 promoter, it was not detected as a component of the NFAT complex. These results suggest that important regulatory sequences in the IL-2 promoter are bound by ILF and that this binding may be involved in the control of IL-2 gene expression.

Organization of the gene encoding transcriptional repressor deltaEF1 and cross-species conservation of its domains

DeltaEF1 (delta-crystallin/E2-box factor 1) is a widely distributed repressor of transcription which binds at the E2-box sequence, CACCTG. It carries seven zinc fingers (Zf) in two clusters and a homeodomain in the middle as potential DNA-binding domains. We cloned the genomic gene encoding chicken deltaEF1 and analyzed its organization. The gene consisted of nine exons, the N-proximal Zf were encoded by exons 5 through 7, and the C-proximal Zf by exons 8 and 9. Exon 7 also coded for the large middle portion of the protein including the homeodomain. Promoter analysis and RNase-protection assay indicated that the gene is driven by a G+C-rich promoter without a TATA box, and the transcription start points (tsp) cluster around 20 bp from the start codon located in exon 1. cDNA and genomic sequences of the mouse delta EF1 were cloned and compared with the chicken sequence. The deduced amino acid (aa) sequence was highly conserved between the chicken and mouse deltaEF1, no only in DNA-binding motifs but also in other blocks (78% overall aa identity). More recently reported DNA-binding proteins, AREB6 (human) ZEB (human) and BZP (hamster), were attributed to homologues of deltaEF1, among which only AREB6 represented full-length sequence. It was also indicated that rodent deltaEF1 lacked exon 3.

A dynamic assembly of diverse transcription factors integrates activation and cell-type information for interleukin 2 gene regulation

The interleukin 2 (IL-2) gene is subject to two types of regulation: its expression is T-lymphocyte-specific and it is acutely dependent on specific activation signals. The IL-2 transcriptional apparatus integrates multiple types of biochemical information in determining whether or not the gene will be expressed, using multiple diverse transcription factors that are each optimally activated or inhibited by different signaling pathways. When activation of one or two of these factors is blocked IL-2 expression is completely inhibited. The inability of the other, unaffected factors to work is explained by the striking finding that none of the factors interacts stably with its target site in the IL-2 enhancer unless all the factors are present. Coordinate occupancy of all the sites in the minimal enhancer is apparently maintained by continuous assembly and disassembly cycles that respond to the instantaneous levels of each factor in the nuclear compartment. In addition, the minimal enhancer undergoes specific increases in DNase I accessibility, consistent with dramatic changes in chromatin structure upon activation. Still to be resolved is what interaction(s) conveys T-lineage specificity. In the absence of activating signals, the minimal IL-2 enhancer region in mature T cells is apparently unoccupied, exactly as in non-T lineage cells. However, in a conserved but poorly studied upstream region, we have now mapped several novel sites of DNase I hypersensitivity in vivo that constitutively distinguish IL-2 producer type T cells from cell types that cannot express IL-2. Thus a distinct domain of the IL-2 regulatory sequence may contain sites for competence- or lineage-marking protein contacts.

The nuclear factor YY1 suppresses the human gamma interferon promoter through two mechanisms: inhibition of AP1 binding and activation of a silencer element

Our group has previously reported that the nuclear factor Yin-Yang 1 (YY1), a ubiquitous DNA-binding protein, is able to interact with a silencer element (BE) in the gamma interferon (IFN-gamma) promoter region. In this study, we demonstrated that YY1 can directly inhibit the activity of the IFN-gamma promoter by interacting with multiple sites in the promoter. In cotransfection assays, a YY1 expression vector significantly inhibited IFN-gamma promoter activity. Mutation of the YY1 binding site in the native IFN-gamma promoter was associated with an increase in the IFN-gamma promoter activity. Analysis of the DNA sequences of the IFN-gamma promoter revealed a second functional YY1 binding site (BED) that overlaps with an AP1 binding site. In this element, AP1 enhancer activity was suppressed by YY1. Since the nuclear level of YY1 does not change upon cell activation, our data support a model that the nuclear factor YY1 acts to suppress basal IFN-gamma transcription by interacting with the promoter at multiple DNA binding sites. This repression can occur through two mechanisms: (i) cooperation with an as-yet-unidentified AP2-like repressor protein and (ii) competition for DNA binding with the transactivating factor AP1.

The effect of age on the expression of interleukin-2

Interleukin-2 (IL-2) is a growth promoting cytokine that has received a great deal of attention over the past decade with respect to aging and cancer. It is produced primarily by helper T cells and regulates the growth and function of various cells that are involved in cellular and humoral immunity. The expression of IL-2 has been found to decrease with age in humans and rodents. The decline in IL-2 production has been shown to parallel the age-related decrease in immunologic function. Several studies indicate that treatment of lymphocytes from old subjects with exogenous IL-2 or infusion of IL-2 into old animals partially or completely restores some of the immune functions that decline with age. The age-related decline in IL-2 production has been shown to arise from a decline in IL-2 transcription, and a recent study suggests that the transcription factor NFAT (nuclear factor of activated T cells) may play a role in the decline in IL-2 transcription.

Alternative splicing gives rise to two isoforms of Zfhep, a zinc finger/homeodomain protein that binds T3-response elements

We have previously isolated a cDNA for a transcription factor referred to as Zfhep (zinc finger homeodomain enhancer-binding protein) containing two separate zinc finger domains, ZD1 and ZD2, each of which binds DNA, and a homeodomain. The rat Zfhep cDNA lacks a 5'-methionine codon, present in some homologs from other species. Hence, the aim of this work was to isolate the 5'-end of the rat Zfhep cDNA. Zfhep-2 cDNA was isolated, having a total length of 2.5 kbp, including more than 1.1 kbp of novel sequence followed by 1.4 kbp identical to the Zfhep-1 clone. The 1.1 kbp of novel sequence contains multiple stop codons in all reading frames, suggesting that it represents the 5'-untranslated (5'-UT) region of the rat Zfhep-2 mRNA. However, the Zfhep-2 clone does not contain the extreme 5'-exon(s) of the Zfhep-1 coding sequence, possibly due to alternative splicing of Zfhep RNA. To distinguish between a splice junction versus an intron-exon junction, the polymerase chain reaction (PCR) with rat genomic DNA and junction-flanking primers from the Zfhep-2 sequence was conducted. No bands were amplified from the genomic DNA by two different pairs of primers, indicating that the Zfhep-2-specific sequence is not intronic. Ribonuclease protection assays were performed to investigate the expression of multiple Zfhep mRNAs. Two protected bands were detected, and both were identified in total RNA or mRNA of rat ovary, hindbrain, forebrain, heart, kidney, small intestine, and GH4C1 cells. Zfhep-2 represents about 20% of the Zfhep RNA in each tissue. Hence, two mRNAs are expressed in these tissues, confirming the alternative splicing. To confirm independently the presence of both Zfhep-2 and Zfhep-1 mRNAs, reverse transcriptase (RT)-PCR was done using primers that span the Zfhep splice site. Specific bands representing both RNAs were obtained. The Zfhep-2 PCR product was subcloned and DNA sequence analysis confirmed the absence of ATG codons near the 5'-end of the open reading frame. The theoretical translation of the Zfhep-2 clone predicts a smaller protein than Zfhep-1. In vitro translation in reticulocyte lysates showed that Zfhep-2 is about 40 kD smaller than Zfhep-1. Hence, Zfhep-2 apparently lacks most of the first zinc finger domain (ZD1) of Zfhep-1. Because the two zinc finger domains bind different DNA sequences, Zfhep-2 is predicted to bind to only a subset of genes recognized by Zfhep-1.

Regulation of gene expression at early stages of B-cell and T-cell differentiation

The expression of distinct sets of genes at different stages of B-lymphocyte and T-lymphocyte differentiation is controlled at the level of transcription. A number of recent studies have described interactions between transcription factors in lymphocytes that provide new insights into mechanisms regulating gene expression. These mechanisms include the assembly of higher order nucleoprotein complexes and other protein-protein interactions that enhance the functional specificity of transcriptional regulators in lymphocytes.

Cloning of a cDNA encoding a mouse transcriptional repressor displaying striking sequence conservation across vertebrates

The nucleotide sequence encoding an approx. 120-kDa transcriptional repressor (MEB1) was determined from a cDNA which was cloned from a mouse brain library. An alignment of the deduced amino-acid sequences of the putative functional domains of MEB1 with those from the human, hamster and chicken homologues reveals a dramatic degree of conservation.

Transcriptional regulation of the interleukin-2 gene in normal human peripheral blood T cells. Convergence of costimulatory signals and differences from transformed T cells

To study transcriptional regulation in normal human T cells, we have optimized conditions for transient transfection. Interleukin-2 (IL-2) promoter-reporter gene behavior closely parallels the endogenous gene in response to T cell receptor and costimulatory signals. As assessed with mutagenized promoters, the most important IL-2 cis-regulatory elements in normal T cells are the proximal AP-1 site and the NF- kappaB site. Both primary activation, with phytohemagglutinin or antibodies to CD3, and costimulation, provided by pairs of CD2 antibodies or B7-positive (B cells) or B7-negative (endothelial) accessory cells, are mediated through the same cis-elements. Interestingly, the nuclear factor of activated T cell sites are much less important in normal T cells than in Jurkat T cells. We conclude that IL-2 transcriptional regulation differs in tumor cell lines compared with normal T cells and that different costimulatory signals converge on the same cis-elements in the IL-2 promoter.

The regulation of GM-CSF is dependent on a complex interplay of multiple nuclear proteins

GM-CSF is an important mediator of hematopoiesis and its dysregulation may play a role in neoplastic and inflammatory conditions. Previous studies have demonstrated that GM-CSF production depends upon the accumulation of specific mRNA, which occurs by transcriptional and post-transcriptional mechanisms. In order to dissect the cis-acting sequences responsible for its regulation, we performed an extensive mutagenesis study spanning 54 nucleotides 5' of the GM-CSF coding region. Our analysis suggests that the previously-described functional elements of the GM-CSF promoter, kappa B and a repetitive CATTT/A motif, the former co-exists with an overlapping 9 nucleotide site which silences promoter activity, and the CATTT/A complex binds multiple polypeptides which differentially contribute to basal and inducible promoter activity. These two sites interact to provide tissue-appropriate and stimulus-specific promoter function. Using DNA-protein cross-linking and co-transfection studies, we demonstrate that the c-rel-related proteins p65 and p50 bind to the GM-CSF promoter and that p65 binding is primarily responsible for the enhancing effects at this site. In addition, we show that the GM-CSF kappa B decanucleotide is inadequate to provide full binding affinity; mutation of nucleotides flanking this site affect promoter function by altering NF-kappa B binding affinity. Together these results suggest that the transcriptional response of GM-CSF is dependent on a complex interplay of multiple DNA binding proteins.

Checklist: vertebrate homeobox genes

Up to now around 170 different homeobox genes have been cloned from vertebrate genomes. A compilation of the various isolates from mouse, chick, frog, fish and man is presented in the form of a concise checklist, including the designations from the original publications. Putative homologs from different species are aligned, and key characteristics of embryonic or adult expression domains, as well as mutant phenotypes are briefly indicated.

Overexpression of the zinc finger protein MZF1 inhibits hematopoietic development from embryonic stem cells: correlation with negative regulation of CD34 and c-myb promoter activity

Zinc finger genes encode proteins that act as transcription factors. The myeloid zinc finger 1 (MZF1) gene encodes a zinc finger protein with two DNA-binding domains that recognize two distinct consensus sequences, is preferentially expressed in hematopoietic cells, and may be involved in the transcriptional regulation of hematopoiesis-specific genes. Reverse transcription-PCR analysis of human peripheral blood CD34+ cells cultured under lineage-restricted conditions demonstrated MZF1 expression during both myeloid and erythroid differentiation. Sequence analysis of the 5'-flanking region of the CD34 and c-myb genes, which are a marker of and a transcriptional factor required for hematopoietic proliferation and differentiation, respectively, revealed closely spaced MZF1 consensus binding sites found by electrophoretic mobility shift assays to interact with recombinant MZF1 protein. Transient or constitutive MZF1 expression in different cell types resulted in specific inhibition of chloramphenicol acetyltransferase activity driven by the CD34 or c-myb 5'-flanking region. To determine whether transcriptional modulation by MZF1 activity plays a role in hematopoietic differentiation, constructs containing the MZF1 cDNA under the control of different promoters were transfected into murine embryonic stem cells which, under defined in vitro culture conditions, generate colonies of multiple hematopoietic lineages. Constitutive MZF1 expression interfered with the ability of embryonic stem cells to undergo hematopoietic commitment and erythromyeloid colony formation and prevented the induced expression of CD34 and c-myb mRNAs during differentiation of these cells. These data indicate that MZF1 plays a critical role in hematopoiesis by modulating the expression of genes involved in this process.

Multiple proteins interact with the nuclear inhibitory protein repressor element in the human interleukin-3 promoter

T cell expression of interleukin 3 (IL-3) is directed by positive and negative cis-acting DNA elements clustered within 300 base pairs of the transcriptional start site. A strong repressor element, termed nuclear inhibitory protein (NIP), was previously mapped to a segment of the IL-3 promoter between nucleotides -271 and -250. Functional characterization of this element demonstrates that it can mediate repression when linked in cis to a heterologous promoter. DNA binding experiments were carried out to characterize the repressor activity. Using varying conditions, three distinct complexes were shown to interact specifically with the NIP region, although only one correlates with repressor activity. Complex 1 results from binding of a ubiquitous polypeptide that recognizes the 3' portion of this sequence and is not required for repression. Complex 2 corresponds to binding of transcription factor (upstream stimulatory factor) to an E-box motif in the 5' portion of the NIP region. DNA binding specificity of complex 3 overlaps with that of upstream stimulatory factor but is clearly distinct. To determine which of the latter two complexes represents NIP activity, we incorporated small alterations into the NIP site of an IL-3 promoter-linked reporter construct and examined their effects on NIP-mediated repression. Functional specificity for repression matches the DNA binding specificity of complex 3; both repressor activity and complex 3 binding require the consensus sequence CTCACNTNC.

Polyclonal hypergammaglobulinaemia in a case of B-cell chronic lymphocytic leukaemia: the result of IL-2 production by the proliferating monoclonal B cells?

SEQ DATA who developed polyclonal hypergammaglobulinaemia: 38.3 milligrams polyclonal IgG, 0.97 milligram IgA and 0.33 milligram IgM. Immunophenotyping showed a monoclonal lymphocytic population CD19+ CD5+ CD40+ CD23+, low sIg+ (95%), kappa type in the great majority (96%). RT-PCR of immunoglobulin genes gave evidence of monoclonal rearrangement of the IgM type. Our tests showed that IL-2 was produced when leukaemic B cells were stimulated with phorbol myristate acetate, ionomycin and lipopolysaccharide. In addition, transfections with the full IL-2 promoter or elements thereof revealed that IL-2 expression is inducible and mediated through the NF-kB-promoter element. Finally, the amount of IL-2 secreted by these cells is about 39 ng/ml/10(6) cells, which is remarkably high for non-T cells. These results suggest that the large amounts of polyclonal IgG seen in this case of B-CLL are secreted by normal B cells which are in turn stimulated by IL-2 produced by proliferating monoclonal (leukaemic) B cells. Under cyclosporin A treatment, immunoglobulin secretion and B cell count remained low.

DNA binding through distinct domains of zinc-finger-homeodomain protein AREB6 has different effects on gene transcription

Transcription factor AREB6 has a unique structure composed of two zinc-finger clusters in N- and C-terminal regions, and one homeodomain in the middle. AREB6 has been known to regulate the expression of the Na, K-ATPase alpha 1 subunit, interleukin 2 and delta-crystallin genes. We determined the optimal binding sites for the N-terminal zinc-finger cluster as GTCACCTGT or TGCACCTGT and for the C-terminal zinc-finger cluster as C/TACCTG/TT by the CASTing method (cyclic amplification and selection of targets). The additional consensus sequence GTTTC/G, in conjunction with the CACCTGT sequence, was selected by the second CASTing for the entire coding region. The N-terminal zinc-finger cluster binds to DNA strongly when the DNA has GTTTC/G in conjunction with the CACCTGT sequence. The homeodomain had no specific DNA binding activity but was found to interact with the N-terminal zinc-finger cluster. Analyses of zinc-finger mutation proteins revealed that the contribution to DNA binding of each N-terminal zinc-finger motif is altered depending on the presence of the additional consensus. Transient transfection assays showed that AREB6 repressed the human 70-kDa heat-shock gene promoter harboring the CACCTGT sequence together with the additional consensus, and that AREB6 activated the promoter harboring the CACCTGT sequence without the additional consensus. These results suggest that AREB6 has multiple conformational states, leading to positive and negative regulations of gene transcription.

In vivo identification of a negative regulatory element in the mouse renin gene using direct gene transfer

DBA/2J mouse contains two renin gene loci (Ren1d and Ren2d). Ren2d but not Ren1d is expressed in submandibular gland (SMG) while both are expressed in the kidney. Based on vitro studies, we have postulated that a negative regulatory element (NRE) in the renin gene promoter is involved in its tissue-specific expression. In this study, we examined the molecular mechanism at the in vivo level using direct gene transfer. Fragments of the Ren1d or Ren2d promoter were fused to a chloramphenicol acetyltransferase (CAT) gene expression vector. These constructs complexed in fusogenic liposomes were injected directly into the mouse SMG or intraarterially into the mouse kidney via the renal artery. The vector containing the CAT exhibited readily detectable in vivo expressions in both SMG and kidney. In the SMG, Ren1d fragment containing the NRE abolished CAT expression while deletion of the NRE restored CAT expression. The homologous fragment from the Ren2d promoter did not inhibit CAT expression while deletion of the 150-bp insertion resulted in the inhibition. Cotransfection of Ren1d construct with Ren1d-NRE oligonucleotides as transcriptional factor decoy restored CAT expression. Contrary to the SMG, transfection with Ren1d fragment-CAT construct or Ren2d fragment-CAT construct into the kidney resulted in similar levels of CAT expression. Interestingly, human c-myc NRE oligonucleotides which share homology with Ren1d-NRE competed effectively with these oligonucleotides for the regulation of Ren1d gene expression in vivo. This NRE sequence is also homologous to silencer elements found in multiple mammalian genes, suggesting the presence of a family of NRE/NRE binding proteins regulating expression of diverse genes.

Negative transcriptional regulation in anergic T cells

Anergy is a mechanism of T-lymphocyte tolerance induced by antigen-receptor stimulation in the absence of costimulation, whereby T cells exhibit a defect in antigen-induced transcription of the interleukin 2 (IL-2) gene. Here we present evidence for a mechanism of negative IL-2 gene regulation in anergic T cells. High amounts of binding activity to the negative regulatory element A (NRE-A) of the IL-2 promotor were detected in nuclear extracts from human T cells shortly after induction of anergy. Rapid induction of this nuclear complex is blocked by cyclosporin A and is found to be independent of protein synthesis. Plasmid DNAs, containing either the human phorbol 12-myristate 13-acetate-responsive element (PRE) or both NRE-A and PRE, were used as template for in vitro transcription assays in the presence of T-cell nuclear extracts. Under these conditions nuclear extracts from both anergic and rested T-cell clones, after crosslinking of CD3 and CD28, induced transcription of plasmids containing only PRE. However, when plasmids containing NRE-A and PRE were used, transcription was only induced by nuclear extracts from rested but not anergic T cells. These findings suggest the functional relevance of transcriptional repression of the IL-2 gene in anergic T cells.

A sequence-specific single-strand DNA binding protein that contacts repressor sequences in the human GM-CSF promoter

NF-GMb is a nuclear factor that binds to the proximal promoter of the human granulocyte-macrophage colony stimulating factor (GM-CSF) gene. NF-GMb has a subunit molecular weight of 22 kDa, is constitutively expressed in embryonic fibroblasts and binds to sequences within the adjacent CK-1 and CK-2 elements (CK-1/CK-2 region), located at approximately -100 in the GM-CSF gene promoter. These elements are conserved in haemopoietic growth factor (HGF) genes. NF-GMb binding requires the presence of repeated 5'CAGG3' sequences that overlap the binding sites for positive activators. Surprisingly, NF-GMb was found to bind solely to single-strand DNA, namely the non-coding strand of the GM-CSF CK-1/CK-2 region. NF-GMb may belong to a family of single-strand DNA binding (ssdb) proteins that have 5'CAGG3' sequences within their binding sites. Functional analysis of the proximal GM-CSF promoter revealed that sequences in the -114 to -79 region of the promoter containing the NF-GMb binding sites had no intrinsic activity in fibroblasts but could, however, repress tumour necrosis factor-alpha (TNF-alpha) inducible expression directed by downstream promoter sequences (-65 to -31). Subsequent mutation analysis showed that sequences involved in repression correlated with those required for NF-GMb binding.

T-cell functional regions of the human IL-3 proximal promoter

The human interleukin-3 (IL-3) gene is expressed almost exclusively in activated T cells. Its expression is regulated at both the transcriptional and post-transcriptional level. We have previously shown that treatment of Jurkat T cells with phytohemaglutinin (PHA) and the phorbol ester, PMA, activated transcription initiation from the IL-3 gene. To define the regions of the gene required for transcription activation, we generated a series of reporter constructs containing different regions of the IL-3 gene 5' and 3' flanking sequences. Both positive and negative regulatory elements were identified in the proximal 5' flanking region of the IL-3 gene. The promoter region between -173 and -60 contained the strongest activating elements. The transcription factor AP-1 could bind to this positive activator region of the promoter. We also examined the function of the IL-3 CK-1/CK-2 elements that are present in many cytokine genes and found that they acted as a repressor of basal level expression when cloned upstream of a heterologous promoter but were also inducible by PMA/PHA.

Displacement of an E-box-binding repressor by basic helix-loop-helix proteins: implications for B-cell specificity of the immunoglobulin heavy-chain enhancer

The activity of the immunoglobulin heavy-chain (IgH) enhancer is restricted to B cells, although it binds both B-cell-restricted and ubiquitous transcription factors. Activation of the enhancer in non-B cells upon overexpression of the basic helix-loop-helix (bHLH) protein E2A appears to be mediated not only by the binding of E2A to its cognate E box but also by the resulting displacement of a repressor from that same site. We have identified a "two-handed" zinc finger protein, denoted ZEB, the DNA-binding specificity of which mimics that of the cellular repressor. By employing a derivative E box that binds ZEB but not E2A, we have shown that the repressor is active in B cells and the IgH enhancer is silenced in the absence of binding competition by bHLH proteins. Hence, we propose that a necessary prerequisite of enhancer activity is the B-cell-specific displacement of a ZEB-like repressor by bHLH proteins.

Displacement of an E-box-binding repressor by basic helix-loop-helix proteins: implications for B-cell specificity of the immunoglobulin heavy-chain enhancer

The activity of the immunoglobulin heavy-chain (IgH) enhancer is restricted to B cells, although it binds both B-cell-restricted and ubiquitous transcription factors. Activation of the enhancer in non-B cells upon overexpression of the basic helix-loop-helix (bHLH) protein E2A appears to be mediated not only by the binding of E2A to its cognate E box but also by the resulting displacement of a repressor from that same site. We have identified a "two-handed" zinc finger protein, denoted ZEB, the DNA-binding specificity of which mimics that of the cellular repressor. By employing a derivative E box that binds ZEB but not E2A, we have shown that the repressor is active in B cells and the IgH enhancer is silenced in the absence of binding competition by bHLH proteins. Hence, we propose that a necessary prerequisite of enhancer activity is the B-cell-specific displacement of a ZEB-like repressor by bHLH proteins.

Distinct effects of glutathione disulphide on the nuclear transcription factor kappa B and the activator protein-1

Oxidative conditions potentiate the activation of the nuclear transcription factor kappa B (NF kappa B) and the activator protein-1 (AP-1) in intact cells, but inhibit their DNA binding activity in vitro. We now show that both the activation of NF kappa B and the inhibition of its DNA binding activity is modulated in intact cells by the physiological oxidant glutathione disulphide (GSSG). NF kappa B activation in human T lineage cells (Molt-4) by 12-O-tetradecanoyl-phorbol 13-acetate was inhibited by dithiothreitol, and this was partly reversed by the glutathione reductase inhibitor 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or by hydrogen peroxide, indicating that GSSG may be required for NF kappa B activation. These effects of BCNU and hydrogen peroxide were not seen in glutathione-depleted cells. However, NF kappa B and AP-1 activation were potentiated by dithiothreitol if added to cell cultures 1 h after the phorbol ester, indicating that a shift of redox conditions may support optimal oxidative activation with minimal inhibition of DNA binding. The elevation of intracellular GSSG levels by BCNU before stimulation suppressed the chloramphenicol acetyltransferase expression dependent on NF kappa B but increased that dependent on AP-1. This selective suppression of NF kappa B was also demonstrable by electrophoretic mobility shift assays. In vitro, GSSG inhibited the DNA binding activity of NF kappa B more effectively than that of AP-1, while AP-1 was inhibited more effectively by oxidized thioredoxin.

Interleukin-2 transcription is regulated in vivo at the level of coordinated binding of both constitutive and regulated factors

Interleukin-2 (IL-2) transcription is developmentally restricted to T cells and physiologically dependent on specific stimuli such as antigen recognition. Prior studies have shown that this stringent two-tiered regulation is mediated through a transcriptional promoter/enhancer DNA segment which is composed of diverse recognition elements. Factors binding to some of these elements are present constitutively in many cell types, while others are signal dependent, T cell specific, or both. This raises several questions about the molecular mechanism by which IL-2 expression is regulated. Is the developmental commitment of T cells reflected molecularly by stable interaction between available factors and the IL-2 enhancer prior to signal-dependent induction? At which level, factor binding to DNA or factor activity once bound, are individual regulatory elements within the native enhancer regulated? By what mechanism is developmental and physiological specificity enforced, given the participation of many relatively nonspecific elements? To answer these questions, we have used in vivo footprinting to determine and compare patterns of protein-DNA interactions at the native IL-2 locus in cell environments, including EL4 T-lymphoma cells and 32D clone 5 premast cells, which express differing subsets of IL-2 DNA-binding factors. We also used the immunosuppressant cyclosporin A as a pharmacological agent to further dissect the roles played by cyclosporin A-sensitive factors in the assembly and maintenance of protein-DNA complexes. Occupancy of all site types was observed exclusively in T cells and then only upon excitation of signal transduction pathways. This was true even though partially overlapping subsets of IL-2-binding activities were shown to be present in 32D clone 5 premast cells. This observation was especially striking in 32D cells because, upon signal stimulation, they mobilized a substantial set of IL-2 DNA-binding activities, as measured by in vitro assays using nuclear extracts. We conclude that binding activities of all classes fail to stably occupy their cognate sites in IL-2, except following activation of T cells, and that specificity of IL-2 transcription is enforced at the level of chromosomal occupancy, which appears to be an all-or-nothing phenomenon.

Characterization of the DNA-binding properties of the myeloid zinc finger protein MZF1: two independent DNA-binding domains recognize two DNA consensus sequences with a common G-rich core

The myeloid zinc finger gene 1, MZF1, encodes a transcription factor which is expressed in hematopoietic progenitor cells that are committed to myeloid lineage differentiation. MZF1 contains 13 C2H2 zinc fingers arranged in two domains which are separated by a short glycine- and proline-rich sequence. The first domain consists of zinc fingers 1 to 4, and the second domain is formed by zinc fingers 5 to 13. We have determined that both sets of zinc finger domains bind DNA. Purified, recombinant MZF1 proteins containing either the first set of zinc fingers or the second set were prepared and used to affinity select DNA sequences from a library of degenerate oligonucleotides by using successive rounds of gel shift followed by PCR amplification. Surprisingly, both DNA-binding domains of MZF1 selected similar DNA-binding consensus sequences containing a core of four or five guanine residues, reminiscent of an NF-kappa B half-site: 1-4, 5'-AGTGGGGA-3'; 5-13, 5'-CGGGnGAGGGGGAA-3'. The full-length MZF1 protein containing both sets of zinc finger DNA-binding domains recognizes synthetic oligonucleotides containing either the 1-4 or 5-13 consensus binding sites in gel shift assays. Thus, we have identified the core DNA consensus binding sites for each of the two DNA-binding domains of a myeloid-specific zinc finger transcription factor. Identification of these DNA-binding sites will allow us to identify target genes regulated by MZF1 and to assess the role of MZF1 as a transcriptional regulator of hematopoiesis.

Interleukin-2 transcription is regulated in vivo at the level of coordinated binding of both constitutive and regulated factors

Interleukin-2 (IL-2) transcription is developmentally restricted to T cells and physiologically dependent on specific stimuli such as antigen recognition. Prior studies have shown that this stringent two-tiered regulation is mediated through a transcriptional promoter/enhancer DNA segment which is composed of diverse recognition elements. Factors binding to some of these elements are present constitutively in many cell types, while others are signal dependent, T cell specific, or both. This raises several questions about the molecular mechanism by which IL-2 expression is regulated. Is the developmental commitment of T cells reflected molecularly by stable interaction between available factors and the IL-2 enhancer prior to signal-dependent induction? At which level, factor binding to DNA or factor activity once bound, are individual regulatory elements within the native enhancer regulated? By what mechanism is developmental and physiological specificity enforced, given the participation of many relatively nonspecific elements? To answer these questions, we have used in vivo footprinting to determine and compare patterns of protein-DNA interactions at the native IL-2 locus in cell environments, including EL4 T-lymphoma cells and 32D clone 5 premast cells, which express differing subsets of IL-2 DNA-binding factors. We also used the immunosuppressant cyclosporin A as a pharmacological agent to further dissect the roles played by cyclosporin A-sensitive factors in the assembly and maintenance of protein-DNA complexes. Occupancy of all site types was observed exclusively in T cells and then only upon excitation of signal transduction pathways. This was true even though partially overlapping subsets of IL-2-binding activities were shown to be present in 32D clone 5 premast cells. This observation was especially striking in 32D cells because, upon signal stimulation, they mobilized a substantial set of IL-2 DNA-binding activities, as measured by in vitro assays using nuclear extracts. We conclude that binding activities of all classes fail to stably occupy their cognate sites in IL-2, except following activation of T cells, and that specificity of IL-2 transcription is enforced at the level of chromosomal occupancy, which appears to be an all-or-nothing phenomenon.

Characterization of the DNA-binding properties of the myeloid zinc finger protein MZF1: two independent DNA-binding domains recognize two DNA consensus sequences with a common G-rich core

The myeloid zinc finger gene 1, MZF1, encodes a transcription factor which is expressed in hematopoietic progenitor cells that are committed to myeloid lineage differentiation. MZF1 contains 13 C2H2 zinc fingers arranged in two domains which are separated by a short glycine- and proline-rich sequence. The first domain consists of zinc fingers 1 to 4, and the second domain is formed by zinc fingers 5 to 13. We have determined that both sets of zinc finger domains bind DNA. Purified, recombinant MZF1 proteins containing either the first set of zinc fingers or the second set were prepared and used to affinity select DNA sequences from a library of degenerate oligonucleotides by using successive rounds of gel shift followed by PCR amplification. Surprisingly, both DNA-binding domains of MZF1 selected similar DNA-binding consensus sequences containing a core of four or five guanine residues, reminiscent of an NF-kappa B half-site: 1-4, 5'-AGTGGGGA-3'; 5-13, 5'-CGGGnGAGGGGGAA-3'. The full-length MZF1 protein containing both sets of zinc finger DNA-binding domains recognizes synthetic oligonucleotides containing either the 1-4 or 5-13 consensus binding sites in gel shift assays. Thus, we have identified the core DNA consensus binding sites for each of the two DNA-binding domains of a myeloid-specific zinc finger transcription factor. Identification of these DNA-binding sites will allow us to identify target genes regulated by MZF1 and to assess the role of MZF1 as a transcriptional regulator of hematopoiesis.

IL-2 mRNA levels and degradation rates change with mode of stimulation and phorbol ester treatment of lymphocytes

Transient expression of interleukin 2 (IL-2) in activated T lymphocytes may be due to transcriptional and post-transcriptional regulation. As incubation of lymphocytes with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) prior to mitogenic stimulation results in decreased levels of IL-2 mRNA, we asked if IL-2 mRNA stability was affected. We found that in TPA-treated cells, IL-2 mRNA was degraded more rapidly than in untreated ones whether the mitogenic stimulus was Concanavalin A (Con A), Con A plus TPA, or TPA plus ionomycin. The degradation was blocked if the TPA pre-incubation included cycloheximide. In contrast, when TPA was included as a co-mitogen, i.e. added at the same time as the mitogen, the IL-2 mRNA levels and stability significantly increased. Compared to the levels found in Con A stimulated cells, TPA plus Con A increased IL-2 mRNA levels by as much as 20-fold and the half-life by 5-fold. TPA plus ionomycin increased the message levels at least 100-fold and half-life by nearly 10-fold. These effects on IL-2 mRNA were not general because IL-2 receptor mRNA stability was not changed even though it also is transiently expressed during the course of lymphocyte activation.

Trypanosoma cruzi infection suppresses nuclear factors that bind to specific sites on the interleukin-2 enhancer

Interleukin-2 (IL-2) gene expression, a critical early event during T lymphocyte activation, is severely suppressed in mice infected with the protozoan parasite Trypanosoma cruzi, the causative agent of human Chagas' disease. Our previous observation that reduction of IL-2 mRNA in T cells from T. cruzi-infected mice is not due to an increased degradation of the mRNA suggests a repression of the IL-2 gene at the transcriptional level. In this study, we have measured the level of nuclear factors that bind to specific sites on the IL-2 enhancer. Splenocytes and splenic T cells from acutely infected mice show a marked decrease in the level of AP-1, and a modest decrease in the level of NF-kappa B and nuclear factor of activated T cells (NF-AT). DNA-binding activity of Oct-1 was least affected in T cells from infected mice. Although the basal level of AP-1 activity is comparable in cells from uninfected and infected mice, mitogen-induced AP-1 activation is absent in the cells from T. cruzi-infected mice. Sodium deoxycholate treatment slightly enhances NF-kappa B-binding activity in splenocyte nuclear and whole-cell extracts from infected mice, suggesting that a blockage of the activation of NF-kappa B is only partially responsible for the decrease in the level of NF-kappa B in T cells from T. cruzi-infected mice. These data identify the molecular basis of IL-2 gene regulation in T. cruzi infection and suggest that T cells are anergized as a result of the infection.

Multiple closely-linked NFAT/octamer and HMG I(Y) binding sites are part of the interleukin-4 promoter

We show here that the immediate upstream region (from position -12 to -270) of the murine interleukin 4 (Il-4) gene harbors a strong cell-type specific transcriptional enhancer. In T lymphoma cells, the activity of the Il-4 promoter/enhancer is stimulated by phorbol esters, Ca++ ionophores and agonists of protein kinase A and inhibited by low doses of the immunosuppressant cyclosporin A. The Il-4 promoter/enhancer is transcriptionally inactive in B lymphoma cells and HeLa cells. DNase I footprint protection experiments revealed six sites of the Il-4 promoter/enhancer to be bound by nuclear proteins from lymphoid and myeloid cells. Among them are four purine boxes which have been described to be important sequence motifs of the Il-2 promoter. They contain the motif GGAAA and are recognized by the inducible and cyclosporin A-sensitive transcription factor NFAT-1. Three of the Il-4 NFAT-1 sites are closely linked to weak binding sites of Octamer factors. Several purine boxes and an AT-rich protein-binding site of the Il-4 promoter are also recognized by the high mobility group protein HMG I(Y). Whereas the binding of NFAT-1 and Octamer factors enhance the activity of the Il-4 promoter, the binding of HMG I(Y) suppresses its activity and, therefore, appears to be involved in the suppression of Il-4 transcription in resting T lymphocytes.

Differential expression of four members of the POU family of proteins in activated and phorbol 12-myristate 13-acetate-treated Jurkat T cells

The POU family of proteins binds specifically to octamer DNA motifs present in the promoters of several genes and regulates their expression. We identified the presence of four members of the POU family of proteins, Oct-1, Oct-2, Oct-T1, and Oct-T2, in the human T-cell line Jurkat. To obtain insight into the physiological role played by these proteins in T cells, we studied the time course of expression of these genes in resting, activated, and phorbol 12-myristate 13-acetate (PMA)-treated cells. The expression of the gene encoding Oct-1 (now assigned the name OTF1 for octamer-binding transcription factor 1) remained unchanged and the levels of Oct-T2 mRNA decreased with increasing time of incubation to undetectable amounts in all three states of T-cell growth. The levels of Oct-2 mRNA and protein were increased in activated cells, were increased to a lesser extent in the PMA-treated cells, and were undetectable in resting cells. The levels of the Oct-T1 transcripts increased dramatically in PMA-treated cells but not in resting or activated cells. Sequence analysis of the Oct-T1 cDNA showed an open reading frame coding for a POU domain-containing protein of 42.7 kDa. Transient transfection of the gene encoding Oct-T1 decreased the activity of the interleukin 2 gene promoter in activated Jurkat cells. Further, there is evidence for an additional octamer-binding protein, Oct-T3, in Jurkat T cells.

Delta-crystallin enhancer binding protein delta EF1 is a zinc finger-homeodomain protein implicated in postgastrulation embryogenesis

We investigated nuclear factors that bind to delta 1-crystallin enhancer core and regulate lens-specific transcription. A nuclear factor delta EF1, which binds to the essential element of the delta 1-crystallin enhancer core, was molecularly cloned from the chicken by a southwestern method. The protein organization of delta EF1 deduced from the cDNA sequence indicated that it has heterogeneous domains for DNA-binding, two widely separated zinc fingers and a homeodomain, analogous to Drosophila ZFH-1 protein. The C-terminal zinc fingers were found to be responsible for binding to the delta 1-crystallin enhancer core sequence. delta EF1 had proline-rich and acidic domains common to various transcriptional activators. During embryogenesis, delta EF1 expression was observed in the postgastrulation period in mesodermal tissues; initially, in the notochord, followed by somites, nephrotomes and other components. The expression level changed dynamically in a tissue, possibly reflecting the differentiation states of the constituent cells. Besides mesoderm, delta EF1 was expressed in the nervous system and the lens, but other ectodermal tissues and endoderm remained very low in delta EF1 expression. Cotransfection experiments indicated that this factor acts as a repressor of delta 1-crystallin enhancer. Possession of heterogeneous DNA-binding domains and its dynamic change of expression in embryogenesis strongly suggest that delta EF1 acts in multiple ways depending on the cell type and the gene under its regulation.

Distinct nuclear proteins competing for an overlapping sequence of cyclic adenosine monophosphate and negative regulatory elements regulate tissue-specific mouse renin gene expression

The mouse renin locus (Ren-1d) exhibits specific patterns of tissue expression. It is expressed in kidney but not submandibular gland (SMG). This locus contains a negative regulatory element (NRE) and a cAMP responsive element (CRE) that share an overlapping sequence. In the kidney, CRE binding proteins (CREB) and NRE binding proteins (NREB) compete for binding to this sequence, with the CREB having a greater affinity. In the SMG, CREB is inactivated by an inhibitory protein, permitting NREB to bind to the sequence, thus inhibiting Ren-1d expression. We hypothesize that the competition between NREB and CREB for this sequence governs tissue-specific expression of mouse renin. We speculate that this may be a general paradigm that determines tissue-specific gene expression.

Occurrence of a silencer of the interleukin-2 gene in naive but not in memory resting T helper lymphocytes

In the immune system the first activation of a naive T cell by antigen is a key step in the shaping of the peripheral T cell specificity repertoire and maintenance of self-tolerance. In the present study, analysis of the interleukin-2 (IL-2) gene activation shows that naive human helper T cells (cord blood CD4+ T cells, adult CD4+CD45RO- T cells) regulate IL-2 transcription by a mechanism involving both a silencer and an activator acting on the purine-rich IL-2 promoter elements (NF-AT binding sites). By contrast, memory cells, either in vitro activated helper T cells reverting to a resting state, or CD4+ T (memory) clones, or CD4+CD45RO+ T cells isolated ex vivo, no longer have a silencer. Their IL-2 transcription seems to be controlled solely by the transition from inactive to active functional state of a positive transcription factor binding to these promoter elements as well as its cytoplasmic or nuclear location: in resting memory T cells the activator is located in the cytoplasm and is inactive, whereas in stimulated cells it is functional in promoting transcription and now resides in the nucleus. Thus, the regulation of the gene coding for the main T cell growth factor changes irreversibly after the first encounter of T cells with antigen. It is most likely that the presence of a silencer contributes to the more stringent activation requirements of naive CD4+ T cells.

Molecular basis of a multiple lymphokine deficiency in a patient with severe combined immunodeficiency

We have previously reported that the T lymphocytes of a child with severe combined immunodeficiency are defective in the transcription of several lymphokine genes that include IL2, IL3, IL4, and IL5, which encode interleukins 2, 3, 4, and 5 (IL-2, -3, -4, and -5). To determine whether the defect in the patient's T lymphocytes involved a trans-acting factor common to the affected lymphokine genes, we examined the ability of nuclear factors from the patient's T lymphocytes to bind response elements present in the regulatory region of IL2. Nuclear factor NF-kB, activation protein 1 (AP-1), OCT-1, and NF-IL-2B binding activity were normal. In contrast, the binding of the nuclear factor of activated T cells (NF-AT) to its response element in the IL2 enhancer and to an NF-AT-like response element present in the IL4 enhancer was abnormal. To ascertain whether the abnormal NF-AT binding activity was related to an impaired function, we transfected patient and control T lymphocytes with constructs containing the reporter gene encoding chloramphenicol acetyl transferase (CAT) under the control of the entire IL2 regulatory region or of multimers of individual enhancer sequences. CAT expression directed by the IL2 regulatory region or by a multimer of the NF-AT-binding site was markedly lower in the patient relative to controls. In contrast, CAT gene expression directed by a multimer of the OCT-1 proximal (OCT-1p)-binding site was equivalent in patient and controls. These results indicate that an abnormality of/or influencing NF-AT may underlie the multiple lymphokine deficiency in this patient.

Negative transcriptional regulation of human interleukin 2 (IL-2) gene by glucocorticoids through interference with nuclear transcription factors AP-1 and NF-AT

IL-2 gene transcription is affected by several nuclear proteins. We asked whether dexamethasone (Dex) and cyclosporin A (CsA) inhibit IL-2 gene transcription by interfering with the activity of nuclear proteins that bind to the IL-2 promoter. Nuclear extracts from primary human T lymphocytes were analyzed by electrophoretic DNA mobility shift assays. Both Dex and CsA inhibited the binding of transcription factors AP-1 and NF-AT, but not of NF-kB and OCT-1/OAF, to their corresponding sites on the IL-2 gene promoter. To correlate changes in nuclear factor binding in vitro with transcriptional activity in vivo and define the structural requirements for IL-2 promoter repression, we used transient DNA transfections. Jurkat cells were transfected with plasmids containing either the intact IL-2 promoter or its AP-1, NF-AT, and NF-kB motifs. Dex inhibited the IL-2 promoter and the AP-1, but not the NF-AT and NF-kB plasmids. In contrast, CsA inhibited the IL-2 promoter and the NF-AT, but not the AP-1 and NF-kB plasmids. These results suggest that in human T lymphocytes both Dex and CsA inhibited IL-2 gene transcription through interference with transcription factors AP-1 and NF-AT. We propose that, while maximum inhibition may involve interaction with both transcription factors, AP-1 is the primary target of Dex.

Accessory cell-derived signals required for T cell activation

Various populations of accessory cells differ in their abilities to function as effective antigen-presenting cells (APC) and stimulate CD4+ T cells to produce interleukin-2. Three important factors directly related to APC potency are the expression of class II major histocompatibility complex molecules and the ability to present peptide antigens to the T cell antigen receptor, the expression of costimulatory ligands which deliver important activation signals independent of T cell receptor occupancy and the expression of adhesion molecules which promote conjugate formation so that these activation signals can be effectively delivered to the T cells. The relative importance of these accessory cell functions in T cell activation will be discussed, with an emphasis on costimulation and the CD28/B7 receptor/ligand pair. The consequence of inadequate costimulation by an otherwise effective APC in inducing T cell anergy will also be discussed.

Genetic evidence that an activation domain of GAL4 does not require acidity and may form a beta sheet

Regulation of gene expression in eukaryotes relies on intricate protein-protein interactions. Transcription of the galactose genes in yeast has been a productive model for this type of interaction. The positive activator in this system, GAL4, has a bifunctional C-terminus. It contains both a prototypic acidic activation domain and a region that binds the negative regulator, GAL80. We have taken advantage of this colocalization of functions to subject the region to a constrained mutagenesis analysis: one function was maintained, while the other one was altered. This analysis and the experiments it suggested have led us to two conclusions: first, the acidic amino acids are not, as commonly thought, required for activation; second, this region is not unstructured or alpha helical, but its function may require a beta sheet.

A novel 7-nucleotide motif located in 3' untranslated sequences of the immediate-early gene set mediates platelet-derived growth factor induction of the JE gene

A cohort of the serum and growth factor regulated immediate-early gene set is induced with slower kinetics than c-fos. Two of the first immediate-early genes characterized as such, c-myc and JE, are contained within this subset. cis-acting genomic elements mediating induction of the slower responding subset of immediate-early genes have never been characterized. Herein we characterize two widely separated genomic elements which are together essential for induction of the murine JE gene by platelet-derived growth factor, serum, interleukin-1, and double-stranded RNA. One of these elements is novel in several regards. It is a 7-mer, TTTTGTA, found in the proximal 3' sequences downstream of the JE stop codon. The 3' element is position dependent and orientation independent. It does not function in polyadenylation, splicing, or destabilization of the JE transcript. Copies of the 7-mer or its inverse are found at comparable 3' sites in 25 immediate-early genes that encode transcription factors or cytokines. Given its general occurrence, the 7-mer may be a required cis-acting control element mediating induction of the immediate-early gene set.

A novel 7-nucleotide motif located in 3' untranslated sequences of the immediate-early gene set mediates platelet-derived growth factor induction of the JE gene

A cohort of the serum and growth factor regulated immediate-early gene set is induced with slower kinetics than c-fos. Two of the first immediate-early genes characterized as such, c-myc and JE, are contained within this subset. cis-acting genomic elements mediating induction of the slower responding subset of immediate-early genes have never been characterized. Herein we characterize two widely separated genomic elements which are together essential for induction of the murine JE gene by platelet-derived growth factor, serum, interleukin-1, and double-stranded RNA. One of these elements is novel in several regards. It is a 7-mer, TTTTGTA, found in the proximal 3' sequences downstream of the JE stop codon. The 3' element is position dependent and orientation independent. It does not function in polyadenylation, splicing, or destabilization of the JE transcript. Copies of the 7-mer or its inverse are found at comparable 3' sites in 25 immediate-early genes that encode transcription factors or cytokines. Given its general occurrence, the 7-mer may be a required cis-acting control element mediating induction of the immediate-early gene set.

Inhibition or activation of human T cell receptor transfectants is controlled by defined, soluble antigen arrays

We present evidence that direct T cell receptor (TCR) occupancy by antigen can either activate or inhibit T cells, depending upon whether or not a threshold number of local TCRs are crosslinked by multivalent arrays of the antigen. Variants of Jurkat cells were previously transfected with TCR alpha and beta chains that bind fluorescein, yielding FL-TCR+ human T cells. The transfectants are activated upon binding soluble multivalent antigen arrays at concentrations well below those required for monovalent interactions. This activation, measured by calcium fluxes and interleukin 2 (IL-2) production, indicates the superior binding avidity of multivalent ligands. Smaller, less multivalent arrays do not activate the cells, but antagonize larger arrays, demonstrating that antigen can bind TCR as either agonist or antagonist. The balance between activation and inhibition depends upon antigen array size, ligand valence, and concentration, indicating that a threshold extent of receptor crosslinking, and not individual perturbations of single TCR, is required for activation by antigen. Approximately 100 stimulatory arrays specifically bind per FL-TCR+ cell at concentrations where IL-2 production is half-maximal.

The TCF8 gene encoding a zinc finger protein (Nil-2-a) resides on human chromosome 10p11.2

The TCF8 gene encodes a zinc finger protein (Nil-2-a). Nil-2-a inhibits T-lymphocyte-specific interleukin 2 (IL2) gene expression by binding to a negative regulatory domain 100 nucleotides 5' of the IL2 transcription start site. Southern hybridization and somatic cell hybrids are used to demonstrate that the murine and human genomes contain related genes for Nil-2-a. TCF8 resides on human chromosome 10. Fluorescent in situ hybridization is employed to localize TCF8 to 10p11.2.