A T cell-specific transcriptional enhancer within the human T cell receptor delta locus

Murine and human T-lymphocyte GATA-3 factors mediate transcription through a cis-regulatory element within the human T-cell receptor delta gene enhancer

A family of transcriptional activators has recently been identified in chickens; these transcriptional activators recognize a common consensus motif (WGATAR) through a conserved C4 zinc finger DNA-binding domain. One of the members of this multigene family, cGATA-3, is most abundantly expressed in the T-lymphocyte cell lineage. Analysis of human and murine GATA-3 factors shows a striking degree of amino acid sequence identity and similar patterns of tissue specificity of expression in these three organisms. The murine and human factors are abundantly expressed in a variety of human and murine T-cell lines and can activate transcription through a tissue-specific GATA-binding site identified within the human T-cell receptor delta gene enhancer. We infer that the murine and human GATA-3 proteins play a central and highly conserved role in vertebrate T-cell-specific transcriptional regulation.

A thymus-specific member of the HMG protein family regulates the human T cell receptor C alpha enhancer

The human T cell-specific transcription factor TCF-1 alpha plays a key role in the tissue-specific activation of the T cell receptor (TCR) C alpha enhancer and binds to pyrimidine-rich elements (5'-PyCTTTG-3') present in a variety of other T cell-specific control regions. Using amino acid sequence information derived from the DNA affinity-purified protein, we have now isolated cDNA clones encoding TCF-1 alpha. The TCF-1 alpha cDNA contains a single 68-amino-acid domain that is homologous to a region conserved among high-mobility group (HMG) and nonhistone chromosomal proteins. Expression of full-length and mutant cDNA clones in bacteria reveal that the single HMG motif, which is predicted to contain two extended alpha-helical segments, is sufficient to direct the sequence-specific binding of TCF-1 alpha to DNA. Northern blot experiments demonstrate further that TCF-1 alpha mRNA is highly tissue specific, found primarily in the thymus or T cell lines. The immature CEM T cell line expresses relatively low levels of TCF-1 alpha mRNA, which are increased upon activation of these cells by phorbol esters. Interestingly, the cloned TCF-1 alpha protein is a potent transcriptional activator of the human TCR alpha enhancer in nonlymphoid cell lines, whereas the activity of the endogenous protein in T cell lines is strongly dependent on an additional T cell-specific protein that interacts with the core enhancer. TCF-1 alpha is currently unique among the newly emerging family of DNA-binding regulatory proteins that share the HMG motif in that it is a highly tissue-specific RNA polymerase II transcription factor.

Regulation of the early stages of T-cell development

During the past year, there have been rapid advances in our understanding of the early events of T-cell development, at the molecular level. Studies at the transcriptional level of T-cell receptor gene regulation have started to yield important clues about how different T-cell-specific genes can share the same transcription factors and how alpha beta and gamma delta T cells are differentially regulated. In addition, studies using transgenic mice with the T-cell receptor gamma delta genes have further strengthened the separate lineage model of alpha beta and gamma delta T cells and brought into play the importance of negative cis-regulatory elements for lineage-specific determination.

Identification of a T-cell-specific enhancer at the locus encoding T-cell antigen receptor gamma chain

The gamma delta and alpha beta T-cell antigen receptor (TCR) heterodimers are expressed in a lineage-specific, mutually exclusive manner. Regulation of expression occurs at the transcriptional level. A 13-kilobase (kb) stretch of DNA encompassing variable-joining-constant segments V gamma 4-J gamma 1-C gamma 1 of the murine gamma-chain gene was examined for the presence of transcriptional enhancing elements by a transient transfection assay. DNA fragments from this region were inserted into a test plasmid containing a heterologous promoter fused to the human growth hormone gene. An 1800-base-pair (bp) fragment located 3 kb 3' to C gamma exon III was found to display enhancing activity in several T-cell lines. Maximum enhancing activity could be localized further to fragments as small as 400 bp in some cell lines. Nucleotide sequence analysis of this 400-bp segment revealed homologies to previously described core enhancer elements and to other TCR gene enhancers. The TCR gamma-chain gene enhancer is active in both gamma delta and alpha beta T cells, indicating that it is not primarily responsible for lineage-specificity of expression, but it is inactive in non-T-cells.

A transcriptional enhancer of the mouse T cell receptor delta gene locus

T cells express receptors for antigen on their surface (TcR) which consists either of alpha/beta or of gamma/delta polypeptide chains. Since the TcR delta chain gene is located within the TcR alpha chain gene locus, strict regulation of expression of the region must operate to ensure that the two loci are not concomitantly expressed in T cells bearing either alpha/beta or gamma/delta TcR. In this report it is demonstrated that elements within the mouse TcR delta gene locus, located between the J delta 2 and C delta exons, enhance transcription from a heterologous promoter five- to tenfold in a T cell hybridoma expressing a TcR gamma/delta, whereas enhancement was only twofold in an alpha/beta-bearing T cell hybridoma. No enhancement of expression was observed in a B cell hybridoma. The sequences responsible for this enhancing activity are largely confined to a 766-bp Hae III DNA restriction fragment. A region within this DNA segment shows significant homology (73% identify) to a recently identified enhancer of the human TcR delta gene locus.

Recombinative events of the T cell antigen receptor delta gene in peripheral T cell lymphomas

Recombinative events of the T cell antigen receptor (TCR) delta-chain gene were studied in 37 cases of peripheral T cell lymphoma (PTCL) and related to their clinical presentation and the expression of the alpha beta or gamma delta heterodimers as determined by immunostaining of frozen tissue samples. There were 22 cases of alpha beta, 5 cases of gamma delta, and 10 cases of silent TCR expressing neither the alpha beta nor gamma delta TCR. 5 different probes were used to examine the delta locus. The 22 cases of alpha beta PTCL displayed biallelic and monoallelic deletions; a monoallelic V delta 1 J delta 1 rearrangement was observed in 1 case and a monoallelic germ line configuration in 7 cases. The 5 cases of gamma delta PTCL displayed biallelic rearrangements: the productive rearrangements could be ascribed to V delta 1J delta 1 joining in 3 cases and VJ delta 1 joining in 2 cases according to the combined pattern of DNA hybridization with the appropriate probes and of cell reactivity with the TCR delta-1, delta TCS-1, and anti-V delta 2 monoclonal antibodies. In the VJ delta 1 joining, the rearranged V segments were located between V delta 1 and V delta 2. Interestingly, in the third group of 10 cases of silent PTCL, 5 cases were found to have a TCR gene configuration identical to that in the TCR alpha beta PTCL, as demonstrated by biallelic delta gene deletion. These 5 cases were CD3 positive. The 5 remaining cases showed a monoallelic delta gene rearrangement with a monoallelic germ line configuration in 4 and a monoallelic deletion in 1. Four of these cases were CD3 negative, which was consistent with an immature genotype the TCR commitent of which could not be ascertained. Finally, TCR gamma delta PTCL consisted of a distinct clinical morphological and molecular entity whereas TCR alpha beta and silent PTCL had a similar presentation.

Identification of a T-cell-specific transcriptional enhancer located 3' of C gamma 1 in the murine T-cell receptor gamma locus

A transcriptional enhancer element has been localized 3 kilobases 3' of the murine T-cell receptor C gamma 1 locus using a chloramphenicol acetyltransferase reporter gene construct. As a monomer the enhancer functions only in PEER gamma delta cells and Jurkat alpha beta cells of the T-cell lines tested. However, a tetramer of the enhancer functions in virtually all T-cell lines tested, including alpha beta T-cell lines, but not in other cell types. These results suggest that elements other than the enhancer are responsible for the failure of rearranged C gamma 1 genes to be expressed in alpha beta T cells. The enhancer has been localized to a 200-base-pair Rsa I restriction fragment, which contains sequence motifs similar to those found in the other T-cell receptor enhancers but not in the immunoglobulin enhancers.

The SCL gene is formed from a transcriptionally complex locus

We describe the structural organization of the human SCL gene, a helix-loop-helix family member which we believe plays a fundamental role in hematopoietic differentiation. The SCL locus is composed of eight exons distributed over 16 kb. SCL shows a pattern of expression quite restricted to early hematopoietic tissues, although in malignant states expression of the gene may be somewhat extended into later developmental stages. A detailed analysis of the transcript(s) arising from the SCL locus revealed that (i) the 5' noncoding portion of the SCL transcript, which resides within a CpG island, has a complex pattern of alternative exon utilization as well as two distinct transcription initiation sites; (ii) the 5' portions of the SCL transcript contain features that suggest a possible regulatory role for these segments; (iii) the pattern of utilization of the 5' exons is cell lineage dependent; and (iv) all of the currently studied chromosomal aberrations that affect the SCL locus either structurally or functionally eliminate the normal 5' transcription initiation sites. These data suggest that the SCL gene, and specifically its 5' region, may be a target for regulatory interactions during early hematopoietic development.

Identification and functional analysis of the transcriptional enhancer of the human T cell receptor beta gene

The productive rearrangement and transcription of T cell receptor (TcR) beta genes is confined to T lymphocytes and is subject to both tissue-specific and developmental regulation. In addition to their function in transcriptional control, cis-acting elements are likely to play a role in the regulation of the rearrangement process. In this report we describe the location of a strong and inducible transcriptional enhancer 3' to the human TcR C beta 2 gene segment. The core enhancer, defined by deletion analysis using a transient transfection assay, resided within 362 bp of DNA. This enhancer core was able to activate transcription from a heterologous promoter and functioned well in T and B lymphocytes, but only minimally in HeLa cells. In contrast, a longer fragment containing the enhancer core showed marked T cell specificity. The enhancer was highly inducible by phorbol esters, the molecular basis for the inducibility residing within a 118-bp region of the enhancer core. This inducibility may be important in modulation of TcR beta gene expression during T cell differentiation and/or activation.

The SCL gene is formed from a transcriptionally complex locus

We describe the structural organization of the human SCL gene, a helix-loop-helix family member which we believe plays a fundamental role in hematopoietic differentiation. The SCL locus is composed of eight exons distributed over 16 kb. SCL shows a pattern of expression quite restricted to early hematopoietic tissues, although in malignant states expression of the gene may be somewhat extended into later developmental stages. A detailed analysis of the transcript(s) arising from the SCL locus revealed that (i) the 5' noncoding portion of the SCL transcript, which resides within a CpG island, has a complex pattern of alternative exon utilization as well as two distinct transcription initiation sites; (ii) the 5' portions of the SCL transcript contain features that suggest a possible regulatory role for these segments; (iii) the pattern of utilization of the 5' exons is cell lineage dependent; and (iv) all of the currently studied chromosomal aberrations that affect the SCL locus either structurally or functionally eliminate the normal 5' transcription initiation sites. These data suggest that the SCL gene, and specifically its 5' region, may be a target for regulatory interactions during early hematopoietic development.

Differences and similarities in DNA-binding preferences of MyoD and E2A protein complexes revealed by binding site selection

A technique was developed for studying protein-DNA recognition that can be applied to any purified protein, partially purified protein, or cloned gene. From oligonucleotides in which particular positions are of random sequence, that subset to which a given protein binds is amplified by the polymerase chain reaction and sequenced as a pool. These selected and amplified binding site (SAAB) "imprints" provide a characteristic set of preferred sequences for protein binding. With this technique, it was shown that homo- and heterooligomers of the helix-loop-helix proteins MyoD and E2A recognize a common consensus sequence, CA--TG, but otherwise bind to flanking and internal positions with different sequence preferences that suggest half-site recognition. These findings suggest that different combinations of dimeric proteins can have different binding sequence preferences.

Identification and functional characterization of the human T-cell receptor beta gene transcriptional enhancer: common nuclear proteins interact with the transcriptional regulatory elements of the T-cell receptor alpha and beta genes

A transcriptional enhancer has been mapped to a region 5.5 kilobases 3' of the C beta 2 gene in the human T-cell receptor (TCR) beta-chain locus. Transient transfections allowed localization of enhancer activity to a 480-base-pair HincII-XbaI restriction enzyme fragment. The TCR beta enhancer was active on both the minimal simian virus 40 promoter and a TCR beta variable gene promoter in both TCR alpha/beta + and TCR gamma/delta + T cells. It displayed significantly less activity in Epstein-Barr virus-transformed B cells and K562 chronic myelogenous leukemia cells and no activity in HeLa fibroblasts. DNA sequence analysis revealed that the enhancer contains a consensus immunoglobulin kappa E2 motif, as well as an AP-1-binding site and a cyclic AMP response element. DNase I footprint analyses using Jurkat T-cell nuclear extracts allowed the identification of five nuclear protein-binding sites, T beta 1 to T beta 5, within the enhancer element. Deletion and in vitro mutagenesis studies demonstrated that the T beta 2- and T beta 3- and T beta 4-binding sites are each required for full transcriptional enhancer activity. In contrast, deletion of the T beta 1- and T beta 5-binding sites had essentially no effect on enhancer function. Electrophoretic mobility shift assays demonstrated that TCR alpha/beta + and TCR gamma/delta + T cells expressed T beta 2-, T beta 3-, and T beta 4-binding activities. In contrast, non-T-cell lines, in which the enhancer was inactive, each lacked expression of at least one of these binding activities. TCR alpha and beta gene expression may be regulated by a common set of T-cell nuclear proteins in that the T beta 2 element binding a set of cyclic AMP response element-binding proteins that are also bound by the T alpha 1 element of the human TCR alpha enhancer and the decamer element present in a large number of human and murine TCR beta promoters. Similarly, the T beta 5 TCR beta-enhancer element and the T alpha 2 TCR alpha-enhancer element bind at least one common T-cell nuclear protein. Taken together, these results suggest that TCR beta gene expression is regulated by the interaction of multiple T cell nuclear proteins with a transcriptional enhancer element located 3' of the C beta 2 gene and that some of these proteins may be involved in the coordinate regulation of TCR alpha and beta gene expression.

Activity and tissue-specific expression of the transcription factor NF-E1 multigene family

NF-E1, a DNA-binding protein that recognizes the general consensus motif WGATAR, is the first tissue-specific factor to be identified in erythroid cells. Using a probe from the murine GF-1 (NF-E1) cDNA clone, we isolated three homologous chicken cDNAs: One of these corresponds to an mRNA (NF-E1a) that is abundantly and exclusively expressed in erythroid cells; a second mRNA (NF-E1b) is also expressed in all developmental stages of erythroid cells but is additionally found in a limited subset of other chicken tissues; mRNA representative of a third gene (NF-E1c) is expressed only in definitive (adult) erythrocytes within the red cell lineage but is also abundantly expressed in T lymphocytes and brain. All NF-E1 proteins are highly conserved within the DNA-binding domain and bind to the consensus motif with similar affinities in vitro; they are also all stimulatory trans-acting factors in vivo. The factors differ quantitatively in their ability to trans-activate reporter genes in which the number and position of cognate binding sites is varied relative to the transcriptional initiation site. These data suggest that the NF-E1 consensus motif directs a broader and more complicated array of developmental transcriptional regulatory processes than has been assumed and that NF-E1c may play a unique regulatory role in the developing chicken brain and in T lymphocytes.

Identification and functional characterization of the human T-cell receptor beta gene transcriptional enhancer: common nuclear proteins interact with the transcriptional regulatory elements of the T-cell receptor alpha and beta genes

A transcriptional enhancer has been mapped to a region 5.5 kilobases 3' of the C beta 2 gene in the human T-cell receptor (TCR) beta-chain locus. Transient transfections allowed localization of enhancer activity to a 480-base-pair HincII-XbaI restriction enzyme fragment. The TCR beta enhancer was active on both the minimal simian virus 40 promoter and a TCR beta variable gene promoter in both TCR alpha/beta + and TCR gamma/delta + T cells. It displayed significantly less activity in Epstein-Barr virus-transformed B cells and K562 chronic myelogenous leukemia cells and no activity in HeLa fibroblasts. DNA sequence analysis revealed that the enhancer contains a consensus immunoglobulin kappa E2 motif, as well as an AP-1-binding site and a cyclic AMP response element. DNase I footprint analyses using Jurkat T-cell nuclear extracts allowed the identification of five nuclear protein-binding sites, T beta 1 to T beta 5, within the enhancer element. Deletion and in vitro mutagenesis studies demonstrated that the T beta 2- and T beta 3- and T beta 4-binding sites are each required for full transcriptional enhancer activity. In contrast, deletion of the T beta 1- and T beta 5-binding sites had essentially no effect on enhancer function. Electrophoretic mobility shift assays demonstrated that TCR alpha/beta + and TCR gamma/delta + T cells expressed T beta 2-, T beta 3-, and T beta 4-binding activities. In contrast, non-T-cell lines, in which the enhancer was inactive, each lacked expression of at least one of these binding activities. TCR alpha and beta gene expression may be regulated by a common set of T-cell nuclear proteins in that the T beta 2 element binding a set of cyclic AMP response element-binding proteins that are also bound by the T alpha 1 element of the human TCR alpha enhancer and the decamer element present in a large number of human and murine TCR beta promoters. Similarly, the T beta 5 TCR beta-enhancer element and the T alpha 2 TCR alpha-enhancer element bind at least one common T-cell nuclear protein. Taken together, these results suggest that TCR beta gene expression is regulated by the interaction of multiple T cell nuclear proteins with a transcriptional enhancer element located 3' of the C beta 2 gene and that some of these proteins may be involved in the coordinate regulation of TCR alpha and beta gene expression.