Molecular organization of the human CD3 gene family on chromosome 11q23

Characterization of the region involved in CD3 pairwise interactions within the T cell receptor complex

Assembly of the six-chain T cell antigen receptor-CD3 complex takes place by pairwise interactions. Thus, CD3-epsilon interacts with either CD3-gamma or CD3-delta, and these dimers then associate with the TCR heterodimer (alpha.beta or gamma.delta) and the CD3-zeta homodimer to constitute a full complex. We have now mapped the site in CD3-epsilon responsible for the interaction with CD3-gamma and CD3-delta by analysis of a series of deletional mutants encompassing the most conserved regions. We found that the highly conserved juxtamembrane domain is mainly responsible for the interaction. Thus, deletion of this 16-amino acid extracellular sequence resulted in the inhibition of up to 95% of the CD3-epsilon/gamma interaction. A highly conserved sequence is also present in both CD3-gamma and CD3-delta, suggesting that the domain in these two chains may reciprocally be involved in the interaction with CD3-epsilon. Indeed, an immobilized synthetic peptide corresponding to the CD3-gamma sequence specifically associated to a bacterially expressed CD3-epsilon protein, suggesting the 16-amino acid domain is sufficient to promote CD3-epsilon/CD3-gamma assembly. The conservation of the motif in the CD3 chains suggest that, in addition to CD3-epsilon/CD3-gamma and CD3-epsilon/CD3-delta interactions, it may also mediate homotypic interactions. Indeed, it is shown that it mediates the formation of disulfide-linked homodimers and that the formation of homo- and heterodimers are mutually excluded. Finally, this domain contains a Cys-X-X-Cys sequence that resembles that of p56(lck), which is responsible for the interaction with the cytoplasmic tails of CD4 and CD8. Since the replacement of the two cysteines (Cys97 and Cys100) in CD3-epsilon by alanines strongly inhibited pair formation, the existence of a Cys-X-X-Cys motif involved in protein-protein interactions is suggested.

Possible association of CD3 and CD4 polymorphisms with insulin-dependent diabetes mellitus (IDDM)

Population and family studies show that predisposition to type I diabetes (IDDM) is multifactorial, and that polymorphisms in the MHC region contribute substantially to the susceptibility to IDDM. In the present study the association of polymorphisms in the CD4 and the delta subunit of CD3 with IDDM were examined in a Belgian population. We observed that the frequency of the CD A4/A4 genotype and of the CD3 91 allele were significantly increased P = 0.0077) and decreased (P = 3.8 x 10(-5), respectively, in IDDM compared with controls. These results therefore suggest that CD4, CD3 or neighbouring genes might contribute to IDDM susceptibility. These results are, however, preliminary and cannot be considered as established until re-tested in a new population.

Structure and linkage of the D2 dopamine receptor and neural cell adhesion molecule genes on human chromosome 11q23

The gene encoding the D2 dopamine receptor (DRD2) is located on human chromosome 11q23 and has been circumstantially associated with a number of human disorders including Parkinson's disease, schizophrenia, and susceptibility to alcoholism. To determine the physical structure of the DRD2 gene, we utilized cosmid cloning, isolation of yeast artificial chromosomes (YACs), and pulsed-field gel electrophoresis to construct a long-range physical map of human chromosome 11q23 linking the genes for the DRD2 and neural cell adhesion molecule (NCAM). The D2 dopamine receptor gene extends over 270 kb and includes an intron of approximately 250 kb separating the putative first exon from the exons encoding the receptor protein. The resulting physical map spans more than 1.5 mb of chromosome band 11q23 and links the DRD2 gene with the gene encoding the NCAM located 150 kb 3' of the DRD2 gene and transcribed from the same DNA strand. We additionally located the sites of at least four hypomethylated HTF islands within the physical map, which potentially indicate the sites of additional genes. High-resolution fluorescent in situ suppression hybridization using cosmid and YAC clones localized this gene cluster between the ApoAI and STMY loci at the interface of bands 11q22.3 and 11q23.1.

Molecular cloning and analysis of chromosome band 11q23 involved in leukaemia-associated translocations

Three overlapping yeast artificial chromosomes (YACs) spanning a 780 kb region of DNA around the CD3 locus on chromosome 11 have been isolated and characterised. The individual cloned regions have been mapped by in situ hybridisation to chromosome band 11q23, and a restriction enzyme map of this region has been constructed. The positions of these clones in relation to a series of leukaemia-associated chromosomal translocations has also been determined. It was concluded that, although two clones lay entirely proximal to the breakpoints examined, the third clone (13HH4) encompassed the breakpoints for the translocations t(4;11), t(6;11), and t(9;11). The t(9;11) was observed in an acute myeloid leukaemia in a patient previously treated for an unrelated malignancy. It would thus appear that the breakpoints at chromosome band 11q23 occurring in therapy-related leukaemias are in the same region as those found in adult and childhood acute leukaemias and may result from a common underlying mechanism.

A trithorax-like gene is interrupted by chromosome 11q23 translocations in acute leukaemias

Some acute lymphocytic leukaemias, particularly those in young children, are associated with a t(4;11)(q21;q23) reciprocal translocation. We have cloned the translocation breakpoint on chromosome 11q23 and isolated corresponding RNA transcripts from this region. The translocation occurs within a cluster of Alu repetitive elements located within an intron of a gene that gives rise to 11.5 (kb) transcript spanning the translocation breakpoint. The 11.5 kb transcript encodes a protein that is highly homologous to the Drosophila trithorax gene, a developmental regulator. An analysis of a series of leukaemic patients carrying t(4;11) and t(9;11) translocations indicate that the majority of breakpoints in infant leukaemias lie within a 5 kb region.

Somatic cell mapping of T-cell receptor CD3 complex and CD8 genes in cattle

Bovine genes encoding T-cell receptor, CD3, and CD8 molecules have been mapped to syntenic groups using bovine x rodent hybrid somatic cells. T-cell receptor alpha and delta chains were assigned to bovine syntenic group U5, and the beta and gamma genes were syntenic with each other and with markers on U13. CD3E and CD3D genes were syntenic with each other and located to bovine syntenic group U19. CD8 was most concordant with markers of syntenic group U16, although the concordancy was only 85% and the assignment must be regarded as tentative. The comparative gene maps of human chromosome 7, bovine syntenic group U13, and mouse chromosomes 6 and 13 suggest extensive evolutionary conservation.

Genetic linkage analysis and homology relationships of genes located on human chromosome 11q

We have used DNA polymorphisms detected by probes for 11q to order 16 genes and to determine the genetic distances between them. Our map includes the genes for CD20, tyrosinase, progesterone receptor, stromelysin, collagenase, N-CAM, dopamine-D2 receptor, apolipoproteins AI-CIII-AIV, CD3-epsilon, -delta, and -gamma, porphobilinogen deaminase, thy-1, and ets-1. These genes have previously been sequenced as well as placed on the 11q cytogenetic map, which now makes them anchor points between the cytogenetic, genetic, and physical maps of this region. The ordering and distances between these genes are of immediate use in testing hypotheses of candidate genes for human genetic diseases associated with chromosome 11q. A comparison between our genetic map and similar maps from other species defines regions of homologous synteny that may be useful in mapping human genetic disease genes localized to the 11q region. Analysis of such homology provides additional bases for speculation of the evolutionary histories of gene families in this region.

The CD3-gamma and CD3-delta subunits of the T cell antigen receptor can be expressed within distinct functional TCR/CD3 complexes

The T cell receptor for antigen (TCR) consists of two glycoproteins containing variable regions (TCR-alpha/beta or TCR-gamma/delta) which are expressed on the cell surface in association with at least four invariant proteins (CD3-gamma, -delta, -epsilon and -zeta). CD3-gamma and CD3-delta chains are highly homologous, especially in the cytoplasmic domain. The similarity observed in their genomic organization and their proximity in the chromosome indicate that both genes arose from duplication of a single gene. Here, we provide several lines of evidence which indicate that in human and murine T cells which expressed both the CD3-gamma and CD3-delta chains on their surface, the TCR/CD3 complex consisted of a mixture of alpha beta gamma epsilon zeta and alpha beta delta epsilon zeta complexes rather than a single alpha beta gamma delta epsilon zeta complex. First, a CD3-gamma specific antibody failed to co-immunoprecipitate CD3-delta and conversely, several CD3-delta specific antibodies did not coprecipitate CD3-gamma. Secondly, analysis of a panel of human and murine T cell lines demonstrated that CD3-gamma and CD3-delta were expressed at highly variable ratios on their surface. This suggested that these chains were not expressed as a single complex. Thirdly, CD3-gamma and CD3-delta competed for binding to CD3-epsilon in transfected COS cells, suggesting that CD3-gamma and CD3-delta formed mutually exclusive complexes. The existence of these two forms of TCR/CD3 complexes could have important implications in the understanding of T cell receptor function and its role in T cell development.

Susceptibility to type I diabetes in women is associated with the CD3 epsilon locus on chromosome 11

Type I diabetes is associated with the DQ loci of the MHC and to a lesser extent with the T cell antigen receptor (TcR) beta chain genes. The non-obese diabetic (NOD) mouse is an animal model of human diabetes, in which up to 90% of female mice develop overt insulin-dependent diabetes. Genetic studies in the NOD mouse suggest that there are at least three diabetogenic genes; one that maps to the MHC, another that may map to the mouse Thy-I locus, and a third that has still to be identified. We have investigated loci in the vicinity of the human Thy-I locus on chromosome 11q23 and report here the results of restriction fragment length polymorphism (RFLP) analysis of the CD3 epsilon locus of 168 Caucasoid patients with type I diabetes. While no association was found between this locus and type I diabetes, a significant difference in the frequency of the CD3 epsilon 8-kb allele was found between male and female patients (0.268 versus 0.430; P less than 0.0025, Pc = 0.02) and between female patients and healthy female controls (0.430 versus 0.267; P less than 0.015). These results suggest that a gene residing on chromosome 11q23 may confer susceptibility to type I diabetes in women.

Structure of the T cell antigen receptor (TCR): two CD3 epsilon subunits in a functional TCR/CD3 complex

Transgenic mice carrying and expressing the human CD3 epsilon gene incorporate the corresponding protein product into T cell receptor (TCR)/CD3 complexes on thymocyte and T cell surfaces. The chimeric antigen receptors allow normal T cell development and selection of repertoires in vivo and are able to transduce activation signals in vitro. We have exploited the ability to distinguish mouse (m) and human (h)CD3 epsilon chains to analyze the stoichiometry of CD3 epsilon in transgenic mouse TCRs. Immunoprecipitation and fluorescence resonance energy transfer experiments demonstrate that such TCRs can contain both h- and mCD3 epsilon chains, implying that more than one CD3 epsilon subunit occurs per TCR. Antigen comodulation studies are consistent with a stochastic use of h- or mCD3 epsilon during receptor assembly, and further suggest a structure for the TCR/CD3 complex with two CD3 epsilon chains. The determination of CD3 epsilon subunit stoichiometry, together with existing biochemical data, allows the generation of a minimal model for the structure of the TCR and illustrates the potential value of the transgenic approach to the analysis of complex receptors.

Mapping chromosome band 11q23 in human acute leukemia with biotinylated probes: identification of 11q23 translocation breakpoints with a yeast artificial chromosome

Translocations involving chromosome 11, band q23, are frequent recurring abnormalities in human acute lymphoblastic and acute myeloid leukemia. We used 19 biotin-labeled probes derived from genes and anonymous cosmids for hybridization to metaphase chromosomes from leukemia cells that contained four translocations involving band 11q23: t(4;11)(q21;q23), t(6;11)(q27;q23), t(9;11)(p22;q23), and t(11;19)(q23;p13). The location of the cosmid probes relative to the breakpoint in 11q23 was the same in all translocations. Of the cosmid clones containing known genes, CD3D was proximal and PBGD, THY1, SRPR, and ETS1 were distal to the breakpoint on 11q23. Hybridization of genomic DNA from a yeast clone containing yeast artificial chromosomes (YACs), that carry 320 kilobases (kb) of human DNA including CD3D and CD3G genes, showed that the YACs were split in all four translocations. These results indicate that the breakpoint at 11q23 in each of these translocations occurs within the 320 kb encompassed by these YACs; whether the breakpoint within the YACs is precisely the same in the different translocations is presently unknown.

A physical linkage group in human chromosome band 11q23 covering a region implicated in leukocyte neoplasia

Six genes on human chromosome band 11q23 have been linked by pulse-field gel electrophoretic analysis with the order cen-CD3E-CD3D-CD3G-PBGD-CBL2-THY1-qter. The corresponding long-range restriction map covers 1.8 Mb, the telomeric half of which (PBGD-CBL2-THY1) is localized to subband 11q23.3. Four genes (CD3E, CD3D, CD3G, and PBGD) can be positioned precisely, and with known transcriptional orientation, with respect to rare-cutter restriction sites. The linkage group covers a region implicated in leukocyte malignancy: several nonrandom neoplasia-associated translocation chromosomes have breakpoints which separate the CD3 genes from PBGD, CBL2, and THY1. Thus, we are able to localize such breakpoints, and consequently any affected candidate genes, to the 750 kb between CD3G and PBGD.

Characterization of the CD3 gamma and delta invariant subunits of the sheep T cell antigen receptor

The CD3 gamma and delta chains of the sheep T cell antigen receptor have been characterized by cDNA cloning. In comparison to human and mouse protein sequences, short oligopeptide stretches have been deleted from both the gamma and delta chains. However, apart from further variability in the number and position of potential N-linked glycosylation sites, the general structure of the CD3 gamma and delta proteins is markedly conserved. Particularly remarkable are two motifs consisting of 8 and 32 amino acids, respectively, which locate in the C-terminal half of each protein and which have been precisely conserved in both the CD3 gamma and delta chains of all three species. These motifs probably contribute structural properties essential for the function of the CD3/T cell receptor complex. mRNA of the sheep CD3 gamma (1.5 and 1.2 kb) and CD3 delta (1.5 kb) chains are transcribed from closely linked, single-copy genes, suggesting that common mechanisms for the regulation of CD3 genes are also preserved between species.

The gamma and epsilon subunits of the CD3 complex inhibit pre-Golgi degradation of newly synthesized T cell antigen receptors

The T cell receptor for antigen (TCR) is composed of six different transmembrane proteins. T cells carefully control the intracellular transport of the receptor and allow only complete receptors to reach the plasma membrane. In an attempt to understand how T cells regulate this process, we used c-DNA transfection and subunit-specific antibodies to follow the intracellular transport of five subunits (alpha beta gamma delta epsilon) of the receptor. In particular, we assessed the intracellular stability of each chain. Our results showed that the chains were markedly different in their susceptibility to intracellular degradation. TCR alpha and beta and CD3 delta were degraded rapidly, whereas CD3 gamma and epsilon were stable. An analysis of the N-linked oligosaccharides of the glycoprotein subunits suggested that the chains were unable to reach the medial Golgi during the metabolic chase. This was supported by immunofluorescence micrographs that showed both the stable CD3 gamma and unstable CD3 delta chain localized in the endoplasmic reticulum. To study the effects of subunit associations on intracellular transport we used cotransfection to reconstitute precise combinations of subunits. Associations between stable and unstable subunits expressed in the same cell led to the formation of stable complexes. These complexes were retained in or close to the endoplasmic reticulum. The results suggested that the intracellular transport of the T cell receptor could be regulated by two mechanisms. The TCR alpha and beta and CD3 delta subunits were degraded rapidly and as a consequence failed to reach the plasma membrane. CD3 gamma or epsilon were stable but were retained inside the cell. The results also demonstrated that there was an interplay between the two pathways such that the CD3 gamma and epsilon subunits were able to protect labile chains from rapid intracellular degradation. In this way, they could seed subunit assembly in or close to the endoplasmic reticulum and allow a stable receptor to form before its transport to the plasma membrane.

DNase I-defined chromatin configuration of the human CD3 gene cluster

The three CD3 genes on human chromosome 11q23 encode proteins (gamma, delta and epsilon) which form part of the antigen receptor on T lymphocytes. All three genes are clustered within 50 kb and are activated approximately contemporaneously during the early stages of T cell ontogeny. In order to pinpoint potential regulatory sequences important for locus activation and tissue-specific gene expression, the chromatin structure of almost 90 kb of this region has been probed in five cell lines using the endonuclease pancreatic DNase I. A set of DNase I hypersensitive (HS) sites has been defined in T cell chromatin, five of which were strong and not found in non-T cells, with the exception of the erythroleukaemia cell line K562, in which three sites were weakly expressed, correlating with a low level of delta mRNA. The subset of five HS sites map close to the CD3 genes and lie in regions which contain elements of defined function: the gamma promoter; the delta promoter and its 3' enhancer; and the epsilon promoter and its 3' enhancer. Since no further major T cell-restricted HS sites lie within the 90kb of the CD3 locus analysed, these five regions may contain all the sequences important for CD3 gene expression.

A primary linkage map of the human chromosome 11q22-23 region

We have constructed a genetic map of the human chromosomal region 11q22-23 by multipoint linkage analysis of 13 DNA polymorphisms that we have condensed into eight loci. An analysis for linkage disequilibrium between tightly linked probe/enzyme systems allows us to make specific recommendations for future DNA typing at these loci. The resulting sex-averaged multipoint map spans approximately 80 cM and differs considerably from previously reported genetic maps of this region. Our mathematically derived "most likely order" of the markers is compatible with physical mapping data using somatic cell hybrids. The known localizations of at least 14 functional genes and several disease loci to 11q22-23, including ataxia telangiectasia, make the mapping of this region especially relevant to studies of disease pathogenesis.

Speculations on ataxia-telangiectasia: defective regulation of the immunoglobulin gene superfamily

In this short article, Raymond Peterson and Jane Funkhouser develop the argument that the common molecular mechanism linking the various clinical manifestations of ataxia-telangiectasia (AT) is a defect in the regulation of the immunoglobulin (Ig) gene superfamily. They propose that the AT gene codes for a protein essential for the orderly expression of this gene family, perhaps regulating the gene rearrangement process that appears to be a unique characteristic of this system. Members of the Ig gene superfamily play a major role in the development and operation of the immune and nervous systems, and any perturbation of their expression would be anticipated to produce a panoply of signs and symptoms, such as those characterizing the AT phenotype.

Physical mapping of complex genomes by cosmid multiplex analysis

A rapid and powerful approach for linking individual clones of a cosmid library and the assembly of a large physical map is presented, which depends on the simultaneous analysis of many cosmid clones for overlapping regions. This method uses cosmid vectors that contain endogenous bacteriophage T3 and T7 promoters to allow for the identification of overlapping clones through the synthesis of end-specific RNA probes. A genomic library is constructed and organized as an ordered matrix such that each clone is assigned an identifying coordinate. DNA from mixtures of cosmid clones is pooled such that each pool contains only one common member with any other pool, RNA probes are prepared from mixtures of cosmid clones, and groups of clones overlapping with the constituents of the mixtures are determined by hybridization. Pooled probes are most simply prepared by grouping clones according to the rows and columns of the library matrix. The pairwise comparison of data generated by the hybridization of mixed probes can be decoded by using simple algorithms that predict the order and linkage of all clones in the collection and organize them into predicted contigs. To demonstrate the feasibility of multiplexed analysis of cosmids, a genomic library was prepared from a mouse-human somatic cell hybrid that contains a portion of the long arm of human chromosome 11. Preparation, arrangement on a matrix, and analysis of pooled cosmid clones from this collection resulted in the detection of 1099 linked pairs of cosmids, which could be assembled into 315 contigs. Thus, with a minimal amount of effort, a substantial portion of this genomic region has been linked in multiple overlapping contigs. This method may have practical applications in the large-scale mapping and sequencing of mammalian genomes.