Molecular characterization of different ataxia telangiectasia T-cell clones. I. A common breakpoint at the 14q11.2 band splits the T-cell receptor alpha-chain gene

Crystal structure of MTCP-1: implications for role of TCL-1 and MTCP-1 in T cell malignancies

Two related oncogenes, TCL-1 and MTCP-1, are overexpressed in T cell prolymphocytic leukemias as a result of chromosomal rearrangements that involve the translocation of one T cell receptor gene to either chromosome 14q32 or Xq28. The crystal structure of human recombinant MTCP-1 protein has been determined at 2.0 A resolution by using multiwavelength anomalous dispersion data from selenomethionine-enriched protein and refined to an R factor of 0.21. MTCP-1 folds into a compact eight-stranded beta barrel structure with a short helix between the fourth and fifth strands. The topology is unique. The structure of TCL-1 has been predicted by molecular modeling based on 40% amino acid sequence identity with MTCP-1. The identical residues are clustered inside the barrel and on the surface at one side of the barrel. The overall structure of MTCP-1 superficially resembles the structures of proteins in the lipocalin family and calycin superfamily. These proteins have diverse functions, including transport of retinol, fatty acids, chromophores, pheromones, synthesis of prostaglandin, immune modulation, and cell regulation. However, MTCP-1 differs in the topology of the beta strands. The structural similarity suggests that MTCP-1 and TCL-1 form a unique family of beta barrel proteins that is predicted to bind small hydrophobic ligands and function in cell regulation.

Purification and characterization of recombinant forms of TCL-1 and MTCP-1 proteins

The TCL-1 gene which is located on chromosome 14 plays a major role in human hematopoeitic malignancies and encodes a 14-kDa protein whose function has not been determined. The TCL-1 gene is expressed in pre-B cells, in immature thymocytes, and at low levels in activated T cells but not in peripheral mature B cells and in normal cells. The TCL-1 protein is similar in its primary structure to a protein encoded by the mature T cell proliferation gene (MTCP-1). The MTCP-1 gene is located on the X chromosome and has been shown to be involved in rare chromosomal translocations in T cell proliferative diseases. The TCL-1 and MTCP-1 genes appear to be members of a family of genes involved in lymphoid proliferation and T cell malignancies. Our laboratory has undertaken the study of the TCL-1 and MTCP-1 proteins to determine the structure and the function of these related proteins. In the present report, we have produced, using a bacterial expression system, both purified TCL-1 and MTCP-1 proteins in forms with and without a six His tag sequence. The recombinant proteins were purified by chromatography on a Ni-NTA resin followed by reverse-phase FPLC using a buffer system at pH 7.9 and a polymeric-based reverse-phase column. The MTCP-1 recombinant proteins display greater solubility, do not form disulfide linked dimers or oligomers, and elute at a lower isopropanol concentration than the corresponding TCL-1 proteins. The purified recombinant TCL-1 and MTCP-1 proteins have been characterized by N-terminal sequence analysis, time of flight mass spectrometry, and circular dichroism spectroscopy. Initial results have indicated that the MTCP-1 protein with the His tag removed is suitable for both NMR and X-ray crystallographic methods of structure determination.

[Leukemia lymphoma T-cell as first manifestation of ataxia-telangiectasia]

BACKGROUND

Variable degrees of T cell deficiency in ataxia-telangiectasia (AT) progressively worsen with time and death from malignant lymphoma is a common terminal event. T-cell lymphoma as the first manifestation of AT has never been reported.

CASE REPORT

A 22 month-old girl born to consanguineous parents, was treated for a thoracic T-cell lymphoma and remained in first complete remission, with a follow-up of 4 years. Prior to chemotherapy, cytogenetic studies on blood showed clonal rearrangements including t(7p;14q), T(2p;7q) and inv (7), while karyotype showed 6q- and 1p-mitoses on bone marrow blasts. Hypotonia became evident at 3 years. One year later, the neurological status deteriorated. The patient presented also severe respiratory tract infections. At that time, immunological investigations showed hypo IgG2, very low T4 lymphocytes level, all harbouring the CD45 RO phenotype. Increase in alpha-foetoprotein level, the ocular movements and the study of DNA synthesis after exposure to gamma-rays confirmed the diagnosis of AT.

CONCLUSION

In cases of childhood lymphoid neoplasia, AT should be considered whenever parental consanguinity, T-cell proliferation and/or unexpected toxic therapeutic responses are noted.

Molecular analysis of a new translocation, t(X;14)(q28;q11), in premalignancy and in leukaemia associated with ataxia telangiectasia

The disease ataxia telangiectasia (A-T) is a multifaceted disorder in which patients have an increased chance of developing a T-cell leukaemia, often with abnormalities of chromosome 14, but sometimes with rare translocations, like t(X;14)(q28;q11). We describe the cloning of the breakpoint of one such novel t(X;14) from an A-T patient. The translocation breaks within the T cell receptor alpha chain gene on chromosome 14 at band q11 and in a region of the X chromosome, within about 1 Mb of the telomere of the long arm. The patient subsequently developed T-cell prolymphocytic leukaemia (T-PLL), and molecular examination showed that the tumour cells carried the same t(X;14) breakpoint as that cloned from the premalignant cells. The same breakpoint could be detected in blood samples taken as much as 5 years prior to diagnosis of T-PLL. This suggests a role for the abnormality in the tumour development in this patient but implies that other mutational events were necessary for overt disease to become manifest.

Cytogenetic analysis in ataxia telangiectasia with malignant lymphoma

We present the results of cytogenetic analysis in a brother and sister with ataxia telangiectasia (AT), one of whom had malignant T-cell lymphoma. In both children, cytogenetic analysis of phytohemagglutinin (PHA)-stimulated lymphocytes showed chromosomal instability and inv(7) in 10% of the cells examined. The malignant lymphoma was analyzed cytogenetically on slides obtained from short-term culture of the lymph node cells; 64 cells were analyzed. A heterogeneous cell population was noted. Fourteen cells (21.9%) had a normal male karyotype; t(7;14)(p14;q12) and inv(7)(p14q35) were observed in 6.3% and 3.1% of metaphases. Owing to low frequency, these cells are probably a characteristic of the basic disease and have no features of malignant cells. Forty cells (62.5%) had a pseudodiploid karyotype 46,XY,dup(1)(p22p36),del(5)(q33),del(12)(p11), without cytogenetically evident aberrations of chromosomes 7 and 14. The results of these investigations suggest that the cells with rearrangements of chromosomes 1, 5, and 12 are malignant cells and did not originate by transformation of cells with inv(7) and t(7;14).

Molecular analysis of an ataxia telangiectasia T-cell clone with a chromosomal translocation t(14;18)--evidence for a breakpoint in the T-cell receptor delta-chain gene

We established a clonal T-cell line with a reciprocal chromosomal translocation t(14;18)(q11;q23) from a patient with ataxia telangiectasia (AT) and T-cell chronic lymphocytic leukemia (T-CLL). The tumor cells and the derived T-cell line were compared with respect to phenotype, karyotype, and rearrangement pattern. Restriction fragment analyses of the T-cell receptor (TCR)-delta gene, which is located within the TCR-alpha gene on chromosome 14q11, indicated that the breakpoint is located within the TCR-delta locus, splitting the TCR-delta gene between the variable and joining segments. This specific chromosomal translocation was only detected in the derived T-cell line and may be involved in the genesis of T-cell malignancies in AT.

Unusual T cell clones in a patient with Nijmegen breakage syndrome

The rare autosomal recessive Nijmegen breakage syndrome is characterised by severe immunodeficiency, microcephaly associated with mental retardation, and typical chromosomal rearrangements in peripheral T lymphocytes. This syndrome, though similar to ataxia telangiectasia, does not exhibit the neurological and cutaneous signs of this disorder. We report here the first patient with Nijmegen breakage syndrome ascertained in France. Chromosome analysis detected, in addition to the specific aberrations, two clonal T cell proliferations which do not involve the usual bands 14q11.2 and 14q32.1.

High recurrence of rearrangements involving chromosome 14 in an ataxia telangiectasia lymphoblastoid cell line and in its mutagen-treated derivatives

The cytogenetic characterization of CH cell line obtained by Epstein-Barr-virus transformation of the lymphocytes of a patient affected by ataxia telangiectasia is reported. Control CH cells and 2 subcultures treated with the mutagens R7000 or NQO were developed in parallel and studied. A common chromosome anomaly, a der(14) t(11;14) (q13.2;q32), was found in all the studied karyotypes, indicating that it occurred either in vivo or early in vitro. In non-treated cultures, additional anomalies were present in 6 derived subclones. All R-7000 treated cells had the same karyotype corresponding to one of the subclones observed without prior treatment. All NQO-treated cells acquired 2 common anomalies, and could be differentiated into 2 subclones because of the addition of a t(7;14) or a t(11;14). Chromosome 14 was involved in various rearrangements after breakage in band q11.2 or q12 in 6/8 subclones. This was not correlated with tumorigenicity, which was clearly increased in mutagen-treated cells as tested by in vitro growth in semi-solid medium and in vivo by grafts into nude mice or growth on the chorio-allantoic membrane of chick embryos. The CH cell line and its derivatives appear to be a promising in vitro system, showing various stages progressing towards malignancy, and reproducing a number of chromosome anomalies spontaneously occurring in AT patients.

Inv(14) with distal breakpoint in 14q32.1 in three cases of T cell lymphoma

The distal breakpoint of inv(14) in T cell clones, established from patients with ataxia telangiectasia, lies outside the immunoglobulin heavy chain gene locus on 14q32.3, and more proximal to the centromere than the distal breakpoint of inv(14) in the T cell lymphoma cell line SUP-T1. We report 3 cases of T cell lymphoma cytogenetically showing the same type of inv(14) as the AT T cell clones. All 3 cases express a similar immunophenotype, which is that of peripheral T lymphocytes with phenotypic remnants of thymic or postthymic lymphoblasts. This finding provides evidence that this type of inv(14) is involved in the malignant transformation of mature T lymphocytes.

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.

Molecular characterization of ataxia telangiectasia T cell clones. III. Mapping the 14q32.1 distal breakpoint

To delimit the 14q32.1 recurrent breakpoint of ataxia telangiectasia clones, we performed an in situ hybridization study with various probes located on the 14q32 band. We thus mapped this breakpoint between the D14S1 and Pi loci. Furthermore, an interstitial duplication including D14S1 and a part of the IgH locus was demonstrated on a t(14;14) clone.

Molecular characterization of ataxia telangiectasia T cell clones. II. The clonal inv(14) in ataxia telangiectasia differs from the inv(14) in T cell lymphoma

We compared inversions of chromosome 14 in an ataxia telangiectasia clone and in a malignant T cell line (SUP-T1). The R-banding chromosome analysis showed a clear difference between the distal breakpoint of the two inversions. Fine mapping of the distal breakpoint in the ataxia telangiectasia inv(14) was performed by in situ hybridization. We conclude that this breakpoint is centromeric to the immunoglobulin heavy chain locus and to the D14S1 anonymous locus. Our results favor the existence of an unknown oncogene in band 14q32.1.