Cloning and sequencing of a t(14;19) breakpoint that involves the C mu switch region

Bcl-3: A Double-Edged Sword in Immune Cells and Inflammation

The NF-κB transcription factor family controls the transcription of many genes and regulates a number of pivotal biological processes. Its activity is regulated by the IκB family of proteins. Bcl-3 is an atypical member of the IκB protein family that regulates the activity of nuclear factor NF-κB. It can promote or inhibit the expression of NF-κB target genes according to the received cell type and stimulation, impacting various cell functions, such as proliferation and differentiation, induction of apoptosis and immune response. Bcl-3 is also regarded as an environment-dependent cell response regulator that has dual roles in the development of B cells and the differentiation, survival and proliferation of Th cells. Moreover, it also showed a contradictory role in inflammation. At present, in addition to the work aimed at studying the molecular mechanism of Bcl-3, an increasing number of studies have focused on the effects of Bcl-3 on inflammation, immunity and malignant tumors in vivo. In this review, we focus on the latest progress of Bcl-3 in the regulation of the NF-κB pathway and its extensive physiological role in inflammation and immune cells, which may help to provide new ideas and targets for the early diagnosis or targeted treatment of various inflammatory diseases, immunodeficiency diseases and malignant tumors.

Regulation of the Adaptive Immune Response by the IκB Family Protein Bcl-3

Bcl-3 is a member of the IκB family of proteins and an important regulator of Nuclear Factor (NF)-κB activity. The ability of Bcl-3 to bind and regulate specific NF-κB dimers has been studied in great depth, but its physiological roles in vivo are still not fully understood. It is, however, becoming clear that Bcl-3 is essential for the proper development, survival and activity of adaptive immune cells. Bcl-3 dysregulation can be observed in a number of autoimmune pathologies, and Bcl3-deficient animals are more susceptible to bacterial and parasitic infection. This review will describe our current understanding of the roles played by Bcl-3 in the development and regulation of the adaptive immune response, including lymphoid organogenesis, immune tolerance, lymphocyte function and dendritic cell biology.

The B cell antigen receptor in atypical chronic lymphocytic leukemia with t(14;19)(q32;q13) demonstrates remarkable stereotypy

The t(14;19)(q32;q13) is a recurrent chromosomal translocation reported in a variety of B-cell leukemias and lymphomas, including chronic lymphocytic leukemia (CLL). CLL cases associated with t(14;19) often have atypical morphologic and immunophenotypic features and unmutated immunoglobulin heavy chain (IGH) variable region (V) genes, associated with an aggressive clinical course. We analyzed IGHV somatic mutation status and gene use in 11 patients with t(14;19)-positive CLL. All cases were unmutated, and the IGHV genes in 10 cases showed minimal deviation from germline sequences. In 7 of 11 patients, we found homologous heavy chain rearrangements using IGHV4-39; light chain analysis revealed identical IGKV1-39 use. Corresponding V-(D)-J sequences demonstrated remarkable stereotypy of the immunoglobulin heavy and kappa light chain complementarity determining region 3 (H/K CDR3) genes. These findings raise the possibility that specific antigen drive is involved in the clonal development and/or selection of t(14;19)(q32;q13)-positive CLL cells. Our findings support the hypothesis that stimulatory signals through specific antigen receptors may promote the expansion of either CLL precursor cells or CLL clones that harbor distinct chromosomal abnormalities.

Splenic small B-cell lymphoma with IGH/BCL3 translocation

Isolated chromosomal translocations are important defining features of many non-Hodgkin lymphomas, especially of B-cell type. In contrast to some other translocations, the significance of IGH/BCL3 translocations is not well defined. Although often considered a feature of the ill-defined entity atypical chronic lymphocytic leukemia, very few cases are reported in which involvement of BCL3 and the precise B-cell neoplasm are both well documented. For this reason, we report a splenic-based CD5(-), CD10(-), CD43(-), CD23(-), CD103(-), FMC7(+), CD25(+) small B-cell lymphoma associated with epithelioid histiocyte clusters and a t(14;19)(q32;q13) representing an IGH/BCL3 translocation based on classical cytogenetic studies, chromosomal painting, and fluorescence in situ hybridization studies. The previously reported neoplasms with t(14;19)(q32;q13) or IGH/BCL3 translocations are also reviewed. The present case did not fall into any of the classic B-cell lymphoma categories and clearly did not represent chronic lymphocytic leukemia/small lymphocytic lymphoma. This case suggests that the IGH/BCL3 translocation may help to define a new clinicopathologic entity.

Isotype switch-mediated CH deletions are a recurrent feature of Myc/CH translocations in peritoneal plasmacytomas in mice

Oncogene activating chromosomal translocations that interrupt IGH switch (S) regions at 14q32 are thought to be caused by misguided IGH isotype switching in postgerminal center B-cell lymphomas and plasma cell myelomas in humans. Aberrant switching also seems to be involved in altering the fine structure of the translocation in some of these tumors, but the significance of these changes is not known. Here we report on 3 cases of IL-6 transgenic mouse plasmacytomas (PCT) that harbor T(12;15) translocations that had been modified by frustrated switch attempts that result in C(H) deletions. When considered together with 6 similar cases of PCT described previously, our observations suggest that secondary deletions in C(H) are a regular feature in the molecular evolution of T(12;15) translocations and, thereby, in the progression of PCT. We propose that the T(12;15)(+) mouse PCT offers a uniquely valuable model system for elucidating the dual role of abnormal isotype switching in causation and 'remodeling' of chromosomal translocations.

Translocation (2;14) associated with complex rearrangements of the Ig heavy chain in non-Hodgkin lymphoma

Cytogenetic analysis of a patient with non-Hodgkin lymphoma revealed the following karyotype: 49,XXX,t(2;14)(q21;q32),+4,+8,del(13)(q14q21). Southern blot analysis with an Ig region probe showed non-productive rearrangements indicative of a translocation involving the Ig locus. However, molecular cloning of the abnormal rearrangements did not show novel sequences derived from chromosome 2 but showed that the BCL-6 gene was juxtaposed to the IgH enhancer. Three further clones with abnormal rearrangements involving the Ig locus, particularly Iggamma3, were isolated. This suggests that the mature lymphoid cells, in this patient, were capable of undergoing indiscriminate switch cleavage and religation.

Molecular analysis of an unstable genomic region at chromosome band 11q23 reveals a disruption of the gene encoding the alpha2 subunit of platelet-activating factor acetylhydrolase (Pafah1a2) in human lymphoma

A region of 150 kb has been analysed around a previously isolated, lymphoma associated, translocation breakpoint located at chromosome band 11q23. This balanced and reciprocal translocation, t(11;14)(q32;q23), has been shown to result in the fusion between chromosome 11 specific sequence and the switch gamma4 region of the IGH locus. The LPC gene, encoding a novel proprotein convertase belonging to the furin family, has been identified in this region. In order to characterize further the region surrounding the translocation, we have determined the detailed structure of LPC. Here we show that LPC consists of at least 16 exons covering 25 kb, and that there is a partial duplication, involving mobile genetic elements and containing LPC exons 13-17 in a tail-tail configuration at 65 kb downstream. Since the chromosomal breakpoint lay between these two structures, the intervening region was further analysed and shown to contain at least two unrelated genes. The previously known SM22 gene was localized close to the 3' tail of LPC. Furthermore, we identified the gene encoding the alpha2 subunit of platelet-activating factor acetylhydrolase (Pafah1a2) at the chromosomal breakpoint. The position of another previously identified breakpoint was also located to within the first intron of this gene. Altogether, our results give evidence of a genomic instability of this area of 11q23 and show that Pafah1a2 and not LPC is the gene disrupted by the translocation, suggesting that deregulated Pafah1a2 may have a role in lymphomagenesis.

Methylation status of the 3rd exon of the c-MYC oncogene in B-cell malignancies

We examined the methylation status of the third exon of the MYC oncogene in 39 patients with B-cell malignancies. DNA was digested with MspI plus EcoRI or HpaII plus EcoRI and hybridised with a probe specific for the third exon of MYC. Thirty four patients showed complete methylation of the CCGG site. Four patients, one with chronic B-cell leukaemia and one with pro-lymphocytic leukaemia (PLL) and two with B-cell lymphoma showed partial hypomethylation of the CCGG site, while another patient with PLL showed complete hypomethylation of the CCGG site. These results suggest that hypomethylation of the MYC oncogene is infrequent in B-cell tumours but may be involved in the development of some cases of B-cell malignancies.

Aberrant rearrangements of the immunoglobulin heavy chain switch region in chronic B-cell leukemia

Analysis of the organisation of the Cmu-switch region of the immunoglobulin heavy chain locus in B-lymphocytes from 80 patients with chronic B-cell leukemia revealed 25 patients with abnormal rearrangements that could not be explained by the normal recombination events that take place in B-lymphocytes. Detailed analysis with probes spanning the Cmu -switch region and various restriction digests localised the rearrangements in two thirds of the patients to a 1300 bp region at the 5' end of the switch region while in the remaining patients the rearrangements occurred in the switch region. The consequences of these aberrant rearrangements remain to be determined, but their clustering to a defined region of the switch region suggests a "hot spot" that may be involved in the aetiology of the disease.

Trans-chromosomal recombination within the Ig heavy chain switch region in B lymphocytes

Somatic DNA rearrangements in B lymphocytes, including V(D)J gene rearrangements and isotype switching, generally occur in cis, i. e., intrachromosomally. We showed previously, however, that 3 to 7% of IgA heavy chains have the VH and Calpha regions encoded in trans. To determine whether the trans-association of VH and Calpha occurred by trans-chromosomal recombination, by trans-splicing, or by trans-chromosomal gene conversion, we generated and analyzed eight IgA-secreting rabbit hybridomas with trans-associated VH and Calpha heavy chains. By ELISA and by nucleotide sequence analysis we found that the VH and Calpha regions were encoded by genes that were in trans in the germline. We cloned the rearranged VDJ-Calpha gene from a fosmid library of one hybridoma and found that the expressed VH and Calpha genes were juxtaposed. Moreover, the juxtaposed VH and Calpha genes originated from different IgH alleles. From the same hybridoma, we also identified a fosmid clone with the other expected product of a trans-chromosomal recombination. The recombination breakpoint occurred within the Smicro/Salpha region, indicating that the trans-association of VH and Calpha genes occurred by trans-chromosomal recombination during isotype switching. We conclude that trans-chromosomal recombination occurs at an unexpectedly high frequency (7%) within the IgH locus of B lymphocytes in normal animals, which may explain the high incidence of B-cell tumors that arise from oncogene translocation into the IgH locus.

Hypermethylation of the M27beta (DXS255) locus in chronic B-cell leukaemia

We have investigated the methylation status of the M27beta (DXS255) locus in 21 female patients with chronic B-cell leukaemia and in 20 normal controls. DNA was digested with Pst1 and then with the methylation sensitive enzyme HpaII and probed with the M27beta probe. Eight patients (38%) showed hypermethylation of the M27beta locus which was not seen in any of the normal controls. Hypermethylation of the M27beta locus has also been found in acute myeloid leukaemia, acute lymphocytic leukaemia and lymphoma, suggesting that hypermethylation of the M27beta locus is associated with the leukaemic process.

Diamond-Blackfan anaemia in a girl with a de novo balanced reciprocal X;19 translocation

A 7 year old girl is described with congenital hypoplastic anaemia (Diamond-Blackfan anaemia, DBA) and an apparently balanced reciprocal translocation, 46,XX,t(X;19)(p21;q13). The girl has associated features including short stature, unilateral kidney hypoplasia, and a branchial cyst. Fluorescent in situ hybridisation (FISH) studies with 19q specific cosmids showed that the chromosome 19 breakpoint is located between the RYR1 and the XRCC11 loci spanning a physical region of 5 Mb. There is no family history of DBA and the parents and two healthy sibs have normal karyotypes. This is the first report of a balanced translocation associated with DBA and we suggest that the distinct phenotype has resulted from a de novo disruption of a functional gene. DBA can be inherited as an autosomal trait and our observation may indicate a candidate gene for the disorder in the 19q13 region.

t(14;19)/BCL3 rearrangements in lymphoproliferative disorders: a review of 23 cases

The t(14;19)(q32.3;q13.2) is a rare but recurrent translocation found in patients with B-cell malignancies, mainly in chronic B-cell lymphoproliferative disorders. When occurring in chronic lymphocytic leukemia (CLL), atypical lymphocyte morphology and immunophenotype have been reported. A high proportion of patients with CLL and t(14;19) are aged less than 40 years. t(14;19) is often associated with rapidly progressive disease, and overall prognosis is poor compared to the expected survival in chronic lymphocytic leukemia and low-grade B-cell lymphoma. t(14;19) is rarely the sole cytogenetic aberration. Trisomy 12 is the most frequent associated abnormality, and is observed in 50% of cases. t(14;19) involves the BCL3 gene, which is located at the breakpoint on chromosome 19 and is juxtaposed to the immunoglobulin heavy chain gene locus on chromosome 14 (often in the switch alpha region) in a "head-to-head" configuration. The translocation does not interrupt the transcriptional integrity of BCL3, but is associated with overexpression of this gene, which encodes an I kappa B-like protein and modulates the activity of the NF-kappa B transcription factors. The genes affected by overexpression of BCL3 remain to be identified.

Genes and chromosomes in chronic B-cell leukemia

Cytogenetic analysis of patients with chronic B-cell leukemia (B-CLL) indicates that 50% have chromosome abnormalities, while fluorescence in situ hybridization (FISH) and molecular techniques reveal an even higher incidence. Trisomy 12 and deletions or translocation of chromosome 13q14 are the most common abnormalities, but in neither case has the gene or genes involved in the abnormalities been identified. Combined FISH and immunophenotyping studies suggest that both abnormalities are secondary events in B-CLL. Other recurring chromosome abnormalities include 6q-, 11q- and 12p-, but the genes involved in these abnormalities have not been identified. Involvement of the BCL1, BCL2, and BCL3 genes has been reported, but the numbers are low and the cases tend to be atypical. Trisomy 12 in association with complex karyotypic abnormalities is associated with a poor prognosis, and FISH studies show a strong correlation between trisomy 12, atypical morphology, and advanced disease. Ten to 15% of patients have mutations of p53 which is associated with advanced disease, resistance to treatment, and poor survival.

BCL3 rearrangement and t(14;19)(q32;q13) in lymphoproliferative disorders

Translocation t(14;19)(q32;q13) is a rare but recurrent abnormality in chronic lymphocytic leukemia and small cell lymphoma. It has been associated with rearrangements of the BCL3 gene, which is located at the breakpoint on chromosome 19 and is juxtaposed to the immunoglobulin heavy chain locus on chromosome 14 as a result of the translocation. This results in transcriptional up-regulation of the BCL3 gene, which encodes a transcription coactivator, an I-kappa B protein, probably contributing to disease progression. We found, among 4,487 cytogenetic analyses of lymphoproliferative disorders, six cases with a t(14;19)(q32;q13), five of which showed the classical t(14;19)(q32;q13) and one of which showed a three-way translocation t(7;19;14)(q21;q13;q32). The 14;19 translocation never occurred as a single abnormality; additional aberrations included trisomy 12 and several structural abnormalities. The cytogenetic examination was supplemented by molecular analysis using available probes for the BCL3 locus (p alpha 1.4P and p alpha 5B) in 1,150 of the 4,487 patients. Rearrangements of BCL3 could be detected in five cases, all of which had the classical t(14;19). In the case with t(7;19;14), the suspected BCL3 involvement could only be confirmed using long-range restriction mapping, indicating that, with the usually available BCL3 probes, rearrangements of this locus may be missed.