bcl-2 translocation in Japanese B cell lymphoma: novel bcl-2 translocation with immunoglobulin heavy chain diversity segment

Characterization of the light chain-restricted clonal B cells in peripheral blood of HCV-positive patients

To investigate the association between hepatitis C virus (HCV) and B cell proliferation, we searched for the clonal B cells by flow cytometric analysis of the surface immunoglobulin kappa (kappa):lambda (lambda) light chain ratios of the circulating B (CD19+) cells in 240 HCV-positive patients and 150 negative controls with liver diseases. Clonal B cells with light chain restriction (kappa:lambda ratio >3:1 or <1:2) were analyzed for CD5 expression and the presence of monoclonal immunoglobulin heavy-chain (IGH) gene rearrangements and the t(14;18) chromosomal translocation. Clonal B cells were detected in 7 cases with HCV (2.9%), but was never detected in the controls (p < 0.05). Of the 7 cases, all had monoclonal IGH gene rearrangements and one had the t(14;18) chromosomal translocation. These HCV-related clonal B cells are not uniform in the intensity of CD5 expression and showed no increase in the frequencies of CD5+ population compared with non-clonal B cells. No "chronic lymphocytic leukemia-phenotype" cells were found. The loss of clonality was observed in 2 cases treated with interferon and in one case treated with splenectomy. The longitudinal study is required to determine whether these circulating clonal B cells progress to lymphoproliferative disorders in future or not.

Detection of t(14;18) in follicular lymphoma by dual-color fluorescence in situ hybridization on paraffin-embedded tissue sections

We studied the incidence of t(14;18)(q32;q21) in 54 patients with follicular lymphoma (FL) by dual-color fluorescence in situ hybridization on paraffin-embedded tissue sections (tissue-FISH) using probes for BCL2 and immunoglobulin heavy chain (IGH) genes. The t(14;18) was detected in 28 (56%) of 50 patients, who were successfully analyzed. On the other hand, BCL2 protein expression was detected in 45 (83%) of 54 patients evaluated by immunohistochemical staining. There was a discrepancy between t(14;18) and BCL2 expression. The absence of t(14;18) was associated with disease-free survival (P=0.02). There was no statistical difference, however, in overall survival and failure-free survival between the t(14;18)-positive and -negative groups. Tissue-FISH should be of great value to detect t(14;18) in FL because this method enabled us to demonstrate specifically t(14;18)-positive individual cells in neoplastic follicles on paraffin-embedded tissue sections. Furthermore, tissue-FISH can be applied to small specimens obtained from endoscopic biopsy or specimens obtained more than 10 years ago. We validated the usefulness of tissue-FISH as a diagnostic procedure and retrospective meta-analysis for malignant lymphoma.

Insights into the molecular pathogenesis of follicular lymphoma arising from analysis of geographic variation

Incidence rates of follicular lymphoma (FL) inexplicably vary markedly between Western and Asian countries. A hallmark of FL is the bcl-2 translocation, characterized by 1 of 2 common breakpoints known as major breakpoint region (MBR) and minor cluster region (mcr). We analyzed previously published data to compare rates of bcl-2 translocation in FL across geographic regions. Available data from the literature suggest that the incidence of bcl-2 in healthy persons in the absence of FL may be as high as 50% in Western and Asian populations. However, in FL our results show that the frequency of bcl-2 positivity was significantly higher for US than for Asian populations (P <.0001). This pattern persisted for MBR and mcr subgroups. We conclude that a significant gradient exists in the bcl-2 frequency between these FL populations. We therefore suggest that the relatively low incidence of FL in Asian populations is caused not by a lower frequency of bcl-2 rearrangements in healthy populations but by distinct molecular pathways developing in different geographic regions that nonetheless culminate in FL, which is morphologically similar but molecularly distinct. Studies demonstrating differences in clinical characteristics according to the presence or absence of bcl-2 rearrangements support this concept. Thus we hypothesize that FL may in fact be a heterogeneous malignancy encompassing entities with distinct molecular pathogenesis and potentially distinct clinical manifestations. If these findings were confirmed in prospective studies, it would imply that different etiologic or genetic factors might influence the development of FL across separate regions.

Refinement of the BCL2/immunoglobulin heavy chain fusion gene in t(14;18)(q32;q21) by polymerase chain reaction amplification for long targets

The t(14;18)(q32;q21) translocation, involving the BCL2 gene and junctional segments (JH) of the immunoglobulin heavy chain gene (IGH), constitutes the most common chromosomal translocation in non-Hodgkin's lymphoma of B-cell type. Although the breakpoints in BCL2 are largely clustered within the major breakpoint region (MBR) and minor cluster region (mcr), it is known that some breakpoints map away from these regions, resulting in negative amplification of the junctional sequence by polymerase chain reaction (PCR) for < 1 kb targets. To circumvent this problem, we applied a novel PCR technology for long DNA targets, long-distance (LD-) PCR, to the detection of t(14;18) in clinical materials. Oligonucleotide primers were designed to be quite distant from the two known cluster regions in BCL2, and those for the corresponding IGH were complementary to the enhancer and constant regions. In all 52 cases identified as carrying BCL2/JH fusion by conventional Southern blot analysis, LD-PCR successfully amplified fragments encompassing the junctions, which were readily identifiable on ethidium bromide-stained gel. The size of the LD-PCR products ranged from 3.9 kb to 10.7 kb in MBR/IGH fusion and 1.9 kb to 16 kb in mcr/IGH fusion. Furthermore, we established an LD-PCR protocol for > 20 kb targets, which covered the intervening region between the MBR and mcr. Restriction analysis of the LD-PCR products revealed that breakpoints in 33 cases fell within the 150 bp-MBR region, and in 3 cases were within the mcr determined previously by others. In contrast, the breakpoints of the remaining 16 cases were distributed over a large region from the MBR through mcr. Nucleotide sequence analysis of a potential cluster region revealed the presence of an Alu repeat sequence. Restriction analysis of LD-PCR products with BstEII demonstrated a predominant usage of the JH6 segment (71%) at the BCL2/JH junctions. LD-PCR using primers for the constant region genes showed that class switch recombination occurred in more than 80% of the IGH genes on the der(14) chromosome. Our study showed that LD-PCR was capable of detecting virtually any t(14;18) that occurred within the approximately 30 kb region downstream of the MBR, and thus is suitable for initial diagnosis of lymphoma tissues. Furthermore, as amplified fragments obtained by the LD-PCR contained distinctive regions of BCL2 and IGH, restriction analysis and nucleotide sequencing of the products refined the characteristics of t(14;18).

New type of t(14;18) in a non-Hodgkin's lymphoma provides insight in molecular events in early B-cell differentiation

In this report a follicular non-Hodgkin's lymphoma (NHL) carrying an unusual t(14;18) is described. This translocation most likely occurred during the VH to D-JH rearrangement process of the IgH locus. From the data combined with data from the literature we conclude that the chance for development of a t(14;18) decreases during progression of the immunoglobulin rearrangement process in the pre-B-cell ontogeny. This is probably due to decreased accessibility of the bcl-2 locus by reduced transcription. We analysed the somatic mutation pattern of the productively rearranged IgH gene. Like other follicular lymphomas, somatic mutations were present in this gene and indicated positive selection, probably for an antigen. We found no evidence for ongoing induction of somatic mutations during lymphoma development. We conclude that bcl-2 gene deregulation, but not the precise moment at which this occurs during the pre-B-cell stage, influences the development of follicular NHL.

Molecular pathology of low grade malignant lymphomas

During the last ten years the combined efforts of pathologists and molecular biologists have helped define several new lymphoma diagnostic categories. In particular, the recognition of chromosomal translocations which have activated the BCL1 and BCL2 proto-oncogenes have strong associations with specific types of non-Hodgkin's malignant lymphomas such as mantle cell lymphoma and follicular center cell lymphoma, respectively. This review will attempt to summarize our current understanding regarding the contributions of BCL1 and BCL2 to lymphomagenesis and diagnosis.

Loss of heterozygosity at the bcl-2 gene locus and expression of bcl-2 in human gastric and colorectal carcinomas

The loss of heterozygosity (LOH) at the bcl-2 gene locus and the expression of the bcl-2 gene were examined in gastric and colorectal carcinoma cell lines and carcinoma tissues. LOH at the bcl-2 locus was detected in 24% (4/17) of gastric and 60% (6/10) of colonic carcinomas, all of which were well differentiated adenocarcinomas, whereas LOH was not seen in poorly differentiated ones. On the other hand, 24% (5/21) of poorly differentiated stomach cancers overexpressed bcl-2 gene, whereas no overexpression was detected in well differentiated stomach cancer. Three gastric and three colorectal carcinoma cell lines, all of which were derived from poorly differentiated adenocarcinomas, expressed considerable levels of bcl-2 mRNA and protein. These results suggest that LOH at the bcl-2 locus is frequently associated with well differentiated adenocarcinomas of the stomach and colon, and bcl-2 overexpression has implications for the development of poorly differentiated adenocarcinomas of the gastrointestinal tract.

Rearrangement of bcl-2 genes in malignant lymphomas in Chinese patients

BACKGROUND

Only a small percentage of Asian patients with non-Hodgkin lymphoma may have follicular type disease. According to molecular analysis done recently, the incidence of rearrangement of bcl-2 gene in patients with follicular lymphoma was lower in Japan than in the United States, suggesting possible geographic or racial differences between Asian and Western populations. The current study was undertaken to obtain data from Taiwan to compare with data from Japan, Hong Kong, and Western countries.

METHODS

Using probes of genomic 5' bcl-2, major breakpoint region (mbr) and minor breakpoint cluster region (mcr) for the breakpoint cluster region of the bcl-2 gene, genomic DNA samples from 55 patients with B-cell lymphoma (17 with follicular type and 38 with diffuse type) were analyzed by Southern blot analysis.

RESULTS

Eleven patients had bcl-2 gene rearrangement, including 9 of 17 (52.9%) patients with follicular lymphoma and 2 of 38 (5.3%) patients with diffuse B-cell lymphoma. Nine patients had the breakpoint located within the mbr, one at both the mbr and the 5' bcl-2 regions, and the other had bcl-2 translocation with involvement of the mcr. DNA fragment of bcl-2 was found to comigrate with JH genes in all patients with follicular lymphoma and diffuse lymphoma who had bcl-2 rearrangement at mbr. The remaining patient who had bcl-2 translocation at mcr had no comigration with JH, Jk, or C lambda genes.

CONCLUSIONS

Despite the low incidence of follicular lymphoma in Chinese patients, the incidence of bcl-2 gene involvement was higher in patients from Taiwan than in those from Japan and Hong Kong, but similar to the incidence of those from Western countries.

Molecular cloning of 19p13 breakpoint region in infantile leukemia with t(11;19)(q23;p13) translocation

We studied the breakpoint regions involved in t(11;19)(q23;p13) translocation associated with infantile leukemias. Southern blot analysis with the partial cDNA clone for the MLL gene at 11q23 which we had isolated previously detected gene rearrangements in all three cell lines and three leukemia samples from the patients with t(11;19) translocation, indicating that these breakpoints were clustered within the 8.5 kb BamHI germline fragment detected by the probe. To study the breakpoint region, a genomic library of one of the cell lines, KOCL-33, was made. We have isolated the der(19) allele containing the breakpoint as well as the germline alleles at 19p13 and 11q23. Using the genomic probes on chromosome 19 near the breakpoint, Southern blot analysis was performed. The breakpoints at 19p13 of the two other cell lines and the three leukemia samples were not located within 36 kilobases of the KOCL-33 breakpoint, although pulsed-field gel electrophoresis showed that the breakpoints of all three cell lines were on the same NruI fragment of 230 kilobases. These results showed that the breakpoints at 19p13 were not clustered like those at 11q23 in t(11;19) translocation.

Detection of the t(14;18) at similar frequencies in hyperplastic lymphoid tissues from American and Japanese patients

Follicular lymphoma shows a wide geographic variation in incidence, occurring more frequently in the U.S. than in Japan. A translocation involving the bcl-2 gene on chromosome 18 and the immunoglobulin heavy chain gene on chromosome 14 is frequently found in follicular lymphomas and is believed to play a critical role in the pathogenesis of these tumors. Recently, bcl-2/IgH rearrangements have been detected in reactive lymphoid tissue obtained from European patients, indicating that such rearrangements occur at some low but measurable background rate. In non-malignant tissues, the polymerase chain reaction was used to study the frequency of bcl-2/IgH rearrangements in reactive lymphoid tissue obtained from American and Japanese patients to find out whether geographic variation in the incidence of follicular lymphoma was caused by differences in sporadic occurrence of the t(14;18). We found such rearrangements in 5 of 15 American hyperplastic tonsils and lymph nodes and 5 of 10 Japanese tonsils, an incidence close to that previously seen in European patients. These data suggest that the background incidence of such rearrangements is similar in all populations, regardless of the incidence of follicular lymphoma.

BCL2 oncogene translocation is mediated by a chi-like consensus

Examination of 64 translocations involving the major breakpoint region (mbr) of the BCL2 oncogene and the immunoglobulin heavy chain locus identified three short (14, 16, and 18 bp) segments within the mbr at which translocations occurred with very high frequency. Each of these clusters was associated with a 15-bp region of sequence homology, the principal one containing an octamer related to chi, the procaryotic activator of recombination. The presence of short deletions and N nucleotide additions at the breakpoints, as well as involvement of JH and DH coding regions, suggested that these sequences served as signals capable of interacting with the VDJ recombinase complex, even though no homology with the traditional heptamer/spacer/nonamer (IgRSS) existed. Furthermore, the BCL2 signal sequences were employed in a bidirectional fashion and could mediate recombination of one mbr region with another. Segments homologous to the BCL2 signal sequences flanked individual members of the XP family of diversity gene segments, which were themselves highly overrepresented in the reciprocal products (18q-) of BCL2 translocation. We propose that the chi-like signal sequences of BCL2 represent a distinct class of recognition sites for the recombinase complex, responsible for initiating interactions between regions of DNA separated by great distances, and that BCL2 translocation begins by a recombination event between mbr and DXP chi signals. Since recombinant joints containing chi, not IgRSS, occur in brain cells expressing RAG-1 (Matsuoka, M., F. Nagawa, K. Okazaki, L. Kingsbury, K. Yoshida, U. Muller, D. T. Larue, J. A. Winer, and H. Sakano. 1991. Science [Wash. DC]. 254:81; reference 1), we further suggest that the product of this gene could mediate both BCL2 translocation and the first step of normal DJ assembly through the creation of chi joints, rather than signal or coding joints.