Minor Cluster Region Research Articles

BCL2 translocations in leukemias of mature B cells

Although translocations of the BCL2 gene are frequent in B-cell non- Hodgkin's lymphomas (B-NHL) the incidence, nature, and prognostic significance of similar translocations in the phenotypically related chronic leukemias of mature B cells are unknown. Therefore, we examined 170 cases of B-cell chronic lymphocytic leukemia (B-CLL), 7 cases of B- cell prolymphocytic leukemia (B-PLL), 25 cases of hairy cell leukemia (HCL) and 22 cases of splenic lymphoma with villous lymphocytes (SLVL) with defined cytogenetic abnormalities by DNA blot using both 5′ and 3′ BCL2 probes to search for rearrangement of the BCL2 locus. Translocation t(14;18) (q32.3;q21.3) was detected cytogenetically in 3 cases of B-CLL. All had breakpoints in the 3′ region of BCL2, mapping between the major breakpoint region (MBR) and the minor cluster region (mcr), the breakpoint clusters commonly detected in B-NHL. In 2 of the 3 cases, the breakpoint within BCL2 was mapped to a 1.0-kb EcoRI- HindIII fragment indicating a clustering of breakpoints. Two cases of B- CLL had cytogenetically detectable t(2;18)(p11;q21.3) or t(18;22)(q21.3;q11). Both had rearranged the 5′ region of the BCL2 gene to the corresponding lg light-chain gene. Molecular cloning of the t(18;22)(q21.3;q11) showed that the translocation disrupted the BCL2 promoter region and the first untranslated BCL2 exon. Nevertheless, high levels of BCL2 protein were seen in this case. Only 2 other cases in whom cytogenetic analysis was not successful showed rearrangement of the 5′ region of BCL2, an overall incidence of 2.3%. No cases of B-PLL, HCL, or SLVL showed either 5′ or 3′ BCL2 rearrangement. These data confirm the cytogenetic observations that translocations involving the BCL2 locus in all forms of leukemia of mature B cells are rare, and limited to a minor subset of B-CLL. BCL2 translocations in B-CLL involve hot spots of recombination of both the 5′ and 3′ regions of the BCL2 gene, which are distinct from those commonly seen in B-NHL, suggesting distinct pathogenic mechanisms.

A new B-cell line showing a complex translocation (8;14;18) and BCL2 rearrangement

A cell line named ROS-50 (Rotterdam suspension cell line no. 50) has been established from peripheral blood of a 69-year-old male with acute lymphoblastic leukemia (FAB type L3). Among the aberrations, cytogenetic analysis showed the presence of 14q+, 18q−, and two 8q− marker chromosomes. With fluorescence in situ hybridization (FISH) we characterized the chromosomal translocations, t(8;14) and t(14;18), in which the same chromosome 14 is involved. PCR analysis demonstrated the presence of an IGH-BCL2 rearrangement with a breakpoint in the minor cluster region (mcr) confirming the t(14;18) characteristic for follicular lymphoma. Additional studies showed high expression of BCL2 protein, an early B-cell immunophenotype, and an unusual pattern of IGH gene rearrangement.

Apparent Absence of BCL-2 Rearrangement in Ten Saudi Follicular Lymphomas: A Preliminary Report

Specific chromosomal translocations are often found to be associated with distinct types of human neoplasms. The t(14;18) is considered to be a cytogenetic hallmark of the follicular lymphomas found mostly in American patients. This chromosomal translocation occurs through a 3' untranslated region (either major breakpoint region [mbr] or minor cluster region [mcr]) of the bcl-2 proto-oncogene in chromosome 18 and the JH region of the immunoglobulin (Ig) gene in chromosome 14. In the present study, the polymerase chain reaction (PCR) was used to detect a fusion DNA fragment generated from bcl-2/JH rearrangement either through mbr or mcr in 10 follicular lymphomas in Saudi Arab patients. Surprisingly, none of these cases showed any evidence of bcl-2 gene rearrangement through mbr or mcr. The absence of usual bcl-2/JH recombination in Saudi follicular lymphomas is intriguing and may suggest that the occurrence and mode of bcl-2 gene rearrangement in this lymphoma varies in different patient populations.

Major and minor breakpoint sites of chromosomal translocation t(14;18) in subtypes of non-Hodgkin's lymphomas

The frequencies of major breakpoint region (MBR) and minor cluster region (MCR) breakpoint sites of t(14;18) were examined by polymerase chain reaction and Southern blotting in 50 non-Hodgkin's lymphomas with cytogenetic evidence of t(14;18). A translocation breakpoint was detected in 41 cases (82%). The MBR was involved in 66%, and the MCR in 16% of the cases. Most cases in the present series were lymphomas with a follicular or diffuse growth pattern, 38 being of the centroblastic/centrocytic type and eight of the centroblastic type. The series also included four lymphomas of probable non-follicular center cell origin. MBR and/or MCR breakpoints were found in all studied lymphoma subtypes and in the majority of these most of the breakpoints were in the MBR and a minor portion of the breakpoints in the MCR. Our results suggest that a breakpoint site is not related to growth pattern or neoplastic cell type in follicular center cell lymphomas with t(14;18).

Persistence of circulating t(14;18)-positive cells in long-term remission after radiation therapy for localized-stage follicular lymphoma.

To determine the prevalence of circulating t(14;18)-positive cells in patients with long-term remission after radiation therapy for stage I and II follicular lymphoma. Peripheral-blood mononuclear cells from 21 patients in continuous remission were examined by a two-step polymerase chain reaction (PCR) assay for the detection of cells carrying a t(14;18) translocation with a breakpoint within the major breakpoint region (MBR) or minor cluster region (mcr). Follow-up duration was between 25 and 160 months, with a median of 6.5 years. Thirteen patients (62%) showed negative results on repetitive testing. Cells that were t(14;18)-positive were found in eight patients (38%), all carrying a breakpoint in the MBR. One patient relapsed in each group. Circulating t(14;18)-positive cells can persist in a high percentage of follicular lymphoma patients in long-term complete remission (CR) after radiation treatment for stage I and II disease. The significance of minimal residual t(14;18)-positive cells with regard to the risk of relapse needs to be investigated in further prospective long-term studies.

Correlation between cytogenetic and molecular analysis of t(14;18) in follicular lymphomas

A comparison between cytogenetic and molecular results of t(14;18) has been performed in 12 patients with follicular lymphomas: five nodular and seven diffuse. Ten cases showed cytogenetic alterations with different markers, including a 14q+ in eight; in four it was the result of a t(14;18). Molecular analysis by Southern blotting with bcl2 probes from major and minor cluster regions, and PCR with primers from major and minor regions showed differences versus the cytogenetic results. The correlation found between cytogenetic and molecular results suggests other factors, such as geographical differences or different pathogenetic mechanisms, more than methodologic aspects, to explain the different frequencies of this marker among countries.

Enhanced Detection of the t(14;18) Translocation in Malignant Lymphoma Using Pulsed-Field Gel Electrophoresis

The t(14;18) chromosomal translocation that results in the juxtaposition of the bcl-2 proto-oncogene with the heavy chain JH locus is a common cytogenetic abnormality in human lymphoma. In particular, it is seen in about 85% of follicular lymphoma (FL) and up to one-third of diffuse lymphomas (DL). The chromosome 18 breakpoints have been shown to cluster into two regions. The major breakpoint region (mbr) within the 3' untranslated region of the bcl-2 proto-oncogene accounts for approximately 60% of the cases and the minor cluster region (mcr) 30 kb 3' of bcl-2 accounts for approximately 25% of the breakpoints. Because of variability in the position of the breakpoint, detection of the t(14;18) by Southern blot analysis provides an important clonal marker for the tumor. However, conventional electrophoresis (CE) fails to detect the translocation in 15% to 25% of cases. We have applied pulsed-field gel electrophoresis (PFGE) to the detection of the t(14;18) in a series of lymphoma prospectively analyzed by CE, polymerase chain reaction (PCR), and cytogenetic analysis. PFGE readily detected t(14;18) rearrangements as indicated by comigration of bands detected with probes for the mbr region (chromosome 18) and the JH locus (chromosome 14). In a series of 40 patients with FL, this method proved to be the most comprehensive for detection of the translocation compared with standard methods; in fact, in one case only PFGE was able to detect the chromosomal rearrangement. Ten percent of the FL cases were negative by all methods tested. In a separate analysis of matched tissue specimens from cases of tumor progression of FL to diffuse lymphoma, PFGE detected a common t(14;18) rearrangement confirming a clonal origin in seven of seven cases, whereas CE detected a rearrangement in only three of seven cases. Overall, PFGE was able to detect a translocation in 8 of 12 cases that were negative by CE and four of eight negative by cytogenetic analysis. In conclusion, PFGE analysis is more comprehensive than CE, PCR, and cytogenetic analysis for the detection of the t(14;18) breakpoint in tissue biopsies of malignant lymphoma.

Enhanced detection of the t(14;18) translocation in malignant lymphoma using pulsed-field gel electrophoresis

The t(14;18) chromosomal translocation that results in the juxtaposition of the bcl-2 proto-oncogene with the heavy chain JH locus is a common cytogenetic abnormality in human lymphoma. In particular, it is seen in about 85% of follicular lymphoma (FL) and up to one-third of diffuse lymphomas (DL). The chromosome 18 breakpoints have been shown to cluster into two regions. The major breakpoint region (mbr) within the 3′ untranslated region of the bcl-2 proto-oncogene accounts for approximately 60% of the cases and the minor cluster region (mcr) 30 kb 3′ of bcl-2 accounts for approximately 25% of the breakpoints. Because of variability in the position of the breakpoint, detection of the t(14;18) by Southern blot analysis provides an important clonal marker for the tumor. However, conventional electrophoresis (CE) fails to detect the translocation in 15% to 25% of cases. We have applied pulsed-field gel electrophoresis (PFGE) to the detection of the t(14;18) in a series of lymphoma prospectively analyzed by CE, polymerase chain reaction (PCR), and cytogenetic analysis. PFGE readily detected t(14;18) rearrangements as indicated by comigration of bands detected with probes for the mbr region (chromosome 18) and the JH locus (chromosome 14). In a series of 40 patients with FL, this method proved to be the most comprehensive for detection of the translocation compared with standard methods; in fact, in one case only PFGE was able to detect the chromosomal rearrangement. Ten percent of the FL cases were negative by all methods tested. In a separate analysis of matched tissue specimens from cases of tumor progression of FL to diffuse lymphoma, PFGE detected a common t(14;18) rearrangement confirming a clonal origin in seven of seven cases, whereas CE detected a rearrangement in only three of seven cases. Overall, PFGE was able to detect a translocation in 8 of 12 cases that were negative by CE and four of eight negative by cytogenetic analysis. In conclusion, PFGE analysis is more comprehensive than CE, PCR, and cytogenetic analysis for the detection of the t(14;18) breakpoint in tissue biopsies of malignant lymphoma.

Structural Alterations in the 5′ Region of the BCL2 Gene in Follicular Lymphomas With BCL2‐MBR or BCL2‐MCR Rearrangements

We report a new class of molecular lesions in the 5' region of the BCL2 protooncogene when it undergoes a t(14;18) translocation-associated rearrangement in the major break cluster (MBR) or minor break cluster (MCR) regions. Among 52 tumors assayed for BCL2 rearrangements using the MBR, MCR, and 5' probes, seven (six with MBR and one with MCR translocation breaks) showed aberrant bands in unique enzyme digests of DNA hybridized with the 5' probe. The aberrant bands in four tumors were in HindIII digests, in two they were in EcoRI digests, while the aberrant band in one was in a BamHI digest. The two EcoRI bands and two of the four HindIII bands were of identical sizes. Germline polymorphisms as the source of these bands was ruled out by appropriate control experiments. These results suggest that the bands were derived from point mutations or small deletions in the 5' region of BCL2. The significance of this alteration to BCL2 function in translocation-carrying tumors remains to be determined.

Translocation of bcl‐2 gene in non‐Hodgkin's lymphomas in Hong Kong Chinese

The close association between translocation of the proto-oncogene bcl-2 and follicular lymphomas has been well established in Caucasian patients and the de-regulation of bcl-2 has been implicated in follicular lymphomagenesis. Similar molecular structural alterations have also been detected in diffuse lymphomas with a previous history of a follicular pattern as well as in a smaller proportion of de novo diffuse lymphomas. There is a lower incidence of follicular lymphomas in Chinese. In order to investigate further this phenomenon, we used bcl-2 translocation as a genetic marker of follicular lymphomas, to study 31 cases of B cell non-Hodgkin's lymphomas in Chinese patients by Southern blot analysis. Eight out of 16 cases of follicular lymphomas showed bcl-2 translocation with involvement of the major breakpoint region (MBR). Six of these cases utilized breakpoints within the 4.3 kb HindIII fragment, while in two cases the breakpoints were more dispersed, but still within the BamHI fragment. An additional case of follicular lymphoma showed translocation of bcl-2 gene with involvement of the minor cluster region (mcr), making a total of nine out of 16. None of the 15 cases of diffuse lymphomas showed similar molecular structural alterations. These data show that bcl-2 translocation is present in 57% of follicular lymphomas in Chinese patients, and support the notion that bcl-2 translocation is a consistent marker for follicular lymphomas irrespective of ethnic differences. As the translocation is not detected in the diffuse lymphomas, there is no evidence to suggest that the low incidence of follicular lymphomas in Chinese patients is due to a greater tendency for follicular tumours to progress rapidly and present as diffuse lymphomas.

Detection of chromosomal translocation t(14;18) within the minor cluster region of bcl-2 by polymerase chain reaction and direct genomic sequencing of the enzymatically amplified DNA in follicular lymphomas

A majority of t(14;18) translocations have been shown to cluster at one of two sites on chromosome 18, called the major breakpoint region (mbr) or the minor cluster region, (mcr), which map within or flanking the bcl-2 proto-oncogene, respectively. We have determined the nucleotide sequence for a portion of the mcr, and constructed oligonucleotides that were used to perform the polymerase chain reaction (PCR) in conjunction with universal immunoglobulin primers to specifically amplify t(14;18) breakpoints in DNA obtained from follicular lymphomas. Eight of ten breakpoints that were detectable on Southern blots using DNA probes for the mcr could be detected due to specific amplification by the PCR technique using an mcr-specific primer. Direct nucleotide sequencing of the enzymatically amplified DNAs showed that the breakpoints clustered within a 500 nucleotide region, and five occurred within three nucleotides of each other. These data show a remarkable clustering of some t(14;18) breakpoints at a site on chromosome 18, at least a 30-kb distance from the bcl-2 gene. Our findings also indicate that mcr-specific primers may be used in conjunction with previously described mbr-specific primers in a highly sensitive DNA amplification technique to detect a large fraction of t(14;18) breakpoints.

Detection of Chromosomal Translocation t( 14; 18) Within the Minor Cluster Region of bcl-2 by Polymerase Chain Reaction and Direct Genomic Sequencing of the Enzymatically Amplified DNA in Follicular Lymphomas

A majority of t(14;18) translocations have been shown to cluster at one of two sites on chromosome 18, called the major breakpoint region (mbr) or the minor cluster region, (mcr), which map within or flanking the bcl-2 proto-oncogene, respectively. We have determined the nucleotide sequence for a portion of the mcr, and constructed oligonucleotides that were used to perform the polymerase chain reaction (PCR) in conjunction with universal immunoglobulin primers to specifically amplify t(14;18) breakpoints in DNA obtained from follicular lymphomas. Eight of ten breakpoints that were detectable on Southern blots using DNA probes for the mcr could be detected due to specific amplification by the PCR technique using an mcr-specific primer. Direct nucleotide sequencing of the enzymatically amplified DNAs showed that the breakpoints clustered within a 500 nucleotide region, and five occurred within three nucleotides of each other. These data show a remarkable clustering of some t(14;18) breakpoints at a site on chromosome 18, at least a 30-kb distance from the bcl-2 gene. Our findings also indicate that mcr-specific primers may be used in conjunction with previously described mbr-specific primers in a highly sensitive DNA amplification technique to detect a large fraction of t(14;18) breakpoints.

GONORRHOEA

<h3>OBJECTIVE:</h3> Follicular lymphoma (FL), a common subtype of non-Hodgkin9s lymphoma (NHL) in the West, represents a rare subtype in Jordan. Bcl-2 gene rearrangement plays a crucial role in the biology of the vast majority of FL and a substantial number of diffuse large B-cell lymphoma (DLBCL) in the West; but its presence has not been studied in Jordan. Our aims are to document if bcl-2 gene rearrangement exists in Jordanian FL and DLBCL, and if present to determine whether its frequency among these lymphomas is different from the West and therefore may be responsible for some of the epidemiological differences seen between Jordan and the West. <h3>METHODS:</h3> The study was conducted in the year 2001 using polymerase chain reaction (PCR), to detect bcl-2 gene rearrangement in paraffin sections in 5 FL and 23 DLBCL cases diagnosed at the Department of Pathology at Jordan University of Science and Technology, Irbid, Jordan. Two sets of primers including the major breakpoint region (MBR) and the minor cluster region (MCR) were used. <h3>RESULTS:</h3> Amplifiable DNA was extracted from all cases. Bcl-2 gene rearrangement was seen among 4 (80%) of 5 FL cases, and 8 (35%) of 23 DLBCL cases. The majority of the rearrangements involved the MBR; however, one fourth of cases (one of 4 FL; 2 of 8 DLBCL) with bcl-2 rearrangement involved the MCR. <h3>CONCLUSION:</h3> Bcl-2 gene rearrangement was seen in the vast majority of Jordanian FL cases and approximately one third of all DLBCL cases. These figures are similar to those reported in the West, and therefore bcl-2 gene rearrangement does not help in explaining the epidemiological differences of NHL between Jordan and the West. The presence of bcl-2 gene rearrangement in DLBCL may define a subset of lymphomas that may be biologically and clinically unique and different from the rest of DLBCL.