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Deregulated BCL2 expression enhances growth of a human B cell line.

The BCL2 (B cell lymphoma/leukemia -2) and C-MYC oncogenes become activated by chromosomal translocations involving the immunoglobulin heavy chain locus in human follicular lymphomas and Burkitt lymphomas, respectively. Though much is known about the biological actions of C-MYC, little information is available concerning the functions of BCL2, particularly in human B cells. Using a gene transfer approach we contrasted the effects of deregulated BCL2 and C-MYC expression in a human EBV-immortalized B cell line GM607B. Both BCL2 and C-MYC enhanced the ability of GM607B cells to grow in reduced serum and in limiting dilution cultures. These findings provide direct evidence that BCL2 can alter the growth characteristics of human B lymphocytes, thus strengthening arguments for its role in the pathogenesis of human lymphomas.

B-Lymphocytes↗

B-cell non-Hodgkin's lymphoma cell line (Karpas 1106) with complex translocation involving 18q21.3 but lacking BCL2 rearrangement and expression.

A B-cell non-Hodgkin's lymphoma (B-NHL) cell line (Karpas 1106) with an unusual three-way translocation involving 18q21.3 has been derived from a patient with mediastinal lymphoblastic B-NHL. Although conventional cytogenetics showed a derivative 18q-identical to that seen in cases with t(14;18)(q32.3;q21.3), no translocations of either chromosome 14 could be detected. Instead fluorescent in situ hybridization analysis using a chromosome-18 paint showed that the segment 18q21.3-18qter had become sandwiched on a derivative chromosome X between segments Xqter-c-Xq28 and 13q12-qter, with the centrometric site of 18q21.3 subband juxtaposed to the X sequences. Pulsed-field DNA blots failed to detect rearrangement of the BCL2 gene. Conventional DNA blots using a variety of restriction digests and both 5' and 3' BCL2 and FVT 1 probes also failed to detect rearrangement in Karpas 1106. A rearranged fragment seen only in HindIII digests with 5' BLC2 probes may represent a local microalteration, which is either a mutation or small deletion involving the HindIII site as seen in other cases of B-NHL. Neither BCL2 RNA nor BCL2 protein expression were detected. These and other data suggest that genes at 18q21.3, other than BCL2 and FVT1, may be targets for translocation in certain subgroups of B-NHL.

Adult↗

Paradoxical inhibition of solid tumor cell growth by bcl2.

The BCL2 gene product has been demonstrated to prevent apoptosis and provide a selective growth advantage to many cell types. We report an unexpected effect of bcl2 expression on the in vitro growth of several solid tumor cell lines. Expression of bcl2 in these cell lines resulted in growth inhibition similar to that seen with p53. In contrast, a COOH-terminal deletion mutant of bcl2 was unable to suppress growth. Thus, the bcl2 protein may exert distinct biological effects in different cell types.

Base Sequence↗

BCL2 gene activation and protein expression in follicular lymphoma: a report on 64 cases.

Rearrangements of the BCL2 gene and expression of bcl-2 protein were analyzed in a series of 64 cases of follicular lymphomas in order to establish a relationship between the rearrangements and the protein overexpression. Of the 64 cases, 41 showed BCL2 rearrangement involving one of the three breakpoint clusters: 30 in mbr, eight in mcr, and three in vcr. A double rearrangement mbr+vcr was detected in two cases. Twenty cases with bcl-2 protein expression in tumor cells exhibited no apparent rearrangement, suggesting the possible existence of other mechanisms activating the gene. Interestingly, expression of the LMP1 protein, the Epstein-Barr virus (EBV) encoded gene, whose capacity to induce BCL2 has been recently demonstrated, was only found in 2/41 cases in which BCL2 was rearranged. These data suggest that EBV infection is not an important mechanism in the activation of BCL2 in follicular lymphoma.

Antigens, Viral↗

Detection of clonal CD34+19+ progenitors in bone marrow of BCL2-IgH-positive follicular lymphoma patients.

The frequent occurrence of BCL2-IgH rearrangements in follicular lymphoma (FL) makes detection of low numbers of tumor cells possible by polymerase chain reaction (PCR). The presence of BCL2-IgH in the bone marrow (BM) and peripheral blood of many FL patients at the time of autografting has led to the suggestion that selection of the CD34-enriched fraction may lead to reinfusion of lower numbers of tumor cells. To address this issue, we PCR-amplified BCL2-IgH from fluorescence-activated cell sorting (FACS)-purified BM CD34+ and CD34- fractions in seven FL patients showing a PCR-detectable translocation in the major breakpoint region of BCL2, five of which showed morphological BM involvement. The total CD34+ fraction showed diminished but residual positivity in the first two cases tested. Therefore, BM cells from the remaining five patients were sorted for the CD34+19- immature population, the CD34+19+ B-cell precursors, and the CD34-19+ mature B-cell fraction. The CD34+19- subpopulation was negative in four of five, despite evident BM infiltration in three cases. In contrast, the CD34+19+ fraction was positive in all three cases tested. These cells represented 0% to 50% (mean, 18%) of the total CD34+ population, suggesting that, if reinfusion of BCL2-IgH-positive cells plays a role in postautograft relapse in FL, therapeutic CD34 selection procedures should include additional purging of the CD34+19+ B-cell precursors or, at least, assessment of the proportion of CD19+ cells in the CD34+ fraction and its correlation with clinical outcome postreinfusion.

Adult↗

Role of three cancer "master genes" p53, bcl2 and c-myc on the apoptotic process.

We review some of the most recent developments concerning three genes involved in human cancer: p53, bcl2 and c-myc. Recent data have demonstrated that the bcl2 gene protects tumor cells from apoptosis induced by a variety of agents, including ionizing radiation, and is thus related to resistance to DNA-damaging therapeutic agents. The p53 tumor suppressor gene, however, has been related with growth arrest, apoptosis and thus with selective sensitivity to the killing effects of ionizing radiation and DNA-damaging drugs. This functional antagonism between the two genes was recently substantiated in molecular terms by demonstration of reciprocal down-regulation due to the presence of a p53-dependent transcription silencer in the untranslated region of the bcl2 gene. Growth arrest in the G1 phase of the cell cycle and induction of apoptosis are two distinct and dissectable functions of p53: bcl2 is able to antagonize the induction of apoptosis by p53, but not the growth arrest in G1. However, coexpression of bcl2 and of the oncogene c-myc efficiently antagonizes effects of p53 on G1 arrest and apoptosis, thus suggesting a cooperation between the two oncogenes. In addition, c-myc disrupts other functions of genetic control in the early G1 phase of the cell cycle including the expression of D1 cyclin. We believe that knowledge of the functional/molecular interactions between these three genes involved in human cancer is a fundamental prerequisite to improve the knowledge on prognosis and to design innovative therapeutic approaches.

Animals↗

Cytogenetic and molecular characterization of an atypical ETP-ALL case with BCL2 dependency: therapeutic implications for Venetoclax use.

BACKGROUND: Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) is a rare, high-risk subtype of T-ALL characterized by distinctive immunophenotypic and genomic features. It is often associated with induction failure and frequent relapses. Despite recent advances in its molecular characterization, the prognosis remains dismal, and effective targeted therapies are limited. METHODS AND RESULTS: We report a pediatric, multi-refractory ETP-ALL case with novel cytogenetic alterations, including a 4q deletion and a t(16;18)(q24;q21) translocation. Molecular profiling revealed progressive activation of the BCL2 pathway and disruption of Th17-related immune markers. Ex vivo sensitivity assays performed at different disease stages demonstrated increasing BCL2 dependency. Based on these findings, venetoclax was administered on a compassionate-use basis, resulting in rapid hematologic recovery and a marked reduction in blast percentage. CONCLUSIONS: This case highlights the role of clonal evolution and immune deregulation in accompanying BCL2 addiction in relapsed ETP-ALL. Altogether, our findings underscore the therapeutic potential of venetoclax in refractory pediatric ETP-ALL cases with progressive BCL2 dependency.

Humans↗

Testicular aggressive B-cell lymphoma with plasmablastic morphology harboring concurrent IGH::MYC and IGH::BCL2 rearrangements.

BACKGROUND: Aggressive B-cell lymphomas with plasmablastic morphology are uncommon neoplasms that may exhibit overlapping morphologic, immunophenotypic, and genetic features of plasmablastic lymphoma (PBL) and double-hit lymphoma (DHL). Concurrent IGH::MYC and IGH::BCL2 rearrangements are rarely encountered in this setting, particularly in the testis. Here, we describe an unusual case presenting significant diagnostic challenges at the interface between PBL and DHL. CASE PRESENTATION: We report a 66-year-old, immunocompetent man presenting with a 5 cm left testicular mass. Histologic examination revealed diffuse proliferation of large atypical lymphoid cells with plasmablastic morphology. Immunohistochemically, the tumor expressed CD138, CD38, and MUM1, with focal BCL2, c-MYC protein, and CD79a positivity, while CD20, CD19, PAX5, CD10, BCL6, and ALK were negative. EBV-encoded RNA in situ hybridization was negative. Fluorescence in situ hybridization identified IGH::MYC [t(8;14)] rearrangement in 45% and IGH::BCL2 [t(14;18)] rearrangement in 21% of analyzed nuclei. Next-generation sequencing additionally revealed BRAF V600E mutation, CDKN2A deletion, and human leukocyte antigen class I genomic alterations. CONCLUSION: This case highlights a rare testicular aggressive B-cell lymphoma with plasmablastic morphology and concurrent IGH::MYC and IGH::BCL2 rearrangements, representing a diagnostically challenging neoplasm at the interface between PBL and DHL. Our findings underscore the value of integrated morphologic, immunophenotypic, cytogenetic, and molecular analyses in evaluating aggressive B-cell lymphomas with plasmablastic features arising in immune-privileged sites.

Humans↗

Increase of MnSOD expression and decrease of JNK activity determine the TNF sensitivity in bcl2-transfected L929 cells.

To investigate the protection mechanism of Bcl-2 against tumour necrosis factor (TNF)-mediated cell death, the bcl2 gene was transfected into the L929 cells and stably expressed. Two clones having different sensitivity among bcl2-transfected L929 clones had been isolated, and termed clone R1 and R2. It was observed that activation of manganese superoxide dismutase (MnSOD) and suppression of Jun kinase of clone R1 and R2 were correlated with protection from TNF cytotoxicity. Upon treatment with TNF, clone R1 and R2 were more resistant than control L929 cells against TNF cytotoxicity and the protective effect of clone R1 was stronger than clone R2. However, in case of TNF plus actinomycin D treatment, clone R1 was still resistant against TNF cytotoxicity, whereas clone R2 became more sensitive than control L929 cells. The JNK activities of clone R1 and R2 were suppressed upon TNF treatment and in case of TNF plus actinomycin D treatment, clone R2 showed a marked increase in JNK activities and had higher activity than control L929 cells. The specific activities of MnSOD of clone R1 and R2 upon TNF treatment were 70 U/ml and 33 U/ml, respectively, while the MnSOD activity was not detectable in control L929 cells. When TNF and actinomycin D were treated simultaneously, MnSOD activity was not detectable in control L929 cells and bcl2 -transfected L929 cells (clone R1, R2). Consistent with these results, both clone R1 and R2 showed higher levels of MnSOD mRNA expression than control L929 cells after TNF treatment. These data suggest that suppression of Jun kinase and increase of MnSOD may be involved in inhibitory action of Bcl-2 against TNF, and the balance between MnSOD and JNK signalling pathway may be an important factor for the protection of bcl2-transfected L929 cells from TNF cytotoxicity.

Animals↗

Mouse vaginal opening is an apoptosis-dependent process which can be prevented by the overexpression of Bcl2.

In the mouse, opening of the vaginal cavity to the skin is a late event, occurring around the fifth week of life; it can be induced in sexually immature mice by beta-estradiol injections. We have generated two lines of transgenic mice expressing the human Bcl2 protein in a variety of tissues. The vaginal cavity of the transgenic females remained permanently closed, a condition completely resistant to beta-estradiol injections; this was accompanied by a considerable distension of the genital tract. Histologic studies of vaginal sections at the time of opening to the skin in normal mice showed, by the TUNEL method which detects nuclei with fragmented DNA characteristic of apoptosis, that this event coincides with extensive apoptosis in the lower part of the vaginal mucosa, a process prevented in the bcl2 transgenic mice, which express Bcl2 in suprabasal epithelial cells and in subepithelial cells of the vaginal mucosa. In contrast, two lines of mice bearing a Bcl2 transgene placed under the control of a K10 keratin promoter, whose expression is restricted to the suprabasal layers of the epidermis, had a normal phenotype. Eyelids' formation and opening of the external ear canals, which also occur after birth in the mouse, were not altered in any of these transgenic lines; histological study of eye and ear sections at the time of these events failed to detect apoptosis. In conclusion, the tissue remodeling required to complete maturation of the mouse female genital tract at the time of puberty is an hormonally triggered apoptosis-dependent process.

Animals↗

Prognostic markers for colorectal cancer: expression of P53 and BCL2.

P53 is a tumor suppressor gene that has been implicated in the pathogenesis of a wide range of tumor types including colorectal cancers. bcl2 is a proto-oncogene that inhibits apoptosis. Immunostaining for P53 and BLC2 protein product was performed in a retrospective series of 80 colorectal carcinomas with a minimum follow-up of 5 years. The aim of the study was to evaluate the prognostic significance of P53 and BCL2 protein expression and their correlation with clinicopathologic variables such as pathologic disease stage (Dukes system), histologic grade, and vascular invasion. The patients were 41 to 76 years of age, and the follow-up ranged between 5 and 10 years. Among the 80 cases, 30 were Dukes stage A and 50 stage B. We found vascular invasion in 21.2%. P53 and BCL2 expression was detected, respectively, in 30.0% and 8.8%. We concluded that the P53 and BCL2 expression detected by immunohistochemistry in routinely processed, paraffin-embedded tissues: (1) has no prognostic significance; and (2) was not correlated with pathologic disease stage, histologic grade, or vascular invasion. Nevertheless, the number of patients in our study was small, and we believe that investigation of a larger series of patients is indicated.

Adult↗

Expression of bcl2 family proteins and active caspase 3 in classical Hodgkin's lymphomas.

The expression of various bcl2 family proteins has been reported in Hodgkin and Reed-Sternberg cells, but the proteins bad, bid, and bim have not been analyzed in classical Hodgkin's lymphomas (HLs). This study aimed to investigate the expression of the proteins bcl2, bcl-xl, mcl1, bax, bak, bad, bid, bim, and active caspase 3, and the TUNEL (terminal deoxynucleotidyl transferase-mediated in situ labeling) index to gain further insight into the apoptosis profile of classical HLs. A high expression of the proteins bcl2, bcl-xl, mcl1, bax, bak, bad, bid, and bim in HRS cells was found in 27 of 101 (27%), 95 of 101 (94%), 27 of 97 (29%), 73 of 95 (77%), 37 of 102 (36%), 85 of 94 (90%), 19 of 109 (17%), and 43 of 91 (47%) cases, respectively. The high expression of bcl-xl, bax, and bad in HRS cells in most classical HLs indicates that these proteins may play predominant roles in the regulation of apoptosis in classical HLs. Active caspase 3-positive and TUNEL-positive Reed-Sternberg cells were detected in 47 of 70 (67%; range, 0%-12%) and 60 of 71 (85%; range, 0%-19%) cases, respectively. Significant positive correlations were found between bax/bcl2 (P = .002), bad/bcl2 (P = .020), bad/bcl-xl (P = .003), and bim/mcl1 (P = .036). Based on these findings, it could be hypothesized that the antiapoptotic proteins bcl2, bcl-xl, and mcl1 may counteract the expression of the proapoptotic proteins bax, bad, and bim, thereby contributing to the survival of Reed-Sternberg cells.

Apoptosis↗

BCL2 translocation defines a unique tumor subset within the germinal center B-cell-like diffuse large B-cell lymphoma.

Gene expression profiling of diffuse large B-cell lymphoma (DLBCL) has revealed prognostically important subgroups: germinal center B-cell-like (GCB) DLBCL, activated B cell-like (ABC) DLBCL, and primary mediastinal large B-cell lymphoma. The t(14;18)(q32;q21) has been reported previously to define a unique subset within the GCB-DLBCL. We evaluated for the translocation in 141 cases of DLBCL that were successfully gene expression profiled. Using a dual-probe fluorescence in situ hybridization assay, we detected the t(14;18) in 17% of DLBCLs and in 34% of the GCB subgroup which contained the vast majority of positive cases. In addition, 12 t(14;18)-positive cases detected by polymerase chain reaction assays on additional samples were added to the fluorescence in situ hybridization-positive cases for subsequent analysis. Immunohistochemical data indicated that BCL2, BCL6, and CD10 protein were preferentially expressed in the t(14;18)-positive cases as compared to t(14;18)-negative cases. Within the GCB subgroup, the expression of BCL2 and CD10, but not BCL6, differed significantly between cases with or without the t(14;18): 88% versus 24% for BCL2 and 72% versus 32% for CD10, respectively. In the GCB-DLBCL subgroup, a heterogeneous group of genes is overexpressed in the t(14;18)-positive subset, among which BCL2 is a significant discriminator. Interestingly, the t(14;18)-negative subset is dominated by overexpression of cell cycle-associated genes, indicating that these tumors are significantly more proliferative, suggesting distinctive pathogenetic mechanisms. However, despite this higher proliferative activity, there was no significant difference in overall or failure-free survival between the t(14;18)-positive and -negative subsets within the GCB subgroup.

Apoptosis Regulatory Proteins↗

bcl2 and v-abl oncogenes cooperate to immortalize murine B cells that secrete antigen specific antibodies.

In this manuscript, a general strategy was designed and used to rapidly test whether any combination(s) of p53, v-abl, bcl2 and ras oncogenes could act cooperatively to immortalize B cells. Here we report that only the combination of v-abl and bcl2 was successful. Splenic B cells from beta galactosidase-immunized mice were stimulated in vitro with lipopolysaccharide and dextran sulphate for 48 h and co-infected with ecotropic A-MuLV (v-abl) and amphotropic pZip-bcl2 (human bcl2) viruses. When inoculated i.p. into naive pristane-primed mice, these B cells generated mesenteric lymphadenopathy, intraperitoneal lymph nodules and ascites in 100% (8/8) of the mice within 36-53 days. The ascites fluid contained 69.5-122 microg/ml IgG and 2.5-13 microg/ml IgM against the immunogen. The ascites cells were passed intraperitoneally up to three times. In all passages, ascites tumors were generated, and the ascites fluid contained beta galactosidase-specific IgG and IgM, indicating that some immunoglobulin secreting B cells had been immortalized. Neither ascites nor tumors were produced when B cells infected with only one of the viruses was injected into the mice. The presence of each oncogene in ascites cells was verified by immunohistochemistry or RT-PCR. This study provides evidence for the cooperativity of an unexpected pair of oncogenes in B cell immortalization.

3T3 Cells↗

Concurrent translocation of BCL2 and MYC with a single immunoglobulin locus in high-grade B-cell lymphomas.

B-cell leukaemia or lymphoma with a combination of t(8;14)(q24;q32) of Burkitt leukaemia/lymphoma and t(14;18)(q32;q21) of follicular lymphoma may present clinically as de novo acute lymphoblastic leukaemia or transformation of follicular lymphoma to aggressive histology diffuse lymphoma. A number of cell lines have been reported with a complex t(8;14;18) with fusion of MYC, IGH and BCL2 on the same derivative 8 chromosome. The objective of this study was to determine the frequency and chromosomal features of this der(8)t(8;14;18) in a series of acute leukaemias and malignant lymphomas. A database of 1350 leukaemia and lymphoma karyotypes was searched for cases with structural alterations affecting both 8q24 and 18q21. A total of 55 cases were identified, of which eight revealed a complex der(8)t(8;14;18) with an MYC-IGH-BCL2 rearrangement resulting from translocation of BCL2 and MYC with a single disrupted IGH allele. Molecular cytogenetic investigation is essential to identify cases of high-grade leukaemia/lymphoma with concurrent translocations affecting the BCL2 and MYC loci.

Adult↗

Analysis of p53 and BAX mutations, loss of heterozygosity, p53 and BCL2 expression and apoptosis in basal cell carcinoma in Korean patients.

BACKGROUND: Apart from some Japanese studies, there are few data on the gene mutations involved in the development of basal cell carcinomas (BCC) in Koreans or other Asians. Objective To gain insight into the molecular pathogenesis of BCC in Koreans. METHODS: A collection of 33 cases of BCC were screened for mutations of p53 and BAX genes, p53 and BCL2 expression, loss of heterozygosity (LOH) and apoptosis. RESULTS: Mutations of p53, found in 9% (three of 33) of the cases, were all mis-sense mutations (G-->C transversions) at codon 246 on exon 7. In 6% (two of 33), BAX gene showed frameshift mutations resulting from deletions in the poly(G) tract. LOH on chromosome 9q was seen in 58% (14 of 24), and p53 mutations developed only among the 9q LOH+ cases; LOH on chromosome 18q, where BCL2 gene is located, was found in 13% (four of 30). Immunohistochemical expression of p53 was seen in 27% (nine of 33), and its expression did not coincide with p53 mutations. BCL2 expression was seen in 39% (13 of 33). Apoptosis was revealed in 21%. In BCC, 9q LOH and p53 mutations seem to be closely related; the immunoreactivity of p53 and its mutations were not directly related; and p53 and BCL2 expression were negatively correlated. Frameshift mutations of the BAX gene in BCC are documented for the first time. CONCLUSIONS: Various molecular mechanisms operate with redundant complexity in the pathogenesis of BCC. The LOH on chromosome 9q is the most frequent genetic alteration, as in other races; however, p53 mutations are much less frequent in Koreans than in Caucasians and suggest aetiologies other than ultraviolet radiation.

Adult↗

Meiotic recombination between yeast artificial chromosomes yields a single clone containing the entire BCL2 protooncogene.

The common translocation found in human follicular lymphoma, t(14;18)(q32;q21), results in deregulation of the BCL2 protoonocogene. The isolation of the intact gene would provide an essential substrate to analyze the molecular basis of this malignancy. Pulsed-field gel electrophoresis suggested that this three-exon gene was several hundred kilobases (kb) long. Therefore, a library of yeast artificial chromosome (YAC) clones was screened to isolate the intact BCL2 gene. Two clones, yA85B6 (200 kb) and yB206A6 (700 kb), were isolated by using polymerase chain reaction (PCR) assays specific for exon I/II and exon III, respectively. However, neither YAC contained the entire BCL2 locus. Since the two YACs were found to overlap by 60 kb, we sought to take advantage of the high recombination frequency in yeast and induce physical recombination between the two clones. Cells containing each YAC were mated and induced to undergo meiotic division and sporulation. Analysis of the resulting tetrads revealed a spore containing a single recombinant YAC of 800 kb. PCR assays and Southern blotting demonstrated that this recombined YAC contained the entire approximately 230-kb BCL2 gene. Furthermore, probe order was conserved and there was no evidence of overt rearrangements or deletions. These results indicate the feasibility of reconstructing large genomic segments with overlapping YAC clones to study genes spanning hundreds of kilobases.

Chromosomes, Fungal↗

MCL1, a gene expressed in programmed myeloid cell differentiation, has sequence similarity to BCL2.

During their lifespan, immature cells normally pass through sequential transitions to a differentiated state and eventually undergo cell death. This progression is aberrant in cancer, although the transition to differentiation can be reestablished in inducible leukemia cell lines. This report describes a gene, MCL1, that we isolated from the ML-1 human myeloid leukemia cell line during phorbol ester-induced differentiation along the monocyte/macrophage pathway. Our results demonstrate that expression of MCL1 increases early in the induction, or "programming," of differentiation in ML-1 (at 1-3 hr), before the appearance of differentiation markers and mature morphology (at 1-3 days). They further show that MCL1 has sequence similarity to BCL2, a gene involved in normal lymphoid development and in lymphomas with the t(14;18) chromosome translocation. MCL1 and BCL2 do not fall into previously known gene families. BCL2 differs from many oncogenes in that it inhibits programmed cell death, promoting viability rather than proliferation; this parallels the association of MCL1 with the programming of differentiation and concomitant maintenance of viability but not proliferation. Thus, in contrast to proliferation-associated genes, expression of MCL1 and BCL2 relates to the programming of differentiation and cell viability/death. The discovery of MCL1 broadens our perspective on an emerging MCL1/BCL2 gene family and will allow further comparison with oncogene families.

Amino Acid Sequence↗