DNA rearrangements in human follicular lymphoma can involve the 5' or the 3' region of the bcl-2 gene

Overview of the Side-Effects of FDA- and/or EMA-Approved Targeted Therapies for the Treatment of Hematological Malignancies

In the last decade there has been tremendous effort in offering better therapeutic management strategies to patients with hematologic malignancies. These efforts have ranged from biological to clinical approaches and resulted in the rapid development of new approaches. The main “problem” that comes with the high influx of newly approved drugs, which not only influences hematologists that frequently work with these drugs but also affects other healthcare professionals that work with hematologists in patient management, including intensive care unit (ICU) physicians, is they have to keep up within their specialty and, in addition, with the side-effects that can occur when encountering hematology-specific therapies. Nonetheless, there are few people that have an in-depth understanding of a specialty outside theirs. Thus, this manuscript offers an overview of the most common side-effects caused by therapies used in hematology nowadays, or that are currently being investigated in clinical trials, with the purpose to serve as an aid to other specialties. Nevertheless, because of the high amount of information on this subject, each chapter will offer an overview of the side-effects of a drug class with each reference of the section being intended as further reading.

Development and antitumor activity of a BCL-2 targeted single-stranded DNA oligonucleotide

PNT100 is a 24-base, chemically unmodified DNA oligonucleotide sequence that is complementary to a region upstream of the BCL-2 gene. Exposure of tumor cells to PNT100 results in suppression of proliferation and cell death by a process called DNA interference. PNT2258 is PNT100 that is encapsulated in protective amphoteric liposomes developed to efficiently encapsulate the PNT100 oligonucleotide, provide enhanced serum stability, optimized pharmacokinetic properties and antitumor activity of the nanoparticle both in vivo and in vitro. PNT2258 demonstrates broad antitumor activity against BCL-2-driven WSU-DLCL2 lymphoma, highly resistant A375 melanoma, PC-3 prostate, and Daudi-Burkitt’s lymphoma xenografts. The sequence specificity of PNT100 was demonstrated against three control sequences (scrambled, mismatched, and reverse complement) all encapsulated in a lipid formulation with identical particle characteristics, and control sequences did not demonstrate antiproliferative activity in vivo or in vitro. PNT2258 is currently undergoing clinical testing to evaluate safety and antitumor activity in patients with recurrent or refractory non-Hodgkin’s lymphoma and additional studies are planned.

A role for eukaryotic initiation factor 4B overexpression in the pathogenesis of diffuse large B-cell lymphoma

Dysregulated expression of factors that control protein synthesis is associated with poor prognosis of many cancers, but the underlying mechanisms are not well defined. Analysis of the diffuse large B-cell lymphoma (DLBCL) translatome revealed selective upregulation of mRNAs encoding anti-apoptotic and DNA repair proteins. We show that enhanced synthesis of these proteins in DLBCL is mediated by the relief of repression that is normally imposed by structure in the 5′-untranslated regions of their corresponding mRNAs. This process is driven by signaling through mammalian target of rapamycin, resulting in increased synthesis of eukaryotic initiation factor (eIF) 4B complex (eIF4B), a known activator of the RNA helicase eIF4A. Reducing eIF4B expression alone is sufficient to decrease synthesis of proteins associated with enhanced tumor cell survival, namely DAXX, BCL2 and ERCC5. Importantly, eIF4B-driven expression of these key survival proteins is directly correlated with patient outcome, and eIF4B, DAXX and ERCC5 are identified as novel prognostic markers for poor survival in DLBCL. Our work provides new insights into the mechanisms by which the cancer-promoting translational machinery drives lymphomagenesis.

Overexpression of phospholipase D enhances Bcl-2 expression by activating STAT3 through independent activation of ERK and p38MAPK in HeLa cells

The purpose of this study was to identify the role of phospholipase D (PLD) isozymes in Bcl-2 expression. Overexpression of PLD1 or PLD2 increased Bcl-2 expression and phosphatidic acid (PA), the product of PLDs, also upregulated Bcl-2 expression. Treatment with PA activated the phospholipase A(2) (PLA(2))/G(i)/ERK1/2, RhoA/Rho-associated kinase (ROCK)/p38 MAPK, and Rac1/p38 MAPK pathways. PA-induced phosphorylation of ERK1/2 was attenuated by a PLA(2) inhibitor (mepacrine) and, a G(i) protein inhibitor (pertussis toxin, PTX). On the other hand, p38 MAPK phosphorylation was attenuated by a dominant negative Rac1 and a specific Rho-kinase inhibitor (Y-27632). These results suggest that PLA(2)/G(i) acts at the upstream of ERK1/2, while Rac1 and RhoA/ROCK act upstream of p38 MAPK. We next, tried to determine which transcription factor is involved in PLD-related Bcl-2 expression. When signal transducer and activator of transcription 3 (STAT3) activity was blocked by a STAT3 specific siRNA, PA-induced Bcl-2 expression was remarkably decreased, suggesting that STAT3 is an essential transcription factor linking PLD to Bcl-2 upregulation. Taken together, these findings indicate that PLD acts as an important regulator in Bcl-2 expression by activating STAT3 involving the phosphorylation of Ser727 through the PLA(2)/G(i)/ERK1/2, RhoA/ROCK/p38 MAPK, and Rac1/p38 MAPK pathways.

Comparison of germinal center markers CD10, BCL6 and human germinal center-associated lymphoma (HGAL) in follicular lymphomas

Background

Recently, human germinal center-associated lymphoma (HGAL) gene protein has been proposed as an adjunctive follicular marker to CD10 and BCL6.

Methods

Our aim was to evaluate immunoreactivity for HGAL in 82 cases of follicular lymphomas (FLs) - 67 nodal, 5 cutaneous and 10 transformed - which were all analysed histologically, by immunohistochemistry and PCR.

Results

Immunostaining for HGAL was more frequently positive (97.6%) than that for BCL6 (92.7%) and CD10 (90.2%) in FLs; the cases negative for bcl6 and/or for CD10 were all positive for HGAL, whereas the two cases negative for HGAL were positive with BCL6; no difference in HGAL immunostaining was found among different malignant subtypes or grades.

Conclusions

Therefore, HGAL can be used in the immunostaining of FLs as the most sensitive germinal center (GC)-marker; when applied alone, it would half the immunostaining costs, reserving the use of the other two markers only to HGAL-negative cases.

Telomerase activity, estrogen receptors (alpha, beta), Bcl-2 expression in human breast cancer and treatment response

Background

The mechanism for maintaining telomere integrity is controlled by telomerase, a ribonucleoprotein enzyme that specifically restores telomere sequences, lost during replication by means of an intrinsic RNA component as a template for polymerization. Among the telomerase subunits, hTERT (human telomerase reverse transcriptase) is expressed concomitantly with the activation of telomerase. The role of estrogens and their receptors in the transcriptional regulation of hTERT has been demonstrated. The current study determines the possible association between telomerase activity, the expression of both molecular forms of estrogen receptor (ERα and ERβ) and the protein bcl-2, and their relative associations with clinical parameters.

Methods

Tissue samples from 44 patients with breast cancer were used to assess telomerase activity using the TRAP method and the expression of ERα, ERβ and bcl-2 by means of immunocytochemical techniques.

Results

Telomerase activity was detected in 59% of the 44 breast tumors examined. Telomerase activity ranged from 0 to 49.93 units of total product generated (TPG). A correlation was found between telomerase activity and differentiation grade (p = 0.03). The only significant independent marker of response to treatment was clinical stage. We found differences between the frequency of expression of ERα (88%) and ERβ (36%) (p = 0.007); bcl-2 was expressed in 79.5% of invasive breast carcinomas. We also found a significant correlation between low levels of telomerase activity and a lack of ERβ expression (p = 0.03).

Conclusion

Lower telomerase activity was found among tumors that did not express estrogen receptor beta. This is the first published study demonstrating that the absence of expression of ERβ is associated with low levels of telomerase activity.

Germline BCL-2 sequence variants and inherited predisposition to prostate cancer

Apoptosis is an essential physiological process that regulates cellular proliferation. Here, we explored the effect of DNA sequence variation within the BCL-2 gene on prostate cancer susceptibility in three clinical populations, consisting of 428 African Americans, 214 Jamaicans and 218 European Americans. We observed a 70% reduced risk for prostate cancer among the European Americans who had possessed two copies of a promoter variant -938C/A. Additionally, common BCL-2 haplotypes appeared to influence prostate cancer risk; however, studies in larger data sets are needed to confirm our findings. Our data suggest that inherited BCL-2 variants may be associated with a decrease in prostate cancer susceptibility.

Interphase fluorescence in situ hybridization with an IGH probe is important in the evaluation of patients with a clinical diagnosis of chronic lymphocytic leukaemia

Translocations involving IGH are common in some lymphoid malignancies but are believed to be rare in chronic lymphocytic leukaemia (CLL). To study the clinical utility of fluorescence in situ hybridization (FISH) for IGH translocations, we reviewed 1032 patients with a presumptive diagnosis of CLL. Seventy-six (7%) patients had IGH translocations. Pathology and clinical data were available for the 24 patients evaluated at the Mayo Clinic. Ten (42%) patients had IGH/cyclin D1 fusion and were diagnosed with mantle cell lymphoma (MCL). The immunophenotype was typical of MCL in three of these patients and atypical for MCL in seven patients. One patient had biclonal disease with typical MCL and CLL with IGH/BCL-2. Eleven (46%) patients had IGH/BCL-2 fusion including the patient with biclonal disease. Two of these patients had leukaemic phase follicular lymphoma and nine patients had CLL. The median progression-free survival of patients with CLL and IGH/BCL-2 translocation was 20.6 months. The two patients with IGH/BCL-3 fusion (one of these also had IGH/BCL-11a) had rapid disease progression. The IGH partner gene was not identified in two patients. We conclude that use of an IGH probe in FISH analysis of monoclonal B-cell lymphocytosis improves diagnostic precision and could have prognostic value in patients with CLL.

Lack of Bcl-2 expression in follicular lymphoma may be caused by mutations in the BCL2 gene or by absence of the t(14;18) translocation

Follicular lymphoma (FL), except grade 3B, is characterized by the chromosomal translocation t(14;18)(q32;q21), which results in over-expression of the Bcl-2 protein. Ten per-cent of all FLs, however, do not show Bcl-2 protein expression with standard immunohistochemistry using a monoclonal Bcl-2 antibody against residues 41-54 of the Bcl-2 protein. In this study, the biological background of 18 Bcl-2-negative FL cases grade I, II, or IIIa was investigated by immunohistochemical staining and western blot analysis with alternative antibodies. Bcl-2 protein was demonstrated in five of the 18 cases and all of these carried the t(14;18) translocation. Of the 13 cases that were Bcl-2 negative with alternative antibodies, 12 lacked the t(14;18) translocation. PCR and subsequent sequence analysis of cDNA demonstrated that three cases with a t(14;18) contained somatic mutations in the translocated BCL2 gene, resulting in amino acid replacements in the region of the epitope recognized by the antibody. In conclusion, the majority of Bcl-2-negative FL lack a t(14;18) but a significant subset of these tumours are false negative due to mutations in the BCL2 gene. These findings may have consequences for the use of Bcl-2 immunohistochemistry for diagnostic purposes.

Sustained phenotypic correction of hemophilia a mice following oncoretroviral-mediated expression of a bioengineered human factor VIII gene in long-term hematopoietic repopulating cells

Hematopoietic stem cells (HSCs) are an attractive target cell population for hemophilia A gene therapy because of their capacity to regenerate the hematolymphoid system permanently following transplantation. Here we transplanted bone marrow (BM) cells transduced with a splicing-optimized MSCV oncoretroviral vector expressing a secretion-improved human factor VIII gene into immunocompromised hemophilic mice that had received a reduced dose conditioning regimen. An enhanced green fluorescent protein (EGFP) reporter gene linked to an encephalomyocarditis virus internal ribosome entry site was incorporated into the vector to allow preselection of transduced cells and facile evaluation of engraftment. Sustained expression of EGFP was demonstrated in the peripheral blood, and therapeutic levels of factor VIII were detected in the plasma of the majority of the recipients for the duration of the observation period (up to 22 weeks). Coordinate expression of factor VIII and EGFP (up to 19 weeks) was transferred to secondary BM transplant recipients, indicating that long-term repopulating HSCs had been successfully gene modified. Notably, the hemophilic phenotype of all treated mice was corrected, thus demonstrating the potential of HSC-directed oncoretroviral-mediated factor VIII gene transfer as a curative therapeutic strategy for hemophilia A.

The pattern and frequency of t(14;18) translocation and immunophenotype in Asian follicular lymphoma

AIMS

Follicular lymphoma is frequently associated with t(14;18)(q32;q21) translocation. This study was undertaken to determine the pattern of Bcl-2, CD10 and Bcl-6 expression in relation to t(14;18) translocation in follicular lymphoma from a cohort of a multi-ethnic Asian population.

METHODS AND RESULTS

Sixty-two cases of follicular lymphoma were retrieved for immunohistochemistry, and t(14;18) translocation analysis by polymerase chain reaction and fluorescent in-situ hybridization techniques. Bcl-2 expression was present in 74% of the cases. CD10 expression was also relatively low (61%), with decreasing frequency of expression in high-grade tumours. Bcl-6 protein was expressed in most of the tumours (88%) regardless of the tumour grade. The t(14;18) translocation was detected in 46 cases (74%) with an extremely high rate of t(14;18) translocation in ethnic Indian cases (100%).

CONCLUSION

The frequency of t(14;18) translocation in this series of follicular lymphomas was higher when compared with previous Asian reports, but in accordance with European and North American findings. CD10 expression is strongly associated with a t(14;18) translocation event, but the overall CD10 expression was relatively low, possibly due to the high proportion of high-grade tumours in the series. t(14;18) translocation was not associated with Bcl-2 or Bcl-6 expression.

Frequent joining of Bcl-2 to a JH6 gene in hepatitis C virus-associated t(14;18)

The t(14;18) chromosomal translocation, which joins the Bcl-2 proto-oncogene to an Ig J(H) gene, has increased prevalence in patients chronically infected with hepatitis C virus (HCV). We now establish a link between the molecular structure and clinical occurrence of HCV-associated t(14;18). A t(14;18) was detected by PCR in leukocytes from 22 of 46 HCV-infected patients (48%) and 11 of 54 healthy controls (20%) (p = 0.0053). Nucleotide sequence analysis of the Bcl-2/J(H) joins found a J(H)6 gene in 18 of 22 (82%) t(14;18) from HCV(+) patients, and 3 of 8 (38%) from controls (p = 0.031). The t(14;18) rarely contained J(H) gene mutations, or an intervening region sequence suggestive of D gene rearrangement or templated nucleotide insertion. Analysis of published t(14;18) nucleotide sequences established that the J(H)6 prevalence in t(14;18) from normal/nonneoplastic controls (48%) was significantly lower than in t(14;18) from our HCV(+) patients (p = 0.004) or from non-Hodgkin's lymphomas (66%, p = 0.003). We conclude that the increased prevalence of t(14;18) in HCV(+) patients occurs with a strong bias for Bcl-2/J(H)6 joins. In this regard, HCV-associated t(14;18) more closely resemble t(14;18) in lymphomas than t(14;18) from normal subjects.

Improvement in the detection rate of t(14;18) translocation on paraffin-embedded tissue: a combination approach using PCR and FISH

AIMS

PCR has been the primary method used for the detection of t(14;18) translocation in formalin-fixed, paraffin-embedded tissues. This technique mainly targets the well-characterised breakpoint regions in chromosomes 14 and 18. FISH is now applicable on paraffin tissue sections and has been suggested to be capable of detecting essentially 100% of t(14;18) translocated cases. In this study, we described the application of both PCR and FISH for the detection of t(14;18) translocation.

METHODS

Fifty follicular lymphoma cases were retrieved from the files of the Department of Pathology, University of Malaya Medical Centre (UMMC). Nested PCR amplification of MBR/JH and mcr/JH was performed in these cases, and those cases that did not demonstrate the translocation were subjected to FISH analysis.

RESULTS

Thirty cases (60%) had t(14;18) translocation detected by PCR, 25 (50%) had breakpoint with MBR and five (10%) involved mcr. Twenty cases without detectable t(14;18) translocation by PCR were analysed by FISH. Eleven cases were successfully probed, and four of them showed positive translocation signal.

CONCLUSIONS

The combination of PCR and FISH analysis on paraffin tissue sections for the detection of t(14;18) translocation increases the sensitivity of detection from 60 to 68%. Problems encountered in our FISH analysis on tissue sections impose certain limitations in using this technique for retrospective screening of large number of samples. Therefore, we suggested the application of PCR as the first screening tool on retrospective archival materials, followed by FISH on those PCR-negative cases.

Translocation and gross deletion breakpoints in human inherited disease and cancer I: Nucleotide composition and recombination-associated motifs

Translocations and gross deletions are important causes of both cancer and inherited disease. Such gene rearrangements are nonrandomly distributed in the human genome as a consequence of selection for growth advantage and/or the inherent potential of some DNA sequences to be frequently involved in breakage and recombination. Using the Gross Rearrangement Breakpoint Database [GRaBD; www.uwcm.ac.uk/uwcm/mg/grabd/grabd.html] (containing 397 germ-line and somatic DNA breakpoint junction sequences derived from 219 different rearrangements underlying human inherited disease and cancer), we have analyzed the sequence context of translocation and deletion breakpoints in a search for general characteristics that might have rendered these sequences prone to rearrangement. The oligonucleotide composition of breakpoint junctions and a set of reference sequences, matched for length and genomic location, were compared with respect to their nucleotide composition. Deletion breakpoints were found to be AT-rich whereas by comparison, translocation breakpoints were GC-rich. Alternating purine-pyrimidine sequences were found to be significantly over-represented in the vicinity of deletion breakpoints while polypyrimidine tracts were over-represented at translocation breakpoints. A number of recombination-associated motifs were found to be over-represented at translocation breakpoints (including DNA polymerase pause sites/frameshift hotspots, immunoglobulin heavy chain class switch sites, heptamer/nonamer V(D)J recombination signal sequences, translin binding sites, and the chi element) but, with the exception of the translin-binding site and immunoglobulin heavy chain class switch sites, none of these motifs were over-represented at deletion breakpoints. Alu sequences were found to span both breakpoints in seven cases of gross deletion that may thus be inferred to have arisen by homologous recombination. Our results are therefore consistent with a role for homologous unequal recombination in deletion mutagenesis and a role for nonhomologous recombination in the generation of translocations.

The detection of t(14;18) in archival lymph nodes: development of a fluorescence in situ hybridization (FISH)-based method and evaluation by comparison with polymerase chain reaction

Fluorescence in situ hybridization (FISH) has been used to demonstrate the t(14;18) in up to 100% of follicular lymphoma (FL) cases, however, there is little reproducible data using fixed tissue. The aim was therefore to develop a robust FISH method for the demonstration of translocations in archival tissue. The technique was evaluated by comparison with multiplex polymerase chain reaction (PCR), capable of detecting the majority of known breakpoints. Twenty-eight paired frozen and fixed cases of FL and 20 reactive controls were analyzed. The t(14;18) was detected in 23 of 28 cases using PCR on frozen material and 8 of 20 in paraffin. Using FISH, 24 of 26 frozen and 26 of 28 paraffin cases had a demonstrable translocation. All 20 reactive nodes were negative for the t(14;18) by PCR. Using FISH, one of the reactive cases had occasional cells with a translocation FISH pattern, demonstrable in frozen and paraffin samples. This is consistent with the presence of the t(14;18), which is well described in normal individuals. Both PCR and FISH are highly effective for t(14;18) analysis in unfixed tissue. When only paraffin blocks are available, FISH is the method of choice, and a result was achieved in 100% of cases. The method is applicable to the retrospective analysis of a range of translocations.

Minimal residual disease (MRD) in follicular lymphoma in the era of immunotherapy with rituximab

The t(14;18)-translocation can be detected by PCR analysis in more than 90% of cytogenetically t(14;18)-positive follicular lymphomas (FLs), thus providing an easily accessible marker for molecular disease monitoring. Various technical aspects of the detection of residual lymphoma cells as well as the prognostic and clinical significance of the detection of minimal residual disease (MRD) after radiotherapy, chemotherapy and therapy with the monoclonal antibody rituximab are discussed. Up to now the comparability of the different studies investigating minimal residual disease in follicular lymphoma patients is hampered by the use of a variety of PCR techniques. A more standardized quantitative approach based on the real-time PCR technique will provide a powerful tool for the evaluation and optimization of therapy for each individual patient.

Viral versus cellular BCL-2 proteins

All gamma herpesviruses and a few other viruses encode at least one homologue of the mammalian cell death inhibitor BCL-2. Gamma herpesviruses are associated with human and animal lymphoid and epithelial tumours. However, the role of these viral BCL-2 homologues in the virus replication cycle or in human disease is not known, though recent developments show progress in this area. The structure of viral BCL-2 family protein, KSBcl-2, is similar to that of cellular family members, but viral BCL-2 proteins differ functionally from the cellular proteins, apparently escaping the regulatory mechanisms to which their cellular counterparts are subjected. Thus, exploring the biochemical and biological functions of the viral BCL-2 family proteins will increase our understanding of their role in virus infections and will undoubtedly teach us something about their cellular kin.

Inverse transposition by the RAG1 and RAG2 proteins: role reversal of donor and target DNA

The lymphoid-specific proteins RAG1 and RAG2 initiate V(D)J recombination by introducing DNA double-strand breaks at the recombination signal sequences (RSSs). In addition to DNA cleavage, the versatile RAG1/2 complex is capable of catalyzing several other reactions, including hybrid joint formation and the transposition of signal ends into a second DNA. Here we show that the RAG1/2 complex also mediates an unusual strand transfer reaction, inverse transposition, in which non-RSS DNA is cleaved and subsequently transferred to an RSS sequence by direct transesterification. Characterization of the reaction products and requirements suggests that inverse transposition is related to both hybrid joint formation and signal-end transposition. This aberrant activity provides another possible mechanism for some chromosomal translocations present in lymphoid tumors.

Deletion of the Ink4-locus (the p16ink4a, p14ARF and p15ink4b genes) predicts relapse in children with ALL treated according to the Nordic protocols NOPHO-86 and NOPHO-92

Inactivation of the Ink4 gene locus locus on 9p comprising the tumour suppressor gene p16ink4a and its neighbours p14ARF and p15ink4b is common in childhood acute lymphoblastic leukaemia (ALL), but the prognostic significance is controversial. DNA from 230 patients was retrospectively analysed by Southern blotting, single strand conformation polymorphism (SSCP) and sequencing techniques. The results were correlated with clinical characteristics and outcome. One hundred and ninety-four fully analysed patients, similarly treated using the Nordic NOPHO-86 or the current NOPHO-92 protocols, were included in the outcome analysis. Deletions approached a minimally deleted region between the p16ink4a and p15ink4b genes, making the p14ARF gene the most commonly deleted coding sequence. Bi-allelic deletion was associated with high white blood cell count (WBC) (P < 0.001), T cell phenotype (P < 0.001) and mediastinal mass (P < 0.001). Patients with Ink4 locus bi-allelic deletions had an inferior pEFS (P < 0.01) and multivariate analysis indicated that bi-allelic deletion of the p16ink4a and the p14ARF genes was an independent prognostic risk factor (P < 0.05). Sub-group analysis revealed a pronounced impact of deletion status for high-risk patients, ie with high WBC. Deletion-status and clinical risk criteria (WBC) could thus be combined to further differentiate risk within the high-risk group. The analysis of the Ink4 locus adds independent prognostic information in childhood ALL treated by Nordic protocols and may help in selection of patients for alternative treatment.

Dysregulation of apoptosis and a novel mechanism of defective apoptotic signal transduction in human B-cell neoplasms

Apoptotic cell death is essential for normal B-cell development and for shaping the B-cell repertoire. Dysregulation of the Bcl-2 related proteins and alterations of the p53/p14ARF pathway are implicated in the pathogenesis and treatment resistance in human B-cell malignancies. We found a novel mechanism of dysregulated apoptosis in human B lymphoma Raji cells that differs from that of altered Bcl-2 and p53 functions. This cell line was resistant to nuclear apoptosis induced by various stimuli, and neither mitochondrial activation nor activation of caspase-3 led to DNA fragmentation. DNA in purified Raji nuclei was degraded in the presence of lysates from the apoptosis-sensitive cell line HL-60, whereas Raji cell lysates did not induce DNA fragmentation in HL-60 nuclei. Cleavage of ICAD/DFF-45 was normal. These results indicate that the apoptosis signal transduction pathway is defective downstream of caspase-3 in Raji cell cytoplasm. Therefore, exploring the molecular mechanism in this system should provide insight into apoptosis resistance in human B-cell malignancies.

Telomerase activity and Bcl-2 expression in human breast cancer

AIMS

Telomerase is a ribonucleoprotein that synthesizes telomeres and plays an important role in cellular immortalization. Bcl-2 gene encodes for a mitochondrial protein thought to prevent apoptosis of normal cells. We previously reported telomerase activity in 74% of human invasive breast cancers and detected a significant association between telomerase activity and prognostic parameters such as nodal status, tumour size and cellular proliferation. We hypothesized that telomerase reactivation in human breast cancer was associated with increased immunohistochemical expression of Bcl-2.

METHODS

Bcl-2 immunohistochemical expression was determined in 25 infiltrating breast carcinomas with known telomerase activity (17 telomerase-positive and 8 telomerase-negative). The percentage of strongly and moderately stained tumour cells for Bcl-2 was determined by a breast pathologist who was blinded to telomerase data. Fisher's exact test was used to examine the association between telomerase activity and Bcl-2 expression.

RESULTS

The median percentage of strongly stained tumour cells was 50% for telomerase-positive tumours (range, 0--100%) and 45% for telomerase-negative tumours (range, 0--100%). Twelve (70%) of 17 telomerase-positive tumours expressed strong or moderate Bcl-2 staining in >50% of tumour cells compared with six (75%) of eight telomerase-negative tumours (P=1.0).

CONCLUSION

Telomerase reactivation seems to be independent of Bcl-2 protein expression in human breast cancer.

Correlation between nuclear grade and biological prognostic variables in invasive breast cancer

BACKGROUND

Grading of carcinomas is an estimation of differentiation. Nuclear grading is the cytological evaluation of tumor nuclei in comparison with the nuclei of normal mammary epithelial cells. Because nuclear grading does not involve an assessment of the growth pattern of the tumor, it applies not only to invasive ductal carcinoma but also to other subtypes of breast carcinoma.

METHODS

A total of 215 primary breast carcinomas obtained from the Affiliated Kihoku Hospital of Wakayama Medical College were enrolled in our present study. Nuclear grade was evaluated according to the criteria of the National Surgical Adjuvant Study of Breast Cancer (NSAS-B) protocol. Immunohistochemistry was also performed to determine Bcl-2, p53, c-erbB-2, estrogen receptor (ER) and MIB-1 expression in paraffin-embedded tissues for all cases.

RESULTS

Thirty-two (14.9%) of the patients were graded as 1,124 (57.7%) as 2, and 59 (27.4%) as 3. Nuclear grade displayed a negative correlation with Bcl-2 expression (r=-0.308, p<0.0001), and a positive correlation with c-erbB-2 overexpression (r= 0.172, p=0.0117) and tumor proliferative index labeling by MIB-1 (r=0.485, p<0.0001).

CONCLUSIONS

These results imply that nuclear grade is related to the characteristics of tumor biology, indicating that the morphology and biology of breast cancer are tightly linked. Our present results also suggest that adding the nuclear grade to the pathological diagnosis of invasive breast carcinoma may be clinically useful for predicting tumor behavior, for example aggressiveness, and for prognostication.

Clearing of cells bearing the bcl-2 [t(14;18)] translocation from blood and marrow of patients treated with rituximab alone or in combination with CHOP chemotherapy

PURPOSE

Patients who were PCR-positive for B-cell leukemia-lymphoma 2 (bcl-2) gene rearrangement [t(14;18)] were evaluated for responses to rituximab alone or combined with CHOP.

PATIENTS AND METHODS

Patients had relapsed or refractory low-grade or follicular non-Hodgkin's lymphoma (IWF: A-D). The single-agent trial used 375 mg/m2 weekly x 4; combination therapy included six cycles of CHOP and six 375 mg/m2 infusions of rituximab. Bcl-2 analyses of bone marrow (BM) and peripheral blood (PB) samples at base-line and following therapy were performed using a PCR assay.

RESULTS

In the single-agent trial, of 70 patients whose peripheral blood (PB) was bcl-2 positive at baseline, 36 became bcl-2-negative, 13 remained positive, and 21 varied between positive and negative. The overall response rates (ORRs) were 72%, 31%, and 57%, respectively. Twelve of twenty-two patients with repeat bone marrow (BM) samples were bcl-2-negative three months post-treatment. Of 18 patients in the combination trial, 8 were bcl-2 positive in PB and/or BM. All of seven patients positive in PB at baseline and six of seven patients positive in BM were negative at the end of therapy; all patients responded to treatment (100% ORR).

CONCLUSIONS

Rituximab, alone or combined with CHOP, eradicated bcl-2 positive cells from PB and BM in over half of the patients treated and was associated with a high overall clinical response rate. The impact on disease-free and overall survival awaits long-term follow up.

Lentiviral vectors for enhanced gene expression in human hematopoietic cells

Accumulated data indicate that current generation lentiviral vectors, which generally utilize an internal human cytomegalovirus (CMV) immediate early region enhancer-promoter to transcribe the gene of interest, are not yet optimized for efficient expression in human hematopoietic stem/progenitor cells (HSPCs). As a first step toward this goal, we constructed self-inactivating derivatives of the HIV-1-based transfer vector pHR' containing the enhanced green fluorescent protein (GFP) gene as reporter and the Woodchuck hepatitis virus posttranscriptional regulatory element (WPRE). GFP expression was driven by a variety of strong viral and cellular promoters, including the murine stem cell virus (MSCV) long terminal repeat (LTR), a Gibbon ape leukemia virus (GALV) LTR, the human elongation factor 1alpha (EF1alpha) promoter, the composite CAG promoter (consisting of the CMV immediate early enhancer and the chicken beta-actin promoter), and the human phosphoglycerate kinase 1 (PGK) promoter. In contrast to results obtained in human embryonic kidney 293T cells and fibrosarcoma HT1080 cells, in which the CMV promoter expressed GFP at the highest levels, significantly higher levels of GFP expression (3- to 5-fold) were achieved with the MSCV LTR, the EF1alpha promoter, and the CAG promoter in the human HSPC line KG1a. Removal of the WPRE indicated that it stimulated GFP expression from all of the vectors in KG1a cells (up to 3-fold), although it only marginally improved the performance of the intron-containing EF1alpha and CAG promoters (<1.5-fold stimulation). The vectors using the MSCV LTR, the GALV LTR, and the PGK promoter were the most efficient at transducing primary human CD34+ cord blood progenitors under the conditions employed. High-level GFP expression in the NOD/SCID xenograft model was demonstrated with the pHR' derivative bearing the MSCV LTR. These new lentiviral vector backbones provide a basis for the rational design of improved delivery vehicles for human HSPC gene transfer applications.

Antiapoptotic herpesvirus Bcl-2 homologs escape caspase-mediated conversion to proapoptotic proteins

The antiapoptotic Bcl-2 and Bcl-x(L) proteins of mammals are converted into potent proapoptotic factors when they are cleaved by caspases, a family of apoptosis-inducing proteases (E. H.-Y. Cheng, D. G. Kirsch, R. J. Clem, R. Ravi, M. B. Kastan, A. Bedi, K. Ueno, and J. M. Hardwick, Science 278:1966-1968, 1997; R. J. Clem, E. H.-Y. Cheng, C. L. Karp, D. G. Kirsch, K. Ueno, A. Takahashi, M. B. Kastan, D. E. Griffin, W. C. Earnshaw, M. A. Veliuona, and J. M. Hardwick, Proc. Natl. Acad. Sci. USA 95:554-559, 1998). Gamma herpesviruses also encode homologs of the Bcl-2 family. All tested herpesvirus Bcl-2 homologs possess antiapoptotic activity, including the more distantly related homologs encoded by murine gammaherpesvirus 68 (gammaHV68) and bovine herpesvirus 4 (BHV4), as described here. To determine if viral Bcl-2 proteins can be converted into death factors, similar to their cellular counterparts, five herpesvirus Bcl-2 homologs from five different viruses were tested for their susceptibility to caspases. Only the viral Bcl-2 protein encoded by gammaHV68 was susceptible to caspase digestion. However, unlike the caspase cleavage products of cellular Bcl-2, Bcl-x(L), and Bid, which are potent inducers of apoptosis, the cleavage product of gammaHV68 Bcl-2 lacked proapoptotic activity. KSBcl-2, encoded by the Kaposi's sarcoma-associated herpesvirus, was the only viral Bcl-2 homolog that was capable of killing cells when expressed as an N-terminal truncation. However, because KSBcl-2 was not cleavable by caspases, the latent proapoptotic activity of KSBcl-2 apparently cannot be released. The Bcl-2 homologs encoded by herpesvirus saimiri, Epstein-Barr virus, and BHV4 were not cleaved by apoptotic cell extracts and did not possess latent proapoptotic activities. Thus, herpesvirus Bcl-2 homologs escape negative regulation by retaining their antiapoptotic activities and/or failing to be converted into proapoptotic proteins by caspases during programmed cell death.

Bcl-2 and p53 protein expression, apoptosis, and p53 mutation in human epithelial ovarian cancers

Bcl-2 and p53 gene products have been both linked to cell death by apoptosis. In the present study, we examined the relationship of Bcl-2 and p53 protein expression, p53 mutation and apoptosis in normal human ovaries and different types of human ovarian epithelial tumors by immunohistochemical localization, in situ terminal transferase-mediated dUTP nick end labeling and polymerase chain reaction-single strand conformation polymorphism. It was found that Bcl-2 expressed strongly in the surface epithelium of normal ovaries and benign and borderline ovarian tumors but weakly in the malignant tumors. On the contrary, strong protein expression of p53 was found in 54% (25/46) of the malignant epithelial tumors examined but similar expression of p53 was not observed in borderline and benign tumors and normal ovarian surface epithelium. A significant inverse correlation between Bcl-2 and p53 expression was found in the malignant ovarian tumors examined. p53 gene mutation at exons 5-11 was however not a pre-requisite for p53 expression in both borderline and malignant tumors. Apoptotic activities, as reflected by apoptotic indices, were low in normal ovarian surface epithelium and benign tumors but were increased in borderline and malignant tumors, with the highest average apoptotic index found in grade III malignant tumors. Statistical analyses showed a positive correlation between apoptosis and p53 expression, but similar correlation was not found between apoptosis and Bcl-2 expression. Our results also indicate that although expression of Bcl-2 is important during ovarian carcinogenesis, the Bcl-2 protein may have other roles to play apart from being a modulator of apoptosis in human ovarian epithelial cancers.

Molecular and clinical features of non-Burkitt's, diffuse large-cell lymphoma of B-cell type associated with the c-MYC/immunoglobulin heavy-chain fusion gene

PURPOSE

t(8;14)(q24;q32) and/or c-MYC/immunoglobulin heavy-chain (IGH) fusion gene have been observed not only in Burkitt's lymphoma (BL) but also in a proportion of non-BL, diffuse large-cell lymphoma of B-cell type (DLCL). We explored molecular features of DLCL with c-MYC/IGH fusion and the impact of this genetic abnormality on clinical outcome of DLCL.

PATIENTS AND METHODS

A total of 203 cases of non-BL DLCL were studied. Genomic DNA extracted from tumor tissues was subjected to long-distance polymerase chain reaction (LD-PCR) using oligonucleotide primers for exon 2 of c-MYC and for the four constant region genes of IGH.

RESULTS

Twelve cases (5.9%) showed positive amplification; one had a c-MYC/Cmicro, nine had a c-MYC/Cgamma, and two had a c-MYC/Calpha fusion sequence. Restriction and sequence analysis of the LD-PCR products, ranging from 2.3 to 9.4 kb in size, showed that breakage in the 12 cases occurred within a 1.5-kb region that included exon 1 of c-MYC in combination with breakpoints at the switch regions of IGH (10 of 12). In 10 cases, Myc protein encoded by the fusion genes demonstrated mutations and/or deletions. Six cases had additional molecular lesions in BCL-2 or BCL-6 and/or p53 genes. The age range of the 12 patients was 44 to 86 years, with a median age of 65.5 years. Five patients had stage I/II disease, and seven had stage III/IV disease. Lactate dehydrogenase was elevated in nine of 11 subjects. Seven showed involvement of the gastrointestinal tract. All patients were treated by surgery and/or chemoradiotherapy; six died of the disease within 1 year, resulting in the poorest 1- and 2-year survival rates among DLCL subgroups.

CONCLUSION

The c-MYC/IGH fusion gene of DLCL is identical to that of the sporadic type of BL (sBL). DLCL with c-MYC/IGH shares clinical features with sBL but is characterized further by an older age distribution.

Quantitative detection of t(14;18)-positive cells in patients with follicular lymphoma before and after autologous bone marrow transplantation

The aim of this study was to evaluate whether a quantitative analysis of circulating t(14;18)-positive cells is of prognostic significance in patients with follicular lymphoma (FL) after myelo-ablative therapy supported by ABMT. We tested DNA from primary lymphoma tissue as well as PBMC before and after ABMT from 15 patients for the presence of the t(14;18) translocation. Nine patients showed a t(14;18) translocation, six patients were t(14;18)-negative. Circulating t(14;18)-positive cells of seven patients were quantitatively determined by limiting dilution assays combined with a two-step PCR and by real-time quantitative PCR. The results of both methods correlate very well. The number of circulating t(14;18)-positive cells decreased significantly in all patients after myeloablative therapy and ABMT, t(14;18)-negative blood samples were found in five of seven patients. In all patients circulating t(14;18)-positive cells reappeared within 2 years after ABMT showing two different patterns. During continuous CR the numbers of circulating t(14;18)-positive cells were found to be stable within one order of magnitude. In contrast, in one patient the relapse was accompanied by a logarithmic increase of t(14;18)-positive cells. In a second patient the enlargement of lymph nodes developing over a period of 12 months was accompanied by very slowly increasing numbers of t(14;18)-positive cells. In all cases where diagnostic lymph node tissue was available, the same t(14;18) translocation was found at first diagnosis and after ABMT as shown by nucleotide sequence analysis. We conclude that the quantitative detection of circulating t(14;18)-positive cells during follow-up of patients with FL after ABMT reflects the clinical course of the disease. Relapses are associated with increasing numbers of circulating t(14;18)-positive cells and continuous complete remissions with stable cell counts.

Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma (KS) is a vascular tumor predominantly found in the immunosuppressed. Epidemiologic studies suggest that an infective agent is the etiologic culprit. Kaposi's sarcoma-associated herpesvirus (KSHV), or human herpesvirus-8 (HHV-8), is a gamma human herpesvirus present in all epidemiologic forms of KS and also in a rare type of a B cell lymphoma, primary effusion lymphoma (PEL). In addition, this virus is present in most biopsies from human immunodeficiency virus (HIV)-associated multicentric Castleman's disease (MCD). MCD is a lymphoproliferative disorder with, like KS, a prominent microvasculature. The genome of KSHV contains the expected open reading frames (ORFs) encoding for enzymes and viral structural proteins found in other herpesviruses, but it also contains an unprecedented number of ORFs pirated during viral evolution from cellular genes. These include proteins that may alter cellular growth (e.g., Bcl-2 and cyclin homologs), induce angiogenesis (e.g., chemokine, chemokine receptor, and cytokine homologs), and regulate antiviral immunity (e.g., CD21 and interferon regulatory factor homologs). No ORF with sequence similarity to the Epstein-Barr nuclear antigens (EBNAs) and latent membrane proteins (LMPs) of Epstein-Barr virus (EBV) is present, but proteins analogous to these in structure and in latent expression are found [e.g., ORF 73 encoding for KSHV latent nuclear antigen (LNA-1) and K12 encoding for a possible latent membrane protein]. Current serologic assays confirm the strong association of infection with KSHV and risk of KS development. The mechanism of how this new virus may trigger the precipitation of KS is still unclear.

Bcl-2 transcription from the proximal P2 promoter is activated in neuronal cells by the Brn-3a POU family transcription factor

The BCL-2 protein is able to protect neuronal and other cell types from apoptotic programmed cell death and plays a key role in regulating the rate of apoptosis during development of the nervous system. We have previously demonstrated that the Brn-3a POU domain transcription factor protects sensory neurons from apoptotic programmed cell death induced by nerve growth factor withdrawal. We report here that Bcl-2 transcription is predominantly initiated from the Bcl-2 P2 promoter in both the ND7 neuronal cell line and primary dorsal root ganglion neurons, in contrast to the predominant use of the Bcl-2 P1 promoter in other cell types. Moreover, Bcl-2 transcription initiated from the P2 region increases in ND7 cells stably overexpressing Brn-3a, resulting in enhanced BCL-2 protein levels. Similarly, the Bcl-2 P2 promoter is directly activated by Brn-3a in co-transfection assays in both ND7 cells and dorsal root ganglion neurons. Analysis of the Bcl-2 regulatory sequence revealed a binding site for Brn-3a that is required for maximal activation by Brn-3a both in transfected cells and during differentiation of ND7 cells. Together these data identify Brn-3a as the first transcription factor regulating Bcl-2 activity specifically in neuronal cells and indicate that the anti-apoptotic effect of Brn-3a is likely to be mediated, at least in part, via the up-regulation of Bcl-2 expression.

bcl-2 rearrangement detected by pulsed-field gel electrophoresis (PFGF) in B-chronic lymphocytic leukemia (CLL) cells

B-chronic lymphocytic leukemia (CLL) is characterized by an accumulation of long-lived, resting B cells expressing the Bcl-2 protein. However, less than 10% of the CLL patients shows bcl-2 gene rearrangement in blood cells, using traditional Southern blotting analysis. In the present study, rearrangement of the bcl-2 gene in CLL cells was studied by pulsed-field gel electrophoresis (PFGE). With this method, large DNA fragments (> 50-10,000 kb) could be analyzed. Blood CLL cells from 9 of 9 patients and 2 of 2 CLL cell lines showed rearranged bcl-2 gene. In comparison, healthy blood B cells and lymphoblastoid cell lines (LCLs) established from normal peripheral blood lymphocytes of the patients showed only germ line configuration. Thus, the possibility of restriction fragment length polymorphisms (RFLPs) in this gene could be excluded. The primary cell involved in CLL might be a progenitor B cell that has accidentally rearranged the bcl-2 gene. As a consequence, such cells express stable amount of Bcl-2 protein and do not enter apoptosis. During prolonged survival, such cells may acquire secondary changes including chromosomal translocations and mutations.

Tumor B Cells From Non-Hodgkin's Lymphoma Are Resistant to CD95 (Fas/Apo-1)–Mediated Apoptosis

Apoptosis mediated by the CD95 (Fas/Apo-1) molecule plays a crucial role in the regulation of the B-cell immune response. In this study, we examined the function of the CD95 antigen in B-cell–derived non-Hodgkin's lymphoma (NHL), a malignant disease of mature B cells. Membrane CD95 molecules were found to be constitutively expressed in a large number of NHL, including mantle cell (MCL, n = 10), lymphocytic (LCL, n = 10), follicular (FL, n = 11), and diffuse large cell lymphoma (DLCL, n = 9) with, however, different levels of intensity. Indeed, the levels of CD95 were low in MCL and LCL as compared with FL and DLCL. However, regardless of the intensity of expression, CD95 triggering with anti-CD95 monoclonal antibody (MoAb) did not induce apoptosis of lymphoma B cells, while these cells underwent apoptosis after irradiation or staurosporine treatment. Further experiments were then performed to address whether apoptosis could be restored by B-cell activation via CD40 cross-linking. We showed that CD40 engagement in the presence of interleukin (IL)-4 was more effective than CD40 engagement alone in upregulating the CD95 antigen and induced CD95-mediated cell death in nontumoral B cells. Concerning malignant B cells, CD40 ligation in the presence of IL-4 strongly increased CD95 expression, but did not markedly increase CD95-induced apoptosis. Furthermore, using cytotoxic T cells, we showed that CD95L was also ineffective in inducing apoptosis in lymphoma B cells, whereas these cells were killed by the perforin pathway. Our findings suggest that the CD95-mediated cell death pathway is altered in malignant cells from the NHL we tested. This could be a mechanism allowing lymphoma B cells to escape from immune regulation.

Novel bcl-2 breakpoints in patients with follicular lymphoma

Using genomic DNA from patients with follicular lymphoma, we performed polymerase chain reaction (PCR) amplifications to detect t(14;18) translocations. Unexpectedly large products of approximately 1 kilobase (kb) were detected by gel electrophoresis in 2 of 50 positive cases. In these 2 cases, sequence analyses showed novel breakpoints in the 3' untranslated region of bcl-2, approximately 800 bp downstream of the major breakpoint region (mbr). The breakpoints in IgH occurred in JH4 in one patient and JH5 in the other. Sequences just upstream of the new bcl-2 breakpoints suggest a mechanism of translocation that may include minisatellite core-mediated recombination. In one of our two patients with novel bcl-2 breakpoints, the approximately 1 kb product obtained using conventional mbr primers was detectable only when a nested PCR was performed. These findings have important implications for diagnosis and minimal residual disease detection in t(14;18)-positive lymphomas.

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).

Analysis of bcl-2 in sporadic breast carcinoma

BACKGROUND

The bcl-2 gene encodes a protein that blocks apoptosis and might help to promote tumor development. It is expressed in a high percentage of breast tumors and is associated with good prognostic features. However, the mechanisms that regulate bcl-2 expression in breast carcinoma are unknown. Moreover, immunohistochemical detection of bcl-2 is related inversely to p53 expression. This notwithstanding, the immunohistochemical detection of p53 does not always correlate with the detection of p53 gene mutations. The authors studied the molecular organization of bcl-2 as well as the methylation status of its CpG island and analyzed the correlation between bcl-2 expression and p53 gene mutations.

METHODS

The molecular organization of the bcl-2 gene and the methylation pattern of its CpG island were analyzed by Southern blot analysis. In addition, immunohistochemical analysis of bcl-2 and p53 protein expression was performed. Finally, the presence of mutations at exons 5-9 of the p53 gene were analyzed by polymerase chain reaction and single-strand conformation polymorphism.

RESULTS

No molecular abnormality was found at the bcl-2 locus in cases of sporadic breast carcinoma. Moreover, loss of heterozygosity analysis failed to detect any allelic loss in the study cases. It also was found that the bcl-2 CpG island was demethylated in all cases. These results point to a lack of correlation between bcl-2 protein expression and the presence of p53 gene mutations.

CONCLUSIONS

The level of bcl-2 expression in breast carcinoma is not associated with any somatic abnormality or epigenetic change at the bcl-2 locus. Conversely, although bcl-2 expression is related inversely to p53 protein expression, the analysis of p53 mutations (limited to exons 5-9) failed to demonstrate any relationship between p53 mutations and bcl-2 protein expression.

Establishment of a novel human B-cell line (OZ) with t(14;18)(q32;q21) and aberrant p53 expression was associated with the homozygous deletions of p15INK4B and p16INK4A genes

The novel human pre-B cell line OZ was established from a patient with an aggressive form of non-Hodgkin's lymphoma. Karyotypic analysis of both the primary tumour and OZ cells revealed several marker chromosomes, including the t(14;18)(q32;q21) translocation, which involves the Bcl-2 gene, and alterations on chromosome 17p. Southern blot analysis found identical rearrangements in the 5' region of Bcl-2 gene in the primary tumour and OZ cells. Homozygous deletions of the p15INK4B and p16INK4A genes, however, were present only in OZ cells. Western blot analysis detected aberrant small molecular-weight p53 proteins in both cell types. In addition, OZ cells no longer expressed the CD20 antigen. These findings suggest that Bcl-2 gene rearrangement and aberrant p53 expression resulted in the original B-cell tumour. A subsequent transforming event involving the p15INK4B and p16INK4A genes may have generated more immature cells with a growth advantage during in vitro culture. The genetic alterations involving p53, p15INK4B, and p16INK4A may be implicated in the aggressive form of t(14;18)(q32;q21)-bearing tumours and their poor prognosis.

Herpesvirus saimiri encodes a functional homolog of the human bcl-2 oncogene

Here we demonstrate that open reading frame 16 (ORF16) of the oncogenic herpesvirus saimiri protects cells from heterologous virus-induced apoptosis. The BH1 and BH2 homology domains are highly conserved in ORF16, and ORF16 heterodimerizes with Bcl-2 family members Bax and Bak. However, ORF16 lacks the core sequence of the conserved BH3 homology domain, suggesting that this region is not essential for anti-apoptotic activity. Conservation of a functional bcl-2 homolog among gammaherpesviruses suggests that inhibition of programmed cell death is important in the biology of these viruses.

Molecular characterization of IgA- and/or IgG-switched chronic lymphocytic leukemia B cells

The immunoglobulin (Ig) variable region (V) genes expressed by IgM chronic lymphocytic leukemia (CLL) B cells display little or no somatic mutations. However, preliminary findings have shown that Ig V genes of IgA and IgG CLLs may be somatically mutated, suggesting that isotype-switched CLLs may represent a "subtype" of the disease. To investigate the degree and nature of somatic mutations and the role of antigen (Ag) in the clonal selection and expansion of isotype-switched CLLs, and to determine whether specific oncogene or tumor suppressor gene mutations are associated with isotype-switched CLLs, we analyzed the expressed Ig VH gene, bcl-1 and bcl-2 proto-oncogene, and p53 tumor suppressor gene configurations of 3 IgA-, 1 IgG-, and 1 IgA/ IgG-expressing CLLs. These isotype-switched CLL B cells expressed surface HLA-DR, CD19, CD23, and CD5, and displayed no alterations of the bcl-1 and bcl-2 oncogenes and the p53 tumor-suppressor gene. The cDNA VH-D-JH gene sequence was joined with that of the C alpha gene in the B cells of the three IgA CLLs, and with that of the C gamma gene in the IgG CLL B cells. In the IgA/IgG-coexpressing CLL B cells, identical VH-D-JH cDNA sequences were spliced to either C alpha or C gamma genes. In all five CLLs, the pattern of C mu DNA probe hybridization to the digested genomic DNAs was consistent with deletion of the C mu exon from the rearranged Ig gene locus, suggesting that these CLL B cells had undergone DNA switch recombination. In one IgA CLL, the expressed VH gene was unmutated. In all other class-switched CLLs, the Ig VH segment gene was mutated, but the point mutations were not associated with intraclonal diversification. In one IgA and in the IgA/IgG-coexpressing CLL, the nature and distribution of the mutations were consistent with Ag selection. These findings suggest that IgA- and/or IgG-expressing CLLs represent, in their VH gene structure, transformants of B cells at different stages of ontogeny. They also suggest that Ag may play a role in the clonal selection of some of these isotype-switched leukemic cells, but bcl-1 and bcl-2 oncogene rearrangements and p53 tumor suppressor gene mutation are not associated with the pathogenesis of isotype-switched CLLs.

Molecular Characterization of IgA- and/or IgG-Switched Chronic Lymphocytic Leukemia B Cells

The immunoglobulin (Ig) variable region (V) genes expressed by IgM chronic lymphocytic leukemia (CLL) B cells display little or no somatic mutations. However, preliminary findings have shown that Ig V genes of IgA and IgG CLLs may be somatically mutated, suggesting that isotype-switched CLLs may represent a “subtype” of the disease. To investigate the degree and nature of somatic mutations and the role of antigen (Ag) in the clonal selection and expansion of isotype-switched CLLs, and to determine whether specific oncogene or tumor suppressor gene mutations are associated with isotype-switched CLLs, we analyzed the expressed Ig VH gene, bcl-1 and bcl-2 proto-oncogene, and p53 tumor suppressor gene configurations of 3 IgA-, 1 IgG-, and 1 IgA/IgG-expressing CLLs. These isotype-switched CLL B cells expressed surface HLA-DR, CD19, CD23, and CD5, and displayed no alterations of the bcl-1 and bcl-2 oncogenes and the p53 tumor-suppressor gene. The cDNA VH -D-JH gene sequence was joined with that of the Cα gene in the B cells of the three IgA CLLs, and with that of the Cγ gene in the IgG CLL B cells. In the IgA/IgG-coexpressing CLL B cells, identical VH -D-JH cDNA sequences were spliced to either Cα or Cγ genes. In all five CLLs, the pattern of Cμ DNA probe hybridization to the digested genomic DNAs was consistent with deletion of the Cμ exon from the rearranged Ig gene locus, suggesting that these CLL B cells had undergone DNA switch recombination. In one IgA CLL, the expressed VH gene was unmutated. In all other class-switched CLLs, the Ig VH segment gene was mutated, but the point mutations were not associated with intraclonal diversification. In one IgA and in the IgA/IgG-coexpressing CLL, the nature and distribution of the mutations were consistent with Ag selection. These findings suggest that IgA- and/or IgG-expressing CLLs represent, in their VH gene structure, transformants of B cells at different stages of ontogeny. They also suggest that Ag may play a role in the clonal selection of some of these isotype-switched leukemic cells, but bcl-1 and bcl-2 oncogene rearrangements and p53 tumor suppressor gene mutation are not associated with the pathogenesis of isotype-switched CLLs.

Molecular Characterization of IgA- and/or IgG-Switched Chronic Lymphocytic Leukemia B Cells

The immunoglobulin (Ig) variable region (V) genes expressed by IgM chronic lymphocytic leukemia (CLL) B cells display little or no somatic mutations. However, preliminary findings have shown that Ig V genes of IgA and IgG CLLs may be somatically mutated, suggesting that isotype-switched CLLs may represent a “subtype” of the disease. To investigate the degree and nature of somatic mutations and the role of antigen (Ag) in the clonal selection and expansion of isotype-switched CLLs, and to determine whether specific oncogene or tumor suppressor gene mutations are associated with isotype-switched CLLs, we analyzed the expressed Ig VH gene, bcl-1 and bcl-2 proto-oncogene, and p53 tumor suppressor gene configurations of 3 IgA-, 1 IgG-, and 1 IgA/IgG-expressing CLLs. These isotype-switched CLL B cells expressed surface HLA-DR, CD19, CD23, and CD5, and displayed no alterations of the bcl-1 and bcl-2 oncogenes and the p53 tumor-suppressor gene. The cDNA VH -D-JH gene sequence was joined with that of the Cα gene in the B cells of the three IgA CLLs, and with that of the Cγ gene in the IgG CLL B cells. In the IgA/IgG-coexpressing CLL B cells, identical VH -D-JH cDNA sequences were spliced to either Cα or Cγ genes. In all five CLLs, the pattern of Cμ DNA probe hybridization to the digested genomic DNAs was consistent with deletion of the Cμ exon from the rearranged Ig gene locus, suggesting that these CLL B cells had undergone DNA switch recombination. In one IgA CLL, the expressed VH gene was unmutated. In all other class-switched CLLs, the Ig VH segment gene was mutated, but the point mutations were not associated with intraclonal diversification. In one IgA and in the IgA/IgG-coexpressing CLL, the nature and distribution of the mutations were consistent with Ag selection. These findings suggest that IgA- and/or IgG-expressing CLLs represent, in their VH gene structure, transformants of B cells at different stages of ontogeny. They also suggest that Ag may play a role in the clonal selection of some of these isotype-switched leukemic cells, but bcl-1 and bcl-2 oncogene rearrangements and p53 tumor suppressor gene mutation are not associated with the pathogenesis of isotype-switched CLLs.

A Bcl-2 homolog encoded by Kaposi sarcoma-associated virus, human herpesvirus 8, inhibits apoptosis but does not heterodimerize with Bax or Bak

The Bcl-2 protein family is characterized by the ability to modulate cell death, and members of this family share two highly conserved domains called Bcl-2 homology 1 (BH1) and 2 (BH2) which have been shown to be critical for the death-repressor activity of Bcl-2 and Bcl-xL. Through sequence analysis we identified a novel viral Bcl-2 homolog, designated KSbcl-2, from human herpesvirus 8 (HHV8) or Kaposi sarcoma-associated herpesvirus. The overall amino acid sequence identity between KSbcl-2 and other Bcl-2 homologs is low (15-20%) but concentrated within the BH1 and BH2 regions. Overexpression of KSbcl-2 blocked apoptosis as efficiently as Bcl-2, Bcl-xL, or another viral Bcl-2 homolog encoded by Epstein-Barr virus, BHRF1. Interestingly, KS-bcl-2 neither homodimerizes nor heterodimerizes with other Bcl-2 family members, suggesting that KSbcl-2 may have evolved to escape any negative regulatory effects of the cellular Bax and Bak proteins. Furthermore, the herpesvirus Bcl-2 homologs including KSbcl-2, BHRF1, and ORF16 of herpesvirus saimiri contain poorly conserved Bcl-2 homology 3 (BH3) domains compared with other mammalian Bcl-2 homologs, implying that BH3 may not be essential for anti-apoptotic function. This is consistent with our observation that amino acid substitutions within the BH3 domain of Bcl-xL had no effect on its death-suppressor activity.

p16INK4/p15INK4B gene inactivation is a frequent event in malignant T-cell lines

The cell cycle regulators p16INK4 and p15INK4B have been mapped to the minimal region of overlap for chromosome 9p21 deletions, observed in a number of malignancies, suggesting that they could be tumor suppressor genes (TSGs). In the case of p16INK4 this has been further substantiated by the finding of small intragenic mutations. In this study we have investigated the p16INK4 and p15INK4B genes in 16 malignant T-cell lines by means of Southern blot, PCR and sequence analysis. p16INK4 allelic deletions occurred in 15 of 16 cell lines; 12 of which were homozygous and 3 hemizygous. In 1 cell line (DND 41) the remaining p16INK4 allele carried a microdeletion of 29 bp of exon 2, supporting the concept that p16INK4 is a target TSG for deletions on 9p21. Most p16INK4 deletions also included the p15INK4B gene. However, 4 of the cell lines deleted for p16INK4 showed no evidence of p15INK4B loss, indicating that p15INK4B is not the target in these cell lines.

The somatic hypermutation activity of a follicular lymphoma links to large insertions and deletions of immunoglobulin genes

A biopsy specimen from a patient with follicular lymphoma was divided into two fragments. DNA was extracted from one fragment and a 1.2 kb region of the functional heavy chain (IgH) gene was amplified, cloned and sequenced (eight clones). From the other fragment a cell line (HF-1) was started. The IgH gene region was amplified from the cell line, and sequenced without cloning. The nine sequences obtained could be arranged into a genealogical tree where the individual sequences differed from the deduced ancestor by 16-29 single nucleotide changes, some also by an insertion and/or a deletion. It is apparent that the sequence alterations were caused by somatic mutations during the growth of the lymphoma. The comparison of the sequences with two published (allelic) germline sequences of the human JH region showed approximately 20% non-homology. The differences included five additional multinucleotide insertion/deletion changes, the longest of them a 101-nucleotide insertion. Two long insertions were homologous to the adjacent germline sequences. We propose that most of the changes observed, including long deletions and insertions, represent or are linked to somatic hypermutation events of the Ig gene type. Although in a few cases large deletions and insertions (> 2 bp) have been found in mutated immunoglobulin genes, our results, for the first time, firmly link these deletions/insertions to somatic hypermutations; their frequency was found to be 2.2% of the observed mutational events in the non-translated gene regions. HF-1 is the first follicular lymphoma line successfully established from a lymphoma known to have hypermutated its Ig genes during the malignant growth. It is a candidate cell line to be studied for its ability to generate mutations of B cell type in cell cultures.