Heterogeneity in cell proliferation and expression of p53 and bcl-2 during the indolent phase of germinal centre cell lymphoma: an explanation for clinical variability

BCL2 protein expression in follicular lymphomas with t(14;18) chromosomal translocations

The t(14;18)(q32;q21) chromosomal translocation induces BCL2 protein overexpression in most follicular lymphomas. However the expression of BCL2 is not always homogeneous and may demonstrate a variable degree of heterogeneity. This study analysed BCL2 protein expression pattern in 33 cases of t(14;18)-positive follicular lymphomas using antibodies against two different epitopes (i.e. the widely used antibody BCL2/124 and an alternative antibody E17). 16/33 (49%) cases demonstrated strong BCL2 expression. In 10/33 (30%) cases, BCL2 expression was heterogeneous and in some of these, its loss appeared to be correlated with cell proliferation, as indicated by Ki67 expression. Double immunofluorescence labelling confirmed an inverse BCL2/Ki67 relationship, where in 24/28 (86%) cases cellular expression of BCL2 and Ki67 was mutually exclusive. In addition, seven BCL2 'pseudo-negative' cases were identified in which immunostaining was negative with antibody BCL2/124, but positive with antibody E17. Genomic DNA sequencing of these 'pseudo-negative' cases demonstrated eleven mutations in four cases and nine of these were missense mutations. It can be concluded that in follicular lymphomas, despite carrying the t(14;18) translocations, BCL2 protein expression may be heterogeneous and loss of BCL2 could be related to cell proliferation. Secondly, mutations in translocated BCL2 genes appear to be common and may cause BCL2 pseudo-negative immunostaining.

Prognosis of follicular lymphomas

Although numerous treatment approaches are proposed for patients with follicular lymphoma, criteria to help in choosing a treatment for a given patient and for comparing trial results are lacking. Several retrospective studies have analyzed prognostic factors, but their conclusions rely on limited numbers of patients treated during long periods, and their results are discordant. The Follicular Lymphoma International Prognostic Index was designed from the data recorded over 8 years of nearly 5000 patients registered worldwide. Five factors are used (age, Ann Arbor stage, number of nodal sites, serum lactate dehydrogenase level, and hemoglobin level) to build a 3-category index. This index, together with new biologic markers such as gene profiling and proteomics, could help provide an optimal treatment option for patients with follicular lymphoma.

Negative regulation of bcl-2 expression by p53 in hematopoietic cells

The p53 protein activates promoters containing p53 binding sites, and it represses other promoters. We examined the effect of p53 on bcl-2 expression in both the DHL-4 B cell line and the K562 erythroleukemia line. Transient transfection analyses revealed that wild-type p53 repressed the bcl-2 full-length promoter. The region of the bcl-2 promoter that was responsive to p53 was mapped to the bcl-2 P2 minimal promoter region, and we showed that p53 and the TATA binding protein bound to the bcl-2 TATA sequence. The TATA binding protein, p53, histone deacetylase-1 and mSin3a could be co-immunoprecipitated from K562 cell nuclear extract. The TATA binding protein and mSin3a could be recovered in a complex at the bcl-2 promoter TATA sequence, however, the formation of this complex was not dependent on the presence of p53. Treatment of K562 cells with the histone deacetylase inhibitor, trichostatin A, resulted in an increase in bcl-2 promoter activity whether p53 was present or not. Therefore, we demonstrated that p53 and the histone deacetylases repress the bcl-2 promoter independently. Similar results were obtained when endogenous bcl-2 mRNA or protein levels were measured in response to either p53 or trichostatin A, and p53 expression resulted in enhanced apoptosis. RNase protection assays demonstrated that transcription from the endogenous 3' bcl-2 promoter was decreased by p53. The regions of p53 that were required for repression of the bcl-2 promoter were defined. We conclude that the TATA sequence in the bcl-2 P2 minimal promoter is the target for repression by p53, and that the interaction between p53 and TBP is most likely responsible for the repression. Mutation of p53 may play a role in the up-regulation of bcl-2 expression in some B cell lymphomas.

Analysis of Bcl-2 protein expression in chronic lymphocytic leukemia. A comparison of three semiquantitation techniques

A number of studies revealed that high expression of the proto-oncogene bcl-2 correlated with poor prognosis or resistance to chemotherapy in some tumors but predicted a favorable clinical course in other neoplasias. In these studies, however, different immunologic techniques for Bcl-2 detection were used, raising the question of whether the methods applied were comparable. Using chronic lymphocytic leukemia (CLL) cells, the aims of our study were as follows: (1) to determine the reproducibility of Bcl-2 semiquantitation by immunocytochemistry, flow cytometry, or immunoblotting; (2) to study the agreement between results obtained by these methods; and (3) to examine the association between Bcl-2 expression in tumor cells of 99 patients with CLL and clinical parameters. We found that determination of Bcl-2 expression by immunocytochemistry was reproducible and the results were comparable with those of flow cytometry and immunoblotting. In the patient collective examined, Bcl-2 expression did not reflect the extent of tumor mass, but higher levels were found more often in patients with progressive disease.

BCL-2 Expression Correlates With Lower Proliferative Activity in the Intermediate- and High-Grade Non-Hodgkin's Lymphomas: An Eastern Cooperative Oncology Group and Southwest Oncology Group Cooperative Laboratory Study

An inverse relationship between BCL-2 expression and cell cycle transition has been suggested by recent studies in murine models. To investigate the clinical relevance of these laboratory studies, a group of 116 paraffin-embedded non-Hodgkin's lymphoma (NHL) biopsy specimens (Working Formulation Groups D-H, and J) from a cooperative group study of cellular DNA content were analyzed for the 14;18 translocation using polymerase chain reaction (PCR)-based methods and, if sufficient tissue remained, for BCL-2 and BAXexpression by immunohistochemistry. The results of these studies were then compared with the results of the previously performed flow cytometric analysis of ploidy and proliferative activity (S-phase-fraction). BCL-2 expression was inversely associated with proliferative activity (P = .001; n = 41), but there was no association between staining for Bax and %S-phase. Ploidy was not associated with either BCL-2 or BAX expression. The t(14;18) was detected in 21 of the 54 cases in which PCR-amplifiable DNA was recovered; 20 of these occurred at the major breakpoint region and 1 at the minor breakpoint region. High levels of BCL-2 orBAX expression occurred independently of t(14;18). There was no association between t(14;18) and either ploidy or proliferative activity. The inverse relationship between BCL-2 expression and proliferative activity in the intermediate- and high-grade NHLs is consistent with recent studies suggesting that Bcl-2 both retards entry into the cell cycle and inhibits apoptosis.

The status of immunohistochemical studies in lymphoma diagnosis

Immunohistochemical studies of formalin fixed paraffin embedded sections today constitute an essential component of the diagnostic process for malignant lymphoma. Lineage related markers are of value in distinguishing various lymphomas from anaplastic large and small cell carcinomas, and from sarcomas. Other more recently available markers are of value in establishing prognosis and, on occasion, in differentiating between neoplastic and reactive proliferations. Meticulous attention to reagent control and technical procedures is essential to all such studies.