Expression of TCF3 target genes defines a subclass of diffuse large B-cell lymphoma characterized by up-regulation of MYC target genes and poor clinical outcome following R-CHOP therapy

TCF3 is a lymphopoietic transcription factor that acquires somatic driver mutations in diffuse large B-cell lymphoma (DLBCL). Hypothesizing that expression patterns of TCF3-regulated genes can inform clinical management, we found that unsupervised clustering analysis with 15 TCF3-regulated genes and eight additional ones resolved local DLBCL cases into two main clusters, denoted Groups A and B, of which Group A manifested inferior overall survival (OS, p = 0.0005). We trained a machine learning model to classify samples into the Groups based on expression of the 23 transcripts in an independent validation cohort of 569 R-CHOP-treated DLBCL cases. Group A overlapped with the ABC cell-of-origin subgroup but its prognostic power was superior. GSEA analysis demonstrated asymmetric expression of 30 gene sets between the Groups, pointing to biological differences. We present, validate and make available a novel method to assign DLBCL cases into biologically-distinct groups with divergent OS following R-CHOP therapy.

Structural insights into TAZ2 domain-mediated CBP/p300 recruitment by transactivation domain 1 of the lymphopoietic transcription factor E2A

The E-protein transcription factors guide immune cell differentiation, with E12 and E47 (hereafter called E2A) being essential for B-cell specification and maturation. E2A and the oncogenic chimera E2A-PBX1 contain three transactivation domains (ADs), with AD1 and AD2 having redundant, independent, and cooperative functions in a cell-dependent manner. AD1 and AD2 both mediate their functions by binding to the KIX domain of the histone acetyltransferase paralogues CREB-binding protein (CBP) and E1A-binding protein P300 (p300). This interaction is necessary for B-cell maturation and oncogenesis by E2A-PBX1 and occurs through conserved ΦXXΦΦ motifs (with Φ denoting a hydrophobic amino acid) in AD1 and AD2. However, disruption of this interaction via mutation of the KIX domain in CBP/p300 does not completely abrogate binding of E2A and E2A-PBX1. Here, we determined that E2A-AD1 and E2A-AD2 also interact with the TAZ2 domain of CBP/p300. Characterization of the TAZ2:E2A-AD1(1-37) complex indicated that E2A-AD1 adopts an α-helical structure and uses its ΦXXΦΦ motif to bind TAZ2. Whereas this region overlapped with the KIX recognition region, key KIX-interacting E2A-AD1 residues were exposed, suggesting that E2A-AD1 could simultaneously bind both the KIX and TAZ2 domains. However, we did not detect a ternary complex involving E2A-AD1, KIX, and TAZ2 and found that E2A containing both intact AD1 and AD2 is required to bind to CBP/p300. Our findings highlight the structural plasticity and promiscuity of E2A-AD1 and suggest that E2A binds both the TAZ2 and KIX domains of CBP/p300 through AD1 and AD2.

Objective quantification of BCL2 protein by multiplex immunofluorescence in routine biopsy samples of diffuse large B-cell lymphoma demonstrates associations with survival and BCL2 gene alterations

Up-regulation of BCL2 in cases of diffuse large B-cell lymphoma (DLBCL) can confer treatment resistance. Quantitative immunofluorescence (QIF) histology allows objective quantification of protein-based biomarkers. We investigated the utility of QIF for evaluating BCL2 as a biomarker in DLBCL by quantifying BCL2 selectively in CD20-expressing lymphoma cells in biopsy samples from 116 cases of DLBCL in two cohorts one of which consisted of relapsed/refractory cases from a clinical trial. BCL2 protein by QIF correlated with BCL2 mRNA abundance and was associated with both translocation and copy number gain of the BCL2 gene. Elevated BCL2 protein expression by QIF, but not immunohistochemistry or mRNA quantification, was associated with inferior overall and relapse-free survival in the relapsed/refractory cohort. QIF is an effective means of quantifying BCL2 protein objectively in routine cancer biopsy specimens and shows promise for identifying relapsed/refractory DLBCL patients at risk of inferior outcomes after salvage therapy.

High-grade B-cell lymphoma with MYC and BCL2 rearrangements arising in a composite lymphoma

Background

We report the first case of composite lymphoma consisting of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), follicular lymphoma (FL) and high-grade B-cell lymphoma with MYC and BCL2 rearrangements within the same needle biopsy in which a clonal relationship between the FL and high-grade B-cell lymphoma components was demonstrated by molecular cytogenetics.

Case presentation

An 85-year-old man presented with masses in his neck and right groin. Cutting needle biopsy of the inguinal mass revealed the three lymphoma types which were morphologically, immunophenotypically and topographically distinct. Fluorescence in situ hybridization (FISH) identified an IGH-BCL2 rearrangement in both the FL and high-grade B-cell components while a MYC rearrangement was detected in the high-grade B-cell component alone.

Conclusions

Our findings suggest that the high-grade lymphoma with MYC and BCL2 translocations evolved through transformation of the FL by a process that entailed acquisition of the MYC translocation. No clonal relationship between the FL and CLL/SLL components was evident since the IGH-BCL2 rearrangement was present in in the former but not the latter. This unique case of co-localized FL, CLL/SLL, and high-grade B-cell lymphoma contributes to our understanding of the clonal relationships that may exist between the components of composite lymphomas.

Abundant expression of BMI1 in follicular lymphoma is associated with reduced overall survival

Although generally indolent, follicular lymphoma (FL) sometimes pursues a more aggressive course leading to early death. B-cell-specific Mo-MLV insertion site-1 (BMI1) is a member of the polycomb group (PcG) proteins that confer stem cell properties through gene silencing. We used multi-channel immunofluorescence and automated image analysis to quantify BMI1 selectively in the nuclei of FL-derived B-cells in routine biopsy specimens. Applying this assay to 109 pretreatment FL biopsy samples demonstrates a significant association between abundant BMI1 and reduced overall survival (p = .001); the statistically significant association with mortality persists in a Cox proportional hazards model that includes Follicular Lymphoma International Prognostic Index (FLIPI) score, histological grade, and the presence of a component of diffuse large B-cell lymphoma in the biopsy sample. Ascertaining BMI1 over-expression may be useful in identifying patients who might benefit from novel therapies directed at reversing the chromatin-modifying functions of BMI1.

First application of the Automated QUantitative Analysis (AQUA) technique to quantify PTEN protein expression in ovarian cancer: A correlative study of NCIC CTG OV.16

BACKGROUND

Platinum resistance is a dominant cause of poor outcomes in advanced ovarian cancer (OC). A mechanism of platinum resistance is the inhibition of apoptosis through phosphatidylinositol 3 kinase (PI3K) pathway activation. The role of phosphatase and tensin homolog (PTEN), a negative regulator of this pathway, as a tumor biomarker is unclear. Quantitative analysis of PTEN expression as an alternative to immunohistochemistry has not been considered.

PATIENTS AND METHODS

In 238 patient tumors from the NCIC-CTG trial OV.16, PTEN protein expression was quantified by Automated QUantitative Analysis (AQUA). Cox model was used to study the association between PTEN expression and clinical outcomes using a minimum p-value approach in univariate analysis. Multivariate analysis was used to adjust for clinical and pathological parameters.

RESULTS

PTEN scores (range 13.9-192.3) of the 202 samples that passed quality control were analyzed. In univariate analysis, there was a trend suggesting an association between PTEN expression by AQUA as a binary variable (low ≤61 vs high >61) and progression free survival (HR=0.77, p=0.083), and in multivariate analysis, this association approached significance (HR=0.74, p=0.059). The relationship between quantitative PTEN expression and PFS differed (p=0.01 for interaction) by the extent of surgical debulking (residual disease (RD) <1cm or ≥1cm), with a numerically superior PFS in patients with high PTEN (23.5 vs 14.9m) only when RD<1cm (p=0.19). There was no association between PTEN levels and overall survival.

CONCLUSIONS

AQUA is a novel method to measure PTEN expression. Further study of PTEN as a biomarker in OC is warranted.

Retrovirus-Mediated Expression of E2A-PBX1 Blocks Lymphoid Fate but Permits Retention of Myeloid Potential in Early Hematopoietic Progenitors

The oncogenic transcription factor E2A-PBX1 is expressed consequent to chromosomal translocation 1;19 and is an important oncogenic driver in cases of pre-B-cell acute lymphoblastic leukemia (ALL). Elucidating the mechanism by which E2A-PBX1 induces lymphoid leukemia would be expedited by the availability of a tractable experimental model in which enforced expression of E2A-PBX1 in hematopoietic progenitors induces pre-B-cell ALL. However, hematopoietic reconstitution of irradiated mice with bone marrow infected with E2A-PBX1-expressing retroviruses consistently gives rise to myeloid, not lymphoid, leukemia. Here, we elucidate the hematopoietic consequences of forced E2A-PBX1 expression in primary murine hematopoietic progenitors. We show that introducing E2A-PBX1 into multipotent progenitors permits the retention of myeloid potential but imposes a dense barrier to lymphoid development prior to the common lymphoid progenitor stage, thus helping to explain the eventual development of myeloid, and not lymphoid, leukemia in transplanted mice. Our findings also indicate that E2A-PBX1 enforces the aberrant, persistent expression of some genes that would normally have been down-regulated in the subsequent course of hematopoietic maturation. We show that enforced expression of one such gene, Hoxa9, a proto-oncogene associated with myeloid leukemia, partially reproduces the phenotype produced by E2A-PBX1 itself. Existing evidence suggests that the 1;19 translocation event takes place in committed B-lymphoid progenitors. However, we find that retrovirus-enforced expression of E2A-PBX1 in committed pro-B-cells results in cell cycle arrest and apoptosis. Our findings indicate that the neoplastic phenotype induced by E2A-PBX1 is determined by the developmental stage of the cell into which the oncoprotein is introduced.

Tumor suppressors in follicular lymphoma

Follicular lymphoma (FL) is the most common indolent lymphoma. The vast majority of cases are associated with the chromosome translocation t(14;18), a somatic rearrangement that leads to constitutive expression of the anti-apoptotic BCL2 protein. Although t(14;18) clearly represents an important early event in FL pathogenesis, abundant evidence indicates that it is not sufficient. In particular, the recent application of next-generation DNA sequencing technology has uncovered numerous recurrent somatic genomic alterations associated with FL, most of which affect tumor suppressor genes (TSGs). In this article we review the existing literature on TSGs involved in the development and progression of FL. We consider the genes that are most frequently targeted by deleterious mutation, deletion or epigenetic silencing, along with strategies for developing new treatments that exploit the susceptibilities that may be conferred on lymphoma cells by the loss of particular TSGs.

Functional redundancy between the transcriptional activation domains of E2A is mediated by binding to the KIX domain of CBP/p300

The E-protein transcription factors play essential roles in lymphopoiesis, with E12 and E47 (hereafter called E2A) being particularly important in B cell specification and maturation. The E2A gene is also involved in a chromosomal translocation that results in the leukemogenic oncoprotein E2A-PBX1. The two activation domains of E2A, AD1 and AD2, display redundant, independent, and cooperative functions in a cell-dependent manner. AD1 of E2A functions by binding the transcriptional co-activator CBP/p300; this interaction is required in oncogenesis and occurs between the conserved ϕ-x-x-ϕ-ϕ motif in AD1 and the KIX domain of CBP/p300. However, co-activator recruitment by AD2 has not been characterized. Here, we demonstrate that the first of two conserved ϕ-x-x-ϕ-ϕ motifs within AD2 of E2A interacts at the same binding site on KIX as AD1. Mutagenesis uncovered a correspondence between the KIX-binding affinity of AD2 and transcriptional activation. Although AD2 is dispensable for oncogenesis, experimentally increasing the affinity of AD2 for KIX uncovered a latent potential to mediate immortalization of primary hematopoietic progenitors by E2A-PBX1. Our findings suggest that redundancy between the two E2A activation domains with respect to transcriptional activation and oncogenic function is mediated by binding to the same surface of the KIX domain of CBP/p300.

Abundant expression of interleukin-21 receptor in follicular lymphoma cells is associated with more aggressive disease

Recombinant interleukin-21 (IL-21) has potential utility in cancer therapy. Stimulation with IL-21 can induce apoptosis in follicular lymphoma (FL) cells, and existing studies have suggested that IL-21 signaling may function in tumor suppression. In order to elucidate the relationship between IL-21 receptor (IL-21R) expression and clinical and pathological features in FL, IL-21R was quantified in 114 pretreatment biopsy samples using either conventional immunohistochemistry or immunofluorescence microscopy and automated quantitative analysis (AQUA). Reduced expression of IL-21R was associated with favorable overall survival (p = 0.048). AQUA analysis showed an association with the presence of diffuse large B-cell lymphoma (DLBCL) in the biopsy sample (p = 0.03), and expression of IL-21R was up-regulated upon transformation of FL to DLBCL in two cases. Our results based on the largest survey to date raise the possibility that IL-21 signaling in FL cells, rather than being tumor suppressive, supports tumor progression and that therapeutic benefit could be realized by blocking IL-21R instead of stimulating it.

The transcription factor encyclopedia

Here we present the Transcription Factor Encyclopedia (TFe), a new web-based compendium of mini review articles on transcription factors (TFs) that is founded on the principles of open access and collaboration. Our consortium of over 100 researchers has collectively contributed over 130 mini review articles on pertinent human, mouse and rat TFs. Notable features of the TFe website include a high-quality PDF generator and web API for programmatic data retrieval. TFe aims to rapidly educate scientists about the TFs they encounter through the delivery of succinct summaries written and vetted by experts in the field. TFe is available at http://www.cisreg.ca/tfe.

E2A proteins enhance the histone acetyltransferase activity of the transcriptional co-activators CBP and p300

The E2A gene encodes the E-protein transcription factors E12 and E47 that play critical roles in B-lymphopoiesis. A somatic chromosomal translocation detectable in 5% of cases of acute lymphoblastic leukemia (ALL) involves E2A and results in expression of the oncogenic transcription factor E2A-PBX1. CREB binding protein (CBP) and its close paralog p300 are transcriptional co-activators with intrinsic histone acetyltransferase (HAT) activity. We and others have shown that direct binding of an N-terminal transcriptional activation domain present in E12/E47 and E2A-PBX1 to the KIX domain of CBP/p300 contributes to E2A protein function. In the current work we show for the first time that the catalytic HAT activity of CBP/p300 is increased in the presence of residues 1-483 of E2A (i.e., the portion present in E2A-PBX1). The addition of purified, recombinant E2A protein to in vitro assays results in a two-fold augmentation of CBP/p300 HAT activity, whereas in vivo assays show a ten-fold augmentation of HAT-dependent transcriptional induction and a five-fold augmentation of acetylation of reporter plasmid-associated histone by CBP in response to co-transfected E2A. Our results indicate that the HAT-enhancing effect is independent of the well-documented E2A-CBP interaction involving the KIX domain and suggest a role for direct, perhaps low affinity binding of E2A to a portion of CBP that includes the HAT domain and flanking elements. Our findings add to a growing body of literature indicating that interactions between CBP/p300 and transcription factors can function in a specific manner to modulate HAT catalytic activity.

Mapping acetylation sites in E2A identifies a conserved lysine residue in activation domain 1 that promotes CBP/p300 recruitment and transcriptional activation

E-proteins are basic helix-loop-helix transcription factors that function in cell type specification. The gene E2A encodes two E-proteins, E12 and E47, which are required in B-lymphopoiesis. E2A proteins can interact directly with the transcriptional co-activators and lysine acetyltranferases (KATs) CBP, p300 and PCAF to induce target gene transcription. Prior investigations have shown that the E2A-encoded isoform E2-5 is acetylated by CBP, p300 or PCAF in vitro or in vivo. However, E2-5 lacks the important N-terminal activation domain AD1. Furthermore, the acetylated residues in E-proteins have not been mapped, and the functional consequences of acetylation are largely unknown. Here, we use mutagenesis to show that a lysine residue at position 34 within AD1 of E12/E47 is acetylated by CBP/p300 and PCAF. Lys34 lies adjacent to a conserved helical LXXLL motif that interacts directly with the KIX domain of CBP/p300. We show that acetylation at Lys34 increases the affinity of AD1 for the KIX domain and enhances AD1-driven transcriptional induction. Our results illustrate for the first time that AD1 can both recruit, and be acetylated by, KATs and that KAT recruitment may promote transcriptional induction in part through acetylation of AD1 itself.

Transplacental benzene exposure increases tumor incidence in mouse offspring: possible role of fetal benzene metabolism

Childhood cancer is the leading cause of disease-related death in children aged 1-14 years in Canada and the USA and it has been hypothesized that transplacental exposure to environmental carcinogens such as benzene may contribute to the etiology of these cancers. Our objectives were to determine if transplacental benzene exposure increased tumor incidence in mouse offspring and assess fetal benzene metabolism capability. Pregnant CD-1 and C57Bl/6N mice were given intraperitoneal injections of corn oil, 200 mg/kg, or 400 mg/kg benzene on gestational days 8, 10, 12 and 14. A significant increase in tumor incidence was observed in CD-1, but not C57BL/6N, 1-year-old offspring exposed transplacentally to 200 mg/kg benzene. Hepatic and hematopoietic tumors were predominantly observed in male and female CD-1 offspring, respectively. Female CD-1 offspring exposed transplacentally to 200 mg/kg benzene had significantly suppressed bone marrow CD11b(+) cells 1 year after birth, correlating with reduced colony-forming unit granulocyte/macrophage numbers in 2-day-old pups. CD-1 and C57Bl/6N maternal blood benzene levels and fetal liver benzene, t, t-muconic acid, hydroquinone and catechol levels were analyzed by gas chromatography/mass spectrometry. Significant strain-, gender- and dose-related differences were observed. Male CD-1 fetuses had high hydroquinone levels, whereas females had high catechol levels after maternal exposure to 200 mg/kg benzene. This is the first demonstration that transplacental benzene exposure can induce hepatic and hematopoietic tumors in mice, which may be dependent on fetal benzene metabolism capability.

Abstract 3890: Induction of cell cycle arrest and apoptosis in mantle cell lymphoma by AZD5438, a novel cyclin-dependent kinase inhibitor

Mantle cell lymphoma (MCL) is recognized as a distinct subtype of B-cell lymphoma and it is characterized by cyclin D1 over-expression, which is caused by t(11;14)(q13;q32) translocation and unregulated cell cycle progression driven by increased cyclin-dependent kinase (CDK) activity. Accordingly, small inhibitors for CDKs represent a potential therapy for MCL. We are investigating a selective small molecule CDK inhibitor, AZD5438, which has nanomolar ranges of IC50 for cyclin E/CDK2, cyclin A/CDK2, cyclin B1/CDK1 and cyclin T/CDK9 and comparing its anti-tumor effects with a pan-CDK inhibitor, Flavopiridol. We hypothesize that inhibition of CDK1/2 by AZD5438 may lead to G1/S and G2 arrest, and therefore inhibit tumor cell proliferation and induce apoptosis in MCL. In Jeko-1 MCL cell lines, AZD5438 has shown both time- and dose-dependent inhibition of cell proliferation, inhibition of the phosphorylation of CDK substrates, and cell cycle arrest in G1 phase. The EC50 for AZD 5438 is 1μM as determined by inhibition of cell viability. We further developed an in vivo MCL xenograft assay: first, to guide the optimization of dosage and dosing schedule for clinical use; and second, to explore the selectivity and potency of this drug using phospho-histone H3 (Ser10) flow cytometry and phosopho-Rb (Ser249/Thr252) immunoblotting as our drug efficacy monitoring system. Recently we have established GFP transduced Jeko-1 cells and inoculated them into 8 to 12 week-old, immune-compromised NOD SCID mice. Investigations of AZD5438 drug dosage in this xenograft model are ongoing. Ultimately, this project is aimed at improving the treatment for MCL patients and reducing the toxic responses to the standard chemotherapeutic regimes.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3890.

Abstract 3097: The leukemogenic protein E2A-PBX1 blocks B-lymphoid commitment in early hematopoietic progenitors

The oncoprotein E2A-PBX1 is produced by the t(1;19) chromosomal translocation in pre-B cell acute lymphoblastic leukemia (ALL). We and others have shown that retrovirus-enforced expression of E2A-PBX1 in mouse bone marrow results in a lethal leukemia with short latency. Suprisingly, almost all animals die of myeloid leukemia rather than the B-lymphoid disease observed clinically. The E-protein E47, a product of the wild-type E2A gene, is required in the earliest stages of B-lymphoid commitment. E47 and E2A-PBX1 are identical in their amino-terminal 483 residues and this region includes transcriptional activation domains capable of recruiting CBP/p300 and presumably other co-regulators. Therefore, we hypothesized that E2A-PBX1 may block B-lymphoid commitment by exerting dominant-negative effects on E-proteins including E47. Bone marrow cells transduced with E2A-PBX1 failed to repopulate the B-lymphoid compartment at two weeks post-reconstitution of sub-lethally-irradiated mice, whereas there was exuberant proliferation of transduced myeloid progenitors suggesting selective intereference with B-lymphopoiesis. This phenomenon was examined further using a more experimentally tractable in vitro system. “Lineage negative” hematopoietic progenitors from fetal livers differentiate rapidly to committed B-lymphoid progenitors (B220+, CD19+, Mac-1-, Gr-1-) on co-culture with OP9 stromal cells in the presence of interleukin-7 (IL-7). However, enforced expression of E2A-PBX1 produced a myeloid immunophenotype (B220-, CD19-, Mac-1+, Gr-1+). Furthermore, these cells are dependent on myeloid cytokines, display no IL-7 responsiveness, and have a high forward scatter/side scatter profile. RT-PCR analysis shows severely reduced levels of lymphoid-associated transcripts (E2A, Ebf1, Pax5 and Irf8) and substantially elevated levels of myeloid associated transcripts (Csfr1, Id1 and Pu.1) relative to control lymphoid cells. All of these properties are characteristic of macrophage progenitors, a fate adopted by E2A−/− cells under similar culture conditions. Our findings showing that E2A-PBX1 is capable of altering the lineage fate of early hematopoietic progenitors in a manner similar to gene targeting of E2A provide support, albeit circumstantial, for a mechanism that involves dominant-negative effects on E-proteins and perhaps competition for limiting co-regulators such as CBP/p300. Consistent with the latter possibility, murine bone marrow cells expressing an E2A-PBX1 mutant impaired in CBP/p300 recruitment retain a minor propensity to repopulate the B-lymphoid compartment of irradiated transplant recipients. The results of experiments to evaluate the impact of E2A-PBX1 on transcriptional induction by E47 will be presented.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3097.

The reliability of lymphoma diagnosis in small tissue samples is heavily influenced by lymphoma subtype

A specific pathologic diagnosis is important in malignant lymphoma because the diverse disease subtypes require tailored approaches to clinical management. Reliance on small samples obtained with cutting needles has been advocated as a less invasive alternative to using larger, excised samples. Although published studies have demonstrated the safety and apparent sufficiency of this approach in informing clinical care, none have systematically determined the accuracy of pathologic lymphoma subtyping based on very small samples. We used a tissue microarray representing 67 cases of malignant lymphoma and 17 samples of nonneoplastic lymphoid tissue to model lymphoma diagnosis in small samples. Overall, 73.8% of the cases were diagnosed with a level of confidence deemed sufficient for directing clinical management; 85.9% of these diagnoses were accurate. Small cell lymphomas with highly distinctive immunophenotypes, including small lymphocytic, mantle cell, and T-lymphoblastic lymphoma, were recognized most consistently and accurately in the small samples. In contrast, follicular lymphoma and marginal zone lymphoma were especially difficult. Our results indicate that the reliability of lymphoma diagnoses based on small samples is heavily influenced by lymphoma subtype.

Critical role for a single leucine residue in leukemia induction by E2A-PBX1

In roughly 5% of cases of acute lymphoblastic leukemia, a chromosomal translocation leads to expression of the oncogenic protein E2A-PBX1. The N-terminal portion of E2A-PBX1, encoded by the E2A gene, is identical in sequence to the corresponding portion of the E proteins E12/E47 and includes transcriptional activation domains. The C terminus consists of most of the HOX interacting transcription factor PBX1, including its DNA-binding homeodomain. Structure-function correlative experiments have suggested that oncogenesis by E2A-PBX1 requires an activation domain, called AD1, at the extreme N terminus. We recently demonstrated that a potentially helical portion of AD1 interacts directly with the transcriptional coactivator protein cyclic AMP response element-binding protein (CBP) and that this interaction is essential in the immortalization of primary bone marrow cells in tissue culture. Here we show that a conserved LXXLL motif within AD1 is required in the interaction between E2A-PBX1 and the KIX domain of CBP. We show by circular dichroism spectroscopy that the LXXLL-containing portion of AD1 undergoes a helical transition upon interacting with the KIX domain and that amino acid substitutions that prevent helix formation prevent both the KIX interaction and cell immortalization by E2A-PBX1. Perhaps most strikingly, substitution of a single, conserved leucine residue (L20) within the LXXLL motif impairs leukemia induction in mice after transplantation with E2A-PBX1-expressing bone marrow. The KIX domain of CBP mediates well-characterized interactions with several transcription factors of relevance to leukemia induction. Circumstantial evidence suggests that the side chain of L20 might interact with a deep hydrophobic pocket in the KIX domain. Therefore, our results serve to identify a potential new drug target.

E2A-PBX1 interacts directly with the KIX domain of CBP/p300 in the induction of proliferation in primary hematopoietic cells

The E2A gene encodes DNA-binding transcription factors, called E12 and E47, involved in cell specification and maturation. E2A is also involved in a chromosomal translocation that leads to the expression of an oncogenic transcription factor called E2A-PBX1 in cases of acute leukemia. In the work described here, we elucidate the interaction between E2A-PBX1 and transcriptional co-activators. We confirm that the E2A portion can interact with CBP and PCAF and map required elements on E2A and CBP. On CBP, the interaction involves the KIX domain, a well characterized domain that mediates interactions with several other oncogenic transcription factors. On E2A, the interaction with CBP requires conserved alpha-helical domains that reside within activation domains 1 and 2 (AD1 and AD2, respectively). Using purified, recombinant proteins, we show that the E2A-CBP interaction is direct. Notwithstanding the previously demonstrated ability of AD1 and AD2 to function independently, some of our findings suggest functional cooperativity between these two domains. Finally, we show that the CBP/p300-interactive helical domains of E2A are important in the induction of proliferation in cultured primary bone marrow cells retrovirally transduced with E2A-PBX1. Our findings suggest that some aspects of E2A-PBX1 oncogenesis involve a direct interaction with the KIX domain of CBP/p300.

E2A basic helix-loop-helix transcription factors in human leukemia

The gene E2A on chromosome 19 is involved in recurrent chromosomal rearrangements associated with pediatric acute lymphoblastic leukemia. The resulting fusion of 5' E2A sequences with 3' portions of other genes leads to the expression of two well-characterized fusion proteins: E2A-PBX1 and E2A-HLF. Since the E2A, PBX1 and HLF proteins all appear to function as transcription factors, it appears likely that the oncogenic fusion proteins contribute to leukemia development by causing abnormal transcriptional regulation of key target genes. Furthermore, since the E2A portion of the fusion proteins contains transcriptional activation domains, and the PBX1 and HLF portions contain DNA binding domains, leukemogenesis may be due, at least in part, to excessive transcriptional induction of target genes defined by PBX1 or HLF. However, recent findings suggest that this model is simplistic and possibly incorrect. In this article, I review the evidence pertaining to leukemogenesis by the well-characterized E2A-fusion proteins and consider its mechanistic implications.

Improved technique for fluorescence in situ hybridisation analysis of isolated nuclei from archival, B5 or formalin fixed, paraffin wax embedded tissue

Fluorescence in situ hybridisation (FISH) is an effective method to detect chromosomal alterations in a variety of tissue types, including archived paraffin wax embedded specimens fixed in B5 or formalin. However, precipitating fixatives such as B5 have been known to produce unsatisfactory results in comparison with formalin when used for FISH. This study describes an effective nuclear isolation and FISH procedure for B5 and formalin fixed tissue, optimising the nuclear isolation step and nuclei pretreatments using tonsil and mantle cell lymphoma specimens. The protocol presented can be used to isolate nuclei and perform FISH on B5 or formalin fixed, paraffin wax embedded samples from a variety of tissue types.

The leukemogenic transcription factor E2a-Pbx1 induces expression of the putative N-myc and p53 target gene NDRG1 in Ba/F3 cells

The chimeric transcription factor E2a-Pbx1 is expressed as a result of the 1;19 chromosomal translocation in some 5% of cases of pediatric acute lymphoblastic leukemia. We investigated the biological and transcriptional consequences of forced expression of E2a-Pbx1 in the interleukin-3 (IL-3) dependent, bone marrow-derived cell line Ba/F3. We show that forced expression of E2a-Pbx1 induces apoptosis in Ba/F3 cells without apparent effects on cell cycle progression. This pro-apoptotic effect is enhanced on cytokine deprivation. Furthermore, using cDNA representational difference analysis (RDA), we show that these cellular effects are associated with marked induction of the gene NDRG1, which was previously identified as a target of transcriptional repression by N-myc and induction by the tumor suppressor protein p53. We identify a portion of the NDRG1 promoter capable of mediating transcriptional induction by E2a-Pbx1 and show that NDRG1 is also induced on simple IL-3 deprivation of BaF3 cells. Although we show that E2a-Pbx1 induction of NDRG1 is not impaired as a result of targeting p53 using HPV E6, and therefore does not appear to be p53-dependent, our results overall are consistent with the notion that induction of NDRG1 by E2a-Pbx1 may represent part of an apoptotic or cytostatic cellular response to oncogene activation.

Role for homodimerization in growth deregulation by E2a fusion proteins

The oncogenic transcription factor E2a-Pbx1 is expressed in some cases of acute lymphoblastic leukemia as a result of chromosomal translocation 1;19. The early observation that E2a-Pbx1 incorporates transcriptional activation domains from E2a and a DNA-binding homeodomain from Pbx1 inspired a model in which E2a-Pbx1 promotes leukemogenic transformation of lymphoid progenitor cells through transcriptional induction of target genes defined by the Pbx1 portion of the molecule. However, the subsequent demonstration that the only known DNA-binding module on the molecule, the Pbx1 homeodomain, is dispensable for the induction of lymphoblastic lymphoma in transgenic mice called into question the contribution made by the Pbx1 portion. In this study, we have used a domain swap approach coupled with a fibroblast-based focus formation assay to evaluate further the requirement for PBX1-encoded peptide elements in growth deregulation by E2a-Pbx1. No impairment of focus formation was observed when the entire Pbx1 portion was replaced with DNA-binding/dimerization domains derived from yeast transcription factor GAL4 or GCN4. Furthermore, replacement of Pbx1 with tandem FKBP domains that mediate homodimerization in the presence of a synthetic ligand led to striking growth deregulation exclusively in the presence of the dimerizing agent. N-terminal elements encoded by E2A, including the AD1 transcriptional activation domain, were required for dimerization-induced focus formation. We conclude that transcriptional target genes defined by heterologous C-terminal DNA-binding modules are not required in growth deregulation by E2a fusion proteins. We speculate that interactions between N-terminal E2a elements and undefined proteins that could function as components of a transcriptional coactivator complex may be more important.

Restricted expression of E2A protein in primary human tissues correlates with proliferation and differentiation

E2A is a basic helix-loop-helix (bHLH) transcription factor required for B cell lymphopoiesis and implicated in myogenesis and the regulation of insulin expression. As E2A is expressed widely in tissues, tissue-specific downstream effects are thought to result primarily from dimerization with other bHLH proteins. To investigate the degree to which regulation of E2A protein abundance may serve to regulate E2A function, expression of E2A was evaluated using immunohistochemistry on histological sections of primary human tissues. Somewhat surprisingly, nuclear staining for E2A was restricted in all tissues examined, often to a small subpopulation of cells. In some tissues, such as adult liver, expression was absent or limited to rare infiltrating lymphocytes. E2A-expressing cells were most abundant in lymphoid tissues. In tonsil, lymph node, and spleen, expression appeared most abundant and prevalent among rapidly proliferating centroblasts of the germinal center dark zone. Scattered E2A-expressing thymocytes were more numerous in the thymic cortex than medulla. In developing skeletal muscle, E2A was detectable in striated myotubes but not in more primitive mononucleated progenitors or mature muscle. Differential E2A expression was also noted in proliferating periventricular neuroepithelial cells in the developing brain. These results suggest that regulation of E2A abundance complements protein-protein interactions in modulating E2A function.

The chimeric oncoproteins E2A-PBX1 and E2A-HLF are concentrated within spherical nuclear domains

Oncogenic mutation of nuclear transcription factors often is associated with altered patterns of subcellular localization that may be of functional importance. The leukemogenic transcription factor gene E2A-PBX1 is created through fusion of the genes E2A and PBX1 as a result of t(1;19) in acute lymphoblastic leukemia. We evaluated subcellular localization patterns of E2A-PBX1 protein in transfected cells using immunofluorescence. Full-length E2A-PBX1 was exclusively nuclear and was concentrated in spherical domains denoted chimeric-E2A oncoprotein domains (CODs). In contrast, nuclear fluorescence for wild-type E2A or PBX1 proteins was diffuse. Enhanced concentrations of RNA polymerase II within many CODs and the requirement for an E2A-encoded activation domain suggested transcriptional relevance. However, in situ co-detection of nascent transcripts labeled with bromouridine failed to confirm altered transcriptional activity in relation to CODs. CODs also failed to co-localize with other proteins known to occupy functional nuclear compartments, including the transcription factor PML, the spliceosome-associated protein SC-35 and the adenovirus replication factor DBP, or with foci of DNA replication. Co-transfection of Hoxb7, a homeodomain protein capable of enhancing DNA binding by PBX1, impaired COD formation, suggesting that CODs contain E2A-PBX1 protein not associated with DNA. We conclude that, as a 'gain of function' phenomenon requiring protein elements from both E2A and PBX1, COD formation may be relevant to the biology of E2A-PBX1 in leukemogenesis.

Interleukin-6 is required for pristane-induced plasma cell hyperplasia in mice

Intraperitoneal injection of pristane induces production of interleukin-6 (IL-6) and either plasmacytosis or plasmacytoma in mice, depending upon the genetic background. Pristane does not induce plasmacytoma in IL-6 knockout (IL-6-/-) mice, suggesting that IL-6 is required for this process. In the present study we determined whether IL-6 is also required for pristane-induced hyperplasia of normal plasma cells. Pristane was injected intraperitoneally into IL-6-/- and IL-6 wild-type (IL-6+/+) mice. Overall there were more deaths in IL-6+/+ mice (85%) than in IL-6-/- mice (40%), P = 0.024. Hyperplastic lymph node and spleen weight did not differ (P = 0.82 and P = 0.15, respectively) in IL-6-/- versus IL-6+/+ mice. Lymphocytosis with similar patterns of expression of B-cell (B220) and T-cell (Thy-1) antigens was noted in both IL-6-/- and IL-6+/+ mice. However, morphological studies, dual fluorescent staining for Syn-1 and B220 antigens (syn-1+ B220+ cells), and intracytoplasmic Ig staining revealed plasma cell hyperplasia in lymph node and spleen from IL-6+/+, but not IL-6-/-, mice. These plasma cells from IL-6+/+ mice were polyclonal and unable to induce tumour formation in severe combined immunodeficient mice. These data demonstrate that IL-6 is required for pristane-induced hyperplasia of polyclonal plasma cells in mice.

bcl-2 expression in primary malignancies of the skin

BACKGROUND AND DESIGN

Basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and malignant melanoma (MM) are the three most common malignant neoplasms that arise in the skin. Deregulation of oncogene function not infrequently leads to an increased rate of cellular proliferation. However, the expansion of malignant cells can also occur if programmed cell death is inhibited. The oncogene bcl-2 participates in the regulation of apoptosis (programmed cell death). In view of this, we determined the presence and possible role of bcl-2 in primary cutaneous malignancies. Routine paraffin sections of formalin-fixed BCCs, SCCs, MMs (primary and metastatic), actinic keratoses, and SCCs in situ were labeled with anti-bcl-2 monoclonal antibody using a biotin-avidin-immunoperoxidase procedure.

RESULTS

Twenty-three BCCs were examined and all expressed cytoplasmic bcl-2. Two of 20 SCCs were positive. One of these had patchy, diffuse staining, and the other stained in only small foci. None of eight SCCs in situ and none of eight actinic keratoses expressed bcl-2. Sixteen of 18 MMs expressed bcl-2.

CONCLUSIONS

The bcl-2 gene product has been found to inhibit apoptosis. Our preliminary results suggest that the expression of bcl-2 is present quite consistently in BCCs and MMs, but not in SCCs or precursor lesions. The expression (or lack thereof) of bcl-2 may reflect the difference in the regulation of cell turnover between these tumors, or histogenetic differences.

Transformation properties of the E2a-Pbx1 chimeric oncoprotein: fusion with E2a is essential, but the Pbx1 homeodomain is dispensable

The t(1;19) chromosomal translocation in acute lymphoblastic leukemias creates chimeric E2a-Pbx1 oncoproteins that can act as DNA-binding activators of transcription. A structural analysis of the functional domains of E2a-Pbx1 showed that portions of both E2a and Pbx1 were essential for transformation of NIH 3T3 cells and transcriptional activation of synthetic reporter genes containing PBX1 consensus binding sites. Hyperexpression of wild-type or experimentally truncated Pbx1 proteins was insufficient for transformation, consistent with their inability to activate transcription. When fused with E2a, the Pbx-related proteins Pbx2 and Pbx3 were also transformation competent, demonstrating that all known members of this highly similar subfamily of homeodomain proteins have latent oncogenic potential. The oncogenic contributions of E2a to the chimeras were localized to transactivation motifs AD1 and AD2, as their mutation significantly impaired transformation. Either the homeodomain or Pbx1 amino acids flanking this region could mediate transformation when fused to E2a. However, the homeodomain was not essential for transformation, since a mutant E2a-Pbx1 protein (E2a-Pbx delta HD) lacking the homeodomain efficiently transformed fibroblasts and induced malignant lymphomas in transgenic mice. Thus, transformation mediated by the chimeric oncoprotein E2a-Pbx1 is absolutely dependent on motifs acquired from E2a but the Pbx1 homeodomain is optional. The latter finding suggests that E2a-Pbx1 may interact with cellular proteins that assist or mediate alterations in gene expression responsible for oncogenesis even in the absence of homeodomain-DNA interactions.

Lymphoid neoplasms in patients with rheumatoid arthritis and dermatomyositis: frequency of Epstein-Barr virus and other features associated with immunosuppression

We recently reported two cases of reversible Epstein-Barr virus (EBV)-associated lymphomas in patients undergoing methotrexate therapy for rheumatic disease. The current study was undertaken to investigate how frequently lymphoid neoplasms in patients with rheumatic disease show features of lymphoproliferations occurring in immunocompromised patients. Eighteen patients (including the two previously reported patients) with rheumatoid arthritis or dermatomyositis who developed lymphoproliferative lesions and on whom detailed clinical information was available were studied. As a group these patients developed a spectrum of lymphoproliferative lesions; however, a subset of patients developed neoplasms with features associated with immunosuppression. The neoplasms occurred in extranodal sites in 10 (56%) patients, showed a diffuse large-cell histology in nine (50%) patients, and contained EBV (EBER1) transcripts and EBV latent membrane protein in six (33%) patients. In three (17%) patients the neoplasms showed the entire constellation of features typical of immunosuppression-associated lymphoproliferations, including extranodal location, large-cell or polymorphous histology, geographic areas of necrosis, and the presence of EBV. These three patients were receiving both steroids and methotrexate at the time they developed their neoplasms. The findings of this study support the hypothesis that a subset of lymphoid neoplasms in rheumatic patients occurs in an immunocompromised setting and suggest that therapeutic immunosuppression may contribute, at least in part, to the development of these lymphoid neoplasms.

Fusion with E2A alters the transcriptional properties of the homeodomain protein PBX1 in t(1;19) leukemias

The t(1;19) chromosomal translocation is observed in pre-B cell acute lymphoblastic leukemias and results in expression of chimeric E2A-PBX1 proteins that contain transcriptional activation domains from E2A and the homeodomain of PBX1. Since homeodomains mediate DNA-binding, a potential model for the action of E2A-PBX1 is that it disrupts the transcriptional regulation of genes normally controlled by PBX1 or its closely-related family members PBX2 or PBX3. Using a binding site selection assay, we identified a consensus nucleotide sequence ATCAATCA specifically bound by the PBX1 homeodomain and those of its closely-related family members PBX2 and PBX3. An endogenous protein with the properties of PBX3b specifically bound to this sequence in nuclear extracts of precursor B cells. Transfection of reporter genes containing PBX binding sites linked to a minimal promoter demonstrated transactivation by E2A-PBX1 fusion protein dependent upon presence of the homeodomain. In contrast, wild-type PBX proteins were incapable of activating transcription. The striking differences in transcriptional properties of fusion and wild-type PBX proteins provides strong functional evidence for the importance of aberrant transcriptional regulation in the genesis of t(1;19)-bearing leukemias.

Floral variant of follicular lymphoma. Immunological and molecular studies support a neoplastic process

In recent reports of the so-called "floral variant" of follicular lymphoma, an unusual variant of follicular lymphoma mimicking progressive transformation of germinal centers, questions have been raised regarding whether this process represents a malignant lymphoma. We studied 19 examples of the floral variant of follicular lymphoma and report our light microscopic, immunohistochemical, and molecular diagnostic findings. Morphologic changes consisted of effacement of normal lymph node architecture by follicles composed of atypical lymphocytes. The follicles were surrounded by prominent mantle zones that invaginated irregularly into the follicle centers, often imparting a "floral" appearance. Sufficient material was available for immunophenotypic or genotypic studies in 15 biopsies. Twelve of 15 cases studied by immunohistochemistry demonstrated phenotypes supporting a diagnosis of lymphoma. Five demonstrated light-chain restriction; one was an immunoglobulin-negative B-cell neoplasm; and six, in which only formalin-fixed, paraffin-embedded tissue was available, demonstrated overexpression of the bcl-2 protein. Southern blot analysis revealed evidence of clonal immunoglobulin heavy-chain gene rearrangement in all five cases tested. Overall, 12 of the 15 biopsies studied with these techniques showed immunologic or genotypic support for malignant lymphoma. The results of this study demonstrate that the floral variant of follicular lymphoma does indeed represent a malignant lymphoma.

The bcl-2 oncogene in Hodgkin's disease arising in the setting of follicular non-Hodgkin's lymphoma

Expression of the bcl-2 proto-oncogene on chromosome 18 is deregulated by the 14; 18 chromosomal translocation, an abnormality that is consistently associated with follicular non-Hodgkin's lymphomas (NHL). Because bcl-2 is believed to function by prolonging cell survival rather than by increasing proliferation, the presence of t(14; 18) in Hodgkin's disease (HD) would have profound implications for the pathogenesis of this neoplasm. We evaluated 32 cases of HD for t(14; 18) by polymerase chain reaction (PCR). These results were correlated with expression of bcl-2 oncogenic protein by Hodgkin cells and with the presence of Epstein-Barr virus (EBV), as determined by immunohistochemistry or in situ hybridization. PCR provided evidence of t(14; 18) in only 2 HD cases (6%), both of which were associated with a prior history of follicular lymphoma, and both of which were among the 7 cases (22%) with strong bcl-2 expression in Hodgkin cells. In at least 1 of the cases, the translocation involved identical chromosomal breakpoints in both types of lymphoma. Furthermore, 7 additional cases of combined follicular NHL and HD showed strong bcl-2 staining in Hodgkin cells. Although EBV was detected in 6 of 30 cases, it was not associated with t(14; 18) and usually not with strong bcl-2 expression. These results suggest that a small proportion of HD cases might evolve from follicular NHL, possibly through molecular events superimposed on the t(14; 18). High-level bcl-2 expression in Hodgkin cells is a potentially useful but not definitive marker for these cases.

Chimeric homeobox gene E2A-PBX1 induces proliferation, apoptosis, and malignant lymphomas in transgenic mice

Expression of the homeobox fusion gene E2A-PBX1 under control of the immunoglobulin heavy chain enhancer efficiently induced malignancies in transgenic mice. All animals died before 5 months of age with lymphomas that demonstrated phenotypes consistent with transitional intermediate thymocytes (CD4+/CD8+/CD3med). E2A-PBX1 also markedly altered lymphoid development in pretumorous animals, reducing the number of thymocytes and bone marrow B lineage progenitors to 20% of normal levels. In spite of the observed reductions in lymphoid cells, premalignant animals contained significantly increased numbers of cycling thymocytes, but a higher proportion was also undergoing apoptosis, suggesting that increased cell death resulted in the marked lymphopenias. These data indicate that the chimeric homeodomain protein E2A-PBX1 paradoxically induces both proliferation and apoptosis in lymphoid cells, suggesting an in vivo association between nuclear oncogene-induced cell cycle progression and programed cell death.

Expression of bcl-2 in fetal tissues suggests a role in morphogenesis

We have studied the distribution of the bcl-2 protein in fetal tissues, in an effort to uncover patterns of expression that may elucidate the potential role of bcl-2 during development. We find that bcl-2 is expressed in many hematolymphoid and non-hematolymphoid tissues, most abundantly in placental trophoblast. In tissues of endocrine and neural derivation and in stem-cell populations of colonic and some stratified epithelia, bcl-2 seems to be involved in tissue homeostasis. However, in developing proximal nephrons of the kidney and other sites characterized by inductive interactions between epithelium and mesenchyme, bcl-2 is apparently involved in morphogenesis, possibly by mediating the formation of condensations of cells that are "committed" to the formation of more differentiated structures. The distribution of bcl-2-protein expression in fetal tissues is consistent with its previously described role in promoting cell survival, presumably by preventing apoptosis in lymphoid and other tissues where cell death represents an active regulatory process. Expression of bcl-2 protein is more widespread in fetal than adult tissues. Our observations therefore represent supportive evidence for the importance of inducible cell survival as a regulatory process in normal homeostasis and morphogenesis in many fetal tissues and structures.

Topographical dissociation of BCL-2 messenger RNA and protein expression in human lymphoid tissues

Immunohistochemistry and in situ hybridization with a synthetic oligonucleotide probe were used to compare the topographical distribution of BCL-2 proto-oncogenic protein with that of its messenger RNA (mRNA) in normal lymphoid tissues, follicular lymphomas, and lymphoma-derived cell lines. In normal lymph nodes, BCL-2 protein was most abundant in the small lymphocytes of primary lymphoid follicles and the mantle zones of secondary follicles, virtually absent within germinal centers, and of variable abundance in many interfollicular cells. In contrast, the distribution of BCL-2 mRNA was roughly reciprocal to that of the protein with intense hybridization signal in germinal centers and almost none in mantle zones. Discordant BCL-2 RNA and protein levels were also observed in tonsillar epithelial cells and cortical thymocytes. Concordant and abundant expression of BCL-2 mRNA and protein was detected in biopsy tissues and cell lines from t(14;18)-carrying lymphomas. The contrasting distributions of BCL-2 protein and RNA in normal lymphoid tissues suggest that translational and posttranslational control mechanisms play a significant role in regulating BCL-2 protein levels in germinal center cells, epithelial cells, and cortical thymocytes. Concordant BCL-2 mRNA and protein levels in follicular lymphomas suggest that translational control mechanisms may be disrupted as part of the sequence of genetic changes that transforms normal lymphoid cells into neoplastic follicular lymphoma cells.

Estimation of tumor growth fractions in archival formalin-fixed, paraffin-embedded tissues using two anti-PCNA/Cyclin monoclonal antibodies. Factors affecting reactivity

Immunohistochemical detection of cell cycle-related markers for estimation of tumor growth fractions using paraffin-embedded tissue sections would have applications in experimental and clinical pathology as an in situ histologic alternative to flow cytometry. The monoclonal antibodies 19A2 and PC10 detect the proliferating cell nuclear antigen (PCNA/Cyclin), an auxiliary protein to DNA polymerase-delta. In a prospective group of uniformly handled, formalin-fixed malignant lymphomas we previously demonstrated 19A2 to be a reliable marker of proliferative activity similar to Ki-67 in frozen tissue. The present study examines the applicability of this technique in archival formalin-fixed material. Studies on tonsilar tissue revealed that formalin fixation beyond 30 hours adversely affected reactivity of 19A2, possibly explaining the variable results in nonuniformly fixed archival material. We found that only 27 (56%) of 48 archival cases of infiltrating ductal carcinoma showed sufficient reactivity with 19A2 to permit reliable quantification of the tumor growth fraction. Acid pretreatment with 2N HCl had no apparent effect on 19A2 reactivity. Using both antibodies on a group of 32 archival lymphomas, carcinomas, and sarcomas, significantly more biopsies stained reliably for PC10 (84%) than for 19A2 (72%; P < 0.036). Further, none of the cases that did not react with PC10 reacted with 19A2. PC10 may recognize a different epitope of PCNA/Cyclin which may be more resistant to alterations by fixation. In the 23 cases that reliably stained for both markers, largely carcinomas, there was excellent correlation between estimated growth fractions (r = 0.96). Although immunostaining provides a useful way to estimate tumor growth fractions in paraffin-embedded tissues, modifications of technique and cautious interpretation of results are advisable when using archival material.

Follicular lymphomas of the gastrointestinal tract. Pathologic features in 31 cases and bcl-2 oncogenic protein expression

The gastrointestinal tract is the most common site for extranodal lymphomas, but follicular lymphomas involving the gut are rare. To study their pathologic features and bcl-2 expression, 31 follicular lymphomas of the GI tract were reviewed and unstained paraffin sections from 24 of the cases were immunohistochemically stained using a monoclonal antibody for the peptide product of the proto-oncogene bcl-2. The most common site of lymphoma involvement was the small intestine, especially the terminal ileum. Gastric lymphomas tended to present clinically with symptomatic ulcers and small intestinal lesions presented with obstruction. Five cases involving the terminal ileum or colon had a gross appearance of multitudinous mucosal polyps and were considered to represent examples of "multiple lymphomatous polyposis." Enhanced expression of the bcl-2 oncogenic protein was detectable in lymphoma cells in 75% of cases and at lower levels in normal lymphoid cells in most cases. Small cleaved or mixed cell lymphomas were more likely to show enhanced expression than were large cell cases. Reactive germinal centers showed no bcl-2 staining. It is concluded that follicular GI lymphomas are associated with distinctive pathological features. In their tendency to express bcl-2, these neoplasms resemble their lymph node-based counterparts. Immunohistochemical staining for enhanced bcl-2 expression is of potential diagnostic utility in distinguishing between follicular lymphoma and follicular lymphoid hyperplasia in the gastrointestinal tract. The relevance of the results to lymphoma of mucosa-associated lymphoid tissue (MALT) is discussed.

Warthin-Finkeldey polykaryocytes demonstrate a T-cell immunophenotype

Warthin-Finkeldey polykaryocytes have been described in various benign and malignant lymphoid conditions since their initial identification in tonsils of patients in the prodromal stage of measles. However, the nature of these multinucleated giant cells is obscure. The authors studied the immunohistochemical profile of the Warthin-Finkeldey-type giant cells in three cases of lymphoid proliferations (two reactive, one neoplastic) containing many multinucleated cells using a panel of paraffin-reactive antibodies. Warthin-Finkeldey polykaryocytes demonstrated reactivity with Leu22 (CD43), anti-CD3, and OPD4, indicating that these cells are multinucleated T lymphocytes. The significance of these results with respect to the disorders in which these cells are found and their possible role in pathogenesis of disease are discussed.

Enhanced staining for Leu M1 (CD15) in Hodgkin's disease using a secondary antibody specific for immunoglobulin M

The utility of staining for Leu M1 (CD15) as a diagnostic aid in Hodgkin's disease has been questioned because of a relative lack of specificity and sensitivity. Furthermore, interpretation is often made difficult by staining that tends to be weak and focal. Because the murine monoclonal anti-Leu M1 antibody is of immunoglobulin M type, it is reasonable to wonder whether improved immunohistochemical staining might result from use of a secondary goat antibody specific for the mouse mu heavy chain instead of the traditional one against mouse immunoglobulin. The two methods were compared, using a biotin-avidin detection system, on paraffin sections from 15 cases of Hodgkin's disease: 9 nodular sclerosing, 1 mixed cellularity, and 5 of nodular lymphocytic and histiocytic (L&H) type. In the nodular sclerosing/mixed cellularity group, the mu-specific detection method resulted in a greater number of cases with reactive Hodgkin's cells (7 versus 5), stained an average of more than three times as many neoplastic cells in each case (49% versus 14%), and usually produced staining that was distinctly more intense, often in a membrane and paranuclear distribution characteristic of Leu M1 in Hodgkin's cells. In the noLeu M1 in Hodgkin's cells. In the nodular L&H group, 1 case showed weak, focal staining with the newer method. None of the L&H cases stained using the traditional technique. It is concluded that use of a second-stage antibody that is directed specifically against mu heavy chains results in an improvement in immunohistochemical staining for Leu M1 in paraffin sections, which is of practical significance.

Essential thrombocythemia with the Philadelphia chromosome and BCR-ABL gene rearrangement. An entity distinct from chronic myeloid leukemia and Philadelphia chromosome-negative essential thrombocythemia

A 64-year-old woman presented with a platelet count of 3,225 x 10(9)/L. Bone marrow morphology showed massive megakaryocytic hyperplasia; cytogenetic studies showed the presence of the Philadelphia chromosome (Ph). The presence of a rearrangement involving the major breakpoint cluster region (mbcr) on chromosome 22 was confirmed by Southern blotting techniques. A diagnosis of Ph positive essential thrombocythemia (ET) was made. Such cases constitute less than 5% of patients with ET and it has been proposed that they be considered examples of chronic myelogenous leukemia (CML) because of a shared propensity to progress to blast crisis. An argument is presented for retaining Ph positive ET as an entity separate from Ph negative ET and Ph positive CML.

Growth fraction estimation of malignant lymphomas in formalin-fixed paraffin-embedded tissue using anti-PCNA/Cyclin 19A2. Correlation with Ki-67 labeling

The immunohistochemical detection of PCNA/Cyclin, a nuclear protein associated with cell proliferation, represents a potentially useful tool for the study of tumor proliferative activity. Previous studies investigating the reactivity of anti-PCNA/Cyclin monoclonal antibody 19A2 have not clearly defined the population of proliferating cells with which 19A2 reacts in tissue sections. The authors describe a method for detection of PCNA/Cyclin in formalin-fixed, paraffin-embedded tissue using a routine biotin-streptavidin immunohistochemical system that employs an anti-IgM, mu-chain-specific second-stage antibody. The authors used this method to study the proliferative activity of 24 malignant lymphomas, consisting of 12 low-grade lymphomas (LGLs) and 12 intermediate-grade lymphomas (IGLs), and five reactive tonsils. 19A2 data was compared with Ki-67 labeling in frozen sections in the same group of cases. 19A2 provided easily detectable nuclear staining of proliferating cells with reactive cells demonstrating varying intensity of staining, this latter finding most likely due to the varying nuclear concentration of PCNA/Cyclin protein during the cell cycle. In tonsils, 19A2 reacted with germinal center cells and basal keratinocytes. In the malignant lymphomas, there was good correlation between 19A2 and Ki-67 data (r = 0.90, P less than 0.001). The subgroup of LGLs showed a mean PCNA/Cyclin of 26% and a mean Ki-67 of 28%. In the subgroup of IGLs, mean PCNA/Cyclin = 54% and mean Ki-67 = 59%. These results indicate that 19A2 detects a fraction of proliferating cells that is similar to that detected by Ki-67, ie, the growth fraction, and that 19A2 is a reliable marker of proliferative activity in uniformly handled, formalin-fixed, paraffin-embedded tissue.

Fibrolamellar carcinoma of the liver in a patient with Fanconi anemia

A 9-year-old boy with Fanconi anemia treated with oxymethalone, a synthetic androgen, died of intracerebral hemorrhage. At autopsy, the liver contained several adenomas and a large fibrolamellar hepatocellular carcinoma, as well as phlebectatic peliosis hepatis. The 11 previously reported cases of hepatocellular carcinoma in Fanconi anemia were not, apparently, of the fibrolamellar type, which has a better prognosis, occurs in children of both sexes, and generally is not associated with cirrhosis. The malignant potential of primary liver tumors associated with Fanconi anemia as well as the nature of their relationship to Fanconi anemia and to anabolic steroid therapy is discussed.