Growth- and tumor-promoting effects of deregulated BCL2 in human B-lymphoblastoid cells

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

B-Cell Lymphoma 2 (BCL-2), c-MYC and related proteins are arguably amongst the most widely studied in all of biology. Every year there are thousands of papers reporting on different aspects of their biochemistry, cellular and physiological mechanisms and functions. This plethora of literature can be attributed to both proteins playing essential roles in the normal functioning of a cell, and by extension a whole organism, but also due to their central role in disease, most notably, cancer. Many cancers arise due to genetic lesions resulting in deregulation of both proteins, and indeed the development and survival of tumours is often dependent on co-operativity between these protein families. In this review we will discuss the individual roles of both proteins in cancer, describe cancers where co-operativity between them has been well-characterised and finally, some strategies to target these proteins therapeutically.

The serine hydroxymethyltransferase-2 (SHMT2) initiates lymphoma development through epigenetic tumor suppressor silencing

Cancer cells adapt their metabolic activities to support growth and proliferation. However, increased activity of metabolic enzymes is not usually considered an initiating event in the malignant process. Here, we investigate the possible role of the enzyme serine hydroxymethyltransferase-2 (SHMT2) in lymphoma initiation. SHMT2 localizes to the most frequent region of copy number gains at chromosome 12q14.1 in lymphoma. Elevated expression of SHMT2 cooperates with BCL2 in lymphoma development; loss or inhibition of SHMT2 impairs lymphoma cell survival. SHMT2 catalyzes the conversion of serine to glycine and produces an activated one-carbon unit that can be used to support S-adenosyl methionine synthesis. SHMT2 induces changes in DNA and histone methylation patterns leading to promoter silencing of previously uncharacterized mutational genes, such as SASH1 and PTPRM. Together, our findings reveal that amplification of SHMT2 in cooperation with BCL2 is sufficient in the initiation of lymphomagenesis through epigenetic tumor suppressor silencing.

BCL-2: Long and winding path from discovery to therapeutic target

In 1988, the BCL-2 protein was found to promote cancer by limiting cell death rather than enhancing proliferation. This discovery set the wheels in motion for an almost 30 year journey involving many international research teams that has recently culminated in the approval for a drug, ABT-199/venetoclax/Venclexta that targets this protein in the treatment of cancer. This review will describe the long and winding path from the discovery of this protein and understanding the fundamental process of apoptosis that BCL-2 and its numerous homologues control, through to its exploitation as a drug target that is set to have significant benefit for cancer patients.

How to unleash mitochondrial apoptotic blockades to kill cancers?

Apoptosis, especially the intrinsic mitochondrial cell death pathway, is regulated by the BCL-2 family of proteins. Defects in apoptotic machinery are one of the main mechanisms that cells employ to evade cell death and become cancerous. Targeting the apoptotic defects, either by direct inhibition of BCL-2 family proteins or through modulation of regulatory pathways, can restore cell sensitivity to cell death. This review will focus on the aspects of BCL-2 family proteins, their interactions with kinase pathways, and how novel targeted agents can help overcome the apoptotic blockades. Furthermore, functional assays, such as BH3 profiling, may help in predicting responses to chemotherapies and aid in the selection of combination therapies by determining the mitochondrial threshold for initiating cell death.

Synergistic activity of Card11 mutant and Bcl6 in the development of diffuse large B-cell lymphoma in a mouse model

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of malignant lymphoma; it derives from germinal center B cells. Although DLBCL harbors many genetic alterations, synergistic roles between such alterations in the development of lymphoma are largely undefined. We previously established a mouse model of lymphoma by transplanting gene-transduced germinal center B cells into mice. Here, we chose one of the frequently mutated genes in DLBCL, Card11 mutant, to explore its possible synergy with other genes, using our lymphoma model. Given that BCL6 and BCL2 expression and/or function are often deregulated in human lymphoma, we examined the possible synergy between Card11, Bcl6, and Bcl2. Germinal center B cells were induced in vitro, transduced with Card11 mutant, Bcl6, and Bcl2, and transplanted. Mice rapidly developed lymphomas, with exogenously transduced Bcl2 being dispensable. Although some mice developed lymphoma in the absence of transduced Bcl6, the absence was compensated by elevated expression of endogenous Bcl6. Additionally, the synergy between Card11 mutant and Bcl6 in the development of lymphoma was confirmed by the fact that the combination of Card11 mutant and Bcl6 caused lymphoma or death significantly earlier and with higher penetrance than Card11 mutant or Bcl6 alone. Lymphoma cells expressed interferon regulatory factor 4 and PR domain 1, indicating their differentiation toward plasmablasts, which characterize activated B cell-like DLBCL that represents a clinically aggressive subtype in humans. Thus, our mouse model provides a versatile tool for studying the synergistic roles of altered genes underlying lymphoma development.

Thirty years of BCL-2: translating cell death discoveries into novel cancer therapies

The 'hallmarks of cancer' are generally accepted as a set of genetic and epigenetic alterations that a normal cell must accrue to transform into a fully malignant cancer. It follows that therapies designed to counter these alterations might be effective as anti-cancer strategies. Over the past 30 years, research on the BCL-2-regulated apoptotic pathway has led to the development of small-molecule compounds, known as 'BH3-mimetics', that bind to pro-survival BCL-2 proteins to directly activate apoptosis of malignant cells. This Timeline article focuses on the discovery and study of BCL-2, the wider BCL-2 protein family and, specifically, its roles in cancer development and therapy.

Targeting BCL-2 to enhance vulnerability to therapy in estrogen receptor-positive breast cancer

The last three decades have seen significant progress in our understanding of the role of the pro-survival protein BCL-2 and its family members in apoptosis and cancer. BCL-2 and other pro-survival family members including Mcl-1 and BCL-XL have been shown to have a key role in keeping pro-apoptotic 'effector' proteins BAK and BAX in check. They also neutralize a group of 'sensor' proteins (such as BIM), which are triggered by cytotoxic stimuli such as chemotherapy. BCL-2 proteins therefore have a central role as guardians against apoptosis, helping cancer cells to evade cell death. More recently, an increasing number of BH3 mimetics, which bind and neutralize BCL-2 and/or its pro-survival relatives, have been developed. The utility of targeting BCL-2 in hematological malignancies has become evident in early-phase studies, with remarkable clinical responses seen in heavily pretreated patients. As BCL-2 is overexpressed in ~75% of breast cancer, there has been growing interest in determining whether this new class of drug could show similar promise in breast cancer. This review summarizes our current understanding of the role of BCL-2 and its family members in mammary gland development and breast cancer, recent progress in the development of new BH3 mimetics as well as their potential for targeting estrogen receptor-positive breast cancer.

The BCL2 Family: Key Mediators of the Apoptotic Response to Targeted Anticancer Therapeutics

The ability of cancer cells to suppress apoptosis is critical for carcinogenesis. The BCL2 family proteins comprise the sentinel network that regulates the mitochondrial or intrinsic apoptotic response. Recent advances in our understanding of apoptotic signaling pathways have enabled methods to identify cancers that are "primed" to undergo apoptosis, and have revealed potential biomarkers that may predict which cancers will undergo apoptosis in response to specific therapies. Complementary efforts have focused on developing novel drugs that directly target antiapoptotic BCL2 family proteins. In this review, we summarize the current knowledge of the role of BCL2 family members in cancer development and response to therapy, focusing on targeted therapeutics, recent progress in the development of apoptotic biomarkers, and therapeutic strategies designed to overcome deficiencies in apoptosis.

SIGNIFICANCE

Apoptosis, long known to be important for response to conventional cytotoxic chemotherapy, has more recently been shown to be essential for the efficacy of targeted therapies. Approaches that increase the likelihood of a cancer to undergo apoptosis following therapy may help improve targeted treatment strategies. Cancer Discov; 5(5); 475-87. ©2015 AACR.

Non-IG aberrations of FOXP1 in B-cell malignancies lead to an aberrant expression of N-truncated isoforms of FOXP1

The transcription factor FOXP1 is implicated in the pathogenesis of B-cell lymphomas through chromosomal translocations involving either immunoglobulin heavy chain (IGH) locus or non-IG sequences. The former translocation, t(3;14)(p13;q32), results in dysregulated expression of FOXP1 juxtaposed with strong regulatory elements of IGH. Thus far, molecular consequences of rare non-IG aberrations of FOXP1 remain undetermined. Here, using molecular cytogenetics and molecular biology studies, we comprehensively analyzed four lymphoma cases with non-IG rearrangements of FOXP1 and compared these with cases harboring t(3;14)(p13;q32)/IGH-FOXP1 and FOXP1-expressing lymphomas with no apparent structural aberrations of the gene. Our study revealed that non-IG rearrangements of FOXP1 are usually acquired during clinical course of various lymphoma subtypes, including diffuse large B cell lymphoma, marginal zone lymphoma and chronic lymphocytic leukemia, and correlate with a poor prognosis. Importantly, these aberrations constantly target the coding region of FOXP1, promiscuously fusing with coding and non-coding gene sequences at various reciprocal breakpoints (2q36, 10q24 and 3q11). The non-IG rearrangements of FOXP1, however, do not generate functional chimeric genes but commonly disrupt the full-length FOXP1 transcript leading to an aberrant expression of N-truncated FOXP1 isoforms (FOXP1(NT)), as shown by QRT-PCR and Western blot analysis. In contrast, t(3;14)(p13;q32)/IGH-FOXP1 affects the 5' untranslated region of FOXP1 and results in overexpress the full-length FOXP1 protein (FOXP1(FL)). RNA-sequencing of a few lymphoma cases expressing FOXP1(NT) and FOXP1(FL) detected neither FOXP1-related fusions nor FOXP1 mutations. Further bioinformatic analysis of RNA-sequencing data retrieved a set of genes, which may comprise direct or non-direct targets of FOXP1(NT), potentially implicated in disease progression. In summary, our findings point to a dual mechanism through which FOXP1 is implicated in B-cell lymphomagenesis. We hypothesize that the primary t(3;14)(p13;q32)/IGH-FOXP1 activates expression of the FOXP1(FL) protein with potent oncogenic activity, whereas the secondary non-IG rearrangements of FOXP1 promote expression of the FOXP1(NT) proteins, likely driving progression of disease.

Multiple functions of BCL-2 family proteins

BCL-2 family proteins are the regulators of apoptosis, but also have other functions. This family of interacting partners includes inhibitors and inducers of cell death. Together they regulate and mediate the process by which mitochondria contribute to cell death known as the intrinsic apoptosis pathway. This pathway is required for normal embryonic development and for preventing cancer. However, before apoptosis is induced, BCL-2 proteins have critical roles in normal cell physiology related to neuronal activity, autophagy, calcium handling, mitochondrial dynamics and energetics, and other processes of normal healthy cells. The relative importance of these physiological functions compared to their apoptosis functions in overall organismal physiology is difficult to decipher. Apoptotic and noncanonical functions of these proteins may be intertwined to link cell growth to cell death. Disentanglement of these functions may require delineation of biochemical activities inherent to the characteristic three-dimensional shape shared by distantly related viral and cellular BCL-2 family members.

Double-hit B-cell lymphomas

In many B-cell lymphomas, chromosomal translocations are biologic and diagnostic hallmarks of disease. An intriguing subset is formed by the so-called double- hit (DH) lymphomas that are defined by a chromosomal breakpoint affecting the MYC/8q24 locus in combination with another recurrent breakpoint, mainly a t(14;18)(q32;q21) involving BCL2. Recently, these lymphomas have received increased attention, which contributed to the introduction of a novel category of lymphomas in the 2008 WHO classification, "B cell lymphoma unclassifiable with features intermediate between DLBCL and BL." In this review we explore the existing literature for the most recurrent types of DH B-cell lymphomas and the involved genes with their functions, as well as their pathology and clinical aspects including therapy and prognosis. The incidence of aggressive B-cell lymphomas other than Burkitt lymphoma with a MYC breakpoint and in particular a double hit is difficult to assess, because screening by methods like FISH has not been applied on large, unselected series, and the published cytogenetic data may be biased to specific categories of lymphomas. DH lymphomas have been classified heterogeneously but mostly as DLBCL, the majority having a germinal center phenotype and expression of BCL2. Patients with DH lymphomas often present with poor prognostic parameters, including elevated LDH, bone marrow and CNS involvement, and a high IPI score. All studies on larger series of patients suggest a poor prognosis, also if treated with RCHOP or high-intensity treatment modalities. Importantly, this poor outcome cannot be accounted for by the mere presence of a MYC/8q24 breakpoint. Likely, the combination of MYC and BCL2 expression and/or a related high genomic complexity are more important. Compared to these DH lymphomas, BCL6(+)/MYC(+) DH lymphomas are far less common, and in fact most of these cases represent BCL2(+)/BCL6(+)/MYC(+) triple-hit lymphomas with involvement of BCL2 as well. CCND1(+)/MYC(+) DH lymphomas with involvement of 11q13 may also be relatively frequent, the great majority being classified as aggressive variants of mantle cell lymphoma. This suggests that activation of MYC might be an important progression pathway in mantle cell lymphoma as well. Based on clinical significance and the fact that no other solid diagnostic tools are available to identify DH lymphomas, it seems advisable to test all diffuse large B-cell and related lymphomas for MYC and other breakpoints.

Genomic profiles in B cell lymphoma

Chromosome translocations found in B cell lymphomas generate typical genome profiles that are characteristic of each disease entity. The mechanisms of lymphomagenesis have been investigated with respect to the involvement of deregulated genes in tumor development, as characterized by the promotion of cell proliferation and the blockage of cell differentiation and anti-apoptosis. It is now well known that chromosome translocation alone does not induce tumor formation. New technology such as array CGH and expression profiling introduced as a result of the human genome project introduced a new paradigm from which to understand the molecular mechanisms of lymphoma development. Analyses with this new technology revealed that genome profiles of disease entities are characteristic and differ from disease to disease, although the genome profile of each patient with the same disease entity varies significantly given the recurrent genetic alterations frequently found. These apparent paradoxical findings are likely to be the cause of heterogeneity of the clinicopathological features associated with the same disease entity. Based on these findings, the future prospect and direction of lymphoma research will be discussed.

EBNA1 regulates cellular gene expression by binding cellular promoters

Epstein-Barr virus (EBV) is associated with several types of lymphomas and epithelial tumors including Burkitt's lymphoma (BL), HIV-associated lymphoma, posttransplant lymphoproliferative disorder, and nasopharyngeal carcinoma. EBV nuclear antigen 1 (EBNA1) is expressed in all EBV associated tumors and is required for latency and transformation. EBNA1 initiates latent viral replication in B cells, maintains the viral genome copy number, and regulates transcription of other EBV-encoded latent genes. These activities are mediated through the ability of EBNA1 to bind viral-DNA. To further elucidate the role of EBNA1 in the host cell, we have examined the effect of EBNA1 on cellular gene expression by microarray analysis using the B cell BJAB and the epithelial 293 cell lines transfected with EBNA1. Analysis of the data revealed distinct profiles of cellular gene changes in BJAB and 293 cell lines. Subsequently, chromatin immune-precipitation revealed a direct binding of EBNA1 to cellular promoters. We have correlated EBNA1 bound promoters with changes in gene expression. Sequence analysis of the 100 promoters most enriched revealed a DNA motif that differs from the EBNA1 binding site in the EBV genome.

Diversity of genome profiles in malignant lymphoma

Characteristic chromosome translocations are associated with specific disease entities, and are known to play a pivotal role in lymphoma development. Chromosome translocation alone, however, is not sufficient to produce tumors. Factors including the microenvironment and epigenetic and genetic alterations other than chromosome translocations have been shown to play a role in lymphoma development. Follicular lymphoma cells proliferate in close contact with follicular dendritic cells. Mucosa-associated lymphoid tissue (MALT) lymphoma cells proliferate at the marginal zone area of reactive follicles which are formed by preceding chronic inflammation. The importance of genetic alterations other than chromosome translocation has been recognized since the introduction of array comparative genomic hybridization (array CGH). Variations in the genomic profile among patients with the same disease entity have been found by array CGH analyses. These variations indicate that multiple genetic pathways leading to the development of lymphomas may exist and hence result in the variable clinicopathological features observed.

Bcl-2 and c-Myc co-operate in the Epstein – Barr virus-immortalized human B-cell line GM607 but do not confer tumorigenicity

Eighty-five percent of follicular lymphomas possess a characteristic t(14;18) translocation that results in the deregulated expression of the proto-oncogene BCL-2. BCL-2 overexpression alone is insufficient for full cellular transformation and at least 1 other genetic event is believed to be necessary for follicular lymphoma development. Deregulated c-Myc expression has previously been shown to cooperate with Bcl-2 to transform murine fibroblast cell lines and lead to tumor development in mice. We have developed a human model system to study early transformation in lymphoid cells using immortalized lymphoblastoid cells. We sequentially introduced BCL-2 and c-MYC, 2 proto-oncogenes known to be involved in the transformation of B cells into Epstein-Barr virus (EBV)-immortalized human B cells. We show that the c-Myc and Bcl-2 overexpression, together with EBV immortalization were insufficient to cause full cellular transformation as measured by cell proliferation rates, soft agar and tumorigenicity assays. These results show that more than 3 genetic hits (EBV infection, Bcl-2 and c-Myc overexpression) were required for the full cellular transformation of human lymphoblastoid cells. However, subtle changes in cellular proliferation and sensitivity to apoptosis were documented, at non-limiting dilutions. These changes may confer a susceptibility to the modified cells such that they are more susceptible to the acquisition of additional genetic changes and evolve towards a fully transformed state. In addition, the model system developed may be suitable for the identification of further known and novel oncogenic events involved in the full transformation of B cells.

The Epstein-Barr virus Bcl-2 homolog, BHRF1, blocks apoptosis by binding to a limited amount of Bim

Current knowledge suggests that the balance between life and death within a cell can be controlled by the stable engagement of Bcl-2-related proapoptotic proteins such as Bak, Bax, and Bim by survival proteins such as Bcl-2. BHRF1 is a prosurvival molecule from Epstein-Barr virus that has a high degree of homology to Bcl-2. To understand how BHRF1 blocks apoptosis, BHRF1 and mutants of BHRF1 were expressed in primary cells and an IL-2-dependent T cell line. BHRF1 bound the Executioner Bak and, when cells were cultured without cytokines, BHRF1 associated with Bim. A point mutation that lost the ability to bind Bak retained its ability to bind Bim and to protect cells. This result demonstrated that it was the capacity of BHRF1 to bind Bim, not Bak, that provided protection. Interestingly, the amount of Bim bound by BHRF1 was minimal when compared with the amount of Bim induced by apoptosis. Thus, BHRF1 does not act by simply absorbing the excess Bim produced while cells prepare for death. Rather, BHRF1 may act either by binding preferentially the most lethal form of Bim or by acting catalytically on Bim to block apoptosis.

Caspase activation cascades in apoptosis

Apoptosis, a highly controlled mode of cell death, is utilized to eliminate superfluous, aged, injured or infected cells from the body. Caspases, a family of aspartic acid-specific proteases, are the major effectors of apoptosis. To curtail their activity, caspases are normally synthesized as inactive precursors, but become activated at the onset of apoptosis by activation signals. Once active, caspases preside over the ordered dismantling of the cell through restricted proteolysis of hundreds of substrate proteins. Over the last 10 years, intense research has focused upon the pathways that control caspase activation. Although some, such as the apoptosome and death receptor-mediated pathways to caspase activation, are well established, others are less clearly defined. In this review, we discuss current perspectives concerning the diverse pathways to caspase activation.

Runx2-mediated activation of the Bax gene increases osteosarcoma cell sensitivity to apoptosis

The Runx family of transcription factors regulate cell growth and differentiation, and control the expression of target genes involved in cell fate decisions. We examined the role of the bone-related member of this family, Runx2, in regulating apoptosis via modulation of the Bcl2 family of genes in the osteosarcoma cell line Saos2. Our data demonstrate that Runx2 directly binds to two Runx-specific regulatory elements on the human bax promoter thereby inducing Bax expression. Furthermore, bone morphogenetic protein-induced or vector-mediated expression of Runx2 resulted in upregulation of Bax expression, and subsequent increased sensitivity of Saos2 cells to apoptosis. Finally, the observed upregulation of Bax expression and increased apoptosis were Runx2 dependent as Runx2 loss of function abrogated these effects. Our study provides the first evidence for Bax as a direct target of Runx2, suggesting that Runx2 may act as a proapoptotic factor in osteosarcoma cells.

Mitochondria potential, bax "activation," and programmed cell death

Since the discovery of the key role of cytochrome C in the activation of caspase 9, intense interest has focused on the role of mitochondria in apoptosis/programmed cell death. Mitochondria undergo two major alterations during apoptosis. The first is the permeabilization of the outer mitochondrial membrane. This event is tightly regulated by members of the Bcl-2 family and involves the conformational change of pro-apoptotic family members such as Bax. Second, the electrochemical gradient that is normally present across the inner mitochondrial membrane is lost (membrane depolarization). This event is sometimes mediated by the permeability transition pore (PTP). The order in which these events occur and whether one causes the other has been hotly debated in the literature. Nonetheless, the majority of reports suggest that mitochondria outer membrane permeabilization (MOMP) precedes membrane depolarization. In this chapter, methods that examine membrane depolarization and the conformational change in Bax are described.

Molecular mediators of cell death in multistep carcinogenesis: a path to targeted therapy

A consistent, if not invariant, feature of cancer cells is the acquired ability to evade apoptosis. The pioneering work of Dr. Stan Korsmeyer was invaluable in characterizing the molecular foundations of cell death signaling mechanisms during normal development and during multistep carcinogenesis. This foundation now forms the basis for the rational design of therapeutic strategies to selectively activate cell death in cancer cell populations. These strategies are currently being evaluated in an increasing number of clinical trials targeting diverse tumor types.

BCL-2 in the crosshairs: tipping the balance of life and death

The discovery of B-cell lymphoma-2 (BCL-2) over 20 years ago revealed a new paradigm in cancer biology: the development and persistence of cancer can be driven by molecular roadblocks along the natural pathway to cell death. The subsequent identification of an expansive family of BCL-2 proteins provoked an intensive investigation of the interplay among these critical regulators of cell death. What emerged was a compelling tale of guardians and executioners, each participating in a molecular choreography that dictates cell fate. Ten years into the BCL-2 era, structural details defined how certain BCL-2 family proteins interact, and molecular targeting of the BCL-2 family has since become a pharmacological quest. Although many facets of BCL-2 family death signaling remain a mechanistic mystery, small molecules and peptides that effectively target BCL-2 are eliminating the roadblock to cell death, raising hopes for a medical breakthrough in cancer and other diseases of deregulated apoptosis.

Antianoikis Effect of Nuclear Factor-κB through Up-regulated Expression of Osteoprotegerin, BCL-2, and IAP-1

Epithelial cells undergo a form of apoptosis termed anoikis when they lose extracellular attachments. We evaluated the role of transcription factor NF-kappaB in the regulation of anoikis susceptibility of intestinal epithelial cells. Culture of rat intestinal epithelial cells in suspension induced NF-kappaB activation, which blocked the anoikis of those cells, as assessed by internucleosomal DNA fragmentation and caspase-3 cleavage. Activation of NF-kappaB after the loss of extracellular attachments required focal adhesion kinase tyrosine 397 phosphorylation. This triggered a signaling cascade through phosphatidylinositol 3-kinase and AKT, to induce DNA binding of the RelA/p65 NF-kappaB polypeptide. NF-kappaB activated in this manner induced the up-regulated expression of a distinct program of genes that included osteoprotegerin, BCL-2, and IAP-1 (inhibitor of apoptosis protein-1). Chromatin immunoprecipitation experiments revealed that NF-kappaB directly regulated the promoters of these 3 genes. Knock-down of the expression of osteoprotegerin, BCL-2, or inhibitor of apoptosis protein-1 by RNA interference showed that these factors inhibit anoikis, and genetic reconstitution of their expression alone or in combination restored normal levels of anoikis to NF-kappaB-inactive intestinal epithelial cells. Together, these findings have identified the molecular components of a previously unrecognized antianoikis pathway in intestinal epithelial cells.

Neuroblastoma, Apoptosis, and Growth Factors

Neuroblastoma is the most common extracranial tumor of childhood. This tumor is associated with alterations in apoptosis and is affected by various growth factors and cytokines. In this short review we will discuss recent findings in our laboratory where we have been studying a cell culture model of neuroblastoma.

Levels of the bcl-2 protein, fibronectin and alpha(5)beta(1) fibronectin receptor in HIV-1-infected patients with Kaposi's sarcoma

Kaposi's sarcoma (KS) is an angioproliferative disease characterized by proliferation of neoplastic cells (spindle cells) mixed with endothelial and inflammatory cells. In this study we evaluated the role of the adhesive glycoprotein, fibronectin (FN) and its receptor alpha(5)beta(1) (FNR), and the proto-oncogene bcl-2, an anti-apoptotic protein. Significantly decreased serum levels of FN were noted in HIV-1-infected patients with KS, whereas serum levels of FNR were significantly increased in the same patients. Furthermore, increased FNR expression was observed on CD4 cells from KS patients. Serum levels of bcl-2 protein were significantly decreased in asymptomatic seropositive patients, whereas HIV-1-infected patients with KS showed increased serum levels of bcl-2. These results provide further information about interaction between integrins and the extracellular matrix and bcl-2 protein that can support cell survival either of neoplastic cells or endothelial and inflammatory cells.

Prognostic factors for hematologic cancers

This article reviews the molecular biology of hematologic cancers and the current understanding of prognostic factors for these cancers. Specific molecular biomarkers that have potential as prognostic factors for various hematologic cancers are discussed. Quantitative and statistical methods of evaluating the usefulness of prognostic factors are presented.

Follicular lymphomas--a review of treatment modalities

Follicular lymphoma is the most common low-grade non Hodgkin's lymphoma and represent an homogeneous entity as defined by pathological, molecular and clinical data. This indolent disease is characterised by a slow growth pattern with possible spontaneous regression, is often disseminated but remains incurable with available treatments when disseminated. For localised stages, involved field radiotherapy remains the standard choice but other approaches remain to be investigated. In advanced disease, chemotherapy has been demonstrated to produce high response rates but recent trials with new treatment strategies including interferon and monoclonal antibodies may improve the current situation. In this article, we will review treatment of follicular lymphomas, specially emphasising published phase III trials.

Neuroblastoma and hepatocyte coculture conditioned media alter apoptosis

BACKGROUND

Neuroblastoma is a childhood tumor that often displays unusual biological behavior. The tumor may present with widespread metastases that are unresponsive to aggressive treatment. At other times, both the metastases and the primary tumor may spontaneously regress without treatment. Apoptosis, or programmed cell death, is thought to play a role in the dichotomous behavior of neuroblastoma. We hypothesize that neuroblastoma cells will interact with host tissues to release mediators that affect apoptosis.

MATERIALS AND METHODS

Human neuroblastoma cells and human Chang hepatocytes are grown in a noncontact, coculture system. After incubation for 4 days, the medium from the coculture system is collected. Neuroblastoma cells and Chang hepatocytes are then plated separately with the conditioned medium and their own standard growth medium as controls. After 4 days, these cells are harvested and cytospins made for immunostaining. Tumor necrosis factor alpha (TNF-alpha), Fas ligand, and Bcl-2, are measured with immunohistochemistry. Apoptosis is detected with the TUNEL method. Immunostaining data are interpreted with computer image analysis and reported as stain index. TUNEL data are reported as percentage apoptotic cells. All data are reported as means +/- SEM. Statistical analysis is performed and P < 0.05 considered significant.

RESULTS

Chang hepatocytes grown in the coculture conditioned media have an increase in TNF-alpha and Fas ligand. The neuroblastoma cells have a significant decrease in Fas ligand. There is a significant increase in the number of apoptotic hepatocytes when they are cultured in the conditioned media. In contrast, the neuroblastoma cells grown in the coculture conditioned media show no increase in apoptosis. Finally, Bcl-2 is significantly increased in the neuroblastoma cells cultured in the conditioned media.

CONCLUSIONS

Neuroblastoma cells grown in coculture conditioned media show increased expression of Bcl-2 and decreased Fas ligand levels. These changes should diminish apoptosis activity in the tumor cells. In contrast, the conditioned media induce elevated levels of proapoptotic mediators in the Chang hepatocytes. A tumor's ability to successfully metastasize may be dependent on mediators generated in the tumor-host interaction, and may not be just an independent characteristic of the tumor itself.

Predicting Metastatic Risk of Gastrointestinal Stromal Tumors: Role of Cell Proliferation and Cell Cycle Regulatory Proteins

Gastrointestinal stromal tumors (GIST) are a heterogeneous group of neoplasms whose biologic behavior is difficult to predict. The aim of this study is to evaluate the prognostic value in GIST of some oncoproteins involved in regulation of cell proliferation. Tumor size, mitosis, necrosis, and p53, c-myc, and bcl-2 protein expression of 32 GIST were studied. Proliferative index was assessed with Ki67. The 32 cases were grouped into the following clinical categories: (1) clinically benign (BN) were defined as disease-free survival greater than 3 years (n=10); (2) clinically malignant (MN) in which local recurrence or metastasis occurred regardless of the follow-up time (n=15); and (3) clinically indeterminate (ID) owing to follow-up <3 years without metastasis or local recurrence (n=seven). Discriminant analysis was used to allocate any tumor to one of the two prognostic groups (BN or MN). In univariate analysis all six factors studied above proved to be of significant prognostic value. Using a multivariate stepwise discriminant analysis to take into account the interrelationship between factors, we found that c-myc expression was the most important prognostic factor, followed, in order of statistical weight, by size and Ki67. These were combined to define a discriminant score ([10.75 x c-myc]+[0.39 x size]+[0.078 x Ki67]-15.54=score), which was capable of correctly identifying tumors in our series whose known clinical behavior was BN or MN in 92% of the cases. The classification score was applied subsequently to the seven clinically ID cases: Three (42.9%) were predicted as BN, and four (57.1%) were predicted as MN. Both expression of oncoprotein c-myc and the proliferative index provide prognostic information in GIST, in addition to morphologically established prognostic factors such as size. These factors in a discriminant analysis proved to be useful for the clinical classification of GIST into BN or MN and to predict the clinical outcome of clinically ID tumors. Int J Surg Pathol 8(2):133-144, 2000

Expression of Bcl-2 and Bax in oligodendrogliomas and their relationship to apoptosis

Apoptotic bodies are frequently found in oligodendrogliomas, particularly in the anaplastic subtype. A range of proteins, such as those of the Bcl family, are implicated in the control of apoptosis. The ratio of antagonists of apoptosis, such as Bcl-2, to agonists, such as Bax, is thought to determine the outcome for a particular cell. This study aimed to determine the expression of Bcl-2 and Bax proteins in a series of oligodendrogliomas and to relate the expression of these to measures of apoptosis. Immunohistochemistry was used to detect the expression of Bcl-2 and Bax in an archival series of 32 oligodendrogliomas. The results were scored semiquantitatively for the extent and intensity of tumour staining. Apoptosis indices were determined by counting apoptotic bodies on haematoxylin and eosin staining and the percentage of cells showing a positive reaction with the TdT-mediated dUTP-biotin nick end-labelling technique (TUNEL). Granular cytoplasmic staining for Bcl-2 was seen in tumour cells in 81% of cases. Cases with a strong intensity (but not extent) of staining showed a lower TUNEL index (P=0.038). Bcl-2 expression was identified in the walls of intratumoural blood vessels in 55% of cases and in peri-tumoural neurones (where present) in 87%. Bax expression was detected in tumour cells in 69% of cases but no relationship to TI was detected. Bax positivity was seen in blood vessels in 44% of cases and peri-tumoural neurones in 60%. Bcl-2 and Bax were concluded to be expressed in a high proportion of oligodendrogliomas, suggesting that they may exert a regulatory role in cell death in these tumours.

Apoptosis in neuroendocrine tumours

Acquired resistance to apoptosis in neuroendocrine tumours (NETs) may promote clonal expansion and enhance the likelihood that subsequent mutations lead to growth or persistence of the neoplastic clone. Recent studies have demonstrated that deregulation of programmed cell death may be a critical component in multistep tumourigenesis of NETs and that the frequent expression of the Bcl-2 oncoprotein in these tumours may contribute to their pathogenesis. The genetic complementation of simultaneously deregulated Bcl-2 and c-Myc may be implicated in the multistep tumourigenesis of human NETs. Furthermore, because the efficacy of cytotoxic chemotherapy relies on its ability to induce programmed cell death, resistance to apoptosis typically correlates with chemoresistance, a phenomenon that is typical in NETs. Consideration of how oncogenes affect rates of cell death, in addition to augmenting growth, has already provided valuable insights into the biology of cancer. Understanding the molecular and cellular features of this process may enable the development and application of more effective and potentially curative treatment strategies in which the induction of programmed cell death is an integral component.

Fas-mediated induction of hepatocyte apoptosis in a neuroblastoma and hepatocyte coculture model

BACKGROUND

We have previously demonstrated an increase in hepatocyte apoptosis when they are cocultured with neuroblastoma cells. Death receptors in the tumor necrosis factor (TNF) family such as TNFR1 and Fas have been identified as regulators of apoptosis and may be responsible for the altered regulation of apoptosis seen in our coculture model. To evaluate the effects of released factors and remove the potential alterations induced by direct contact, a noncontact coculture system was used to study the interaction between hepatocytes and neuroblastoma cells.

METHODS

Human Chang hepatocytes (HC) were plated onto Falcon cell culture inserts with 0.45-micrometer pores in the permeable membrane. Human neuroblastoma cells (NB-IMR-32) were seeded into wells of the Falcon companion plate. After 24 h, inserts containing HC were placed into wells containing NB cells and incubated for 4 days. This provided a coculture environment without actual cellular contact. Immunohistochemical staining for TNFalpha, Fas, and Fas ligand (Fas-L) was performed. Apoptosis was detected via the TUNEL method. Images were analyzed with ImagePro-Plus. Statistical analyses were done with significance determined at P < 0.05.

RESULTS

Chang hepatocytes demonstrated a significant increase in the levels of TNF, Fas, and Fas-L when cocultured with neuroblastoma cells (P < 0.005). In addition, the cocultured hepatocytes had a 20-fold increase in the apoptotic rate (P < 0.001). Neuroblastoma cells had no demonstrable level of Fas or TNF when grown alone and in cocultures. Neuroblastoma cells that were grown alone had an elevated level of Fas-L, but this level diminished by 44% when cocultured with hepatocytes (P < 0.001).

CONCLUSION

An upregulated TNF/Fas receptor-ligand system may be responsible for increased apoptosis in hepatocytes when cocultured with neuroblastoma. This upregulation may be due to release of neuroblastoma-derived Fas ligand into the media. Tumors may alter the regulation of apoptosis in surrounding tissues via the death receptors.

Flow cytometric analysis of BHRF1 expression prohibiting apoptosis induced by radiation

The Epstein-Barr virus gene BHRFI has homology with proto-oncogene bcl-2, which can protect cells from apoptosis. In order to investigate the effect of BHRF1 expression on the anti-apoptotic ability of nasopharyngeal carcinoma (NPC) cells after irradiation, a high-BHRF1 expression vector was constructed and transfected into the NPC cell line CNE2. Then, the alteration of proliferation and apoptosis in the cells was tested by flow cytometry after cobalt 60 irradiation. The results showed that BHRF1 expression could increase G1 delay and decrease the cell percentage in S phase before irradiation, and reduce the apoptotic rate of CNE2 cells and increase the cell percentage in S phase after irradiation. The results suggest that BHRF1 expression is able to alter the cell cycle and protect CNE2 cells from apoptosis induced by radiation.

Expression of Bcl-2 in inflammatory sites from patients with active Behçet's disease

Behçet's disease (BD) is a current systemic vasculitis of unknown aetiology. Eyes, skin, joints, the oral cavity, genital system, blood vessels, central nervous system and lung are usually involved. Defective regulation of programmed cell death (apoptosis) may play a role in the development of (BD), and the proto-oncogene Bcl-2 is involved in the control of apoptosis in immunocompetent cells. We therefore wished to investigate the expression of Bcl-2 in the peripheral lymphocytes and in two inflammatory sites of patients with active BD: bronchoalveolar lavage (BAL) and cerebrospinal fluid (CSF) lymphocytes. Levels of Bcl-2 expression in the lymphocytes of patients with BD and, for comparison, in the lymphocytes of healthy controls and non-inflammatory neurological diseases (NIND), were studied by two-colour cytofluorography and RNA analysis. In BD patients, a significant proportion of T cells expressed increased amounts of Bcl-2 protein, both in peripheral blood and in inflammatory sites. Mononuclear cells of patients with BD showed increased amount of Bcl-2 messenger RNA. The in vitro incubation of T lymphocytes with IL-10, significantly increased the Bcl-2 expression, specifically in T lymphocytes from inflammatory sites. In active BD, stimulation of HSV-1 T lymphocytes slightly increased Bcl-2 expression, not significantly different from unstimulated HSV-1 T cells. The occurrence of circulating T lymphocytes with abnormally high Bcl-2 expression in peripheral circulation and in inflammatory sites may be explained in part by the increased in vivo activation levels, and by aetiopathological agent(s): our findings seem to indicate an important role in the chronic inflammation in BD.

Induction of apoptosis in a neuroblastoma and hepatocyte coculture model

BACKGROUND

The dysregulation of apoptosis may alter the progression of tumor growth and explain the clinical dichotomy observed in children with neuroblastoma (NB). An overexpression of the bcl-2 proto-oncogene induces resistance to apoptosis and has been observed in unfavorable NB. We hypothesized that alterations in apoptosis may be a result of the interactions between NB and the tissues surrounding it.

MATERIALS AND METHODS

Human Chang liver cells (HCL, 10(4) cells/cm2) were plated in two-chamber slides for 3 days. Human NB cells (10(5) cells/cm2) were added to one of the chambers and incubated for 3 more days. Control NB were plated under identical conditions in its own medium and in the HCL medium with growth curves measured. DNA fragmentation was detected via the TUNEL method (TdT-mediated nick end-labeling) and bcl-2 expression was determined by immunostaining.

RESULTS

NB growth was unaltered by the change in medium. NB stained mildly positive for bcl-2 when plated alone but became markedly positive in coculture. Histologically, HCL and NB appeared healthy when plated alone, but a halo of apoptotic HCL was seen around NB in the coculture. When plated alone, both NB and HCL demonstrated minimal apoptotic activity as detected via the TUNEL method. In the coculture, a halo of HCL surrounding the NB exhibited markedly increased DNA fragmentation and this intensity diminished in cells distant from the NB.

CONCLUSIONS

The regulation of apoptosis was altered in this coculture model of NB and HCL. HCL stimulated NB to overexpress bcl-2 and presumably become resistant to apoptosis. Conversely, NB induced the surrounding HCL to undergo apoptosis. The interaction between the local tissue and NB induced alterations in apoptosis in both cell types and resulted in a survival advantage for NB.

Epstein-Barr virus BHRF1 prohibits the cells of nasopharyngeal carcinoma from apoptosis

Epstein-Barr virus (EBV) is associated with nasopharyngeal carcinoma (NPC). The BHRF1 EBV protein is expressed at high levels in productively infected cells and certain latently infected cells. In order to investigate the effect of expression of BHRF1 on the biological behaviour of NPC cells, we constructed the BHRF1 high expression vector and transfected it into the NPC cell line, CNE2. Then, the alteration of proliferation and apoptotic rates in the cells were tested before and after camptothecin treatment. After treatment by camptothecin, BHRF1-CNE2 cells could constantly and slowly proliferate and its apoptotic rate was less than in control groups, and the number of cells in the G phase decreased and in the S phase increased. So, it suggests that BHRF1 expression can enhance the resistibility of CNE2 cells to DNA-damaging agents that cause apoptosis.

The structure of the human ALL-1/MLL/HRX gene

The human ALL-1/MLL/HRX gene on chromosome 11q23 is the site of many locally clustered chromosomal alterations associated with several types of acute leukemias, including deletions. partial duplications and reciprocal translocations. Structurally variant proteins derived from an altered ALL-1 gene presumably make essential contributions to the malignant transformation of hematopoietic progenitor cells. The ALL-1 gene is spread over approximately 92 kb and consists of at least 37 exons. An exon/intron map including the position of the 3'-end of the gene and a detailed restriction map were produced and an updated map is presented. Data from other laboratories were incorporated where compatible. Exon/intron boundaries were sequenced and an intron-phase analysis was performed. The results are expected to contribute to a better understanding of those structural alterations of the gene that conserve the open reading frame and produce presumably oncogenic variants of the ALL-1 protein. They will also facilitate the rapid molecular diagnosis of structural alterations of this gene and the choice of therapeutic options. Mechanisms that may potentially account for the striking clustering of the translocation breakpoints in the breakpoint cluster region of the gene are discussed.

bcl-2 enhancement of malignant transformation in mouse epidermal JB6 cells

Increased bcl-2 expression is a common feature of many types of human malignancies, which implies that bcl-2 plays an important role in tumorigenesis. To better understand the molecular mechanisms of bcl-2-induced oncogenesis, we examined the effects of bcl-2 expression on transformation of mouse epidermal JB6 cells induced by the tumor promoter 12-O-tetradecanoylphorbol-13 acetate (TPA). Promotion-sensitive JB6 clone41 cells were transfected with the bcl-2-containing expression vector pD5-neo/bcl-2, and the soft agar growth of bcl-2-transfected cells and control cells were compared. bcl-2 overexpression in JB6 clone41 cells caused a TPA-induced soft-agar growth fivefold greater than the growth of nontransfected or vector-transfected (neo control) cells. bcl-2 expression in the absence of TPA did not lead to colony formation in soft agar. Because the level of the transcription factor activator protein 1 (AP-1) has been shown to be critical for the responsiveness of JB6 cells to TPA-induced transformation, we compared c-jun and c-fos expression as well as the AP-1-binding activity and the AP-1-mediated transactivation of the reporter construct TRE-CAT between bcl-2-expressing cells and control cells. When compared with control cells, bcl-2-transfected cells expressed significantly more c-fos but not c-jun after TPA treatment. Furthermore, the levels of AP-1 and AP-1-induced transactivation of TRE-CAT were greater in bcl-2-transfected cells than in control cells after TPA treatment. These results showed that bcl-2 cooperates with a tumor promoter such as TPA in the induction of malignant transformation in mouse epidermal cells and that bcl-2 enhances soft-agar growth by stimulating signaling pathways that led to increased AP-1 expression.

Induction of apoptosis in small-cell lung cancer cells by an antisense oligodeoxynucleotide targeting the Bcl-2 coding sequence

BACKGROUND

The emergence of resistance to chemotherapy remains a major problem in the treatment of patients with small-cell lung cancer. Elevated expression of Bcl-2, a protein that inhibits programmed cell death or apoptosis, has been associated with radiation and drug resistance and has been observed in the majority of small-cell lung cancer specimens and cell lines.

PURPOSE

To test the hypothesis that Bcl-2 expression levels are critical for inhibiting apoptosis in small-cell lung cancer cells, we used an antisense strategy to reduce Bcl-2 expression in these cells in an attempt to restore the natural occurrence of apoptosis.

METHODS

Thirteen antisense oligodeoxynucleotides (ODNs) targeting various regions of the bcl-2 messenger RNA and a control scrambled-sequence ODN were tested to identify the most effective sequence(s) for reducing Bcl-2 protein levels. Northern and western blot analyses were used to examine basal bcl-2 messenger RNA and protein levels, respectively, in four human small-cell lung cancer cell lines (SW2, NCI-H69, NCI-H82, and NCI-N417). SW2 cells were treated with the antisense ODNs in the presence of cationic lipids (to facilitate uptake), and cytotoxic effects were measured by use of a cell viability assay. Flow cytometric analysis of DNA fragmentation and cell morphology was also performed. The cytotoxic effect of the most potent antisense ODN was also tested on the three other cell lines.

RESULTS

The viability of SW2 cells was effectively reduced by ODNs that targeted the translation initiation and termination sites of the bcl-2 messenger RNA, but ODN 2009 that targeted the coding region was the most cytotoxic. Treatment of SW2 cells with 0.15 microM ODN 2009 for 96 hours reduced their viability by 91% (95% confidence interval [CI] = 88%-94%) and caused a dose-dependent reduction in Bcl-2 levels that became detectable 24 hours after treatment and persisted up to 96 hours; analysis of cellular morphology demonstrated that viability was reduced through apoptosis. Moreover, ODN 2009 at 0.15 microM was cytotoxic to NCI-H69, NCI-H82, and NCI-N417 cells, resulting in decreases in cell viability of 82% (95% CI = 78%-86%), 100%, and 100%, respectively, after 96 hours of treatment. The cytotoxic effects were inversely correlated with the basal Bcl-2 levels in the cell lines (r = -9964). A control scrambled-sequence oligodeoxynucleotide had no statistically significant effect on the cell lines (P values ranging from .38 to .89).

CONCLUSION

We have identified a novel antisense ODN sequence (ODN 2009) that effectively reduces the viability of small-cell lung cancer cells by reducing Bcl-2 levels and facilitating apoptosis.

Kaposi's sarcoma-associated herpesvirus encodes a functional bcl-2 homologue

Kaposi's sarcoma-associated herpesvirus (KSHV) is a newly discovered herpesvirus etiologically associated with Kaposi's sarcoma (KS) and two lymphoproliferative disorders. We describe a KSHV vbcl-2 gene with homology to the proto-oncogene bcl-2. It is expressed in KS lesions and in cell lines derived from primary effusion lymphomas. Using yeast and human cells we demonstrate the ability of KSHV vBcl-2 protein to suppress Bax toxicity. We show that KSHV vBcl-2 heterodimerizes with human Bcl-2 in a yeast two-hybrid system. These results suggest that KSHV vBcl-2 plays an anti-apoptotic role in virus infected cells.

Impaired recovery and cytolytic function of CD56+ T and non-T cells in systemic lupus erythematosus following in vitro polyclonal T cell stimulation. Studies in unselected patients and monozygotic disease-discordant twins

OBJECTIVE

To determine whether there is impaired generation and cytolytic function of CD56+ T cells and non-T cells in human systemic lupus erythematosus (SLE).

METHODS

Peripheral blood mononuclear cells (PBMC) were obtained from 73 patients with SLE, 39 normal controls, and 9 pairs of monozygotic (MZ) twins discordant for SLE. PBMC were stimulated with anti-CD3 monoclonal antibody, maintained in interleukin-2, and assayed for percentages of total CD56+ cells and CD56+ T cells by flow cytometry, and for cytolytic activity against 51Cr-labeled Daudi target cells.

RESULTS

Despite normal total cell expansion, the percentages of recovered CD56+ T cells and total CD56+ cells were 1.6-fold and 1.8-fold lower, respectively, in patients with SLE compared with normal controls (P = 0.011 and P < 0.001, respectively). Cytolytic activities of isolated total CD56+ cells and CD56+ T cells and were also reduced in patients with SLE compared with normal controls (P = 0.033). These defects associated with SLE were independent of disease activity and immunosuppressive medications, and they reflected impaired maturation of cytolytic effector cells rather than a deficiency in precursor cell number. In MZ twins discordant for SLE, recovered percentages of CD56+ cells and cytolytic responses were very low in 4 of 8 and 6 of 9 co-twins with SLE, respectively. Cellmixing experiments with the PBMC of the MZ twins demonstrated that the E+ cell fractions (containing all T cells and CD56+ non-T cells) from the co-twins with SLE had decreased ability to generate cytolytic activity compared with the corresponding E+ cell fractions from the healthy co-twins. However, recovered percentages of CD56+ cells and non-T cells and cytolytic responses were also depressed in 4 of 8 and 4 of 9 healthy co-twins, respectively.

CONCLUSION

Impaired CD56+ T cell and non-T cell responses are a feature of SLE and may antedate the onset of clinical disease.

Quantitation of resistance to cytosine arabinoside by myeloid leukemic cells expressing bcl-2

The presence of bcl-2 in myeloid leukemias has been associated with a decrease in therapy-induced apoptosis, reduced patient survival and in vitro autonomous growth of leukemic cells. The present study focuses on the quantitation of resistance to increasing doses of 1-beta-d-arabinofuranosylcytosine (Ara-C) by using hematological tumors expressing different levels of bcl-2. Scanning densitometry of Western blots demonstrated that the myeloid U-937 cells express low levels of bcl-2 (RD = 0.008), whereas the follicular lymphoma RL-7 expressed very high levels (RD = 3.084). Colony formation was also examined following incubation with Ara-C and RL-7 cells demonstrated a higher clonogenic survival (LD50 = 0.5 microns) when compared with U-937 cells (LD50 = 0.005 microM). Similarly, the level of bcl-2 expression in each cell line was also related to apoptosis with U-937 cells demonstrating increased DNA fragmentation when compared with RL-7 cells. To further evaluate the effect of upregulated bcl-2 on Ara-C treatment, U-937 cells were transfected with a retroviral vector carrying the murine bcl-2 or vector alone. Upregulation of bcl-2 by myeloid leukemic cells increased the resistance by 3 logs to Ara-C when comparing LD50 values from clonogenic assays, and decreased apoptosis by at least 3 logs when measuring dUTP positive cells by flow cytometry.

Oncogene expression in carotid body tumors

BACKGROUND

The genetic etiology of carotid body tumors is suggested by the familial occurrence of the neoplasm. Environmental influences are also implied by the fact that the tumor is more common in those living at high altitudes. However, the development of sporadic tumors occurring at sea level, which account for the majority of cases, remains unknown.

METHODS

The clinical and pathologic features of 13 carotid body tumors excised in 13 patients were reviewed. Two patients had bilateral tumors, one with a strong family history, and two patients had recurrent carotid body tumors. All tumors were benign except for one that had local lymph gland metastases. All patients were followed up for a period ranging from 1 to 17 years. Each tumor was examined for the oncoproteins c-myc, bcl-2 c-erbB-2, c-erbB-3 and c-jun and for the proliferating cell nuclear antigen (PCNA) by immunohistochemistry.

RESULTS

c-myc immunoreactivity was observed in all tumors and, in 12 of 13 cases, was present in more than 10% of tumor cells, bcl-2 immunoreactivity was found in 11 cases with 6 tumors exhibiting more than 10% immunopositive cells, c-jun expression was found in 5 cases with 3 tumors containing more than 10% immunopositive cells. Only two tumors were positive for c-erb-B2 immunoreactivity with a cytoplasmic staining pattern. One tumor was positive for c-erb-B3.

CONCLUSIONS

The oncogenes c-myc, bcl-2 and c-jun, are abnormally expressed in some carotid body tumors. Their expression may contribute to the genesis of carotid body tumors.