Immunohistochemical detection of BCL-3 in lymphoid neoplasms: a survey of 353 cases

Multifaceted roles for BCL3 in cancer: a proto-oncogene comes of age

In the early 1990's a group of unrelated genes were identified from the sites of recurring translocations in B-cell lymphomas. Despite sharing the nomenclature 'Bcl', and an association with blood-borne cancer, these genes have unrelated functions. Of these genes, BCL2 is best known as a key cancer target involved in the regulation of caspases and other cell viability mechanisms. BCL3 on the other hand was originally identified as a non-canonical regulator of NF-kB transcription factor pathways - a signaling mechanism associated with important cell outcomes including many of the hallmarks of cancer. Most of the early investigations into BCL3 function have since focused on its role in NF-kB mediated cell proliferation, inflammation/immunity and cancer. However, recent evidence is coming to light that this protein directly interacts with and modulates a number of other signaling pathways including DNA damage repair, WNT/β-catenin, AKT, TGFβ/SMAD3 and STAT3 - all of which have key roles in cancer development, metastatic progression and treatment of solid tumours. Here we review the direct evidence demonstrating BCL3's central role in a transcriptional network of signaling pathways that modulate cancer biology and treatment response in a range of solid tumour types and propose common mechanisms of action of BCL3 which may be exploited in the future to target its oncogenic effects for patient benefit.

Noncanonical NF-κB in Cancer

The NF-κB pathway is a critical regulator of immune responses and is often dysregulated in cancer. Two NF-κB pathways have been described to mediate these responses, the canonical and the noncanonical. While understudied compared to the canonical NF-κB pathway, noncanonical NF-κB and its components have been shown to have effects, usually protumorigenic, in many different cancer types. Here, we review noncanonical NF-κB pathways and discuss its important roles in promoting cancer. We also discuss alternative NF-κB-independent functions of some the components of noncanonical NF-κB signaling. Finally, we discuss important crosstalk between canonical and noncanonical signaling, which blurs the two pathways, indicating that understanding the full picture of NF-κB regulation is critical to deciphering how this broad pathway promotes oncogenesis.

NF-κB Activation in Lymphoid Malignancies: Genetics, Signaling, and Targeted Therapy

The NF-κB transcription factor family plays a crucial role in lymphocyte proliferation and survival. Consequently, aberrant NF-κB activation has been described in a variety of lymphoid malignancies, including diffuse large B-cell lymphoma, Hodgkin lymphoma, and adult T-cell leukemia. Several factors, such as persistent infections (e.g., with Helicobacter pylori), the pro-inflammatory microenvironment of the cancer, self-reactive immune receptors as well as genetic lesions altering the function of key signaling effectors, contribute to constitutive NF-κB activity in these malignancies. In this review, we will discuss the molecular consequences of recurrent genetic lesions affecting key regulators of NF-κB signaling. We will particularly focus on the oncogenic mechanisms by which these alterations drive deregulated NF-κB activity and thus promote the growth and survival of the malignant cells. As the concept of a targeted therapy based on the mutational status of the malignancy has been supported by several recent preclinical and clinical studies, further insight in the function of NF-κB modulators and in the molecular mechanisms governing aberrant NF-κB activation observed in lymphoid malignancies might lead to the development of additional treatment strategies and thus improve lymphoma therapy.

IκBζ: an emerging player in cancer

IκBζ, an atypical member of the nuclear IκB family of proteins, is expressed at low levels in most resting cells, but is induced upon stimulation of Toll-like/IL-1 receptors through an IRAK1/IRAK4/NFκB-dependent pathway. Like its homolog Bcl3, IκBζ can regulate the transcription of a set of inflamatory genes through its association with the p50 or p52 subunits of NF-κB. Long studied as a key component of the immune response, IκBζ emerges as an important regulator of inflammation, cell proliferation and survival. As a result, growing evidence support the role of this transcription factor in the pathogenesis number of human hematological and solid malignancies.

Hepatic B cell leukemia-3 suppresses chemically-induced hepatocarcinogenesis in mice through altered MAPK and NF-κB activation

The transcriptional nuclear factor kappa B (NF-κB)-coactivator B cell leukemia-3 (Bcl-3) is a molecular regulator of cell death and proliferation. Bcl-3 has been shown to be widely expressed in different cancer types including hepatocellular carcinoma (HCC). Its influence on hepatocarcinogenesis is still undetermined. To examine the role of Bcl-3 in hepatocarcinogenesis mice with hepatocyte-specific overexpression of Bcl-3 (Bcl-3^Hep) were exposed to diethylnitrosamine (DEN) and phenobarbital (PB). Hepatic Bcl-3 overexpression attenuated DEN/PB-induced hepatocarcinogenesis. Bcl-3^Hep mice exhibited a lower number and smaller tumor nodules in response to DEN/PB at 40 weeks of age. Reduced HCC formation was accompanied by a lower rate of cell proliferation and a distinct expression pattern of growth and differentiation-related genes. Activation of c-Jun N-terminal kinase (JNK) and especially extracellular-signal regulated kinase (ERK) was reduced in tumor and tumor-surrounding liver tissue of Bcl-3^Hep mice, while p38 and NF-κB p65 were phosphorylated to a higher extent compared to the wild type. In parallel, the absolute number of intrahepatic macrophages, CD8⁺ T cells and activated B cells was reduced in DEN/PB-treated Bcl-3^Hep mice mirroring a reduction of tumor-associated inflammation. Interestingly, at the early time point of 7 weeks following tumor initiation, a higher rate of apoptotic cell death was observed in Bcl-3^Hep mice. In summary, hepatocyte-restricted Bcl-3 overexpression reduced hepatocarcinogenesis related to prolonged liver injury early after tumor initiation likely due to decreased survival of DEN/PB-damaged, premalignant cells. Therefore, Bcl-3 could become a novel player in the development of therapeutic and diagnostic tools for HCC.

BCL-3 expression promotes colorectal tumorigenesis through activation of AKT signalling

OBJECTIVE

Colorectal cancer remains the fourth most common cause of cancer-related mortality worldwide. Here we investigate the role of nuclear factor-κB (NF-κB) co-factor B-cell CLL/lymphoma 3 (BCL-3) in promoting colorectal tumour cell survival.

DESIGN

Immunohistochemistry was carried out on 47 tumour samples and normal tissue from resection margins. The role of BCL-3/NF-κB complexes on cell growth was studied in vivo and in vitro using an siRNA approach and exogenous BCL-3 expression in colorectal adenoma and carcinoma cells. The question whether BCL-3 activated the AKT/protein kinase B (PKB) pathway in colorectal tumour cells was addressed by western blotting and confocal microscopy, and the ability of 5-aminosalicylic acid (5-ASA) to suppress BCL-3 expression was also investigated.

RESULTS

We report increased BCL-3 expression in human colorectal cancers and demonstrate that BCL-3 expression promotes tumour cell survival in vitro and tumour growth in mouse xenografts in vivo, dependent on interaction with NF-κB p50 or p52 homodimers. We show that BCL-3 promotes cell survival under conditions relevant to the tumour microenvironment, protecting both colorectal adenoma and carcinoma cells from apoptosis via activation of the AKT survival pathway: AKT activation is mediated via both PI3K and mammalian target of rapamycin (mTOR) pathways, leading to phosphorylation of downstream targets GSK-3β and FoxO1/3a. Treatment with 5-ASA suppressed BCL-3 expression in colorectal cancer cells.

CONCLUSIONS

Our study helps to unravel the mechanism by which BCL-3 is linked to poor prognosis in colorectal cancer; we suggest that targeting BCL-3 activity represents an exciting therapeutic opportunity potentially increasing the sensitivity of tumour cells to conventional therapy.

BCL-3 promotes the tumor growth of hepatocellular carcinoma by regulating cell proliferation and the cell cycle through cyclin D1

Previous studies have demonstrated the aberrant expression and oncogenic role of B-cell CLL/lymphoma-3 (BCL-3) in human malignancies. However, the clinical significance of BCL-3 and its biological function in human hepatocellular carcinoma (HCC) remain unknown. In the present study, the expression levels of BCL-3 protein and mRNA in 90 pairs of HCC and matched non-tumor tissues were analyzed using immunohistochemistry and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). We found that the expression levels of BCL-3 protein and mRNA in HCC tissues were significantly higher than those in the matched tumor-adjacent tissues. In addition, positive expression of BCL-3 was associated with adverse clinicopathological characteristics of the HCC patients including hepatitis B virus (HBV) infection, tumor size, cirrhosis and advanced tumor-node-metastasis (TNM) stage. Moreover, HCC patients with positive expression of BCL-3 had significantly decreased 5-year overall survival and recurrence-free survival. Importantly, BCL-3 expression was an independent prognostic factor for indicating the survival of the HCC patients. Functionally, BCL-3 knockdown markedly inhibited cell viability, proliferation and cell cycle progression in HepG2 cells, while BCL-3 overexpression promoted these cellular processes in Huh7 cells. Accordingly, in vivo experiments indicated that BCL-3 knockdown prominently suppressed the tumor growth of HepG2 cells in nude mice. Mechanistically, we revealed that the expression of cyclin D1 was decreased after BCL-3 knockdown in the HepG2 cells and was increased after BCL-3 overexpression in the Huh7 cells. Cyclin D1 silencing was found to abrogate the functional effects of BCL-3 on cellular processes in Huh7 cells. Taken together, our data suggest that BCL-3 may serve as a promising biomarker and an effective therapeutic target of HCC.

Induction of IκB-ζ by Epstein-Barr virus latent membrane protein-1 and CD30

Activation of nuclear factor-κB (NF-κB) in Burkitt's lymphoma (BL) and Hodgkin's lymphoma (HL) cells is important in the transformation and development process of these lymphomas. Epstein-Barr virus (EBV) latent membrane protein-1 (LMP-1) and ligand-independent signaling by overexpressed CD30 are known to cause permanent activation of NF-κB in lymphomas. However, hyperactivation of NF-κB triggers cellular senescence and apoptosis. Here, we show that IκB-ζ, an inducible regulator of NF-κB, is constitutively expressed in BL and HL cell lines. In addition, immunohistochemical staining identified nuclear IκB-ζ‑positive BL cells, and Hodgkin and Reed-Sternberg cells in lymph nodes. Expression of LMP-1 and CD30 increased IκB-ζ expression at the transcriptional level. IκB-ζ promoter was regulated by activation of the NF-κB‑inducing kinase (NIK)/IκB kinase/NF-κB pathway via the carboxyl‑terminal tumor necrosis factor (TNF) receptor‑associated factor (TRAF)-interacting regions of LMP-1 and CD30. Interestingly, IκB-ζ inhibited NF-κB activation by LMP-1 and CD30. The results suggest that NF-κB-induced IκB-ζ negatively modulates NF-κB hyperactivation, resulting in a fine balance that ultimately endows a net evolutionary benefit to the survival of BL and HL cells.

The cnidarian origin of the proto-oncogenes NF-κB/STAT and WNT-like oncogenic pathway drives the ctenophores (Review)

The cell survival pathways of the diploblastic early multicellular eukaryotic hosts contain and operate the molecular machinery resembling those of malignantly transformed individual cells of highly advanced multicellular hosts (including Homo). In the present review, the STAT/NF-κB pathway of the cnidarian Nematostella vectensis is compared with that of human tumors (malignant lymphomas, including Reed-Sternberg cells) pointing out similarities, including possible viral initiation in both cases. In the ctenophore genome and proteome, β-catenin gains intranuclear advantages due to a physiologically weak destructive complex in the cytoplasm, and lack of natural inhibitors (the Dickkopfs). Thus, a scenario similar to what tumor cells initiate and achieve is presented through several constitutive loss-of-function type mutations in the destructive complex and in the elimination of inhibitors. Vice versa, malignantly transformed individual cells of advanced multicellular hosts assume pheno-genotypic resemblance to cells of unicellular or early multicellular hosts, and presumably to their ancient predecessors, by returning to the semblance of immortality and to the resumption of the state of high degree of resistance to physicochemical insults. Human leukemogenic and oncogenic pathways are presented for comparisons. The supreme bioengineers RNA/DNA complex encoded both the malignantly transformed immortal cell and the human cerebral cortex. The former generates molecules for the immortality of cellular life in the Universe. The latter invents the inhibitors of the process in order to gain control over it.

Variant of BCL3 gene is strongly associated with five-year survival of non-small-cell lung cancer patients

OBJECTIVES

BCL3, a known atypical IκB family member, has been documented to be upregulated in hematological malignancies and in some solid tumors, functioning as a crucial player in tumor development. Recently, rs8100239, a tag-Single Nucleotide Polymorphism (SNP) in BCL3 (T>A) has been identified, but there are no data regarding its involvement in non-small-cell lung cancer (NSCLC) initiation and progression.

MATERIALS AND METHODS

To study the possible association of BCL3 with NSCLC, 268 patients and 279 healthy controls were genotyped for rs8100239. Moreover, BCL3 protein expression was also investigated in 112 NSCLC cases through an immunohistochemical analysis.

RESULTS

NSCLC patients with AA genotype displayed significantly worse prognosis compared to T allele carriers (P<0.001), who had less frequent intermediate nuclear BCL3 expression (P=0.042). In addition, overexpression of BCL3 was detected in tumor specimens, compared to normal tissue (P<0.001). Furthermore, BCL3 protein levels were associated with five-year survival (P=0.039), maximum diameter of lesion (P=0.012), grade (P=0.002) and relapse frequency (P=0.041).

CONCLUSIONS

The present study is the first to show a relationship between the genetic variation rs8100239 of BCL3 and cancer patients' survival. It also represents the first quantitative evaluation of BCL3 expression in NSCLC. Our findings indicate that rs8100239 may be considered as a novel prognostic indicator, demonstrating also the overexpression of BCL3 protein in NSCLC and implicating this pivotal molecule in the pathogenesis of NSCLC.

NF-κB-induced KIAA1199 promotes survival through EGFR signalling

Constitutive activation of EGFR- and NF-κB-dependent pathways is a hallmark of cancer, yet signalling proteins that connect both oncogenic cascades are poorly characterized. Here we define KIAA1199 as a BCL-3- and p65-dependent gene in transformed keratinocytes. KIAA1199 expression is enhanced on human papillomavirus (HPV) infection and is aberrantly expressed in clinical cases of cervical (pre)neoplastic lesions. Mechanistically, KIAA1199 binds Plexin A2 and protects from Semaphorin 3A-mediated cell death by promoting EGFR stability and signalling. Moreover, KIAA1199 is an EGFR-binding protein and KIAA1199 deficiency impairs EGF-dependent Src, MEK1 and ERK1/2 phosphorylations. Therefore, EGFR stability and signalling to downstream kinases requires KIAA1199. As such, KIAA1199 promotes EGF-mediated epithelial-mesenchymal transition (EMT). Taken together, our data define KIAA1199 as an oncogenic protein induced by HPV infection and constitutive NF-κB activity that transmits pro-survival and invasive signals through EGFR signalling.

Bcl3 regulates pro-survival and pro-inflammatory gene expression in cutaneous T-cell lymphoma

The advanced stages of cutaneous T cell lymphoma (CTCL) are characterized not only by decreased levels of pro-inflammatory cytokines, resulting in high susceptibility to infections, but also by high constitutive activity of NFκB, which promotes cell survival and resistance to apoptosis. The increased expression of the proto-oncogene Bcl3 belonging to IκB family is associated with the pathogenesis of the different types of human cancer, yet, the function and regulation of Bcl3 in CTCL have not been studied. Here, we show that Bcl3 is highly expressed in CTCL Hut-78 and HH cells. The suppression of Bcl3 levels decreases the expression of the pro-survival genes cIAP1 and cIAP2, reduces cell viability, and increases CTCL apoptosis. Interestingly, Bcl3 suppression concomitantly increases expression and the release of the pro-inflammatory cytokines IL-8 and IL-17 in CTCL cells. Chromatin immunoprecipitation studies show that Bcl3 regulates cIAP1, cIAP2, IL-8 and IL-17 gene expression through direct binding to their promoters. Bcl3 expression is regulated by bortezomib (BZ)-mediated proteasome inhibition, and BZ inhibits Bcl3 recruitment to its target promoters, resulting in decreased expression of cIAP1 and cIAP2, but increased expression of IL-8 and IL-17. The Bcl3 expression is regulated through NFκB subunit exchange on Bcl3 promoter. In untreated cells, the Bcl3 promoter is occupied predominantly by p65/p50 heterodimers, inducing Bcl3 expression; however, in BZ-treated cells, the p65/50 heterodimers are replaced by p52 subunits, resulting in Bcl3 transcriptional repression. These data provide the first insights into the function and regulation of Bcl3 in CTCL, and indicate that Bcl3 has an important pro-survival and immunosuppressive role in these cells.

The tumor promoter and NF-κB modulator Bcl-3 regulates splenic B cell development

Bcl-3 is an atypical member of the family of IκB proteins. Unlike the classic members, Bcl-3 functions as a nuclear transcriptional cofactor that may, depending on context, promote or suppress genes via association with p50/NF-κB1 or p52/NF-κB2 homodimers. Bcl-3 is also an oncogene, because it is a partner in recurrent translocations in B cell tumors, resulting in deregulated expression. Bcl-3 functions, however, remain poorly understood. We have investigated the role of Bcl-3 in B cells and discovered a previously unknown involvement in the splenic development of these cells. Loss of Bcl-3 in B cells resulted in significantly more marginal zone (MZ) and fewer follicular (FO) B cells. Conversely, transgenic expression of Bcl-3 in B cells generated fewer MZ and more FO B cells. Both Bcl-3(-/-) FO and MZ B cells were more responsive to LPS stimulation compared with their wild-type counterparts, including increased proliferation. By contrast, Bcl-3(-/-) FO B cells were more prone to apoptosis upon BCR stimulation, also limiting their expansion. The data reveal Bcl-3 as a regulator of B cell fate determination, restricting the MZ path and favoring the FO pathway, at least in part, via increased signal-specific survival of the latter, a finding of relevance to its tumorigenic activity.

Atypical IκB proteins - nuclear modulators of NF-κB signaling

Nuclear factor κB (NF-κB) controls a multitude of physiological processes such as cell differentiation, cytokine expression, survival and proliferation. Since NF-κB governs embryogenesis, tissue homeostasis and the functions of innate and adaptive immune cells it represents one of the most important and versatile signaling networks known. Its activity is regulated via the inhibitors of NF-κB signaling, the IκB proteins. Classical IκBs, like the prototypical protein IκBα, sequester NF-κB transcription factors in the cytoplasm by masking of their nuclear localization signals (NLS). Thus, binding of NF-κB to the DNA is inhibited. The accessibility of the NLS is controlled via the degradation of IκBα. Phosphorylation of the conserved serine residues 32 and 36 leads to polyubiquitination and subsequent proteasomal degradation. This process marks the central event of canonical NF-κB activation. Once their NLS is accessible, NF-κB transcription factors translocate into the nucleus, bind to the DNA and regulate the transcription of their respective target genes. Several studies described a distinct group of atypical IκB proteins, referred to as the BCL-3 subfamily. Those atypical IκBs show entirely different sub-cellular localizations, activation kinetics and an unexpected functional diversity. First of all, their interaction with NF-κB transcription factors takes place in the nucleus in contrast to classical IκBs, whose binding to NF-κB predominantly occurs in the cytoplasm. Secondly, atypical IκBs are strongly induced after NF-κB activation, for example by LPS and IL-1β stimulation or triggering of B cell and T cell antigen receptors, but are not degraded in the first place like their conventional relatives. Finally, the interaction of atypical IκBs with DNA-associated NF-κB transcription factors can further enhance or diminish their transcriptional activity. Thus, they do not exclusively act as inhibitors of NF-κB activity. The capacity to modulate NF-κB transcription either positively or negatively, represents their most important and unique mechanistic difference to classical IκBs. Several reports revealed the importance of atypical IκB proteins for immune homeostasis and the severe consequences following their loss of function. This review summarizes insights into the physiological processes regulated by this protein class and the relevance of atypical IκB functioning.

Role of Bcl-3 in solid tumors

Bcl-3 is an established oncogene in hematologic malignancies, such as B-cell chronic lymphocytic leukemias. Nevertheless, recent research has shown that it also participates in progression of diverse solid tumors. The present review summarizes the current knowledge of Bcl3 role in solid tumors progression, including some new insights in its possible molecular mechanisms of action.

BCL3 rearrangement, amplification and expression in diffuse large B-cell lymphoma

AIMS

Aim of the study is to investigate diffuse large B-cell lymphoma (DLBCL) for the presence of BCL3 gene rearrangement and protein expression and to correlate these with immunophenotypic subsets of DLBCL. We aimed to investigate the pathogenetic implication of BCL3 in DLBCL.

METHODS AND RESULTS

Tissue microarray sections from 78 DLBCLs were evaluated for BCL3 protein expression using immunohistochemistry and for BCL3 and IGH rearrangement using Fluorescent in situ hybridisation (FISH) with split-apart probes. BCL3 expression was positive in 36/78 cases, of which BCL3 rearrangement was seen seen in one case. Three additional cases showed evidence of trisomy of BCL3/chromosome 19, and two of these three cases showed BCL3 expression. The four cases with FISH-detectable abnormalities showed MUM1 expression and had a non-germinal center (GC) phenotype. The median [and inter-quartile range (IQR)] percentage of BCL3-positive cells in MUM1-positive and MUM1-negative subsets was 65% (5-85%) and 5% (0-20%), respectively (P < 0.001). The median (IQR) percentage of BCL3-positive cells among GC and non-GC subsets of DLBCLs was 12% (12-81%) and 60% (6-87%), respectively (P = 0.022).

CONCLUSION

Rearrangement or amplification involving the BCL3 gene is a rare event in DLBCL but is likely to play a role in the pathogenesis of a minority of de novo DLBCL. BCL3 over-expression is more frequent and occurs in the absence of rearrangement or amplification and is a feature of the non-GC subset of DLBCL.

Chronic lymphocytic leukemia with t(14;19)(q32;q13) is characterized by atypical morphologic and immunophenotypic features and distinctive genetic features

The t(14;19)(q32;q13) involving the IGH@ and BCL3 loci is an infrequent cytogenetic abnormality detected in B-cell malignancies. We describe the clinicopathologic, cytogenetic, and molecular genetic characteristics of 14 cases of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) with t(14;19)(q32;q13). All patients (10 men and 4 women) had lymphocytosis; 10 had lymphadenopathy. Blood and bone marrow lymphocytes were predominantly small, but cytologically and immunophenotypically atypical. In all cases, t(14;19) was found in the neoplastic stem line; it was the sole abnormality in 4. Ten cases showed additional cytogenetic abnormalities, including trisomy 12 in 9 and complex karyotypes in 7. Fluorescence in situ hybridization demonstrated IGH@/BCL3 fusion gene in all cases. In all cases, the IGHV genes were unmutated, but only 7 expressed ZAP70. Seven cases preferentially used IGHV4-39. Our results indicate that t(14;19)(q32;q13) identifies a subset of CLL/SLL with distinctive clinicopathologic and genetic features. Furthermore, t(14;19) may represent an early, possibly primary, genetic event.

BCL-3 degradation involves its polyubiquitination through a FBW7-independent pathway and its binding to the proteasome subunit PSMB1

The oncogenic protein BCL-3 activates or represses gene transcription through binding with the NF-kappaB proteins p50 and p52 and is degraded through a phospho- and GSK3-dependent pathway. However, the mechanisms underlying its degradation remain poorly understood. Yeast two-hybrid analysis led to the identification of the proteasome subunit PSMB1 as a BCL-3-associated protein. The binding of BCL-3 to PSMB1 is required for its degradation through the proteasome. Indeed, PSMB1-depleted cells are defective in degrading polyubiquitinated BCL-3. The N-terminal part of BCL-3 includes lysines 13 and 26 required for the Lys(48)-linked polyubiquitination of BCL-3. Moreover, the E3 ligase FBW7, known to polyubiquitinate a variety of substrates phosphorylated by GSK3, is dispensable for BCL-3 degradation. Thus, our data defined a unique motif of BCL-3 that is needed for its recruitment to the proteasome and identified PSMB1 as a key protein required for the proteasome-mediated degradation of a nuclear and oncogenic IkappaB protein.

The repressing function of the oncoprotein BCL-3 requires CtBP, while its polyubiquitination and degradation involve the E3 ligase TBLR1

The nuclear and oncogenic BCL-3 protein activates or represses gene transcription when bound to NF-kappaB proteins p50 and p52, yet the molecules that specifically interact with BCL-3 and drive BCL-3-mediated effects on gene expression remain largely uncharacterized. Moreover, GSK3-mediated phosphorylation of BCL-3 triggers its degradation through the proteasome, but the proteins involved in this degradative pathway are poorly characterized. Biochemical purification of interacting partners of BCL-3 led to the identification of CtBP as a molecule required for the ability of BCL-3 to repress gene transcription. CtBP is also required for the oncogenic potential of BCL-3 and for its ability to inhibit UV-mediated cell apoptosis in keratinocytes. We also defined the E3 ligase TBLR1 as a protein involved in BCL-3 degradation through a GSK3-independent pathway. Thus, our data demonstrate that the LSD1/CtBP complex is required for the repressing abilities of an oncogenic I kappaB protein, and they establish a functional link between the E3 ligase TBLR1 and NF-kappaB.

High expression of BCL3 in human myeloma cells is associated with increased proliferation and inferior prognosis

BACKGROUND

BCL3 is a putative oncogene encoding for a protein belonging to the inhibitory kappaB-family. We experienced that this putative oncogene was a common target gene for growth-promoting cytokines in myeloma cell lines.

METHODS

Gene expression of BCL3 was studied in 351 newly diagnosed myeloma patients, 12 patients with smouldering myeloma, 44 patients with monoclonal gammopathy of undetermined significance and 22 healthy individuals. Smaller material of samples was included for mRNA detection by RT-PCR, protein detection by Western blot and immunohistochemistry, and for cytogenetic studies. A total of eight different myeloma cell lines were studied.

RESULTS

Bcl-3 was induced in myeloma cell lines by interleukin (IL)-6, IL-21, IL-15, tumor necrosis factor-alpha and IGF-1, and its upregulation was associated with increased proliferation of the cells. In a population of 351 patients, expression levels of BCL3 above 75th percentile were associated with shorter 5-yr survival. When this patient population was divided into subgroups based on molecular classification, BCL3 was significantly increased in a poor risk subgroup characterized by overexpression of cell cycle and proliferation related genes. Intracellular localization of Bcl-3 was dependent on type of stimulus given to the cell.

CONCLUSION

BCL3 is a common target gene for several growth-promoting cytokines in myeloma cells and high expression of BCL3 at the time of diagnosis is associated with poor prognosis of patients with multiple myeloma (MM). These data may indicate a potential oncogenic role for Bcl-3 in MM.

The proto-oncogene Bcl3, induced by Tax, represses Tax-mediated transcription via p300 displacement from the human T-cell leukemia virus type 1 promoter

The etiology of human T-cell leukemia virus type 1 (HTLV-1)-induced adult T-cell leukemia is linked to the expression of the viral oncoprotein Tax. Although the mechanism of retroviral transformation is unknown, Tax interferes with fundamental cellular processes, including proliferation and apoptosis, and these events may directly link Tax to early steps in malignant progression. In this study, we examined the interplay between Tax and the potent proto-oncogene B-cell chronic leukemia protein 3 (Bcl3). Bcl3 is a critical regulator of cell survival and proliferation and is overexpressed in HTLV-1-infected cells. We found that Tax induced Bcl3 expression through stimulation of the NF-kappaB pathway. An intronic NF-kappaB binding site within the Bcl3 gene served as the primary target of Tax-induced NF-kappaB activation. We next considered the consequence of Bcl3 overexpression on Tax function. Interestingly, we found that Bcl3 formed a stable complex with Tax and that this complex potently inhibited Tax-dependent HTLV-1 transcription. Importantly, Bcl3 associated with the HTLV-1 promoter in a Tax-dependent manner and inhibited the binding of the critical cellular coactivator p300. The conserved ankyrin repeat domain of Bcl3 mediated both Tax binding and inhibition of p300 recruitment to the HTLV-1 promoter. Together, these data suggest that Tax-induced Bcl3 overexpression benefits the virus in two important ways. First, Bcl3 may promote cell division and thus clonal proliferation of the virus. Second, Bcl3 may attenuate virion production, facilitating immune evasion. One consequence of this regulatory loop may be Bcl3-induced malignant transformation of the host cell.

PVRL2 is translocated to the TRA@ locus in t(14;19)(q11;q13)-positive peripheral T-cell lymphomas

Very few recurrent chromosomal abnormalities have been identified in T-cell non-Hodgkin lymphomas. These involve the TRA@/TRD@ gene at chromosome band 14q11 in up to 15% of cases. We recently reported a novel and recurrent translocation, t(14;19)(q11;q13), in peripheral T-cell lymphoma (PTCL). Fluorescence in situ hybridization analysis performed in three cases suggested an involvement of the TRA@/TRD@ locus at 14q11 and of a region telomeric to BCL3 on 19q13. We now report the molecular cloning of these translocations. Sequence analysis confirmed the involvement of the TRA@/TRD@ and indicated that the breakpoints were located mainly in the TRAJ region. On chromosome 19, our results revealed a new clustering of breakpoints outside the region involved in t(14;19)(q32;q13)-positive B-cell malignancies. Remarkably, all three breaks were located downstream or within the PVRL2 gene, in a small 10.3 kb interval, suggesting a nonrandom location of the breakpoints. For two patients, a high mRNA expression of both PVRL2 and BCL3 was found. In conclusion, we identified PVRL2 as a new recurrent partner gene of the TRA@ locus in PTCL. These results suggest that both BCL3 and PVRL2 may participate in the pathogenesis of these PTCLs, but further studies should be undertaken to investigate the precise role of these genes.

A comprehensive genetic and histopathologic analysis identifies two subgroups of B-cell malignancies carrying a t(14;19)(q32;q13) or variant BCL3-translocation

The biologic and pathologic features of B-cell malignancies bearing a translocation t(14;19)(q32;q13) leading to a fusion of IGH and BCL3 are still poorly described. Herein we report the results of a comprehensive cytogenetic, fluorescence in situ hybridization (FISH), molecular and histopathological survey of a large series of B-cell malignancies with t(14;19) or variant translocations. A total of 56 B-cell malignancies with a FISH-proven BCL3 involvement were identified with the translocation partners being IGH (n=51), IGL (n=2), IGK (n=2) and a non-IG locus (n=1). Hierarchical clustering of chromosomal changes associated with the t(14;19) indicated the presence of two different groups of IG/BCL3-positive lymphatic neoplasias. The first group included 26 B-cell malignancies of various histologic subtypes containing a relatively high number of chromosomal changes and mostly mutated IgVH genes. This cluster displayed three cytogenetic branches, one with rearrangements in 7q, another with deletions in 17p and a third one with rearrangements in 1q and deletions in 6q and 13q. The second group included 19 cases, mostly diagnosed as B-cell chronic lymphocytic leukemia (B-CLL), and characterized by few additional chromosomal changes (e.g. trisomy 12) and unmutated IgVH genes. In conclusion, our study indicates that BCL3 translocations are not restricted to B-CLL but present in a heterogeneous group of B-cell malignancies.

Mutations in the NF-kappaB signaling pathway: implications for human disease

The nuclear factor-kappa B (NF-kappaB) signaling pathway is a multi-component pathway that regulates the expression of hundreds of genes that are involved in diverse and key cellular and organismal processes, including cell proliferation, cell survival, the cellular stress response, innate immunity and inflammation. Not surprisingly, mis-regulation of the NF-kappaB pathway, either by mutation or epigenetic mechanisms, is involved in many human and animal diseases, especially ones associated with chronic inflammation, immunodeficiency or cancer. This review describes human diseases in which mutations in the components of the core NF-kappaB signaling pathway have been implicated and discusses the molecular mechanisms by which these alterations in NF-kappaB signaling are likely to contribute to the disease pathology. These mutations can be germline or somatic and include gene amplification (e.g., REL), point mutations and deletions (REL, NFKB2, IKBA, CYLD, NEMO) and chromosomal translocations (BCL-3). In addition, human genetic diseases are briefly described wherein mutations affect protein modifiers or transducers of NF-kappaB signaling or disrupt NF-kappaB-binding sites in promoters/enhancers.

The t(14;19)(q32;q13)-positive small B-cell leukaemia: a clinicopathologic and cytogenetic study of seven cases

The t(14;19)(q32;q13), involving the BCL3 locus at chromosome 19q13 and the immunoglobulin heavy chain gene at 14q32, is a rare recurrent cytogenetic abnormality identified in B-cell neoplasms, most of which have been classified as chronic lymphocytic leukaemia (CLL) in the literature. We describe the clinicopathological, immunophenotypic and cytogenetic findings in seven patients with B-cell neoplasms associated with t(14;19)(q32;q13). There were five men and two women, with a median age of 48 years (range 33-68). All had absolute lymphocytosis, six had lymphadenopathy, and one had splenomegaly. Lymphocytes in blood and bone marrow aspirate smears were predominantly small and cytologically atypical. Flow cytometric immunophenotyping showed an atypical immunophenotype with low CLL scores. The growth pattern in bone marrow biopsy specimens was interstitial to diffuse; immunohistochemical stains were positive for bcl3 and negative for cyclin D1. Lymph node biopsy specimens of two patients revealed total architectural effacement by neoplasm with proliferation centres. In addition to t(14;19), cytogenetic studies demonstrated trisomy 12 in five patients. These results suggest that B-cell neoplasms with the t(14;19)(q32;q13) present frequently as leukaemia composed of small B-lymphocytes and share many features with CLL. However, these neoplasms also differ from CLL cytologically and in their immunophenotype.

Splenic small B-cell lymphoma with IGH/BCL3 translocation

Isolated chromosomal translocations are important defining features of many non-Hodgkin lymphomas, especially of B-cell type. In contrast to some other translocations, the significance of IGH/BCL3 translocations is not well defined. Although often considered a feature of the ill-defined entity atypical chronic lymphocytic leukemia, very few cases are reported in which involvement of BCL3 and the precise B-cell neoplasm are both well documented. For this reason, we report a splenic-based CD5(-), CD10(-), CD43(-), CD23(-), CD103(-), FMC7(+), CD25(+) small B-cell lymphoma associated with epithelioid histiocyte clusters and a t(14;19)(q32;q13) representing an IGH/BCL3 translocation based on classical cytogenetic studies, chromosomal painting, and fluorescence in situ hybridization studies. The previously reported neoplasms with t(14;19)(q32;q13) or IGH/BCL3 translocations are also reviewed. The present case did not fall into any of the classic B-cell lymphoma categories and clearly did not represent chronic lymphocytic leukemia/small lymphocytic lymphoma. This case suggests that the IGH/BCL3 translocation may help to define a new clinicopathologic entity.

Expression of the Bcl-3 proto-oncogene suppresses p53 activation

While Bcl-3 expression in cancer was originally thought to be limited to B-cell lymphomas with a 14;19 chromosomal translocation, more recent evidence indicates that expression of this presumptive oncoprotein is significantly more widespread in cancer. However, an oncogenic role for Bcl-3 has not been clearly identified. Experiments presented here indicate that Bcl-3 is inducible by DNA damage and is required for the induction of Hdm2 gene expression and the suppression of persistent p53 activity. Furthermore, constitutive expression of Bcl-3 suppresses DNA damage-induced p53 activation and inhibits p53-induced apoptosis through a mechanism that is at least partly dependent on the up-regulation of Hdm2. The results provide insight into a mechanism whereby altered expression of Bcl-3 leads to tumorigenic potential. Since Bcl-3 is required for germinal center formation, these results suggest functional similarities with the unrelated Bcl-6 oncoprotein in suppressing potential p53-dependent cell cycle arrest and apoptosis in response to somatic hypermutation and class switch recombination.

Regulation of Bcl-3 through interaction with the Lck tyrosine kinase

bcl-3 is a protooncogene which undergoes chromosomal translocation in a subset of chronic B-cell lymphocytic leukemia cells. Bcl-3 is a unique IkappaB family protein that regulates transcription of a number of NF-kappaB target genes through interactions with NF-kappaB dimers. Based on previous studies, suggesting that Bcl-3 interacts with the Fyn tyrosine kinase in platelets, we investigated possible interactions of Bcl-3 with Lck, a related tyrosine kinase important in lymphoid cells. Protein-protein interactions between Bcl-3 and the Lck tyrosine kinase were identified both in vitro and in vivo. Lck enhanced Bcl-3-mediated activation of a p52/Bcl-3-responsive promoter in reporter gene assays independent of its tyrosine kinase activity, but requiring the Lck SH3 protein interaction domain. These studies suggest that Bcl-3 might participate in oncogenic pathways involving Lck.

NF-kB in development and progression of human cancer

The nuclear factor kB (NF-kB) comprises a family of transcription factors involved in the regulation of a wide variety of biological responses. NF-kB plays a well-known function in the regulation of immune responses and inflammation, but growing evidences support a major role in oncogenesis. NF-kB regulates the expression of genes involved in many processes that play a key role in the development and progression of cancer such as proliferation, migration and apoptosis. Aberrant or constitutive NF-kB activation has been detected in many human malignancies. In recent years, numerous studies have focused on elucidating the functional consequences of NF-kB activation as well as its signaling mechanisms. NF-kB has turned out to be an interesting therapeutic target for treatment of cancer.