Anaplastic, plasmablastic, and plasmacytic plasmacytomas of mice: relationships to human plasma cell neoplasms and late-stage differentiation of normal B cells

Wwox Deletion in Mouse B Cells Leads to Genomic Instability, Neoplastic Transformation, and Monoclonal Gammopathies

WWOX (WW domain containing oxidoreductase) expression loss is common in various cancers and characteristic of poor prognosis. Deletions, translocations, and loss of expression affecting the WWOX gene are a common feature of various B cell neoplasms such as certain B cell lymphomas and multiple myeloma. However, the role of this common abnormality in B cell tumor initiation and/or progression has not been defined. In this study, we conditionally deleted Wwox early in B cell development by means of breeding Cd19-Cre transgenic mice crossed to Wwox floxed mice (Cd19 Wwox KO). We observed a significant reduced survival in Cd19 Wwox KO mice and the development of B cell neoplasms including B cell lymphomas, plasma cell neoplasias characterized by increased numbers of CD138+ populations as well as monoclonal gammopathies detected by serum protein electrophoresis. To investigate whether Wwox loss could play a role in genomic instability, we analyzed DNA repair functions during immunoglobulin class switch joining between DNA segments in antibody genes. While class switch recombination (CSR) was only slightly impaired, Wwox deficiency resulted in a dramatic shift of double strand break (DSB) repair from normal classical-NHEJ toward the microhomology-mediated alternative-NHEJ pathway, a pathway associated with chromosome translocations and genome instability. Consistent with this, Wwox deficiency resulted in a marked increase of spontaneous translocations during CSR. This work defines for the first time a role for Wwox for maintaining B cell genome stability during a process that can promote neoplastic transformation and monoclonal gammopathies.

Transgenic mouse model of IgM+ lymphoproliferative disease mimicking Waldenström macroglobulinemia

Waldenström macroglobulinemia (WM) is a low-grade incurable immunoglobulin M⁺ (IgM⁺) lymphoplasmacytic lymphoma for which a genetically engineered mouse model of de novo tumor development is lacking. On the basis of evidence that the pro-inflammatory cytokine, interleukin 6 (IL6), and the survival-enhancing oncoprotein, B cell leukemia 2 (BCL2), have critical roles in the natural history of WM, we hypothesized that the enforced expression of IL6 and BCL2 in mice unable to perform immunoglobulin class switch recombination may result in a lymphoproliferative disease that mimics WM. To evaluate this possibility, we generated compound transgenic BALB/c mice that harbored the human BCL2 and IL6 transgenes, EμSV-BCL2-22 and H2-L^d-hIL6, on the genetic background of activation-induced cytidine deaminase (AID) deficiency. We designated these mice BCL2⁺IL6⁺AID^- and found that they developed-with full genetic penetrance (100% incidence) and suitably short latency (93 days median survival)-a severe IgM⁺ lymphoproliferative disorder that recapitulated important features of human WM. However, the BCL2⁺IL6⁺AID^- model also exhibited shortcomings, such as low serum IgM levels and histopathological changes not seen in patients with WM, collectively indicating that further refinements of the model are required to achieve better correlations with disease characteristics of WM.

Hematopoietic neoplasms in Prkar2a-deficient mice

Background

Protein kinase A (PKA) is a holoenzyme that consists of a dimer of regulatory subunits and two inactive catalytic subunits that bind to the regulatory subunit dimer. Four regulatory subunits (RIα, RIβ, RIIα, RIIβ) and four catalytic subunits (Cα, Cβ, Cγ, Prkx) have been described in the human and mouse genomes. Previous studies showed that complete inactivation of the Prkar1a subunit (coding for RIα) in the germline leads to embryonic lethality, while Prkar1a–deficient mice are viable and develop schwannomas, thyroid, and bone neoplasms, and rarely lymphomas and sarcomas. Mice with inactivation of the Prkar2a and Prkar2b genes (coding for RIIα and RIIβ, respectively) are also viable but have not been studied for their susceptibility to any tumors.

Methods

Cohorts of Prkar1a^+/−, Prkar2a^+/−, Prkar2a^−/−, Prkar2b^+/− and wild type (WT) mice have been observed between 5 and 25 months of age for the development of hematologic malignancies. Tissues were studied by immunohistochemistry; tumor-specific markers were also used as indicated. Cell sorting and protein studies were also performed.

Results

Both Prkar2a^−/− and Prkar2a^+/− mice frequently developed hematopoietic neoplasms dominated by histiocytic sarcomas (HS) with rare diffuse large B cell lymphomas (DLBCL). Southern blot analysis confirmed that the tumors diagnosed histologically as DLBCL were clonal B cell neoplasms. Mice with other genotypes did not develop a significant number of similar neoplasms.

Conclusions

Prkar2a deficiency predisposes to hematopoietic malignancies in vivo. RIIα’s likely association with HS and DLBCL was hitherto unrecognized and may lead to better understanding of these rare neoplasms.

Nfatc2 and Tob1 have non-overlapping function in T cell negative regulation and tumorigenesis

Nfatc2 and Tob1 are intrinsic negative regulators of T cell activation. Nfatc2-deficient and Tob1-deficient T cells show reduced thresholds of activation; however, whether these factors have independent or overlapping roles in negative regulation of T cell responses has not been previously examined. Here, we show that Nfatc2 knockout (KO) but not Tob1 KO mice have age-associated accumulation of persistently activated T cells in vivo and expansion of the CD44+ memory cell compartment and age-associated lymphocytic infiltrates in visceral organs, without significant changes in numbers of CD4+CD25+Foxp3+ regulatory T cells (Treg). In vitro, CD4+CD25- "conventional" T cells (Tconvs) from both KO strains showed greater proliferation than wild type (WT) Tconvs. However, while Tregs from Nfatc2 KO mice retained normal suppressive function, Tregs from Tob1 KOs had enhanced suppressive activity. Nfatc2 KO Tconvs expanded somewhat more rapidly than WT Tconvs under conditions of homeostatic proliferation, but their accelerated growth capacity was negated, at least acutely, in a lymphoreplete environment. Finally, Nfatc2 KO mice developed a previously uncharacterized increase in B-cell malignancies, which was not accelerated by the absence of Tob1. The data thus support the prevailing hypothesis that Nfatc2 and Tob1 are non-redundant regulators of lymphocyte homeostasis.

(18)F-FDG-PET/CT imaging in an IL-6- and MYC-driven mouse model of human multiple myeloma affords objective evaluation of plasma cell tumor progression and therapeutic response to the proteasome inhibitor ixazomib

(18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) and computed tomography (CT) are useful imaging modalities for evaluating tumor progression and treatment responses in genetically engineered mouse models of solid human cancers, but the potential of integrated FDG-PET/CT for assessing tumor development and new interventions in transgenic mouse models of human blood cancers such as multiple myeloma (MM) has not been demonstrated. Here we use BALB/c mice that contain the newly developed iMyc(ΔEμ) gene insertion and the widely expressed H2-L(d)-IL6 transgene to demonstrate that FDG-PET/CT affords an excellent research tool for assessing interleukin-6- and MYC-driven plasma cell tumor (PCT) development in a serial, reproducible and stage- and lesion-specific manner. We also show that FDG-PET/CT permits determination of objective drug responses in PCT-bearing mice treated with the investigational proteasome inhibitor ixazomib (MLN2238), the biologically active form of ixazomib citrate (MLN9708), that is currently in phase 3 clinical trials in MM. Overall survival of 5 of 6 ixazomib-treated mice doubled compared with mice left untreated. One outlier mouse presented with primary refractory disease. Our findings demonstrate the utility of FDG-PET/CT for preclinical MM research and suggest that this method will play an important role in the design and testing of new approaches to treat myeloma.

A computational profiling of changes in gene expression and transcription factors induced by vFLIP K13 in primary effusion lymphoma

Infection with Kaposi's sarcoma associated herpesvirus (KSHV) has been linked to the development of primary effusion lymphoma (PEL), a rare lymphoproliferative disorder that is characterized by loss of expression of most B cell markers and effusions in the body cavities. This unique clinical presentation of PEL has been attributed to their distinctive plasmablastic gene expression profile that shows overexpression of genes involved in inflammation, adhesion and invasion. KSHV-encoded latent protein vFLIP K13 has been previously shown to promote the survival and proliferation of PEL cells. In this study, we employed gene array analysis to characterize the effect of K13 on global gene expression in PEL-derived BCBL1 cells, which express negligible K13 endogenously. We demonstrate that K13 upregulates the expression of a number of NF-κB responsive genes involved in cytokine signaling, cell death, adhesion, inflammation and immune response, including two NF-κB subunits involved in the alternate NF-κB pathway, RELB and NFKB2. In contrast, CD19, a B cell marker, was one of the genes downregulated by K13. A comparison with K13-induced genes in human vascular endothelial cells revealed that although there was a considerable overlap among the genes induced by K13 in the two cell types, chemokines genes were preferentially induced in HUVEC with few exceptions, such as RANTES/CCL5, which was induced in both cell types. Functional studies confirmed that K13 activated the RANTES/CCL5 promoter through the NF-κB pathway. Taken collectively, our results suggest that K13 may contribute to the unique gene expression profile, immunophenotype and clinical presentation that are characteristics of KSHV-associated PEL.

Soft-Tissue Plasmacytomas in Multiple Myeloma: Incidence, Mechanisms of Extramedullary Spread, and Treatment Approach

We provide an overview on soft-tissue extramedullary plasmacytomas (EMPs) in multiple myeloma (MM). We reviewed the incidence of EMPs in MM, myeloma bone marrow homing, possible mechanisms of extramedullary spread, and prognosis and response to therapy. The incidence of EMPs is 7% to 18% at MM diagnosis and up to 20% at relapse. The current notion that EMPs are more frequent after treatment with novel agents remains to be proven, especially considering that different patterns of disease recurrence can emerge as patients live longer in the era of novel drugs. Bone marrow genetic abnormalities are not associated with extramedullary spread per se, which also suggests that microenvironmental interactions are key. Possible mechanisms of extramedullary spread include decreased adhesion molecule expression and downregulation of chemokine receptors. EMPs usually show plasmablastic morphology with negative CD56 expression. High-dose therapy with autologous stem-cell transplantation (ASCT) can overcome the negative prognostic impact of extramedullary disease in younger selected patients. EMPs do not typically respond to thalidomide alone, but in contrast, responses to bortezomib have been reported. The incidence of EMPs in patients with MM is high and is associated with poor outcome in patients treated conventionally. A potential first-line treatment option seems to be a bortezomib-containing regimen followed by ASCT, whenever possible. Experimental studies on the mechanisms of myeloma cell adhesion, myeloma growth at extramedullary sites, and drug sensitivity are priorities for this area of continuing therapeutic challenge.

A Novel Transgenic Mouse Model of the Human Multiple Myeloma Chromosomal Translocation t(14;16)(q32;q23)

Multiple myeloma (MM) is a currently incurable neoplasm of terminally differentiated B cells. The translocation and/or overexpression of c-MAF have been observed in human MM. Although c-MAF might function as an oncogene in human MM, there has been no report thus far describing the direct induction of MM by c-MAF overexpression in vivo. In this study, we have generated transgenic (TG) mice that express c-Maf specifically in the B-cell compartment. Aged c-Maf TG mice developed B-cell lymphomas with some clinical features that resembled those of MM, namely, plasma cell expansion and hyperglobulinemia. Quantitative RT-PCR analysis demonstrated that Ccnd2 and Itgb7, which are known target genes of c-Maf, were highly expressed in the lymphoma cells. This novel TG mouse model of the human MM t(14;16)(q32;q23) chromosomal translocation should serve to provide new insight into the role of c-MAF in tumorigenesis. Cancer Res; 71(2); 339–48. ©2011 AACR.

Msh6 protects mature B cells from lymphoma by preserving genomic stability

Most human B-cell non-Hodgkin's lymphomas arise from germinal centers. Within these sites, the mismatch repair factor MSH6 participates in antibody diversification. Reminiscent of the neoplasms arising in patients with Lynch syndrome III, mice deficient in MSH6 die prematurely of lymphoma. In this study, we characterized the B-cell tumors in MSH6-deficient mice and describe their histological, immunohistochemical, and molecular features, which include moderate microsatellite instability. Based on histological markers and gene expression, the tumor cells seem to be at or beyond the germinal center stage. The simultaneous loss of MSH6 and of activation-induced cytidine deaminase did not appreciably affect the survival of these animals, suggesting that these germinal center-like tumors arose by an activation-induced cytidine deaminase-independent pathway. We conclude that MSH6 protects B cells from neoplastic transformation by preserving genomic stability.

Eef1a2 promotes cell growth, inhibits apoptosis and activates JAK/STAT and AKT signaling in mouse plasmacytomas

Background

The canonical function of EEF1A2, normally expressed only in muscle, brain, and heart, is in translational elongation, but recent studies suggest a non-canonical function as a proto-oncogene that is overexpressed in a variety of solid tumors including breast and ovary. Transcriptional profiling of a spectrum of primary mouse B cell lineage neoplasms showed that transcripts encoding EEF1A2 were uniquely overexpressed in plasmacytomas (PCT), tumors of mature plasma cells. Cases of human multiple myeloma expressed significantly higher levels of EEF1A2 transcripts than normal bone marrow plasma cells. High-level expression was also a feature of a subset of cell lines developed from mouse PCT and from the human MM.

Methodology/Principal Findings

Heightened expression of EEF1A2 was not associated with increased copy number or coding sequence mutations. shRNA-mediated knockdown of Eef1a2 transcripts and protein was associated with growth inhibition due to delayed G1-S progression, and effects on apoptosis that were seen only under serum-starved conditions. Transcriptional profiles and western blot analyses of knockdown cells revealed impaired JAK/STAT and PI3K/AKT signaling suggesting their contributions to EEF1A2-mediated effects on PCT induction or progression.

Conclusions/Significance

EEF1A2 may play contribute to the induction or progression of some PCT and a small percentage of MM. Eef1a2 could also prove to be a useful new marker for a subset of MM and, ultimately, a possible target for therapy.

Anaplastic plasmacytomas: relationships to normal memory B cells and plasma cell neoplasms of immunodeficient and autoimmune mice

Anaplastic plasmacytomas (APCTs) from NFS.V(+) congenic mice and pristane-induced plasmacytic PCTs from BALB/c mice were previously shown to be histologically and molecularly distinct subsets of plasma cell neoplasms (PCNs). Here we extended these comparisons, contrasting primary APCTs and PCTs by gene expression profiling in relation to the expression profiles of normal naïve, germinal centre, and memory B cells and plasma cells. We also sequenced immunoglobulin genes from APCT and APCT-derived cell lines and defined surface phenotypes and chromosomal features of the cell lines by flow cytometry and by spectral karyotyping and fluorescence in situ hybridization. The results indicate that APCTs share many features with normal memory cells and the plasma cell-related neoplasms (PLs) of FASL-deficient mice, suggesting that APCTs and PLs are related and that both derive from memory B cells. Published in 2010 by John Wiley & Sons, Ltd.

IL-6 and MYC collaborate in plasma cell tumor formation in mice

Interleukin-6 (IL-6) plays a critical role in the natural history of human plasma cell neoplasms (PCNs), such as plasma cell myeloma and plasmacytoma (PCT). IL-6 is also at the center of neoplastic plasma cell transformation in BALB/c (C) mice carrying a transgene, H2-L(d)-IL6, that encodes human IL-6 under control of the major histocompatibility complex H2-L(d) promoter: strain C.H2-L(d)-IL6. These mice are prone to PCT, but tumor development is incomplete with long latencies ( approximately 40% PCT at 12 months of age). To generate a more robust mouse model of IL-6-dependent PCN, we intercrossed strain C.H2-L(d)-IL6 with strains C.iMyc(Emu) or C.iMyc(Calpha), 2 interrelated gene-insertion models of the chromosomal T(12;15) translocation causing deregulated expression of Myc in mouse PCT. Deregulation of MYC is also a prominent feature of human PCN. We found that double-transgenic C.H2-L(d)-IL6/iMyc(Emu) and C.H2-L(d)-IL6/iMyc(Calpha) mice develop PCT with full penetrance (100% tumor incidence) and short latencies (3-6 months). The mouse tumors mimic molecular hallmarks of their human tumor counterparts, including elevated IL-6/Stat3/Bcl-X(L) signaling. The newly developed mouse strains may provide a good preclinical research tool for the design and testing of new approaches to target IL-6 in treatment and prevention of human PCNs.

Emu-BCL10 mice exhibit constitutive activation of both canonical and noncanonical NF-kappaB pathways generating marginal zone (MZ) B-cell expansion as a precursor to splenic MZ lymphoma

BCL10, required for nuclear factor kappaB (NF-kappaB) activation during antigen-driven lymphocyte responses, is aberrantly expressed in mucosa-associated lymphoid tissue-type marginal zone (MZ) lymphomas because of chromosomal translocations. Emu-driven human BCL10 transgenic (Tg) mice, which we created and characterize here, had expanded populations of MZ B cells and reduced follicular and B1a cells. Splenic B cells from Tg mice exhibited constitutive activation of both canonical and noncanonical NF-kappaB signaling pathways is associated with increased expression of NF-kappaB target genes. These genes included Tnfsf13b, which encodes the B-cell activating factor (BAFF). In addition, levels of BAFF were significantly increased in sera from Tg mice. MZ B cells of Tg mice exhibited reduced turnover in vivo and enhanced survival in vitro, indicative of lymphoaccumulation rather than lymphoproliferation as the cause of MZ expansion. In vivo antibody responses to both T-independent, and especially T-dependent, antigens were significantly reduced in Tg mice. Mortality was accelerated in Tg animals, and some mice older than 8 months had histologic and molecular findings indicative of clonal splenic MZ lymphoma. These results suggest that, in addition to constitutive activation of BCL10 in MZ B cells, other genetic factors or environmental influences are required for short latency oncogenic transformation.

A mutant collagen XIII alters intestinal expression of immune response genes and predisposes transgenic mice to develop B-cell lymphomas

Epithelial cells of mucosal surfaces are critical for maintaining immune homeostasis by aiding in the discrimination of pathogenic and commensal microorganisms and modulating the activities of antigen-presenting cells and lymphocytes. Functional breakdowns resulting in chronic infection and inflammation are associated with the development of hematologic and solid neoplasms for which detailed pathogenetic mechanisms are poorly understood. Mice heterozygous for a transgene Col13a1(del) expressing a mutant collagen XIII developed clonal mature B-cell lineage lymphomas originating in mesenteric lymph nodes (MLN). The tumors were associated with T cells and macrophages. The incidence of disease was reduced 2-fold in transgenic mice raised under specific pathogen-free conditions, suggesting a role for infectious agents. The lymphomas did not express the mutant collagen XIII, indicating that its influence on tumorigenesis was B-cell extrinsic and likely to be associated with collagen XIII-positive tissues drained by the MLN. Studies of the small intestines of transgenic mice showed that the subepithelial basement membranes (BM) were highly abnormal and that they exhibited heightened expression of genes involved in immune responses. These results define collagen XIII-dependent maintenance of the intestinal BM as a previously unappreciated component of immune responses and a critical determinant of cancer susceptibility.

NOTCH is part of the transcriptional network regulating cell growth and survival in mouse plasmacytomas

Aside from Myc-activating translocations characteristic of plasmacytomas (PCT), little is known about genetic factors and signaling pathways responsible for the development of spontaneous B-cell lineage lymphomas of mice. Here, we characterized the transcriptional profiles of PCT, centroblastic diffuse large B-cell lymphomas (CBL), and high-grade splenic marginal zone B-cell lymphoma (MZL++) using high-throughput quantitative reverse transcription-PCR. Expression profiles of CBL and MZL++ were strikingly similar and quite unlike that of PCT. Among the genes expressed at significantly higher levels by PCT were a number involved in NOTCH signaling, a finding supported by gene set enrichment analyses of microarray data. To investigate the importance of this pathway, NOTCH signaling was blocked in PCT cell lines by treatment with a gamma-secretase inhibitor (GSI) or transduction of a dominant-negative mutant of MAML1. These treatments resulted in reduced expression of NOTCH transcriptional targets in association with impaired proliferation and increased apoptosis. GSI treatment of transformed plasma cells in a primary PCT also induced apoptosis. These results integrate NOTCH activation with oncogenic signaling pathways downstream of translocated Myc in the pathogenesis of mouse PCT, two signaling pathways also implicated in development of human multiple myeloma and T-cell lymphoblastic lymphoma.