Expression of cyclin D1 in mouse B cell lymphomas of different histologic types and differentiation stages

Early Generated B-1-Derived B Cells Have the Capacity To Progress To Become Mantle Cell Lymphoma-like Neoplasia in Aged Mice

In mice, fetal/neonatal B-1 cell development generates murine CD5⁺ B cells (B1a) with autoreactivity. We analyzed B1a cells at the neonatal stage in a V_H11/D/J_H knock-in mouse line (V_H11t) that generates an autoreactive antiphosphatidylcholine BCR. Our study revealed that antiphosphatidylcholine B1a cells develop in liver, mature in spleen, and distribute in intestine/colon, mesenteric lymph node (mLN), and body cavity as the outcome of B-1 cell development before B-2 cell development. Throughout life, self-renewing B-1 B1a cells circulate through intestine, mesenteric vessel, and blood. The body cavity-deposited B1a cells also remigrate. In old age, some B1a cells proceed to monoclonal B cell lymphocytosis. When neonatal B-1 B1a cells express an antithymocyte/Thy-1 autoreactivity (ATA) BCR transgene in the C.B17 mouse background, ATA B cells increase in PBL and strongly develop lymphomas in aging mice that feature splenomegaly and mLN hyperplasia with heightened expression of CD11b, IL-10, and activated Stat3. At the adult stage, ATA B cells were normally present in the mantle zone area, including in intestine. Furthermore, frequent association with mLN hyperplasia suggests the influence by intestinal microenvironment on lymphoma development. When cyclin D1 was overexpressed by the Eμ-cyclin D1 transgene, ATA B cells progressed to further diffused lymphoma in aged mice, including in various lymph nodes with accumulation of IgM^hiIgD^loCD5⁺CD23^-CD43⁺ cells, resembling aggressive human mantle cell lymphoma. Thus, our findings reveal that early generated B cells, as an outcome of B-1 cell development, can progress to become lymphocytosis, lymphoma, and mantle cell lymphoma-like neoplasia in aged mice.

Leptin signaling maintains B-cell homeostasis via induction of Bcl-2 and Cyclin D1

Regulation of apoptosis and cell cycle progression plays an essential role in the maintenance of B-cell homeostasis, because a fine balance of survival and expansion is critical for preventing lymphocytic disorders. Although remarkable progress in understanding B-cell development has been achieved, much less is known concerning niches that are critical to the maintenance of B-cell homeostasis. Leptin has recently been recognized to be important for modulating the immune responses, but it has remained unclear how leptin signaling influences B-cell physiology. A variety of lymphocytic malignancies have been reported to be linked to leptin, and therefore it is necessary to elucidate the mechanisms involved. Here we demonstrate that leptin promotes B-cell homeostasis by inhibiting apoptosis and by inducing cell cycle entry through the activation of expressions of B-cell CLL/lymphoma 2 (Bcl-2) and cyclin D1. We further show that leptin can induce Bcl-2 and cyclin D1 expression by two pathways, including the direct activation of their promoters and suppression of microRNAs (miRNAs) that target their putative 3'untranslated regions. Amplification of these leptin-modulated miRNAs inhibited B lymphoma cell growth. These findings provide insights into mechanisms for leptin regulation of the humoral immune system and suggest new therapeutic strategies for leptin receptor expressing malignancies.

A comprehensive antibody panel for immunohistochemical analysis of formalin-fixed, paraffin-embedded hematopoietic neoplasms of mice: analysis of mouse specific and human antibodies cross-reactive with murine tissue

Immunohistochemistry is an indispensable tool in human pathology enabling immunophenotypic characterization of tumor cells. Immunohistochemical analyses of mouse models of human hematopoietic neoplasias have become an important aspect for comparison of murine entities with their human counterparts. The aim of this study was to establish a diagnostic antibody panel for analysis of murine lymphomas/leukemias, useful in formalin-fixed/paraffin-embedded tissue. Overall, 48 antibodies (4 rabbit monoclonal, 12 rabbit polyclonal, 2 goat polyclonal, 11 rat, and 19 mouse monoclonal), which were either mouse-specific (14) or cross-reactive with murine tissue (34) were tested for staining quality and diagnostic value in 468 murine hematopoietic neoplasms. Specific staining was achieved with 29 antibodies, of which 18 were human antibodies cross-reactive with murine tissue. Only 23 (B220, BCL-2, BCL-6, CD117, CD138 (2x), CD3 (2x), CD43, CD45, CD5, CD79 alpha cy, cyclin D1, Ki-67 (2x), Mac-3, Mac-2, lysozyme, mast cell tryptase, MPO, Pax-5, TdT, and TER-119) were regarded as valuable for diagnostic evaluation. Immunohistochemistry was also established in an automated immunostainer for high throughput analysis. The antibody panel developed is useful for the classification of murine lymphomas and leukemias analyzed, and a valuable tool for human and veterinary pathologists involved in the diagnostic interpretation of murine models of hematopoietic neoplasias.

Expression of the cyclin-dependent kinase inhibitor p27 and its deregulation in mouse B cell lymphomas

CDKN1B (p27) regulates cell-cycle progression at the G1-S transition by suppressing the cyclin E/CDK2 kinase complex. In normal lymphocytes and most human B cell non-Hodgkin lymphomas (NHL), there is an inverse correlation between proliferative activity and expression of p27; however, a subset of NHL with high mitotic indices expresses p27, which is inactive due to sequestration in nuclear protein complexes or due to cytoplasmic retention. Our studies of mouse B cell NHL also identified cases with high proliferative activity and high levels of p27 at a surprisingly high frequency. Here, p27 was complexed with D-type cyclins 1 and 3 and with the COPS9 protein, JAB1. In addition, we found cytoplasmic sequestration following phosphorylation by activated AKT.

Genomic organisation and expression of BCL6 in murine B-cell lymphomas

BCL6 encodes a transcription factor deregulated by chromosomal translocations in human diffuse large cell B lymphomas (DLCL). This study was designed to determine whether Bcl6 might also be involved in lymphomas of mice. BCL6 protein was expressed at high levels in 90% or more of DLCL but not in low grade B lymphomas. Southern hybridisation studies demonstrated altered organisation of Bcl6 in three primary DLCL and the WEHI 231 B-cell lymphoma cell line but not in low grade tumours. Chromosomal painting and fluorescence in situ hybridisation (FISH) analyses of the WEHI 231 metaphase spreads revealed a T(5;16) translocation with Bcl6 on Chromosome 16 at the translocation breakpoint. Deregulated expression of BCL6 is thus likely to contribute to the genesis of DLCL of mice as well as of humans.

Accelerated appearance of multiple B cell lymphoma types in NFS/N mice congenic for ecotropic murine leukemia viruses

Spontaneous lymphomas occur at high frequency in NFS x V+ mice, strains congenic for ecotropic murine leukemia virus (MuLV) proviral genes and expressing virus at high titer. In the present study, a total of 703 NFS x V+ lymphomas were studied by histopathology, immunophenotypic analysis, immunoglobulin heavy chain or T cell receptor beta chain rearrangements, and somatic ecotropic MuLV integrations; 90% of the lymphomas tested were of B cell lineage. Low-grade tumors included small lymphocytic, follicular, and splenic marginal zone lymphomas, while high-grade tumors comprised diffuse large-cell (centroblastic and immunoblastic types), splenic marginal zone, and lymphoblastic lymphomas. Comparison of mice of similar genetic background except for presence (NFS x V+) or absence (NFS x V-) of functional ecotropic MuLV genomes showed that NFS x V-clonal lymphomas developed at about one-half the rate of those occurring in NFS x V+ mice, and most were low-grade B cell lymphomas with extended latent periods. In NFS x V+ mice, clonal outgrowth, defined by Ig gene rearrangements, was associated with acquisition of somatic ecotropic proviral integrations, suggesting that, although generation of B cell clones can be virus independent, ecotropic virus may act to increase the rate of generation of clones and speed their evolution to lymphoma. The mechanism remains undefined, because only rare rearrangements were detected in several cellular loci previously associated with MuLV insertional mutagenesis.

Differential regulation of germinal center genes, BCL6 and SWAP-70, during the course of MAIDS

Germinal centers (GC) are the sites of antigen-driven B cell switch recombination, V(D)J gene hypermutation, and selection to generate high-afinity CD38+ memory B cells. A marked expansion of GC associated with hypergammaglobulinemia followed by complete disruption of normal splenic architecture and a striking drop in immunoglobulin levels are prominent features of the murine retrovirus-induced immunodeficiency syndrome, MAIDS. B cell lymphomas are frequent in long-term infected mice. Normal GC formation is critically dependent on a number of genes including the transcription factor, Bcl6. Deregulated expression of BCL6 protein has been implicated in the development of human and mouse B cell lymphomas. Another nuclear protein, SWAP-70, has been identified as a subunit of the protein complex, SWAP, that recombines switch regions in vitro. To develop a fuller understanding of B cell biology in MAIDS, we examined the characteristics of BCL6, SWAP-70, CD38, and peanut agglutinin (PNA)-staining cells during the course of the disease. The levels of both nuclear proteins increased rapidly until 6-8 weeks after infection. During this time frame, BCL6 was expressed at highest levels in the usually rare CD4+ Thyl- T cell subset as well as in B cells. At later times. BCL6 levels dropped to undetectable levels while SWAP-70 levels continued to increase. Changes in the levels of either protein could not be ascribed to transcriptional regulation. PNA-reactive cells decreased in concert with BCL6 while CD38 staining increased with SWAP-70. These results demonstrate that progression of MAIDS results in the massive accumulation of B cells with the morphology of secretory cells that behave like post-GC cells for expression of BCL6 and CD38, and for PNA-staining but with abnormally high-level expression of SWAP-70.