Frap, FKBP12 rapamycin-associated protein, is a candidate gene for the plasmacytoma resistance locus Pctr2 and can act as a tumor suppressor gene

Critical role for cap-independent c-myc translation in progression of multiple myeloma

Dysregulated c-myc is a determinant of multiple myeloma (MM) progression. Translation of c-myc can be achieved by an mTOR-mediated, cap-dependent mechanism or a cap-independent mechanism where a sequence in the 5'UTR of mRNA, termed the IRES (internal ribosome entry site), recruits the 40S ribosomal subunit. This mechanism requires the RNA-binding factor hnRNP A1 (A1) and becomes critical when cap-dependent translation is inhibited during endoplasmic reticulum (ER) stress. We, thus, studied the role of A1 and the myc IRES in myeloma biology. A1 expression correlated with enhanced c-myc expression in patient samples. Expression of A1 in MM lines was mediated by c-myc itself, suggesting a positive feed-back circuit where myc induces A1 and A1 enhances myc translation. We then deleted the A1 gene in a myc-driven murine myeloma model. A1-deleted MM cells demonstrated down-regulated myc expression and were inhibited in their growth in vivo. Decreased myc expression was due to reduced translational efficiency and depressed IRES activity. We also studied the J007 inhibitor which prevents A1's interaction with the myc IRES. J007 inhibited myc translation and IRES activity and diminished myc expression in murine and human MM lines as well as primary samples. J007 also inhibited tumor outgrowth in mice after subcutaneous or intravenous challenge and prevented osteolytic bone disease. When c-myc was ectopically re-expressed in A1-deleted MM cells, tumor growth was re-established. These results support the critical role of A1-dependent myc IRES-translation in myeloma.

Conditional deletion of mTOR discloses its essential role in early B-cell development

Mechanistic target of rapamycin (mTOR) is a serine-threonine kinase and central regulator of cell growth, differentiation, and survival. mTOR is commonly hyperactivated in a diverse number of cancers and critical roles for mTOR in regulating immune cell differentiation and function have been demonstrated. However, there is little work investigating the roles of mTOR in early B-cell development. Here we demonstrate that conditional disruption of mTOR in developing mouse B cells results in reduced pre-B-cell proliferation and survival, as well as a developmental block at the pre-B-cell stage, with a corresponding lack of peripheral B cells. Upon immunization with NP-CGG antigen, mice with Mtor conditional disruption in early B cells lost their ability to form germinal centers and produce specific antibodies. In competitive BM repopulation assays, donor BM cells from conditional knock-out mice were completely impaired in their ability to reconstitute B cells. Our data reveal the essential role of mTOR in early pre-B-cell development and survival.

Laboratory Mice - A Driving Force in Immunopathology and Immunotherapy Studies of Human Multiple Myeloma

Mouse models of human cancer provide an important research tool for elucidating the natural history of neoplastic growth and developing new treatment and prevention approaches. This is particularly true for multiple myeloma (MM), a common and largely incurable neoplasm of post-germinal center, immunoglobulin-producing B lymphocytes, called plasma cells, that reside in the hematopoietic bone marrow (BM) and cause osteolytic lesions and kidney failure among other forms of end-organ damage. The most widely used mouse models used to aid drug and immunotherapy development rely on in vivo propagation of human myeloma cells in immunodeficient hosts (xenografting) or myeloma-like mouse plasma cells in immunocompetent hosts (autografting). Both strategies have made and continue to make valuable contributions to preclinical myeloma, including immune research, yet are ill-suited for studies on tumor development (oncogenesis). Genetically engineered mouse models (GEMMs), such as the widely known Vκ*MYC, may overcome this shortcoming because plasma cell tumors (PCTs) develop de novo (spontaneously) in a highly predictable fashion and accurately recapitulate many hallmarks of human myeloma. Moreover, PCTs arise in an intact organism able to mount a complete innate and adaptive immune response and tumor development reproduces the natural course of human myelomagenesis, beginning with monoclonal gammopathy of undetermined significance (MGUS), progressing to smoldering myeloma (SMM), and eventually transitioning to frank neoplasia. Here we review the utility of transplantation-based and transgenic mouse models of human MM for research on immunopathology and -therapy of plasma cell malignancies, discuss strengths and weaknesses of different experimental approaches, and outline opportunities for closing knowledge gaps, improving the outcome of patients with myeloma, and working towards a cure.

Mouse tumor susceptibility genes identify drug combinations for multiple myeloma

Long-term genetic studies utilizing backcross and congenic strain analyses coupled with positional cloning strategies and functional studies identified Cdkn2a, Mtor, and Mndal as mouse plasmacytoma susceptibility/resistance genes. Tumor incidence data in congenic strains carrying the resistance alleles of Cdkn2a and Mtor led us to hypothesize that drug combinations affecting these pathways are likely to have an additive, if not synergistic effect in inhibiting tumor cell growth. Traditional and novel systems-level genomic approaches were used to assess combination activity, disease specificity, and clinical potential of a drug combination involving rapamycin/everolimus, an Mtor inhibitor, with entinostat, an histone deacetylase inhibitor. The combination synergistically repressed oncogenic MYC and activated the Cdkn2a tumor suppressor. The identification of MYC as a primary upstream regulator led to the identification of small molecule binders of the G-quadruplex structure that forms in the NHEIII region of the MYC promoter. These studies highlight the importance of identifying drug combinations which simultaneously upregulate tumor suppressors and downregulate oncogenes.

The transcription factor MZF1 differentially regulates murine Mtor promoter variants linked to tumor susceptibility

Mechanistic target of rapamycin (MTOR) is a highly conserved serine/threonine kinase that critically regulates cell growth, proliferation, differentiation, and survival. Previously, we have implicated Mtor as a plasmacytoma-resistance locus, Pctr2, in mice. Here, we report that administration of the tumor-inducing agent pristane decreases Mtor gene expression to a greater extent in mesenteric lymph nodes of BALB/cAnPt mice than of DBA/2N mice. We identified six allelic variants in the Mtor promoter region in BALB/cAnPt and DBA/2N mice. To determine the effects of these variants on Mtor transcription, we constructed a series of luciferase reporters containing these promoter variants and transfected them into mouse plasmacytoma cells. We could attribute the differences in Mtor promoter activity between the two mouse strains to a C → T change at the -6 position relative to the transcriptional start site Tssr 40273; a T at this position in the BALB promoter creates a consensus binding site for the transcription factor MZF1 (myeloid zinc finger 1). Results from electrophoretic mobility shift assays and DNA pulldown assays with ChIP-PCR confirmed that MZF1 binds to the cis-element TGGGGA located in the -6/-1 Mtor promoter region. Of note, MZF1 significantly and differentially down-regulated Mtor promoter activity, with MZF1 overexpression reducing Mtor expression more strongly in BALB mice than in DBA mice. Moreover, MZF1 overexpression reduced Mtor expression in both fibroblasts and mouse plasmacytoma cells, and Mzf1 knockdown increased Mtor expression in BALB3T3 and NIH3T3 fibroblast cells. Our results provide evidence that MZF1 down-regulates Mtor expression in pristane-induced plasmacytomas in mice.

The Effects of Genetic Background of Mouse Models of Cancer: Friend or Foe?

Over the past century, mice have been selectively bred to give rise to the strains used in biomedical research today. Mouse models of cancer allow researchers to control variables of diet, environment, and genetic heterogeneity to better dissect the role of these factors in cancer in humans. Because of the important role of genetic background in cancer, the strain of the mouse can introduce confounding results in studies of mouse models if not properly controlled. Conversely, genetic variation between strains can also provide important new insights into cancer mechanisms. Here, the sources of genetic heterogeneity in mouse models are reviewed, with an explanation of how heterogeneity modifies cancer phenotypes.

Therapeutic potential of targeting IRES-dependent c-myc translation in multiple myeloma cells during ER stress

Protein translation is inhibited by the unfolded protein response (UPR)-induced eIF-2α phosphorylation to protect against endoplasmic reticulum (ER) stress. In addition, we found additional inhibition of protein translation owing to diminished mTORC1 (mammalian target of rapamycin complex1) activity in ER-stressed multiple myeloma (MM) cells. However, c-myc protein levels and myc translation was maintained. To ascertain how c-myc was maintained, we studied myc IRES (internal ribosome entry site) function, which does not require mTORC1 activity. Myc IRES activity was upregulated in MM cells during ER stress induced by thapsigargin, tunicamycin or the myeloma therapeutic bortezomib. IRES activity was dependent on upstream MAPK (mitogen-activated protein kinase) and MNK1 (MAPK-interacting serine/threonine kinase 1) signaling. A screen identified hnRNP A1 (A1) and RPS25 as IRES-binding trans-acting factors required for ER stress-activated activity. A1 associated with RPS25 during ER stress and this was prevented by an MNK inhibitor. In a proof of principle, we identified a compound that prevented binding of A1 to the myc IRES and specifically inhibited myc IRES activity in MM cells. This compound, when used alone, was not cytotoxic nor did it inhibit myc translation or protein expression. However, when combined with ER stress inducers, especially bortezomib, a remarkable synergistic cytotoxicity ensued with associated inhibition of myc translation and expression. These results underscore the potential for targeting A1-mediated myc IRES activity in MM cells during ER stress.

Identification of known drugs targeting the endoplasmic reticulum stress response

The endoplasmic reticulum (ER), a multifunctional organelle, plays a central role in cellular signaling, development, and stress response. Dysregulation of ER homeostasis has been associated with human diseases, such as cancer, inflammation, and diabetes. A broad spectrum of stressful stimuli including hypoxia as well as a variety of pharmacological agents can lead to the ER stress response. In this study, we have developed a stable ER stress reporter cell line that stably expresses a β-lactamase reporter gene under the control of the ER stress response element (ESRE) present in the glucose-regulated protein, 78 kDa (GRP78) gene promoter. This assay has been optimized and miniaturized into a 1536-well plate format. In order to identify clinically used drugs that induce ER stress response, we screened approximately 2800 drugs from the NIH Chemical Genomics Center Pharmaceutical Collection (NPC library) using a quantitative high-throughput screening (qHTS) platform. From this study, we have identified several known ER stress inducers, such as 17-AAG (via HSP90 inhibition), as well as several novel ER stress inducers such as AMI-193 and spiperone. The confirmed drugs were further studied for their effects on the phosphorylation of eukaryotic initiation factor 2α (eIF2α), the X-box-binding protein (XBP1) splicing, and GRP78 gene expression. These results suggest that the ER stress inducers identified from the NPC library using the qHTS approach could shed new lights on the potential therapeutic targets of these drugs.

DEPTOR is linked to a TORC1-p21 survival proliferation pathway in multiple myeloma cells

We investigated the mechanism by which gene silencing of the mTOR inhibitor, DEPTOR, induces cytoreductive effects on multiple myeloma (MM) cells. DEPTOR knockdown resulted in anti-MM effects in several MM cell lines. Using an inducible shRNA to silence DEPTOR, 8226 MM cells underwent TORC1 activation, downregulation of AKT/SGK activity, apoptosis, cell cycle arrest and senescence. These latter cytotoxic effects were prevented by TORC1 paralysis (Raptor knockdown) but not by over-expression of AKT activity. In addition, DEPTOR knockdown-induced MM death was not associated with activation of the unfolded protein response, suggesting that enhanced ER stress did not play a role. In contrast, DEPTOR knockdown in 8226 cells induced p21 expression, independent of p53, and p21 knockdown prevented all of the cytotoxic effects following DEPTOR silencing. DEPTOR silencing resulted in p21 upregulation in additional MM cell lines. Furthermore, DEPTOR silencing in a murine xenograft model resulted in anti-MM effects associated with p21 upregulation. DEPTOR knockdown also resulted in a decreased expression of p21-targeting miRNAs and transfection of miRNA mimics prevented p21 upregulation and apoptosis following DEPTOR silencing. Use of a shRNA-resistant DEPTOR construct ruled out off-target effects of the shRNA. These results indicate that DEPTOR regulates growth and survival of MM cells via a TORC1/p21 pathway and suggest an involvement of p21-targeted miRNAs.

Preclinical validation of interleukin 6 as a therapeutic target in multiple myeloma

Studies on the biologic and molecular genetic underpinnings of multiple myeloma (MM) have identified the pleiotropic, pro-inflammatory cytokine, interleukin-6 (IL-6), as a factor crucial to the growth, proliferation and survival of myeloma cells. IL-6 is also a potent stimulator of osteoclastogenesis and a sculptor of the tumor microenvironment in the bone marrow of patients with myeloma. This knowledge has engendered considerable interest in targeting IL-6 for therapeutic purposes, using a variety of antibody- and small-molecule-based therapies. However, despite the early recognition of the importance of IL-6 for myeloma and the steady progress in our knowledge of IL-6 in normal and malignant development of plasma cells, additional efforts will be required to translate the promise of IL-6 as a target for new myeloma therapies into significant clinical benefits for patients with myeloma. This review summarizes published research on the role of IL-6 in myeloma development and describes ongoing efforts by the University of Iowa Myeloma Multidisciplinary Oncology Group to develop new approaches to the design and testing of IL-6-targeted therapies and preventions of MM.

TORC1 and class I HDAC inhibitors synergize to suppress mature B cell neoplasms

Enhanced proliferative signaling and loss of cell cycle regulation are essential for cancer progression. Increased mitogenic signaling through activation of the mTOR pathway, coupled with deregulation of the Cyclin D/retinoblastoma (Rb) pathway is a common feature of lymphoid malignancies, including plasmacytoma (PCT), multiple myeloma (MM), Burkitt's lymphoma (BL), and mantle cell lymphoma (MCL). Here we evaluate the synergy of pharmacologically affecting both of these critical pathways using the mTOR inhibitor sirolimus and the histone deacetylase inhibitor entinostat. A dose-matrix screening approach found this combination to be highly active and synergistic in a panel of genetically diverse human MM cell lines. Synergy and activity was observed in mouse PCT and human BL and MCL cell lines tested in vitro, as well as in freshly isolated primary MM patient samples tested ex vivo. This combination had minimal effects on healthy donor cells and retained activity when tested in a co-culture system simulating the protective interaction of cancer cells with the tumor microenvironment. Combining sirolimus with entinostat enhanced cell cycle arrest and apoptosis. At the molecular level, entinostat increased the expression of cell cycle negative regulators including CDKN1A (p21) and CDKN2A (p16), while the combination decreased critical growth and survival effectors including Cyclin D, BCL-XL, BIRC5, and activated MAPK.

Waldenström macroglobulinemia: clinical and immunological aspects, natural history, cell of origin, and emerging mouse models

Waldenström macroglobulinemia (WM) is a rare and currently incurable neoplasm of IgM-expressing B-lymphocytes that is characterized by the occurrence of a monoclonal IgM (mIgM) paraprotein in blood serum and the infiltration of the hematopoietic bone marrow with malignant lymphoplasmacytic cells. The symptoms of patients with WM can be attributed to the extent and tissue sites of tumor cell infiltration and the magnitude and immunological specificity of the paraprotein. WM presents fascinating clues on neoplastic B-cell development, including the recent discovery of a specific gain-of-function mutation in the MYD88 adapter protein. This not only provides an intriguing link to new findings that natural effector IgM⁺IgD⁺ memory B-cells are dependent on MYD88 signaling, but also supports the hypothesis that WM derives from primitive, innate-like B-cells, such as marginal zone and B1 B-cells. Following a brief review of the clinical aspects and natural history of WM, this review discusses the thorny issue of WM's cell of origin in greater depth. Also included are emerging, genetically engineered mouse models of human WM that may enhance our understanding of the biologic and genetic underpinnings of the disease and facilitate the design and testing of new approaches to treat and prevent WM more effectively.

Global gene expression profiling in mouse plasma cell tumor precursor and bystander cells reveals potential intervention targets for plasma cell neoplasia

Tumor progression usually proceeds through several sequential stages, any of which could be targets for interrupting the progression process if one understood these steps at the molecular level. We extracted nascent plasma cell tumor (PCT) cells from within inflammatory oil granulomas (OG) isolated from IP pristane-injected BALB/c.iMyc(Eμ) mice at 5 different time points during tumor progression. We used laser capture microdissection to collect incipient PCT cells and analyzed their global gene expression on Affymetrix Mouse Genome 430A microarrays. Two independent studies were performed with different sets of mice. Analysis of the expression data used ANOVA and Bayesian estimation of temporal regulation. Genetic pathway analysis was performed using MetaCore (GeneGo) and IPA (Ingenuity). The gene expression profiles of PCT samples and those of undissected OG samples from adjacent sections showed that different genes and pathways were mobilized in the tumor cells during tumor progression, compared with their stroma. Our analysis implicated several genetic pathways in PCT progression, including biphasic (up- and then down-regulation) of the Spp1/osteopontin-dependent network and up-regulation of mRNA translation/protein synthesis. The latter led to a biologic validation study that showed that the AMPK-activating diabetes drug, metformin, was a potent specific PCT inhibitor in vitro.

Loci controlling lymphocyte production of interferon c after alloantigen stimulation in vitro and their co-localization with genes controlling lymphocyte infiltration of tumors and tumor susceptibility

Low infiltration of lymphocytes into cancers is associated with poor prognosis, but the reasons why some patients exhibit a low and others a high infiltration of tumors are unknown. Previously we mapped four loci (Lynf1–Lynf4) controlling lymphocyte infiltration of mouse lung tumors. These loci do not encode any of the molecules that are involved in traffic of lymphocytes. Here we report a genetic relationship between these loci and the control of production of IFNγ in allogeneic mixed lymphocyte cultures (MLC). We found that IFNγ production by lymphocytes of O20/A mice is lower than by lymphocytes of OcB-9/Dem mice (both H2^pz) stimulated in MLC by irradiated splenocytes of C57BL/10SnPh (H2^b) or BALB/cHeA (H2^d) mice, or by ConA. IFNγ production in MLCs of individual (O20 × OcB-9)F₂ mice stimulated by irradiated C57BL/10 splenocytes and genotyped for microsatellite markers revealed four IFNγ-controlling loci (Cypr4-Cypr7), each of which is closely linked with one of the four Lynf loci and with a cluster of susceptibility genes for different tumors. This suggests that inherited differences in certain lymphocyte responses may modify their propensity to infiltrate tumors and their capacity to affect tumor growth.

Constitutive reductions in mTOR alter cell size, immune cell development, and antibody production

Mammalian TOR (mTOR) regulates cell growth, proliferation, and migration. Because mTOR knock-outs are embryonic lethal, we generated a viable hypomorphic mouse by neo-insertion that partially disrupts mTOR transcription and creates a potential physiologic model of mTORC1/TORC2 inhibition. Homozygous knock-in mice exhibited reductions in body, organ, and cell size. Although reductions in most organ sizes were proportional to decreased body weight, spleens were disproportionately smaller. Decreases in the total number of T cells, particularly memory cells, and reduced responses to chemokines suggested alterations in T-cell homing/homeostasis. T-cell receptor-stimulated T cells proliferated less, produced lower cytokine levels, and expressed FoxP3. Decreased neutrophil numbers were also observed in the spleen, despite normal development and migration in the bone marrow. However, B-cell effects were most pronounced, with a partial block in B-cell development in the bone marrow, altered splenic populations, and decreases in proliferation, antibody production, and migration to chemokines. Moreover, increased AKT(Ser473) phosphorylation was observed in activated B cells, reminiscent of cancers treated with rapamycin, and was reduced by a DNA-pk inhibitor. Thus, mTOR is required for the maturation and differentiation of multiple immune cell lineages. These mice provide a novel platform for studying the consequences of constitutively reduced mTORC1/TORC2 activity.

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.

Pharmacogenomics: a new paradigm to personalize treatments in nephrology patients

Although notable progress has been made in the therapeutic management of patients with chronic kidney disease in both conservative and renal replacement treatments (dialysis and transplantation), the occurrence of medication-related problems (lack of efficacy, adverse drug reactions) still represents a key clinical issue. Recent evidence suggests that adverse drug reactions are major causes of death and hospital admission in Europe and the United States. The reasons for these conditions are represented by environmental/non-genetic and genetic factors responsible for the great inter-patient variability in drugs metabolism, disposition and therapeutic targets. Over the years several genetic settings have been linked, using pharmacogenetic approaches, to the effects and toxicity of many agents used in clinical nephrology. However, these strategies, analysing single gene or candidate pathways, do not represent the gold standard, being the overall pharmacological effects of medications and not typically monogenic traits. Therefore, to identify multi-genetic influence on drug response, researchers and clinicians from different fields of medicine and pharmacology have started to perform pharmacogenomic studies employing innovative whole genomic high-throughput technologies. However, to date, only few pharmacogenomics reports have been published in nephrology underlying the need to enhance the number of projects and to increase the research budget for this important research field. In the future we would expect that, applying the knowledge about an individual's inherited response to drugs, nephrologists will be able to prescribe medications based on each person's genetic make-up, to monitor carefully the efficacy/toxicity of a given drug and to modify the dosage or number of medications to obtain predefined clinical outcomes.

Mndal, a new interferon-inducible family member, is highly polymorphic, suppresses cell growth, and may modify plasmacytoma susceptibility

The human HIN-200 gene cluster and its mouse counterpart, the interferon inducible-200 (Ifi200) family, both on Chr 1, are associated with several diseases, including solid tumors and lupus. Our study was initiated to identify the modifier gene(s) encoded by the Pctm locus, in which mouse B-cell plasmacytomas induced by pristane are associated with heterozygosity of Chr 1 genes near the Ifi200 cluster. A screen for differentially expressed genes in granulomatous tissues induced by pristane in resistant and susceptible strains identified a new Ifi200 member whose expression was 1000-fold higher in the strain carrying the resistant allele of Pctm and was the most highly expressed Ifi200 gene. The gene, designated Mndal (for MNDA-like, myeloid nuclear differentiation antigen-like), was absent in the susceptible genome, as were genomic sequences upstream of Ifi203, the gene adjacent to Mndal. Ectopic expression of MNDAL suppressed cell growth, which, together with the disease susceptibility of heterozygotes at the Pctm locus, suggests that Mndal, perhaps with Ifi203, acts as a tumor suppressor and display(s) haploinsufficiency. Mndal is highly polymorphic among inbred mouse strains, because it is absent in 10 of 24 strains. This polymorphism may have implications for other disease modifiers mapping to the same region.

DEPTOR is an mTOR inhibitor frequently overexpressed in multiple myeloma cells and required for their survival

The mTORC1 and mTORC2 pathways regulate cell growth, proliferation, and survival. We identify DEPTOR as an mTOR-interacting protein whose expression is negatively regulated by mTORC1 and mTORC2. Loss of DEPTOR activates S6K1, Akt, and SGK1, promotes cell growth and survival, and activates mTORC1 and mTORC2 kinase activities. DEPTOR overexpression suppresses S6K1 but, by relieving feedback inhibition from mTORC1 to PI3K signaling, activates Akt. Consistent with many human cancers having activated mTORC1 and mTORC2 pathways, DEPTOR expression is low in most cancers. Surprisingly, DEPTOR is highly overexpressed in a subset of multiple myelomas harboring cyclin D1/D3 or c-MAF/MAFB translocations. In these cells, high DEPTOR expression is necessary to maintain PI3K and Akt activation and a reduction in DEPTOR levels leads to apoptosis. Thus, we identify a novel mTOR-interacting protein whose deregulated overexpression in multiple myeloma cells represents a mechanism for activating PI3K/Akt signaling and promoting cell survival.

Brain tumor susceptibility: the role of genetic factors and uses of mouse models to unravel risk

Brain tumors are relatively rare but deadly cancers, and present challenges in the determination of risk factors in the population. These tumors are inherently difficult to cure because of their protected location in the brain, with surgery, radiation and chemotherapy options carrying potentially lasting morbidity for patients and incomplete cure of the tumor. The development of methods to prevent or detect brain tumors at an early stage is extremely important to reduce damage to the brain from the tumor and the therapy. Developing effective prevention or early detection methods requires a deep understanding of the risk factors for brain tumors. This review explores the difficulties in assessing risk factors in rare diseases such as brain tumors, and discusses how mouse models of cancer can aid in a better understanding of genetic risk factors for brain tumors.

A Transgenic Mouse Model of Plasma Cell Malignancy Shows Phenotypic, Cytogenetic, and Gene Expression Heterogeneity Similar to Human Multiple Myeloma

Multiple myeloma is an incurable plasma cell malignancy for which existing animal models are limited. We have previously shown that the targeted expression of the transgenes c-Myc and Bcl-X(L) in murine plasma cells produces malignancy that displays features of human myeloma, such as localization of tumor cells to the bone marrow and lytic bone lesions. We have isolated and characterized in vitro cultures and adoptive transfers of tumors from Bcl-xl/Myc transgenic mice. Tumors have a plasmablastic morphology and variable expression of CD138, CD45, CD38, and CD19. Spectral karyotyping analysis of metaphase chromosomes from primary tumor cell cultures shows that the Bcl-xl/Myc tumors contain a variety of chromosomal abnormalities, including trisomies, translocations, and deletions. The most frequently aberrant chromosomes are 12 and 16. Three sites for recurring translocations were also identified on chromosomes 4D, 12F, and 16C. Gene expression profiling was used to identify differences in gene expression between tumor cells and normal plasma cells (NPC) and to cluster the tumors into two groups (tumor groups C and D), with distinct gene expression profiles. Four hundred and ninety-five genes were significantly different between both tumor groups and NPCs, whereas 124 genes were uniquely different from NPCs in tumor group C and 204 genes were uniquely different from NPCs in tumor group D. Similar to human myeloma, the cyclin D genes are differentially dysregulated in the mouse tumor groups. These data suggest the Bcl-xl/Myc tumors are similar to a subset of plasmablastic human myelomas and provide insight into the specific genes and pathways underlying the human disease.

Plasma cell tumour progression in iMycEmu gene-insertion mice

The authors have recently reported that gene-targeted iMyc(Emu) mice that carry a His(6)-tagged mouse Myc cDNA, Myc(His), just 5' of the immunoglobulin heavy-chain enhancer, Emu, are prone to 'spontaneous' neoplasms of the B-lymphocyte lineage. The present study has used histological, immunohistochemical, and molecular genetic methods to investigate a subset of these neoplasms referred to as extraosseous plasmacytomas (PCTs). It is shown that 20.8% (20/96) of tumour-bearing iMyc(Emu) mice on a mixed genetic background of segregating C57BL/6 and 129/SvJ alleles develop PCT by 500 days. The Myc(His)-induced PCTs produced monoclonal immunoglobulin and developed in the gut-associated lymphoid tissue (GALT), particularly the mesenteric node and Peyer's patches. The PCTs overexpressed Myc(His), at the expense of normal Myc, and exhibited gene expression changes on cDNA macroarrays that were consistent with Myc(His)-driven neoplasia. Surprisingly, in one of three PCT-derived cell lines, Myc(His) was 'replaced' by a naturally occurring T(12;15) translocation, which changed the mode of Myc deregulation from gene insertion (Myc(His) transgene) to chromosomal translocation (juxtaposition of normal Myc to the immunoglobulin heavy-chain locus Igh). These findings provide evidence that recreation of the mouse PCT-associated T(12;15)(Igh(Emu)-Myc) translocation by gene insertion in mice results in the predictable development of PCTs in approximately one-fifth of the tumour-bearing mice. Myc(His)-driven PCTs recapitulate aspects of human plasma cell neoplasms, for which relatively few models exist in mice. For example, PCT development in the iMyc(Emu) mice may provide a good system to study the mechanism by which human MYC facilitates the progression of plasma cell myeloma (multiple myeloma) in humans.

Rapamycin-Sensitive Pathway Regulates Mitochondrial Membrane Potential, Autophagy, and Survival in Irradiated MCF-7 Cells

Radiation-induced inhibition of rapamycin-sensitive pathway and its effect on the cellular response to radiation were studied in the human breast cancer cell line MCF-7. Both radiation and rapamycin shared molecular targets and induced similar physiologic responses. Each of these treatments increased immunostaining of mammalian target of rapamycin (mTOR) in the nucleus, and radiation led to decreased phosphorylation of its autophosphorylation site Ser2481. In addition to dephosphorylation of established mTOR downstream effectors 4E-binding protein 1 and p70 ribosomal S6 kinase, both treatments decreased the level of eukaryotic initiation factor 4G. Experiments with the potentiometric dye, JC-1, revealed an oligomycin-dependent increase in mitochondrial membrane potential following radiation or rapamycin treatment, suggesting that both lead to reversal of F0F1ATPase activity. Both radiation and rapamycin induced sequestration of cytoplasmic material in autophagic vacuoles. In both cases, appearance of autophagic vacuoles involved the participation of microtubule-associated protein 1 light chain 3 (LC3). Transient cotransfection of green fluorescent protein-LC3 with either wild-type or dominant-negative mTOR further showed that inactivation of mTOR pathway is sufficient to induce autophagy in these cells. Finally, administration of rapamycin in combination with radiation led to enhanced mitochondria hyperpolarization, p53 phosphorylation, and increased cell death. Taken together, these experiments show that radiation-induced inhibition of rapamycin-sensitive pathway in MCF-7 cells causes changes in mitochondria metabolism, development of autophagy, and an overall decrease in cell survival.

Insertion of Myc into Igh accelerates peritoneal plasmacytomas in mice

Gene-targeted mice that contain a His6-tagged mouse c-Myc cDNA, Myc(His), inserted head to head into different sites of the mouse immunoglobulin heavy-chain locus, Igh, mimic the chromosomal T(12;15)(Igh-Myc) translocation that results in the activation of Myc in the great majority of mouse plasmacytomas. Mice carrying Myc(His) just 5' of the intronic heavy-chain enhancer Emu (strain iMyc(Emu)) provide a specific model of the type of T(12;15) found in a subset (approximately 20%) of plasmacytomas that develop "spontaneously" in the gut-associated lymphoid tissue (GALT) of interleukin-6 transgenic BALB/c (C) mice. Here we show that the transfer of the iMyc(Emu) transgene from a mixed genetic background of segregating C57BL/6 x 129/SvJ alleles to the background of C increased the incidence of GALT plasmacytomas by a factor of 2.5 in first-generation backcross mice (C.iMyc(Emu) N1). Third-generation backcross mice (C.iMyc(Emu) N3, approximately 94% C alleles) were hypersusceptible to inflammation-induced peritoneal plasmacytomas (tumor incidence, 100%; mean tumor onset, 86 +/- 28 days) compared with inbred C mice (tumor incidence, 5% on day 150 after tumor induction). Peritoneal plasmacytomas of C.iMyc(Emu) N3 mice overexpressed Myc(His), produced monoclonal immunoglobulin, and exhibited a unique plasma cell signature upon gene expression profiling on mouse Lymphochip cDNA microarrays. These findings indicated that the iMyc(Emu) transgene accelerates plasmacytoma development by collaborating with tumor susceptibility alleles of strain C and circumventing the requirement for tumor precursors to acquire deregulated Myc by chromosomal translocation.