scholarly journals 2313 Characterization of the host pericyte role in glioblastoma angiogenesis

2018 ◽  
Vol 2 (S1) ◽  
pp. 1-1
Author(s):  
Frank Attenello ◽  
Frank Attenello ◽  
Yingxi Wu ◽  
Kathleen Tsung ◽  
William Mack ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Tumor Growth ◽  
Effect Size ◽  
Tumor Size ◽  
Lung Tumor ◽  
Cell Activity ◽  
Feasibility Studies ◽  
Wild Type ◽  
Cerebral Vessel

OBJECTIVES/SPECIFIC AIMS: Glioblastoma (GBM) carries a prognosis of 14.6 months mean survival despite maximal surgical, chemotherapeutic, and radiation therapy. The pericyte is a recently characterized cell shown to be a critical component of cerebral vessel physiology and pathology. Importantly, alterations in pericyte densities have shown resulting changes in breast and lung tumor growth. We leverage transgenic pericyte-deficient mouse models to evaluate resulting behavior of implanted patient-derived GBM. METHODS/STUDY POPULATION: Patient-derived, green fluorescent protein labeled, GBM will be implanted in right frontal bregma of both 6-month old pericyte-deficient (PDGFR+/−) mice and age-matched wild-type littermate controls (IACUC 20755, IRB 16-00929), which are immunosuppressed via daily intraperitoneal cyclosporine injection. In total, 30 mice of both genders are included in tumor and control cohorts. Fixed cortical sections following 3-week period will be stained for pericytes (NG2), endothelium (CD31), hypoxia (piminidazole), and tumor size. One-way ANOVA with will used to compare groups using SAS software (Cary, NC). RESULTS/ANTICIPATED RESULTS: Feasibility studies show robust in vitro growth of patient-derived GBM cells, showing continued growth over 10 cellular division passages. Lentivirally transduced GFP reveals reliable tumor tracking both in vitro and in vivo. Transgenic mice at 6 months display reproducibly decreased pericyte and microvascular density in triplicate. Wild-type mice tolerate tumor injection up to three weeks with visible tumor growth, peritumoral hypervascularity, and no evidence of mouse neural dysfunction. With current cohorts recently implanted with tumor, we anticipate a significant decrease in tumor size with Cohen’s d effect size of 0.5 in GBM implanted in pericyte-deficient mice when compared to control. Effect sizes are based moderate to large (effect size 0.5–0.8) reductions of in vitro GBM growth in vascular gene (TGF-β knockdown studies). In addition, tagged tumor-derived pericytes should comprise a greater proportion of new vasculature in pericyte-knockdown mice to overcome host pericyte depletion. Finally, tumors in transgenic mice should show increased hypoxia from limitations in angiogenesis. DISCUSSION/SIGNIFICANCE OF IMPACT: Feasibility studies show successful tracking of fluorescently tagged-patient derived GBM samples in transgenic mice with decreased vasculature. GBM grafts show no evidence of immunogenic response with cyclosporine protocol. Successful limitation of tumor size with reduced pericyte density will provide support to increasing study of blood-brain barrier, stem cell activity and inflammatory activity of pericyte microenvironments altering GBM behavior. Furthermore, implementation of known pericyte targeted therapies, such as imantinib, can be evaluated for GBM patient treatment efficacy. Studies with assembled clinical translational research scholar mentorship team will allow the principal investigator to develop an independent career with laboratory focused on contributing to improved patient outcomes, translating successful pericyte-targeted results to patient trials.

scholarly journals Mice that overexpress Cu/Zn superoxide dismutase are resistant to allergen-induced changes in airway control

2000 ◽  
Vol 279 (2) ◽  
pp. L350-L359 ◽  
Author(s):  
Gary L. Larsen ◽  
Carl W. White ◽  
Katsuyuki Takeda ◽  
Joan E. Loader ◽  
Dee Dee H. Nguyen ◽  
...  
Keyword(s):  
Superoxide Dismutase ◽  
Smooth Muscle ◽  
Transgenic Mice ◽  
Neural Control ◽  
Electrical Field Stimulation ◽  
Tracheal Smooth Muscle ◽  
Wild Type ◽  
Airway Control ◽  
Induced Changes

Within the respiratory epithelium of asthmatic patients, copper/zinc-containing superoxide dismutase (Cu/Zn SOD) is decreased. To address the hypothesis that lung Cu/Zn SOD protects against allergen-induced injury, wild-type and transgenic mice that overexpress human Cu/Zn SOD were either passively sensitized to ovalbumin (OVA) or actively sensitized by repeated airway exposure to OVA. Controls included nonsensitized wild-type and transgenic mice given intravenous saline or airway exposure to saline. After aerosol challenge to saline or OVA, segments of tracheal smooth muscle were obtained for in vitro analysis of neural control. In response to electrical field stimulation, wild-type sensitized mice challenged with OVA had significant increases in cholinergic reactivity. Conversely, sensitized transgenic mice challenged with OVA were resistant to changes in neural control. Stimulation of tracheal smooth muscle to elicit acetylcholine release showed that passively sensitized wild-type but not transgenic mice released more acetylcholine after OVA challenge. Function of the M2 muscarinic autoreceptor was preserved in transgenic mice. These results demonstrate that murine airways with elevated Cu/Zn SOD were resistant to allergen-induced changes in neural control.

scholarly journals Dextran sulphate-induced tau assemblies cause endogenous tau aggregation and propagation in wild-type mice

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Masami Masuda-Suzukake ◽  
Genjiro Suzuki ◽  
Masato Hosokawa ◽  
Takashi Nonaka ◽  
Michel Goedert ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Tau Protein ◽  
Guanidine Hydrochloride ◽  
Intracerebral Injection ◽  
Dextran Sulphate ◽  
Wild Type ◽  
Synthetic Filament ◽  
Biochemical Analyses ◽  
Tau Aggregation

Abstract Accumulation of assembled tau protein in the central nervous system is characteristic of Alzheimer’s disease and several other neurodegenerative diseases, called tauopathies. Recent studies have revealed that propagation of assembled tau is key to understanding the pathological mechanisms of these diseases. Mouse models of tau propagation are established by injecting human-derived tau seeds intracerebrally; nevertheless, these have a limitation in terms of regulation of availability. To date, no study has shown that synthetic assembled tau induce tau propagation in non-transgenic mice. Here we confirm that dextran sulphate, a sulphated glycosaminoglycan, induces the assembly of recombinant tau protein into filaments in vitro. As compared to tau filaments induced by heparin, those induced by dextran sulphate showed higher thioflavin T fluorescence and lower resistance to guanidine hydrochloride, which suggests that the two types of filaments have distinct conformational features. Unlike other synthetic filament seeds, intracerebral injection of dextran sulphate-induced assemblies of recombinant tau caused aggregation of endogenous murine tau in wild-type mice. AT8-positive tau was present at the injection site 1 month after injection, from where it spread to anatomically connected regions. Induced tau assemblies were also stained by anti-tau antibodies AT100, AT180, 12E8, PHF1, anti-pS396 and anti-pS422. They were thioflavin- and Gallyas-Braak silver-positive, indicative of amyloid. In biochemical analyses, accumulated sarkosyl-insoluble and hyperphosphorylated tau was observed in the injected mice. In conclusion, we revealed that intracerebral injection of synthetic full-length wild-type tau seeds prepared in the presence of dextran sulphate caused tau propagation in non-transgenic mice. These findings establish that propagation of tau assemblies does not require tau to be either mutant and/or overexpressed.

scholarly journals A potent CBP/p300-Snail interaction inhibitor suppresses tumor growth and metastasis in wild-type p53-expressing cancer

2020 ◽  
Vol 6 (17) ◽  
pp. eaaw8500
Author(s):  
Hong-Mei Li ◽  
Yan-Ran Bi ◽  
Yang Li ◽  
Rong Fu ◽  
Wen-Cong Lv ◽  
...  
Keyword(s):  
Tumor Growth ◽  
Epithelial Mesenchymal Transition ◽  
Therapeutic Effects ◽  
Creb Binding Protein ◽  
Wild Type ◽  
Mesenchymal Transition ◽  
Patients With Cancer ◽  
Wild Type P53

The zinc finger transcription factor Snail is aberrantly activated in many human cancers and associated with poor prognosis. Therefore, targeting Snail is expected to exert therapeutic benefit in patients with cancer. However, Snail has traditionally been considered “undruggable,” and no effective pharmacological inhibitors have been identified. Here, we found a small-molecule compound CYD19 that forms a high-affinity interaction with the evolutionarily conserved arginine-174 pocket of Snail protein. In aggressive cancer cells, CYD19 binds to Snail and thus disrupts Snail’s interaction with CREB-binding protein (CBP)/p300, which consequently impairs CBP/p300-mediated Snail acetylation and then promotes its degradation through the ubiquitin-proteasome pathway. Moreover, CYD19 restores Snail-dependent repression of wild-type p53, thus reducing tumor growth and survival in vitro and in vivo. In addition, CYD19 reverses Snail-mediated epithelial-mesenchymal transition (EMT) and impairs EMT-associated tumor invasion and metastasis. Our findings demonstrate that pharmacologically targeting Snail by CYD19 may exert potent therapeutic effects in patients with cancer.

Hyperactivable NFAT1 Ameliorates Autoimmune Encephalitis In Vivo.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 711-711
Author(s):  
Srimoyee Ghosh ◽  
Sergei B Koralov ◽  
Irena Stevanovic ◽  
Mark S Sundrud ◽  
Yoshiteru Sasaki ◽  
...  
Keyword(s):  
T Cells ◽  
Transgenic Mice ◽  
Cd4 T Cells ◽  
Th17 Cells ◽  
Autoimmune Encephalitis ◽  
Cell Types ◽  
Wild Type ◽  
Ifn Γ

Abstract Abstract 711 Naïve CD4 T cells differentiate into diverse effector and regulatory subsets to coordinate the adaptive immune response. TH1 and TH2 effector subsets produce IFN-γ and IL-4, respectively, whereas proinflammatory TH17 cells are key regulators of autoimmune inflammation, characteristically produce IL-17 and IL-22 and differentiate in the presence of inflammatory cytokines like IL-6 and IL-21 together with TGF-β. Naive T cells can also differentiate into tissue-protective induced T regulatory (iTreg) cells. NFAT proteins are highly phosphorylated and reside in the cytoplasm of resting cells. Upon dephosphorylation by the Ca2+/calmodulin-dependent serine phosphatase calcineurin, NFAT proteins translocate to the nucleus, where they orchestrate developmental and activation programs in diverse cell types. In this study, we investigated the role of the Ca/NFAT signaling pathway in regulating T cell differentiation and the development of autoimmune diseases. We generated transgenic mice conditionally expressing a hyperactivable version of NFAT1 (AV-NFAT1) from the ROSA26 locus. To restrict AV-NFAT1 expression to the T cell compartment, ROSA26-AV-NFAT1 transgenic mice were bred to CD4-Cre transgenic mice. Naïve CD4 T cells freshly isolated from AV mice produced significantly less IL-2 but increased amounts of the inhibitory cytokine IL-10. To investigate the role of NFAT1 in the generation of TH1, TH2, Tregand TH17 cells, the respective cell types were generated from CD4 T cells of AV mice by in vitro differentiation. T cells from AV-NFAT1 mice exhibited a dysregulation of cytokine expression, producing more IFN-γ and less IL-4. While the numbers of CD4+CD25+ “natural” Treg cells in peripheral lymphoid organs and their in vitro suppressive functions were slightly decreased in AV mice, iTreg generation from CD4+CD25- T cells of AV mice as compared to wild type cells was markedly enhanced. Moreover, TH17 cells generated in vitro from CD4 T cells of AV mice in the presence of IL-6, IL-21 and TGF-β exhibited dramatically increased expression of both IL-10 and IL-17 as compared to wild type controls. To investigate putative NFAT binding sites in the IL-10 and IL-17 gene loci, we performed chromatin immunoprecipitation experiments. We show that NFAT1 can bind at the IL-17 locus at 3 out of 9 CNS regions which are accessible specifically during TH17 but not during TH1 and TH2 differentiation. Furthermore, we provide evidence that NFAT1 binds one CNS region in the IL10-locus in TH17 cells. To verify our observations in vivo, we induced experimental autoimmune encephalitis (EAE) in AV mice and wild type controls with the immunodominant myelin antigen MOG33-55 emulsified in complete Freund‘s adjuvant. While wild type animals showed a normal course of disease with development of tail and hind limb paralysis after approximately 10 days, AV mice showed a markedly weaker disease phenotype with less severe degrees of paralysis and accelerated kinetics of remission. Moreover at the peak of the response, there were fewer CD4+CD25- but more CD4+CD25+ T cells in the CNS of AV animals compared to wild type controls. Surprisingly, these cells produced significantly more IL-2, IL-17 and IFN-γ upon restimulation, even though they displayed decreased disease. In summary, our data provide strong evidence that NFAT1 contributes to the regulation of IL-10 and IL-17 expression in TH17 cells and show that increasing NFAT1 activity can ameliorate autoimmune encephalitis. This could occur in part through upregulation of IL-10 expression as observed in vitro, but is also likely to reflect increased infiltration of regulatory T cells into the CNS as well as increased conversion of conventional T cells into Foxp3+ regulatory T cells within the CNS. Disclosures: No relevant conflicts of interest to declare.

CD30/CD16A Tandab AFM13-Induced Target Cell Lysis By NK-Cells Is Enhanced By CD137 Co-Stimulation and Blocking PD-1

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 2747-2747 ◽  
Author(s):  
Xing Zhao ◽  
Narendiran Rajasekaran ◽  
Uwe Reusch ◽  
Jens-Peter Marschner ◽  
Martin Treder ◽  
...  
Keyword(s):  
Tumor Growth ◽  
Nk Cells ◽  
Target Cell ◽  
Tumor Size ◽  
Target Cells ◽  
In Vivo Models ◽  
Effector Cells ◽  
Cytotoxicity Assays

Abstract Introduction: AFM13 is a CD30/CD16A bispecific tetravalent TandAb antibody that recruits and activates NK-cells by specific binding to CD16A for targeted lysis of CD30+ tumor cells. Given promising clinical activity and safety profile of AFM13 and proof-of-mechanism demonstrating dependence on the immune response, potential synergy of AFM13 and checkpoint modulators was evaluated. Methods: Efficacy of AFM13 alone or in combination with anti-CTLA-4, anti-PD-1, or anti-CD137 antibodies was assessed by in vitro cytotoxicity assays with human PBMCs or enriched NK-cells and CD30+ target cells as well as patient-derived xenograft in vivo models with autologous PBMC. To evaluate NK-cell-mediated lysis of CD30+ lymphoma cell lines, 4 hour cytotoxicity assays were performed with PBMCs or enriched NK-cells as effector cells in the presence of suboptimal concentrations of AFM13 alone, and in combination with anti-CTLA-4, anti-PD-1, or anti-CD137 antibodies. For the in vivo model tumor fragments derived from surgical specimens of newly diagnosed patients with CD30+ Hodgkin Lymphoma were xenografted (PDX) in immuno-deficient mice. After 28 days mice were reconstituted with autologous patient-derived PBMC and treated with AFM13 alone and in combination with anti-CTLA-4, anti-PD-1, or anti-CD137 antibodies weekly for a total of three weeks. Tumor size, tumor-infiltrating human lymphocytes and intra-tumoral cytokines were evaluated on day 58. Results: AFM13 as a single agent at suboptimal concentrations induced effector-to-target cell-dependent lysis of CD30+ lymphoma cells up to 40% using enriched NK-cells as effector cells in a 4 hour in vitro assay. Immune-modulating antibodies alone mediated substantially lower lysis (<25%). However, the addition of anti-PD-1 or anti-CD137 to AFM13 strongly enhanced specific lysis up to 70%, whereas the addition of anti-CTLA-4 to AFM13 showed no beneficial effect. The most impressive increase of efficacy was observed when AFM13 was applied together with a combination of anti-PD-1 and anti-CD137. In vivo, reduction of tumor growth was observed when AFM13 and anti-PD-1 were used as single agents or when AFM13 was combined with anti-CD137. Synergy was most impressive in these PDX models for the combination of AFM13 and anti-PD-1 which led to a very strong reduction of tumor size. Of note, reduction of tumor growth was strongly correlated with infiltrating NK- and T-cells and intra-tumoral cytokines. Conclusions: The combination trials performed with companion intra-tumoral assessment of lymphocytes and cytokines may enhance the efficacy of AFM13 in patients. This may be explained by a potential cross-talk between NK-cells and T-cell which was enhanced when AFM13 was used in combination with checkpoint modulators. Disclosures No relevant conflicts of interest to declare.

scholarly journals Targeted knock-in mice expressing the oxidase-fixed form of xanthine oxidoreductase favor tumor growth

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Teruo Kusano ◽  
Driss Ehirchiou ◽  
Tomohiro Matsumura ◽  
Veronique Chobaz ◽  
Sonia Nasi ◽  
...  
Keyword(s):  
Tumor Growth ◽  
Immune Surveillance ◽  
Tumor Development ◽  
Cancer Growth ◽  
Xanthine Oxidoreductase ◽  
Oxygen Species ◽  
Wild Type ◽  
Macrophage Depletion

Abstract Xanthine oxidoreductase has been implicated in cancer. Nonetheless, the role played by its two convertible forms, xanthine dehydrogenase (XDH) and oxidase (XO) during tumorigenesis is not understood. Here we produce XDH-stable and XO-locked knock-in (ki) mice to address this question. After tumor transfer, XO ki mice show strongly increased tumor growth compared to wild type (WT) and XDH ki mice. Hematopoietic XO expression is responsible for this effect. After macrophage depletion, tumor growth is reduced. Adoptive transfer of XO-ki macrophages in WT mice increases tumor growth. In vitro, XO ki macrophages produce higher levels of reactive oxygen species (ROS) responsible for the increased Tregs observed in the tumors. Blocking ROS in vivo slows down tumor growth. Collectively, these results indicate that the balance of XO/XDH plays an important role in immune surveillance of tumor development. Strategies that inhibit the XO form specifically may be valuable in controlling cancer growth.

scholarly journals Cd8− T Cell Transfectants That Express a High Affinity T Cell Receptor Exhibit Enhanced Peptide-Dependent Activation

2001 ◽  
Vol 194 (8) ◽  
pp. 1043-1052 ◽  
Author(s):  
Phillip D. Holler ◽  
Alice R. Lim ◽  
Bryan K. Cho ◽  
Laurie A. Rund ◽  
David M. Kranz
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Cell Receptor ◽  
Cytotoxic T Lymphocyte ◽  
Cell Activity ◽  
Cell Receptor ◽  
Wild Type ◽  
High Affinity ◽  
Antigen Presenting

T cells are activated by binding of the T cell receptor (TCR) to a peptide-major histocompatibility complex (MHC) complex (pMHC) expressed on the surface of antigen presenting cells. Various models have predicted that activation is limited to a narrow window of affinities (or dissociation rates) for the TCR–pMHC interaction and that above or below this window, T cells will fail to undergo activation. However, to date there have not been TCRs with sufficiently high affinities in order to test this hypothesis. In this report we examined the activity of a CD8-negative T cell line transfected with a high affinity mutant TCR (KD = 10 nM) derived from cytotoxic T lymphocyte clone 2C by in vitro engineering. The results show that despite a 300-fold higher affinity and a 45-fold longer off-rate compared with the wild-type TCR, T cells that expressed the mutant TCRs were activated by peptide. In fact, activation could be detected at significantly lower peptide concentrations than with T cells that expressed the wild-type TCR. Furthermore, binding and functional analyses of a panel of peptide variants suggested that pMHC stability could account for apparent discrepancies between TCR affinity and T cell activity observed in several prior studies.

scholarly journals Hmgb1-IL-23-IL-17-IL-6-Stat3 Axis Promotes Tumor Growth in Murine Models of Melanoma

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Qiu Tang ◽  
Jian Li ◽  
Hongfei Zhu ◽  
Pan Li ◽  
Zhenwei Zou ◽  
...  
Keyword(s):  
Tumor Growth ◽  
Tumor Cells ◽  
Tumor Size ◽  
Immune Surveillance ◽  
Tumor Development ◽  
Murine Models ◽  
Wild Type ◽  
Proliferating Cells ◽  
Melanoma Tumor ◽  
Tumor Bearing

In order to understand how tumor cells can escape immune surveillance mechanisms and thus develop antitumor therapies, it is critically important to investigate the mechanisms by which the immune system interacts with the tumor microenvironment. In our current study, IL-17 deficiency results in reduced melanoma tumor size, diminished numbers of proliferating cells and blood vessels, and decreased percentage of CD11b+Gr-1+MDSCs in tumor tissues. IL-17 promotes IL-6 induction and Stat3 activation. Treatment of Stat3 inhibitor WP1066 in B16-F10 tumor cells inoculated wild-type mice inhibits tumor growth. Additional administration of recombinant IL-6 into B16-F10 tumor-bearing IL-17−/−mice results in markedly increased tumor size and p-Stat3 expression, whereas additional recombinant IL-17 administration into B16-F10 tumor-bearing wild-type mice treated with anti-IL-6 mAb does not significantly alter the tumor growth and p-Stat3 expression. In our further study, blockade of Hmgb1-RAGE pathway inhibits melanoma tumor growth and reduces production of IL-23 and IL-17. All these data suggest that Hmgb1-IL-23-IL-17-IL-6-Stat3 axis plays a pivotal role in tumor development in murine models of melanoma, and blocking any portion of this axis will attenuate melanoma tumor growth.

scholarly journals Characterization of Nonpathogenic, Live, Viral Vaccine Vectors Inducing Potent Cellular Immune Responses

2004 ◽  
Vol 78 (17) ◽  
pp. 9317-9324 ◽  
Author(s):  
Jean Publicover ◽  
Elizabeth Ramsburg ◽  
John K. Rose
Keyword(s):  
T Cell ◽  
Immune Responses ◽  
Cell Activity ◽  
T Cell Responses ◽  
Cytotoxic T Cell ◽  
Wild Type ◽  
Intranasal Route ◽  
Cell Responses ◽  
Viral Vaccine

ABSTRACT Experimental vaccines based on recombinant vesicular stomatitis viruses (VSV) expressing foreign viral proteins are protective in several animal disease models. Although these attenuated viruses are nonpathogenic in nonhuman primates when given by nasal, oral, or intramuscular routes, they are pathogenic in mice when given intranasally, and further vector attenuation may be required before human trials with VSV-based vectors can begin. Mutations truncating the VSV glycoprotein (G) cytoplasmic domain from 29 to 9 or 1 amino acid (designated CT9 or CT1, respectively) were shown previously to attenuate VSV growth in cell culture and pathogenesis in mice. Here we show that VSV recombinants carrying either the CT1 or CT9 deletion and expressing the human immunodeficiency virus (HIV) Env protein are nonpathogenic in mice, even when given by the intranasal route. We then carried out a detailed analysis of the CD8+ T-cell responses, including in vivo cytotoxic T-cell activity, induced by these vectors. When given by either the intranasal or intraperitoneal route, the VSV-CT9 vector expressing HIV Env elicited primary and memory CD8+ T-cell responses to Env equivalent to those elicited by recombinant wild-type VSV expressing Env. The VSV-CT1 vector also induced potent CD8+ T-cell responses after intraperitoneal vaccination, but was less effective when given by the intranasal route. The VSV-CT1 vector was also substantially less effective than the VSV-CT9 or wild-type vector at inducing antibody to Env. The VSV-CT9 vector appears ideal because of its lack of pathogenesis, propagation to high titers in vitro, and stimulation of strong cellular and humoral immune responses.

scholarly journals Selection for Loss of p53 Function in T-Cell Lymphomagenesis Is Alleviated by Moloney Murine Leukemia Virus Infection in myc Transgenic Mice

2001 ◽  
Vol 75 (20) ◽  
pp. 9790-9798 ◽  
Author(s):  
Euan W. Baxter ◽  
Karen Blyth ◽  
Ewan R. Cameron ◽  
James C. Neil
Keyword(s):  
Transgenic Mice ◽  
Leukemia Virus ◽  
Moloney Murine Leukemia Virus ◽  
Tumor Cell Lines ◽  
Wild Type ◽  
Allele Loss ◽  
Selection For

ABSTRACT Thymic lymphomas induced by Moloney murine leukemia virus (MMLV) have provided many examples of oncogene activation, but the role of tumor suppressor pathways in these tumors is less clear. These tumors display little evidence of loss of heterozygosity, and MMLV is only weakly synergistic with the Trp53 null genotype, suggesting that viral lymphomagenesis involves mechanisms which do not require mutational loss of Trp53function. To explore this relationship in greater depth, we infected CD2-myc transgenic mice with MMLV and examined the role of Trp53 in the genesis of these tumors. Most (19 of 27) of the tumors from MMLV-infected, CD2-myc Trp53 +/− mice retained the wild-typeTrp53 allele in vivo while tumors of uninfected CD2-myc Trp53 +/− mice invariably showed allele loss from a significant fraction of primary tumor cells. The functional integrity of the Trp53gene in these tumors was indicated by ongoing allele loss or selection for mutational stabilization during in vitro propagation and by the radiosensitivity of selected Trp53 +/−tumor cell lines. An inverse correlation was noted between retention of the wild-type Trp53 allele and expression of p19ARF, providing further evidence of negative-feedback control of the latter by p53. However, expression of p19ARFdoes not appear to be counterselected in the absence of p53, and its integrity in Trp53 +/− tumors was indicated by its transcriptional upregulation on Trp53 wild-type allele loss in vitro in selected tumor cell lines. The role of MMLV was investigated further by analysis of proviral insertion sites in tumors of CD2-myc transgenic mice sorted forTrp53 genotype. A proportion of tumors showed insertions at Runx2, an oncogene which has been shown to collaborate independently with CD2-myc and with theTrp53 null genotype, and at a novel common integration site (ptl-1) on chromosome 8. Genotypic analysis of the panel of tumors suggested that neither of these integrations is functionally redundant with loss of p53, but it appears that the combination of the MMLV oncogenic program with the CD2-myc oncogene relegates p53 loss to a late step in tumor progression or in vitro culture. While the means by which these tumors preempt the p53 tumor suppressor response remains to be established, this study provides further evidence that irreversible inactivation of this pathway is not a prerequisite for tumor development in vivo.

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