Transgenic Expression of Bach1 Transcription Factor Results in Down-Regulation of the p45 Target Genes in Megakaryocytic Lineage Cells.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1605-1605 ◽  
Author(s):  
Tsutomu Toki ◽  
Fumiki Katsuoka ◽  
Rika Kanezaki ◽  
Seiji Watanabe ◽  
Takuya Kamio ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Target Genes ◽  
Fetal Liver ◽  
Regulatory Element ◽  
Mutant Mice ◽  
Transgenic Expression ◽  
Transgenic Lines ◽  
Recognition Elements ◽  
Null Mutant Mice

Abstract Both p45 and BACH transcription factors can form dimers with one of the small Maf proteins, and these heterodimers bind to Maf recognition elements (MARE). MARE is known to act as a critical cis-regulatory element of erythroid and megakaryocytic genes. While detailed analyses of p45 -null mutant mice and small maf compound mutant mice revealed that these factors are both critical for platelet production, the functional contributions of BACH1 and the relationship or redundancy between BACH1 and p45 in megakaryocytes remain to be clarified. To address these issues, we generated transgenic lines of mice bearing human BACH1 cDNA under the control of the GATA-1 locus hematopoietic regulatory domain. The transgenic mouse lines showed significant thrombocytopenia associated with impaired maturation of the megakaryocytes, and they developed myelofibrosis. The megakaryocytes overexpressing the BACH1 transgene exhibited reduced proplatelet formation. Since the phenotype of the BACH1 transgenic mice resembled that of the p45 -deficient mice, we examined the expression of the p45 NF-E2 target genes in the primary megakaryocytes from fetal liver cells of the BACH1 transgenic mice. RT-PCR analyses showed that expression of the hematopoietic-specific ß1-tubulin, thromboxane synthase ( TXAS), and of the 3ß-hydroxy-steroid dehydrogenase genes was significantly downregulated in the megakaryocytes from BACH1 transgenic mice. The TXAS gene is a well-known MARE-dependent gene containing functional MAREs in its promoter and in the second intron. To ask whether BACH1 actually binds to MARE in the megakaryocytic genes, we then performed chromatin immunoprecipitation (ChIP) analysis with a BACH1-specific antibody. A ChIP assay with a human megakaryocytic cell line, UT-7/TPO, demonstrated that BACH1 bound to the promoter and enhancers region in vivo. As expected, co-transfection with BACH1 or Bach1-MafK fusion protein (B1K) expression plasmids repressed the reporter gene activity driven by the TXAS promoter. These findings thus provide evidence that BACH1 acts as a transcriptional repressor in the regulation of MARE-dependent genes in megakaryocytes.

Mechanisms of Tumor Suppression by the Hematopoietic Transcription Factor PU.1.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2432-2432
Author(s):  
Mark D McKenzie ◽  
Luisa Cimmino ◽  
Yifang Hu ◽  
Ladina Di Rago ◽  
Sandra Mifsud ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Transgenic Mice ◽  
Myeloid Leukemia ◽  
Target Genes ◽  
Fetal Liver ◽  
Liver Cells ◽  
Myeloid Lineage ◽  
Fetal Liver Cells

Abstract Abstract 2432 Introduction Acute myeloid leukemia (AML) is a genetically and morphologically heterogeneous disease characterized by the accumulation of immature myeloid lineage cells in the bone marrow and blood. It results from genetic alterations that cause increased self-renewal of myeloid progenitors, accompanied by a block in their normal differentiation programs. Studies in mice and humans have shown that loss of expression of PU.1, a master transcription factor that is critical for lymphoid and myeloid lineage development, is a recurrent feature of AML1. Restoring the PU.1 differentiation program in AML is an attractive therapeutic strategy, but remains elusive due to a poor understanding of PU.1 target genes and tumor suppressive mechanisms. In a novel approach to understanding PU.1 function, we have used in vivo RNA interference to inducibly inhibit and restore PU.1 expression in normal hematopoietic cells and leukemias. Results PU.1 knockdown promotes leukemia in mice We identified several short hairpin RNAs that can effectively knockdown PU.1 (Fig 1A). We infected primary fetal liver cells with the most effective LMP-shPU.1 retroviruses and performed in vitro and in vivo assays to assess the effect of PU.1 knockdown (Fig 1B). We found that PU.1 knockdown drives 1) an increased frequency of blast colony-forming cells and self-generation of granulocytic progenitors in vitro (Fig 1C) and 2) a GFP+ myeloid leukemia after several months characterized by accumulation of cKit+Gr1+Mac1+ cells (Fig 1D, E). These findings verify that shRNA-mediated PU.1 knockdown can effectively disable its tumor suppressive functions. Inducible restoration of PU.1 in leukemia in vivo To identify transcriptional targets of PU.1 in vivo, we utilized a recently generated reversible RNAi strategy that allows acute restoration of endogenous PU.1 expression upon Dox treatment in leukemias driven by PU.1 knockdown2. This TRMPV vector strategy allows tet-regulated co-expression of an shRNA and the fluorescent marker dsRed, with stable expression of GFP to mark infected cells. We transduced fetal liver cells derived from Vav-tTA transgenic mice with TRMPV-shPU.1 to drive reversible PU.1 knockdown across the hematopoietic system of reconstituted recipient mice. In contrast to the myeloid leukemia generated earlier using LMP-shPU.1, these mice developed pre-B cell (CD19+CD25+) leukemia with a latency of several months. To acutely restore endogenous PU.1 expression in leukemia, primary tumor cells were transplanted into several recipient mice to generate a cohort for analysis of Dox responses (Figure 2A). We found that dsRed intensity decreased incrementally upon Dox treatment of leukemic transplant recipient mice allowing FACS sorting of leukemia cells from triplicate untreated mice (dsRedhigh, minimal PU.1 expression) or after three days of Dox treatment (dsRedmid, partially restored PU.1 expression). We identified gene expression changes associated with PU.1 restoration using RNA sequencing (RNA-seq). Development of a transgenic mouse allowing inducible PU.1 knockdown in vivo To further investigate PU.1 target genes in vivo, we have recently generated TRE-GFP-shPU.1 transgenic mice allowing inducible knockdown and restoration of PU.1 in adult mice. To test this strain we crossed it to CAGs-rtTA3 mice and treated bitransgenic mice with Dox. Western blot analysis of GFP+ Gr1+Mac1+ sorted myeloid cells showed effective PU.1 knockdown in vivo. We are currently using these mice to identify PU.1 regulated genes in normal myeloblasts in vivo. Conclusions These studies have identified several new candidate PU.1-regulated genes. Further experiments may shed light on whether there is a common novel tumor suppressive mechanism for PU.1 in myeloid and lymphoid leukemias driven by loss of PU.1. Disclosures: No relevant conflicts of interest to declare.

scholarly journals p90 ribosomal S6 kinase 3 contributes to cardiac insufficiency in α-tropomyosin Glu180Gly transgenic mice

2013 ◽  
Vol 305 (7) ◽  
pp. H1010-H1019 ◽  
Author(s):  
Catherine L. Passariello ◽  
Marjorie Gayanilo ◽  
Michael D. Kritzer ◽  
Hrishikesh Thakur ◽  
Zoharit Cozacov ◽  
...  
Keyword(s):  
Heart Failure ◽  
Transgenic Mice ◽  
Cardiac Function ◽  
Interstitial Fibrosis ◽  
Cardiac Insufficiency ◽  
S6 Kinase ◽  
Transgenic Expression ◽  
P90 Ribosomal S6 Kinase ◽  
Ribosomal S6 Kinase

Myocardial interstitial fibrosis is an important contributor to the development of heart failure. Type 3 p90 ribosomal S6 kinase (RSK3) was recently shown to be required for concentric myocyte hypertrophy under in vivo pathological conditions. However, the role of RSK family members in myocardial fibrosis remains uninvestigated. Transgenic expression of α-tropomyosin containing a Glu180Gly mutation (TM180) in mice of a mixed C57BL/6:FVB/N background induces a cardiomyopathy characterized by a small left ventricle, interstitial fibrosis, and diminished systolic and diastolic function. Using this mouse model, we now show that RSK3 is required for the induction of interstitial fibrosis in vivo. TM180 transgenic mice were crossed to RSK3 constitutive knockout ( RSK3−/−) mice. Although RSK3 knockout did not affect myocyte growth, the decreased cardiac function and mild pulmonary edema associated with the TM180 transgene were attenuated by RSK3 knockout. The improved cardiac function was consistent with reduced interstitial fibrosis in the TM180; RSK3−/− mice as shown by histology and gene expression analysis, including the decreased expression of collagens. The specific inhibition of RSK3 should be considered as a potential novel therapeutic strategy for improving cardiac function and the prevention of sudden cardiac death in diseases in which interstitial fibrosis contributes to the development of heart failure.

A Single Pitx1 Binding Site Is Essential for Activity of the LHβ Promoter in Transgenic Mice

2001 ◽  
Vol 15 (5) ◽  
pp. 734-746 ◽  
Author(s):  
Christine C. Quirk ◽  
Kristen L. Lozada ◽  
Ruth A. Keri ◽  
John H. Nilson
Keyword(s):  
Transgenic Mice ◽  
Binding Site ◽  
Cell Lines ◽  
Regulatory Element ◽  
Regulatory Elements ◽  
Vital Role ◽  
Proximal Region ◽  
Expression Vectors ◽  
Homeodomain Protein

Abstract Reproduction depends on regulated expression of the LHβ gene. Tandem copies of regulatory elements that bind early growth response protein 1 (Egr-1) and steroidogenic factor 1 (SF-1) are located in the proximal region of the LHβ promoter and make essential contributions to its activity as well as mediate responsiveness to GnRH. Located between these tandem elements is a single site capable of binding the homeodomain protein Pitx1. From studies that employ overexpression paradigms performed in heterologous cell lines, it appears that Egr-1, SF-1, and Pitx1 interact cooperatively through a mechanism that does not require the binding of Pitx1 to its site. Since the physiological ramifications of these overexpression studies remain unclear, we reassessed the requirement for a Pitx1 element in the promoter of the LHβ gene using homologous cell lines and transgenic mice, both of which obviate the need for overexpression of transcription factors. Our analysis indicated a striking requirement for the Pitx1 regulatory element. When assayed by transient transfection using a gonadotrope-derived cell line (LβT2), an LHβ promoter construct harboring a mutant Pitx1 element displayed attenuated transcriptional activity but retained responsiveness to GnRH. In contrast, analysis of wild-type and mutant expression vectors in transgenic mice indicated that LHβ promoter activity is completely dependent on the presence of a functional Pitx1 binding site. Indeed, the dependence on an intact Pitx1 binding site in transgenic mice is so strict that responsiveness to GnRH is also lost, suggesting that the mutant promoter is inactive. Collectively, our data reinforce the concept that activity of the LHβ promoter is determined, in part, through highly cooperative interactions between SF-1, Egr-1, and Pitx1. While Egr-1 can be regarded as a key downstream effector of GnRH, and Pitx1 as a critical partner that activates SF-1, our data firmly establish that the Pitx1 element plays a vital role in permitting these functions to occur in vivo.

High incidence of lung, bone, and lymphoid tumors in transgenic mice overexpressing mutant alleles of the p53 oncogene

1989 ◽  
Vol 9 (9) ◽  
pp. 3982-3991
Author(s):  
A Lavigueur ◽  
V Maltby ◽  
D Mock ◽  
J Rossant ◽  
T Pawson ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Malignant Transformation ◽  
P53 Protein ◽  
P53 Gene ◽  
Cell Types ◽  
Molecular Events ◽  
High Incidence ◽  
Transgenic Lines ◽  
Functional Inactivation

We have investigated the role of the p53 gene in oncogenesis in vivo by generating transgenic mice carrying murine p53 genomic fragments isolated from a mouse Friend erythroleukemia cell line or BALB/c mouse liver DNA. Elevated levels of p53 mRNA were detected in several tissues of two transgenic lines tested. Increased levels of p53 protein were also detected in most of the tissues analyzed by Western blotting (immunoblotting). Because both transgenes encoded p53 proteins that were antigenically distinct from wild-type p53, it was possible to demonstrate that overexpression of the p53 protein was mostly, if not entirely, due to the expression of the transgenes. Neoplasms developed in 20% of the transgenic mice, with a high incidence of lung adenocarcinomas, osteosarcomas, and lymphomas. Tissues such as ovaries that expressed the transgene at high levels were not at higher risk of malignant transformation than tissues expressing p53 protein at much lower levels. The long latent period and low penetrance suggest that overexpression of p53 alone is not sufficient to induce malignancies and that additional events are required. These observations provide direct evidence that mutant alleles of the p53 oncogene have oncogenic potential in vivo and that different cell types show intrinsic differences in susceptibility to malignant transformation by p53. Since recent data suggest that p53 may be a recessive oncogene, it is possible that the elevated tumor incidence results from functional inactivation of endogenous p53 by overexpression of the mutant transgene. The high incidence of lung and bone tumors suggests that p53 transgenic mice may provide a useful model to investigate the molecular events that underlie these malignancies in humans.

Beta-MHC and SMLC1 transgene induction in overloaded skeletal muscle of transgenic mice

1996 ◽  
Vol 270 (4) ◽  
pp. C1111-C1121 ◽  
Author(s):  
J. L. Wiedenman ◽  
I. Rivera-Rivera ◽  
D. Vyas ◽  
G. Tsika ◽  
L. Gao ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Troponin C ◽  
Type I ◽  
Initial Attempt ◽  
Specific Expression ◽  
Slow Type ◽  
Transgenic Lines ◽  
Fast Twitch Muscle ◽  
Mechanical Overload

The hypertrophic responses of white fast-twitch muscle to mechanical overload has been investigated using transgenic mice. After 7 wk of overload, endogenous beta-myosin heavy chain (MHC) and slow myosin light chain 1 and 2 (SMLC1, SMLC2) protein were increased in the overloaded plantaris (OP) muscle compared with sham-operated control plantaris (CP)muscle. Concurrently, the levels of endogenous beta-MHC, SMLC1, SMLC2, and cardiac/slow troponin C (CTnC) mRNA transcripts were significantly increased in OP muscles, whereas skeletal troponin C (sTnC) mRNA transcript levels decreased. As an initial attempt to locate DNA sequence(s) that governs beta-MHC induction in response to mechanical overload, multiple independent transgenic lines harboring four different human beta-MHC transgenes (beta 1286, beta 988, beta 450, beta 141) were generated. Except for transgene beta 141, muscle-specific expression and induction (3- to 22-fold) in OP muscles were observed by measuring chloramphenicol acetyltransferase activity (CAT assay). Induction of a SMLC1 transgene (3920SMLC1) in OP muscles was also observed. Collectively, these in vivo data provide evidence that 1) a mechanical overload inducible element(s) is located between nucleotides -450 and +120 of the human beta-MHC transgene, 2) 3,900 bp of 5' sequence is sufficient to confer mechanical overload induction of a SMLC1 transgene, and 3) the increased expression of slow/type I isomyosin (beta-MHC, SMLC1, SMLC2) in response to mechanical overload is regulated, in part, transcriptionally.

scholarly journals Transcription of Drosophila Troponin I Gene Is Regulated by Two Conserved, Functionally Identical, Synergistic Elements

2004 ◽  
Vol 15 (3) ◽  
pp. 1185-1196 ◽  
Author(s):  
María-Cruz Marín ◽  
José-Rodrigo Rodríguez ◽  
Alberto Ferrús
Keyword(s):  
Transcription Initiation ◽  
Troponin I ◽  
Regulatory Element ◽  
Expression Patterns ◽  
In Silico Analysis ◽  
Initiation Site ◽  
Transcription Initiation Site ◽  
Upstream Regulatory Element ◽  
Transgenic Lines

The Drosophila wings-up A gene encodes Troponin I. Two regions, located upstream of the transcription initiation site (upstream regulatory element) and in the first intron (intron regulatory element), regulate gene expression in specific developmental and muscle type domains. Based on LacZ reporter expression in transgenic lines, upstream regulatory element and intron regulatory element yield identical expression patterns. Both elements are required for full expression levels in vivo as indicated by quantitative reverse transcription-polymerase chain reaction assays. Three myocyte enhancer factor-2 binding sites have been functionally characterized in each regulatory element. Using exon specific probes, we show that transvection is based on transcriptional changes in the homologous chromosome and that Zeste and Suppressor of Zeste 3 gene products act as repressors for wings-up A. Critical regions for transvection and for Zeste effects are defined near the transcription initiation site. After in silico analysis in insects (Anopheles and Drosophila pseudoobscura) and vertebrates (Ratus and Coturnix), the regulatory organization of Drosophila seems to be conserved. Troponin I (TnI) is expressed before muscle progenitors begin to fuse, and sarcomere morphogenesis is affected by TnI depletion as Z discs fail to form, revealing a novel developmental role for the protein or its transcripts. Also, abnormal stoichiometry among TnI isoforms, rather than their absolute levels, seems to cause the functional muscle defects.

scholarly journals A New Role for Sterol Regulatory Element Binding Protein 1 Transcription Factors in the Regulation of Muscle Mass and Muscle Cell Differentiation

2009 ◽  
Vol 30 (5) ◽  
pp. 1182-1198 ◽  
Author(s):  
Virginie Lecomte ◽  
Emmanuelle Meugnier ◽  
Vanessa Euthine ◽  
Christine Durand ◽  
Damien Freyssenet ◽  
...  
Keyword(s):  
Transcription Factors ◽  
Muscle Mass ◽  
Target Genes ◽  
Binding Protein ◽  
Regulatory Element ◽  
Element Binding Protein ◽  
Sterol Regulatory Element ◽  
Myogenic Program

ABSTRACT The role of the transcription factors sterol regulatory element binding protein 1a (SREBP-1a) and SREBP-1c in the regulation of cholesterol and fatty acid metabolism has been well studied; however, little is known about their specific function in muscle. In the present study, analysis of recent microarray data from muscle cells overexpressing SREBP1 suggested that they may play a role in the regulation of myogenesis. We then demonstrated that SREBP-1a and -1c inhibit myoblast-to-myotube differentiation and also induce in vivo and in vitro muscle atrophy. Furthermore, we have identified the transcriptional repressors BHLHB2 and BHLHB3 as mediators of these effects of SREBP-1a and -1c in muscle. Both repressors are SREBP-1 target genes, and they affect the expression of numerous genes involved in the myogenic program. Our findings identify a new role for SREBP-1 transcription factors in muscle, thus linking the control of muscle mass to metabolic pathways.

scholarly journals The pancreatic islet factor STF-1 binds cooperatively with Pbx to a regulatory element in the somatostatin promoter: importance of the FPWMK motif and of the homeodomain.

1995 ◽  
Vol 15 (12) ◽  
pp. 7091-7097 ◽  
Author(s):  
B Peers ◽  
S Sharma ◽  
T Johnson ◽  
M Kamps ◽  
M Montminy
Keyword(s):  
Target Genes ◽  
Gene Selection ◽  
Regulatory Element ◽  
Regulatory Elements ◽  
Cooperative Binding ◽  
Homeodomain Protein ◽  
Homeodomain Proteins ◽  
Target Sites

A number of homeodomain proteins have been shown to regulate cellular development by stimulating the transcription of specific target genes. In contrast to their distinct activities in vivo, however, most homeodomain proteins bind indiscriminately to potential target sites in vitro, suggesting the involvement of cofactors which specify target site selection. One such cofactor, termed extradenticle, has been shown to influence segmental morphogenesis in Drosophila melanogaster by binding cooperatively with certain homeodomain proteins to target regulatory elements. Here we demonstrate that STF-1, an orphan homeodomain protein required for pancreatic development in mammals, binds cooperatively to DNA with Pbx, the mammalian homolog of extradenticle. Cooperative binding with Pbx requires a pentapeptide motif (FPWMK) which is well conserved among a large subset of homeodomain proteins. The FPMWK motif is not sufficient to confer Pbx cooperativity on other homeodomain proteins, however; the N-terminal arm of the STF-1 homeodomain is also essential. As cooperative binding with Pbx occurs on only a subset of potential STF-1 target sites, our results suggest that Pbx may specify target gene selection in the developing pancreas by forming heterodimeric complexes with STF-1.

3′ Distal Regulatory Elements Required for Human CD34 Expression in Transgenic Mice.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 125-125
Author(s):  
Elena Levantini ◽  
Yutaka Okuno ◽  
Pu Zhang ◽  
Steffen Koschmieder ◽  
Hanna S. Radomska ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Transgenic Mice ◽  
Progenitor Cells ◽  
Regulatory Element ◽  
Restriction Enzymes ◽  
Regulatory Elements ◽  
Hematopoietic Stem ◽  
Human Cd34 ◽  
Cd34 Expression

Abstract CD34 is the best-defined human hematopoietic stem cell (HSC) marker, however the regulation of its gene expression is still largely unknown. Therefore, unraveling the elements that regulate human CD34 expression would be an invaluable tool for a broad range of studies, including the establishment of models of leukemia in mice, which require targeting of the transgene to stem and/or early progenitor cells. Moreover, identification of such regulatory elements will provide important insights into the transcriptional agenda of stem and progenitor cells and most importantly will prove useful for gene therapy protocols. Studies from our laboratory demonstrated that human CD34 transgenes are expressed in murine repopulating HSCs, which resembles the expression of the CD34 gene in human hematopoiesis, thus indicating the mouse model as an excellent way to study the expression of human CD34. Using P1 derived artificial chromosome (PAC) clones encompassing the human CD34 gene to generate transgenic mice, we showed that 90kb of upstream and 26kb of downstream flanking sequences were capable of regulating human CD34 expression in murine transgenic lines. Successive deletions of this larger construct were then performed to identify the important control regions. Deletion of the 5′ region from −90kb to −18kb did not result in any loss of activity. PAC54A19, a clone extending from −18kb to +26kb, expressed RNA in various tissues in a manner similar to that of larger fragments. In contrast, deletions creating a construct spanning from −10kb to +17kb led to complete loss of expression in transgenic animals, indicating that critical distal elements are located between −18kb to −10kb and/or +17kb to +26kb. In order to facilitate identification of important regulatory elements present in the upstream (−18kb to −10 kb) and/or downstream (+17kb to +26kb) regions of human CD34, we created further deletions of PAC54A19 using rare-cutting restriction enzymes, and studied the effects of the deletions on human CD34 expression in transgenic mice. Interestingly, we did not detect any human CD34 mRNA and protein expression in bone marrow and HSCs from transgenic mice carrying a construct spanning from −18kb to +17.4kb. In contrast, we observed expression of human CD34 transcripts in the bone marrow of transgenic mice containing a PAC spanning from −12.8kb to +26kb. Furthermore, HSCs from this latter group of mice presented the human CD34 antigen on their surface, as detected by FACS. Taken together, these data are highly suggestive that critical cis regulatory element(s) required to drive human CD34 in vivo expression are located in a 8.6kb fragment placed between +17.4kb and +26kb downstream of the human CD34 gene. Our current efforts focus on identifying the element(s) within the 8.6kb 3′ region that might be required to achieve human CD34 expression in HSCs.

Myc Promotes Tumorigenesis by Supressing Nfkb2.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1422-1422
Author(s):  
Ulrich Keller ◽  
Juergen Huber ◽  
Jonas Nilsson ◽  
Mark Hall ◽  
Christian Peschel ◽  
...  
Keyword(s):  
B Cells ◽  
Transgenic Mice ◽  
Burkitt Lymphoma ◽  
Transcriptional Repression ◽  
Early Passage ◽  
Transgenic Expression ◽  
Myc Oncogene ◽  
Protein Levels ◽  
Induced Apoptosis

Abstract Rel/NF-kappaB transcription factors are mediators of immune responses, cell survival, and transformation, and are frequently deregulated in cancer. The NF-kappaB2 subunit is associated with chromosomal translocations or deletions in lymphoid malignancies, and deletion of the COOH-terminal ankyrin domain of NF-kappaB2 results in increased lymphocyte proliferation. Here, we report that activation of the Myc oncogene leads to suppression of Nfkb2 expression in early passage mouse embryonic fibroblasts and primary bone marrow-derived B cells. Accordingly, transgenic expression of c-Myc in the Eμ-Myc model of human Burkitt lymphoma results in reduced nfkb2 transcript and NF-kappaB2 p100 and p52 protein levels in pre-cancerous B cells. Nfkb2 expression is further reduced in the majority of Eμ-Myc lymphomas and in human Burkitt lymphoma. Nfkb2 suppression by Myc occurs at least in part by transcriptional repression as shown by promoter studies. To evaluate the relevance of Myc-mediated suppression of Nfkb2 for tumorigenesis, consequences of complete Nfkb2 loss were evaluated in vivo. In pre-cancerous B cells of Myc-transgenic mice, loss of Nfkb2 affects Myc-induced apoptosis while B cell proliferation is unaffected. Deletion of Nfkb2 results in an acceleration of lymphoma development in Eμ-Myc transgenic mice. Therefore, Myc-induced Nfkb2 suppression promotes lymphomagenesis.

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