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NEOPLASIA
From the Department of Hematology, Clinic of Internal
Medicine I, the Department of Blood Group Serology and Transfusion
Medicine, and the Ludwig Boltzmann-Institute for Cytokine Research,
University of Vienna, Vienna, Austria.
Members of the Notch family encode transmembrane receptors that
modulate differentiation, proliferation, and apoptotic programs of many
precursor cells, including hematopoietic progenitors. Stimulation of
Notch causes cleavage followed by translocation of the intracellular
domain (NotchIC) to the nucleus, where it activates transcription of
CBF1 responsive genes. The aim of this study was to elucidate the
mechanisms leading to the overexpression of CD23, a striking feature of
B-cell chronic lymphocytic leukemia (B-CLL) cells. By electrophoretic
mobility shift assays, we identified a transcription factor complex
(C1) that binds sequence specific to one known and 4 newly identified
putative CBF1 recognition sites in the CD23a core promoter
region. With the use of Epstein-Barr virus (EBV)-infected B cells as a
model for CBF1 mediated CD23a expression, C1 was found to
be EBV inducible. Supershift assays revealed that the nuclear form of
Notch2 is a component of C1 in B-CLL cells, supporting a model in which
NotchIC activates transcription by binding to CBF1 tethered to DNA.
Transient transfection of REH pre-B cells with an activated form of
Notch2 induced endogenous CD23a, confirming that
CD23a is a target gene of Notch2 signaling. Finally,
reverse transcription-polymerase chain reaction and kinetic analysis
demonstrated that the Notch2 oncogene is not only
overexpressed in B-CLL cells but might also be related to the failure
of apoptosis characteristic for this disease. In conclusion, these data
suggest that deregulation of Notch2 signaling is involved in the
aberrant expression of CD23 in B-CLL.
(Blood. 2002;99:3742-3747) B-cell chronic lymphocytic leukemia (B-CLL) is
characterized by the relentless accumulation of monoclonal anergic B
cells that coexpress CD5 and CD19 with faint to virtually undetectable amounts of surface immunoglobulins.1,2 The pathomechanisms underlying the disease primarily involve defects that prevent cell
turnover because of apoptosis, rather than alterations in cell cycle
regulation.1,2
One of the hallmarks of B-CLL cells is the overexpression of the
transmembrane glycoprotein CD23,1-3 which undergoes
spontaneous proteolysis, giving rise to soluble CD23 (sCD23)
molecules.4 The serum concentration of sCD23 can be
several hundred-fold higher than in healthy individuals and parallels
the clinical stage of the disease.5,6
Two isoforms of CD23 exist, CD23a and CD23b, which are expressed from 2 different promoters.7 Expression of CD23a is restricted to
B lymphocytes, whereas CD23b is found on a number of different hematopoietic cell types, predominantly after interleukin 4 (IL-4) treatment.8 In B-CLL cells, selective expression of
CD23a has been found to be concurrent to a state of cell
survival, thereby providing a link between CD23a and the
regulation of apoptosis.9
CD23 is also closely associated with Epstein-Barr virus (EBV)-mediated
B-cell immortalization, because a naturally occurring EBV mutant
(P3HR1), carrying a deletion of the EBNA2 gene, has lost its
ability to induce CD23 expression and to transform primary B cells in
vitro.10-12 EBNA2 activates the CD23a gene
through a CBF1 repressor site located in the CD23a proximal
promoter.13-15 Several lines of evidence strongly suggest
that EBNA2 mimics Notch signaling by acting as a transcriptional
activator after binding and masking the repression domain of
CBF1.16-19
The Notch gene family encodes transmembrane receptors that modulate
differentiation, proliferation, and apoptotic programs in response to
extracellular ligands expressed on neighboring cells.20,21
Ligand-mediated stimulation of Notch causes the proteolytic release of
the intracellular domain (NotchIC), which then passes into the nucleus
where it activates transcription of CBF1 responsive
genes.22-25 Deregulation of this pathway by overexpression
of a constitutively activated form of Notch not only diverts cell fate
decisions but is also tumorigenic. For example, truncation of
Notch1 found in a subset of human T-cell leukemias leads to
the expression of a ligand-independent oncogenic protein lacking the
extracellular domain.26 The truncated Notch proteins
consist primarily of the intracellular domain and localize predominantly in the nucleus. Enforced expression of Notch1IC in bone
marrow stem cells causes T-cell leukemia in mice, indicating a
causative role for Notch1 in T-cell oncogenesis.27
To elucidate the mechanisms leading to the up-regulation of
CD23a in B-CLL cells, we analyzed the CD23a
proximal promoter for sequence-specific DNA-protein interactions. By
electrophoretic mobility shift assays (EMSAs), we detected a
transcription factor complex containing Notch2IC that binds to
5 different CBF1 responsive elements. Our data indicate that
Notch2 is overexpressed in B-CLL cells, suggesting that
deregulation of Notch2 signaling is involved in the pathogenesis of
this disease.
Cell lines and culture
Flow cytometry
Sequence analysis of the CD23a promoter Potential transcription factor binding sites in the CD23a proximal promoter were identified by using the matrix search program MatInspector V2.2 that is based on the transcription factor database TRANSFAC 4.0 (http://transfac.gbf.de).29Preparation of nuclear extracts and EMSA Nuclear extracts were prepared as described with minor modifications.30 Briefly, 15 × 106 cells were lysed in 1 mL hypotonic buffer (10 mM HEPES, pH 7.9; 1.5 mM MgCl2; 10 mM KCL) containing 0.15% NP-40 at 4°C for 10 minutes. The nuclear proteins were extracted from the nuclear fraction by resuspending the nuclei in 600 µL extraction buffer (300 mM KCl; 1.5 mM MgCl2; 20 mM HEPES, pH 7.9; 0.2 mM EDTA; 25% glycerin) at 4°C for 20 minutes with constant agitation. After removing the pellet by centrifugation, the supernatant was dialyzed against dialysis buffer (20 mM HEPES, pH 7.9; 100 mM KCl, 0.2 mM EDTA, 20% glycerol) for 45 minutes. EMSA probes (for sequence information see Figure 1) were Digoxigenin end-labeled (Roche, Mannheim, Germany). The binding reaction was performed by preincubating 3 µg nuclear proteins with 2.5 µg poly(dI-dC) in a buffer containing 10 mM HEPES, pH 7.9; 80 mM KCl, and 10% glycerol for 10 minutes at room temperature. All buffers were supplemented with 0.5 mM dithiothreitol, 0.2 mM phenylmethyl sulfonyl fluoride, and complete protease inhibitor cocktail (Roche, Mannheim, Germany). Competition experiments were performed by the addition of 2.5-, 5-, 25-, 125-fold excess of unlabeled probe EBV.Cp (5'-TGGTGTAAACACGCCGTGGGAAAAAATTTA-3') and CBF1.2 (5'-CTCTAGTTCTCACCCAATTC-3') to the binding reactions. All oligonucleotides were annealed with the respective reverse complementary strands. For immunodetection of DNA binding proteins, antisera were incubated with nuclear extracts 30 minutes at 4°C before addition of probe DNA. Anti-Pax5 (BSAP)-purified polyclonal immunoglobulin (Ig)G was obtained from Santa Cruz Biotechnology (Santa Cruz, CA). The Notch1IC (bTAN 20) and Notch2IC (C651.6DbHN) antibodies were obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the National Institute of Child Health and Human Development and maintained by the University of Iowa, Department of Biological Science, Iowa City, IA. End-labeled probes (30 fmol) were added to the reaction mixture and incubated for an additional 15 minutes at room temperature.
Transient transfection experiments REH pre-B cells were transiently transfected by electroporation. Cells (1-2 × 106) were resuspended in 500 µL serum-free medium and were mixed with 10 µg plasmid DNA (pSG5-rN2IC and pCMV-green fluorescent protein [GFP], respectively) in 0.4-cm electroporation cuvettes. Electroporation was carried out after 5 minutes of incubation on ice on a BioRad gene pulser set at 950 µF and 280 V. Immediately after pulsing, cells were transferred to 4 mL culture medium and were incubated for 48 hours. Transfection efficiency was determined by quantification of GFP-positive cells by using flow cytometry analysis.Determination of sCD23 concentration Blood was obtained by venipuncture. After clotting, samples were centrifuged, and serum was stored at 20°C. The levels of sCD23 from
sera and culture supernatants were measured by using the Cellfree CD23
enzyme-linked immunosorbent assay kit (Endogen, Woburn, MA).
RT-PCR analysis Total RNA was extracted by using the RNAzol isolation system (CINNA/MRC) according to the manufacturer's instructions. One-step RT-PCR reactions (Titan; Roche, Mannheim, Germany) were performed on total RNA (50 ng per reaction) by using primer sequences as follows: Notch2, forward 5'-CTGGATGCAGGTGCAGATGCCAATGC-3' and reverse 5'-GCAGAAGTCAACACGGTGCCTGGAGG-3' (25 cycles; annealing temperature [AT], 65°C; product size, 540 base pair [bp]); CD23a, forward 5'-ATGGAGGAAGGTCAATATTCA-3' and reverse 5'-GCATCATCACGCAGTCCTCGC-3' (30 cycles; AT, 45°C; product size, 790 bp). Primer sequences and conditions for bcl-2 RT-PCR were performed according to Erlacher et al.31 The integrity of the isolated RNA and efficiency of complementary DNA synthesis was assessed by amplification of -actin by using the following primers: forward
5'-GTGGGAATTCGTCAGAAGGACTCCTATGTG-3' and reverse
5'-GAAGTCTAGAGCAACATAGCACAGCTTCTC-3' (25 cycles; AT, 60°C; product
size, 260 bp). Consequently, laser-scanning densitometry was performed,
and the amount of RNA used for detection of the target genes was
accordingly adjusted. PCR products were sequenced to verify specificity
of amplified DNA.
CD23a promoter sequence analysis Figure 1 depicts the sequence upstream of the transcriptional initiation site of the CD23a gene that has been shown to be sufficient for an efficient expression of CD23a in B cells.7 This region corresponds also to a nuclease hypersensitive site found in B cells but not in T cells.32 In most cases such hypersensitive sites reflect the binding of transcription factors to specific DNA sequences, resulting in nucleosome displacement. Instead of a canonical TATA box, 2 putative Pax5 (BSAP) binding sites between29 bp and 90 bp could be
predicted.33 The upper Pax5 site is situated close to a
previously described NF- B-like element (89 to 98) that has been
shown to cooperate with a STAT6 site (117 to 126) in
CD40/IL-4-mediated induction of the highly homologous murine
CD23 promoter.34 In addition to one known CBF1
site (CBF1.1 in Figure 1),14,15 we were able to identify 4 putative CBF1 recognition sites matching the consensus (GTGG/AGAA) in
at least 6 of 7 positions.35 Furthermore, by using the
matrix search program MatInspector V2.2 (Research Group
Bioinformatics, Braunschweig, Germany),29 several
potential binding sites for Ikaros (IK1-2), GATA1-3, LMO2, and MZF1
could be predicted.
B-CLL-specific DNA-protein interactions in the CD23a proximal promoter To identify transcription factors implicated in the up-regulation of the CD23a gene in B-CLL cells, EMSAs were performed with 4 oligonucleotide probes derived from the CD23a core promoter region (Figure 1). Nuclear extracts were prepared from freshly isolated B-CLL cells (n = 6, Table 1), from PBMCs (n = 3), and from tonsillar B cells (n = 1). The Burkitt lymphoma cell line BL41 infected with the EBV strain B95-8 (Table 1) served as a positive control for CBF1-mediated CD23a expression.14,15 Nuclear proteins isolated from Th cells (n = 3) were included as a negative control for B-cell- and EBV-specific transcription factors.
As demonstrated in Figure 2, EMSA with
probe A to D, encompassing one known (Figure 1, probe A) and 3 newly
identified putative CBF1 sites (Figure 1, probes B to D), visualized a
prominent, slow-migrating DNA-protein complex designated as complex 1 (C1, Figure 2A-D). The significance of this complex was underlined by
the fact that in all B-cell samples the intensity of C1 correlated with
their respective levels of CD23a transcription. Most
notable, C1 was found to be EBV inducible (Figure 2A-D, lanes 4 and 5), indicating that this complex is involved in CBF1-mediated
CD23a expression. To support this finding, EMSA was
performed, including an unlabeled competitor oligonucleotide (CBF1.Cp)
spanning a well-characterized CBF1 site derived from the EBV C
promoter.15 C1 was completely abolished upon the addition
of the competitor (Figure 3A), confirming that C1 binds sequence specific to the CBF1 recognition sites. An
additional putative CBF1 site matching the consensus at 7 of 7 positions (CBF1 site 2; GTGAGAA,
Because B-CLL cells do not express detectable amounts of the EBV-encoded CBF1 activator EBNA2,36,37 we conducted supershift assays, including antibodies raised against the nuclear forms of Notch1 and Notch2,38 2 members of the Notch family known to be expressed in normal B cells.18,39,40 Whereas antibodies specific for Notch1IC had no discernible effect on the formation or migration of C1 (data not shown), antibodies specific for Notch2IC led to a marked decrease in the intensity of C1 in Th cells and in B-CLL samples (Figure 3C). This result indicates that in B-CLL cells the nuclear form of Notch2 is a major part of the cellular activity that binds to the CBF1 recognition sites in the CD23a core promoter region. EMSA with probe C and D (Figure 2C,D), spanning 2 predicted Pax5 sites,
revealed the appearance of an additional complex, designated C2. This
complex appeared in all B-cell samples (Figure 2C, lanes 4-10, and
Figure 2D, lanes 3-10) but was absent in the Th-cell control (Figure
2C, lane 3, and Figure 2D, lane 2). Incubation of nuclear extracts with
Pax5 antibodies before the addition of probe C diminished the signal of
C2 (Figure 3D), implying that this complex contains Pax5. A higher
order complex was observed in all samples positive for both, C1 and C2
(Figure 3E), suggesting that these factors bind the shared DNA regions
in a cooperative manner. The presence of 2 Pax5 binding sites in the
Notch2 is overexpressed in B-CLL cells To examine whether elevated levels of Notch2IC in nuclear extracts from B-CLL cells were caused by increased transcription of the corresponding Notch2 gene, RT-PCR analysis was performed. As demonstrated in Figure 4, Notch2 was found to be consistently overexpressed in B-CLL cells (6 of 6) as compared with resting peripheral blood B cells from healthy donors (Figure 4B, lane 7, representative for n = 3) and to other B-non-Hodgkin lymphoma cell lines (Figure 4B, lanes 4 and 5). In total PBMCs from healthy donors, relative high levels of Notch2 transcription were observed in purified Th cells (Figure 4B, lane 3) and in peripheral blood B cells (Figure 4B, lane 7) that are in accordance with published data.40 No signals for Notch1 were detected under these conditions (data not shown). Remarkably, neither Notch1 (data not shown) nor Notch2 messages (Figure 4B, lane 6) were found in a rare case of B-CLL (B-CLLCD23+/ ) in which the leukemic cells
expressed low amounts of surface CD23 (Table 1). Because no detectable
amounts of CD23a messenger RNA (mRNA) were found in this
sample (Figure 4B, lane 6), it is likely that the surface expression of
CD23 on these cells resulted from CD23b that is differently
regulated.7,8 Figure 4B shows also the induction of the
CD23a gene through EBV (lanes 4 and 5).
Notch2IC induces endogenous CD23a in B cells To directly demonstrate that CD23a is a target gene of Notch2 signaling in B lymphocytes, the CD23 pre-B-cell
line REH42 was transiently transfected with a mammalian expression vector containing the complementary DNA coding for rat
Notch2IC (kindly provided by Dr Diane Hayward).18 This
vector leads to the expression of a ligand-independent
constitutive-active Notch2IC protein lacking the extracellular
domain.18 The transfection efficiency in the living cell
population was 28% as determined by flow cytometry (not shown). After
2 days of incubation, RT-PCR analysis demonstrated that ectopic
expression of Notch2IC induces CD23a transcription (Figure
5, lane 3), whereas a GFP-encoding control plasmid had no effect (Figure 5, lane 2).
Expression of CD23a correlates with B-CLL cell survival CD23 is detectable on virtually all resting B cells that coexpress surface IgM and IgD.4 In vitro, freshly isolated normal B cells rapidly lose both, CD23 protein and mRNA, suggesting that the expression of CD23 on resting B cells is not constitutive.4 To compare the expression of CD23a in normal B cells with B-CLL cells, gene expression kinetic studies were performed. The results confirmed that after 24 hours of incubation purified normal B cells completely lose CD23a transcription (Figure 6D, lane 3). Down-regulation of CD23a was accompanied by a down-modulation of Notch2, the antiapoptotic gene bcl-2, and by a rapid increase in cell death by apoptosis as determined by FACS analysis (Figure 6B,C) and by RT-PCR (Figure 6D, lane 3). In contrast, CD23a, bcl-2, and Notch2 remained high in B-CLL cells, and this finding was associated with high cell viability.
The overexpression of the transmembrane glycoprotein CD23 is one of the major characteristics of B-CLL cells. Besides the prognostic potential of its soluble cleavage product, sCD23, which reflects tumor load and progression of disease,5,6 selective expression of the CD23a isoform is concurrent to a state of B-CLL cell survival,9 thereby providing a link between CD23a and the malfunction of apoptosis characteristic for this neoplastic B-cell type. The molecular basis underlying the up-regulation of CD23a on the gene level, however, has remained elusive. In this report, we provide evidence that the Notch2 proto-oncogene plays a critical role in this process. Bandshift assays visualized a prominent transcription factor complex (C1) that binds sequence specific to one known and 4 newly identified putative CBF1 sites in the CD23a core promoter region.7,14,15 The significance of this complex was underlined because in all B-cell samples the intensity of C1 correlated with their respective levels of CD23a transcription. Moreover, by using EBV-infected BL41 cells as a positive control for CBF1-mediated CD23a expression,14,15 C1 was found to be EBV inducible. Supershift assays with antibodies raised against the nuclear forms of Notch1 and Notch2 pointed to the fact that Notch2IC is a component of C1 in B-CLL cells. Because transfection of REH pre-B cells with Notch2IC confirmed that CD23a is a target gene of Notch2 signaling, it is reasonable to conclude that Notch2 is involved in the overexpression of CD23a in B-CLL cells. Considering that induction of CD23 through EBNA2 is an initiating event in EBV-driven B-cell immortalization,10-13 it is tempting to speculate that the Notch2 proto-oncogene plays an equally important role in the transformation process of B-CLL cells. In this context, Notch2 might not only account for B-CLL-specific CD23a expression but also for other phenotypic changes characteristic for this B-cell malignancy. In T cells, for instance, ectopic expression of Notch1IC results in the up-regulation of bcl-2 and renders thymomas resistant to glucocorticoid-induced apoptosis.43 Given these observations, the oncogenic nature of Notch receptors may reflect an inhibition of programmed cell death that would be consistent with the phenotype of B-CLL cells.1,2,20,21 Another characteristic feature of B-CLL lymphocytes that might be explained by Notch2 signaling is the low expression of surface immunoglobulins. Recently, it has been demonstrated that activated Notch1, which shares many functions with Notch2,18 acts as transcriptional suppressor of the Igµ gene, indicating that IgM expression is negatively controlled by the Notch signal transduction pathway.44,45 So far, however, the role of Notch2 signaling in B-cell differentiation and tumorigenesis is still not clear. In human fetal B cells, Notch2 expression is restricted to the late pre-B (CD19+ Igµlow) compartment, suggesting that Notch2 confers an antiapoptotic signal when these cells undergo selection through the pre-B-cell receptor.39 In the current study, we show that Notch2 as well as CD23a are also expressed in normal peripheral blood B cells that served as control because they were clustered next to B-CLL cells by genomic scale gene expression profiling.37 Recirculating blood B lymphocytes comprise naive and memory B cells and are characterized by their low proliferation rate and by their relative long life span. As compared with these cells, Notch2 was found to be consistently overexpressed in B-CLL cells, thereby explaining the up-regulation of CD23a. Another clear difference between normal B cells and B-CLL lymphocytes was observed by in vitro kinetic studies showing that in normal B-cells CD23a is down-regulated within 24 hours, whereas in B-CLL cells CD23a levels remain high during 5 days of incubation. Interestingly, the CD23a levels correlate not only with Notch2 expression but also with the levels of the antiapoptotic gene bcl-2 together with enhanced cell viability pointing to a link between the Notch2/CD23a axis and the failure of apoptosis in B-CLL cells. Several lines of evidence suggest that deregulation of Notch signaling locks cells into a less differentiated, proliferative state and inhibits apoptosis in certain leukemic cell lines.20,21 Therefore, a structure-function analysis together with approaches to determine Notch2 function in vivo should provide further insights into the molecular mechanisms underlying the regulation of Notch2 and its role in the pathophysiology of B-CLL.
We thank Drs M. Busslinger and T. Decker for critically reviewing the manuscript and Dr Diane Hayward for providing the pSG5-rN2IC plasmid.
Submitted May 2, 2001; accepted January 6, 2002.
Supported by grant 12210 from the Austrian Science Foundation, by the "Josefine Hirtl and Maria Buss Stiftung," and by the Commission Oncology, Medical Faculty, University of Vienna.
The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked "advertisement" in accordance with 18 U.S.C. section 1734.
Reprints: Josef D. Schwarzmeier, University of Vienna, Dept of Internal Medicine I, Div of Hematology, Waehringer Guertel 18-20, A-1090 Vienna, Austria; e-mail: josef.schwarzmeier{at}akh-wien.ac.at.
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© 2002 by The American Society of Hematology.
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  H. Kohlhof, F. Hampel, R. Hoffmann, H. Burtscher, U. H. Weidle, M. Holzel, D. Eick, U. Zimber-Strobl, and L. J. Strobl Notch1, Notch2, and Epstein-Barr virus-encoded nuclear antigen 2 signaling differentially affects proliferation and survival of Epstein-Barr virus-infected B cells Blood, May 28, 2009; 113(22): 5506 - 5515. [Abstract] [Full Text] [PDF]
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P. Secchiero, E. Melloni, M. G. di Iasio, M. Tiribelli, E. Rimondi, F. Corallini, V. Gattei, and G. Zauli Nutlin-3 up-regulates the expression of Notch1 in both myeloid and lymphoid leukemic cells, as part of a negative feedback antiapoptotic mechanism Blood, April 30, 2009; 113(18): 4300 - 4308. [Abstract] [Full Text] [PDF]
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E. Rosati, R. Sabatini, G. Rampino, A. Tabilio, M. Di Ianni, K. Fettucciari, A. Bartoli, S. Coaccioli, I. Screpanti, and P. Marconi Constitutively activated Notch signaling is involved in survival and apoptosis resistance of B-CLL cells Blood, January 22, 2009; 113(4): 856 - 865. [Abstract] [Full Text] [PDF]
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 B. Sivasankaran, M. Degen, A. Ghaffari, M. E. Hegi, M.-F. Hamou, M.-C. S. Ionescu, C. Zweifel, M. Tolnay, M. Wasner, S. Mergenthaler, et al. Tenascin-C Is a Novel RBPJ{kappa}-Induced Target Gene for Notch Signaling in Gliomas Cancer Res., January 15, 2009; 69(2): 458 - 465. [Abstract] [Full Text] [PDF]
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Y. Nefedova, D. M. Sullivan, S. C. Bolick, W. S. Dalton, and D. I. Gabrilovich Inhibition of Notch signaling induces apoptosis of myeloma cells and enhances sensitivity to chemotherapy Blood, February 15, 2008; 111(4): 2220 - 2229. [Abstract] [Full Text] [PDF]
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 V. Bolos, J. Grego-Bessa, and J. L. de la Pompa Notch Signaling in Development and Cancer Endocr. Rev., May 1, 2007; 28(3): 339 - 363. [Abstract] [Full Text] [PDF]
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 S. Maier, G. Staffler, A. Hartmann, J. Hock, K. Henning, K. Grabusic, R. Mailhammer, R. Hoffmann, M. Wilmanns, R. Lang, et al. Cellular Target Genes of Epstein-Barr Virus Nuclear Antigen 2 J. Virol., October 1, 2006; 80(19): 9761 - 9771. [Abstract] [Full Text] [PDF]
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J. Mohan, J. Dement-Brown, S. Maier, T. Ise, B. Kempkes, and M. Tolnay Epstein-Barr virus nuclear antigen 2 induces FcRH5 expression through CBF1 Blood, June 1, 2006; 107(11): 4433 - 4439. [Abstract] [Full Text] [PDF]
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K. G. Leong and A. Karsan Recent insights into the role of Notch signaling in tumorigenesis Blood, March 15, 2006; 107(6): 2223 - 2233. [Abstract] [Full Text] [PDF]
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 L. Miele Notch Signaling Clin. Cancer Res., February 15, 2006; 12(4): 1074 - 1079. [Full Text] [PDF]
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P. A. Zweidler-McKay, Y. He, L. Xu, C. G. Rodriguez, F. G. Karnell, A. C. Carpenter, J. C. Aster, D. Allman, and W. S. Pear Notch signaling is a potent inducer of growth arrest and apoptosis in a wide range of B-cell malignancies Blood, December 1, 2005; 106(12): 3898 - 3906. [Abstract] [Full Text] [PDF]
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H. Chang, Y. Gwack, D. Kingston, J. Souvlis, X. Liang, R. E. Means, E. Cesarman, L. Hutt-Fletcher, and J. U. Jung Activation of CD21 and CD23 Gene Expression by Kaposi's Sarcoma-Associated Herpesvirus RTA J. Virol., April 15, 2005; 79(8): 4651 - 4663. [Abstract] [Full Text] [PDF]
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 G. Troen, V. Nygaard, T.-K. Jenssen, I. M. Ikonomou, A. Tierens, E. Matutes, A. Gruszka-Westwood, D. Catovsky, O. Myklebost, G. Lauritzsen, et al. Constitutive Expression of the AP-1 Transcription Factors c-jun, junD, junB, and c-fos and the Marginal Zone B-Cell Transcription Factor Notch2 in Splenic Marginal Zone Lymphoma J. Mol. Diagn., November 1, 2004; 6(4): 297 - 307. [Abstract] [Full Text] [PDF]
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 H. Kiaris, K. Politi, L. M. Grimm, M. Szabolcs, P. Fisher, A. Efstratiadis, and S. Artavanis-Tsakonas Modulation of Notch Signaling Elicits Signature Tumors and Inhibits Hras1-Induced Oncogenesis in the Mouse Mammary Epithelium Am. J. Pathol., August 1, 2004; 165(2): 695 - 705. [Abstract] [Full Text] [PDF]
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F. Jundt, K. S. Probsting, I. Anagnostopoulos, G. Muehlinghaus, M. Chatterjee, S. Mathas, R. C. Bargou, R. Manz, H. Stein, and B. Dorken Jagged1-induced Notch signaling drives proliferation of multiple myeloma cells Blood, May 1, 2004; 103(9): 3511 - 3515. [Abstract] [Full Text] [PDF]
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C. Debacq, B. Asquith, M. Reichert, A. Burny, R. Kettmann, and L. Willems Reduced Cell Turnover in Bovine Leukemia Virus-Infected, Persistently Lymphocytotic Cattle J. Virol., December 15, 2003; 77(24): 13073 - 13083. [Abstract] [Full Text] [PDF]
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A. Cooper, E. Johannsen, S. Maruo, E. Cahir-McFarland, D. Illanes, D. Davidson, and E. Kieff EBNA3A Association with RBP-J{kappa} Down-Regulates c-myc and Epstein-Barr Virus-Transformed Lymphoblast Growth J. Virol., December 20, 2002; 77(2): 999 - 1010. [Abstract] [Full Text] [PDF]
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 P. M. Coussens, C. J. Colvin, K. Wiersma, A. Abouzied, and S. Sipkovsky Gene Expression Profiling of Peripheral Blood Mononuclear Cells from Cattle Infected with Mycobacterium paratuberculosis Infect. Immun., October 1, 2002; 70(10): 5494 - 5502. [Abstract] [Full Text] [PDF]
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Abstract
Introduction
