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Prepublished online as a Blood First Edition Paper on October 24, 2002; DOI 10.1182/blood-2002-06-1797.
NEOPLASIA
From the Departments of Pathobiology, Pathology and
Laboratory Medicine, and Animal Biology, University of Pennsylvania,
Philadelphia, PA.
B lymphomagenesis is an uncontrolled expansion of immature
precursors that fail to complete their differentiation program. This
failure could be at least partly explained by inappropriate expression
of several oncogenic transcription factors, such as Pax5 and Myc. Both
Pax5 and c-Myc are implicated in the pathogenesis of non-Hodgkin
lymphomas. To address their role in lymphomagenesis, we analyzed B-cell
lymphomas derived from p53-null bone marrow progenitors infected in
vivo by a Myc-encoding retrovirus. All Myc-induced lymphomas invariably
maintained expression of Pax5, which is thought to be incompatible with
terminal differentiation. However, upon culturing in vitro, several
cell lines spontaneously down-regulated Pax5 and its target
genes CD19, N-Myc, and MB1. Unexpectedly, other B-cell markers
(eg, CD45R) were also down-regulated, and markers of myeloid lineage
(CD11b and F4/80 antigen) were acquired instead. Moreover, cells
assumed the morphology reminiscent of myeloid cells. A pool of
F4/80-positive cells as well as several single-cell clones were
obtained and reinjected into syngeneic mice. Remarkably, pooled cells
rapidly re-expressed Pax5 and formed tumors of relatively mature
lymphoid phenotype, with surface immunoglobulins being abundantly
expressed. Approximately half of tumorigenic single-cell clones also
abandoned myeloid differentiation and gave rise to B lymphomas.
However, when secondary lymphoma cells were returned to in vitro
conditions, they once again switched to myeloid differentiation. This
process could be curbed via enforced expression of retrovirally encoded
Pax5. Our data demonstrate that some Myc target cells are bipotent
B-lymphoid/myeloid progenitors with the astonishing capacity to undergo
successive rounds of lineage switching.
(Blood. 2003;101:1950-1955) Trillions of highly specialized cells in the body
of a multicellular organism are derived from a single totipotent
cell One of their functions is to ensure expression of genes required for
B-cell maturation. For instance, E2A and EBF govern production of
immunoglobulin (Ig) light chains and recombinases responsible for Ig gene rearrangements.2 The other function of these
transcription factors is to preclude expression of genes specific for
alternative cell fates. Failure to do so could have unwanted
consequences. For example, ectopic expression of Notch on the surface
of bone marrow (BM) progenitors causes a switch from B- to
T-cell differentiation.3 Furthermore, the receptor for
granulocyte-macrophage colony-stimulating factor (GM-CSF) causes
preferential proliferation of myeloid precursors, potentially at the
expense of B-cell precursors. Thus, for B-lymphoid differentiation,
both Notch and GM-CSF receptor need to be silenced. Which transcription
factor precludes expression of Notch in B-cell progenitors is not
clear, but expression of GM-CSF receptor is known to be inhibited by
Pax5.4,5 Consequently, in Pax5-null mice, pro-B
lymphocytes are generated but do not remain committed to B-cell
lineage.6 Under certain circumstances, they can even differentiate into functional T cells.7 Pax5 also plays a
role in maintaining lineage identity: its forced inactivation in
previously committed pro-B cells via homologous recombination results
in the capacity to differentiate into macrophages in vitro and to reconstitute T-cell development in vivo.8
While the choice between pathways is obviously driven by transcription
factors, how these transcription factors themselves are regulated is
not completely understood.9,10 One possibility is that
their regulation is extrinsic, or instructive, whereby the cell reacts
to environmental and positional cues. The other, not necessarily
mutually exclusive scenario, involves an intrinsic mechanism: each cell
makes its choice in a random, stochastic manner. Busslinger et al have
proposed that Pax5 activation occurs in such an inefficient manner to
ensure that the progenitor cell retains other differentiation
options.11 Moreover, since gene expression during
differentiation is based largely on epigenetic mechanisms, there is
always a potential for reversal.12 Thus, some cells,
despite their seemingly committed status, might be able to
redifferentiate into a different lineage, in particular during hematopoiesis.
Neoplastic cells have been very useful for the studies on "lineage
promiscuity"13 as their differentiation programs are seldom completed. As early as 1957, a B-lymphoma cell line was established that upon culturing in vitro morphed into macrophagelike cells.14 Upon reinjection into animals, these cells were
tumorigenic and gave rise to myeloid tumors. Similar cell lines were
described in subsequent years: 70Z/3,15 Raf+Myc-induced
neoplasms,16 and several others (referenced in Borrello
and Phipps17). Interestingly, the conversion of
macrophages into B cells has not been documented. Moreover, the
propensity of B cells, but not T cells, to convert into
macrophages was unexpected, in light of the prevailing view that B and
T lymphocytes share a common nonmyeloid progenitor. It also implied the
existence of bipotential B-macrophage progenitors. Indeed, such
progenitors have been identified in hematopoietic malignancies,18 in fetal liver,19 and more
recently in adult bone marrow.20 These and other findings
have established that lineage switching is an integral part of at least
some differentiation programs.
Still, the role of lineage infidelity in cell fate specification is
poorly understood. Intriguing questions are (1) whether the
reversal of cell fate is itself reversible, allowing myeloidlike ex-B
cells to regain their lymphoid phenotype; and (2) how many transcription factors would need to oscillate to make such recurrent lineage infidelity possible. To answer these questions, we drew upon
our recently developed model for B-cell lymphoma based on the infection
of p53-null bone marrow progenitors with a retrovirus encoding the Myc
oncoprotein.21 Using this approach, we have generated
neoplastic lines that exclusively expressed B-cell markers when
passaged in vivo. However, several of them, obtained from independently
derived tumors, spontaneously acquired myeloid markers upon culturing
in vitro. We thus set out to determine what transcription factors are
involved in the switch between lymphoid and myeloid differentiation and
whether this process could occur repeatedly in the same cell.
Cell lines, tumors, and animals
Flow cytometric analyses and cell sorting
Histologic and cytochemical staining All tumor tissues were fixed in 10% neutral buffered-formalin (Fisher Scientific, Fair Lawn, NJ) and embedded in paraffin. Then, 5-micrometer sections were stained with hematoxylin and eosin (H&E). Cultured cells were spun onto slides, air-dried for 5 minutes, and stained with Hema-Quick II (Wright-Giemsa stain solution, Biochemical Sciences, Swedesboro, NJ) according to the manufacturer's recommendation.Polymerase chain reaction (PCR) analyses RNA isolation was performed using Tri-reagent (Sigma-Aldrich). Reverse transcription (RT) reactions were performed using SuperScript First-Strand Synthesis System for RT-PCR (Gibco BRL, Rockville, MD). PCRs were performed under the following conditions: denaturation at 95°C for 45 seconds, annealing at indicated temperatures for 45 seconds, and extension at 72°C for 60 seconds. All reactions were carried out for 35 cycles, with 5 minutes initial denaturing and 7 minutes final extension. "S" and "A" refer to sense and antisense primers, respectively. PCR analysis for VDJ-recombination was performed on genomic DNA, not cDNA (Table 1).
Generation of and infection by a murine Pax5-encoding retrovirus Full-length Pax5 cDNA flanked by EcoRI sites27 was subcloned into the MIGR1 bicistronic retrovirus.28 Subconfluent BOSC packaging cells were transfected with 10 µg of the Pax5 retroviral DNA using Lipofectamine Plus (Gibco BRL). At 3 days after transfection, the conditioned medium was harvested, supplemented with polybrene (10 mg/mL, Sigma-Aldrich), and mixed with Myc5 secondary tumor cells. Infected cells were cultured in vitro and subjected to flow cytometric analyses.
In vitro conversion to the myeloid phenotype of Myc-induced B lymphomas To determine whether any of the Myc/p53-null B lymphomas described in our earlier paper21 had been derived from B-macrophage precursors, cells from primary tumors were cultured in vitro on the monolayer of gamma-irradiated S17 cells in the presence of IL-7.22 In the first experiment, none of 7 tumor explants tested were immediately capable of growing in vitro: all cultures went through crises in which the majority of cells died. From such crises, 2 apparently immortal cell lines have emerged, corresponding to tumors Myc3 and Myc5.On gross and histolopathologic examinations, both tumors exhibited
typical lymphoma characteristics: soft texture, scant stroma, and the
presence of relatively monomorphic neoplastic cells with round or ovoid
basophilic nuclei with clumped chromatin at the periphery and thin rims
of eosinophilic cytoplasm (Figure 1A, top
left and bottom left panels). However, upon culturing in vitro, profound changes between Myc3 and Myc5 have emerged. While Myc3 cells
remained round and strictly nonadherent, Myc5 cells were somewhat
irregularly shaped and often adhered to the S17 feeder layer (data not
shown). To further contrast their morphologies, cells were spun onto
the surface of glass slides and stained with the Wright-Giemsa dye.
While cultured Myc3 cells resembled lymphocytes (top right panel), most
Myc5 cells were much larger, with irregularly shaped nuclei, and often
resembled granulocytes or monocytes (bottom right panel, top right and
bottom right corners, respectively). These differences were suggestive
of Myc3 retaining its B-cell differentiation and Myc5 converting to a
myeloid lineage.
To confirm that this was indeed the case, cultured cells were stained
with fluorescently labeled antibodies against B-lymphoid (CD45R and
CD19) and myeloid (F4/80 and CD11b) markers. As evidenced by data
presented in Figure 1B, top row, Myc3 cells were positive for the
former and negative for the latter, regardless of growth conditions (in
vivo as tumors or in vitro as cultured cells). In contrast, Myc5 cells
(bottom row) expressed lymphoid markers in vivo but almost exclusively
myeloid markers in vitro. No detectable CD19 and very little CD45R
expression was seen using flow cytometric analysis. To rule out
contamination with host macrophages or monocytes, we isolated genomic
DNA from "converted" Myc5 cells and performed VDJ-recombination
analysis as described in Li et al.23 Myc5 cells from both
the primary tumor and cell culture (but not control murine fibroblasts)
clearly contained the rearrangement, which was indicative of their
B-cell origin (Figure 2A). We thus
concluded that under our cell-culture conditions Myc5 cells
spontaneously acquire a myeloid phenotype. In subsequent experiments,
we have identified 2 additional Myc-induced tumors (MycA and MycB)
whose cells adopted myeloid Myc5-like phenotype when cultured in vitro (data not shown). This suggested that lineage plasticity is a common
attribute of Myc-transformed BM cells, not a peculiar trait of a
single-cell clone.
The switch between B-lymphoid and myeloid phenotypes is reversible To determine whether adoption of the myeloid fate is a terminal decision or could be reversed, we first obtained a pure population of CD45R-negative, F4/80-positive cells using fluorescent-activated cell sorting (FACS) (Figure 2B, fraction R3). These cells were separated from CD45R singly positive cells which have retained the B-cell phenotype (fraction R1) and from doubly positive cells undergoing transition to the myeloid phenotype (fraction R2). Cells from R3 fraction were expanded as described in "Materials and methods," analyzed using flow cytometry, and injected subcutaneously into syngeneic mice. Injected cells readily formed tumors after a short latent period (2-3 weeks). However, staining with lineage-specific antibodies revealed that, unlike parental R3 cells, tumor cells no longer expressed myeloid markers (eg, CD11b, Figure 2C) but were once again strongly positive for B-cell markers (eg, CD45R and CD19). Interestingly, these secondary B lymphomas were also positive for sIgM and sIgD and thus possessed a more mature phenotype than primary Myc5 neoplasms (Figure 2C).To rule out the possibility that secondary tumors were derived from rare CD45R-positive cells present in the R3 fraction, we obtained single-cell clones with confirmed myeloid phenotype. Expansion of such clones took several weeks, and during this period further myeloid differentiation occurred, as evidenced by their yet more adherent phenotype. Consequently, some of the clones were no longer tumorigenic. Those that were fell into 2 groups. Approximately half of clones (exemplified by clone 5/12) formed slow-growing tumors that have not acquired B-cell markers (Figure 2D, top left). Consistent with this, on histopathologic examination neoplastic cells exhibited nuclear and cellular polymorphism, with a large number of cells possessing lobated nuclei suggestive of granulocyte differentiation (Figure 2D, top right). However, other clones (exemplified by clone 5/5) were growing faster and formed tumors composed of cells that were strongly CD45R-positive and only weakly CD11b-positive (Figure 2C, bottom left). This suggested that they were undergoing the process of differentiation back to B-cell lineage. Indeed, H&E staining has revealed that cells with lobated nuclei were interspersed among larger cells with round hyperchromatic nuclei, distinct nucleoli, and a small amount of eosinophilic cytoplasm (Figure 2C, bottom right). The latter type was reminiscent of B cells comprising the original Myc5 tumor. Therefore, we concluded that even Myc5 single-cell clones of apparently myeloid phenotype were capable of resuming their original differentiation program. EBF and Pax5 genes are silenced upon the switch to the myeloid phenotype To determine what transcription factors are responsible for lineage infidelity in Myc5 cells, we utilized an RT-PCR approach. Oligonucleotide primers specific for genes encoding B-cell-specific transcription factors were generated. They were used to probe expression of PU.1, E12, E47, EBF, and Pax5. These factors are thought to appear in that order in differentiating B cells.1 Predictably, all of them were expressed in control Myc3 cells, whether they had been obtained from the primary tumor, in vitro cultures, or a secondary tumor (Figure 3). In contrast, in Myc5 cells only the first 3 factors were expressed under all conditions, but EBF and Pax5 were expressed only in tumors but not cultured cells (Figure 3, dotted rectangle). Consistent with this finding, expression of several Pax5 target genes, such as N-Myc and MB1, was also undetectable in vitro. To extend the correlation between Pax5 silencing and the myeloid phenotype, we have also analyzed 2 other Myc5-like tumors, MycA and MycB. As evidenced by data in the bottom 2 panels, MycA and MycB tumors were positive for Pax5 expression, but the corresponding cell lines were not. We thus hypothesized that lineage infidelity was attributable to the silencing of EBF and Pax5 and could be prevented by enforced expression of one of these factors.
Enforced expression of Pax5 prevents acquisition of the myeloid-specific marker CD11b To assess the role of Pax5 in lineage infidelity, we have generated a Pax5-encoding retrovirus. Pax5 cDNA was inserted into the bicistronic MIGR1 retrovirus carrying the GFP gene and the long terminal repeats from murine stem cell retrovirus28 (Figure 4A). The retroviral construct was transiently transfected into packaging BOSC23 cells, and the supernatant was used to infect Myc5 cells from a secondary tumor. Upon infection, cells were subjected to FACS, and single "green" cells were sorted, placed into individual wells, and expanded. Control clones expressing "empty" vector were also obtained. Both types of clones were then stained with antibodies against B-cell marker CD19 and myeloid marker CD11b. None of the clones analyzed were positive for CD19, confirming the earlier observation that Pax5 alone is not sufficient for CD19 expression5 and differentiation into bona fide B cells. However, GFP and Pax5/GFP clones differed drastically in the pattern of CD11b expression. All 8 GFP clones were positive for this marker, indicating that they once again had reverted to the myeloid phenotype (Figure 4C, top row). In contrast, all 8 GFP/Pax5 clones were CD11b-negative (bottom row) and thus were not undergoing conversion to macrophagelike cells. This finding suggested that while enforced expression of Pax5 alone is not sufficient to maintain the B-cell phenotype, it is sufficient to block the switch from B-cell to myeloid differentiation.
Here we demonstrate for the first time the existence of bone marrow precursors that upon neoplastic transformation "freeze" in a peculiar differentiation stage. The hallmark of this stage is the ability to retain the potential for both B-cell and myeloid differentiation even after the choice of fate is seemingly made. While the ability of some immature B lymphomas to acquire the myeloid phenotype has been previously reported,14-16 it was assumed that switching from lymphoid to myeloid lineage was irreversible. We have discovered that cells with overt myeloid phenotype could, upon return to in vivo conditions, retrace their steps and resume differentiation into relatively mature B cells expressing surface immunoglobulins, even though the original tumor was composed of prepro-B cells.21 Remarkably, even these sIgM- and sIgD-positive cells are not firmly committed to B-lymphoid lineage either as they readily reacquire the myeloid markers in culture. It is also noteworthy that this astonishing capacity to undergo successive rounds of lineage switching apparently relies on a single pair of transcription factors, EBF and Pax5. We do not know at present whether regulations of EBF and Pax5 are achieved independently or whether gain and loss of Pax5 rely on regulation of EBF, its upstream activator.2 We have learned, however, that enforced expression of Pax5 is sufficient to prevent myeloid differentiation, although it is clearly not sufficient to sustain B-lymphoid differentiation. The latter finding corroborates earlier observations that concerted expression of several transcription factors is required for the B-cell phenotype.5,29,30 However, it appears that targeted inactivation of just one transcription factor (ie, Pax5) in neoplastic B cells would have a profound effect not only on their differentiation, but also on the rate of tumor growth. Thus, our results suggest that Pax5 might be a legitimate therapeutic target in lymphoplasmacytoid lymphomas with t(9;14)(p13;q32) translocations affecting the Pax5 gene. This hypothesis is in accord with the recent findings that even a brief inactivation of the Myc oncoprotein in pre-existing neoplasms results in sustained tumor regression.31,32 Whether or not this holds true for Pax5 could be verified in the future, as new gene targeting techniques are becoming available.
We thank Xin Yin and Gautam Rajpal for their help with performing RT-PCR assays and Dr Christopher Hunter (University of Pennsylvania) for the gift of several antibodies. We are indebted to various members of our laboratories for many stimulating discussions.
Submitted June 19, 2002; accepted October 10, 2002.
Prepublished online as Blood First Edition Paper, October 24, 2002; DOI 10.1182/blood-2002-06-1797.
Supported by National Cancer Institute grants CA 71881 and CA 97932 (A.T.-T.).
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: Andrei Thomas-Tikhonenko, Department of Pathobiology, University of Pennsylvania, 3800 Spruce St, M/C 6051, Philadelphia, PA 19104-6051; e-mail: andreit{at}mail.vet.upenn.edu.
1. Kee BL, Murre C. Transcription factor regulation of B lineage commitment. Curr Opin Immunol. 2001;13:180-185[CrossRef][Medline] [Order article via Infotrieve]. 2. O'Riordan M, Grosschedl R. Coordinate regulation of B cell differentiation by the transcription factors EBF and E2A. Immunity. 1999;11:21-31[CrossRef][Medline] [Order article via Infotrieve]. 3. Pui JC, Allman D, Xu LW, et al. Notch1 expression in early lymphopoiesis influences B versus T lineage determination. Immunity. 1999;11:299-308[CrossRef][Medline] [Order article via Infotrieve].
4.
Chiang MY, Monroe JG.
Role for transcription Pax5A factor in maintaining commitment to the B cell lineage by selective inhibition of granulocyte-macrophage colony-stimulating factor receptor expression.
J Immunol.
2001;166:6091-6098
5.
Chiang MY, Monroe JG.
BSAP/Pax5A expression blocks survival and expansion of early myeloid cells implicating its involvement in maintaining commitment to the B-lymphocyte lineage.
Blood.
1999;94:3621-3632 6. Nutt SL, Heavey B, Rolink AG, Busslinger M. Commitment to the B-lymphoid lineage depends on the transcription factor Pax5. Nature. 1999;401:556-562[CrossRef][Medline] [Order article via Infotrieve]. 7. Rolink AG, Nutt SL, Melchers F, Busslinger M. Long-term in vivo reconstitution of T-cell development by Pax5-deficient B-cell progenitors. Nature. 1999;401:603-606[CrossRef][Medline] [Order article via Infotrieve].
8.
Mikkola I, Heavey B, Horcher M, Busslinger M.
Reversion of B cell commitment upon loss of Pax5 expression.
Science.
2002;297:110-113
9.
Metcalf D.
Lineage commitment and maturation in hematopoietic cells: The case for extrinsic regulation.
Blood.
1998;92:345-348
10.
Enver T, Heyworth CM, Dexter TM.
Do stem cells play dice?
Blood.
1998;92:348-351 11. Busslinger M, Nutt SL, Rolink AG. Lineage commitment in lymphopoiesis. Curr Opin Immunol. 2000;12:151-158[CrossRef][Medline] [Order article via Infotrieve]. 12. Surani MA. Reprogramming of genome function through epigenetic inheritance. Nature. 2001;414:122-128[CrossRef][Medline] [Order article via Infotrieve].
13.
Greaves MF, Chan LC, Furley AJW, Watt SM, Molgaard HV.
Lineage promiscuity in hematopoietic differentiation and leukemia.
Blood.
1986;67:1-11 14. Dawe CJ, Potter M. Morphologic and biologic progression of a lymphoid neoplasm of the mouse in vitro and in vivo. Am J Pathol. 1957;33:603[Medline] [Order article via Infotrieve].
15.
Hara H, Sam M, Maki RA, Wu GE, Paige CJ.
Characterization of A 70Z/3 pre-B-cell derived macrophage clone 16. Klinken SP, Alexander WS, Adams JM. Hemopoietic lineage switch: v-raf oncogene converts Eµ-myc transgenic B cells into macrophages. Cell. 1988;53:857-867[CrossRef][Medline] [Order article via Infotrieve]. 17. Borrello MA, Phipps RP. The B/macrophage cell: An elusive link between CD5(+) B lymphocytes and macrophages. Immunol Today. 1996;17:471-475[CrossRef][Medline] [Order article via Infotrieve].
18.
Davidson WF, Pierce JH, Rudikoff S, Morse HC.
Relationships between B-cell and myeloid differentiation 19. Cumano A, Paige CJ, Iscove NN, Brady G. Bipotential precursors of B-cells and macrophages in murine fetal liver. Nature. 1992;356:612-615[CrossRef][Medline] [Order article via Infotrieve]. 20. Montecino-Rodriguez E, Leathers H, Dorshkind K. Bipotential B-macrophage progenitors are present in adult bone marrow. Nat Immun. 2001;2:83-88[CrossRef]. 21. Yu D, Thomas-Tikhonenko A. A non-transgenic mouse model for B-cell lymphoma: in vivo infection of p53-null bone marrow progenitors by a myc retrovirus is sufficient for tumorigenesis. Oncogene. 2002;21:1922-1927[CrossRef][Medline] [Order article via Infotrieve]. 22. Cumano A, Dorshkind K, Gillis S, Paige CJ. The influence of S17 stromal cells and interleukin-7 on B-cell development. Eur J Immunol. 1990;20:2183-2189[Medline] [Order article via Infotrieve].
23.
Li YS, Hayakawa K, Hardy RR.
The regulated expression of B lineage associated genes during B cell differentiation in bone marrow and fetal liver.
J Exp Med.
1993;178:951-960 24. Lin HH, Grosschedl R. Failure of B-cell differentiation in mice lacking the transcription factor EBF. Nature. 1995;376:263-267[CrossRef][Medline] [Order article via Infotrieve]. 25. Li YS, Wasserman R, Hayakawa K, Hardy RR. Identification of the earliest B lineage stage in mouse bone marrow. Immunity. 1996;5:527-535[CrossRef][Medline] [Order article via Infotrieve]. 26. Nagy A, Moens C, Ivanyi E, et al. Dissecting the role of N-myc in development using a single targeting vector to generate a series of alleles. Curr Biol. 1998;8:661-664[CrossRef][Medline] [Order article via Infotrieve].
27.
Maitra S, Atchison M.
BSAP can repress enhancer activity by targeting PU.1 function.
Mol Cell Biol.
2000;20:1911-1922
28.
Pear WS, Miller JP, Xu L, et al.
Efficient and rapid induction of a chronic myelogenous leukemia-like myeloproliferative disease in mice receiving P210 bcr/abl-transduced bone marrow.
Blood.
1998;92:3780-3792
29.
Kee BL, Murre C.
Induction of early B cell factor (EBF) and multiple B lineage genes by the basic helix-loop-helix transcription factor E12.
J Exp Med.
1998;188:699-713 30. Sigvardsson M, ORiordan M, Grosschedl R. EBF and E47 collaborate to induce expression of the endogenous immunoglobulin surrogate light chain genes. Immunity. 1997;7:25-36[CrossRef][Medline] [Order article via Infotrieve].
31.
Jain M, Arvanitis C, Chu K, et al.
Sustained loss of a neoplastic phenotype by brief inactivation of MYC.
Science.
2002;297:102-104 32. Pelengaris S, Khan M, Evan GI. Suppression of Myc-induced apoptosis in beta cells exposes multiple oncogenic properties of Myc and triggers carcinogenic progression. Cell. 2002;109:321-334[CrossRef][Medline] [Order article via Infotrieve].
© 2003 by The American Society of Hematology.
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  D. Schneider, M. A. Manzan, R. B. Crawford, W. Chen, and N. E. Kaminski 2,3,7,8-Tetrachlorodibenzo-p-dioxin-Mediated Impairment of B Cell Differentiation Involves Dysregulation of Paired Box 5 (Pax5) Isoform, Pax5a J. Pharmacol. Exp. Ther., August 1, 2008; 326(2): 463 - 474. [Abstract] [Full Text] [PDF]
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 A. L. Feldman, D. A. Arber, S. Pittaluga, A. Martinez, J. S. Burke, M. Raffeld, M. Camos, R. Warnke, and E. S. Jaffe Clonally related follicular lymphomas and histiocytic/dendritic cell sarcomas: evidence for transdifferentiation of the follicular lymphoma clone Blood, June 15, 2008; 111(12): 5433 - 5439. [Abstract] [Full Text] [PDF]
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F. Mora-Lopez, E. Reales, J. A. Brieva, and A. Campos-Caro Human BSAP and BLIMP1 conform an autoregulatory feedback loop Blood, November 1, 2007; 110(9): 3150 - 3157. [Abstract] [Full Text] [PDF]
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D. Yu, M. Carroll, and A. Thomas-Tikhonenko p53 status dictates responses of B lymphomas to monotherapy with proteasome inhibitors Blood, June 1, 2007; 109(11): 4936 - 4943. [Abstract] [Full Text] [PDF]
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 S. Hodawadekar, F. Wei, D. Yu, A. Thomas-Tikhonenko, and M. L. Atchison Epigenetic Histone Modifications Do Not Control Ig{kappa} Locus Contraction and Intranuclear Localization in Cells with Dual B Cell-Macrophage Potential J. Immunol., November 1, 2006; 177(9): 6165 - 6171. [Abstract] [Full Text] [PDF]
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 K. A. O'Donnell, D. Yu, K. I. Zeller, J.-w. Kim, F. Racke, A. Thomas-Tikhonenko, and C. V. Dang Activation of Transferrin Receptor 1 by c-Myc Enhances Cellular Proliferation and Tumorigenesis. Mol. Cell. Biol., March 1, 2006; 26(6): 2373 - 2386. [Abstract] [Full Text] [PDF]
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 S. Buonocore, A. L. Valente, D. Nightingale, J. Bogart, and A.-K. Souid Histiocytic Sarcoma in a 3-Year-Old Male: A Case Report Pediatrics, August 1, 2005; 116(2): e322 - e325. [Abstract] [Full Text] [PDF]
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 D. Yu, M. Dews, A. Park, J. W. Tobias, and A. Thomas-Tikhonenko Inactivation of Myc in Murine Two-Hit B lymphomas Causes Dormancy with Elevated Levels of Interleukin 10 Receptor and CD20: Implications for Adjuvant Therapies Cancer Res., June 15, 2005; 65(12): 5454 - 5461. [Abstract] [Full Text] [PDF]
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M. S. Ricci, Z. Jin, M. Dews, D. Yu, A. Thomas-Tikhonenko, D. T. Dicker, and W. S. El-Deiry Direct Repression of FLIP Expression by c-myc Is a Major Determinant of TRAIL Sensitivity Mol. Cell. Biol., October 1, 2004; 24(19): 8541 - 8555. [Abstract] [Full Text] [PDF]
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H. M. Bond, M. Mesuraca, E. Carbone, P. Bonelli, V. Agosti, N. Amodio, G. De Rosa, M. Di Nicola, A. M. Gianni, M. A. S. Moore, et al. Early hematopoietic zinc finger protein (EHZF), the human homolog to mouse Evi3, is highly expressed in primitive human hematopoietic cells Blood, March 15, 2004; 103(6): 2062 - 2070. [Abstract] [Full Text] [PDF]
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Top
Abstract
Introduction
the fertilized egg. The descendants of this cell form the
blastocyst and the inner cell mass, the latter being composed of
pluripotent stem cells still capable of adopting any cell fate.
However, with each successive differentiation step, the choice of fates
becomes more limited. For instance, hematopoietic stem cells give rise to lymphoid and myeloid progenitors but not stromal tissues.
Furthermore, lymphoid stem cells give rise to B and T lymphocytes and
natural killer cells but not to macrophages, granulocytes, or
other cells of myeloid lineage. Such lineage commitment relies on
timely activation of appropriate transcription factors and silencing of
inappropriate ones. In B-cell differentiation, key transcription
factors are PU.1, E2A, EBF, and Pax5 (also known as BSAP;
reviewed in Kee and Murre
refer to
positive and negative staining, respectively.
