Published by Oxford University Press 2008.
Genetic and Environmental Cofactors of Myc Translocations in Plasma Cell Tumor Development in Mice
Affiliation of author: Laboratory of Genetics, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
Correspondence to: Siegfried Janz, Laboratory of Genetics, National Cancer Institute, Bldg 37, Rm 2B10, Bethesda, MD 20892-4256 (e-mail: sj4s{at}nih.gov).
 |
ABSTRACT |
|---|
 Top Abstract Lymphoma- and Leukemia...LLA-CTs Are Insufficient to...Myc Translocation in Mouse...Features of Mouse T(12;15)(Igh...Genetic Host Susceptibility Is...Environmental Influences Promote...NotesReferences |
|---|
Peritoneal plasmacytomagenesis in inbred BALB/c mice affords an experimental model system for the study of the mechanism by which naturally occurring Myc (c-myc) translocations collaborate with host susceptibility factors and environmental influences in tumor development. Mouse plasmacytoma is initiated in
80% of cases by a balanced chromosomal T(12;15)(Igh-Myc) translocation that results in a mode of Myc deregulation that renders the survival and outgrowth of the translocation-bearing tumor precursor exquisitely dependent upon factors provided by sustained inflammation (IL-6) and gut flora microbes. Tumor susceptibility genes of BALB/c, such as weak efficiency alleles of genes encoding p16Ink4a and Frap (mTOR), are also required for plasmacytoma, although the pathways linking these genes with deregulated Myc and the environment have not yet been elucidated. The findings in mouse plasmacytoma may be relevant for hematopoietic neoplasms in human beings, in which leukemia- and lymphoma-associated chromosomal translocation (LLA-CT) is much more frequent than subsequent neoplasia. Just like T(12;15)-carrying B-lymphocytes and plasma cells in mice, the malignant transformation of LLA-CT–bearing blood cells in humans may be a rare occurrence that requires several genetic and environmental cofactors to take place.
|
Lymphoma- and Leukemia-Associated Chromosomal Translocations |
|---|
|
TopAbstractLymphoma- and Leukemia...LLA-CTs Are Insufficient to...Myc Translocation in Mouse...Features of Mouse T(12;15)(Igh...Genetic Host Susceptibility Is...Environmental Influences Promote...NotesReferences |
|---|
Although balanced chromosomal translocations that result in deregulated expression of cellular oncogenes or generation of novel fusion genes occur consistently in hematopoietic neoplasms, these translocations by themselves are insufficient to cause malignant cell transformation. This contention is supported by evidence on the occurrence of lymphoma- and leukemia-associated chromosomal translocations (LLA-CTs) in blood cells that are not neoplastic. Relying on highly sensitive genomic polymerase chain reaction (PCR) methods and reverse transcriptase (RT)–PCR methods as research tools, genomic rearrangements and chimeric transcripts underlying LLA-CTs have been repeatedly detected in healthy individuals. The implication is that LLA-CT may be silently present in healthy individuals if they are protected from the corresponding neoplasms by the lack of cofactors that would otherwise collaborate with translocation to promote oncogenesis. Cofactors of this sort may be genetic (eg, tumor susceptibility and modifier genes) or environmental (often concealed in complex dietary, microbial, infectious, or life-style influences). To uncover cofactors of translocation in tumor development, epidemiologists study the direct association of LLA-CT with risk of subsequent lymphoma or leukemia. Tumor biologists complement this effort by evaluating the conditions under which clones of translocation-harboring cells persist, expand, and finally undergo transformation to malignancy. Enhanced understanding of the cellular pathways that link LLA-CT with neoplasia is an important goal of these studies. Experimental model systems of hematopoietic neoplasms in mice may aid this goal by permitting us to define the factors that select subsets of translocation-bearing cells to become the clonogenic founders of malignant lymphoma or leukemia. This report will focus on insights gathered from a uniquely useful mouse model to that end, BALB/c plasmacytoma.
|
LLA-CTs Are Insufficient to Cause Blood Cancer in Human Beings |
|---|
|
TopAbstractLymphoma- and Leukemia...LLA-CTs Are Insufficient to...Myc Translocation in Mouse...Features of Mouse T(12;15)(Igh...Genetic Host Susceptibility Is...Environmental Influences Promote...NotesReferences |
|---|
Cancer cytogenetics has firmly associated specific translocations with specific kinds of blood cancers. Among the most widely known examples are t(14;18)(q32;q21) in follicular lymphoma and t(9;22)(q34;q11) in chronic myelogenous leukemia. These translocations illustrate the two main types of LLA-CT: those that deregulate oncogenes by promoter and/or enhancer juxtaposition as opposed to those that create novel in-frame fusion genes by illegitimate recombination of two different loci (usually) residing on two different chromosomes. The emerging understanding that such translocations can also be detected in healthy individuals has replaced the long-standing assumption that LLA-CT indicates the presence of hematopoietic malignancy. The first report on translocation occurrence in healthy individuals was that of Philip Kluin and his colleagues in 1991 on the BCL2-activating t(14;18)(q32;q21) translocation (1). Since this seminal publication, evidence for two other oncogene-activating translocations has been obtained: t(8;14)(q24;q32) (2), which results in the deregulated expression of MYC (c-myc), and t(11;14)(q13;q32) (3), which deregulates CCND1 (cyclin D1). The evidence for fusion-gene translocations in healthy individuals is even stronger, as six different examples have been reported thus far: t(9;22)(q34;q11), t(4;11)(q21;q23), t(15;17)(q22;q11), t(12;21)(p13;q22), t(8;21)(q22;q22), and t(2;5)(p23;q35) [reviewed in (4)]. These translocations encode the BCR-ABL, MLL-AF4, PML-RAR
, TEL-AML1, AML1-ETO, and NPM-ALK fusion proteins, respectively. The detection of LLA-CT in healthy individuals has not only challenged the paradigm that these genetic accidents are oncogenic per se but also focused our attention on the cofactors that may drive translocation-bearing cells in some cases to undergo full malignant transformation. |
Myc Translocation in Mouse Plasmacytoma—The Premier Experimental Model System of LLA-CT |
|---|
|
TopAbstractLymphoma- and Leukemia...LLA-CTs Are Insufficient to...Myc Translocation in Mouse...Features of Mouse T(12;15)(Igh...Genetic Host Susceptibility Is...Environmental Influences Promote...NotesReferences |
|---|
Numerous LLA-CTs in human beings, including all translocations detected thus far in healthy individuals, have been recapitulated in transgenic mice with varying degrees of accuracy. Excellent reviews are available of the models for t(14;18)(q32;q21) (5), t(8;14)(q24;q32) (6), t(11;14)(q13;q32) (7), t(9;22)(q34;q11) (8), t(4;11)(q21;q23) (9), t(15;17)(q22;q11) (10), t(12;21)(p13;q22) and t(8;21)(q22;q22) (11), and t(2;5)(p23;q35) (12). Mice harboring transgenes that mimic these LLA-CTs have been invaluable in establishing the role of translocations in tumor etiology; elucidating the collaboration of LLA-CTs with oncogenes and tumor suppressor genes; and, in one specific case of fusion-gene translocation, PML-RAR
, demonstrating that both products of translocation are required to recreate the neoplastic phenotype (13). The transgenic recapitulation of LLA-CT in mice has also provided biologic understanding of the existence and implications of oncogenic translocations in the absence of lymphoma or leukemia. A general limitation of most transgenic mouse models of LLA-CT is that they bypass the acquisition of chromosomal translocation, which, under normal conditions, is a stochastic, spontaneous, rare somatic mutation event that either results in the generation of a tumor precursor (initiating oncogenic event) or promotes the ongoing neoplastic transformation of a preexisting precursor (tumor progression event). The only mouse model without this limitation is peritoneal plasmacytomagenesis [reviewed in (14)]. Mouse plasmacytomas are inflammation-dependent neoplasms of terminally differentiated B-lymphocytes, plasma cells, that can be readily induced in strain BALB/c by intraperitoneal administration of proinflammatory agents, such as pristane [reviewed in (15)]. Virtually, all plasmacytomas contain a naturally occurring, balanced chromosomal translocation that results in the deregulated expression of the Myc (c-myc) oncogene (Figure 1). Analogous translocations are seen in mature B-cell neoplasms in human beings (most commonly in Burkitt lymphoma) and rats (immunocytoma) [reviewed in (14)].
|
Myc-dependent plasmacytoma development in highly prolific, manipulable, and genetically defined BALB/c mice maintained under controlled environmental conditions is a good model system to determine biological factors that collaborate during oncogenesis with a specific, spontaneously acquired LLA-CT. Cofactors of this sort may be of further relevance for LLA-CT–driven blood cancer in human beings, particularly MYC-induced Burkitt lymphoma.
|
Features of Mouse T(12;15)(Igh-Myc) |
|---|
|
TopAbstractLymphoma- and Leukemia...LLA-CTs Are Insufficient to...Myc Translocation in Mouse...Features of Mouse T(12;15)(Igh...Genetic Host Susceptibility Is...Environmental Influences Promote...NotesReferences |
|---|
Most BALB/c plasmacytomas contain a reciprocal T(12;15) translocation that rearranges the immunoglobulin heavy-chain locus, Igh, and Myc. T(12;15)(Igh-Myc) is the only cancer-associated chromosomal translocation in mice that takes place with high incidence (approximately 80% of tumors). Furthermore, translocation occurs predictably in a specific cell type (B-lymphocyte lineage) that can be readily obtained ex vivo and studied in vitro. This affords an experimental model system in which the molecular mechanism of translocation (16,17) and the biology of the translocation-bearing cell can be evaluated. A range of PCR methodologies has been developed to detect T(12;15) in various genetic backgrounds, ages, and treatment conditions. The ability to identify and follow changes in the reciprocal Igh-Myc breakpoint junctions that underlie T(12;15) has provided a powerful tool to study the time of occurrence and fine structure of translocation. It is now known that the T(12;15) translocation is an initiating event in inflammation-induced plasmacytoma development, as translocation-bearing cell clones can be detected long before tumors arise (18, 19). T(12;15) appears to be a dynamic process that begins with a reciprocal exchange between Myc and the far upstream region of the Igh constant gene locus, CH, progresses by aberrant isotype switching that approximates Myc to the E
enhancer (20), and undergoes further clonal diversification by microdeletions in the junction flanks (21). The breakpoint sequence has also been employed as a clonotypic marker to evaluate the trafficking of Igh-Myc–containing cell clones in mice undergoing tumor induction (22) and to monitor the transfer of cell clones in vivo (23). |
Genetic Host Susceptibility Is a Crucial Cofactor of T(12;15) in Tumor Development |
|---|
|
TopAbstractLymphoma- and Leukemia...LLA-CTs Are Insufficient to...Myc Translocation in Mouse...Features of Mouse T(12;15)(Igh...Genetic Host Susceptibility Is...Environmental Influences Promote...NotesReferences |
|---|
There is a striking difference in genetic susceptibility to plasmacytoma development in mice. Strain BALB/c is highly susceptible, whereas DBA/2N and many other common strains of inbred mice are solidly resistant. Despite its genetic resistance, DBA/2N generates Igh-Myc–containing cell clones, albeit with low frequency and minimal clonal expansion. After treatment with pristane, 2 out of 20 (10%) DBA/2N mice compared to 32 of 44 (73%) BALB/c mice were positive for reciprocal Igh-Myc junctions by semi-quantitative competitive PCR. The average clone size in DBA/2N was smaller than in BALB/c (24). In a second study using a more sensitive PCR method, the findings in strain DBA/2N were extended to two additional plasmacytoma-resistant strains: C3H/HeJ and C57BL/6. The three plasmacytoma-resistant strains were confirmed to have a lower prevalence of aberrant clones, 33% overall, compared to 91% for BALB/c (22). These studies have implicated plasmacytoma susceptibility alleles of strain BALB/c, including weak alleles of genes encoding p16INK4a (25) and Frap (26), in the survival and expansion of T(12;15)-bearing cell clones.
|
Environmental Influences Promote T(12;15)-Containing Tumor Precursors |
|---|
|
TopAbstractLymphoma- and Leukemia...LLA-CTs Are Insufficient to...Myc Translocation in Mouse...Features of Mouse T(12;15)(Igh...Genetic Host Susceptibility Is...Environmental Influences Promote...NotesReferences |
|---|
Exposure to cholera toxin, a strong stimulator of IgA antibody production, increased the frequency of Igh(C
)-Myc–bearing clones in mice by 3- to 5-fold (27), thus associating translocation occurrence with normal immune responses. This finding is consistent with tumor induction studies in BALB/c mice that have implicated immune stimulation of the B-cell compartment as a cofactor of plasmacytomagenesis. Forty to sixty percent of mice raised in a "gut flora-rich" nonspecific pathogen-free (SPF) colony developed plasmacytoma by day 300 after tumor induction, whereas mice raised in a germ-free (gnotobiotic) environment or a "gut flora-poor" SPF environment were either resistant to these tumors (28) or exhibited a very low tumor incidence of 
5% (29). It is not known whether gut flora antigens promote plasmacytoma by increasing the probability of translocation, enhancing the survival and outgrowth of translocation-bearing cells, or both. The inflammatory milieu of plasmacytoma development, with the principal driver being IL-6, is of further importance for the fate of translocation-bearing cells. IL-6 is a multifunctional cytokine that stimulates the growth, survival, and terminal differentiation of normal and neoplastic B-lymphocytes. Plasmacytoma development requires that the BALB/c mice be treated with an inflammatory agent that provokes the formation of a chronic granulomatous tissue, a source of IL-6 in situ (30). Plasmacytomagenesis is inhibited when the mice are treated with antibody to IL-6 or IL-6 receptor (31). Tumors are abrogated in BALB/c mice homozygous for an IL-6 null allele (32). Conversely, BALB/c mice carrying a widely expressed human IL6 transgene develop T(12;15)-harboring plasmacytomas spontaneously; ie, without treatment with an inflammatory agent (23).
These findings indicate that environmental influences interact with host susceptibility factors to determine the frequency and outcome of T(12;15). That this interaction is not always easy to demonstrate is illustrated by one study in which the administration of indomethacin to BALB/c mice undergoing plasmacytoma induction resulted in a striking inhibition of plasmacytomagenesis without corresponding reduction of Igh-Myc recombination frequency (33). Thus, even in a controlled mouse study that minimizes all variables related to host susceptibility and environment, it can be difficult to establish the direct association of translocation frequency and tumor incidence. Considering the complexities encountered in epidemiologic studies in human beings, the identification of cofactors of LLA-CT in neoplastic development remains a big challenge.
|
NOTES |
|---|
The contribution of former laboratory members, particularly Jürgen R. Müller, Alexander L. Kovalchuk, and Allen E. Coleman, is gratefully acknowledged. This research was supported by the Intramural Research Program of the National Institutes of Health, National Cancer Institute, Center for Cancer Research.
|
REFERENCES |
|---|
|
TopAbstractLymphoma- and Leukemia...LLA-CTs Are Insufficient to...Myc Translocation in Mouse...Features of Mouse T(12;15)(Igh...Genetic Host Susceptibility Is...Environmental Influences Promote...NotesReferences |
|---|
1. Limpens J, de Jong D, van Krieken JH, et al. Bcl-2/JH rearrangements in benign lymphoid tissues with follicular hyperplasia. Oncogene (1991) 6(12):2271–2276.[Web of Science][Medline]
2. Müller JR, Janz S, Goedert JJ, Potter M, Rabkin CS. Persistence of immunoglobulin heavy chain/c-myc recombination-positive lymphocyte clones in the blood of human immunodeficiency virus-infected homosexual men. Proc Natl Acad Sci USA (1995) 92(14):6577–6581.
3. Hirt C, Schuler F, Dolken L, Schmidt CA, Dolken G. Low prevalence of circulating t(11;14)(q13;q32)-positive cells in the peripheral blood of healthy individuals as detected by real-time quantitative PCR. Blood (2004) 104(3):904–905.
4. Janz S, Potter M, Rabkin CS. Lymphoma- and leukemia-associated chromosomal translocations in healthy individuals. Genes Chromosomes Cancer (2003) 36(3):211–223.[CrossRef][Web of Science][Medline]
5. Strasser A, O’Connor L, Huang DC, et al. Lessons from bcl-2 transgenic mice for immunology, cancer biology and cell death research. Behring Institute Mitteilungen (1996) (97):101–117.
6. Boxer LM, Dang CV. Translocations involving c-myc and c-myc function. Oncogene (2001) 20(40):5595–5610.[CrossRef][Web of Science][Medline]
7. Nakagawa M, Seto M, Hosokawa Y. Molecular pathogenesis of MALT lymphoma: two signaling pathways underlying the antiapoptotic effect of API2-MALT1 fusion protein. Leukemia (2006) 20(6):929–936.[CrossRef][Web of Science][Medline]
8. Wong S, Witte ON. The BCR-ABL story: bench to bedside and back. Annu Rev Immunol (2004) 22:247–306.[CrossRef][Web of Science][Medline]
9. Ayton PM, Cleary ML. Molecular mechanisms of leukemogenesis mediated by MLL fusion proteins. Oncogene (2001) 20(40):5695–5707.[CrossRef][Web of Science][Medline]
10. Bernardi R, Pandolfi PP. Role of PML and the PML-nuclear body in the control of programmed cell death. Oncogene (2003) 22(56):9048–9057.[CrossRef][Web of Science][Medline]
11. Licht JD. AML1 and the AML1-ETO fusion protein in the pathogenesis of t(8;21) AML. Oncogene (2001) 20(40):5660–5679.[CrossRef][Web of Science][Medline]
12. Turner SD, Alexander DR. What have we learnt from mouse models of NPM-ALK-induced lymphomagenesis? Leukemia (2005) 19(7):1128–1134.[CrossRef][Web of Science][Medline]
13. He L, Bhaumik M, Tribioli C, et al. Two critical hits for promyelocytic leukemia. Mol Cell. (2001) 6(5):1131–1141.[Web of Science]
14. Janz S. Myc translocations in B cell and plasma cell neoplasms. DNA Repair (Amst) (2006) 5(9–10):1213–1224.[CrossRef][Medline]
15. Potter M. Neoplastic development in plasma cells. Immunol Rev. (2003) 194:177–195.[CrossRef][Web of Science][Medline]
16. Ramiro AR, Jankovic M, Eisenreich T, et al. AID is required for c-myc/IgH chromosome translocations in vivo. Cell. (2004) 118(4):431–438.[CrossRef][Web of Science][Medline]
17. Unniraman S, Zhou S, Schatz DG. Identification of an AID-independent pathway for chromosomal translocations between the Igh switch region and Myc. Nat Immunol (2004) 5(11):1117–1123.[CrossRef][Web of Science][Medline]
18. Janz S, Müller J, Shaughnessy J, Potter M. Detection of recombinations between c-myc and immunoglobulin switch alpha in murine plasma cell tumors and preneoplastic lesions by polymerase chain reaction. Proc Natl Acad Sci USA (1993) 90:7361–7365.
19. Müller JR, Potter M, Janz S. Differences in the molecular structure of c-myc-activating recombinations in murine plasmacytomas and precursor cells. Proc Natl Acad Sci USA (1994) 91(25):12066–12070.
20. Kovalchuk AL, Müller JR, Janz S. Deletional remodeling of c-myc-deregulating translocations. Oncogene (1997) 15:2369–2377.[CrossRef][Web of Science][Medline]
21. Kovalchuk AL, Mushinski EB, Janz S. Clonal diversification of primary BALB/c plasmacytomas harboring T(12;15) chromosomal translocations. Leukemia (2000) 14:909–921.[CrossRef][Web of Science][Medline]
22. Müller JR, Jones GM, Janz S, Potter M. Migration of cells with immunoglobulin/c-myc recombinations in lymphoid tissues of mice. Blood (1997) 89:291–296.
23. Kovalchuk AL, Kim JS, Park SS, et al. IL-6 transgenic mouse model for extraosseous plasmacytoma. Proc Natl Acad Sci USA (2002) 99(3):1509–1514.
24. Müller JR, Jones GM, Potter M, Janz S. Detection of immunoglobulin/c-myc recombinations in mice that are resistant to plasmacytoma induction. Cancer Res. (1996) 56(2):419–423.
25. Zhang S, Ramsay ES, Mock BA. Cdkn2a, the cyclin-dependent kinase inhibitor encoding p16INK4a and p19ARF, is a candidate for the plasmacytoma susceptibility locus, Pctr1. Proc Natl Acad Sci USA (1998) 95:2429–2434.
26. Bliskovsky V, Ramsay ES, Scott J. Frap, FKBP12 rapamycin-associated protein, is a candidate gene for the plasmacytoma resistance locus Pctr2 and can act as a tumor suppressor gene. Proc Natl Acad Sci USA (2003) 100(25):14982–14987.
27. Roschke V, Kopantzev E, Dertzbaugh M, Rudikoff S. Chromosomal translocations deregulating c-myc are associated with normal immune responses. Oncogene (1997) 14:3011–3016.[CrossRef][Web of Science][Medline]
28. McIntire KR, Princler GL. Prolonged adjuvant stimulation in germ-free BALB-c mice: development of plasma cell neoplasia. Immunology (1969) 17(3):481–487.[Web of Science][Medline]
29. Byrd LG, McDonald AH, Gold LG, Potter M. Specific pathogen-free BALB/cAn mice are refractory to plasmacytoma induction by pristane. J Immunol (1991) 147:3632–3637.[Abstract]
30. Potter M, MacCardle RC. Histology of developing plasma cell neoplasia induced by mineral oil in BALB/c mice. J Natl Cancer Inst (1964) 33:497.[Web of Science][Medline]
31. Vink A, Coulie P, Warnier G, et al. Mouse plasmacytoma growth in vivo: enhancement by interleukin 6 (IL-6) and inhibition by antibodies directed against IL-6 or its receptor. J Exp Med (1990) 172:997–1000.
32. Lattanzio G, Libert C, Aquilina M, et al. Defective development of pristane-oil-induced plasmacytomas in interleukin-6-deficient BALB/c mice. Am J Pathol (1997) 151:689–696.[Abstract]
33. Potter M, Wax J, Jones GM. Indomethacin is a potent inhibitor of pristane and plastic disc induced plasmacytomagenesis in a hypersusceptible BALB/c congenic strain. Blood (1997) 90:260–269.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  C. S. Rabkin and S. Janz Overview of Mechanisms and Consequences of Chromosomal Translocation J Natl Cancer Inst Monographs, July 1, 2008; 2008(39): 1 - 1. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||