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Myc suppression of Nfkb2 accelerates lymphomagenesis.

Keller U, Huber J, Nilsson JA, Fallahi M, Hall MA, Peschel C, Cleveland JL - BMC Cancer (2010)

Bottom Line: Myc overexpression is associated with reduced activity of Rel/NF-kappaB, transcription factors that control the immune response, cell survival, and transformation, and that are frequently altered in cancer.NFKB2 suppression by Myc was also confirmed in primary human BL.These data thus link Myc-driven lymphomagenesis to the non-canonical NF-kappaB pathway.

View Article: PubMed Central - HTML - PubMed

Affiliation: III. Medical Department, Technische Universität München, Munich, Germany. ulrich.keller@lrz.tum.de

ABSTRACT

Background: Deregulated c-Myc expression is a hallmark of several human cancers where it promotes proliferation and an aggressive tumour phenotype. Myc overexpression is associated with reduced activity of Rel/NF-kappaB, transcription factors that control the immune response, cell survival, and transformation, and that are frequently altered in cancer. The Rel/NF-kappaB family member NFKB2 is altered by chromosomal translocations or deletions in lymphoid malignancies and deletion of the C-terminal ankyrin domain of NF-kappaB2 augments lymphocyte proliferation.

Methods: Precancerous Emicro-Myc-transgenic B cells, Emicro-Myc lymphomas and human Burkitt lymphoma samples were assessed for Nfkb2 expression. The contribution of Nfkb2 to Myc-driven apoptosis, proliferation, and lymphomagenesis was tested genetically in vivo.

Results: Here we report that the Myc oncoprotein suppresses Nfkb2 expression in vitro in primary mouse fibroblasts and B cells, and in vivo in the Emicro-Myc transgenic mouse model of human Burkitt lymphoma (BL). NFKB2 suppression by Myc was also confirmed in primary human BL. Promoter-reporter assays indicate that Myc-mediated suppression of Nfkb2 occurs at the level of transcription. The contribution of Nfkb2 to Myc-driven lymphomagenesis was tested in vivo, where Nfkb2 loss was shown to accelerate lymphoma development in Emicro-Myc transgenic mice, by impairing Myc's apoptotic response.

Conclusions: Nfkb2 is suppressed by c-Myc and harnesses Myc-driven lymphomagenesis. These data thus link Myc-driven lymphomagenesis to the non-canonical NF-kappaB pathway.

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Nfkb2 loss accelerates Myc-induced lymphomagenesis by impairing apoptosis. a) Effects of Nfkb2 deficiency on Myc-induced lymphomagenesis. The survival of Eμ-Myc transgenic littermates of the indicated Nfkb2 genotypes is shown. The differences in the rates of tumor incidence between the Nfkb2+/+ and the Nfkb2-/- littermates is statistically significant (p = 0.0307). b) Eμ-Myc transgenic littermates of the indicated Nfkb2 genotypes were injected with BrdU, and cells from bone marrow and spleen were harvested 12 hr later. BrdU-incorporation was analyzed using an antibody-dependent fluorescence assay. The bars show the mean percentage of cells in S phase ± SEM (three independent experiments). c) The apoptotic index of the indicated genotypes was analyzed using an antibody dependent fluorescence assay. Annexin V+ B220+ cells of sIgM- or sIgM+ phenotype are shown. The bars represent the mean ± SEM from three independent experiments. * indicates p < 0.05.
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Figure 4: Nfkb2 loss accelerates Myc-induced lymphomagenesis by impairing apoptosis. a) Effects of Nfkb2 deficiency on Myc-induced lymphomagenesis. The survival of Eμ-Myc transgenic littermates of the indicated Nfkb2 genotypes is shown. The differences in the rates of tumor incidence between the Nfkb2+/+ and the Nfkb2-/- littermates is statistically significant (p = 0.0307). b) Eμ-Myc transgenic littermates of the indicated Nfkb2 genotypes were injected with BrdU, and cells from bone marrow and spleen were harvested 12 hr later. BrdU-incorporation was analyzed using an antibody-dependent fluorescence assay. The bars show the mean percentage of cells in S phase ± SEM (three independent experiments). c) The apoptotic index of the indicated genotypes was analyzed using an antibody dependent fluorescence assay. Annexin V+ B220+ cells of sIgM- or sIgM+ phenotype are shown. The bars represent the mean ± SEM from three independent experiments. * indicates p < 0.05.

Mentions: The remarkable changes in the expression of components of the Rel/NF-κB signalling pathway, and particularly the suppression of Nfkb2 by c-Myc, suggested that NF-kB2 might play critical roles in Myc-driven tumorigenesis. If Myc-mediated reductions in Nfkb2 expression in Eμ-Myc B cells were important for Myc-mediated lymphomagenesis, we reasoned that total loss of Nfkb2 should affect lymphoma development. To test this hypothesis, Eμ-Myc transgenic mice were mated to Nfkb2-/- mice [6] and F1 offspring were bred to Nfkb2+/- mice to obtain the desired Eμ-Myc;Nfkb2+/+ and Eμ-Myc;Nfkb2-/- cohorts. These littermates were then observed for lymphoma onset. Eμ-Myc transgenic mice usually succumb to aggressive lymphoma within 4-8 months of birth [23]. As expected, non-transgenic Nfkb2-/- littermates showed no signs of tumour development throughout their lifespan (data not shown). Importantly, Eμ-Myc;Nfkb2-/- transgenic displayed a moderately accelerated course of lymphoma development and, accordingly, had a shorter lifespan, with a median survival of 171 days compared to 205 days median survival in their Eμ-Myc;Nfkb2+/+ littermates (Figure 4a, p = 0.0307). The lymphomas that arose in Eμ-Myc;Nfkb2-/- transgenics were phenotypically identical to those that arose in Eμ-Myc;Nfkb2+/+ mice, and full necropsy and histopathological examination demonstrated similar dissemination of disease in Eμ-Myc;Nfkb2+/+ versus Eμ-Myc;Nfkb2-/- mice (data not shown). Thus, Nfkb2 loss accelerates Myc-driven lymphomagenesis without overtly affecting the disease phenotype.


Myc suppression of Nfkb2 accelerates lymphomagenesis.

Keller U, Huber J, Nilsson JA, Fallahi M, Hall MA, Peschel C, Cleveland JL - BMC Cancer (2010)

Nfkb2 loss accelerates Myc-induced lymphomagenesis by impairing apoptosis. a) Effects of Nfkb2 deficiency on Myc-induced lymphomagenesis. The survival of Eμ-Myc transgenic littermates of the indicated Nfkb2 genotypes is shown. The differences in the rates of tumor incidence between the Nfkb2+/+ and the Nfkb2-/- littermates is statistically significant (p = 0.0307). b) Eμ-Myc transgenic littermates of the indicated Nfkb2 genotypes were injected with BrdU, and cells from bone marrow and spleen were harvested 12 hr later. BrdU-incorporation was analyzed using an antibody-dependent fluorescence assay. The bars show the mean percentage of cells in S phase ± SEM (three independent experiments). c) The apoptotic index of the indicated genotypes was analyzed using an antibody dependent fluorescence assay. Annexin V+ B220+ cells of sIgM- or sIgM+ phenotype are shown. The bars represent the mean ± SEM from three independent experiments. * indicates p < 0.05.
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Figure 4: Nfkb2 loss accelerates Myc-induced lymphomagenesis by impairing apoptosis. a) Effects of Nfkb2 deficiency on Myc-induced lymphomagenesis. The survival of Eμ-Myc transgenic littermates of the indicated Nfkb2 genotypes is shown. The differences in the rates of tumor incidence between the Nfkb2+/+ and the Nfkb2-/- littermates is statistically significant (p = 0.0307). b) Eμ-Myc transgenic littermates of the indicated Nfkb2 genotypes were injected with BrdU, and cells from bone marrow and spleen were harvested 12 hr later. BrdU-incorporation was analyzed using an antibody-dependent fluorescence assay. The bars show the mean percentage of cells in S phase ± SEM (three independent experiments). c) The apoptotic index of the indicated genotypes was analyzed using an antibody dependent fluorescence assay. Annexin V+ B220+ cells of sIgM- or sIgM+ phenotype are shown. The bars represent the mean ± SEM from three independent experiments. * indicates p < 0.05.
Mentions: The remarkable changes in the expression of components of the Rel/NF-κB signalling pathway, and particularly the suppression of Nfkb2 by c-Myc, suggested that NF-kB2 might play critical roles in Myc-driven tumorigenesis. If Myc-mediated reductions in Nfkb2 expression in Eμ-Myc B cells were important for Myc-mediated lymphomagenesis, we reasoned that total loss of Nfkb2 should affect lymphoma development. To test this hypothesis, Eμ-Myc transgenic mice were mated to Nfkb2-/- mice [6] and F1 offspring were bred to Nfkb2+/- mice to obtain the desired Eμ-Myc;Nfkb2+/+ and Eμ-Myc;Nfkb2-/- cohorts. These littermates were then observed for lymphoma onset. Eμ-Myc transgenic mice usually succumb to aggressive lymphoma within 4-8 months of birth [23]. As expected, non-transgenic Nfkb2-/- littermates showed no signs of tumour development throughout their lifespan (data not shown). Importantly, Eμ-Myc;Nfkb2-/- transgenic displayed a moderately accelerated course of lymphoma development and, accordingly, had a shorter lifespan, with a median survival of 171 days compared to 205 days median survival in their Eμ-Myc;Nfkb2+/+ littermates (Figure 4a, p = 0.0307). The lymphomas that arose in Eμ-Myc;Nfkb2-/- transgenics were phenotypically identical to those that arose in Eμ-Myc;Nfkb2+/+ mice, and full necropsy and histopathological examination demonstrated similar dissemination of disease in Eμ-Myc;Nfkb2+/+ versus Eμ-Myc;Nfkb2-/- mice (data not shown). Thus, Nfkb2 loss accelerates Myc-driven lymphomagenesis without overtly affecting the disease phenotype.

Bottom Line: Myc overexpression is associated with reduced activity of Rel/NF-kappaB, transcription factors that control the immune response, cell survival, and transformation, and that are frequently altered in cancer.NFKB2 suppression by Myc was also confirmed in primary human BL.These data thus link Myc-driven lymphomagenesis to the non-canonical NF-kappaB pathway.

View Article: PubMed Central - HTML - PubMed

Affiliation: III. Medical Department, Technische Universität München, Munich, Germany. ulrich.keller@lrz.tum.de

ABSTRACT

Background: Deregulated c-Myc expression is a hallmark of several human cancers where it promotes proliferation and an aggressive tumour phenotype. Myc overexpression is associated with reduced activity of Rel/NF-kappaB, transcription factors that control the immune response, cell survival, and transformation, and that are frequently altered in cancer. The Rel/NF-kappaB family member NFKB2 is altered by chromosomal translocations or deletions in lymphoid malignancies and deletion of the C-terminal ankyrin domain of NF-kappaB2 augments lymphocyte proliferation.

Methods: Precancerous Emicro-Myc-transgenic B cells, Emicro-Myc lymphomas and human Burkitt lymphoma samples were assessed for Nfkb2 expression. The contribution of Nfkb2 to Myc-driven apoptosis, proliferation, and lymphomagenesis was tested genetically in vivo.

Results: Here we report that the Myc oncoprotein suppresses Nfkb2 expression in vitro in primary mouse fibroblasts and B cells, and in vivo in the Emicro-Myc transgenic mouse model of human Burkitt lymphoma (BL). NFKB2 suppression by Myc was also confirmed in primary human BL. Promoter-reporter assays indicate that Myc-mediated suppression of Nfkb2 occurs at the level of transcription. The contribution of Nfkb2 to Myc-driven lymphomagenesis was tested in vivo, where Nfkb2 loss was shown to accelerate lymphoma development in Emicro-Myc transgenic mice, by impairing Myc's apoptotic response.

Conclusions: Nfkb2 is suppressed by c-Myc and harnesses Myc-driven lymphomagenesis. These data thus link Myc-driven lymphomagenesis to the non-canonical NF-kappaB pathway.

Show MeSH
Related in: MedlinePlus