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BCL6 controls the expression of the B7-1/CD80 costimulatory receptor in germinal center B cells.

Niu H, Cattoretti G, Dalla-Favera R - J. Exp. Med. (2003)

Bottom Line: Our results show that BCL6 prevents CD40-induced expression of CD80 by binding its promoter region in vivo and suppressing its transcriptional activation by NF-kappaB.Consistent with a physiologic role for BCL6 in suppressing CD80, the expression of these two genes is mutually exclusive in B cells, and BCL6-defective mice show increased expression of CD80 in B cells.The results suggest that BCL6 may directly control the ability of B cell to interact with T cells during normal GC development.

View Article: PubMed Central - PubMed

Affiliation: Institute for Cancer Genetics, Columbia University, 1150 St. Nicholas Ave., New York, NY 10032, USA.

ABSTRACT
The BCL6 proto-oncogene encodes a transcriptional repressor required for the development of germinal centers (GCs) and implicated in the pathogenesis of GC-derived B cell lymphoma. Understanding the precise role of BCL6 in normal GC formation and in lymphomagenesis depends on the identification of genes that are direct targets of its transcriptional repression. Here we report that BCL6 directly controls the expression of B7-1/CD80, a costimulatory receptor involved in B-T cell interactions critical for the development of T cell-mediated antibody responses. Upon CD40 signaling, transcription of the CD80 gene is induced by the nuclear factor (NF)-kappaB transcription factor. Our results show that BCL6 prevents CD40-induced expression of CD80 by binding its promoter region in vivo and suppressing its transcriptional activation by NF-kappaB. Consistent with a physiologic role for BCL6 in suppressing CD80, the expression of these two genes is mutually exclusive in B cells, and BCL6-defective mice show increased expression of CD80 in B cells. The results suggest that BCL6 may directly control the ability of B cell to interact with T cells during normal GC development. In addition, these findings imply that T-B cell interactions may be disrupted in B cell lymphoma expressing deregulated BCL6 genes.

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Constitutive expression of exogenous BCL6 in Ramos cells transduced with PINCO retroviral vectors. (a) Schematic representation of PINCO, PINCO-HA-BCL6, and PINCO-HA-BCL6ΔPEST viral vectors. (b) Northern (left panels) and Western (right panels) blot analysis of endogenous (endo) and exogenous (exo) BCL6 expression in Ramos cell clones transduced with PINCO, PINCO-HA-BCL6, and PINCO-HA-BCL6ΔPEST after treatment with CD40L for the indicated time. The β-actin expression was analyzed as a control.
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fig1: Constitutive expression of exogenous BCL6 in Ramos cells transduced with PINCO retroviral vectors. (a) Schematic representation of PINCO, PINCO-HA-BCL6, and PINCO-HA-BCL6ΔPEST viral vectors. (b) Northern (left panels) and Western (right panels) blot analysis of endogenous (endo) and exogenous (exo) BCL6 expression in Ramos cell clones transduced with PINCO, PINCO-HA-BCL6, and PINCO-HA-BCL6ΔPEST after treatment with CD40L for the indicated time. The β-actin expression was analyzed as a control.

Mentions: The observation that CD40 down-regulates BCL6 expression (14; unpublished data) raised the possibility that BCL6 may influence the expression of genes induced by CD40. To test this hypothesis, we infected Ramos cells, which represent transformed GC B cells, with a retroviral vector (PINCO; reference 34) that encodes HA-tagged BCL6 to obtain cells that constitutively express exogenous BCL6 since the retroviral promoter is resistant to CD40 induced down-regulation. The PINCO vector also encodes a GFP for efficient selection of transduced cells by FACS®. Ramos cells were infected with vectors (Fig. 1 a) expressing either the wild-type BCL6 protein (PINCO -HA-BCL6) or a deletion mutant (PINCO-HA-BCL6ΔPEST) that is still capable of transcriptional repression, but has a longer half life due to deletion of the PEST domains recognized by the ubiquitin-proteasome complex (18). Northern blot analysis of representative clones confirmed that endogenous BCL6 RNAs were down-regulated by anti-CD40 treatment in all transduced clones, while exogenous HA-BCL6 or HA-BCL6ΔPEST RNAs were constitutively expressed (Fig. 1 b). Western blot analysis of the same cells showed that the BCL6 proteins were constitutively expressed in the BCL-transduced cells.


BCL6 controls the expression of the B7-1/CD80 costimulatory receptor in germinal center B cells.

Niu H, Cattoretti G, Dalla-Favera R - J. Exp. Med. (2003)

Constitutive expression of exogenous BCL6 in Ramos cells transduced with PINCO retroviral vectors. (a) Schematic representation of PINCO, PINCO-HA-BCL6, and PINCO-HA-BCL6ΔPEST viral vectors. (b) Northern (left panels) and Western (right panels) blot analysis of endogenous (endo) and exogenous (exo) BCL6 expression in Ramos cell clones transduced with PINCO, PINCO-HA-BCL6, and PINCO-HA-BCL6ΔPEST after treatment with CD40L for the indicated time. The β-actin expression was analyzed as a control.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2194068&req=5

fig1: Constitutive expression of exogenous BCL6 in Ramos cells transduced with PINCO retroviral vectors. (a) Schematic representation of PINCO, PINCO-HA-BCL6, and PINCO-HA-BCL6ΔPEST viral vectors. (b) Northern (left panels) and Western (right panels) blot analysis of endogenous (endo) and exogenous (exo) BCL6 expression in Ramos cell clones transduced with PINCO, PINCO-HA-BCL6, and PINCO-HA-BCL6ΔPEST after treatment with CD40L for the indicated time. The β-actin expression was analyzed as a control.
Mentions: The observation that CD40 down-regulates BCL6 expression (14; unpublished data) raised the possibility that BCL6 may influence the expression of genes induced by CD40. To test this hypothesis, we infected Ramos cells, which represent transformed GC B cells, with a retroviral vector (PINCO; reference 34) that encodes HA-tagged BCL6 to obtain cells that constitutively express exogenous BCL6 since the retroviral promoter is resistant to CD40 induced down-regulation. The PINCO vector also encodes a GFP for efficient selection of transduced cells by FACS®. Ramos cells were infected with vectors (Fig. 1 a) expressing either the wild-type BCL6 protein (PINCO -HA-BCL6) or a deletion mutant (PINCO-HA-BCL6ΔPEST) that is still capable of transcriptional repression, but has a longer half life due to deletion of the PEST domains recognized by the ubiquitin-proteasome complex (18). Northern blot analysis of representative clones confirmed that endogenous BCL6 RNAs were down-regulated by anti-CD40 treatment in all transduced clones, while exogenous HA-BCL6 or HA-BCL6ΔPEST RNAs were constitutively expressed (Fig. 1 b). Western blot analysis of the same cells showed that the BCL6 proteins were constitutively expressed in the BCL-transduced cells.

Bottom Line: Our results show that BCL6 prevents CD40-induced expression of CD80 by binding its promoter region in vivo and suppressing its transcriptional activation by NF-kappaB.Consistent with a physiologic role for BCL6 in suppressing CD80, the expression of these two genes is mutually exclusive in B cells, and BCL6-defective mice show increased expression of CD80 in B cells.The results suggest that BCL6 may directly control the ability of B cell to interact with T cells during normal GC development.

View Article: PubMed Central - PubMed

Affiliation: Institute for Cancer Genetics, Columbia University, 1150 St. Nicholas Ave., New York, NY 10032, USA.

ABSTRACT
The BCL6 proto-oncogene encodes a transcriptional repressor required for the development of germinal centers (GCs) and implicated in the pathogenesis of GC-derived B cell lymphoma. Understanding the precise role of BCL6 in normal GC formation and in lymphomagenesis depends on the identification of genes that are direct targets of its transcriptional repression. Here we report that BCL6 directly controls the expression of B7-1/CD80, a costimulatory receptor involved in B-T cell interactions critical for the development of T cell-mediated antibody responses. Upon CD40 signaling, transcription of the CD80 gene is induced by the nuclear factor (NF)-kappaB transcription factor. Our results show that BCL6 prevents CD40-induced expression of CD80 by binding its promoter region in vivo and suppressing its transcriptional activation by NF-kappaB. Consistent with a physiologic role for BCL6 in suppressing CD80, the expression of these two genes is mutually exclusive in B cells, and BCL6-defective mice show increased expression of CD80 in B cells. The results suggest that BCL6 may directly control the ability of B cell to interact with T cells during normal GC development. In addition, these findings imply that T-B cell interactions may be disrupted in B cell lymphoma expressing deregulated BCL6 genes.

Show MeSH
Related in: MedlinePlus