Germinal center dysregulation by histone methyltransferase EZH2 promotes lymphomagenesis
Marieta Caganova, … , I-hsin Su, Stefano Casola
Marieta Caganova, … , I-hsin Su, Stefano Casola
Published November 8, 2013
Citation Information: J Clin Invest. 2013;123(12):5009-5022. https://doi.org/10.1172/JCI70626.
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Research Article Immunology

Germinal center dysregulation by histone methyltransferase EZH2 promotes lymphomagenesis

Abstract

Protection against deadly pathogens requires the production of high-affinity antibodies by B cells, which are generated in germinal centers (GCs). Alteration of the GC developmental program is common in many B cell malignancies. Identification of regulators of the GC response is crucial to develop targeted therapies for GC B cell dysfunctions, including lymphomas. The histone H3 lysine 27 methyltransferase enhancer of zeste homolog 2 (EZH2) is highly expressed in GC B cells and is often constitutively activated in GC-derived non-Hodgkin lymphomas (NHLs). The function of EZH2 in GC B cells remains largely unknown. Herein, we show that Ezh2 inactivation in mouse GC B cells caused profound impairment of GC responses, memory B cell formation, and humoral immunity. EZH2 protected GC B cells against activation-induced cytidine deaminase (AID) mutagenesis, facilitated cell cycle progression, and silenced plasma cell determinant and tumor suppressor B-lymphocyte–induced maturation protein 1 (BLIMP1). EZH2 inhibition in NHL cells induced BLIMP1, which impaired tumor growth. In conclusion, EZH2 sustains AID function and prevents terminal differentiation of GC B cells, which allows antibody diversification and affinity maturation. Dysregulation of the GC reaction by constitutively active EZH2 facilitates lymphomagenesis and identifies EZH2 as a possible therapeutic target in NHL and other GC-derived B cell diseases.

Authors

Marieta Caganova, Chiara Carrisi, Gabriele Varano, Federica Mainoldi, Federica Zanardi, Pierre-Luc Germain, Laura George, Federica Alberghini, Luca Ferrarini, Asoke K. Talukder, Maurilio Ponzoni, Giuseppe Testa, Takuya Nojima, Claudio Doglioni, Daisuke Kitamura, Kai-M. Toellner, I-hsin Su, Stefano Casola

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Figure 1

EZH2 is upregulated in mouse GC B cells and required for GC formation.

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EZH2 is upregulated in mouse GC B cells and required for GC formation. (...
(A) Ezh2 transcript levels in B cell subsets relative to Rplp0. Columns represent mean ± SD of triplicates. Experiments were performed on pools of B cells sorted from 3 mice. (B) FACS analysis of EZH2 protein levels in follicular (FO) and GC B cells. Numbers indicate mean expression. (C) Representative FACS analysis of splenic B cells in NP-CGG–immunized Ezh2 control (Ezh2fl/+:Cγ1-cre) and mutant (Ezh2fl/fl:Cγ1-cre) mice. Numbers indicate percentage of boxed GC B cells. (D) Frequency of splenic GC B cells in NP-CGG–immunized Ezh2 control (Ezh2fl/+:Cγ1-cre [Ezh2+/–]; n = 17) and mutant (Ezh2fl/fl:Cγ1-cre [Ezh2–/–]; n = 22) mice. Symbols represent individual mice; bars refer to mean values. *P = 0.013 (t test). (E) Representative histological analysis of PNA-positive (brown) GCs (arrowheads) in the spleens of NP-CGG–immunized Ezh2 control (Ezh2fl/+:Cγ1-cre; n = 6) and mutant (Ezh2fl/fl:Cγ1-cre; n = 6) mice. Scale bar: 200 μm. (F) Frequency of Ezh2 inactivation in GC B cells of Ezh2 control (Ezh2fl/+:Cγ1-cre; n = 3) and mutant (Ezh2fl/fl:Cγ1-cre; n = 4) animals, quantified by genomic qPCR. (G) Frequency of YFP+ GC B cells in R26-yfp;Ezh2 control (Ezh2fl/+) and mutant (Ezh2fl/fl) mice. (H) Summary of data on frequencies of YFP+ GC B cells in R26-yfp;Cγ1-cre;Ezh2 control (n = 4) and mutant (n = 6) mice. (F and H) Columns indicate mean ± SD. **P = 0.002 (t test). Data represent (C and D) 10, (G) 5, (F, and H) 3, and (B, E, and F) 2 experiments, respectively.