Activation-induced cytidine deaminase targets SUV4-20-mediated histone H4K20 trimethylation to class-switch recombination sites

Virginia C Rodríguez-Cortez,Antonio Garcia-Gomez,Javier Rodríguez-Ubreva,Ganesh Poorani-Subramani,Laura Ciudad,Carlos Company,Francesc Català-Moll,Javier M Di Noia,Paloma Martínez-Redondo,Arantxa Pérez-García,Alejandro Vaquero,Esteban Ballestar,Henar Hernando,José M Urquiza,Almudena R Ramiro

doi:10.1038/s41598-017-07380-9

Abstract

Activation-induced cytidine deaminase (AID) triggers antibody diversification in B cells by catalysing deamination and subsequently mutating immunoglobulin (Ig) genes. Association of AID with RNA Pol II and occurrence of epigenetic changes during Ig gene diversification suggest participation of AID in epigenetic regulation. AID is mutated in hyper-IgM type 2 (HIGM2) syndrome. Here, we investigated the potential role of AID in the acquisition of epigenetic changes. We discovered that AID binding to the IgH locus promotes an increase in H4K20me3. In 293F cells, we demonstrate interaction between co-transfected AID and the three SUV4-20 histone H4K20 methyltransferases, and that SUV4-20H1.2, bound to the IgH switch (S) mu site, is replaced by SUV4-20H2 upon AID binding. Analysis of HIGM2 mutants shows that the AID truncated form W68X is impaired to interact with SUV4-20H1.2 and SUV4-20H2 and is unable to bind and target H4K20me3 to the Smu site. We finally show in mouse primary B cells undergoing class-switch recombination (CSR) that AID deficiency associates with decreased H4K20me3 levels at the Smu site. Our results provide a novel link between SUV4-20 enzymes and CSR and offer a new aspect of the interplay between AID and histone modifications in setting the epigenetic status of CSR sites.

Highlights

Activation-induced cytidine deaminase (AID; gene symbol AICDA) is a key enzyme in B cell biology because it is needed to generate immunoglobulin (Ig) diversification by inducing class switch recombination (CSR) and somatic hypermutation (SHM)[1]
We show that mouse primary B cells activated for CSR with LPS + IL4 undergo an increase in H4K20me[3] that does not occur in AID-deficient mice
To investigate the ability of AID to target epigenetic modifications at its cognate sites in B cells, and how these changes may be impaired in hyper-IgM type 2 (HIGM2) individuals, we first generated an inducible retroviral system to express wild type AID (Fig. 1A)

Summary

Introduction

Activation-induced cytidine deaminase (AID; gene symbol AICDA) is a key enzyme in B cell biology because it is needed to generate immunoglobulin (Ig) diversification by inducing class switch recombination (CSR) and somatic hypermutation (SHM)[1]. It has been proposed that AID’s catalytic activity, which mediates the conversion of cytosines to uracils, may participate in the removal of methylated cytosines as a two-step mechanism leading to active demethylation In this context, AID would result in demethylating and activating critical pluripotency genes, OCT4 and NANOG, during reprogramming of somatic cells to pluripotent stem cells[11]. These findings strongly suggest that AID acts on CSR as a cytidine deaminase enzyme, and as a docking protein, recruiting specific cofactors to a multimeric complex These interactions probably include epigenetic enzymes and influence the epigenetic status of AID target sites, preparing the chromatin context for efficient CSR and SHM, and perhaps directly regulating its transcriptional status. Our results demonstrate for the first time the AID-dependent recruitment of SUV4-20 enzymes at Ig switch regions and suggest a direct interaction with AID, providing a novel link between these two enzymes that explains the effects on CSR of abrogating Suv4-20h enzymes in mice[19]

Methods

Results

Conclusion