B cell Tet2 promotes maturation of the antibody response through active DNA demethylation and OGT-mediated histone glycosylation of Aicdaand Prdm1loci

Abstract

Abstract Epigenetic DNA methylation regulates gene expression and, therefore, cellular functions. It typically represses gene transcription, which can be re-activated by demethylation in the absence of cell division by the recently characterized Tet1, Tet2 and Tet3 dioxygenases. Tet2, the most abundant Tet protein in B cells, not only actively demethylates DNA but also promotes Ogt recruitment to chromatin to effect Ogt-dependent histone O-GlcNAcylation. This potentiates catalytic DNA demethylation to activate gene expression. To define the role of Tet2 in B cell functions and antibody responses, we generated Aicda creTet2 fl/flmice, which specifically delete Tet2 in activated B cells. Aicda creTet2 fl/flmice showed significantly reduced antibody responses to T-dependent and T-independent antigens, due to downregulation of AID and Blimp-1 expression, CSR/SHM and plasma cell differentiation. Accordingly, activated Aicda creTet2 fl/flB cells reduced DNA hydroxymethylation (resulting in increased methylation) and histone O-GlcNAcylation of Aicda and Prdm1 promoters and enhancers, thereby dampening CSR/SHM and plasma cell differentiation. These were partially rescued by enforced expression of Tet2 mutants defective in catalytic activity or Ogt-binding, but not by a double mutant lacking both activities. Accordingly, Tet2 and Ogt inhibitors synergistically inhibited Aicda and Prdm1 expression in both human and mouse B cells. Conversely, Tet2 activation by vitamin C enhanced CSR and plasma cell differentiation. Thus, Tet2 plays a B cell-intrinsic role in modulation of CSR/SHM and plasma cell differentiation through catalytic active DNA demethylation and (non-catalytic) Ogt-mediated histone O-GlcNAcylation. Supported by NIH grants AI 079705, AI 105813/105813S1, AI138944, AI 167416 and Lupus Research Alliance grant LRA 641363 to PC.