TET enzymes augment activation-induced deaminase (AID) expression via 5-hydroxymethylcytosine modifications at the <i>Aicda</i> superenhancer

Abstract

TET enzymes are dioxygenases that promote DNA demethylation by oxidizing the methyl group of 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Here, we report a close correspondence between 5hmC-marked regions, chromatin accessibility and enhancer activity in B cells, and a strong enrichment for consensus binding motifs for basic region-leucine zipper (bZIP) transcription factors at TET-responsive genomic regions. Functionally, Tet2 and Tet3 regulate class switch recombination (CSR) in murine B cells by enhancing expression of <i>Aicda</i>, which encodes the activation-induced cytidine deaminase (AID) enzyme essential for CSR. TET enzymes deposit 5hmC, facilitate DNA demethylation, and maintain chromatin accessibility at two TET-responsive enhancer elements, <i>TetE1</i> and <i>TetE2</i>, located within a superenhancer in the <i>Aicda</i> locus. Our data identify the bZIP transcription factor, ATF-like (BATF) as a key transcription factor involved in TET-dependent <i>Aicda</i> expression. 5hmC is not deposited at <i>TetE1</i> in activated <i>Batf</i>-deficient B cells, indicating that BATF facilitates TET recruitment to this <i>Aicda</i> enhancer. Our study emphasizes the importance of TET enzymes for bolstering AID expression and highlights 5hmC as an epigenetic mark that captures enhancer dynamics during cell activation.