The RNA-binding protein ROD1/PTBP3 cotranscriptionally defines AID-loading sites to mediate antibody class switch in mammalian genomes

• DOI: 10.1038/s41422-018-0076-9
• Publication Date: 2018-08-24T06:26:48Z
• Authors: Juan Chen; Zhaokui Cai; Meizhu Bai; Xiaohua Yu; Chao Zhang; Changchang Cao; Xihao Hu; Lei Wang; Ruibao Su; Di Wang; Lei Wang; Yingpeng Yao; Rong Ye; Baidong Hou; Yang Yu; Shuyang Yu; Jinsong Li; Yuanchao Xue
• Keywords: Lipopolysaccharides; Mice, Knockout; 0301 basic medicine; B-Lymphocytes; Genome; Hyper-IgM Immunodeficiency Syndrome; Article; Immunoglobulin Isotypes; Mice, Inbred C57BL; Mice; 03 medical and health sciences; HEK293 Cells; Cytidine Deaminase; Mutation; Animals; Humans; RNA; RNA Interference; Amino Acid Sequence; RNA, Small Interfering; Polypyrimidine Tract-Binding Protein; Protein Binding

AbstractActivation-induced cytidine deaminase (AID) mediates class switching by binding to a small fraction of single-stranded DNA (ssDNA) to diversify the antibody repertoire. The precise mechanism for highly selective AID targeting in the genome has remained elusive. Here, we report an RNA-binding protein, ROD1 (also known as PTBP3), that is both required and sufficient to define AID-binding sites genome-wide in activated B cells. ROD1 interacts with AID via an ultraconserved loop, which proves to be critical for the recruitment of AID to ssDNA using bi-directionally transcribed nascent RNAs as stepping stones. Strikingly, AID-specific mutations identified in human patients with hyper-IgM syndrome type 2 (HIGM2) completely disrupt the AID interacting surface with ROD1, thereby abolishing the recruitment of AID to immunoglobulin (Ig) loci. Together, our results suggest that bi-directionally transcribed RNA traps the RNA-binding protein ROD1, which serves as a guiding system for AID to load onto specific genomic loci to induce DNA rearrangement during immune responses.