Cutting Edge: The Transcription Factor Sox2 Regulates AID Expression in Class-Switched B Cells.

IgH class switch recombination (CSR) occurs through the deliberate introduction of activation-induced cytidine deaminase (AID)-instigated DNA double-strand breaks into the IgH loci. Because double-strand breaks are generally highly toxic, mechanisms that regulate AID expression are of much relevance to CSR and genomic integrity; however, effectors of such regulatory processes are still poorly understood. In this article, we show that the transcription factor sex determining region Y-box 2 (Sox2) is expressed in activated B cells, but almost exclusively in those that have undergone CSR. We demonstrate that enforced expression of Sox2 in splenic B cells severely inhibits AID expression and CSR, whereas deletion of Sox2 increases the frequency of IgH:c-Myc translocations. These results suggest that Sox2 may regulate AID expression in class-switched B cells to suppress genomic instability associated with CSR.