14-3-3 adaptor proteins recruit AID to 5′-AGCT-3′-rich switch regions for class switch recombination

AID is a DNA cytidine deaminase with a central role in the generation of antibody diversity. AID initiates class switch recombination by modifying DNA within the switch (S) regions in the IgH locus. Now AID is shown to be targeted to the S regions by interaction with adaptor proteins 14-3-3, which in turn bind directly to the DNA motif 5'AGCT. Class switch DNA recombination (CSR) is the mechanism that diversifies the biological effector functions of antibodies. Activation-induced cytidine deaminase (AID), a key protein in CSR, targets immunoglobulin H (IgH) switch regions, which contain 5′-AGCT-3′ repeats in their core. How AID is recruited to switch regions remains unclear. Here we show that 14-3-3 adaptor proteins have an important role in CSR. 14-3-3 proteins specifically bound 5′-AGCT-3′ repeats, were upregulated in B cells undergoing CSR and were recruited with AID to the switch regions that are involved in CSR events (Sμ→Sγ1, Sμ→Sγ3 or Sμ→Sα). Moreover, blocking 14-3-3 by difopein, 14-3-3γ deficiency or expression of a dominant-negative 14-3-3σ mutant impaired recruitment of AID to switch regions and decreased CSR. Finally, 14-3-3 proteins interacted directly with AID and enhanced AID-mediated in vitro DNA deamination, further emphasizing the important role of these adaptors in CSR.