Role of APOBEC Family Proteins in Immunoglobulin Class Switch Recombination
Activation-induced cytidine deaminase (AID) functions in activated mammalian B cells to vary antibody effector function via deletion of immunoglobulin constant region DNA in the process of class switch recombination (CSR). AID deaminates cytidine to uridine, creating mismatch targets for cellular DNA repair mechanisms. Other deaminases closely related to AID are the APOBEC proteins. APOBEC proteins are expressed in activated B cells as well, however they have no known role in CSR. To evaluate the potential involvement of APOBEC1 and APOBEC2 in CSR we used shRNA to knock down their expression in the CH12 B cell line, which is known to switch from IgM to IgA upon stimulation. FACS analysis of membrane IgA expression revealed no significant change in CSR levels after APOBEC1 and APOBEC2 knockdown, while AID knockdown reduces CSR by 60% as expected.