Figure 2.

The diverse functions of the AID/APOBEC family. APOBECs are expressed in different cell types and have many diverse functions. A1 and A3A can undergo RNA editing in the small intestine and in monocytes, respectively. A3G (not shown) can catalyze RNA editing in 293T cells, but the physiological role is not known. In B cells, AID plays an essential role in immunoglobulin diversification through somatic hypermutation and class switch recombination. When dysregulated, AID can cause inflammation and autoimmunity. In CD4⁺ T cells, A3s supress retroviruses through deamination of ssDNA intermediates and inhibition of reverse transcriptase. A3A and A3B can also restrict dsDNA viruses during viral replication in epithelial cells. In CD4⁺ T cells and monocytes, restriction of foreign DNA by A3s can suppress the DNA-induced inflammatory response. In germ and somatic cells, restriction of endogenous retroelements occurs through deamination of ssDNA intermediates or RNA binding. Aberrant expression of APOBECs can lead to ‘off-target’ deaminations in genomic DNA that could result in cellular transformation or cancer.