SENP1 Regulates Germinal Center B Cell Responses through PAX5-deSUMOylation mediated AID expression

Humoral immunity depends on germinal center reaction where B cells are tightly controlled for class switch recombination (CSR) and somatic hypermutation, and finally generated into plasma and memory B cells. However, how protein SUMOylation control the key events of GC B cells remains to be understood. Here, we show that SUMO-specific protease 1 (SENP1) is upregulated in GC B cells. Selective ablation of Senp1 within GC B cells led to defective dark zone versus light zone GC B organization, impaired IgG1-switched GC B cells, and compromised antibody response. In addition, the formation of antigen-specific plasma and memory B cells were also diminished when SENP1 was deleted in GC B cells. Mechanistically, SENP1 was indispensable for expression of activation-induced cytidine deaminase (AID). SENP1-mediated Paired box protein 5 deSUMOylation suppressed the transcription to AID, which might be responsible for defective CSR in vivo. Our study not only established the importance of protein SUMOylation for the maintenance of GC B cell function but also clarified a novel mechanism to the modulation of AID expression.