Protein kinase GIα oxidation negatively regulates antibody production by B cells

Endogenous oxidants induce a C42-dependent interprotein disulfide between the subunits of protein kinase G (PKG) Iα in cardiovascular tissues to control blood pressure and ventricular relaxation during diastole. PKGIα is expressed in other cell types, including those of the immune system, where the redox state of this kinase is likely to regulate other important physiological processes. The role of PKGIα oxidation in antibody production by B cells, which produce oxidants such as hydrogen peroxide during differentiation, was examined by comparing the immune response of oxidation-resistant C42S PKGIα knock-in (KI) mice to their wild type (WT) littermates. Immunization with the 4-hydroxy-3-nitrophenyl acetyl (NP)-chicken gamma globulin with adjuvant increased NP + B cells (NP + B220+), germinal center B cells (NP + GL-7+CD95⁺), IgG1+ B cells (NP + IgG1+B220+), plasmablast (NP + CD138+B220+) and plasma cells (NP + CD138+B220-) in spleen, with these responses being significantly potentiated in KI mice. The C42S PKGIα KI mice also secreted significantly more NP + IgG1 antibody in plasma compared to WTs. Adoptive transfer of B cells into B cell-deficient mice confirmed that the observed enhancements were intrinsic to the donor population. PKGIα physically interacted with activation-induced cytidine deaminase (AID), an essential enzyme for antibody diversity by deamination of cytosine to uracil in DNA, phosphorylating it at S38 to increase activity. Oxidation of PKGIα to interprotein disulfide form reduced its ability to bind and phosphorylate AID at S38, as demonstrated by in vitro and ex vivo co-immunoprecipitation, kinase assays, class-switch recombination assays, somatic hypermutation analyses, and western blotting in both in vitro and in vivo studies. In conclusion, PKGIα C42 oxidation in B cells decreases its interaction with and phosphorylation of AID, thereby reducing their antibody production.