Btk regulation in human and mouse B cells via protein kinase C phosphorylation of IBtkgamma.

摘要

The inhibitor of Bruton tyrosine kinase gamma (IBtkgamma) is a negative regulator of the Bruton tyrosine kinase (Btk), which plays a major role in B-cell differentiation; however, the mechanisms of IBtkgamma-mediated regulation of Btk are unknown. Here we report that B-cell receptor (BCR) triggering caused serine-phosphorylation of IBtkgamma at protein kinase C consensus sites and dissociation from Btk. By liquid chromatography and mass-mass spectrometry and functional analysis, we identified IBtkgamma-S87 and -S90 as the critical amino acid residues that regulate the IBtkgamma binding affinity to Btk. Consistently, the mutants IBtkgamma carrying S87A and S90A mutations bound constitutively to Btk and down-regulated Ca(2+) fluxes and NF-kappaB activation on BCR triggering. Accordingly, spleen B cells from Ibtkgamma(-/-) mice showed an increased activation of Btk, as evaluated by Y551-phosphorylation and sustained Ca(2+) mobilization on BCR engagement. These findings identify a novel pathway of Btk regulation via protein kinase C phosphorylation of IBtkgamma.