Department of Experimental and Clinical Medicine, University of Catanzaro Magna Graecia, Catanzaro, Italy.
Blood. 2011 Jun 16;117(24):6520-31. doi: 10.1182/blood-2010-09-308080. Epub 2011 Apr 11.
The inhibitor of Bruton tyrosine kinase γ (IBtkγ) is a negative regulator of the Bruton tyrosine kinase (Btk), which plays a major role in B-cell differentiation; however, the mechanisms of IBtkγ-mediated regulation of Btk are unknown. Here we report that B-cell receptor (BCR) triggering caused serine-phosphorylation of IBtkγ at protein kinase C consensus sites and dissociation from Btk. By liquid chromatography and mass-mass spectrometry and functional analysis, we identified IBtkγ-S87 and -S90 as the critical amino acid residues that regulate the IBtkγ binding affinity to Btk. Consistently, the mutants IBtkγ carrying S87A and S90A mutations bound constitutively to Btk and down-regulated Ca(2+) fluxes and NF-κB activation on BCR triggering. Accordingly, spleen B cells from Ibtkγ(-/-) 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 IBtkγ.
布鲁顿酪氨酸激酶γ（IBtkγ）抑制剂是布鲁顿酪氨酸激酶（Btk）的负调节剂，Btk 在 B 细胞分化中起主要作用；然而，IBtkγ 介导的 Btk 调节的机制尚不清楚。在这里，我们报告 B 细胞受体（BCR）触发导致 IBtkγ 在蛋白激酶 C 共有位点的丝氨酸磷酸化，并与 Btk 解离。通过液相色谱和质谱-质谱联用和功能分析，我们确定了 IBtkγ-S87 和 -S90 是调节 IBtkγ 与 Btk 结合亲和力的关键氨基酸残基。一致地，携带 S87A 和 S90A 突变的 IBtkγ 突变体与 Btk 持续结合，并下调 BCR 触发时的 Ca（2+）通量和 NF-κB 激活。因此，Ibtkγ（-/-）小鼠的脾 B 细胞在 BCR 结合时显示出 Btk 的激活增加，如 Y551 磷酸化和持续的 Ca（2+）动员所评估的那样。这些发现确定了通过 IBtkγ 的蛋白激酶 C 磷酸化来调节 Btk 的新途径。
