Selenoprotein K Is a Novel Target of m-Calpain, and Cleavage Is Regulated by Toll-like Receptor-induced Calpastatin in Macrophages
Selenoprotein K Is a Novel Target of m-Calpain, and Cleavage Is Regulated by Toll-like Receptor-induced Calpastatin in Macrophages
复制标题
DOI：
10.1074/jbc.m111.265520
复制
发表时间：
2011-10-07
影响因子：
4.8
通讯作者：
Hoffmann, Peter R.
中科院分区：
文献类型：
--
作者：
Huang, Zhi;Hoffmann, Fukun W.;Hoffmann, Peter R.
钙蛋白酶是一种蛋白水解酶，它通过切割靶标来调节细胞功能，从而改变它们的行为。钙调蛋白在调节炎症和免疫反应中的重要作用正在显现，尽管具体的发生机制还没有明确的定义。在这项研究中，我们发现了钙蛋白酶的一个新靶点，硒蛋白K(SelenoProtein K，SELK)，它是一种内质网跨膜蛋白，对免疫细胞中的钙离子流动非常重要。在髓系细胞(巨噬细胞、中性粒细胞和树突状细胞)中检测到钙蛋白酶介导的SELK的切割，而在淋巴细胞(B细胞和T细胞)中未检测到。M-钙蛋白和m-钙蛋白均能裂解免疫沉淀的SELK，但m-钙蛋白是小鼠免疫细胞表达的主要亚型。与这些结果一致的是，特定的抑制剂被用来表明只有m-calain在巨噬细胞中裂解SELK。SELK的切割位点位于Arg(81)和Gly(82)之间，由此产生的截短的SELK缺乏硒半胱氨酸，这是定义硒蛋白的氨基酸。静息巨噬细胞主要表达裂解的SELK，当被不同的Toll样受体(TLRs)激活时，SELK的裂解被抑制。我们发现，Calain裂解减少是由于TLR诱导内源性抑制物calastatin上调所致。TLR诱导的calastatin的表达不仅抑制了Selk的切割，而且还抑制了另一个calain靶标talin的切割。此外，巨噬细胞中的钙蛋白酶亚型和钙粘蛋白的表达与T细胞和B细胞不同。总体而言，我们的发现确定SELK是一个新的Calain靶标，并揭示了在TLR诱导的巨噬细胞激活过程中calain/calastatin系统的动态变化。
Calpains are proteolytic enzymes that modulate cellular function through cleavage of targets, thereby modifying their actions. An important role is emerging for calpains in regulating inflammation and immune responses, although specific mechanisms by which this occurs have not been clearly defined. In this study, we identify a novel target of calpain, selenoprotein K (SelK), which is an endoplasmic reticulum transmembrane protein important for Ca2+ flux in immune cells. Calpain-mediated cleavage of SelK was detected in myeloid cells (macrophages, neutrophils, and dendritic cells) but not in lymphoid cells (B and T cells). Both m- and mu-calpain were capable of cleaving immunoprecipitated SelK, but m-calpain was the predominant isoform expressed in mouse immune cells. Consistent with these results, specific inhibitors were used to show that only m-calpain cleaved SelK in macrophages. The cleavage site in SelK was identified between Arg(81) and Gly(82) and the resulting truncated SelK was shown to lack selenocysteine, the amino acid that defines selenoproteins. Resting macrophages predominantly expressed cleaved SelK and, when activated through different Toll-like receptors (TLRs), SelK cleavage was inhibited. We found that decreased calpain cleavage was due to TLR-induced up-regulation of the endogenous inhibitor, calpastatin. TLR-induced calpastatin expression not only inhibited SelK cleavage, but cleavage of another calpain target, talin. Moreover, the expression of the calpain isoforms and calpastatin in macrophages were different from T and B cells. Overall, our findings identify SelK as a novel calpain target and reveal dynamic changes in the calpain/calpastatin system during TLR-induced activation of macrophages.