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      Selenoprotein K is a novel target of m-calpain, and cleavage is regulated by Toll-like receptor-induced calpastatin in macrophages.

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          Abstract

          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 Ca(2+) 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 μ-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.

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          Author and article information

          Journal
          J. Biol. Chem.
          The Journal of biological chemistry
          American Society for Biochemistry & Molecular Biology (ASBMB)
          1083-351X
          0021-9258
          Oct 07 2011
          : 286
          : 40
          Affiliations
          [1 ] Department of Cell and Molecular Biology, John A Burns School of Medicine, University of Hawaii, Honolulu, Hawaii 96813, USA.
          Article
          M111.265520
          10.1074/jbc.M111.265520
          3186414
          21849499
          5648ff48-2f3d-4fcf-aee1-7c7dea03b386
          History

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