Selenoprotein K Knockout Mice Exhibit Deficient Calcium Flux in Immune Cells and Impaired Immune Responses

Abstract

Selenoprotein K (Sel K) is a selenium-containing protein for which no function has been identified. We found that Sel K is an endoplasmic reticulum (ER) transmembrane protein expressed at relatively high levels in immune cells and is regulated by dietary selenium. Sel K−/− mice were generated and found to be similar to WT controls regarding growth and fertility. Immune system development was not affected by Sel K deletion, but specific immune cell defects were found in Sel K−/− mice. Receptor-mediated Ca2+ flux was decreased in T cells, neutrophils, and macrophages from Sel K−/− mice compare to controls. Ca2+-dependent functions including T cell proliferation, T cell and neutrophil migration, and Fcγ-receptor-mediated oxidative burst in macrophages were decreased in cells from Sel K−/− mice compared to controls. West Nile virus (WNV) infections were performed and Sel K−/− mice exhibited decreased viral clearance in the periphery and increased viral titers in brain. Furthermore, WNV-infected Sel K−/− mice demonstrated significantly lower survival (2/23; 8.7%) compared to WT controls (10/26; 38.5%). These results establish Sel K as an ER-membrane protein important for promoting effective Ca2+ flux during immune cell activation and provide insight into molecular mechanisms by which dietary selenium enhances immune responses.

Stable expression and function of the inositol 1,4,5-triphosphate receptor requires palmitoylation by a DHHC6/selenoprotein K complex

“…The addition of fatty acid residues to the cytosolic region of the IP3R subunits may facilitate assembly of the subunits or stabilize the assembled complex within the ER membrane. This study, to our knowledge, is the first to describe palmitoylation of the IP3R as well as the enzyme complex consisting of DHHC6 and Selk, which provides mechanistic data to explain previous reports of regulation of Ca 2+ flux by dietary selenium and Selk expression in immune cells (15,16,31). Whereas the list of palmitoylated proteins has rapidly increased, surprisingly limited information is available regarding the members of the palmitoyl acyl transferase (PAT) family that carry out this posttranslational modification in mammalian cells.…”

“…2 for the IP3R in mouse tissues shows high expression of multiple isoforms of IP3R in brain that is clearly decreased in Selk knockout mice. We have not detected any neurological problems or learning or behavioral defects in the Selk knockout mice compared with wild-type controls, and the only evident impairment related to the brain was the increased neuropathology induced by West Nile virus infection (16). This was shown to be related to the reduced clearance of virus in the periphery in Selk knockout mice, but our new data raise the possibility that low IP3R expression in the brain may also contribute to viral encephalitis.…”

“…C57BL/6J wild-type controls were generated from mice originally purchased from The Jackson Laboratory. Generation of selk −/− mice on a C57BL/6J background was previously described (16). All animal protocols were approved by the University of Hawaii Institutional Animal Care and Use Committee.…”

“…Our previous studies have demonstrated that low levels of dietary selenium as well as a deficiency in a specific ER-localized selenium-containing protein, selenoprotein K (Selk), led to impaired SOCE (15,16). The specific mechanism by which Selk deficiency affected Ca 2+ flux was not apparent, but the fact that…”

Selenoprotein S-dependent Selenoprotein K Binding to p97(VCP) Protein Is Essential for Endoplasmic Reticulum-associated Degradation

“…Furthermore, SelS is known to be associated with the maintenance and intracellular membrane-based transport of multiprotein complexes (39). SelK has been reported to regulate Ca 2ϩ flux during immune responses and to protect cells from ER stress-mediated apoptosis (27,50). However, the way in which SelS and SelK interact and the subsequent effect on the ER stress response is not well understood.…”