Required for Ca(2+) flux in immune cells and plays a role in T-cell proliferation and in T-cell and neutrophil migration (By similarity). Involved in endoplasmic reticulum-associated degradation (ERAD) of soluble glycosylated proteins (PubMed:22016385). Required for palmitoylation and cell surface expression of CD36 and involved in macrophage uptake of low-density lipoprotein and in foam cell formation (By similarity). Together with ZDHHC6, required for palmitoylation of ITPR1 in immune cells, leading to regulate ITPR1 stability and function (PubMed:25368151). Plays a role in protection of cells from ER stress-induced apoptosis (PubMed:20692228). Protects cells from oxidative stress when overexpressed in cardiomyocytes (PubMed:16962588). Interacts with DERL1, DERL2, DERL3 and SELENOS (PubMed:22016385). The SELENOK-SELENOS complex interacts with VCP (PubMed:22016385). Interacts with ZDHHC6 (PubMed:25368151). Probably mainly localized in the ER. Highly expressed in heart. By ER stress (at protein level). Displays a slow increase with a lag phase of 6 hours but exhibits a dramatic increase after incubation with ER stress agents for more than 12 hours with maximum induction at 24 hours. Also induced by accumulation of misfolded proteins in the ER. Cleaved by CAPN2/m-calpain in resting macrophages but not in activated macrophages. Macrophage activation up-regulates expression of the calpain inhibitor CAST/calpastatin, resulting in inhibition of CAPN2 activity (By similarity). Truncated SELENOK proteins produced by failed UGA/Sec decoding are ubiquitinated by the CRL2(KLHDC2) complex, which recognizes the diglycine (Gly-Gly) at the C-terminus of truncated SELENOK proteins. Belongs to the selenoprotein K family. Truncated C-terminus. Truncated C-terminus.