ABSTRACT
SEPS1 (also called selenoprotein S, SelS, Tanis or VIMP) is a selenoprotein, localized predominantly in the ER membrane and also on the cell surface. In this report, we demonstrate that SEPS1 protein is also secreted from hepatoma cells but not from five other types of cells examined. The secretion can be abolished by the ER-Golgi transport inhibitor Brefeldin A and by the protein synthesis inhibitor cycloheximide. Using a sandwich ELISA, SEPS1 was detected in the sera of 65 out of 209 human subjects (31.1%, average=15.7+/-1.1 ng/mL). Fractionation of human serum indicated that SEPS1 was associated with LDL and possibly with VLDL. The function of plasma SEPS1 is unclear but may be related to lipoprotein metabolism.
Subject(s)
Carcinoma, Hepatocellular/metabolism , Liver Neoplasms/metabolism , Membrane Proteins/metabolism , Selenoproteins/metabolism , 3T3-L1 Cells , Animals , COS Cells , Cells, Cultured , Chlorocebus aethiops , Enzyme-Linked Immunosorbent Assay , Humans , Lipoproteins, LDL/blood , Lipoproteins, VLDL/blood , Membrane Proteins/blood , Mice , Rats , Selenoproteins/bloodABSTRACT
SEPS1 (also called selenoprotein S, SelS) plays an important role in the production of inflammatory cytokines and its expression is activated by endoplasmic reticulum (ER) stress. In this report, we have identified two binding sites for the nuclear factor kappa B in the human SEPS1 promoter. SEPS1 gene expression, protein levels and promoter activity were all increased 2-3-fold by TNF-alpha and IL-1beta in HepG2 cells. We have also confirmed that the previously proposed ER stress response element GGATTTCTCCCCCGCCACG in the SEPS1 proximate promoter is fully functional and responsive to ER stress. However, concurrent treatment of HepG2 cells with IL-1beta and ER stress produced no additive effect on SEPS1 gene expression. We conclude that SEPS1 is a new target gene of NF-kappaB. Together with our previous findings that SEPS1 may regulate cytokine production in macrophage cells, we propose a regulatory loop between cytokines and SEPS1 that plays a key role in control of the inflammatory response.
Subject(s)
Cytokines/metabolism , Gene Expression Regulation , Membrane Proteins/metabolism , Selenoproteins/metabolism , Cell Line , Endoplasmic Reticulum/metabolism , Glucose/metabolism , Humans , Inflammation , Interleukin-1/metabolism , NF-kappa B/metabolism , Plasmids/metabolism , Promoter Regions, Genetic , Tumor Necrosis Factor-alpha/metabolismABSTRACT
SelS is a newly identified selenoprotein and its gene expression is up-regulated in the liver of Psammomys obesus after fasting. We have examined whether SelS is regulated by glucose deprivation and endoplasmic reticulum (ER) stress in HepG2 cells. Glucose deprivation and the ER stress inducers tunicamycin and thapsigargin increased SelS gene expression and protein content several-fold in parallel with glucose-regulated protein 78. The overexpression of SelS increased Min6 cell resistance to oxidative stress-induced toxicity. These results indicate that SelS is a novel member of the glucose-regulated protein family and its function is related to the regulation of cellular redox balance.
Subject(s)
Endoplasmic Reticulum/physiology , Gene Expression Regulation, Neoplastic , Glucose/metabolism , HSP70 Heat-Shock Proteins , Membrane Proteins , Proteins/genetics , Stress, Physiological/metabolism , Amino Acid Sequence , Carcinoma, Hepatocellular/genetics , Carcinoma, Hepatocellular/pathology , Cell Line, Tumor , Cell Survival , Endoplasmic Reticulum/drug effects , Enzyme Inhibitors/pharmacology , Genes, Reporter , Humans , Hydrogen Peroxide/pharmacology , Luciferases/genetics , Luciferases/metabolism , Molecular Sequence Data , Mutagenesis, Insertional , Oxidants/pharmacology , Promoter Regions, Genetic , Proteins/chemistry , Proteins/metabolism , RNA, Messenger/metabolism , Selenoproteins , Sequence Homology, Amino Acid , Thapsigargin/pharmacology , Time Factors , Tunicamycin/pharmacologyABSTRACT
Increased hepatic glucose output and decreased glucose utilization are implicated in the development of type 2 diabetes. We previously reported that the expression of a novel gene, Tanis, was upregulated in the liver during fasting in the obese/diabetic animal model Psammomys obesus. Here, we have further studied the protein and its function. Cell fractionation indicated that Tanis was localized in the plasma membrane and microsomes but not in the nucleus, mitochondria, or soluble protein fraction. Consistent with previous gene expression data, hepatic Tanis protein levels increased more significantly in diabetic P. obesus than in nondiabetic controls after fasting. We used a recombinant adenovirus to increase Tanis expression in hepatoma H4IIE cells and investigated its role in metabolism. Tanis overexpression reduced glucose uptake, basal and insulin-stimulated glycogen synthesis, and glycogen content and attenuated the suppression of PEPCK gene expression by insulin, but it did not affect insulin-stimulated insulin receptor phosphorylation or triglyceride synthesis. These results suggest that Tanis may be involved in the regulation of glucose metabolism, and increased expression of Tanis could contribute to insulin resistance in the liver.
