ABSTRACT
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.
Subject(s)
Gene Expression , Glucose/metabolism , Insulin/pharmacology , Liver/metabolism , Membrane Proteins/genetics , Amino Acid Sequence , Animals , Cell Fractionation , Cell Membrane/chemistry , Cell Nucleus/chemistry , Diabetes Mellitus/metabolism , Gerbillinae , Glycogen/analysis , Glycogen/biosynthesis , Liver/ultrastructure , Membrane Proteins/chemistry , Membrane Proteins/physiology , Microsomes, Liver/chemistry , Mitochondria, Liver/chemistry , Molecular Sequence Data , Obesity/metabolism , Peptide Fragments/chemistry , Phosphoenolpyruvate Carboxykinase (GTP)/genetics , Phosphorylation , Receptor, Insulin/metabolism , Transfection , Triglycerides/biosynthesis , Tumor Cells, CulturedABSTRACT
Here we describe a novel protein, which we have named Tanis, that is implicated in type 2 diabetes and inflammation. In Psammomys obesus, a unique polygenic animal model of type 2 diabetes and the metabolic syndrome, Tanis is expressed in the liver in inverse proportion to circulating glucose (P = 0.010) and insulin levels (P = 0.004) and in direct proportion with plasma triglyceride concentrations (P = 0.007). Hepatic Tanis gene expression was markedly increased (3.1-fold) after a 24-h fast in diabetic but not in nondiabetic P. obesus. In addition, glucose inhibited Tanis gene expression in cultured hepatocytes (P = 0.006) as well as in several other cell types (P = 0.001-0.011). Thus, Tanis seems to be regulated by glucose and is dysregulated in the diabetic state. Yeast-2 hybrid screening identified serum amyloid A (SAA), an acute-phase inflammatory response protein, as an interacting protein of Tanis, and this was confirmed by Biacore experiments. SAA and other acute-phase proteins have been the focus of recent attention as risk factors for cardiovascular disease, and we contend that Tanis and its interaction with SAA may provide a mechanistic link among type 2 diabetes, inflammation, and cardiovascular disease.
