After observing that expression of two NR4A orphan nuclear receptors, NR4A3 and NR4A1, was altered by insulin in cDNA microarray analyses of human skeletal muscle, we studied whether these receptors could modulate insulin sensitivity. We found that both NR4A3 and NR4A1 were induced by insulin and by thiazolidinedione drugs (pioglitazone and troglitazone) in 3T3-L1 adipocytes. Furthermore, gene expression of NR4A3 and NR4A1 was reduced in skeletal muscles and adipose tissues from multiple rodent models of insulin resistance. To determine whether NR4A3 could modulate insulin sensitivity, 3T3-L1 adipocytes were stably transduced with NR4A3 or LacZ (control) lentiviral vectors. Compared with LacZ expressing cells, hyperexpression of NR4A3 increased the ability of insulin to augment glucose transport activity, and the mechanism involved increased recruitment of GLUT4 glucose transporters to the plasma membrane. NR4A3 hyperexpression also led to an increase in insulin-mediated tyrosine phosphorylation of insulin receptor substrate-1 as well as Akt phosphorylation. Suppression of NR4A3 using lentiviral short hairpin RNA constructs reduced the ability of insulin to stimulate glucose transport and phosphorylate Insulin receptor substrate-1 and Akt. Thus, NR4A3 and NR4A1 are attractive novel therapeutic targets for potential amelioration of insulin resistance, and treatment and prevention of type 2 diabetes and the metabolic syndrome.Type 2 diabetes is a disease caused by defects in insulin secretion combined with the presence of insulin resistance in peripheral target tissues that results in dysregulation of glucose metabolism. Among non-diabetic individuals, there is a wide variation in the degree of insulin sensitivity, and relative insulin resistance is associated with a cluster of clinical and metabolic traits including central obesity, glucose intolerance, dyslipidemia, and elevated blood pressure. This trait cluster is referred to as the metabolic syndrome and confers increased risk of both type 2 diabetes and cardiovascular disease (1-3).The primary target tissues for insulin action are skeletal muscle, adipose tissue, and liver. To better understand the molecular defects responsible for human insulin resistance, we have recently assessed differential gene expression in human skeletal muscle biopsies from insulin-sensitive and -resistant individuals using cDNA microarray technology (4). These studies identified two differentially expressed genes that are members of the NR4A (NGFI-B) family of orphan nuclear receptors within the greater steroid/thyroid receptor superfamily, namely, NR4A3 and NR4A1.NR4A3 (also known as NOR-1, TEC, CHN, and MINOR) was originally identified as a protein induced in primary cultures of rat embryonic forebrain neurons undergoing apoptosis (5). Based on homology within the DNA binding domain, there are two additional members of the NR4A (NGFI-B) family of orphan nuclear receptors, NR4A2 (also known as TINUR, NOT, and Nurr1) and NR4A1 (also known as Nur77, NGFI-B, and TR3). NR4A/NGFI-B rec...

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Resistin is secreted from adipocytes, and high circulating levels have been associated with obesity and insulin resistance. To investigate whether resistin could exert autocrine effects in adipocytes, we expressed resistin gene in 3T3-L1 fibroblasts using a lentiviral vector, and selected several stably-transduced cell lines under blasticidin selection.We observed that 3T3-L1 adipocytes expressing resistin have a decreased gene expression for related transcriptional factors (CCAAT/enhancer binding protein α(C/EBPα) , peroxisome proliferator-activated receptor gamma (PPARγ), and adipocyte lipid binding protein (ALBP/aP2) which is one of target genes for the PPARγ during adipocyte differentiation,. Overexpression of resistin increased the levels of three proinflammatory cytokines, tumor necrosis factor alpha (TNFα), interleukin 6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1), which play important roles for insulin resistance, glucose and lipid metabolisms during adipogenesis. Furthermore, overexpressing resistin in adipocytes inhibits glucose transport 4 (GLUT4) activity and its gene expression, reducing insulin's ability for glucose uptake by 30 %.In conclusion, resistin overexpression in stably transduced 3T3-L1 cells resulted in: 1) Attenuation of programmed gene expression responsible for adipogenesis; 2) Increase in expression of proinflammatory cytokines; 3) Decrease in insulin responsiveness of the glucose transport system. These data suggest a new role for resistin as an autocrine/paracrine factor affecting inflammation and insulin sensitivity in adipose tissue.