NR4A Orphan Nuclear Receptors Modulate Insulin Action and the Glucose Transport System

Abstract

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...

Quantitative Analysis of Orphan Nuclear Receptors in Insulin-Resistant C2C12 Skeletal Muscle Cells

“…A representative figure (Figure 2) shows in graphical form a number of the orphan nuclear receptors that insulin resistant. There is little information available on the role of the NR4As in insulin resistance however, studies by Fu et al [24] found that Nur77 and Nor-1 were induced with 10 nM insulin in 3T3-L1 adipocytes cells at 1 h and 2 h, respectively. This is in collaboration to our studies were we show both Nur77 and Nor-1 induced by 10 nM insulin at 30 min and 2 h (Nur77) and 2 h (Nor-1).…”

Liver X receptor is a regulator of orphan nuclear receptor NOR-1 gene transcription in adipocytes

“…18 Both LXRa and LXRb increase target gene transcription by binding to DNA sequence motifs composed of two hexameric nucleotide direct repeats separated by four bases (DR-4). 19 Although in the earlier study, LXRa and NOR-1 were separately shown to participate in regulating genes involved in metabolic fuel usage, [7][8][9][10]16,20 our current studies in adipocytes identify a direct involvement of LXRa to regulate NOR-1 gene transcription through a DR-4 element in the NOR-1 promoter.…”

“…NR4A receptors were shown to contribute to the cAMP-dependent transcription of glucose-6-phosphatase in the liver, a key step in hepatic gluconeogenesis, 10 as well as to the regulation of genes involved in glucose and oxidative metabolism in skeletal muscle. 8,26 In adipose tissue, NR4As have been linked to the recruitment of GLUT4 receptors to the plasma membrane, resulting in improved insulin sensitivity, 7 and in brown adipocytes, NOR-1 contributes to the cAMP-dependent transcription of the Ucp1 gene, the induction of which is necessary for sustained adaptive thermogenesis. 9 Our finding of another transcriptional regulatory pathway to regulate NR4As, and the NOR-1 gene in particular in response to LXR, underscores the fact that we still do not know the full extent to which there is cross-talk between the nuclear receptor families to modulate each other's expression.…”

“…[2][3][4][5][6] More recently, these receptors have been shown to function in the regulation of important genes involved in metabolic homeostasis in the liver, adipose and muscle. [7][8][9][10] From structural considerations, the NR4As do not appear to contain a functional ligand-binding pocket, and thus are ligand-independent transcriptional regulators. 11,12 Of the several stimuli known to increase the expression of the NR4As, many do so through elevations in cyclic adenosine monophosphate (cAMP) levels.…”

DNA Microarray Analysis of Whole Blood Cells and Insulin-Sensitive Tissues Reveals the Usefulness of Blood RNA Profiling as a Source of Markers for Predicting Type 2 Diabetes

“…In particular, Ucp3 is involved in lipid metabolism (GO:6629). Cluster 2 includes five genes Hepattic protein EIIH, 15) Nr4a3, 16) Adrb3, [17][18][19][20] Adiponectin, 21) and Rbp4. 22,23) In particular, Nr4a3 and Adrb3 genes were involved in responses to stimulus (GO:50896), and Adiponectin genes were involved in lipid metabolism (GO:6629).…”