Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Inhibitory serine phosphorylation is a potential molecular mechanism for insulin resistance. We have developed a new variant of the yeast two-hybrid method, referred to as disruptive yeast tri-hybrid (Y3H), to identify inhibitory kinases and sites of phosphorylation in insulin receptors (IR) and IR substrates, IRS-1. Using IR and IRS-1 as bait and prey, respectively, and c-Jun NH(2)-terminal kinase (JNK1) as the disruptor, we now show that phosphorylation of IRS-1 Ser-307, a previously identified site, is necessary but not sufficient for JNK1-mediated disruption of IR/IRS-1 binding. We further identify a new phosphorylation site, Ser-302, and show that this too is necessary for JNK1-mediated disruption. Seven additional kinases potentially linked to insulin resistance similarly block IR/IRS-1 binding in the disruptive Y3H, but through distinct Ser-302- and Ser-307-independent mechanisms. Phosphospecific antibodies that recognize sequences surrounding Ser(P)-302 or Ser(P)-307 were used to determine whether the sites were phosphorylated under relevant conditions. Phosphorylation was promoted at both sites in Fao hepatoma cells by reagents known to promote Ser/Thr phosphorylation, including the phorbol ester phorbol 12-myristate 13-acetate, anisomycin, calyculin A, and insulin. The antibodies further showed that Ser(P)-302 and Ser(P)-307 are increased in animal models of obesity and insulin resistance, including genetically obese ob/ob mice, diet-induced obesity, and upon induction of hyperinsulinemia. These findings demonstrate that phosphorylation at both Ser-302 and Ser-307 is necessary for JNK1-mediated inhibition of the IR/IRS-1 interaction and that Ser-302 and Ser-307 are phosphorylated in parallel in cultured cells and in vivo under conditions that lead to insulin resistance.
 ...
PMID:Insulin resistance due to phosphorylation of insulin receptor substrate-1 at serine 302. 1519 52

Insulin resistance is a characteristic feature of obesity and type 2 diabetes mellitus, but it is also present in up to 25% of healthy nonobese individuals. The molecular mechanisms causing insulin resistance are not yet fully understood. Recently, overexpression of several potential inhibitors of the insulin receptor tyrosine-kinase activity, a key step in insulin signaling, has been described in insulin-resistant subjects . PC-1 is expressed in many tissues and inhibits insulin signaling either at the level of the insulin receptor or downstream at a postreceptor site. An elevated PC-1 content in insulin target tissues may play an important role in the development of insulin resistance in obesity and type 2 diabetes mellitus. A polymorphism in PC-1 has been demonstrated to be associated with insulin resistance. This was a DNA polymorphism in exon 4 that causes an amino acid change from lysine to glutamine at codon 121 (K121Q). PC-1 121Q allele might predispose independently of other well established risk factors for early myocardial infarction. Testing for the PC-1 K121Q polymorphism might be valuable in patients with a family history of atherosclerotic vascular disease and myocardial infarction. There is growing evidence that genetic factors play an important role in the development of diabetic nephropathy (DN). Efforts to identify these factors rely primarily on the candidate gene approach; candidate genes for insulin resistance may be considered candidates for DN as well. In a stratified analysis according to duration of diabetes, the risk of early-onset end-stage renal disease (ESRD) for carriers of the Q variant was 2.3 times that for noncarriers. The cellular mechanisms for the insulin resistance of pregnancy and gestational diabetes mellitus (GDM) are unknown. Women with GDM have an increased PC-1 content and excessive phosphorylation of serine/threonine residues in muscle insulin receptors. The postreceptor defects in insulin signaling may contribute to the pathogenesis of GDM and the increased risk for type 2 diabetes later in life. Although widely explored, the true cause of insulin resistance in uremic patients is not entirely elucidated yet. During the last decade it was found that erythropoietin (EPO) therapy, used for correction of anemia in patients with end stage renal failure, ameliorates insulin resistance. An increased lymphocyte PC-1 activity over control was found in hemodialysis patients. A two-month EPO therapy significantly decreased PC-1 activity to the control values, suggesting that an effect on PC-1 expression could be implicated in the amelioration of insulin resistance in uremic patients treated with EPO. Current investigations implicate that therapeutic modification of PC-1 expression would be of great benefit for insulin-resistant type 2 diabetics. Metformin, a biguanide oral antidiabetic agent, was shown to affect insulin resistance by decreasing enzymatic activity of overexpressed PC-1 molecules in obese type 2 diabetics. Thiazolidinedione (TZD) insulin-sensitizing drugs are a class of compounds that improve insulin action in vivo. Treatment of patients with TZDs seems to have a beneficial effect on most, if not all, components of metabolic syndrome. TZDs have also been used in the treatment of nondiabetic human insulin-resistant states, and have demonstrated an improvement in insulin sensitivity. Although much remains to be learned about PPAR gamma receptor and TZD action, the advent of TZD insulin-sensitizing agents has an enormous impact on our understanding of insulin resistance. The great potential of insulin resistance therapy illuminated by the TZDs will continue to catalyze research in this area directed toward the discovery of new insulin-sensitizing agents that work through other mechanisms.
 ...
PMID:Plasma cell membrane glycoprotein 1 (PC-1): a marker of insulin resistance in obesity, uremia and diabetes mellitus. 1520 35

Fenofibrate, a peroxisome proliferated activated receptor alpha (PPARalpha) agonist, has been shown to decrease plasma triglyceride (TG) and increase plasma high-density lipoprotein (HDL) cholesterol levels despite a large interindividual variation in the response. Fenofibrate-activated PPARalpha binds to a DNA sequence element termed PPAR response element (PPRE) present in regulatory regions of target genes. A PPRE has been identified in the proximal 5' flanking region of the gene encoding the liver fatty acid binding protein (LFABP). LFABP is a small cytosolic protein of 14 kDa present in the liver and the intestine and is a member of the superfamily of the fatty acid binding proteins (FABPs). FABPs play a role in the solubilization of long-chain fatty acids (LCFAs) and their CoA-ester to various intracellular organelles. FABPs serves as intracellular acceptors of LCFAs, and they may also have an impact in ligand-dependent transactivation of PPARs in trafficking LCFAs to the nucleus. Since PPARs are known to regulate the transcription of many genes involved in lipid metabolism, the importance of LFABP in fatty acid uptake has to be considered. The aim of this study was to verify whether genetic variations in the LFABP gene may impact on plasma lipoprotein/lipid levels in the fasting state as well as on the response to a lipid-lowering therapy with fenofibrate on plasma lipids and obesity variables. We also wanted to verify whether the presence of the PPARalpha L162V mutation interacts with genetic variants in LFABP gene. To achieve this goal, we first determined the genomic structure of the human LFABP gene and then designed intronic primers to sequence the coding regions, all exon-intron splicing boundaries, and the promoter region of the gene in 24 patients showing divergent plasma lipoprotein/lipid response to fenofibrate. Sequence analysis revealed the presence of a T94A missense mutation in exon 3. Interspecies comparison revealed that threonine 94 is conserved among species. We subsequently screened another sample of 130 French Canadian subjects treated with fenofibrate for the presence of the LFABP T94A mutation. Carriers of the A94 allele were at increased risk to exhibit plasma TG levels above 2.00 mmol/l after treatment with fenofibrate [2.75 (1.03-7.34); OR 95% confidence interval (CI)]. In addition, carriers of the A94 allele were characterized by higher baseline plasma-free fatty acid levels (FFA) ( p=0.01) and by a lower body mass index (BMI) ( p=0.05) and waist circumference ( p=0.005) than T94 homozygotes. Moreover, PPARalpha L162V and LFABP T94A showed to have a synergistic effect on BMI ( p interaction = 0.03). These results suggest that the LFABP T94A missense mutation could influence obesity indices as well as the risk to exhibit residual hypertriglyceridmia following a lipid-lowering therapy with fenofibrate.
 ...
PMID:Effect of liver fatty acid binding protein (FABP) T94A missense mutation on plasma lipoprotein responsiveness to treatment with fenofibrate. 1524 72

Skeletal muscle insulin resistance is a co-morbidity of obesity and a risk factor for the development of type 2 diabetes mellitus. Insulin resistance is associated with the accumulation of intramyocellular lipids. Intramyocellular triacylglycerols do not appear to be the cause of insulin resistance but are more likely to be a marker of other lipid intermediates such as fatty acyl-CoA, ceramides or diacylglycerols. Fatty acyl-CoA, ceramides and diacylglycerols are known to directly alter various aspects of the insulin signalling cascade. Insulin signalling is inhibited by the phosphorylation of serine and threonine residues at the levels of the insulin receptor and insulin receptor substrate 1. Protein kinase C is responsible for the phosphorylation of the serine and threonine residues. Fatty acyl-CoA and diacylglycerols are known to activate protein kinase C. The cause of the intramyocellular accumulation of fatty acyl-CoA and diacylglycerols is unclear at this time. Reduced fatty acid oxidation does not appear to be responsible, as fatty acyl-CoA accumulates in skeletal muscle with a normal fatty acid oxidative capacity. Other potential mechanisms include oversupply of lipids to muscle and/or up regulated fatty acid transport.
 ...
PMID:The molecular mechanism linking muscle fat accumulation to insulin resistance. 1529 58

RAB, ADP-ribosylation factors (ARFs) and ARF-like (ARL) proteins belong to the Ras superfamily of small GTP-binding proteins and are essential for various membrane-associated intracellular trafficking processes. None of the approximately 50 known members of this family are linked to human disease. Using a bioinformatic screen for ciliary genes in combination with mutational analyses, we identified ARL6 as the gene underlying Bardet-Biedl syndrome type 3, a multisystemic disorder characterized by obesity, blindness, polydactyly, renal abnormalities and cognitive impairment. We uncovered four different homozygous substitutions in ARL6 in four unrelated families affected with Bardet-Biedl syndrome, two of which disrupt a threonine residue important for GTP binding and function of several related small GTP-binding proteins. Analysis of the Caenorhabditis elegans ARL6 homolog indicates that it is specifically expressed in ciliated cells, and that, in addition to the postulated cytoplasmic functions of ARL proteins, it undergoes intraflagellar transport. These findings implicate a small GTP-binding protein in ciliary transport and the pathogenesis of a pleiotropic disorder.
 ...
PMID:Mutations in a member of the Ras superfamily of small GTP-binding proteins causes Bardet-Biedl syndrome. 1531 42

The agouti-related protein (AGRP) is an endogenous antagonist of the centrally expressed melanocortin receptors. The melanocortin-4 receptor (MC4R) is involved in energy homeostasis, food intake, sexual function, and obesity. The endogenous hAGRP protein is 132 amino acids in length, possesses five disulfide bridges at the C-terminus of the molecule, and is expressed in the hypothalamus of the brain. We have previously reported that a monocyclic hAGRP(103-122) peptide is an antagonist at the melanocortin receptors expressed in the brain. Stereochemical inversion from the endogenous l- to d-isomers of single or multiple amino acid modifications in this monocyclic truncated hAGRP sequence resulted in molecules that are converted from melanocortin receptor antagonists into melanocortin receptor agonists. The Asp-Pro-Ala-Ala-Thr-Ala-Tyr-cyclo[Cys-Arg-DPhe-DPhe-Asn-Ala-Phe-Cys]-Tyr-Ala-Arg-Lys-Leu peptide resulted in a 60 nM melanocortin-1 receptor agonist that is 100-fold selective versus the mMC4R, 1000-fold selective versus the mMC3R, and ca. 180-fold selective versus the mMC5R. In attempts to identify putative ligand-receptor interactions that may be participating in the agonist induced stimulation of the MC4R, selected ligands were docked into a homology molecular model of the mMC4R. These modeling studies have putatively identified hAGRP ligand DArg111-mMC4RAsn115 (TM3) and the hAGRP DPhe113-mMC4RPhe176 (TM4) interactions as important for agonist activity.
 ...
PMID:Stereochemical studies of the monocyclic agouti-related protein (103-122) Arg-Phe-Phe residues: conversion of a melanocortin-4 receptor antagonist into an agonist and results in the discovery of a potent and selective melanocortin-1 agonist. 1561 19

We investigated the relationship between Ala54Thr variant allele of the fatty acid-binding protein 2 (FABP2) gene (Ala54Thr) and development of obesity in Japanese obese women. FABP2 genotypes were determined with a fluorescent allele-specific DNA primer assay system. Body weight, waist and hip circumference, amounts of visceral and subcutaneous white adipose tissue measured by computed tomography (CT) were compared between subjects with Thr allele and without Thr allele before and after the diet and exercise therapy in 80 Japanese obese women. The frequency of the Thr54 allele did not differ between obese and control subjects (0.388 versus 0.329, respectively). In subjects with Ala/Thr and Thr/Thr genotype, adjusted resting metabolic rate (RMR) was significantly lower than the subjects with Ala/Ala genotype. Subjects with the Thr54 allele showed significantly greater waist circumference after diet and exercise therapy than subjects with Ala/Ala genotype. They also demonstrated greater body weight at 20 years of age compared to subjects with Ala/Ala genotype. In conclusion, Thr54 allele of FABP2 has associations with lower adjusted resting metabolic rate, resistance in reducing visceral white adipose tissue (WAT) and early onset of obesity in Japanese obese women.
 ...
PMID:Thr54 allele of the FABP2 gene affects resting metabolic rate and visceral obesity. 1562 Apr 32

Reduced insulin-mediated glucose transport in skeletal muscle is a hallmark of the pathophysiology of T2DM (Type II diabetes mellitus). Impaired intracellular insulin signalling is implicated as a key underlying mechanism. Attention has focused on early signalling events such as defective tyrosine phosphorylation of IRS1 (insulin receptor substrate-1), a major target for the insulin receptor tyrosine kinase. This is required for normal induction of signalling pathways key to many of the metabolic actions of insulin. Conversely, increased serine/threonine phosphorylation of IRS1 following prolonged insulin exposure (or in obesity) reduces signalling capacity, partly by stimulating IRS1 degradation. We now show that IRS1 levels in human muscle are actually increased 3-fold following 1 h of hyperinsulinaemic euglycaemia. Similarly, transient induction of IRS1 (3-fold) in the liver or muscle of rodents occurs following feeding or insulin injection respectively. The induction by insulin is also observed in cell culture systems, although to a lesser degree, and is not due to reduced proteasomal targeting, increased protein synthesis or gene transcription. Elucidation of the mechanism by which insulin promotes IRS1 stability will permit characterization of the importance of this novel signalling event in insulin regulation of liver and muscle function. Impairment of this process would reduce IRS1 signalling capacity, thereby contributing to the development of hyperinsulinaemia/insulin resistance prior to the appearance of T2DM.
 ...
PMID:A novel regulation of IRS1 (insulin receptor substrate-1) expression following short term insulin administration. 1612 72

Insulin has a major anabolic function leading to storage of lipidic and glucidic substrates. All its effects result from insulin binding to a specific membrane receptor which is expressed at a high level on the 3 insulin target tissues: liver, adipose tissue and muscles. The insulin receptor exhibits a tyrosine-kinase activity which leads, first, to receptor autophosphorylation and then to tyrosine phosphorylation of substrates proteins, IRS proteins in priority. This leads to the formation of macromolecular complexes close to the receptor. The two main transduction pathways are the phosphatidylinositol 3 kinase pathway activating protein kinase B which is involved in priority in metabolic effects, and the MAP kinase pathway involved in nuclear effects, proliferation and differentiation. However, in most cases, a specific effect of insulin requires the participation of the two pathways in a complex interplay which could explain the pleiotropy and the specificity of the insulin signal. The negative control of the insulin signal can result from hormone degradation or receptor dephosphorylation. However, the major negative control results from phosphorylation of serine/threonine residues on the receptor and/or IRS proteins. This phosphorylation is activated in response to different signals involved in insulin resistance, hyperinsulinism, TNFalpha or increased free fatty acids from adipose tissue, which are transformed inside the cell in acyl-CoA. A deleterious role for molecules issued from the adipose tissue is postulated in the resistance to insulin of the liver and muscles present in type 2 diabetes, obesity and metabolic syndrome.
 ...
PMID:[Insulin signaling: mechanisms altered in insulin resistance]. 1659 3

Ghrelin, identified as an endogenous ligand for the growth hormone secretagogue receptor, functions as a somatotrophic and orexigenic signal from the stomach. Ghrelin has a unique post-translational modification: the hydroxyl group of the third amino acid, usually a serine but in some species a threonine, is esterified by octanoic acid and is essential for ghrelin's biological activities. The secretion of ghrelin increases under conditions of negative energy-balance, such as starvation, cachexia, and anorexia nervosa, whereas its expression decreases under conditions of positive energy-balance such as feeding, hyperglycemia, and obesity. In addition to having a powerful effect on the secretion of growth hormone, ghrelin stimulates food intake and transduces signals to hypothalamic regulatory nuclei that control energy homeostasis. Thus, it is interesting to note that the stomach may play an important role in not only digestion but also pituitary growth hormone release and central feeding regulation. We summarized recent findings on the integration of ghrelin into neuroendocrine networks that regulate food intake, energy balance, gastrointestinal function and growth.
 ...
PMID:Biological, physiological, and pharmacological aspects of ghrelin. 1661 45


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>