epidermal-growth-factor and Insulin-Resistance

We report the case of a 63-year-old obese man with a rapid-onset of widespread acanthosis nigricans (AN) in the setting of having recently initiated treatment with niacin for dyslipidemia. Although obesity and insulin-resistance are risk factors for AN, AN associated with endocrine dysfunction tends to have a more gradual onset and limited involvement. Owing to our patient's age, the rapid onset, and extensive distribution of his eruption, we initially were concerned about paraneoplastic AN. However, an evaluation for a malignant condition was negative. The timing of the onset of our patient's eruption within several months of starting niacin therapy is consistent with niacin-induced AN. Niacin is known to cause rapidly progressive, widespread AN that is reversible upon discontinuation of the medication. We discuss the pathogenesis of AN, which is thought to be the final common manifestation of stimulation of different subtypes of tyrosine kinase receptors by various epidermal growth factors.

Topics: Acanthosis Nigricans; Cardiovascular Diseases; Diagnosis, Differential; Dyslipidemias; Epidermal Growth Factor; Humans; Hyperinsulinism; Hypolipidemic Agents; Insulin Resistance; Male; Middle Aged; Niacin; Obesity; Paraneoplastic Syndromes; Receptor Protein-Tyrosine Kinases

Topics: Adiponectin; Animals; Epidermal Growth Factor; Estrogens; Female; Humans; Insulin Resistance; Lipoprotein Lipase; Menopause; Metabolic Syndrome; Obesity; Tumor Necrosis Factor-alpha

The etiology of polycystic ovary syndrome (PCOS) has not yet been fully elucidated but involves a disruption of normal ovarian function and multisystem sequelae. A combination of abnormally functioning genes whose expression is influenced by environmental, extra-ovarian factors determines the symptoms. Growth factors are heavily involved in the pathophysiology, either contributing to or as a consequence of the arrested development of follicles, abnormal steroidogenesis and hyperinsulinemia. Hyperactivity of a--transforming growth factor (TGFa) and epidermal growth factor (EGF) may block stimulation of aromatase and attenuate apoptosis of follicles and other factors may interface with the insulin-like growth factor (IGF) system preventing arrested follicles from becoming atretic and preventing the selection of a dominant follicle. IGF-binding protein concentrations are decreased by insulin, freeing biologically active IGF-I which augments the action of luteinizing hormone (LH) by inducing LH receptors, hyperactivating the enzymes P450c17a and 17,20 lyase resulting in hyperandrogenism. Growth hormone itself may be involved in the pathophysiology, as in normoinsulinemic PCOS patients it is hypersecreted and its actions on growth factors and their binding proteins are similar to those of insulin.

Topics: Androgens; Epidermal Growth Factor; Female; Growth Substances; Humans; Insulin Resistance; Ovarian Follicle; Polycystic Ovary Syndrome; Somatomedins; Transforming Growth Factor alpha

Diabetes mellitus is associated with typical patterns of long term vascular complications which vary with the organ involved. The microvascular kidney disease (Olgemoller and Schleicher, 1993) is characterized by thickening of the capillary basement membranes and increased deposition of extracellular matrix components (ECM), while loss of microvessels with subsequent neovascularisation is predominant in the eye and peripheral nerves. On the other hand macrovascular disease is characterized by accelerated atherosclerosis. These complications are dependent on long term hyperglycemia. Specific biochemical pathways linking hyperglycaemia to microvascular changes were proposed: the polyol pathway (Greene et al., 1987), non-enzymatic glycation of proteins (Brownlee et al., 1988), glucose autooxidation and oxidative stress (Hunt et al., 1990), hyperglycemic pseudohypoxia (Williamson et al., 1993) enhanced activation of protein kinase C by de novo-synthesis of diacyl glycerol (Lee et al., 1989; DeRubertis and Craven 1994) and others. These pathways are not mutually exclusive (Larkins and Dunlop, 1992; Pfeiffer and Schatz, 1992). They may be linked to alterations in the synthesis of growth factors particularly since atherosclerosis and angioneogenesis are associated with increased proliferation of endothelial and smooth muscle cells. Increased synthesis of ECM components is stimulated by growth factors like transforming growth factor beta (TGF beta) (Derynck et al., 1984) and insulin-like growth factor I (IGF-I) (Moran et al., 1991). This review will summarize some of the recent evidence for an involvement of growth factors in diabetic vascular complications and will attempt to assign their emergence in the sequence of events leading to vascular complications.

Topics: Animals; Arteriosclerosis; Diabetic Angiopathies; Diabetic Nephropathies; Diabetic Retinopathy; Epidermal Growth Factor; Fibroblast Growth Factor 2; Growth Hormone; Growth Substances; Humans; Hyperglycemia; Insulin Resistance; Insulin-Like Growth Factor I; Receptors, Somatotropin; Transforming Growth Factor beta; Tumor Necrosis Factor-alpha

Inflammation, along with aging processes, contributes to the development of insulin resistance (IR), but the roles of different inflammatory and other cytokines in this process remain unclear. Thus, we aimed to analyze the association between several plasma cytokines with IR as evaluated by the metabolic score for insulin resistance, METS-IR.. We measured the plasma concentrations of thirty cytokines from a cohort of older persons and analyzed their role as independent factors for IR. We used regression analyses adjusted for known IR-associated factors (including age, gender, cholesterol levels, and BMI) to find the determinants of IR.. The study evaluated 132 subjects, mostly women (82F/50M), slightly overweight, and with a mean age of 78.5 ± 6.5 years. In the overall population, IL-15 significantly and negatively correlates with METS-IR (r = -0.183,. Our results indicate the association between cytokines and IR has to be interpreted in a gender-specific manner. In women, EGF, Eotaxin, and MCP-1 circulating levels are associated with METS-IR being BMI a significant mediator. Understanding the role of gender in the relationship between cytokines and IR will help to define individualized preventive and treatment interventions to reduce the risk of age-related metabolic disorders.

Topics: Aged; Aged, 80 and over; Body Mass Index; Cytokines; Epidermal Growth Factor; Female; Humans; Insulin Resistance; Interleukin-15; Male; Metabolic Syndrome

To assess changes in metabolic risk factors and cancer-related growth factors associated with short-term abstinence from alcohol.. Prospective, observational study.. Single tertiary centre.. Healthy subjects were recruited based on intention to: (1) abstain from alcohol for 1 month (abstinence group), or (2) continue to drink alcohol (control group). Inclusion criteria were baseline alcohol consumption >64 g/week (men) or >48 g/week (women). Exclusion criteria were known liver disease or alcohol dependence.. The primary outcome was change in insulin resistance (homeostatic model assessment (HOMA) score). Secondary outcomes were changes in weight, blood pressure (BP), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF) and liver function tests. Primary and secondary outcomes were adjusted for changes in diet, exercise and cigarette smoking.. The abstinence group comprised 94 participants (mean age 45.5 years, SD ±1.2) and the control group 47 participants (mean age 48.7 years, SD ±1.8). Baseline alcohol consumption in the abstinence group was 258.2 g/week, SD ±9.4, and in the control group 233.8 g, SD ±19.0. Significant reductions from baseline in the abstinence group (all p<0.001) were found in: HOMA score (-25.9%, IQR -48.6% to +0.3%), systolic BP (-6.6%, IQR -11.8% to 0.0%), diastolic BP (-6.3%, IQR -14.1% to +1.3%), weight (-1.5%, IQR -2.9% to -0.4%), VEGF (-41.8%, IQR -64.9% to -17.9%) and EGF (-73.9%, IQR -86.1% to -36.4%). None of these changes were associated with changes in diet, exercise or cigarette smoking. No significant changes from baseline in primary or secondary outcomes were noted in the control group.. These findings demonstrate that abstinence from alcohol in moderate-heavy drinkers improves insulin resistance, weight, BP and cancer-related growth factors. These data support an independent association of alcohol consumption with cancer risk, and suggest an increased risk of metabolic diseases such as type 2 diabetes and fatty liver disease.

Topics: Adult; Alcohol Drinking; Alcoholism; Blood Pressure; Body Weight; Cardiovascular Diseases; Diabetes Mellitus, Type 2; Epidermal Growth Factor; Ethanol; Fatty Liver; Female; Humans; Insulin Resistance; Liver; Liver Function Tests; Male; Middle Aged; Neoplasms; Prospective Studies; Risk Factors; Vascular Endothelial Growth Factor A

Calorie restriction is a common strategy for weight loss in obese individuals. However, little is known about the impact of moderate hypocaloric diets on obesity-related laboratory parameters in a short-term period. Aim of this study was to evaluate the variation of laboratory biomarkers in obese individuals following a Mediterranean, hypocaloric (1400-1600 Kcal/die) diet. 23 obese, pharmacologically untreated patients were enrolled and subjected to the determination of anthropometric variables and blood collection at baseline, 1 and 4 months after diet initiation. After 4 months of calorie restriction, we observed a significant decrease in body weight and BMI (both P < 0.0001), insulin (P = 0.037), HOMA-IR (P = 0.026), leptin (P = 0.008), and LDH (P = 0.023) and an increase in EGF (P = 0.013). All these parameters, except LDH, varied significantly already at 1 month after diet initiation. Also, lower levels of insulin (P = 0.025), leptin (P = 0.023), and EGF (P = 0.035) were associated with a greater (>5%) weight loss. Collectively, our data support a precocious improvement of insulin and leptin sensitivity after a modest calorie restriction and weight reduction. Moreover, EGF and LDH may represent novel markers of obesity, which deserve further investigations.

Topics: Adipokines; Anthropometry; Biomarkers; Body Mass Index; Caloric Restriction; Diet; Diet, Mediterranean; Epidermal Growth Factor; Female; Humans; Insulin; Insulin Resistance; L-Lactate Dehydrogenase; Leptin; Male; Middle Aged; Obesity; Prospective Studies; Weight Loss

Type 1 diabetes (T1D) results from an autoimmune destruction of insulin-producing β cells. Currently, islet transplantation is the only curative therapy for late-stage T1D, but the beneficial effect is limited in its duration, even under chronic immunosuppression, because of the chronic graft rejection mediated by both auto- and alloimmunity. Clinical islet transplantation is also restricted by a severe shortage of donor islets. Induction of mixed chimerism reverses autoimmunity, eliminates insulitis, and reverses new-onset but not late-stage disease in the nonobese diabetic (NOD) mouse model of T1D. Administration of gastrin and epidermal growth factor (EGF) also reverses new-onset but not late-stage T1D in this animal model. Here, we showed that combination therapy of induced mixed chimerism under a radiation-free nontoxic anti-CD3/CD8 conditioning regimen and administration of gastrin/EGF augments both β cell neogenesis and replication, resulting in reversal of late-stage T1D in NOD mice. If successfully translated into humans, this combination therapy could replace islet transplantation as a long-term curative therapy for T1D.

Topics: Animals; Combined Modality Therapy; Diabetes Mellitus, Type 1; Disease Models, Animal; Epidermal Growth Factor; Female; Gastrins; Humans; Insulin Resistance; Insulin-Secreting Cells; Islets of Langerhans Transplantation; Mice; Mice, Inbred C57BL; Mice, Inbred NOD; Mice, SCID; Mice, Transgenic; Regeneration; Translational Research, Biomedical; Transplantation Chimera; Transplantation Conditioning

On activation by receptors, the ubiquitously expressed class IA isoforms (p110alpha and p110beta) of phosphatidylinositol-3-OH kinase (PI(3)K) generate lipid second messengers, which initiate multiple signal transduction cascades. Recent studies have demonstrated specific functions for p110alpha in growth factor and insulin signalling. To probe for distinct functions of p110beta, we constructed conditional knockout mice. Here we show that ablation of p110beta in the livers of the resulting mice leads to impaired insulin sensitivity and glucose homeostasis, while having little effect on phosphorylation of Akt, suggesting the involvement of a kinase-independent role of p110beta in insulin metabolic action. Using established mouse embryonic fibroblasts, we found that removal of p110beta also had little effect on Akt phosphorylation in response to stimulation by insulin and epidermal growth factor, but resulted in retarded cell proliferation. Reconstitution of p110beta-null cells with a wild-type or kinase-dead allele of p110beta demonstrated that p110beta possesses kinase-independent functions in regulating cell proliferation and trafficking. However, the kinase activity of p110beta was required for G-protein-coupled receptor signalling triggered by lysophosphatidic acid and had a function in oncogenic transformation. Most strikingly, in an animal model of prostate tumour formation induced by Pten loss, ablation of p110beta (also known as Pik3cb), but not that of p110alpha (also known as Pik3ca), impeded tumorigenesis with a concomitant diminution of Akt phosphorylation. Taken together, our findings demonstrate both kinase-dependent and kinase-independent functions for p110beta, and strongly indicate the kinase-dependent functions of p110beta as a promising target in cancer therapy.

Topics: Animals; Cell Proliferation; Cell Transformation, Neoplastic; Epidermal Growth Factor; Fibroblasts; Glucose; Glucose Intolerance; Homeostasis; Humans; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Phosphatidylinositol 3-Kinases; Phosphorylation; Prostatic Neoplasms; Proto-Oncogene Proteins c-akt; PTEN Phosphohydrolase; Signal Transduction

Leprechaunism features a clinical constellation characterized by extreme insulin resistance, growth retardation, and several distinct developmental abnormalities. One puzzling observation about leprechaunism is that mutations in the insulin receptor gene frequently associated with this syndrome cannot account for the aberrant responses of cultured cells to other growth factors. Here we report that the generation of reactive oxygen species (ROS) is impaired in cells from leprechaunism patients, thus shedding new light on this issue. Stimulation of patients' skin fibroblast cells with platelet-derived growth factor (PDGF) resulted in a lower-level tyrosine phosphorylation of cytosolic proteins compared with that seen in normal cells. In addition, consistent with the hypothesis that ROS mediate the level of tyrosine phosphorylation of cytosolic proteins through inactivation of protein tyrosine phosphatases (PTPases), patient fibroblast cells showed a significantly higher phosphatase activity than normal cells. We further showed that the lower-level tyrosine phosphorylation in response to growth factors results from the downregulation of an NADPH oxidase, Nox4, which in turn results in the reduction of ROS generation. Ectopic expression of Nox4 in the patient fibroblast cells consistently restored PDGF-induced ROS production and regulation of PTPase activities. Taken together, these data provide insight into the mechanisms through which growth retardation is associated with leprechaunism syndrome.

Topics: Abnormalities, Multiple; Cells, Cultured; Down-Regulation; Epidermal Growth Factor; Fibroblasts; Gene Expression Regulation, Enzymologic; Humans; Insulin Resistance; NADPH Oxidase 4; NADPH Oxidases; Phenotype; Phosphorylation; Platelet-Derived Growth Factor; Reactive Oxygen Species; Tyrosine

Recent evidence has shown that activation of phosphatidyinositol-3-kinase (PI3K) and Akt, necessary for insulin stimulation of glucose transport, is impaired in insulin resistance. It is unknown, however, which Akt isoform shows impaired activation in insulin resistance. Additionally, related growth factors (epidermal or platelet-derived vascular) also stimulate PI3K, but it is unknown whether production of 3,4,5 phosphatidyinositol is sufficient to stimulate glucose transport in insulin-resistant muscle. Moreover, these studies were performed in rodents, and little data exists from humans. Hence, we investigated the stimulation of PI3K and Akt-1, -2, and -3 by insulin and epidermal growth factors (EGFs) in skeletal muscles from lean and obese insulin-resistant humans. Insulin activated all Akt isoforms in lean muscles, whereas only Akt-1 was activated in obese muscles. Insulin receptor substrate (IRS)-1 was associated with PI3K activity, which is necessary for Akt activation by insulin, and was reduced in obese muscles, and this was accompanied by decreased IRS-1 expression. In contrast, insulin- or EGF-stimulated phosphotyrosine-associated PI3K activity was not different between lean and obese muscles. These results show that a defect in the ability of insulin to activate Akt-2 and -3 may explain the impaired insulin-stimulated glucose transport in insulin resistance. Additionally, these data also show that different upstream or downstream signals may regulate the activity of the various Akt isoforms.

Topics: Adult; Body Mass Index; Deoxyglucose; Enzyme Activation; Epidermal Growth Factor; Female; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Male; Muscle, Skeletal; Obesity; Oncogene Proteins; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphotyrosine; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction

The ability of the growth factors epidermal growth factor (EGF), transforming growth factor alpha, and platelet-derived growth factor to exert insulin-like effects on glucose transport and lipolysis were examined in human and rat fat cells. No effects were found in rat fat cells, whereas EGF (EC(50) for glucose transport approximately 0.02 nm) and transforming growth factor alpha (EC(50) approximately 0.2 nm), but not platelet-derived growth factor, mimicked the effects of insulin (EC(50) approximately 0.2 nm) on both pathways. EGF receptors, but not EGF, were abundantly expressed in human fat cells as well as in human skeletal muscle. EGF increased the tyrosine phosphorylation of several proteins (the EGF receptor, insulin receptor substrate (IRS)-1, IRS-2, and Grb2-associated binder 1), whereas Shc and Gab2 were only weakly and inconsistently phosphorylated. p85, the regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase), was also found to associate with all of these docking molecules, showing that EGF activated PI 3-kinase pools that were additional to those of insulin. EGF and/or insulin increased protein kinase B/Akt serine phosphorylation to a similar extent, whereas mitogen-activated protein kinase phosphorylation was more pronounced for EGF than for insulin. The impaired insulin-stimulated downstream signaling, measured as protein kinase B/Akt serine phosphorylation, in insulin-resistant cells (Type 2 diabetes) was improved by the addition of EGF. Thus, EGF receptors, but not EGF, are abundantly expressed in human fat cells and skeletal muscle. EGF mimics the effects of insulin on both the metabolic and mitogenic pathways but utilize in part different signaling pathways. Both insulin and EGF increase the tyrosine phosphorylation and activation of IRS-1 and IRS-2, whereas EGF is also capable of activating additional PI 3-kinase pools and, thus, can augment the downstream signaling of insulin in insulin-resistant states like Type 2 diabetes.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Adipocytes; Cell Membrane; Electrophoresis, Polyacrylamide Gel; Enzyme Inhibitors; Epidermal Growth Factor; Humans; Insulin; Insulin Resistance; Muscle, Skeletal; Phosphatidylinositol 3-Kinases; Phosphorylation; Precipitin Tests; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Subcellular Fractions; Transforming Growth Factor alpha; Tyrosine

Tumor necrosis factor-alpha (TNFalpha) has been implicated as a contributing mediator of insulin resistance observed in pathophysiological conditions such as obesity, cancer-induced cachexia, and bacterial infections. Previous studies have demonstrated that TNFalpha confers insulin resistance by promoting phosphorylation of serine residues on insulin receptor substrate 1 (IRS-1), thereby diminishing subsequent insulin-induced tyrosine phosphorylation of IRS-1. However, little is known about which signaling molecules are involved in this process in adipocytes and about the temporal sequence of events that ultimately leads to TNFalpha-stimulated IRS-1 serine phosphorylation. In this study, we demonstrate that specific inhibitors of the MAP kinase kinase (MEK)1/2-p42/44 mitogen-activated protein (MAP) kinase pathway restore insulin signaling to normal levels despite the presence of TNFalpha. Additional experiments show that MEK1/2 activity is required for TNFalpha-induced IRS-1 serine phosphorylation, thereby suggesting a mechanism by which these inhibitors restore insulin signaling. We observe that TNFalpha requires 2.5-4 h to markedly reduce insulin-triggered tyrosine phosphorylation of IRS-1 in 3T3-L1 adipocytes. Although TNFalpha activates p42/44 MAP kinase, maximal stimulation is observed within 10-30 min. To our surprise, p42/44 activity returns to basal levels well before IRS-1 serine phosphorylation and insulin resistance are observed. These activation kinetics suggest a mechanism of p42/44 action more complicated than a direct phosphorylation of IRS-1 triggered by the early spike of TNFalpha-induced p42/44 activity. Chronic TNFalpha treatment (>> 72 h) causes adipocyte dedifferentiation, as evidenced by the loss of triglycerides and down-regulation of adipocyte-specific markers. We observe that this longer term TNFalpha-mediated dedifferentiation effect utilizes alternative, p42/44 MAP kinase-independent intracellular pathways. This study suggests that TNFalpha-mediated insulin resistance, but not adipocyte dedifferentiation, is mediated by the MEK1/2-p42/44 MAP kinase pathway.

Topics: 3T3 Cells; Adipocytes; Animals; Anisomycin; Cell Differentiation; Enzyme Inhibitors; Epidermal Growth Factor; Flavonoids; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Kinetics; MAP Kinase Kinase 1; MAP Kinase Kinase 2; Mice; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; Phosphoproteins; Phosphoserine; Phosphotyrosine; Protein Serine-Threonine Kinases; Protein-Tyrosine Kinases; Signal Transduction; Tumor Necrosis Factor-alpha

A serious insulin resistance characterizes pancreatic cancer-associated diabetes mellitus. Elsewhere, we demonstrated that MIA PaCa2 cultured cells secrete a soluble factor responsible for reduced glucose tolerance induced in SCID mice. The intracellular mechanism of insulin resistance was investigated in isolated and perfused rat hepatocytes incubated with MIA PaCa2 conditioned medium. Lactate production was reduced compared to hepatocytes incubated with control medium while 1,2-DAG was increased and PKC was activated in the hepatocytes incubated with MIA PaCa2 conditioned medium. This behavior was not reproduced treating the hepatocytes with the growth factors EGF, interleukin Ibeta, interleukin-6, and TGF-beta1. In an attempt to make a biochemical identification of the hypothesized tumor associated-diabetogenic factors we observed a low molecular weight protein in the conditioned medium, absent in the nonconditioned one, that may be responsible for the described behaviors.

Topics: Animals; Biological Factors; Cell Membrane; Cells, Cultured; Culture Media, Conditioned; Cytosol; Diglycerides; Epidermal Growth Factor; Glucose; Humans; Insulin Resistance; Interleukins; Lactic Acid; Liver; Male; Molecular Weight; Pancreatic Neoplasms; Perfusion; Protein Kinase C; Rats; Rats, Wistar; Transforming Growth Factor beta; Tumor Cells, Cultured

Elevated serum-free fatty acid (FFA) levels induce insulin resistance in whole animals and humans. To understand the direct mechanism by which FFAs impact insulin-responsive tissue, we have used our previously developed in vitro model of long-chain saturated fatty acids (LCSFA)-induced insulin resistance in adipocytes. In addition to explanted rat adipocytes, we now demonstrate that overnight exposure of 3T3-L1 adipocytes to 1 mM individually of the LCSFA palmitate, myristate, and stearate, leads to an approximately 50% inhibition of insulin-induced glucose transport. Insulin resistance can be accomplished at 0.3 mM palmitate, which is within the range ofpalmitate found in diabetic and obese individuals. This inhibition was noted within 4 h of exposure to FFA, which is comparable to in vivo lipid infusion studies. Initial LCSFA-induced resistance is specific to glucose transport and does not affect insulin stimulation of glucose incorporation into glycogen. In 3T3-L1 adipocytes overexpressing the EGF receptor, LCSFA exposure also specifically inhibited EGF-induced GLUT4-mediated glucose transport, but not EGF-induced glycogen synthesis. We find that LCSFA treatment did not impair insulin stimulation of GLUT4 translocation or exofacial presentation on the cell surface as determined by trypsin accessibility. Our results suggest that the initial direct effect of elevated LCSFA is to impair activation of GLUT4 transporter activity and that this effect is specific for glucose transport.

Topics: Adipocytes; Animals; Cells, Cultured; Deoxyglucose; Epidermal Growth Factor; Fatty Acids; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Myristates; Palmitates; Phosphorylation; Rats; Rats, Sprague-Dawley; Receptor, Insulin; Stearates

Leprechaunism is an autosomal recessive syndrome of severe insulin resistance and is characterized by intrauterine growth restriction, acanthosis nigricans, hirsutism, and loss of glucose homeostasis. Here we report a new female patient of Hispanic and Afro-American descent whose fibroblasts and lymphoblasts had markedly impaired insulin binding (less than 10% of that in controls). Insulin binding to lymphoblasts established from both unrelated parents was partially impaired. Insulin-like growth factor-I (IGF-I) and epidermal growth factor (EGF) binding to the patient's fibroblasts were within the normal range. Insulin stimulation of receptor autophosphorylation and kinase activity was markedly reduced in the patient's fibroblasts. The patient's fibroblasts had both a reduced number of immunoreactive insulin receptor (6% of those in controls) and concomitantly reduced amounts of insulin-receptor mRNA, suggesting that both mutations inherited by the patient reduced insulin-receptor mRNA. Sequencing of the insulin-receptor gene and cDNA indicated that the patient was heterozygous for a paternally derived mutation at bp 1333, converting Arg372 to a STOP codon. This nonsense mutation was observed in the insulin-receptor gene, but not in cDNA, indicating reduced amounts of mRNA for the allele containing this mutation. The coding sequence of the maternally inherited insulin-receptor allele was normal. Both the marked reduction in insulin-receptor mRNA in the compound heterozygous fibroblasts of the proband and the partially reduced insulin binding in maternal cells suggest that the maternally derived mutation is located in an insulin-receptor gene sequence that controls cellular mRNA content.

Topics: Base Sequence; Black People; Blotting, Northern; Cells, Cultured; Epidermal Growth Factor; Female; Growth Disorders; Heterozygote; Humans; Infant; Insulin; Insulin Resistance; Insulin-Like Growth Factor I; Molecular Sequence Data; Mutation; Phosphorylation; Phosphotransferases; Receptor, Insulin; RNA, Messenger

Leprechaunism is a rare genetic disorder characterized by severe growth retardation and insulin resistance. Maximal epidermal growth factor (EGF) binding was reduced in fibroblasts from three unrelated patients with leprechaunism (Ark-1, Can-1, and Minn-1) compared with control (0.8-2.2%/mg protein vs. 5.5%/mg protein). This was due to a decrease in receptor affinity in Ark-1 and Can-1 and a decrease in receptor number in Minn-1. In all cell lines, EGF-stimulated receptor autophosphorylation was also decreased to 18-60% of control, whereas EGF internalization and degradation was normal. Sphingosine (40 microM), a protein kinase C inhibitor, increased EGF receptor affinity twofold in control cells and six- to nine-fold in cells of leprechaunism. However, sphingosine did not enhance EGF-stimulated receptor autophosphorylation in either the controls or the patients' cells. By contrast, only one of the three cell lines of patients with the type A syndrome demonstrated a decrease in EGF binding and all demonstrated normal or near normal EGF-stimulated receptor autophosphorylation. These data indicate that in patients with leprechaunism, there are functional abnormalities of the EGF receptor, as well as of the insulin receptor, that may contribute to the severity of the syndrome. These data also suggest a role for the insulin receptor in maintaining normal EGF receptor function in these cells.

Topics: Drug Resistance; Epidermal Growth Factor; ErbB Receptors; Fibroblasts; Growth Disorders; Humans; Insulin Resistance; Phosphorylation; Protein Kinase C; Receptor, Insulin; Sphingosine

To explore a possible mechanism for the diminished growth potential in a patient with an unusual form of insulin resistance, somatomedin C/insulin-like growth factor I (SM-C/IGF-I) and insulin stimulation of [3H]thymidine incorporation and cell replication were compared in skin fibroblasts from the patient (DF) and normal controls. There appeared to be no generalized abnormality in cellular responsiveness to growth factors. In both DF and control cells, SM-C/IGF-I (50 ng/ml), insulin (100 ng/ml), and epidermal growth factor (5 ng/ml) stimulated [3H]thymidine incorporation 5-, 2-, and 6-fold, respectively. Low concentrations of human hypopituitary serum (0.25%) enhanced the effectiveness of SM-C/IGF-I and insulin to a similar extent in both DF and control cells. On the other hand, 10% calf serum stimulated [3H]thymidine incorporation 37-fold in control cells, while DF cells were only 50% as responsive. Preincubation of control cells with dexamethasone (10(-7) M) caused a marked synergistic increase in SM-C/IGF-I stimulated [3H]thymidine incorporation (15- to 20-fold in serum-free medium; 50- to 80-fold in 0.25% human hypopituitary serum). In contrast, preexposure to dexamethasone did not augment SM-C/IGF-I stimulation of thymidine incorporation into DNA of DF cells. Furthermore, the stimulation of cell replication by SM-C/IGF-I and insulin was potentiated by dexamethasone in control but not DF cultures. These data suggest that impairment of the synergistic action of glucocorticoids with SM-C/IGF-I and insulin regulation of fibroblast growth may be involved in the pathology of this insulin-resistant growth disorder.

Topics: Cell Division; Cells, Cultured; Dexamethasone; Drug Synergism; Epidermal Growth Factor; Fibroblasts; Growth Disorders; Humans; Insulin Resistance; Insulin-Like Growth Factor I; Somatomedins; Thymidine

Postreceptor defects in insulin action have been reported in fibroblasts isolated from two patients with Leprechaunism, Leprechaun/Ark-1 and Leprechaun NC-1. We have extended the published reports on glucose, aminoisobutyric acid, and thymidine uptake in these cells to measurements of protein synthesis and protein breakdown. We found a remarkably consistent pattern of responsiveness between the two Leprechaun fibroblast lines. First, protein synthesis proceeded at a low basal rate that was only slightly stimulated by insulin. Second, basal rates of protein breakdown were significantly higher than in normal skin fibroblasts, with approximately equal inhibitory effects produced by 100 nM insulin. Third, the responses of protein synthesis and protein breakdown to insulin required higher concentrations of the hormone to elicit half-maximal effects. Fourth, both Leprechaun cell lines were slow growing in complete medium, a situation that results from low rates of protein synthesis and high rates of protein breakdown. Fifth, the abnormal rates of protein metabolism in the presence of serum were caused not by the inability of serum to produce anabolic responses but because the unstimulated rates reflect a more catabolic basal state. Taken together with previous published results, our measurements suggest a generalized metabolic defect in Leprechaun fibroblasts that can only partly be explained by the reduced sensitivity of the cells to insulin.

Topics: Blood; Cell Division; Epidermal Growth Factor; Face; Fibroblasts; Humans; In Vitro Techniques; Infant; Insulin; Insulin Resistance; Proteins; Skin; Syndrome

Leprechaunism is a rare inherited disorder characterized by severe intrauterine growth retardation and insulin resistance. Cultured skin fibroblasts from an infant with Leprechaunism were previously reported to show decreased stimulation of DNA synthesis by insulin despite apparently normal binding of [125I]insulin and [125I]somatomedin C. We have now further investigated the growth of this patient's fibroblasts and compared their metabolic responses to insulin and various peptide growth factors with responses in normal foreskin-derived fibroblasts. The doubling time of Leprechaun fibroblasts was prolonged (90 vs. 29 h), and their morphology was abnormal. Stimulation of [3H]glucose uptake was minimal with low insulin levels (1--10 ng/ml) relative to controls, but was comparable at higher insulin concentrations (1--10 micrograms/ml). Stimulation of [3H] aminoisobutyric acid uptake by insulin, epidermal growth factor (EGF), multiplication-stimulating activity, and somatomedin C (Sm-C) in Leprechaun cells was diminished relative to control cells at all concentrations tested. Furthermore, stimulation of [3H]thymidine incorporation in Leprechaum cells by EGF, Sm-C, and fibroblast growth factor was also subnormal. Binding of [125I]EGF to Leprechaun fibroblasts was not decreased. It is concluded that fibroblasts from this patient are resistant to the metabolic effects of insulin, EGF, Sm-C, and fibroblast growth factor. Since receptors for three of these peptides are apparently normal, it is likely that the defect in these cells is at the postreceptor level, perhaps involving a metabolic pathway common to the action of multiple growth factors.

Topics: Aminoisobutyric Acids; Cell Division; Cells, Cultured; Drug Resistance; Dwarfism; Epidermal Growth Factor; ErbB Receptors; Fibroblast Growth Factors; Fibroblasts; Glucose; Humans; Infant; Insulin Resistance; Insulin-Like Growth Factor I; Peptides; Receptors, Cell Surface; Somatomedins; Syndrome; Thymidine

Topics: Animals; Cell Membrane; Cells, Cultured; Diabetes Mellitus; Epidermal Growth Factor; ErbB Receptors; Hormones; Humans; Insulin Resistance; Macromolecular Substances; Mice; Microscopy, Fluorescence; Models, Biological; Receptor, Insulin; Receptors, Cell Surface