Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011860 (type 2 diabetes)
 57,723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To explore the role of chronically elevated free fatty acids (FFAs) in the pathogenesis of the hyperproinsulinemia of type 2 diabetes, we have investigated the effect of FFAs on proinsulin processing and prohormone convertases PC2 and PC1/PC3 in MIN6 cells cultured in Dulbecco's modified Eagle's medium with or without 0.5 mmol/l FFA mixture (palmitic acid:oleic acid = 1:2). After 7 days of culture, the percent of proinsulin in FFA-exposed cells was increased (25.9 +/-0.3% intracellular and 75.4 +/- 1.2% in medium vs. 13.5 +/-0.2 and 56.2 +/- 4.1%, respectively, in control cells). The biosynthesis and secretion of proinsulin and insulin were analyzed by comparing the incorporation of [3H]Leu and [35S]Met. In pulse-chase studies, proinsulin-to-insulin conversion was inhibited, and proinsulin in the medium was increased by 50% after 3 h of chase, while insulin secretion was decreased by 50% after FFA exposure. Levels of cellular PC2 and PC3 analyzed by Western blotting were decreased by 23 and 15%, respectively. However, PC2, PC3, proinsulin, and 7B2 mRNA levels were not altered by FFA exposure. To test for an effect on the biosynthesis of PC2, PC3, proinsulin, and 7B2, a protein required for PC2 activation, MIN6 cells were labeled with [35S]Met for 10-15 min, followed by a prolonged chase. Most proPC2 was converted after 6 h of chase in control cells, but conversion was incomplete even after 6 h of chase in FFA-exposed MIN6 cells. Media from chase incubations showed that FFA-exposed cells secreted more proPC2 than controls. Similar inhibitory effects were noted on the processing of proPC3, proinsulin, and 7B2. In conclusion, prolonged exposure of beta-cells to FFAs may affect the biosynthesis and posttranslational processing of proinsulin, PC2, PC3, and 7B2, and thereby contribute to the hyperproinsulinemia of type 2 diabetes. The mechanism of inhibition of secretory granule processing by FFAs may be through changes in Ca2+ concentration, the pH in the secretory granules, and/or other factors that may influence the activation and function of the convertases.
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PMID:Long-term elevation of free fatty acids leads to delayed processing of proinsulin and prohormone convertases 2 and 3 in the pancreatic beta-cell line MIN6. 1038 44

Great progress has been made in identifying several genes and in understanding the molecular pathogenesis of inherited syndromes of obesity and diabetes mellitus (DM). In humans, mutations in leptin, leptin receptor, proopiomelanocortin (POMC), melanocortin-4 receptor (MC4R) and prohormone convertase 1 (PC1) have been described in patients with severe obesity. Most of these obesity disorders, with the exception of the MC4R mutations, exhibit recessive inheritance and a distinct phenotype with varying degrees of hypothalamic dysfunction, and they unravel the critical role of the central leptin and melanocortin pathways in human appetite control and energy homeostasis. Maturity onset diabetes of the young (MODY) is a genetically and clinically heterogeneous subtype of type 2 DM with early onset autosomal dominant inheritance and a primary defect in insulin secretion. To date, six MODY genes have been identified, the glucokinase gene and five beta cell-specific transcription factor genes, hepatocyte nuclear factor-1alpha (HNF-1alpha), HNF-1beta, HNF-4alpha, insulin promoter factor-1 (IPF-1) and NeuroD1/BETA2. Mitochondrial DNA mutations cause another form of DM with an insulin secretory defect that is commonly associated with neurosensory hearing impairment, and has strict maternal inheritance. At the other end of the spectrum are the inherited syndromes of insulin resistance that are caused by mutations in the insulin receptor gene and in the adipocyte-specific transcription factor PPARgamma. The advances in our knowledge of the phenotypic manifestations and underlying molecular mechanisms of genetic syndromes of obesity and DM raise expectations for molecular diagnosis, as well as for more etiological therapies and better prevention of the continuously increasing prevalence of obesity and DM in our modern societies.
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PMID:Monogenic forms of obesity and diabetes mellitus. 1192 26

The epithelial Ca2+ channel, ECaC1, is primarily expressed in the apical membrane of vitamin D-responsive tissues. This study characterizes for the first time the presence of this novel channel in pancreatic tissue by reverse transcriptase-polymerase chain reaction and immunohistochemistry. In addition, the expression of ECaC1 was investigated in an animal model for Type 2 diabetes mellitus, the Zucker diabetic fatty (ZDF) rat. Identical staining patterns for ECaC1 and insulin were observed, whereas no co-localization of ECaC1 with glucagon was found. ECaC1, insulin, and prohormone convertase 1 (a neuroendocrine endoprotease expressed in secretory granules) showed a similar punctate staining. ECaC1 co-localized with the Ca2+ binding protein calbindin-D(28K) in the beta-cells. Furthermore, in contrast to wild-type rats, in ZDF rats aging led to a progressive decrease in both insulin and ECaC1 staining. Plasma 1,25-dihydroxyvitamin D3 levels were similar in both control and ZDF rats and decreased with aging. Taken together, our findings indicate that this novel Ca2+ channel may play a role in the regulation of endocrine Ca2+ homeostasis.
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PMID:Expression of the novel epithelial Ca2+ channel ECaC1 in rat pancreatic islets. 1201 95

Glucagon-like peptide-1 (GLP-1) is a potent stimulator of glucose-dependent insulin secretion. Exendin-4(1-39) (Ex-4), isolated from Gila monster venom, is a highly specific GLP-1 receptor agonist that exhibits a prolonged duration of action in vivo. Although the processing mechanisms underlying liberation of GLP-1 from its prohormone have been elucidated, those for Ex-4 remain unknown. To examine the requirements for proEx-4 processing in mammalian cells, BHK fibroblasts, InR1-G9 islet A cells, and AtT-20 corticotropes, which express different prohormone convertases (furin, prohormone convertase 2, and prohormone convertase 1, respectively) were transfected with full-length lizard proEx-4, and the processing of proexendin was examined by HPLC and RIA (n = 3). All of the transfected cell lines exhibited Ex-4-like immunoreactivity in the media, and Ex-4-like immunoreactivity was detected in extracts of InR1-G9 and AtT-20 cells. However, only media and extracts from AtT-20 cells (not InR1-G9 and BHK cells) contained a single peak by HPLC corresponding to synthetic Ex-4. To establish whether proEx-4 can be processed to Ex-4 in nonimmortalized mammalian cells in vivo, the molecular forms of exendin-4 were examined in mice expressing a metallothionein-proEx-4 transgene (n = 3-6 for both males and females). ProEx4 mRNA transcripts were detected by RT-PCR in a broad range of both endocrine and nonendocrine tissues. Ex-4-like immunoreactivity was detected in pituitary, fat, adrenals, and testes; however HPLC analyses demonstrated that processed Ex-4 was found only in adrenals and testes. These results indicate that lizard proEx-4 is processed to mature bioactive Ex-4 in both rodent endocrine and nonendocrine mammalian cell types in vitro and in murine tissues in vivo. These findings may be useful for engineering cells that express a lizard pro-Ex4 transgene for the treatment of type 2 diabetes.
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PMID:Cellular specificity of proexendin-4 processing in mammalian cells in vitro and in vivo. 1219 59

Islet amyloid polypeptide (IAPP; amylin) is a peptide hormone that is cosecreted with insulin from beta-cells. Impaired processing of proIAPP, the IAPP precursor, has been implicated in islet amyloid formation in type 2 diabetes. We previously showed that proIAPP is processed to IAPP by the prohormone convertases PC1/3 and PC2 at its carboxyl (COOH) and amino (NH(2)) termini, respectively. In this study, we investigated the role of carboxypeptidase E (CPE) in the processing of proIAPP using mice lacking active CPE (Cpe(fat)/Cpe(fat)) and NIT-2 cells, a beta-cell line derived from their islets. Western blot analysis demonstrated that an approximately 6-kDa NH(2)-terminally unprocessed form of proIAPP was elevated approximately 86% in islets from Cpe(fat)/Cpe(fat) mice, compared with wild type. This increase was independent of the development of hyperglycemia (8 wk male) or obesity (18 wk female). Impaired proIAPP processing was associated with a decrease in PC2 (but not PC1/3) and both the 21- and 27-kDa forms of the PC2 chaperone protein 7B2, suggesting that PC2-mediated processing of proIAPP at its NH(2) terminus was impaired in the absence of CPE. Formation of COOH-terminally amidated (pro)IAPP was reduced approximately 75% in NIT-2, compared with NIT-1 beta-cells, supporting a direct role for CPE in maturation of IAPP by removal of its COOH-terminal dibasic residues, the step essential for IAPP amidation. We conclude that lack of CPE in islet beta-cells results in a marked decrease in processing of proIAPP at its NH(2) (but not COOH) terminus that is associated with attenuated levels of PC2 and (pro)7B2 and a great reduction in formation of mature amidated IAPP.
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PMID:Role of carboxypeptidase E in processing of pro-islet amyloid polypeptide in {beta}-cells. 1561 58

Islet amyloid is a pathologic characteristic of the pancreas in type 2 diabetes comprised mainly of the beta-cell peptide islet amyloid polypeptide (IAPP; amylin). We used a pulse-chase approach to investigate the kinetics of processing and secretion of the IAPP precursor, proIAPP, in beta cells. By only 20 min after synthesis, a COOH-terminally processed proIAPP intermediate (approximately 6 kDa) was already present in beta cells. Formation of this NH2-terminally extended intermediate was not prevented by arresting secretory pathway transport at the trans-Golgi network (TGN) by either brefeldin A or temperature blockade, suggesting that this initial cleavage step occurs in the TGN before entry of (pro)IAPP into granules. Mature IAPP (approximately 4 kDa) was not detected until 60 min of chase, suggesting that NH2-terminal cleavage occurs in granules. Cells chased in low glucose without Ca2+ or with diazoxide, to block regulated release, secreted both proIAPP (approximately 8 kDa) and a partially processed form (approximately 6 kDa) via the constitutive secretory pathway. Stimulation of regulated secretion resulted in secretion primarily of mature IAPP as well as low levels of both unprocessed (approximately 8 kDa) and partially processed (approximately 6 kDa) proIAPP. We conclude that normal processing of proIAPP is a two-step process initiated by cleavage at its COOH terminus (likely by prohormone convertase 1/3 in the TGN) followed by cleavage at its NH2 terminus (by prohormone convertase 2 in granules) to form IAPP. Both proIAPP and its NH2-terminally extended intermediate appear to be normal secretory products of the beta cell that can be released via either the regulated or constitutive secretory pathways.
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PMID:Processing of pro-islet amyloid polypeptide in the constitutive and regulated secretory pathways of beta cells. 1580 74

The amyloid present in the islets of Langerhans in type 2 diabetes is polymerized islet amyloid polypeptide (IAPP). The precursor protein proIAPP is posttranslationally modified, a process involving the removal of NH2- and COOH-terminal flanking peptides. This step is performed by the prohormone convertases PC2 and PC1/3. PC2 processes proIAPP preferably at the NH2-terminal processing site, and PC1/3 processes proIAPP exclusively at the COOH-terminal site. Little is known regarding the exact circumstances leading to islet amyloid formation. In this study, we have examined the possible significance of aberrant processing of proIAPP on amyloid formation in several in vitro cellular systems. In our studies, human (h)-proIAPP was transfected into beta-TC-6 cells expressing both prohormone convertases and in which proIAPP is processed into IAPP. Additionally, h-proIAPP was transfected into three different pituitary-derived cell lines with different prohormone convertase profiles: AtT-20 cells (deficient in PC2), GH3 cells (deficient in PC1/3), and GH4C1 cells (deficient in both convertases). We followed the processing of h-proIAPP with antibodies specific for the respective cleavage sites and stained the cells with Congo red to verify the accumulation of amyloid. Incomplete processing of h-proIAPP that occurs in AtT-20 and GH4C1 cells resulted in the formation of intracellular amyloid. No amyloid developed in beta-TC-6 and GH3 cells lines with full processing of proIAPP. An intracellular increase in proIAPP and/or its metabolic products may thus promote intracellular amyloid formation, thereby causing cell death. When extracellularly exposed, this amyloid might act as template for continuing amyloid formation from processed IAPP released from the surrounding beta-cells.
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PMID:Aberrant processing of human proislet amyloid polypeptide results in increased amyloid formation. 1598 13

The physiology of the incretin hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), and their role in type 2 diabetes currently attract great interest. Recently we reported an essential role for prohormone convertase (PC) 1/3 in the cleavage of intestinal proglucagon, resulting in formation of GLP-1, as demonstrated in PC1/3-deficient mice. However, little is known about the endoproteolytic processing of the GIP precursor. This study investigates the processing of proGIP in PC1/3 and PC2 null mice and in cell lines using adenovirus-mediated overexpression. Supporting a role for PC1/3 in proGIP processing, we found co-localization of GIP and PC1/3 but not PC2 in intestinal sections by immunohistochemistry, and analysis of intestinal extracts from PC1/3-deficient animals demonstrated severely impaired processing to GIP, whereas processing to GIP was unaltered in PC2-deficient mice. Accordingly, overexpression of preproGIP in the neuroendocrine AtT-20 cell line that expresses high levels of endogenous PC1/3 and negligible levels of PC2 resulted in production of GIP. Similar results were obtained after co-expression of preproGIP and PC1/3 in GH4 cells that express no PC2 and only low levels of PC1/3. In addition, studies in GH4 cells and the alpha-TC1.9 cell line, expressing PC2 but not PC1/3, indicate that PC2 can mediate processing to GIP but also to other fragments not found in intestinal extracts. Taken together, our data indicate that PC1/3 is essential and sufficient for the production of the intestinal incretin hormone GIP, whereas PC2, although capable of cleaving proGIP, does not participate in intestinal proGIP processing and is not found in intestinal GIP-expressing cells.
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PMID:Prohormone convertase 1/3 is essential for processing of the glucose-dependent insulinotropic polypeptide precursor. 1647 26

Islet amyloid, formed by aggregation of islet amyloid polypeptide (IAPP; amylin), is a pathological characteristic of the pancreas in type 2 diabetes and may contribute to the progressive loss of beta-cells in this disease. We tested the hypothesis that impaired processing of the IAPP precursor proIAPP contributes to amyloid formation and cell death. GH3 cells lacking the prohormone convertase 1/3 (PC1/3) and IAPP and with very low levels of prohormone convertase 2 (PC2) were transduced with adenovirus (Ad) expressing human or rat (control) proIAPP linked to green fluorescent protein, with or without Ad-PC2 or Ad-PC1/3. Expression of human proIAPP increased the number of transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells 96 h after transduction (+hIAPP 8.7 +/- 0.4% vs. control 3.0 +/- 0.4%; P < 0.05). COOH-terminal processing of human proIAPP by PC1/3 increased (hIAPP+PC1/3 10.4 +/- 0.7%; P < 0.05), whereas NH(2)-terminal processing of proIAPP by addition of PC2 markedly decreased (hIAPP+PC2 5.5 +/- 0.5%; P < 0.05) the number of apoptotic GH3 cells. Islets from mice lacking PC2 and with beta-cell expression of human proIAPP (hIAPP(+/+)/PC2(-/-)) developed amyloid associated with beta-cell death during 2-week culture. Rescue of PC2 expression by ex vivo transduction with Ad-PC2 restored NH(2)-terminal processing to mature IAPP and decreased both the extent of amyloid formation and the number of TUNEL-positive cells (-PC2 26.5 +/- 4.1% vs. +PC2 16.1 +/- 4.3%; P < 0.05). These findings suggest that impaired NH(2)-terminal processing of proIAPP leads to amyloid formation and cell death and that accumulation of the NH(2)-terminally extended human proIAPP intermediate may be a critical initiating step in amyloid formation.
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PMID:Impaired NH2-terminal processing of human proislet amyloid polypeptide by the prohormone convertase PC2 leads to amyloid formation and cell death. 1687 81

Recently, the glucose-stimulated insulin release of isolated human islets has been shown to deteriorate progressively with advancing donor age. This decline in beta cell function with aging may contribute to the increasing development of IGT and type 2 diabetes and also to the progressive nature of the disease. This study was to see whether there is any change in expression of beta cell function-related genes in islets with aging. Islets were isolated from young (2-month old) and old (22-24-month old) LETO rats and C57BL/6N mice. The in vitro GSIR index was significantly lower in islets from old mice compared with young mice. In real-time RT-PCR, PDX-1, insulin, GLUT2 and prohormone convertase 1/3 gene expression in islets was markedly lower in old rats (33%, 13%, 20% and 34%, respectively) and old mice (56%, 42%, 28% and 22%, respectively) compared with young animals. On the other hand, genes not specifically related to beta cell-specific function, such as caspase 3, superoxide dismutase 2 and glycerol kinase were not significantly different in expression in islets according to age. In conclusion, with increasing age, insulin secretory function of islets deteriorates accompanied with a decrease in expression of beta cell-specific genes including PDX-1.
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PMID:Effect of aging on insulin secretory function and expression of beta cell function-related genes of islets. 1746 45


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