Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have previously reported that in the well-differentiated beta-cell line MIN6 cells, the beta-cell-specific differentiated characteristics, such as insulin content, expression of prohormone convertases PC2 and PC3, and glucose-regulated insulin secretion, diminished when the proprotein-processing endoprotease furin was highly expressed. Since furin converts many growth-related protein precursors to their bioactive forms, we compared the four pancreatic islet cell lines RINm5F, betaTC3, betaHC9, and MIN6 with respect to cell growth rate, furin expression, endoprotease activity, and insulin content. RINm5F cells exhibited the strongest furin expression, higher furin-type endoprotease activity, and the fastest cell growth, but had the least insulin content. In contrast, MIN6 cells exhibited only a weak furin expression, little furin-type endoprotease activity, and the slowest cell growth, but had the highest insulin content. To test whether furin-expressing cells secrete growth-promoting factors cleaved by furin, we prepared conditioned media from RINm5F and furin cDNA-introduced MIN6 (MIN6-F) cells. The conditioned media from RINm5F and MIN6-F induced increased DNA synthesis and promoted the growth of normal MIN6 cells, compared with the medium from the empty vector-introduced MIN6-0 cells. We then examined the effect of the protease inhibitors alpha1-antitrypsin and its variants by infecting their vaccinia recombinants to the four cell lines. All conditioned media from each cell line expressing the furin-specific alpha1-antitrypsin variant exhibited the least DNA synthetic capacity on normal MIN6 cells. Furthermore, all three sublines of MIN6-F grew faster than MIN6-0 and MIN6. Thus, we suggest that the islet cells with higher furin expression may induce increased production of growth factors, which result in an increase in cell growth, through an autocrine/paracrine mechanism.
Diabetes 1997 Aug
PMID:Proprotein-processing endoprotease furin controls growth of pancreatic beta-cells. 923 54

In non-insulin-dependent diabetes, circulating insulin-related immunoreactivity (IRI) is often composed of a higher fraction of the incompletely converted forms proinsulin and des-31,32 proinsulin. The present study describes an immunoadsorption method for measuring the proportions of proinsulin, its two split products, and insulin in human pancreatic tissue and for determining their rates of formation in human isolated islets. The method uses two junction-specific monoclonal proinsulin antibodies in a protein G fractionation; it is validated by > or = 90% specificity and recovery. The peptide contents measured in tissue extracts were comparable to those determined in a previously developed immunoradiometric assay. In the nine tissue extracts from nondiabetic donor organs, 97% of IRI corresponded to insulin, 1% to proinsulin, 2% to the des-31,32 proinsulin conversion product, and 0.1% to des-64,65 proinsulin. Two samples from non-insulin-dependent diabetics under sulfonylurea treatment contained a fourfold lower content of IRI but the peptide distribution was comparable except for a low percentage (0.3) of proinsulin in one case. In pulse-chase experiments on three-preparations of human islets isolated from nondiabetic donors, proinsulin represented the major (> 90%) IRI that was synthesized at the end of the 30-min pulse; a subsequent 90-min chase at either 2.5 or 10 mM glucose resulted in conversion of 75% of proinsulin to des-31,32 (20%) and des-64,65 (2%) intermediates and to insulin (50%); after a 180-min chase, 88% of proinsulin was converted to insulin, but 10% remained present as proinsulin. In a pulse-chase experiment on islets isolated from tissue with a high proportion of des-31,32 intermediate (5% instead of 2%), the conversion process was slower (45% after 90 min and 70% after 180 min) and resulted in a higher fraction of des-31,32 intermediate, suggesting that the elevated tissue content in this intermediate is caused by a reduced PC2 converting activity. These data confirm that des-31,32 proinsulin represents the major conversion intermediate in normal human islets and indicate the existence of slow converters, possibly as a result of decreased enzymatic processing of the prohormone's AC junction.
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PMID:Proinsulin and its conversion intermediates in human pancreas and isolated islet tissue: kinetics and steady-state analysis. 926 Jan 95

The production of insulin from proinsulin involves cleavage of intact proinsulin into proinsulin conversion intermediates by the processing of enzymes PC2 and PC3 before fully processed insulin is produced. Intact proinsulin and these conversion intermediates are measured in many immunoreactive insulin (IRI) assays, and therefore contribute to the absolute IRI measurement. The proportion of basal IRI made up of proinsulin (PI)-like molecules (PI/IRI) is increased in NIDDM. Whether stimulated IRI levels are similarly made up of disproportionately increased PI/IRI or whether the relative proportions of proinsulin and its conversion intermediates are altered has not been evaluated. An index of the efficiency of proinsulin processing within the pancreatic beta-cell can be achieved by measuring PI/IRI immediately following acute stimulation of beta-cell secretion, and then determining the proportion of intact proinsulin and proinsulin conversion intermediates contributing to circulating proinsulin-like molecules. In this study, we determined the PI/IRI levels under basal and arginine-stimulated conditions in 17 healthy and 16 NIDDM subjects; high-performance liquid chromatography (HPLC) was also performed in a subset of these subjects to measure the relative contribution of intact proinsulin and its conversion intermediates to total proinsulin-like molecules. In NIDDM subjects, levels of both basal (44.6 +/- 9.6 vs. 9.3 +/- 1.5 pmol/l; P = 0.0007) and stimulated (64.0 +/- 12.7 vs. 19.8 +/- 2.8 pmol/l; P = 0.001) proinsulin-like molecules were higher than in healthy subjects. Although IRI was higher in NIDDM than in control subjects under basal conditions (106 +/- 19 vs. 65.1 +/- 8.1 pmol/l; P = 0.05), it was lower in NIDDM than in control subjects following stimulation (increment: 257 +/- 46 vs. 416 +/- 51 pmol/l; P = 0.03). PI/IRI ratios were increased in NIDDM subjects under both basal (43.3 +/- 5.0 vs. 14.0 +/- 1.3%; P < 0.0001) and stimulated (increment: 10.1 +/- 2.1 vs. 2.5 +/- 0.2%; P = 0.0006) conditions, compatible with the release of a disproportionately increased amount of proinsulin-like products. HPLC analysis revealed that, in the stimulated state, intact proinsulin made up 40.1 +/- 6.7% of proinsulin-like molecules in NIDDM individuals (n = 9) and 30.1 +/- 5.6% in healthy subjects (n = 7; NS). The remainder of the proinsulin-like molecules comprised the des-31,32-split proinsulin conversion intermediate. The increase in PI/IRI in NIDDM under basal and especially under stimulated conditions suggests that proinsulin conversion is indeed perturbed in this disorder. Because the relative proportions of intact and des-31,32-split proinsulin are similar in both healthy and NIDDM subjects, the orderly cleavage of proinsulin at its two junctions appears preserved. However, at the time of exocytosis, the secretory granule in the islet of NIDDM subjects contains an increased proportion of incompletely processed proinsulin, presumably reflecting a slower rate of conversion or granules' reduced time of residence in beta-cells.
Diabetes 1997 Nov
PMID:Release of incompletely processed proinsulin is the cause of the disproportionate proinsulinemia of NIDDM. 935 18

Wolfram syndrome (WS) is characterized by optic atrophy, insulin-dependent diabetes mellitus, vasopressin (VP)-sensitive diabetes insipidus, and neurosensory hearing loss. Here we report a disturbance in VP precursor processing in the supraoptic and paraventricular nuclei of WS patients. In these patients with diabetes insipidus we could hardly detect any cellular immunoreactivity for processed VP in the supraoptic and paraventricular nuclei. On the other hand, in the paraventricular nucleus a considerable number of cells immunoreactive for the VP precursor were present. In addition, the proprotein convertase PC2 and the molecular chaperone 7B2 were absent. As expression of PC2 and 7B2 was detected in the nearby nucleus basalis of Meynert of one WS patient and in the anterior lobe of the other WS patient, the absence of the two proteins in the paraventricular nucleus was not due to mutations in their genes. These results indicate that in WS patients with diabetes insipidus, not only does VP neuron loss occur in the supraoptic nucleus, but there is also a defect in VP precursor processing.
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PMID:The vasopressin precursor is not processed in the hypothalamus of Wolfram syndrome patients with diabetes insipidus: evidence for the involvement of PC2 and 7B2. 981 87

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.
Diabetes 1999 Jul
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

Proopiomelanocortin (POMC) is a precursor to various, bioactive peptides including ACTH, beta LPH, alpha MSH, and beta endorphin (beta END). Processing of POMC at dibasic residues is tissue-specific and is performed by either PC1 alone (resulting in ACTH and beta LPH, anterior pituitary corticotrophes) or by a combination of PC1 and PC2 (yielding alpha MSH and beta END, pituitary neurointermediate lobe and hypothalamus). The PC2-specific binding protein 7B2 is intimately involved in the zymogen activation of proPC2 into PC2. Structure-function studies of these enzymes demonstrated the presence of N- and C-terminal domains, as well as specific amino acids within the catalytic segment that influence the degree of activity of each enzyme and the interaction of PC2 with 7B2. The tissue distribution, plasticity of expression, and the multiple precursors that are differentially cleaved by PC1 and/or PC2, predict a wide array of combinatorial activities of these convertases within the endocrine and neuroendocrine system. The phenotypic consequences of the absence of genetic expression of either PC1 or PC2 are now explored using knockout mice and in human patients suffering from obesity and diabetes.
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PMID:The subtilisin/kexin family of precursor convertases. Emphasis on PC1, PC2/7B2, POMC and the novel enzyme SKI-1. 1081 41

Previous work has shown that interleukin-1beta (IL-1beta) alters protein expression in beta-cells. This alteration is associated with cell death in isolated rat islets but not in isolated rat beta-cells. We examined whether IL-1beta pretreatment of isolated beta-cells influences their sensitivity to toxic agents. After a 24-h culture with IL-1beta (30 U/ml), beta-cells exhibited a lower expression of the beta-cell-specific protein transcription factor pancreatic and duodenal homeobox gene (PDX)-1, glucose transporter GLUT2, and proinsulin convertase PC2, with a marked reduction (60-70%) in glucose-induced insulin production and selective sensitivity to the toxins alloxan (ALX) and streptozotocin (STZ). On the other hand, the cells presented an increased expression of Mn-superoxide dismutase, heat shock protein 70, inducible heme oxygenase, and inducible nitrite oxide synthase. This IL-1beta-induced alteration in beta-cell phenotype resulted in a reduced cellular sensitivity to the beta-cell-specific toxins ALX and STZ; the production of nontoxic conditions of nitric oxide (NO) also rendered the cells less susceptible to radical-induced damage. Exposure to IL-1beta can thus protect beta-cells against conditions that cause necrosis; however, it did not protect against apoptosis induced by the additional presence of interferon-gamma or tumor necrosis factor-alpha. Release of IL-1beta in the endocrine pancreas is thus not necessarily the cause of massive NO-dependent beta-cell destruction. On the contrary, IL-1beta may protect these cells against necrosis, though with a loss of their characteristic phenotype and homeostatic functions.
Diabetes 2000 Mar
PMID:Interleukin-1beta-induced alteration in a beta-cell phenotype can reduce cellular sensitivity to conditions that cause necrosis but not to cytokine-induced apoptosis. 1086 54

Islet amyloid polypeptide (IAPP), amylin, is the constituent peptide of pancreatic islet amyloid deposits which form in islets of Type 2 diabetic subjects. Human IAPP is synthesized as a 67-residue propeptide in islet beta-cells and colocalized with insulin in beta-cell granules. The mature 37-amino acid peptide is produced by proteolysis at pairs of basic residues at the C- and N-termini of the mature peptide. To determine the enzymes responsible for proteolysis and their activity at the potential cleavage sites, synthetic human proIAPP was incubated (0.5-16 h) with recombinant prohormone convertases, PC2 or PC3 at appropriate conditions of calcium and pH. The products were analysed by MS and HPLC. Proinsulin was used as a control and was cleaved by both recombinant enzymes resulting in intermediates. PC3 was active initially at the N-terminal-IAPP junction and later at the C-terminus, whereas initial PC2 activity was at the IAPP-C-terminal junction. Processing at the basic residues within the C-terminal flanking peptide rarely occurred. There was no evidence for substantial competition for the processing enzymes when the combined substrates proinsulin and proIAPP were incubated with both PC2 and PC3. As proinsulin cleavage is sequential in vivo (PC3 active at the B-chain-C-peptide junction, followed by PC2 at A chain-C-peptide junction), these data suggest that proteolysis of proIAPP and proinsulin is coincident in secretory granules and increased proinsulin secretion in diabetes could be accompanied by increased production of proIAPP.
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PMID:Processing of synthetic pro-islet amyloid polypeptide (proIAPP) 'amylin' by recombinant prohormone convertase enzymes, PC2 and PC3, in vitro. 1093 Nov 81

Impaired processing of pro-islet amyloid polypeptide (proIAPP), the precursor of the beta-cell peptide islet amyloid polypeptide (IAPP) (amylin), has been implicated in islet amyloid formation in type 2 diabetes. The prohormone convertase enzymes PC3 (also known as PC1) and PC2 are localized to beta-cell secretory granules with proIAPP and proinsulin and are responsible for proinsulin processing. To determine whether PC2 might be essential for proIAPP processing, we performed Western blot analysis of freshly isolated islets from normal mice and mice lacking active PC2. As expected, the primary species of IAPP immunoreactivity in islets from wild-type mice was fully processed (4-kDa) IAPP, with only small amounts of the 8-kDa precursor (unprocessed proIAPP) present. Islets from heterozygous PC2 null mice were identical to wild-type animals, suggesting that half the normal complement of PC2 is sufficient for normal proIAPP processing. By contrast, in islets from homozygous PC2 null mice, the predominant IAPP-immunoreactive form was of intermediate size (approximately 6 kDa), with no detectable mature IAPP and slightly elevated amounts of the 8-kDa precursor form present. Thus, in the absence of PC2, proIAPP processing appears to be blocked at the level of a proIAPP conversion intermediate. Immunofluorescence of pancreas sections and immunoblotting using antisera raised to the NH2- and COOH-terminal flanking regions of mouse proIAPP demonstrated that the 6-kDa intermediate form was an NH2-terminally extended proIAPP conversion intermediate (processed only at the COOH-terminus). These data indicate that PC2 is essential for processing of proIAPP at the NH2-terminal cleavage site in vivo and that PC3 is likely only capable of processing proIAPP at the COOH-terminal cleavage site.
Diabetes 2001 Mar
PMID:The prohormone convertase enzyme 2 (PC2) is essential for processing pro-islet amyloid polypeptide at the NH2-terminal cleavage site. 1124 72

Organisms respond to infection in a complex manner involving bidirectional interactions between the neuroendocrine and immune systems. Many of the bioactive endocrine/immune factors are synthesized in a precursor form and are expected to be activated by prohormone convertases (PCs). Since patients with both type 1 and type 2 diabetes have an increased incidence and severity of infections, we hypothesized that in a condition of hyperglycemia, these processing enzymes would be activated in an immune tissue, the spleen. To test this hypothesis, we treated rats with intraperitoneal streptozotocin (STZ) (50 mg/kg/day) daily for 5 days and measured splenic PC1 and PC2 mRNA by ribonuclease protection assay. We found that PC1 mRNA was increased 6.0+/-0.02-fold (P<0.05) and PC2 mRNA was increased 1.80+/-0.01-fold (P<0.005) in the spleen of rats that received STZ compared to rats that received vehicle. Western blot indicated that the 75-kDa form of PC1 was the only form of PC1 present in the spleen and that this form increased with STZ treatment. Immunohistochemistry revealed that PC1 was found in both the white pulp (T-lymphocytes) and red pulp (monocytes and macrophages) and that its increase in immunoreactivity occurred primarily in the white pulp. PC2 and pro-opiomelanocortin (POMC, a possible splenic substrate for PC1/PC2) immunoreactivity was found predominantly in the red pulp. STZ induced an increase in splenic PC1 and POMC, but not PC2 protein levels. We conclude that in the STZ model of diabetes, splenic PCs are induced, which could lead to an increased activation of many immune-derived hormones. We speculate that this up-regulation of prohormone converting enzymes may be related to the increased infections seen in patients with both type 1 and type 2 diabetes.
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PMID:Up-regulation of splenic prohormone convertases PC1 and PC2 in diabetic rats. 1173 Sep 86


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