Proinsulin and Its Conversion Intermediates in Human Pancreas and Isolated Islet Tissue

Hou, Xiaomei; Ling, Zhidong; Zambre, Yasmeeni; Foriers, André; Houssa, P.; Deberg, Michelle; Sodoyez, J. C.; Hales, C. N.; Auwera, Bart J. Van der; Pipeleers, Daniël; Schravendijk, Christiaan Van

doi:10.1097/00006676-199708000-00002

Cited by 5 publications

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“…Equivalent changes in PC2 expression in human diabetic islets might nevertheless impede conversion of des 31,32 proinsulin to insulin and lead to elevation in the circulation of that intermediate (Hou et al 1997). In this context it is notable that it is des 31,32 proinsulin more than proinsulin or the des 64,65 intermediate that contributes to the increase of (pro)insulin immunoreactivity in diabetes (Clark et al 1992).…”

Section: Discussionmentioning

confidence: 99%

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Proinsulin processing in the diabetic Goto-Kakizaki rat

Guest¹,

Abdel‐Halim²,

Gross³

et al. 2002

Journal of Endocrinology

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The biosynthesis and processing of proinsulin was investigated in the diabetic Goto-Kakizaki (GK) rat. Immunofluorescence microscopy comparing GK and Wistar control rat pancreata revealed marked changes in the distribution of -cells and pronounced -cell heterogeneity in the expression patterns of insulin, prohormone convertases PC1, PC2, carboxypeptidase E (CPE) and the PC-binding proteins 7B2 and ProSAAS. Western blot analyses of isolated islets revealed little difference in PC1 and CPE expression but PC2 immunoreactivity was markedly lower in the GK islets. The processing of the PC2-dependent substrate chromogranin A was reduced as evidenced by the appearance of intermediates. No differences were seen in the biosynthesis and post-translational modification of PC1, PC2 or CPE following incubation of islets in 16·7 mM glucose, but incubation in 3·3 mM glucose resulted in decreased PC2 biosynthesis in the GK islets. The rates of biosynthesis, processing and secretion of newly synthesized (pro)insulin were comparable. Circulating insulin immunoreactivity in both Wistar and GK rats was predominantly insulin 1 and 2 in the expected ratios with no (pro)insulin evident. Thus, the marked changes in islet morphology and PC2 expression did not impact the rate or extent of proinsulin processing either in vitro or in vivo in this experimental model.

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Section: Discussionmentioning

confidence: 99%

“…They are secreted in a regulated manner from the pancreatic -cells of islets where they make up around 1-2% islet insulin immunoreactivity (Hou et al 1997). They accumulate in the circulation due to their longer half-lives (t 1/2 ) relative to insulin, but have only weak hypoglycemic activity (Creemers et al 1998).…”

Section: Introductionmentioning

confidence: 99%

Proinsulin processing in the diabetic Goto-Kakizaki rat

Guest¹,

Abdel‐Halim²,

Gross³

et al. 2002

Journal of Endocrinology

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“…The inter-assay and intra-assay coefficients of variation were 8 and 7 %, respectively. The insulin radioimmunoassay was carried out as described previously [12]; its cross reactivity with proinsulin was 25 % [17].…”

Section: Methodsmentioning

confidence: 99%

Prolonged exposure of pancreatic beta cells to raised glucose concentrations results in increased cellular content of islet amyloid polypeptide precursors

et al. 1999

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Islet amyloid polypeptide (IAPP) is a 37 amino acid peptide that is produced by pancreatic beta cells following synthesis of (pre)pro-IAPP and proteolytic cleavage at dibasic lys-arg residues [1]. The peptide is the predominant component of the amyloid deposits which are often observed in pancreatic islets of non-insulin dependent diabetic patients [2,3]. Formation of amyloid fibrils appears dependent on an amyloidogenic region (amino acids 20±29) in the IAPP-amino acid sequence, known to be present in the human peptide [4,5]. Overproduction and increased secretion of IAPP have been suggested to be predisposing conditions [6,7] but their relation to amyloid formation is not yet understood [8]. Newly diagnosed patients with Type II (non-insulin-dependent) diabetes have increased circulating concentrations of IAPP-like immunoreactivity, containing high MW IAPP-like peptides [9]. Islet amyloid polypeptide precursors also seem to be present in the amyloid deposits, as documented by their immunocytochemical reactivity for a flanking peptide sequence of pro-IAPP [10]. It is still not clear to which extent precursor forms are present in islet beta cells and whether continuously raised glucose concentrations ± as occurring in non-insulin dependent diabetes ± can increase their abundance, intra-and extracellu- Diabetologia (1999) Summary Most non-insulin dependent diabetic patients have amyloid deposits in their pancreatic islets. It is not known whether chronic hyperglycaemia contributes to the formation of amyloid fibrils from the islet amyloid polypeptide that is produced by the pancreatic beta cells. Since islet amyloid exhibits islet amyloid polypeptide precursors immunoreactivity, we examined whether sustained in vitro exposure to raised glucose increases the abundance of these precursors in human beta cells. After 6 days stimulation with 20 mmol/l glucose the cellular content of insulin but not islet amyloid polypeptide was decreased leading to an increase in the ratio of the latter over insulin (3.0 ± 0.6 vs 1.8 ± 0.3 after 6 mmol/l glucose culture, p < 0.05). Similar changes occurred in rat beta cells cultured for 3 days in the presence of 20 mmol/1 glucose plus 3-isobutyl-1-methylxanthine. Western blot analysis of cellular islet amyloid polypeptide after prolonged exposure to high glucose indicated the presence of higher proportions of its precursor-and intermediate forms. In human beta cells cultured in 20 mmol/l glucose, the major form corresponds to an intermediate species which exhibits an immunoreactivity for the N-flanking peptide, as is also the case in islet amyloid. We concluded that prolonged in vitro exposure of beta cells to raised glucose concentrations increases the relative proportion of islet amyloid polypeptide over insulin, as well as of its precursors over the mature form of islet amyloid polypeptide. [Diabetologia (1999)

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“…1B). This shoulder could be immunoprecipitated by polyclonal anti-(pro)insulin serum, by monoclonal antibody S2 to the intact AC junction of human PI, but not by monoclonal antibody S53 to the BC junction (19,20). Therefore, it is considered a des 31,32 -PI-related truncation product and was added to the des 31,32 -PI peak in the analysis.…”

Section: High Performance Liquid Chromatography (Hplc)mentioning

confidence: 99%

Effect of Glucose on Production and Release of Proinsulin Conversion Products by Cultured Human Islets1

Zambre

Ling

Hou

et al. 1998

The Journal of Clinical Endocrinology &Amp; Metabolism

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Isolated human islets were examined for the rates of conversion and release of newly formed (pro)insulin-like peptides. The rate of proinsulin (PI) conversion was 2-fold slower in human ␤-cells (t 1/2 ϭ 50 min) than in rat ␤-cells (t 1/2 ϭ 25 min). During the first hour following labeling of newly synthesized proteins, PI represented the main newly formed hormonal peptide in the medium; its release was stimulated 2-fold over the basal level by 20 mmol/L glucose. During the second hour, newly synthesized hormone was mainly released as insulin, with 10-to 20-fold higher rates at 20 mmol/L glucose. Prolonged preculture of the islets at 20 mmol/L glucose did not delay PI conversion, but markedly increased the release of newly formed PI, des 31,32 -PI, and insulin at both low and high glucose levels. Our data demonstrate that 1) the release of PI provides an extracellular index for the hormone biosynthetic activity of human ␤-cells; 2) an acute rise in glucose exerts a stronger amplification of the release of converted hormone than in that of nonconverted hormone; and 3) prolonged exposure to high glucose levels results in an elevated basal release of converted and nonconverted PI; this elevation is not associated with a delay in PI conversion, but is attributed to the hyperactivated state of the human ␤-cell population, which was recently found to be responsible for an elevation in basal rates of hormone synthesis. These in vitro observations on human ␤-cells provide a possible explanation for the altered circulating (pro)insulin levels measured in nondiabetic and noninsulin-dependent diabetic subjects. (J Clin Endocrinol

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Proinsulin and Its Conversion Intermediates in Human Pancreas and Isolated Islet Tissue

Cited by 5 publications

References 0 publications

Proinsulin processing in the diabetic Goto-Kakizaki rat

Proinsulin processing in the diabetic Goto-Kakizaki rat

Prolonged exposure of pancreatic beta cells to raised glucose concentrations results in increased cellular content of islet amyloid polypeptide precursors

Effect of Glucose on Production and Release of Proinsulin Conversion Products by Cultured Human Islets1

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