JOE
HOME HELP CONTACT US SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Journal of Endocrinology (2007) 192, 381-387       DOI: 10.1677/joe.1.06676
© 2007 Society for Endocrinology
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (6)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Börjesson, A.
Right arrow Articles by Carlsson, C.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Börjesson, A.
Right arrow Articles by Carlsson, C.

Altered proinsulin conversion in rat pancreatic islets exposed long-term to various glucose concentrations or interleukin-1ß

 Andreas Börjesson and Carina Carlsson

Department of Medical Cell Biology, Uppsala University, BMC, Box 571, SE-751 23 Uppsala, Sweden

(Requests for offprints should be addressed to A Börjesson; Email: Andreas.Borjesson{at}mcb.uu.se)


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
In order to elucidate a possible relationship between ß-cell function and conversion of proinsulin to insulin, isolated rat pancreatic islets were maintained in tissue culture for 1 week at various glucose concentrations (5.6–56 mM). Studies were also conducted on islets cultured for 48 h with interleukin-1ß (IL-1ß). By pulse-chase labelling and immunoprecipitation, the relative contents of newly synthesized proinsulin and insulin were determined. ELISA was used to analyse insulin and proinsulin content in medium and within islets. Using real-time PCR, the mRNA levels of proinsulin converting enzymes (PC1 and PC2) were studied. Islets cultured at 56 mM glucose had an increased proportion of newly synthesized proinsulin when compared with islets cultured at 5.6 mM glucose after a 90-min chase periods, however, no difference was observed after culture at 11 and 28 mM glucose. ELISA measurements revealed that culture at increased glucose concentrations as well as islet exposure to IL-1ß increased proinsulin accumulation in the culture media. The mRNA expression of PC1 was increased after culture at 11 and 28 mM glucose. Treatment for 48 h with IL-1ß increased the proportion of proinsulin both at 45 and 90 min when compared with control islets. These islets also displayed a decreased mRNA level of PC1 as well as PC2. Calculations of the half-time for proinsulin demonstrated a significant prolongation after treatment with IL-1ß. We conclude that a sustained functional stimulation by glucose of islets is coupled to a decreased conversion of proinsulin which is also true for islets treated with IL-1ß. This may contribute to the elevated levels of proinsulin found both at the onset of type 1 diabetes as well as in type 2 diabetes.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
High concentrations of proinsulin and abnormal proinsulin conversion have been associated with type II diabetes (T2D) as well as subjects at risk for T2D (Gordon et al. 1974, Mako et al. 1977, Heding et al. 1981, Ward et al. 1987, Yoshioka et al. 1988, Temple et al. 1989, Saad et al. 1990, Haffner et al. 1994, Kahn et al. 1995, Mykkannen et al. 1995, Roder et al. 1995). Increased levels of proinsulin have also been found at the onset of type I diabetes (T1D) and in relatives of T1D patients (Ludvigsson & Heding 1982, Hartling et al. 1989, Snorgaard et al. 1990). In rat models of hyperglycaemia, increased ratios of circulating proinsulin to insulin have been determined (Leahy et al. 1991, Leahy 1993, Alarcon et al. 1995, Gadot et al. 1995).

Biosynthesis of proinsulin in ß-cells is stimulated by glucose and this imposes an increased demand on the mechanism for proinsulin to insulin conversion. The endoproteolytic processing of proinsulin to insulin is mediated by proinsulin convertases 1 and 2 (PC1 and PC2) (Bailyes et al. 1992, Bennett et al. 1992, Steiner et al. 1996). The conversion of proinsulin to insulin is regulated by glucose, acutely, partly through effects on the biosynthesis of PC1 and PC2 (Alarcon et al. 1993, Martin et al. 1994, Schuppin & Rhodes 1996).

Most studies of glucose regulation of the proinsulin conversion in ß-cells have been performed over relatively short-time periods. In addition, previous studies of proinsulin conversion have been studied using isolated pancreatic ß-cells or cell lines. Herein, we investigated the effects of long-time glucose culture on proinsulin conversion in isolated rat pancreatic islets.

The proinflammatory cytokine interleukin-1ß (IL-1ß) is a central mediator of ß-cell destruction (Bendtzen et al. 1986). For instance, rat islets cultured for 48 h with IL-1ß has decreased insulin secretion, insulin biosynthesis and oxidative metabolism (Sandler et al. 1987).

The present study examines the possibility that rat pancreatic islets may adapt to change functional demands or the cytokines by altering the rate of conversion of proinsulin to insulin. In order to elucidate this issue, the intracellular ratio of newly synthesized proinsulin/insulin was assessed, and proinsulin/insulin accumulation and content were measured as well as the levels of mRNAs encoding for PC1 and PC2, in isolated rat islets maintained in tissue culture at high glucose concentrations or after exposure to the cytokine IL-1ß.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Islet isolation and culture

Pancreatic islets were isolated from adult Sprague–Dawley rats by collagenase digestion and hand-picked with a braking pipette. The use of animals was in accordance with international guidelines (National Institutes of Health publication 85–23) and approved by the regional laboratory animal ethics committee in Tierp, Sweden. Preculture of islets was performed for 3–4 days at 37 °C on non-attachment Sterilin dishes (Bibby Sterilin Ltd, Stone, Staffs, UK) using Roswell Park memorial institute (RPMI) 1640 medium containing 10% fetal calf serum, 2 mM L-glutamine, benzyl penicillin (100 U/ml), streptomycin (0.1 mg/ml) and 11 mM glucose, in an atmosphere of air +5% CO2.

Groups of 50–60 islets were then treated with IL-1ß as described below or cultured at different glucose concentrations (5.6, 11, 28 or 56 mM) for 7 days. The medium was changed every second day.

Treatment of islets with IL-1ß

Treatment with human IL-1ß (PeproTech, London, UK) was performed by the addition of the cytokine at an activity of 25 U/ml. Culture was continued for 48 h in medium RPMI 1640 supplemented with 11 mM glucose.

Proinsulin and insulin accumulation and islet content

During the experiments, samples of culture medium were taken and analysed for insulin using a rat insulin ELISA according to the manufacturer’s instructions (Mercodia, Uppsala, Sweden). To analyse insulin content, islets were ultrasonically disrupted in 0.5 ml acid ethanol and the insulin extracted overnight at 4 °C. For analysis of proinsulin accumulation in medium and islet content, we used a rat proinsulin ELISA according to the manufacturer’s instructions (Mercodia).

Radioactive labelling of newly synthesized proinsulin and insulin

Pulse-chase labelling of islet proteins was achieved by incubating in each experiment three groups of 50 islets, with 100 µCi L-[4.5-3H]leucine in 100 µl bicarbonate buffer supplemented with 10 mM Hepes (Krebs–Ringer bicarbonate buffer supplemented 10 mM Hepes, KRBH), 50 µg/ml BSA and 16.7 mM glucose for 30 min at 37 °C. The islets were subsequently washed with KRBH and one sample of islets immediately frozen, whilst two of the samples were further incubated for 45 or 90 min after addition of KRBH supplemented with 16.7 mM glucose. This incubation in non-radioactive medium was designated as the chase period. The samples were then washed with KRBH and frozen at –70 °C before further processing as described below.

Immunoprecipitation of insulin

Labelled islets were sonicated in 50 µl of a 50 mM glycine buffer (pH 8.8) supplemented with 2.5% BSA and 0.1% Triton X-100. After addition of 70 µl solution of antibovine insulin antisera (Biomakor, Rehovot, Israel), the samples were shaken and left for 1 h at room temperature. Subsequently, 100 µl protein A-Sepharose CL-4B suspended in glycine buffer, was added and the samples gently shaken for 15 min. After sedimentation by gentle centrifugation, the pellet was rinsed twice with the glycine buffer and frozen at –70 °C.

Separation by PAGE

The antibody precipitated proteins were dissociated from the protein A complex and separated on a gradient gel of 10–15% acrylamide/0.5–0.75% methylenebisacrylamide with 6 M urea. For this purpose, the Sepharose pellet was resuspended in 30 µl sample buffer (62.5 mM Tris–Cl (pH 6.8), 2% SDS, 5% ß-mercaptoethanol and 6 M urea), briefly, boiled and the supernatant loaded on the gel. The electrophoresis was run in a Tris–glycine buffer (25 mM Tris-base and 0.2 M glycine) supplemented with 0.1% SDS at 12 mA for 6–7 h. The gel was subsequently soaked in amplifier (Amplify) for 20–30 min and dried overnight. The dried gel was exposed at –70 °C to Hyperfilm-MP with an intensifying screen. The intensities of the spots were determined by densitometry (DU-62 spectrophotometer, Beckman Instruments, Fullerton, CA, USA). A protein standard (Rainbow Markers) with molecular weight ranging from 2350 to 46 000 Da was run in parallel with the samples. Two distinct protein bands were found in the gel, one around 9000 Da and the other at 3500 Da. These were regarded as proinsulin and the B chain of insulin. The insulin A chain migrated with the protein front and was not measured.

RNA isolation and cDNA synthesis

Total RNA from 50 to 60 islets in each experimental group was isolated with RNeasy Mini Kit (Qiagen) and digested with RNAse free DNAse (Qiagen). RNA was concentrated by sodium acetate/ethanol precipitation (0.3 M sodium acetate in 66% ethanol (vol%)), dried and dissolved in 10 µl RNase free water and stored at –70 °C. Synthesis of cDNA was performed with Reversed Transcription System (Promega) using 9 µl total RNA per 20 µl cDNA synthesis reaction and 5 mmol/l MgCl2, 1 x reverse transcription buffer, 1 mmol/l of each dNTP, 1 U/µl Recombinant RNasin ribonuclease inhibitor, 15 U/µl Avarian myeloblastosis virus (AMV) Reverse transcriptase and 1 µg (dT)15 primer. The reactions were incubated for 60 min at 42 °C followed by 5 min at 99 °C and stored at –20 °C.

RT-PCR

Light Cycler Instrument (Roche) combined with sequence independent detection with SYBR Green I was used to amplify and analyse generated cDNA. Primers for glucose-6-phosphate dehydrogenase (G6PDH), PC1, PC2 and porphobilinogen deaminase haem biosynthetic enzyme (PBG) were as follows (TIB Molbiol Syntheselabor, Berlin, Germany): G6PDH f 5'-ATTGACCACTACCTGGGCAA- 3 ', G6PDH r 5'-GAGATACACTTCAACACTTTGACCT-3 ', PC1 f 5'-TGAATGTTGTGGAGAAGCGG-3', PC1 r 5 '-GCACTTGGAGACTTCTTTGGTG-3', PC2 f 5'-CT GAGGCTGGTGTGGCTAC-3', PC2 r 5'-AGCTGGC GTGTTTGCATTA-3', PBG f 5'-CCTGGCATAC AGTTTGAAATCAT-3', PBG r 5'-TTTCCCTAAAAAC AACAGCAT-3'.

PCRs were performed in a total volume of 10 µl, containing 1 µl cDNA, 1 µM of each primer, 1 x LightCycler Fast Start reaction mixture (Roche) and 5.0 mmol/l MgCl2 (Roche). Before PCR amplification, the Taq polymerase was added and activated by incubating the samples for 10 min at 95 °C. Amplification was performed by denaturing for 15 s at 95 °C, annealing for 10 s at 60 °C and elongation for 15 s at 72 °C for 45 cycles. In our RT-PCR experiments we used G6PDH as the housekeepinggene. However, increasing glucose concentrations seemed to induce the transcription of this gene. Therefore, we set up our glucose experiments with the gene for PBG as the housekeeping gene. Transcription of this gene was not affected by culture of the islets at different glucose concentrations.

Data computation

When calculating the half-time (T1/2) for conversion, time 0 was arbitrarily determined as 15 min after the labelling started. For RT-PCR experiments, the Ct (cycle threshold) values were used to calculate the amount of amplified PCR product when compared with the housekeeping gene. Relative amount of mRNA was calculated as 2–{Delta}Ct. The results are expressed as means ± S.E.M. Statistical analysis was performed with Student’s t-test for paired samples. A probability (P) for a chance difference <0.05 was regarded as significant.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
The effect of increasing glucose concentrations on proinsulin conversion

The accumulation of insulin in culture medium from rat islets kept in the 1-week culture at different glucose concentrations is shown in Fig. 1aGo. The insulin accumulation in medium from islets cultured at 5.6 mM glucose was decreased when compared with the medium from islets cultured at 11 mM. At the end of the culture period, the insulin accumulation was elevated in the 28 and 56 mM glucose medium.


Figure 1
View larger version (18K):
[in this window]
[in a new window]

  		Figure 1 Insulin (a) and proinsulin (b) accumulation from rat pancreatic islets cultured at different glucose concentrations 5.6 (dark grey bars), 11 (grey bars), 28 (striped bars) or 56 mM (black bars) for 1 week. The percentage of proinsulin is shown in Fig. 1c. Values are means ± S.E.M. for four experiments. *P < 0.05 using Student’s paired t-test when compared with islets cultured at 11 mM glucose.

 
During the culture period, the proinsulin accumulation in media from islets kept at 11 mM glucose was 0.5 ng proinsulin per 10 islets and hour (Fig. 1bGo). This corresponded to 2–3% of secreted insulin+proinsulin (molecular weights were used for calculation).

Culture of islets at increased glucose concentrations (28 and 56 mM) resulted in elevated levels of proinsulin in the culture medium (Fig. 1b and cGo). The proinsulin accumulation in media of the 5.6 mM group was decreased (Fig. 1b and cGo).

There was a tendency toward decreased proinsulin content in islets cultured at 56 mM glucose as well as in islets cultured at 5.6 mM when compared with islets cultured at 11 mM glucose (Table 1Go).


View this table:
[in this window]
[in a new window]

  		Table 1 Insulin and proinsulin content in islets cultured at different glucose concentrations. Values are means ± S.E.M. for four experiments
 
Exposure of islets for 1 week to increasing glucose concentrations consistently revealed that after a chase period of 45 min about 30–40% of the immunoprecipitated proteins migrated with molecules of the same size as proinsulin (Table 2Go). After a 90-min chase period, the proportion of proinsulin was less but the same (about 20%) in islets cultured at 5.6, 11 or 28 mM glucose, whereas a significant increase was found after culture at 56 mM glucose (55%, Table 2Go). The T1/2 of conversion was similar at all glucose concentrations (43–52 min). Decreased PC1 mRNA levels were observed in rat islets incubated for 7 days at 5.6 mM glucose when compared with islets cultured at 11 mM glucose. After culture at 56 mM glucose, a tendency to increased levels was seen, however, this was not statistically significant (Fig. 2aGo). No alterations in the levels of PC2 were detected when islets were incubated at various glucose concentrations (Fig. 2bGo). Interestingly, the RT-PCR results reveal considerably higher mRNA levels of PC2 when compared with PC1 (1000-fold).


View this table:
[in this window]
[in a new window]

  		Table 2 Proinsulin as a percent of newly synthesized proinsulin+ insulin in rat islets cultured for 1 week at different glucose concentrations. Values are means ± S.E.M. for six experiments
 

Figure 2
View larger version (21K):
[in this window]
[in a new window]

  		Figure 2 Relative mRNA levels of PC1 (a) and PC2 (b) in rat pancreatic islets cultured at different glucose concentrations (labels described in Fig. 1Go) for 1 week. Relative mRNA expression (2–{Delta}Ct) was calculated by subtracting Ct values for PBG from the Ct values for PC1 or PC2. Values are means ± S.E.M. for four experiments. *P < 0.05 using Student’s paired t-test when compared with islets cultured at 11 mM glucose.

 
The effect of IL-1ß on proinsulin conversion

Exposure to IL-1ß for 48 h tended to result both in decreased insulin content (Table 3Go) and in insulin accumulation (Table 4Go). The proinsulin content within islets exposed to IL-1ß was decreased when compared with control islets (Table 3Go). Islet exposure to IL-1ß resulted in an increase in the proinsulin ratio in the culture media (Table 4Go). Islets treated with IL-1ß (25 U/ml) for 48 h had a marked increased proportion of labelled proinsulin when compared with control islets (Fig. 3Go). There was a notable increase in the T1/2 in islets treated with IL-1ß to 68 ± 7.8 min, which should be compared with 37 ± 10 min in the controls (n = 6, P < 0.05). A modest decrease in PC1 mRNA levels and a 70% decrease of PC2 mRNA expression were detected in pancreatic islets incubated with IL-1ß (Fig. 4a and bGo).


View this table:
[in this window]
[in a new window]

  		Table 3 Insulin and proinsulin content in islets exposed to IL-1ß for 48 h. Values are means ± S.E.M. for three experiments
 

View this table:
[in this window]
[in a new window]

  		Table 4 Insulin and proinsulin accumulation in medium from rat pancreatic in islets exposed to IL-1ß for 48 h. Values are means ± S.E.M. for three experiments
 

Figure 3
View larger version (9K):
[in this window]
[in a new window]

  		Figure 3 Proinsulin in percent of newly synthesized proinsulin+ insulin in rat islets cultured without (black bars) or with 25 U/ml IL-1ß (grey bars) for 48 h. Islets were labelled with L-[4.5-3H]leucine for 30 min and then incubated without radioactivity at 16.7 mM glucose for 45 and 90 min. Values are means ± S.E.M. for six experiments. *P < 0.05 and {dagger}P < 0.01 using Student’s paired t-test.

 

Figure 4
View larger version (12K):
[in this window]
[in a new window]

  		Figure 4 Relative mRNA expression of PC1 (a) and PC2 (b) in rat pancreatic islets cultured without (black bars) or with 25 U/ml IL-1ß (grey bars) for 48 h. Relative mRNA expression (2–{Delta}Ct) was calculated by subtracting Ct values for G6PDH from the Ct values for PC1 or PC2. Values are means ± S.E.M. for five experiments. *P < 0.05 using Student’s paired t-test.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Our results from the 1-week culture at various glucose concentrations revealed that increasing glucose concentrations lead to an increased proinsulin secretion to the culture medium. We believe that the increase in proinsulin secretion could be explained by a sustained state of cellular activation.

The half-time of conversion of newly synthesized proinsulin from the intracellular pool was determined using three time points. In all experiments, except those in which islets were treated with IL-1ß, the T1/2 was found to be 40–50 min when 15 min after the start of radioactive labelling was set as time 0. This agrees well with previously published studies (Steiner et al. 1972, Rhodes & Halban 1987 Nagamatsu et al. 1987) indicating an intracellular T1/2 of proinsulin of about 60 min in freshly isolated islets. In the present study, this rate of conversion was maintained after culture in glucose concentrations in the range 5.6–28 mM, whereas a decreased rate was measured only in islets which had been cultured for 7 days at 56 mM glucose and incubated for 90 min after the labelling period. The increase in proinsulin to insulin indicates unresponsiveness of the islets after the treatment at high glucose (56 mM). These data are in agreement with previous work on human isolated ß-cells (Hostens et al. 1999).

A general observation in this study was that the mRNA levels of PC2 were considerably higher than those of PC1. Using the Ct values, taking into consideration the relative comparison, we could estimate that the mRNA levels of PC2 were up to a thousand times higher than the PC1 mRNA levels. This observation is also in agreement with the results of Hostens et al.(1999), showing higher protein levels of PC2 than PC1 in human ß-cell preparations.

It has been suggested that in rat islets, PC1 biosynthesis, but not PC2, appears to be acutely regulated by glucose (Alarcon et al. 1993). Both these studies indicate that PC1 is the rate limiting enzyme in proinsulin conversion, acutely as well as long-term. This is in line with our observations with increased levels of PC1 mRNA but no differences in the expression of PC2 after culture at different glucose concentrations. That is, in a situation with a sustained hypersecretion of insulin, the ß-cells therefore seem to be unable to sufficiently enhance the conversion of proinsulin to maintain a normal ratio in the secretory granule. This is, in line with clinical observations where increased proportion of proinsulin in the plasma of diabetic patients as well as in glucose intolerant subjects was published (Duckworth & Kitabchi 1972, Gordon et al. 1974, Mako et al. 1977, Heding et al. 1981, Ludvigsson & Heding 1982, Rhodes & Halban 1987, Hartling et al. 1989, Snorgaard et al. 1990).

Our results from islets being exposed to IL-1ß for 48 h lead to an increased secretion of proinsulin. IL-1ß treatment of pancreatic islets decreased the mRNA levels of both PC1 and PC2, indicating a decreased proinsulin conversion. Indeed, our data show a marked increase in the proportion of newly synthesized proinsulin after 48 h IL-1ß treatment. These islets have previously been shown to have decreased insulin release in response to glucose and decreased insulin and DNA content (Bendtzen et al. 1986, Sandler et al. 1987, Spinas et al. 1992). Our results are in line with previously published data, indicating decreased conversion rate in rat islets after 24-h IL-1ß (Hansen et al. 1988) and that exposure of ß-cells to IL-1ß for 24 h suppresses both proinsulin biosynthesis as well as the expression of PC2 by 46% via an NO-mediated pathway (Zambre et al. 2001). These results are in line with ours showing 70% reduction in PC2 transcription after 48 h. In previous experiments with human ß-cell preparations, the cytokine combinations, in particular IL-1ß and interferen (IFN)-{gamma}, revealed disproportionately increased medium proinsulin levels (Hostens et al. 1999). In view of the role for IL-1ß in the ß-cell destruction leading to T1D, it is of note that increased circulating levels of proinsulin have been observed during the period preceding the clinical manifestation of the disease. The possibility that a high local concentration of IL-1ß in the islets may contribute to an increased proinsulin release should therefore be considered.

Our observations suggest that a lasting increased functional stimulation of islets causes an increase in proinsulin ratio as well as in converting enzymes. This may reflect an adaptive response of the ß-cell to an enhanced turnover of a diminished insulin pool. This adaptation, however, appears insufficient after culture at 56 mM glucose, as shown by increased levels of proinsulin and no adaptation of the converting enzymes. These data are in accordance with previous data indicating slightly impaired effect by slight lowering of the ATP:ADP ratio and glucose oxidation (Sandler et al. 1991). Furthermore, IL-1ß stimulation of islets decreases the conversion of proinsulin and is associated with a decrease in conversion enzymes. This is applicable to in vivo findings, showing increased levels of circulating proinsulin levels in hyperglycaemic states (Duckworth & Kitabchi 1972).

We conclude that a sustained functional stimulation by glucose of islets is coupled to a decreased conversion of proinsulin which is also true for islets treated with IL-1ß. This may contribute to the elevated levels of proinsulin found both at the onset of type 1 diabetes as well as in type 2 diabetes.


   Acknowledgements
 
We thank Professor Stellan Sandler, Professor Michael Welsh and the late Professor Claes Hellerström for valuable advice during the course of this study and we gratefully acknowledge the skilled technical assistance of Ing-Britt Hallgren. This work was supported by grants from the Swedish Research Council, the Swedish Diabetes Association, the Magnus Bergvall Foundation and the Swedish Childhood Diabetes Foundation. The authors declare that there is no conflict of interest that would prejudice the impartiality of this scientific work.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Alarcon C, Lincoln B & Rhodes CJ 1993 The biosynthesis of the subtilisin-related proprotein convertase PC3, but not that of the PC2 convertase, is regulated by glucose in parallel to proinsulin biosynthesis in rat pancreatic islets. Journal of Biological Chemistry 268 4276–4280.[Abstract/Free Full Text]

Alarcon C, Leahy JL, Schuppin GT & Rhodes CJ 1995 Increased secretory demand rather than a defect in the proinsulin conversion mechanism causes hyperproinsulinemia in a glucose-infusion rat model of non-insulin-dependent diabetes mellitus. Journal of Clinical Investigation 95 1032–1039.[Web of Science][Medline]

Bailyes EM, Shennan KI, Seal AJ, Smeekens SP, Steiner DF, Hutton JC & Docherty K 1992 A member of the eukaryotic subtilisin family (PC3) has the enzymic properties of the type 1 proinsulin-converting endopeptidase. Biochemical Journal 285 391–394.[Web of Science][Medline]

Bendtzen K, Mandrup-Poulsen T, Nerup J, Nielsen JH, Dinarello CA & Svenson M 1986 Cytotoxicity of human pI 7 interleukin-1 for pancreatic islets of Langerhans. Science 232 1545–1547.[Abstract/Free Full Text]

Bennett DL, Bailyes EM, Nielsen E, Guest PC, Rutherford NG, Arden SD & Hutton JC 1992 Identification of the type 2 proinsulin processing endopeptidase as PC2, a member of the eukaryote subtilisin family. Journal of Biological Chemistry 267 15229–15236.[Abstract/Free Full Text]

Duckworth WC & Kitabchi AE 1972 Direct measurement of plasma proinsulin in normal and diabetic subjects. American Journal of Medicine 53 418–427.[CrossRef][Web of Science][Medline]

Gadot M, Ariav Y, Cerasi E, Kaiser N & Gross DJ 1995 Hyperproinsulinemia in the diabetic Psammomys obesus is a result of increased secretory demand on the beta-cell. Endocrinology 136 4218–4223.[Abstract]

Gordon P, Hendricks CM & Roth J 1974 Circulating proinsulin-like component in man: increased proportion in hypoinsulinemic states. Diabetologia 10 469–474.[CrossRef][Web of Science][Medline]

Haffner SM, Bowsher RR, Mykkanen L, Hazuda HP, Mitchell BD, Valdez RA, Gingerich R, Monterossa A & Stern MP 1994 Proinsulin and specific insulin concentration in high- and low-risk populations for NIDDM. Diabetes 43 1490–1493.[Abstract]

Hansen BS, Nielsen JH, Linde S, Spinas GA, Welinder BS, Mandrup-Poulsen T & Nerup J 1988 Effect of interleukin-1 on the biosynthesis of proinsulin and insulin in isolated rat pancreatic islets. Biomedica Biochimica Acta 47 305–309.[Web of Science][Medline]

Hartling SG, Lindgren F, Dahlqvist G, Persson B & Binder C 1989 Elevated proinsulin in healthy siblings of IDDM patients independent of HLA identity. Diabetes 38 1271–1274.[Abstract]

Heding LG, Ludvigsson J & Kasperska-Czyzykowa T 1981 B-cell secretion in non-diabetics and insulin-dependent diabetics. Acta Medica Scandinavica. Supplementum 659 5–9.

Hostens K, Pavlovic D, Zambre Y, Ling Z, Van Schravendijk C, Eizirik DL & Pipeleers DG 1999 Exposure of human islets to cytokines can result in disproportionately elevated proinsulin release. Journal of Clinical Investigation 104 67–72.[Web of Science][Medline]

Kahn SE, Leonetti DL, Prigeon RL, Boyko EJ, Bergstrom RW & Fujimoto WY 1995 Proinsulin as a marker for the development of NIDDM in Japanese–American men. Diabetes 44 173–179.[Abstract]

Leahy JL 1993 Increased proinsulin/insulin ratio in pancreas extracts of hyperglycemic rats. Diabetes 42 22–27.[Abstract]

Leahy JL, Halban PA & Weir GC 1991 Relative hypersecretion of proinsulin in rat model of NIDDM. Diabetes 40 985–989.[Abstract]

Ludvigsson J & Heding LG 1982 Abnormal proinsulin/C peptide ratio in juvenile diabetes. Acta Diabetologica Latina 19 351–358.[Web of Science][Medline]

Mako ME, Starr JI & Rubenstein AH 1977 Circulating proinsulin in patients with maturity onset diabetes. American Journal of Medicine 63 865–869.[CrossRef][Web of Science][Medline]

Martin SK, Carroll R, Benig M & Steiner DF 1994 Regulation by glucose of the biosynthesis of PC2, PC3 and proinsulin in (ob/ob) mouse islets of Langerhans. FEBS Letters 356 279–282.[CrossRef][Web of Science][Medline]

Mykkannen L, Haffner SM, Kuusisto J, Pyorala K, Hales CN & Laakso M 1995 Serum proinsulin levels are disproportionately increased in elderly prediabetic subjects. Diabetologia 38 1176–1182.[Web of Science][Medline]

Nagamatsu S, Bolaffi JL & Grodsky GM 1987 Direct effects of glucose on proinsulin synthesis and processing during desensitization. Endocrinology 120 1225–1231.[Abstract/Free Full Text]

Rhodes CJ & Halban PA 1987 Newly synthesized proinsulin/insulin and stored insulin are released from pancreatic B cells predominantly via a regulated, rather than a constitutive, pathway. Journal of Cell Biology 105 145–153.[Abstract/Free Full Text]

Roder ME, Vaag A, Hartling SG, Dinesen B, Lanng S, Beck-Nielsen H & Binder C 1995 Proinsulin immunoreactivity in identical twins discordant for noninsulin-dependent diabetes mellitus. Journal of Clinical Endocrinology and Metabolism 80 2359–2363.[Abstract]

Saad MF, Kahn SE, Nelson RG, Pettitt DJ, Knowler WC, Schwartz MW, Kowalyk S, Bennett PH & Porte D Jr 1990 Disproportionately elevated proinsulin in Pima Indians with noninsulin-dependent diabetes mellitus. Journal of Clinical Endocrinology and Metabolism 70 1247–1253.[Abstract/Free Full Text]

Sandler S, Andersson A & Hellerstrom C 1987 Inhibitory effects of interleukin 1 on insulin secretion, insulin biosynthesis, and oxidative metabolism of isolated rat pancreatic islets. Endocrinology 121 1424–1431.[Abstract/Free Full Text]

Sandler S, Bendtzen K, Eizirik DL, Strandell E, Welsh M & Welsh N 1991 Prolonged exposure of pancreatic islets isolated from ‘pre-diabetic’ non-obese diabetic mice to a high glucose concentration does not impair beta-cell function. Diabetologia 34 6–11.[CrossRef][Web of Science][Medline]

Schuppin GT & Rhodes CJ 1996 Specific co-ordinated regulation of PC3 and PC2 gene expression with that of preproinsulin in insulin-producing beta TC3 cells. Biochemical Journal 313 259–268.[Web of Science][Medline]

Snorgaard O, Hartling SG & Binder C 1990 Proinsulin and C-peptide at onset and during 12 months cyclosporin treatment of type 1 (insulin-dependent) diabetes mellitus. Diabetologia 33 36–42.[CrossRef][Web of Science][Medline]

Spinas GA, Snorgaard O, Hartling SG, Oberholzer M & Berger W 1992 Elevated proinsulin levels related to islet cell antibodies in first-degree relatives of IDDM patients. Diabetes Care 15 632–637.[Abstract]

Steiner DF, Kemmler W, Clark JL, Oyer PE & Rubenstein AH 1972 The biosynthesis of insulin. In Handbook of Physiology, vol 1, pp 175–198. Eds N Freinkel & DF Steiner (The endocrine pancreas).

Steiner DF, Rouille Y, Gong Q, Martin S, Carroll R & Chan SJ 1996 The role of prohormone convertases in insulin biosynthesis: evidence for inherited defects in their action in man and experimental animals. Diabetes and Metabolism 22 94–104 (Review).

Temple RC, Carrington CA, Luzio SD, Owens DR, Schneider AE, Sobey WJ & Hales CN 1989 Insulin deficiency in non-insulin-dependent diabetes. Lancet 1 293–295.[CrossRef][Web of Science][Medline]

Ward WK, LaCava EC, Paquette TL, Beard JC, Wallum BJ & Porte D Jr 1987 Disproportionate elevation of immunoreactive proinsulin in type 2 (non-insulin-dependent) diabetes mellitus and in experimental insulin resistance. Diabetologia 30 698–702.[CrossRef][Web of Science][Medline]

Yoshioka N, Kuzuya T, Matsuda A, Taniguchi M & Iwamoto Y 1988 Serum proinsulin levels at fasting and after oral glucose load in patients with type 2 (non-insulin-dependent) diabetes mellitus. Diabetologia 31 355–360.[CrossRef][Web of Science][Medline]

Zambre Y, Van Schravendijk C & Ling Z 2001 Interleukin-1 beta inhibits proinsulin conversion in rat beta-cells via a nitric oxide-dependent pathway. Hormone and Metabolic Research 33 639–644.[CrossRef][Web of Science][Medline]

Received in final form 20 October 2006
Accepted 26 October 2006
Made available online as an Accepted Preprint 15 November 2006




This article has been cited by other articles:


Home page
 Am. J. Physiol. Endocrinol. Metab.Home page
A. Alberti, P. Karamessinis, M. Peroulis, K. Kypreou, P. Kavvadas, S. Pagakis, P. K. Politis, and A. Charonis
ERp46 is reduced by high glucose and regulates insulin content in pancreatic {beta}-cells
Am J Physiol Endocrinol Metab, September 1, 2009; 297(3): E812 - E821.
[Abstract] [Full Text] [PDF]

Home page
 Proc. Natl. Acad. Sci. USAHome page
J. A. Ehses, G. Lacraz, M.-H. Giroix, F. Schmidlin, J. Coulaud, N. Kassis, J.-C. Irminger, M. Kergoat, B. Portha, F. Homo-Delarche, et al.
IL-1 antagonism reduces hyperglycemia and tissue inflammation in the type 2 diabetic GK rat
PNAS, August 18, 2009; 106(33): 13998 - 14003.
[Abstract] [Full Text] [PDF]

Home page
 Mol. Cell. ProteomicsHome page
W. D'Hertog, L. Overbergh, K. Lage, G. B. Ferreira, M. Maris, C. Gysemans, D. Flamez, A. K. Cardozo, G. Van den Bergh, L. Schoofs, et al.
Proteomics Analysis of Cytokine-induced Dysfunction and Death in Insulin-producing INS-1E Cells: New Insights into the Pathways Involved
Mol. Cell. Proteomics, December 1, 2007; 6(12): 2180 - 2199.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (6)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Börjesson, A.
Right arrow Articles by Carlsson, C.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Börjesson, A.
Right arrow Articles by Carlsson, C.

HOME HELP CONTACT US SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS