FREE NEJM E-TOC    HOME   |   SUBSCRIBE   |   CURRENT ISSUE   |   PAST ISSUES   |   COLLECTIONS   |   Search Term  Advanced Search

Sign in | Get NEJM's E-Mail Table of Contents — Free | Subscribe

Previous Volume 333:1386-1391 November 23, 1995 Number 21 Next

PDF Add to Personal Archive Add to Citation Manager Notify a Friend E-mail When Cited Related Article PubMed Citation

Insulin, the central hormone controlling the utilization of fuel, is initially synthesized in pancreatic beta cells as its relatively inactive precursor, proinsulin. A series of enzymes that process prohormones act on proinsulin to produce mature insulin and C peptide. Abnormalities in the secretory products of beta cells are a rare but well-documented cause of impairment in glucose tolerance and hyperinsulinemia.¹

Two specific syndromes have been defined. First, mutations in the insulin gene that lead to the production of biologically ineffective insulin have been described in several families.^2,3,4 All cases described to date have involved heterozygotes who produce normal insulin molecules from the unaffected allele. The second syndrome is familial hyperproinsulinemia,^5,6 in which heterozygous mutations affecting the cleavage of proinsulin lead to the secretion of excessive amounts of proinsulin.

We report a case that represents a third disorder. In the patient we describe here the sequence of the proinsulin gene was normal but plasma concentrations of proinsulin and one of the early products of proinsulin cleavage were high, and plasma insulin concentrations were low. In addition to the abnormality of proinsulin processing, there was evidence of impaired processing of proopiomelanocortin (POMC), secondary hypocortisolism, and hypogonadotropic hypogonadism, suggesting the possibility of a more generalized defect related to impaired processing of prohormones.

Case History

The patient, a 43-year-old woman, was referred for the evaluation of symptoms suggestive of postprandial hypoglycemia. These symptoms were long-standing, and the referral was precipitated by a particularly severe episode. The patient's history included severe childhood obesity (weight at the age of three years, 36 kg), for which she had been treated successfully with diet. Her subsequent development, including the development of secondary sexual characteristics, was normal, except that she did not begin menstruating and continued to have moderate obesity. Studies undertaken at the age of 21 detected no cause of her primary amenorrhea. At the age of 30, ovulation was induced with gonadotropins. She became pregnant and delivered healthy quadruplets. The pregnancy was complicated by gestational diabetes mellitus that required treatment with insulin. After this pregnancy, her fasting plasma glucose level was normal, but persistent amenorrhea recurred.

The patient, an only child, weighed 89.2 kg at presentation and was 1.61 m tall. She had a body-mass index (calculated as the weight in kilograms divided by the square of the height in meters) of 34.4, a waist:hip ratio of 0.83, and a blood pressure of 130/70 mm Hg. Her parents had died, and her only living first-degree relatives were her four children, who were clinically normal. In addition to symptoms suggestive of reactive hypoglycemia, she reported fatigue and excessive daytime somnolence. She gave informed consent for all studies.

Methods

The normal pathways of proinsulin processing are shown in Figure 1. (Details are given in the Discussion section.) Plasma concentrations of insulin, proinsulin, and products of proinsulin cleavage (32,33 split proinsulin and 65,66 split proinsulin) were assayed with two-site immunoradiometric or immunoenzymometric assays as previously described,⁷ and these values are expressed in Système International (SI) units to facilitate the comparison of molar ratios. The assay for 32,33 split proinsulin did not distinguish between 32-33 split proinsulin and des-31,32 proinsulin, the product formed when the dibasic residues of 32-33 split proinsulin are removed. To simplify this presentation, the two molecules detected in this assay are referred to as 32,33 split proinsulin. Similarly, the assay for 65,66 split proinsulin did not distinguish between 65-66 split proinsulin and des-64,65 proinsulin; therefore, the former term is used here for simplicity. Insulin did not cross-react in any of the other assays. However, 65,66 split proinsulin cross-reacted completely in the insulin assay (unpublished data).

View larger version (9K): [in this window] [in a new window]   Figure 1. Normal Pathways of Proinsulin Processing and Effects of the Putative Defect in Prohormone Convertase 1 in the Study Patient. Normally, prohormone convertase 1 (PC1) and prohormone convertase 2 (PC2) both act on proinsulin, but the major pathway involves the initial cleavage of proinsulin by PC1 to form 32-33 split proinsulin, followed by the rapid removal of Arg31 and Arg32 (small circles) by the ubiquitous carboxypeptidase H (CPH) to form des-31,32 proinsulin. This intermediate product is then cleaved by PC2 and CPH to form insulin and C peptide, with the removal of Lys64 and Arg65 (small circles) at the 65-66 site. Ordinarily, PC2 activity at the 65-66 site appears to be facilitated by prior cleavage by Pc1 at the 32-33 site. In vitro, PC2 has low but detectable activity at the 32-33 site, but this is not thought to be biologically relevant. A defect in PC1 activity in the patient at the sites marked by an X would explain the high plasma concentrations of proinsulin and 65-66 split proinsulin and the low and undetectable concentrations of 32-33 split proinsulin and insulin, respectively.

 
For the analysis by high-performance liquid chromatography (HPLC), immunoreactive insulin, proinsulin, and proinsulin-cleavage products were extracted from plasma by immunoaffinity chromatography,⁸ and the resulting material was then separated by reverse-phase HPLC. Immunoreactivity was measured in the insulin peak by an immunoradiometric assay using an insulin standard, and in the peaks corresponding to proinsulin and the intermediate cleavage products by an enzyme-linked immunosorbent assay for proinsulin using a proinsulin standard.⁸

Corticotropin precursors were measured with a two-site immunoradiometric assay.⁹ This assay measures both full-length POMC and procorticotropin (the species containing the N terminal of POMC, -melanocyte–stimulating hormone, the joining peptide, and corticotropin). Corticotropin was measured by a two-site immunoradiometric assay specific for the mature sequence of corticotropin, with less than 1 percent cross-reactivity with POMC and less than 10 percent cross-reactivity with procorticotropin.⁹

Glucagon-like molecules were assayed with a two-site immunoradiometric assay that identified all species containing the core sequence of glucagon.¹⁰ Because plasma concentrations of glucagon-like immunoreactivity in our patient were low, no specific assays for glucagon precursors or mature glucagon were undertaken.

To establish the nucleotide sequence of the coding region of the insulin gene, exons 2 and 3 of the patient's genomic DNA were amplified with use of the polymerase chain reaction.⁵ One of the primers for each exon was biotinylated, to allow the sequencing of single-stranded DNA with modified T7 polymerase.¹¹ In exon 2 there were a number of ambiguities in the sequence that could not be resolved on repeated direct sequencing. Exon 2 was therefore subcloned into PCR-Script (Stratagene, La Jolla, Calif.), and eight independent clones were sequenced.

Results

Glucose Homeostasis

The patient's fasting plasma glucose concentration was normal (87 mg per deciliter [4.9 mmol per liter]), but the plasma glucose concentration two hours after the oral administration of 75 g of glucose was high (206 mg per deciliter [11.5 mmol per liter]). The plasma concentrations of intact proinsulin and 65,66 split proinsulin two hours after the oral administration of glucose were very high (>5000 pmol per liter and >500 pmol per liter, respectively). Considering the cross-reactivity of 65,66 split proinsulin in the insulin assay, negligible amounts of plasma insulin were detected. In an HPLC analysis of the insulin-containing immunoreactive material in 1.0 ml of plasma, the principal peak was for proinsulin; des-64,65 proinsulin was the next most abundant species, and no insulin was detected (Figure 2). In a 10-ml sample of plasma, insulin was barely detectable (data not shown). These results contrast sharply with the findings in the plasma of normal subjects or patients with non-insulin-dependent diabetes mellitus, in which the concentrations of 32,33 split proinsulin usually exceeded those of proinsulin and 65,66 split proinsulin and in which des-64,65 proinsulin was undetectable.⁷ The nucleotide sequences of both exons of the insulin gene were normal.

View larger version (5K): [in this window] [in a new window]   Figure 2. Quantitation of Insulin and Insulin-Precursor Molecules from the Study Patient by High-Performance Liquid Chromatography, and Assay Standards. The patient's plasma contained no detectable insulin, large amounts of proinsulin, and smaller amounts of des-64,65 proinsulin. Des-31,32 proinsulin and 32-33 split proinsulin were detectable in low amounts. (The relative amounts of proinsulin precursors and insulin shown in the lower panel are not indicative of those in the plasma of normal subjects.)

 
Measurements obtained before and after two standardized meals are shown in Table 1. The patient had borderline hypoglycemia after the first meal (plasma glucose at 5 hours, 50 mg per deciliter [2.8 mmol per liter]), accompanied by mild lightheadedness and somnolence. The fasting plasma concentrations of proinsulin and 65,66 split proinsulin were markedly elevated; they increased after the meals in a normal fashion. Although the absence of a history of fasting hypoglycemia and the normal responsiveness of plasma proinsulin to meals and oral glucose made the diagnosis of an insulinoma unlikely, the patient underwent a 48-hour fast, during which she had no symptoms or hypoglycemia.

View this table: [in this window] [in a new window]   Table 1. Plasma Concentrations of Glucose, Insulin, and Insulin Precursors in the Study Patient in Response to Test Meals.

 
Processing of Other Prohormones

Table 2 shows the plasma concentrations of corticotropin and corticotropin precursors, as measured basally and during an insulin-tolerance test. The concentration of corticotropin precursors in the basal sample, obtained at 9 a.m., was high (151 pmol per liter),¹² and precursor molecules were present in a molar excess of 50 to 75 times the number of molecules of mature corticotropin throughout the test. Although this ratio was higher than normal (normal molar excess of precursor molecules at 9 a.m., 1 to 10 times the number of molecules of mature corticotropin),¹³ it was less abnormal than the defect in proinsulin processing. Because corticotropin precursors have some (<10 percent) cross-reactivity in the corticotropin assay, the concentrations of mature corticotropin were probably lower than the assay values indicate.

View this table: [in this window] [in a new window]   Table 2. Hormonal Responses to Insulin-Induced Hypoglycemia.

 
The fasting plasma concentration of glucagon-like molecules was 20 pmol per liter (normal range, 20 to 40). Although no assays for specific proglucagon gene products were undertaken, the low-normal overall concentrations of glucagon-like molecules make a major defect in proglucagon processing unlikely.

Investigation of Other Endocrine Systems

            Hypothalamic–Pituitary–Adrenal Function

Although the plasma cortisol concentration at 9 a.m. on the day of the cosyntropin test was low (1.6 µg per deciliter [44 nmol per liter]), the concentration 30 minutes after the intramuscular injection of 0.25 mg of cosyntropin was normal (23.4 µg per deciliter [646 nmol per liter]), indicating normal adrenal responsiveness. The results of a test of responses to insulin-induced hypoglycemia performed at 9 a.m. are shown in Table 2. Both the plasma cortisol concentration and the growth hormone responses to insulin-induced hypoglycemia showed impairment. In addition, the plasma cortisol values obtained at 9 a.m. on three other days were all below 5 µg per deciliter (138 nmol per liter). Plasma concentrations of 17-hydroxyprogesterone, dehydroepiandrosterone, and androstenedione were all in the normal range. The low 9 a.m. plasma cortisol concentrations and slight impairment of the plasma cortisol response to hypoglycemia were interpreted as indicating the presence of hypoadrenalism. Despite this finding, the adrenal responsiveness to 0.25 mg of cosyntropin was normal, a fact that suggested the absence of substantial adrenal atrophy. The patient's fatigue and excessive daytime somnolence lessened with hydrocortisone-replacement therapy.

            Other Endocrine Investigations

The patient's linear growth during childhood was normal, and the plasma concentration of insulin-like growth factor I was normal (500 U per liter; normal range for the patient's age, 300 to 1200). The poor response of plasma growth hormone to hypoglycemia (Table 2) can be explained by the patient's obesity.¹⁴

The serum estradiol concentration was 27 pg per milliliter (99 pmol per liter) (normal range in the follicular phase, 27 to 204 pg per milliliter [99 to 749 pmol per liter]). The serum concentration of follicle-stimulating hormone (FSH) was 1.5 IU per liter (normal follicular-phase range, 2.9 to 8.4), and that of luteinizing hormone (LH) 0.3 IU per liter (normal follicular-phase range, 1.3 to 8.4). The results of a stimulation test with 100 µg of gonadotropin-releasing hormone indicated hypogonadotropic hypogonadism (basal and peak plasma FSH values, 0.7 and 3.5 IU per liter, respectively; basal and peak plasma LH values, 0.3 and 2.1 IU per liter). Plasma concentrations of testosterone, sex hormone–binding globulin, and prolactin were normal, as were the results of magnetic resonance imaging of the hypothalamus. There was no abnormality of thirst, and the osmolality of plasma and urine was consistently normal. Plasma concentrations of renin and aldosterone were normal.

The patient was clinically euthyroid, with no thyroid enlargement. A test for antithyroid microsomal antibodies was strongly positive. The serum thyrotropin concentration was slightly high (5.8 mU per liter; normal range, 0.4 to 4); the concentrations of free thyroxine (0.7 ng per deciliter [9.0 pmol per liter]; normal range, 0.7 to 1.6 ng per deciliter [9.0 to 20.6 pmol per liter]) and free triiodothyronine (0.27 ng per deciliter [4.1 pmol per liter]; normal range, 0.20 to 0.50 ng per deciliter [3.1 to 7.7 pmol per liter]) were at the low end of the normal range. The serum thyrotropin response to the administration of 200 µg of thyrotropin-releasing hormone was normal (basal, 3.1 µU per milliliter; peak [after 40 minutes], 29). The plasma prolactin values before and after the administration of thyrotropin-releasing hormone were 3.7 and 24.1 ng per milliliter, respectively. These results indicated that the patient had intermittent subclinical hypothyroidism caused by chronic autoimmune thyroiditis.

Discussion

This woman with impaired glucose tolerance and reactive hypoglycemia had a barely detectable plasma insulin concentration and high plasma proinsulin concentrations — indications that the primary defect was one of proinsulin processing. There was a coexistent, although less severe, defect in the processing of corticotropin precursors that led to mild hypocortisolemia. Thus, the patient's hyperproinsulinemia was accompanied by features suggestive of a more widespread endocrine disorder.

With regard to the circulating proinsulin-like molecules, the previously reported defects in proinsulin processing were caused by heterozygous mutations in the insulin gene that resulted in the synthesis of abnormal molecules resistant to processing.^5,6 In another family in which a primary defect in proinsulin processing was proposed,¹⁵ the affected subjects had substantial amounts of circulating true insulin; subsequently, linkage to the insulin gene was demonstrated.¹⁶ The results in our patient provide biochemical evidence of primary defects in insulin processing.

Proinsulin has about 5 percent of the biologic activity of insulin.¹⁷ Therefore, at least in the basal state, this patient's beta cells have compensated for the failure of normal processing by secreting large amounts of proinsulin and thus maintaining fasting normoglycemia. The combination of impaired glucose tolerance and reactive hypoglycemia 5 hours after a meal is probably related to the considerably slower clearance of proinsulin (plasma half-life of proinsulin, approximately 20 minutes, vs. approximately 4 minutes for insulin¹⁸).

The normal sequence of the proinsulin gene and the absence of any abnormally migrating peaks in the HPLC analysis of insulin rule out an intrinsic abnormality in the insulin molecule itself. Insulin is normally produced by two prohormone-cleaving enzymes on the proinsulin molecule (Figure 1).¹⁹ One of these, prohormone convertase 1 (PC1), cleaves proinsulin between the 32 position and the 33 position, and the other, prohormone convertase 2 (PC2), cleaves it between the 65 position and the 66 position, and the resultant intermediate product is trimmed of its terminal lysines or arginines by the action of carboxypeptidase H (also known as carboxypeptidase E). Further details about the normal processing of proinsulin are given in the legend to Figure 1. A defect in PC2 would be expected to lead to an excess of des-31,32 proinsulin over proinsulin, the opposite of the findings in this patient. In addition, PC2 cleaves proglucagon in alpha cells,²⁰ which appeared to be normal in the patient. Thus, the cleavage of proinsulin at the 65,66 site and the absence of an elevation of the proglucagon concentration make it unlikely that a primary defect in PC2 explains the findings in our patient.

If, on the other hand, the activity of PC1 is defective, one would predict a low concentration of 32,33 split proinsulin, but to some extent proinsulin should be processed by PC2 to 65,66 split proinsulin. However, because PC2 processes 32,33 split proinsulin more efficiently than proinsulin, a large excess of intact proinsulin over 65,66 split proinsulin would also be predicted. Because 65,66 split proinsulin cannot be processed further without PC1, a substantial elevation in plasma concentrations of this molecule would be expected. All the abnormalities of proinsulin processing that would be expected as a result of defective PC1 activity were found in this patient.

In addition to its role in the processing of proinsulin, PC1 may be involved in the production of corticotropin from POMC in the corticotrophs. The precise series of events by which POMC is converted to corticotropin is not known, however. For example, PC2, which is expressed at a low level in corticotrophs, has some activity at various POMC-cleavage sites,²¹ and the widely expressed processing enzyme furin may be capable of processing some POMC.²² Our patient had a moderate elevation of corticotropin precursors in plasma, together with sufficient corticotropin to maintain nearly normal adrenal production of glucocorticoid. This suggests that the underlying defect affects the processing of proinsulin more than that of POMC. An infant with severe hypocortisolemia who had a very high ratio of precursors to corticotropin in plasma despite a normal POMC gene sequence was recently described.²³ In contrast to our patient, that infant had no evidence of an abnormality in proinsulin processing.

Given the probable nature of the defect in the processing of prohormones, a genetic defect appears most likely. Unfortunately, our patient was an only child whose parents are no longer living. Plasma proinsulin concentrations in the patient's four children were normal, but the children did have a slight increase in the fasting plasma proinsulin concentration relative to the concentration of 32,33 split proinsulin (data not shown), which would be consistent with a mild defect in PC1 activity. Complementary DNa for PC1 has been isolated,^24,25,26 but no information about its genomic structure is available. Because PC1 has restricted expression in tissue,²⁴ this information will be needed before this candidate gene can be readily examined for mutations.

The finding of abnormalities in our patient other than those directly related to the defect of proinsulin processing is unusual, in that such abnormalities were not described previously in patients with disorders of insulin processing. The potential relevance of the early-onset obesity, hypogonadotropic hypogonadism, and defective POMC processing in the patient has been highlighted by the recent discovery of the molecular basis for the fat/fat phenotype in mice.²⁷ This recessive syndrome of obesity, hyperglycemia, and impaired fertility is associated with abnormalities of proinsulin and POMC processing and results from a mutation in the gene for carboxypeptidase H.²⁷ Although the precise nature of our patient's defect in proinsulin cleavage is not identical to that in fat/fat mice, there are similarities in the morphologic and endocrine phenotypes.

In summary, our patient was almost completely unable to process normal proinsulin to insulin. Despite the presumed absence of insulin, she had fasting normoglycemia, although impaired glucose tolerance and mild reactive hypoglycemia were present, presumably because of the altered plasma kinetics of proinsulin as compared with insulin. The associated clinical features of early-onset obesity, hypogonadotropic hypogonadism, and mild secondary hypoadrenalism in association with biochemical evidence of a moderate defect in the processing of POMC to corticotropin suggest, but do not prove, that the expression of this disorder may not be restricted to pancreatic beta cells.

Dr. O'Rahilly and Dr. Gray are supported by the Wellcome Trust.

We are indebted to Professor C.N. Hales, Dr. J. Hutton, Dr. J. Creemers, Dr. P. Raggett, Dr. S. Nussey, Mr. C. Montague, Dr. C. Matthews, Dr. K. Chatterjee, and Dr. O.M. Edwards for helpful discussion; to Dr. Cathrin Orskov for the glucagon assays; to Dr. Nick Martensz, Dr. Fatima Zaidi, and Ms. Fiona Tulloch for technical assistance; and to Ms. Louise Sanders for careful reading of the manuscript.

Source Information

From the Departments of Medicine (S.O., H.G., P.J.H., A.K.) and Clinical Biochemistry (S.O., H.G., P.J.H., A.K., K.T., C.C.), University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom; the Department of Medicine, University of Chicago, Chicago (K.S.P.); and the Department of Medicine, University of Manchester, Hope Hospital, Salford, United Kingdom (A.W., S.G.).

Address reprint requests to Dr. O'Rahilly at the University of Cambridge, Departments of Medicine and Clinical Biochemistry, Addenbrooke's Hospital, Cambridge CB2 2QR, United Kingdom.

References

1. Steiner DF, Tager HS, Chan SJ, Nanjo K, Sanke T, Rubenstein AH. Lessons learned from molecular biology of insulin-gene mutations. Diabetes Care 1990;13:600-609. [Abstract]
2. Haneda M, Polonsky KS, Bergenstal RM, et al. Familial hyperinsulinemia due to a structurally abnormal insulin: definition of an emerging new clinical syndrome. N Engl J Med 1984;310:1288-1294. [Abstract]
3. Nanjo K, Sanke T, Miyano M, et al. Diabetes due to secretion of a structurally abnormal insulin (insulin Wakayama): clinical and functional characteristics of [LeuA3] insulin. J Clin Invest 1986;77:514-519.
4. Nanjo K, Miyano M, Kondo M, et al. Insulin Wakayama: familial mutant insulin syndrome in Japan. Diabetologia 1987;30:87-92. [Medline]
5. Yano H, Kitano N, Morimoto M, Polonsky KS, Imura H, Seino Y. A novel point mutation in the human insulin gene giving rise to hyperproinsulinemia (proinsulin Kyoto). J Clin Invest 1992;89:1902-1907.
6. Chan SJ, Seino S, Gruppuso PA, Schwartz R, Steiner DF. A mutation in the B chain coding region is associated with impaired proinsulin conversion in a family with hyperproinsulinemia. Proc Natl Acad Sci U S A 1987;84:2194-2197. [Free Full Text]
7. Clark PMS, Hales CN. How to measure plasma insulin. Diabetes Metab Rev 1994;10:79-90. [Medline]
8. Given BD, Cohen RM, Shoelson SE, Frank BH, Rubenstein AH, Tager HS. Biochemical and clinical implications of proinsulin conversion intermediates. J Clin Invest 1985;76:1398-1405.
9. White A, Smith H, Hoadley M, Dobson SH, Ratcliffe JG. Clinical evaluation of a two-site immunoradiometric assay for adrenocorticotrophin in unextracted human plasma using monoclonal antibodies. Clin Endocrinol (Oxf) 1987;26:41-51. [Medline]
10. Holst JJ. Evidence that glicentin contains the entire sequence of glucagon. Biochem J 1980;187:337-343. [Medline]
11. Krook A, Kumar S, Laing I, Boulton AJM, Wass JAH, O'Rahilly S. Molecular scanning of the insulin receptor in syndromes of insulin resistance. Diabetes 1994;43:357-368. [Abstract]
12. Crosby SR, Stewart MF, Ratcliffe JG, White A. Direct measurement of the precursors of adrenocorticotropin in human plasma by two-site immunoradiometric assay. J Clin Endocrinol Metab 1988;67:1272-1277. [Free Full Text]
13. Stewart PM, Gibson S, Crosby SR, et al. ACTH precursors characterize the ectopic ACTH syndrome. Clin Endocrinol (Oxf) 1994;40:199-204. [Medline]
14. Williams T, Berelowitz M, Joffe SN, et al. Impaired growth hormone responses to growth hormone-releasing factor in obesity: a pituitary defect reversed with weight reduction. N Engl J Med 1984;311:1403-1407. [Abstract]
15. Gruppuso PA, Gorden P, Kahn CR, Cornblath M, Zeller WP, Schwartz R. Familial hyperproinsulinemia due to a proposed defect in conversion of proinsulin to insulin. N Engl J Med 1984;311:629-634. [Abstract]
16. Elbein SC, Gruppuso P, Schwartz R, Skolnick M, Permutt MA. Hyperproinsulinemia in a family with a proposed defect in conversion is linked to the insulin gene. Diabetes 1985;34:821-824. [Abstract]
17. Revers RR, Henry R, Schmeiser L, et al. The effects of biosynthetic human proinsulin on carbohydrate metabolism. Diabetes 1984;33:762-770. [Abstract]
18. Robbins DC, Tager HS, Rubenstein AH. Biologic and clinical importance of proinsulin. N Engl J Med 1984;310:1165-1175. [Medline]
19. Rhodes CJ, Alarcón C. What beta-cell defect could lead to hyperproinsulinemia in NIDDM? Some clues from recent advances made in understanding the proinsulin-processing mechanism. Diabetes 1994;43:511-517. [Abstract]
20. Rouille Y, Westermark G, Martin SK, Steiner DF. Proglucagon is processed to glucagon by prohormone convertase PC2 in alpha TC1-6 cells. Proc Natl Acad Sci U S A 1994;91:3242-3246. [Free Full Text]
21. Friedman TC, Loh YP, Birch NP. In vitro processing of proopiomelanocortin by recombinant PC1 (SPC3). Endocrinology 1994;135:854-862. [Abstract]
22. Steiner DF, Smeekens SP, Ohagi S, Chan SJ. The new enzymology of precursor processing endoproteases. J Biol Chem 1992;267:23435-23438. [Free Full Text]
23. Nussey SS, Soo SC, Gibson S, et al. Isolated congenital ACTH deficiency: a cleavage enzyme defect? Clin Endocrinol (Oxf) 1993;39:381-385. [Medline]
24. Seidah NG, Marcinkiewicz M, Benjannet S, et al. Cloning and primary sequence of a mouse candidate prohormone convertase PC1 homologous to PC2, Furin, and Kex2: distinct chromosomal localization and messenger RNA distribution in brain and pituitary compared to PC2. Mol Endocrinol 1991;5:111-122. [Free Full Text]
25. Smeekens SP, Avruch AS, LaMendola J, Chan SJ, Steiner DF. Identification of a cDNA encoding a second putative prohormone convertase related to PC2 in AT20 cells and islets of Langerhans. Proc Natl Acad Sci U S A 1991;88:340-344. [Free Full Text]
26. Nakayama K, Hosaka M, Hatsuzawa K, Murakami K. Cloning and functional expression of a novel endoprotease involved in prohormone processing at dibasic sites. J Biochem (Tokyo) 1991;109:803-806. [Free Full Text]
27. Naggert JK, Fricker LD, Varlamov O, et al. Hyperproinsulinaemia in the obese fat/fat mice associated with a carboxypeptidase E mutation which reduces enzyme activity. Nat Genet 1995;10:135-142. [Medline]

PDF Add to Personal Archive Add to Citation Manager Notify a Friend E-mail When Cited Related Article PubMed Citation

This article has been cited by other articles:

• De Pauw, P. E.M., Vermeulen, I., Ubani, O. C., Truyen, I., Vekens, E. M.F., van Genderen, F. T., De Grijse, J. W., Pipeleers, D. G., Van Schravendijk, C., Gorus, F. K. (2008). Simultaneous Measurement of Plasma Concentrations of Proinsulin and C-Peptide and Their Ratio with a Trefoil-Type Time-Resolved Fluorescence Immunoassay. Clin. Chem. 54: 1990-1998 [Abstract] [Full Text]  
• Farooqi, I. S., Volders, K., Stanhope, R., Heuschkel, R., White, A., Lank, E., Keogh, J., O'Rahilly, S., Creemers, J. W. M. (2007). Hyperphagia and Early-Onset Obesity due to a Novel Homozygous Missense Mutation in Prohormone Convertase 1/3. J. Clin. Endocrinol. Metab. 92: 3369-3373 [Abstract] [Full Text]  
• Farooqi, I. S., O'Rahilly, S. (2006). Genetics of Obesity in Humans. Endocr. Rev. 27: 710-718 [Abstract] [Full Text]  
• O'Rahilly, S., Farooqi, I.S. (2006). Genetics of obesity. Phil Trans R Soc B 361: 1095-1105 [Abstract] [Full Text]  
• Lloyd, D. J., Bohan, S., Gekakis, N. (2006). Obesity, hyperphagia and increased metabolic efficiency in Pc1 mutant mice. Hum Mol Genet 15: 1884-1893 [Abstract] [Full Text]  
• Perello, M., Friedman, T., Paez-Espinosa, V., Shen, X., Stuart, R. C., Nillni, E. A. (2006). Thyroid Hormones Selectively Regulate the Posttranslational Processing of Prothyrotropin-Releasing Hormone in the Paraventricular Nucleus of the Hypothalamus. Endocrinology 147: 2705-2716 [Abstract] [Full Text]  
• Richard, I (2005). The genetic and molecular bases of monogenic disorders affecting proteolytic systems. J. Med. Genet. 42: 529-539 [Abstract] [Full Text]  
• Shen, X., Li, Q.-L., Brent, G. A., Friedman, T. C. (2005). Regulation of regional expression in rat brain PC2 by thyroid hormone/characterization of novel negative thyroid hormone response elements in the PC2 promoter. Am. J. Physiol. Endocrinol. Metab. 288: E236-E245 [Abstract] [Full Text]  
• McCarthy, M. I. (2004). Progress in defining the molecular basis of type 2 diabetes mellitus through susceptibility-gene identification. Hum Mol Genet 13: R33-R41 [Abstract] [Full Text]  
• Marzban, L., Trigo-Gonzalez, G., Zhu, X., Rhodes, C. J., Halban, P. A., Steiner, D. F., Verchere, C. B. (2004). Role of {beta}-Cell Prohormone Convertase (PC)1/3 in Processing of Pro-Islet Amyloid Polypeptide. Diabetes 53: 141-148 [Abstract] [Full Text]  
• TAYLOR, N. A., VAN DE VEN, W. J. M., CREEMERS, J. W. M. (2003). Curbing activation: proprotein convertases in homeostasis and pathology. FASEB J. 17: 1215-1227 [Abstract] [Full Text]  
• Fu, Y., Campbell, E. J., Shepherd, T. G., Nachtigal, M. W. (2003). Epigenetic Regulation of Proprotein Convertase PACE4 Gene Expression in Human Ovarian Cancer Cells. Mol Cancer Res 1: 569-576 [Abstract] [Full Text]  
• Chin, D., Oberfield, S. E., Silfen, M. E., McMahon, D. J., Manibo, A. M., Accili, D., Levine, L. S. (2002). Proinsulin in Girls: Relationship to Obesity, Hyperinsulinemia, and Puberty. J. Clin. Endocrinol. Metab. 87: 4673-4677 [Abstract] [Full Text]  
• Zhu, X., Zhou, A., Dey, A., Norrbom, C., Carroll, R., Zhang, C., Laurent, V., Lindberg, I., Ugleholdt, R., Holst, J. J., Steiner, D. F. (2002). Disruption of PC1/3 expression in mice causes dwarfism and multiple neuroendocrine peptide processing defects. Proc. Natl. Acad. Sci. USA 99: 10293-10298 [Abstract] [Full Text]  
• Zhu, X., Orci, L., Carroll, R., Norrbom, C., Ravazzola, M., Steiner, D. F. (2002). Severe block in processing of proinsulin to insulin accompanied by elevation of des-64,65 proinsulin intermediates in islets of mice lacking prohormone convertase 1/3. Proc. Natl. Acad. Sci. USA 99: 10299-10304 [Abstract] [Full Text]  
• Kalantaridou, S. N., Chrousos, G. P. (2002). Monogenic Disorders of Puberty. J. Clin. Endocrinol. Metab. 87: 2481-2494 [Full Text]  
• Pierroz, D. D., Ziotopoulou, M., Ungsunan, L., Moschos, S., Flier, J. S., Mantzoros, C. S. (2002). Effects of Acute and Chronic Administration of the Melanocortin Agonist MTII in Mice With Diet-Induced Obesity. Diabetes 51: 1337-1345 [Abstract] [Full Text]  
• Li, Q.-L., Jansen, E., Brent, G. A., Friedman, T. C. (2001). Regulation of prohormone convertase 1 (PC1) by thyroid hormone. Am. J. Physiol. Endocrinol. Metab. 280: E160-E170 [Abstract] [Full Text]  
• Li, Q.-L., Jansen, E., Brent, G. A., Naqvi, S., Wilber, J. F., Friedman, T. C. (2000). Interactions between the Prohormone Convertase 2 Promoter and the Thyroid Hormone Receptor. Endocrinology 141: 3256-3266 [Abstract] [Full Text]  
• Farooqi, I S., O'Rahilly, S. (2000). Recent advances: Recent advances in the genetics of severe childhood obesity. Arch. Dis. Child. 83: 31-34 [Abstract] [Full Text]  
• Yeo, G.S.H., Farooqi, I.S., Challis, B.G., Jackson, R.S., O'Rahilly, S. (2000). The role of melanocortin signalling in the control of body weight: evidence from human and murine genetic models. QJM 93: 7-14 [Abstract] [Full Text]  
• Zhou, A., Webb, G., Zhu, X., Steiner, D. F. (1999). Proteolytic Processing in the Secretory Pathway. J. Biol. Chem. 274: 20745-20748 [Full Text]  
• Lee, E. C. C., Walmsley, S., Fantus, I. G. (1999). New-onset diabetes mellitus associated with protease inhibitor therapy in an HIV-positive patient: case report and review. CMAJ 161: 161-164 [Full Text]  
• Bogardus, S. T. Jr, Concato, J., Feinstein, A. R. (1999). Clinical Epidemiological Quality in Molecular Genetic Research: The Need for Methodological Standards. JAMA 281: 1919-1926 [Abstract] [Full Text]  
• Furuta, M., Carroll, R., Martin, S., Swift, H. H., Ravazzola, M., Orci, L., Steiner, D. F. (1998). Incomplete Processing of Proinsulin to Insulin Accompanied by Elevation of Des-31,32 Proinsulin Intermediates in Islets of Mice Lacking Active PC2. J. Biol. Chem. 273: 3431-3437 [Abstract] [Full Text]  
• Gabreëls, B. A. Th. F., Swaab, D. F., de Kleijn, D. P. V., Seidah, N. G., Van de Loo, J.-W., Van de Ven, W. J. M., Martens, G. J. M., van Leeuwen, F. W. (1998). Attenuation of the Polypeptide 7B2, Prohormone Convertase PC2, and Vasopressin in the Hypothalamus of Some Prader-Willi Patients: Indications for a Processing Defect. J. Clin. Endocrinol. Metab. 83: 591-599 [Abstract] [Full Text]  
• Jansen, E., Ayoubi, T. A.Y., Meulemans, S. M.P., Van de Ven, W. J.M. (1997). Cell Type-specific Protein-DNA Interactions at the cAMP Response Elements of the Prohormone Convertase 1Promoter. EVIDENCE FOR ADDITIONAL TRANSACTIVATORS DISTINCT FROM CREB/ATF FAMILY MEMBERS. J. Biol. Chem. 272: 2500-2508 [Abstract] [Full Text]  
• Nishigori, H., Tomura, H., Tonooka, N., Kanamori, M., Yamada, S., Sho, K., Inoue, I., Kikuchi, N., Onigata, K., Kojima, I., Kohama, T., Yamagata, K., Yang, Q., Matsuzawa, Y., Miki, T., Seino, S., Kim, M.-Y., Choi, H.-S., Lee, Y.-K., Moore, D. D., Takeda, J. (2001). Mutations in the small heterodimer partner gene are associated with mild obesity in Japanese subjects. Proc. Natl. Acad. Sci. USA 98: 575-580 [Abstract] [Full Text]