Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Proprotein Convertases”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36Linked to original sources
PubMed1995

Immunocytochemical investigation of insulin secretion by pancreatic beta-cells in control and diabetic Psammomys obesus.

Hyperproinsulinemia is a characteristic feature of non-insulin-dependent diabetes mellitus (NIDDM) caused by pancreatic beta-cell dysfunction through a secretion-related alteration or impaired proinsulin processing. We have investigated the insulin processing and secretion in Psammomys obesus fed with low- and high-energy diets, which represent a model for diet-induced NIDDM. With a high-energy diet the animals develop hyperglycemia and hyperinsulinemia, whereas those maintained on a low-energy diet remain normoglycemic. Although a large amount of insulin immunoreactivity was detected in beta-cells of the normoglycemic compared to hyperglycemic animals, in situ hybridization for insulin mRNA demonstrated a particularly high signal in the beta-cells of the hyperglycemic animals. By electron microscopy, the beta-cells of normoglycemic animals displayed large accumulations of secretory granules, whereas those of the hyperglycemic animals contained very few granules and large deposits of glycogen. These results reflect a secretory resting condition for the cells of the normoglycemic animals in contrast to stimulated synthetic and secretory activities in the cells of the hyperglycemic ones. Using colloidal gold immunocytochemistry at the electron microscopic level, we have examined subcellular proinsulin processing in relation to the convertases PC1 and PC2. Immunolabeling of proinsulin, insulin, C-peptide, PC1, and PC2 in different cell compartments involved in beta-cell secretion were evaluated. Both PC1 and PC2 antigenic sites were detected in beta-cells of hyperglycemic Psammomys, but their labeling intensity was weak compared to the cells of normoglycemic animals. In both groups of animals, higher levels of PC2 were found in the Golgi apparatus than in the immature granules. Major decreases in proinsulin, insulin, PC1, and PC2 immunoreactivity were recorded in beta-cells of the hyperglycemic Psammomys. In addition, all these antigenic sites were detected in lysosome-like structures, revealing a major degradation process. These results suggest that the insulin-secreting cells in hyperglycemic Psammomys obesus are in a chronic secretory state during which impaired processing of proinsulin appears to take place.

Animals↗
PubMed1992

Prohormone convertase-1 will process prorelaxin, a member of the insulin family of hormones.

Relaxin is a polypeptide hormone involved in remodeling of the birth canal during parturition. It is synthesized as a preprohormone precursor, which undergoes specific processing to form the mature two-chain disulfide-linked active species that is secreted by the cell. A major part of this processing requires endoproteolytic cleavage at specific pairs of basic amino acid residues, an event necessary for the maturation of a variety of important biologically active proteins, such as insulin and nerve growth factor. Human type 2 preprorelaxin was coexpressed in human kidney 293 cells with the candidate prohormone convertase-processing enzymes mPC1 or mPC2, both cloned from the mouse pituitary tumor AtT-20 cell line, or with the yeast kex2 alpha-mating factor-converting enzyme from Saccharomyces cerevisiae. Prorelaxin expressed alone in 293 cells was secreted into the culture medium unprocessed. Transient coexpression with mPC1 or kex2, but not with mPC2, resulted in the secretion of a low mol wt species with an electrophoretic mobility very similar, if not identical, to that of authentic mature relaxin purified from human placenta. This species was precipitable by monoclonal antibodies specific for relaxin and had a retention time on reverse phase HPLC comparable to that of relaxin. Its analysis by both electrospray and fast atom bombardment mass spectrometry generated mass data that were consistent only with mature relaxin. The basic residues required for mPC1-dependent cleavage of prorelaxin are defined by site-directed mutagenesis.

Amino Acid Sequence↗
PubMed1997

Obesity and impaired prohormone processing associated with mutations in the human prohormone convertase 1 gene.

Human obesity has an inherited component, but in contrast to rodent obesity, precise genetic defects have yet to be defined. A mutation of carboxypeptidase E (CPE), an enzyme active in the processing and sorting of prohormones, causes obesity in the fat/fat mouse. We have previously described a women with extreme childhood obesity (Fig. 1), abnormal glucose homeostasis, hypogonadotrophic hypogonadism, hypocortisolism and elevated plasma proinsulin and pro-opiomelanocortin (POMC) concentrations but a very low insulin level, suggestive of a defective prohormone processing by the endopeptidase, prohormone convertase 1 (PC1; ref. 4). We now report this proband to be a compound heterozygote for mutations in PC1. Gly-->Arg483 prevents processing of proPC1 and leads to its retention in the endoplasmic reticulum (ER). A-->C+4 of the intro-5 donor splice site causes skipping of exon 5 leading to loss of 26 residues, a frameshift and creation of a premature stop codon within the catalytic domain. PC1 acts proximally to CPE in the pathway of post-translational processing of prohormones and neuropeptides. In view of the similarity between the proband and the fat/fat mouse phenotype, we infer that molecular defects in prohormone conversion may represent a generic mechanism for obesity, common to humans and rodents.

Amino Acid Sequence↗
PubMed2004

Perinatal food deprivation induces marked alterations of the hypothalamo-pituitary-adrenal axis in 8-month-old male rats both under basal conditions and after a dehydration period.

Dehydration is a classic homeostatic stressor in rats that leads to a series of endocrine responses including stimulation of the hypothalamo-pituitary-adrenal (HPA) axis. During the last decade, it has been well established that perinatal food restriction is associated with the onset of diseases in adults. Our previous demonstration of long-term alterations in HPA axis activity in both basal conditions and after a 72-hour dehydration period in 4-month-old rats exposed to a 50% maternal food restriction (FR50) in late gestation and lactation prompted us to investigate whether such perinatal undernutrition further affects HPA axis activity in mature animals. As previously described in 4-month-old rats under basal conditions, 8-month-old FR50 rats showed reduced body weight and an enhanced ratio between mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) mRNA levels in the hippocampus, as well as increased pro-opiomelanocortin (POMC) mRNA levels in the adenohypophysis. In addition, numerous additional alterations appeared in mature rats. In the hypothalamus, levels of vasopressin (VP) mRNAs were increased both in the paraventricular nucleus (PVN) and in the supraoptic nucleus (SON). In the adenohypophysis, GR and prohormone-convertase 2 (PC2) mRNA levels were significantly increased, whereas prohormone-convertase 1 (PC1) mRNA was not affected by maternal undernutrition. Interestingly, undernourished animals exhibited high plasma levels of total and free corticosterone in spite of normal corticotropin (ACTH) levels, an indication that HPA basal activity is enhanced by maternal undernutrition in 8-month-old animals. Dehydration for 72 h induced a rise in ACTH plasma levels, but did not modify total and free corticosterone plasma levels in 8-month-old FR50 animals. In the adenopituitary, POMC mRNA levels were decreased after dehydration but PC1 mRNA levels were unaffected. The present study indicates that maternal food restriction during the perinatal period dramatically affects the activity of the HPA axis until the age of 8 months. We speculate that higher basal HPA activity and an inadequate HPA response after dehydration in mature animals may contribute to diseases such as hypertension, known to develop with aging in perinatally growth-restricted rats.

Adrenocorticotropic Hormone↗
PubMed2001

Human dermal fibroblasts express prohormone convertases 1 and 2 and produce proopiomelanocortin-derived peptides.

In the last few years it has become apparent that the skin is a locoregional source for several proopiomelanocortin-derived peptides including alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin. The enzymes that regulate expression of these neuropeptides are the prohormone convertases 1 and 2. In this study we demonstrate, by reverse transcriptase polymerase chain reaction and Western immunoblotting, that cultured human dermal fibroblasts express prohormone convertases 1 and 2 as well as 7B2, which is an essential cofactor for enzymatic activity of prohormone convertase 2. Immunofluorescence studies revealed prohormone convertase 1 to be mainly expressed in the perinuclear region in vesicular structures resembling the trans-Golgi network, whereas prohormone convertase 2 was found in the trans-Golgi network as well as in vesicular structures diffusely distributed in the peripheral cytoplasm. Expression of both enzymes was also confirmed in fibroblasts of normal adult human skin by immunohistochemistry using antibodies against prohormone convertases 1 and 2 and vimentin. To assess the relevance of prohormone convertase 1 and 2 expression in human dermal fibroblasts, we studied the expression of proopiomelanocortin and proopiomelanocortin-derived peptides. Proopiomelanocortin expression was detected by reverse transcriptase polymerase chain reaction and Western immunoblotting. Alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin were mainly located in vesicular structures as demonstrated by immunofluorescence. Production of these peptides was confirmed by radioimmunoassay, immunoradiometric assay, or enzyme immunoassay. Among several stimuli tested, interleukin-1 was found to upregulate production of alpha-melanocyte-stimulating hormone in human dermal fibroblasts. In summary, we have shown that human dermal fibroblasts express the enzymatic machinery for proopiomelanocortin processing and make proopiomelanocortin, alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin. Production of proopiomelanocortin peptides by human dermal fibroblasts may be relevant for fibroblast functions such as collagen degradation and/or regulation of dermal immune responses.

Adrenocorticotropic Hormone↗
PubMed2006

Thyroid hormones selectively regulate the posttranslational processing of prothyrotropin-releasing hormone in the paraventricular nucleus of the hypothalamus.

Over the last few years, our laboratory has demonstrated that different physiological conditions or stressors affect the posttranslational processing of hypophysiotropic and nonhypophysiotropic proTRH and, consequently, the output of TRH and other proTRH-derived peptides. These alterations in proTRH processing are generally associated with parallel changes in the levels of two members of the family of prohormone convertases 1/3 and 2 (PC1/3 and PC2). An important regulator of proTRH is thyroid hormone, which is the peripheral end product of the hypothalamic (TRH)-pituitary (TSH)-thyroid (T3/4) (HPT) axis. In this study we investigated the effect of thyroid status on the processing of proTRH inside and outside the HPT axis. Our data showed that high levels of thyroid hormone down-regulated PC1/3 and PC2 and TRH synthesis, which led to an accumulation of intermediate forms of proTRH processing. Conversely, low levels of thyroid hormone up-regulated proTRH synthesis and PC1/3 and PC2 levels. Control of the activity of PCs and proTRH processing occurred specifically in the paraventricular nucleus, whereas no change due to thyroid status was found in the lateral hypothalamus or preoptic area. The posttranslational regulation of proTRH processing in the paraventricular nucleus by thyroid status is a novel aspect of the regulation of the HPT axis, which may have important implications for the pathophysiology of hypo- and hyperthyroidism.

Animals↗
PubMed1998

Prohormone convertase 1 (PC1) when expressed with pro cholecystokinin (pro CCK) in L cells performs three endoproteolytic cleavages which are observed in rat brain and in CCK-expressing endocrine cells in culture, including the production of glycine and arginine extended CCK8.

Pro CCK was expressed in an L cell line engineered to express PC1 and the products secreted into the media were characterized by a combination of RIA, gel filtration and HPLC. PC1 released from L cells, cleaved pro CCK generating the amino terminal pro peptide. PC1 also generated a peptide which after carboxypeptidase B treatment, was detected with an antiserum specific for CCK Gly. Neither of these peptides was found in media from L cells expressing pro CCK alone. This CCK Gly immunoreactive peptide was similar in size to CCK 8, and after treatment with arylsulfatase and carboxypeptidase B, it co-eluted on HPLC with unsulfated CCK 8 Gly. These results agree with previous studies which support a role for PC1 in generation of CCK 8. This is the first demonstration that PC1 acting alone is able to cleave pro CCK liberating the amino terminal pro peptide and a glycine and arginine extended CCK 8 which is the immediate precursor of CCK 8 amide.

Amino Acid Sequence↗
PubMed2003

Frequent appearance of autoantibodies against prohormone convertase 1/3 and neuroendocrine protein 7B2 in patients with nonfunctioning pituitary macroadenoma.

Among pituitary disorders having mass effect of the pituitary gland, nonfunctioning pituitary macroadenoma and lymphocytic hypophysitis are difficult to differentiate without histological examination. In order to efficiently distinguish lymphocytic hypophysitis and pituitary tumors, we studied the presence of autoantibodies against prohormone-processing enzymes, prohormone convertase (PC) 1/3, PC2, carboxypeptidase E (CPE), and PC2 regulatory protein, 7B2, by radioligand assay using recombinant human 35S-labeled protein in patients with clinically nonfunctioning pituitary macroadenoma, lymphocytic hypophysitis, and other pituitary diseases. The indexes for anti-PC1/3 antibodies (Ab) were significantly higher in patients with nonfunctioning pituitary macroadenoma than in patients with lymphocytic hypophysitis. Patients positive for either anti-PC1/3 or anti-7B2 Ab were significantly frequent among patients with nonfunctioning pituitary macroadenoma than in other pituitary diseases and healthy controls. None of the patients was positive for anti-PC2 Ab or anti-CPE Ab. These results suggest that autoantibodies against PC1/3 and 7B2 are novel tumor-associated autoantibodies and can be helpful in the diagnosis of clinically nonfunctioning pituitary macroadenoma.

Adenoma↗
PubMed1998

Localization of prohormone convertases 1/3 and 2 in the human pituitary gland and pituitary adenomas: analysis by immunohistochemistry, immunoelectron microscopy, and laser scanning microscopy.

Prohormone convertase (PC) 1/3 and PC2 are involved in post-translational processing of endocrine tissues, including the pancreatic islets and pituitary glands. Our immunohistochemical studies disclosed the presence of PC1/3 and PC2 in non-neoplastic pituitary glands, especially in corticotrophs, gonadotrophs, and thyrotrophs. Among 58 pituitary adenomas obtained by trans-sphenoidal surgery, adrenocorticotropin (ACTH)-secreting adenomas showed a high incidence of the presence of PC1/3 and PC2, i.e., nine of nine cases were positive for ACTH. Five of nine cases showed consistency between PC2 localization and alpha-melanocyte stimulating hormone immunoreactivity, which suggests the functional correlation between PC2 and the processing of ACTH. In four cases, we observed inconsistency in immunolocalization, which suggested the possibility of inactive PC2 and abnormal processing of alpha-melanocyte stimulating hormone. The high incidence of PC1/3 and PC2 in nonfunctioning adenomas might be related to the processing of chromogranin A.

Adenoma↗
PubMed2000

Processing of synthetic pro-islet amyloid polypeptide (proIAPP) 'amylin' by recombinant prohormone convertase enzymes, PC2 and PC3, in vitro.

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.

Amyloid↗
PubMed1997

Molecular characterization and differential gene induction of the neuroendocrine-specific genes neurotensin, neurotensin receptor, PC1, PC2, and 7B2 in the human ocular ciliary epithelium.

The ocular ciliary epithelium is a bilayer of neuroepithelial cells specialized in the secretion of aqueous humor fluid and the regulation of intraocular pressure. In this study, we report on the expression of the regulatory peptide neurotensin (NT) and a set of differentiated neuroendocrine markers including neurotensin receptors (NTrs), the prohormone convertases furin, PC1, and PC2, and the neuroendocrine polypeptide 7B2 in the ciliary epithelium. Using a human cell line, ODM-2, derived from the nonpigmented ciliary epithelium, we demonstrate that (1) NT expression is highly activated by nerve growth factor, glucocorticoid, and activators of adenylate cyclase; (2) NTr expression is up-regulated by selective ligand-activated beta2-adrenergic receptor; and (3) PC1 and PC2 expression are up-regulated via distinct signaling transduction pathways. PC1 gene expression is activated by phorbol ester, and PC2 by the same inducers as those of NT expression. A radioimmunoassay for NT detected an NT-like immunoreactivity in human ciliary epithelium and ODM-2 cell extracts, in aqueous humor, and in conditioned culture medium. The results support the view that the entire ciliary epithelium functions as a neuroendocrine tissue, synthesizing, processing, and releasing NT into the aqueous humor where it may exert important physiological functions through autocrine and/or paracrine mechanisms.

Aspartic Acid Endopeptidases↗
PubMed1991

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.

Using a 796-basepair cDNA fragment obtained from a mouse pituitary library we have screened two mouse insulinoma libraries and isolated a full-length cDNA clone (2516 basepairs; 753 amino acids), designated mPC1. The cDNA sequence of mPC1 codes for a protein containing 753 amino acids and three potential N-glycosylation sites. This cDNA encodes a putative novel subtilisin-like proteinase, exhibiting within its presumed catalytic domain 64%, 55%, and 47% amino acid sequence identity to the recently characterized candidate prohormone convertases human Furin, mouse PC2, and yeast Kex2 gene products, respectively. An identical sequence to mPC1 was derived from a cDNA library of mouse corticotroph AtT-20 tumor cells. An ArgGlyAsp tripeptide identical to the recognition sequence of integrins was observed in the structures of the mammalian PC1, PC2, and Furin. In situ hybridization results demonstrated a distinct localization of the mPC1 and mPC2 transcripts in pituitary and brain. Thus, whereas both mPC1 and mPC2 are found in the intermediate lobe of the pituitary, only mPC1 is easily detected in the anterior lobe. In extrahypothalamic regions of the brain, including cortex, hippocampus, thalamus, and spinal cord, mPC2 transcripts predominate over mPC1. Both mRNAs are found in only a fraction of hypothalamic neurons, with greater abundance of mPC1 over mPC2 in the supraoptic nucleus. The genes coding for mPC1 and mPC2 map to the murine chromosomes 13 (band 13c) and 2 (2F3-2H2 region), respectively.

Amino Acid Sequence↗
PubMed1998

Immunocytochemical localization of the prohormone convertases PC1 and PC2 in rat prolactin cells.

The prohormone convertases PC1 and PC2 are subtilisin-related endopeptidases that process prohormone and neuropeptide precursors. Using different ultrastructural immunocytochemical approaches, we have investigated their intracellular distribution in a neuroendocrine cell type that has not been examined thus far, the rat anterior pituitary lactotrope. These cells secrete mainly prolactin and also express the neuroendocrine-specific protein secretogranin II, which is considered a peptide precursor. Our study provides evidence for the expression of PC1 and PC2 in rat lactotropes and provides new information on their subcellular localization. Apart from their presence in the secretory granules, PC1 and PC2 displayed different major localization along the secretory pathway. PC1 immunoreactivity was concentrated in the Golgi apparatus, whereas PC2 immunoreactivity was prominent in the rough endoplasmic reticulum (RER). These observations provide morphological support for previous biochemical analysis of proPC1 and proPC2 post-translational processing, which has demonstrated that PC1 exits very rapidly from the RER, whereas PC2 is retained much longer in this compartment. (J Histochem Cytochem 46:101-108, 1998)

Animals↗
PubMed2000

Regulation of the biosynthesis and processing of chromogranins in organotypic slices: influence of depolarization, forskolin and differentiating factors.

Slices from rat hippocampus in organotypic culture were used to study the biosynthesis regulation of chromogranins A and B and secretogranin II. Additionally, we investigated the proteolytic conversion of secretogranin II and the levels of prohormone convertases putatively involved. Forskolin treatment and depolarization with potassium plus BayK 8644 led to significant increases in secretogranin II mRNA in the principal cells of the hippocampus. Enhanced expression of secretogranin II was also reflected by a rise in peptide levels. Despite this induction of biosynthesis the extensive processing to secretoneurin normally observed in brain was maintained. Both forskolin and depolarization upregulated the prohormone convertase (PC)1, but not PC2, indicating that PC1 levels are critical for secretoneurin production under stimulating conditions. Results obtained for chromogranins A and B were less consistent. For chromogranin A mRNA, changes were restricted to granule cells; for chromogranin B, a response in granule cells was observed to depolarization but not to forskolin, and effects in pyramidal neurons were weak. Accordingly, we were unable to detect alterations in chromogranin A and B protein levels. Furthermore, we tested several neurotrophic growth factors and found that only basic fibroblast growth factor raised secretogranin II expression without affecting chromogranins A and B. The hippocampal slice preparation allowed well controlled treatment with identification of neuronal subpopulations and yielded data largely matching experiments in vivo and in cell culture. The pronounced regulation of secretogranin II and its effective processing underlines the importance of the resulting peptide secretoneurin as an active neuropeptide in the nervous system.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2003

Molecular cloning and expression of prohormone convertases PC1 and PC2 in the pituitary gland of the bullfrog, Rana catesbeiana.

We cloned cDNAs encoding PC1 and PC2 from a cDNA library constructed for the anterior pituitary gland of the bullfrog (Rana catesbeiana) and sequenced them. The bullfrog PC1 cDNA consisted of 2972 base pairs (bp) with an open reading frame of 2208 bp and encoded a protein of 736 amino acids, including a putative signal peptide of 26 amino acids. The protein showed a high homology to R. ridibunda PC1 (95.1%) and mammalian PC1 (72.6%). The bullfrog PC2 cDNA consisted of 2242 bp with an open reading frame of 1914 bp and encoded a protein of 638 amino acids, including a putative signal peptide of 23 amino acids. This protein showed a high homology to R. ridibunda PC2 (95.5%) and mammalian PC2 (84.8%). The catalytic triad of serine proteinases of the subtilisin family was found at Asp-168, His-209, and Ser-383 in the PC1 protein and at Asp-167, His-208, and Ser-384 in the PC2 protein. In situ hybridization staining revealed that PC2 mRNA was detected in corticotrope cells of the tadpoles, but not in those of the adults. In the adult, only PC1 mRNA was detected in the pars distalis but both PC1 and PC2 mRNAs were detected in the pars intermedia. The data also showed that PC1 mRNA was expressed in gonadotrope cells.

Amino Acid Sequence↗
PubMed2000

Immunohistochemical expression of chromogranins A and B, prohormone convertases 2 and 3, and amidating enzyme in carcinoid tumors and pancreatic endocrine tumors.

Although chromogranin A (CgA) is widely distributed in neuroendocrine tumors, the distribution of chromogranin B (CgB) has not been elucidated. Hormones produced by tumors are sometimes prohormones and not necessarily bioactive hormones. Prohormones have to be processed into bioactive peptides by prohormone convertases (PCs), and some of them have to be amidated by peptidylglycine a-amidating monooxygenase (PGM). Whether PCs and PGM are present or not in tumors may explain why some tumors are functioning and some are nonfunctioning. We investigated 45 carcinoids and 16 pancreatic endocrine tumors. Of the carcinoids, CgA was expressed in most of the tumors, except for the rectal and ovarian carcinoids, which expressed CgB strongly. The expressions of PC2, PC3, and PGM were 31%, 100%, and 87%, respectively. In the pancreatic tumors, CgA was expressed in all tumors, whereas CgB was not expressed in any tumor. The expressions of PC2, PC3, and PGM were 63%, 88%, and 63%, respectively. PC3 was expressed in all of the functioning tumors but not in two of the four nonfunctioning tumors. PC2 and PGM were not expressed in three of the four nonfunctioning tumors. In conclusion, expression of CgA and CgB was different depending on the tumor location. High frequency of PCs and PGM may explain why even nonfunctioning tumors produce some inconspicuous peptides.

Adenoma, Islet Cell↗
PubMed1997

Proteolytic processing of pro-opiomelanocortin occurs in acidifying secretory granules of AtT-20 cells.

Using antibodies specific for pro-opiomelanocortin (POMC), amidated joining peptide (JP), and the prohormone convertase PC1, we showed immunocytochemically that PC1 in a corticotrophic tumor cell line, AtT-20, was co-localized either with POMC or with amidated JP in secretory granules, and also confirmed that POMC was cleaved mainly in secretory granules. Analysis using DAMP (3- [2,4-dinitroanilino]-3'-amino-N-methyldipropylamine) as the pH probe suggested a correlation between POMC processing and acidic pH in the secretory granules. Bafilomycin A1, a specific inhibitor of vacuolar-type H(+)-ATPase, completely inhibited POMC processing and caused constitutive secretion of the unprocessed precursor. By contrast, chloroquine, a weak base that is known to neutralize acidic organelles, was unable to inhibit POMC processing. Electron microscopic analysis revealed that, in AtT-20 cells treated with bafilomycin A1, the trans-Golgi cisternae were dilated and few secretory granules were present in the cytoplasm. These observations suggest that acidic pH provides a favorable environment for proteolytic processing of POMC by PC1 but is not required, and that integrity of the trans-Golgi network and sorting of POMC into secretory granules are important for POMC processing.

Animals↗
PubMed2000

The C-terminal region of proSAAS is a potent inhibitor of prohormone convertase 1.

ProSAAS is a recently discovered 26-kDa neuroendocrine protein that was previously found to inhibit prohormone convertase (PC) 1 and not PC2. In the present study, the specificity of proSAAS toward other members of the prohormone convertase family was determined. Two microm proSAAS selectively inhibits PC1 but not furin, PACE4, PC5A, or PC7. The PC1 inhibitory region of proSAAS was mapped to an 8-12-residue region near the C terminus that includes a critical Lys-Arg sequence. Synthetic peptides corresponding to this region are competitive inhibitors of PC1 with apparent K(i) values of 14-40 nm. The inhibition becomes more effective with incubation time, indicating that the inhibitor is slow binding. A fusion protein containing the inhibitory region of proSAAS linked to the C terminus of glutathione S-transferase binds the 71-kDa form but not the 85-kDa form of PC1. This binding, which occurs at pH 5.5 and not at pH 7.4, is stable to incubation at room temperature for 1 h in the presence or absence of 0.5% Triton X-100 and/or 0.5 m NaCl. The removal of Ca(2+) with chelating agents partially releases the bound PC1. High concentrations of the inhibitory peptide quantitatively release the bound PC1. Taken together, these data support the proposal that proSAAS functions as an endogenous inhibitor of PC1.

Amino Acid Sequence↗