Isolation of human pancreastatin fragment containing the active sequence from a glucagonoma

The immunomodulatory functions of chromogranin A-derived peptide pancreastatin

Chromogranin A (CgA) is a 439 amino acid protein secreted by neuroendocrine cells. Proteolytic processing of CgA results in the production of different bioactive peptides. These peptides have been associated with inflammatory bowel disease, diabetes, and cancer. One of the chromogranin A-derived peptides is ∼52 amino acid long Pancreastatin (PST: human (h)CgA250-301, murine (m)CgA263-314). PST is a glycogenolytic peptide that inhibits glucose-induced insulin secretion from pancreatic islet β-cells. In addition to this metabolic role, evidence is emerging that PST also has inflammatory properties. This review will discuss the immunomodulatory properties of PST and its possible mechanisms of action and regulation. Moreover, this review will discuss the potential translation to humans and how PST may be an interesting therapeutic target for treating inflammatory diseases.

Naturally occurring variants of the dysglycemic peptide pancreastatin: differential potencies for multiple cellular functions and structure-function correlation

Pancreastatin (PST), a chromogranin A-derived peptide, is a potent physiological inhibitor of glucose-induced insulin secretion. PST also triggers glycogenolysis in liver and reduces glucose uptake in adipocytes and hepatocytes. Here, we probed for genetic variations in PST sequence and identified two variants within its functionally important carboxyl terminus domain: E287K and G297S. To understand functional implications of these amino acid substitutions, we tested the effects of wild-type (PST-WT), PST-287K, and PST-297S peptides on various cellular processes/events. The rank order of efficacy to inhibit insulin-stimulated glucose uptake was: PST-297S > PST-287K > PST-WT. The PST peptides also displayed the same order of efficacy for enhancing intracellular nitric oxide and Ca(2+) levels in various cell types. In addition, PST peptides activated gluconeogenic genes in the following order: PST-297S ≈ PST-287K > PST-WT. Consistent with these in vitro results, the common PST variant allele Ser-297 was associated with significantly higher (by ∼17 mg/dl, as compared with the wild-type Gly-297 allele) plasma glucose level in our study population (n = 410). Molecular modeling and molecular dynamics simulations predicted the following rank order of α-helical content: PST-297S > PST-287K > PST-WT. Corroboratively, circular dichroism analysis of PST peptides revealed significant differences in global structures (e.g. the order of propensity to form α-helix was: PST-297S ≈ PST-287K > PST-WT). This study provides a molecular basis for enhanced potencies/efficacies of human PST variants (likely to occur in ∼300 million people worldwide) and has quantitative implications for inter-individual variations in glucose/insulin homeostasis.

Production and Regulation of Levels of Amidated Peptide Hormones

Peptide hormones with a C-terminal amide regulate numerous physiological processes and are associated with many disease states. Consequently, the key enzymes involved in their production, peptidylglycine α-amidating monooxygenase and carboxypeptidase E, have been studied intensively. This review surveys what is known about the enzymes themselves and their cofactors, as well as their substrates and competitive and mechanism-based inhibitors.

Reprint of: Metabolic effects and mechanism of action of the chromogranin A-derived peptide pancreastatin

Pancreastatin is one of the regulatory peptides derived from intracellular and/or extracellular processing of chromogranin A, the soluble acidic protein present in the secretory granules of the neuroendocrine system. While the intracellular functions of chromogranin A include formation and maturation of the secretory granule, the major extracellular functions are generation of biologically active peptides with demonstrated autocrine, paracrine or endocrine activities. In this review, we will focus on the metabolic function of one of these peptides, pancreastatin, and the mechanisms underlying its effects. Many different reported effects have implicated PST in the modulation of energy metabolism, with a general counterregulatory effect to that of insulin. Pancreastatin induces glycogenolysis in liver and lipolysis in adipocytes. Metabolic effects have been confirmed in humans. Moreover, naturally occurring human variants have been found, one of which (Gly297Ser) occurs in the functionally important carboxy-terminus of the peptide, and substantially increases the peptide's potency to inhibit cellular glucose uptake. Thus, qualitative hereditary alterations in pancreastatin's primary structure may give rise to interindividual differences in glucose and lipid metabolism. Pancreastatin activates a receptor signaling system that belongs to the seven-spanning transmembrane receptor coupled to a Gq-PLCβ-calcium-PKC signaling pathway. Increased pancreastatin plasma levels, correlating with catecholamines levels, have been found in insulin resistance states, such as gestational diabetes or essential hypertension. Pancreastatin plays important physiological role in potentiating the metabolic effects of catecholamines, and may also play a pathophysiological role in insulin resistance states with increased sympathetic activity.

Metabolic effects and mechanism of action of the chromogranin A-derived peptide pancreastatin

Pancreastatin is one of the regulatory peptides derived from intracellular and/or extracellular processing of chromogranin A, the soluble acidic protein present in the secretory granules of the neuroendocrine system. While the intracellular functions of chromogranin A include formation and maturation of the secretory granule, the major extracellular functions are generation of biologically active peptides with demonstrated autocrine, paracrine or endocrine activities. In this review, we will focus on the metabolic function of one of these peptides, pancreastatin, and the mechanisms underlying its effects. Many different reported effects have implicated PST in the modulation of energy metabolism, with a general counterregulatory effect to that of insulin. Pancreastatin induces glycogenolysis in liver and lipolysis in adipocytes. Metabolic effects have been confirmed in humans. Moreover, naturally occurring human variants have been found, one of which (Gly297Ser) occurs in the functionally important carboxy-terminus of the peptide, and substantially increases the peptide's potency to inhibit cellular glucose uptake. Thus, qualitative hereditary alterations in pancreastatin's primary structure may give rise to interindividual differences in glucose and lipid metabolism. Pancreastatin activates a receptor signaling system that belongs to the seven-spanning transmembrane receptor coupled to a Gq-PLCbeta-calcium-PKC signaling pathway. Increased pancreastatin plasma levels, correlating with catecholamines levels, have been found in insulin resistance states, such as gestational diabetes or essential hypertension. Pancreastatin plays important physiological role in potentiating the metabolic effects of catecholamines, and may also play a pathophysiological role in insulin resistance states with increased sympathetic activity.

The chromogranins: their roles in secretion from neuroendocrine cells and as markers for neuroendocrine neoplasia

Chromogranins are the major components of the secretory granules of most neuroendocrine cells. Within the secretory pathway, chromogranins are involved in granulogenesis, and in sorting and processing of secretory protein cargo prior to secretion. Once secreted, they have hormonal, autocrine, and paracrine activities. The chromogranin family includes chromogranins A (CgA) and B (CgB) and secretogranin II (SgII, once called chromogranin C). The related "granins" NESP55, 7B2, secretogranin III/1B 1075 (SgIII), and secretogranin IV/HISL-19 antigen (SgIV), are also sometimes included when considering the chromogranins. While it is useful to consider the granin proteins as a family with many common features, it is also necessary to examine the distinct features and properties of individual members of the granin family to understand fully their functions, employ them efficiently as tissue, serum, and urinary markers for neuroendocrine neoplasia, and develop an evolutionary-biologic perspective on their contribution to mammalian physiology. Recent advances in chromogranin research include establishing the role of CgA in granulogenesis and the role of CgB in nuclear transcription; new biologic activities for CgA-, CgB-, and SgII-derived peptides; and new marker functions for granins and their proteolytically processed products in endocrine neoplasias.

Prohormone convertase-1 is essential for conversion of chromogranin A to pancreastatin

The purpose of this study was to test the hypothesis that the endoprotease, prohormone convertase-1 (PC-1), is involved in the processing of the precursor protein chromogranin A (CGA) to a smaller peptide called pancreastatin (PST). A human pancreatic carcinoid cell line (BON) that expresses PC-1, CGA and PST was stably transfected with antisense PC-1 mRNA. BON cells expressing antisense PC-1 mRNA showed nearly complete abolishment of PC-1 protein (approximately 95% reduction) and an 80% reduction in cell content of PST immunoreactivity (PST-IR) as assessed by high-performance liquid chromatography in combination with measurement of PST-IR. These findings indicate that PC-1 is essential for processing CGA to PST.

Chromogranin A: its clinical value as marker of neuroendocrine tumours

Chromogranin A (CgA) belongs to a family of secretory proteins that are present in densecore vesicles of neuroendocrine cells. Owing to its widespread distribution in neuroendocrine tissues, it can be used as an excellent immunohistochemical marker of neoplasms of neuroendocrine origin. It can also serve as serum marker of neuroendocrine activity because it is co-released with the peptide hormone content of the secretory granules. The serum concentration of CgA is elevated in patients with various neuroendocrine tumours. Elevated levels are strongly correlated with tumour volume. Although its sensitivity and specificity cannot compete with that of the specific hormonal secretion products of most of these tumours, it can nevertheless have useful clinical applications. Neuroendocrine tumours for which no peptide marker is available usually retain the capacity to secrete CgA. CgA can thus be used as serum marker for these so-called 'non-functioning' endocrine tumours. Moreover, in patients with carcinoids and phaeochromocytomas, CgA is a more stable and thus more easily manageable marker than plasma levels of respectively serotonin and catecholamines and their urinary metabolites. Its role as an important general neuroendocrine marker may be extended in the future by the development of immunoscintigraphy of membrane-bound CgA, allowing in vivo visualization of neuroendocrine neoplasms.

Recombinant human chromogranin A: expression, purification and characterization of the N-terminal derived peptides

Chromogranin A (CGA) is an ubiquitous 48 kDa secretory protein stored and released from most endocrine cells and is present in nanomolar concentration in the human vascular system. Recent data suggest that CGA may be the precursor of several peptides with a defined biological activity. The present report describes the expression of human CGA in Escherichia coli using the pET3a vector system, the purification and characterization of the recombinant protein and the production of antibody against the expressed protein. The expressed CGA was purified by a multi-step protocol including heat treatment, gel filtration and high performance-anion exchange chromatography and two-dimensional gel electrophoresis. Two major forms of recombinant human CGA (rhCGA) were purified from the bacterial cytosol: a 70 kDa form which corresponded to the native full-length CGA and a major proteolytic 63 kDa product recognized by antibodies raised against the 70 kDa rhCGA or to synthetic peptides localized in the N-terminal part of the bovine CGA sequence. This E. coli expression system provides a method for producing a suitable protein which will permit the identification of CGA-derived peptides with defined biological function in human. Fragments containing the N-terminal domain were generated by acidic cleavage of the two forms of rhCGA. A two-step purification using high-performance reverse-phase chromatography yielded 6 peptide bands ranging in apparent molecular mass from 7 to 18 kDa. Four components (molecular mass range 12-18 kDa) were immunostained with antibodies directed against synthetic sequences of bovine vasostatin II (bCGA1-113) while the two others (molecular mass range 7-8 kDa) were immunostained only with antibodies directed against vasostatin I (bCGA1-76). From protein staining the ratio vasostatins II/I was 10:1. The vasoinhibitory activity of this preparation was examined on isolated human saphenous vein segments. An inhibitory effect was obtained in paired vessel segments from 7 patients undergoing surgery for coronary artery bypass, however with low potency for supression of the endothelin-1 evoked sustained tension in these vessels.

Unique change of pancreastatin-like immunoreactivity in cerebrospinal fluid by aging

Using a specific antiserum for the C-terminal glycine amide region of human pancreastatin (PST), pancreastatin-like immunoreactivity (PST-LI) was measured in cerebrospinal fluid (CSF) from 447 subjects (368 +/- 10.8 pmol/l, mean +/- S.E.M.) free from endocrine diseases. The CSF contents of PST-LI showed a mountain-shape type change which peaked at 40 years of age. The highest concentration was found in the group of ages 40-49 years old (412 +/- 22.9 pmol/l) and the lowest concentration was found in the group of ages 80-89 years old (293.2 +/- 45.2 pmol/l) among various age groups. Gel chromatographic examination revealed the presence of two major forms (MW 13,500 and 5,400) of PST-LI in CSF. Because of the character of this antibody, the large molecular form is possibly an N-terminally elongated PST and the other may be PST-52. This may be the first report on the unique age-related change of PST concentration in CSF.

Chromogranin A(210-301) is the major form of pancreastatin-like material in human gut extracts and endocrine tumors

A radioimmunoassay of human pancreastatin was developed using a rabbit antiserum that selectively recognized the C-terminal amidated end of the peptide, and it was used for the identification of the molecular forms of pancreastatin in human gut (stomach, duodenum, small intestine, colon) and endocrine tumor extracts (liver metastasis of a gastrinoma and a medullary carcinoma of thyroid, one nonsecreting pancreatic tumor, one recurrence of a gut carcinoid, one vipoma and one insulinoma). In all gut extracts, a gel filtration chromatography revealed the presence of three peaks of pancreastatin-like immunoreactivity. The predominant form eluted with an apparent molecular weight higher than that of pancreastatin. This form was also predominant in the endocrine tumors analyzed, except in the insulinoma, where a lower molecular weight form predominated. The high molecular form was further purified from a liver metastasis of a gastrinoma. The pancreastatin-like immunoreactivity eluted in all the chromatographical systems (reverse-phase, ion exchange) as a single peak that was finally purified to homogeneity and sequenced. The sequence of the first 29 N-terminal amino acids was obtained unambiguously and corresponded to the sequence 210-238 of chromogranin A. Considering the selectivity of the assay used for peptide identification, this major form was identified as the fragment 210-301 of chromogranin A. It is likely that the predominant form of pancreastatin in human gut extracts and noninsular tumors is a 92 amino acid peptide.

Posttranslational processing of proenkephalins and chromogranins/secretogranins

Posttranslational processing of peptide-precursors is nowadays believed to play an important role in the functioning of neurons and endocrine cells. Both proenkephalins and chromogranins/secretogranins are considered as precursor molecules in these tissues, resulting in posttranslationally formed degradation products with potential biological activities. Among the proteins and peptides of neuronal and endocrine secretory granules, the enkephalins and enkephalin-containing peptides have been most extensively studied. The characterization of the post-translationally formed degradation products of the proenkephalins have enabled the understanding of their processing pathway. Chromogranins/secretogranins represent a group of acidic glycoproteins, contained within hormone storage granules. The biochemistry, biogenesis and molecular properties of these proteins have already been studied for 25 years. The chromogranins/secretogranins have a widespread distribution throughout the neuroendocrine system, the adrenal medullary chromaffin granules being the major source of these storage components. Recent data provide evidence for a precursor role for all members of the chromogranins/secretogranins family although also several other functions have been proposed. In this review, some of the methods applied to study proteolytic processing are described. In addition, the posttranslational processing of chromogranins/secretogranins and proenkephalins, especially the biochemical aspects, will be discussed and compared. Recent exciting developments on the generation and identification of potential physiologically active fragments will be covered.

Isolation and primary structure of a novel chromogranin A-derived peptide, WE-14, from a human midgut carcinoid tumour

The primary structure of a novel human chromogranin A-derived tetradecapeptide, WE-14, possessing N-terminal tryptophanyl (W) and C-terminal glutamyl (E) residues was isolated from a hepatic metastasis of an human ileal carcinoid tumour. Human and bovine WE-14 are structurally identical, while rat, mouse and porcine analogues exhibit 93% homology. WE-14 is flanked by paired basic residues (KR) in all known chromogranin A sequences.

Effects of synthetic human pancreastatin on pancreatic secretion and blood flow in rats and dogs

Effects of synthetic human pancreastatin-52 and human pancreastatin-29 on pancreatic secretion and blood flow were examined in rats and dogs. Synthetic human pancreastatin-52 and human pancreastatin-29 were equally potent in suppressing the release of amylase stimulated by cholecystokinin in rats in vivo. However, neither human pancreastatin-52 nor human pancreastatin-29 altered basal and cholecystokinin-stimulated amylase release from isolated dispersed rat pancreatic acini. In studies in dogs, human pancreastatin-29 suppressed releases of amylase and protein stimulated by cholecystokinin, but did not alter pancreatic blood flow. These results suggest that the inhibitory effects of pancreastatin on pancreatic secretion do not involve a direct action on pancreatic acinar cells nor alteration of pancreatic blood flow. Pancreastatin probably is important in regulating exocrine pancreatic secretions as well as endocrine pancreatic secretions.

Pancreastatin-like immunoreactivity in human carcinoid disease

Pancreastatin-like immunoreactivity has been demonstrated in human carcinoid tumors by immunohistochemistry and radioimmunoassay, employing antisera raised to a synthetic C-terminal fragment of porcine pancreastatin. Immunohistochemistry revealed intense immunoreactivity in all tumors. By radioimmunoassay, high concentrations of pancreastatin-like immunoreactivity were measured in carcinoid tumors arising from the fore-gut (mean +/- S.D. and range: 369 +/- 955 and 9.4-3670 pmol g-1, respectively, n = 14), mid-gut (mean +/- S.D. and range: 1354 +/- 1538 and 337-3978 pmol g-1, respectively, n = 5) and in metastases associated with mid-gut tumors (mean +/- S.D. and range: 684 +/- 739 and 31-2255 pmol g-1, respectively, n = 7), compared to corresponding normal tissues (less than 1.4 pmol g-1). Individuals with hepatic metastases and carcinoid syndrome had elevated circulating levels of pancreastatin-like immunoreactivity (mean +/- S.D. and range: 770 +/- 1249 and 42-4120 pmol l-1; n = 12), significantly above the normal, fasting range (mean +/- S.D. and range: 14.9 +/- 7.5 and 4-37.5 pmol l-1, respectively, n = 42). However, patients with non-metastatic carcinoid tumors (n = 4), who had been clinically cured after primary tumor resection, had plasma levels within the normal range. Chromatographic analysis of extracts of primary lung and ileal tumors, hepatic metastases from ileal tumors and plasma from individuals with carcinoid syndrome revealed molecular heterogeneity of pancreastatin-like immunoreactivity.

Pancreastatin--a novel regulatory peptide?

Pancreastatin is a 49 amino acid peptide originally isolated from porcine pancreas on the basis of its C-terminal glycinamide as isolation criterion. It is derived by proteolytic processing from chromogranin A, an acidic protein component of secretory granules in endocrine and neuronal cells. The primary structures of human, porcine, bovine and rat pancreastatin have been determined on the protein or cDNA level and show 70% sequence homology. By immunocytochemistry, pancreastatin has been detected in the pituitary, adrenal gland, pancreas, CNS and throughout the gastrointestinal tract. In pancreatic islets, pancreastatin is co-localized with insulin, glucagon and somatostatin. The principle biological activities of this peptide are: inhibition of insulin release and of exocrine pancreatic secretion. These effects which can be assigned to the amidated C-terminal part of the molecule have been demonstrated in several species. Whether or not pancreastatin can be classified as a novel peptide hormone that under physiological conditions plays a role in the regulation of the endocrine and exocrine pancreas, is still a matter of controversy.

Isolation and characterization of a tumor-derived human protein related to chromogranin A and its in vitro conversion to human pancreastatin-48

A protein with pancreastatin-like immunoreactivity has been isolated and purified from liver metastasis of a patient with insulinoma. NH2-terminal residue analysis, in conjunction with the use of antibodies that are specific for the C-terminal amide peptide of porcine pancreastatin, identified this protein as a 186-amino-acid protein corresponding to human chromogranin A-116-301 (the fragment corresponding to the positions from 116 to 301 of human chromogranin A). Digestion of this protein with trypsin yielded a 48-amino-acid peptide with the retention of full pancreastatin activity. Serum from patient with insulinoma contains a peptide specie(s) that comigrates with the 48-amino-acid pancreastatin, suggesting that this peptide might be a physiologically important circulation form of pancreastatin in humans. A sensitive radioimmunoassay was established using antibody developed against a synthetic 29-amino-acid peptide amide of pancreastatin. Immunocytochemical staining revealed that a major population of human pancreatic islet cells were immunoreactive to the antiserum but with varying intensity of staining. Pancreastatin-like immunoreactivity was not observed in exocrine acinar cells.

Pancreastatin producing cell line from human pancreatic islet cell tumor

It has been characterized that cell line QGP-1 derived from human non-functioning pancreatic islet cell tumor produces human pancreastatin. Exponentially growing cultures produced 5.7 fmol of pancreastatin/10(6) cells/hr. Human pancreastatin immunoreactivities in plasma and tumor after xenografting with QGP-1 into nude mouse were 92.7 fmol/ml and 160.2 pmol/g wet weight, respectively. Immunocytochemical study revealed both chromogranin A and pancreastatin immunoreactive cells in the tumor. Gel filtrations of culture medium and tumor extract identified heterogenous molecular forms of PST-LI which eluted as large and smaller molecular species. These results suggest that plasma pancreastatin levels may be useful as a tumor marker of endocrine tumor of the pancreas, and the pancreastatin producing cell line may be useful for studies of the mechanism of secretions and processing of chromogranin A and pancreastatin.

Gut endocrine and neural peptides

The once exponential growth in the number of new gut endocrine peptides being discovered has become slightly slower in recent years, and expansion of the field of gut hormones has involved mainly the application of new investigative methods. Some new peptides have been described and major inroads have been made into establishing the ontogeny of gut endocrine cells, the origins and pathways of the enteric innervation, and the involvement of the diffuse neuroendocrine system as a whole in disease states. Further insight is being gained into the functional activity of the peptide cell system by studying the control, sites and rates of peptide gene expression, and the localization and characterization of peptide binding sites on target cells.

Light and electron microscopical immunocytochemical localization of pancreastatin-like immunoreactivity in porcine tissues

Pancreastatin is a 49 amino acid comprising peptide isolated from porcine pancreas that is derived by proteolytic processing from chromogranin A. Using an antibody against the synthetic C-terminal fragment pancreastatin (33-49), we examined the light and electron microscopical immunocytochemical localization of this peptide in porcine tissues. Pancreastatin-like immunoreactivity (PLI) was found in pancreatic somatostatin-, insulin- and glucagon cells in varying intensities; pancreatic polypeptide cells were always negative. At the electron microscopical (EM) level the immunoreactivity was confined to the electron dense core of the secretory granules in the case of somatostatin and insulin cells or to the less electron dense "halo" of the glucagon granules. In the antrum PLI positive cells represented gastrin (G), somatostatin (D) and enterochromaffin (EC) cells, in the duodenum in addition to EC- and G-cells a small number of PLI positive cells showed a positive immunoreaction for glucagon-like peptide (GLP) I and secretin in serial sections. Both norepinephrine and epinephrine containing cells of the adrenal medulla exhibited a strong reaction for PLI. In the pituitary several cell populations stained with varying intensities, including gonadotrophs and thyrotrophys. PLI is present in a distinct and characteristic subpopulation of neuroendocrine cells in various organs. The subcellular localization may indicate a function in the granular concentration, packaging and storage of peptides and amines in the brain-gut endocrine system.

Synaptophysin and chromogranins/secretogranins--widespread constituents of distinct types of neuroendocrine vesicles and new tools in tumor diagnosis

Normal and neoplastic neuroendocrine (NE) cells have been identified for many years by morphological criteria only. With the advent of immunocytochemistry, antibodies against NE-specific polypeptides have been used to identify NE cells that had been missed by conventional techniques, thus improving the diagnosis of NE cells. In this review article we discuss (i) the biochemical, cell biological and molecular biological data obtained so far for two major types of NE markers, synaptophysin, which is characteristic of the small "transparent-looking" neurosecretory vesicles, and the chromogranins/secretogranins, which are widespread constituents of the larger "dense-cored" secretory granules; (ii) the immunohistochemical data obtained for these marker proteins in normal and neoplastic human NE cells and tissues; and (iii) future possible developments involving these as well as other proteins that are associated with these two distinct secretory organelles of NE cells and may serve as potential markers in NE cell diagnosis.

High plasma pancreastatinlike immunoreactivity in a patient with malignant insulinoma

High levels of pancreastatinlike immunoreactivity were detected in the plasma (2.9 pmol/ml, greater than 200-fold the normal level), pancreas (2.9 nmol/g wet wt, greater than 450-fold the normal level), and liver (1.6 nmol/g wet wt) of a patient with pancreatic insulinoma with metastasis to the liver by a sensitive and specific radioimmunoassay for human pancreastatin. Antiserum was produced against the C-terminal fragment of human pancreastatin-(24-52), which was synthesized according to the sequence of human chromogranin A corresponding to that of pancreastatin. With the antiserum, intense immunocytochemical staining was detected in the tumors. Sephadex G-50 gel filtration showed that the tumors and plasma contained two molecular forms of pancreastatinlike immunoreactivity--a molecular form coeluted with synthetic human pancreastatin-52 and a larger molecular form (Mr approximately 12,000-15,000). The smaller form eluted in the same position as synthetic human pancreastatin-52 on reverse-phase high-performance liquid chromatography.

Novel peptide pancreastatin: its occurrence and codistribution with chromogranin A in the central nervous system of the pig

The distribution of pancreastatin immunoreactivity was investigated in porcine brain, spinal cord, dorsal root ganglia, and pituitary. In the brain, immunoreactive cell bodies were present in many areas including the cortex, basal ganglia, hippocampus, thalamus, hypothalamus, mesencephalic reticular formation, cerebellum, and medulla oblongata. Immunoreactive fibres were most abundant in the globus pallidus, stria terminalis, entopeduncular nucleus, hippocampus, and in the substantia nigra. In the spinal cord, immunoreactive cells were found in laminae IV-IX. Immunoreactive fibres were concentrated in the dorsal horn. Pancreastatin immunoreactivity was localised to fibres and small cells (5-10% of the total) in the dorsal root ganglia. In the posterior pituitary, many immunoreactive fibres were present and in the anterior lobe subsets of gonadotrophs and thyrotrophs were pancreastatin-immunoreactive. The localisation of pancreastatin showed a parallel distribution with chromogranin A. Coexistence of pancreastatin with calcitonin gene-related peptide (CGRP) immunoreactivity in cell bodies in the spinal cord, including motoneurones, and with CGRP or galanin immunoreactivities in dorsal root ganglion cells was also noted. The differential pattern of pancreastatin immunostaining was reflected in the extractable levels of peptide with highest concentrations in the cortex (55.8 +/- 6.0 pmol/g wet weight, mean +/- S.E.M.), thalamus (60.0 +/- 5.0 pmol/g), hypothalamus (54.4 +/- 6.5 pmol/g), and anterior pituitary (2,714 +/- 380 pmol/g). Characterisation of pancreastatin immunoreactivity in the hypothalamus and pituitary by gel permeation and high-pressure liquid chromatography revealed multiple molecular forms, one of which was indistinguishable from natural porcine pancreastatin. The widespread distribution of pancreastatin immunoreactivity suggests this peptide may play a part in several neuroendocrine, autonomic, somatic, and sensory functions, and its colocalisation with chromogranin A is consistent with a precursor-product relationship.

Isolation and characterization of a tumor-derived human pancreastatin-related protein

A protein with pancreastatin-like immunoreactivity has been isolated and purified from liver metastasis of a patient with insulinoma. NH2-terminal sequence analysis in conjunction with the use of antibodies specific for the C-terminal structure of pancreastatin identified this protein as a 186-amino acid residue protein corresponding to human chromogranin A-116-301. Using a sensitive radioimmunoassay it was found that serum from the patient with insulinoma contains two peptide species; one comigrates with the 186-amino acid residue pancreastatin and the other the 48-residue pancreastatin.

Biochemistry of the chromogranin A protein family

Images

Pancreastatin inhibits insulin secretion as induced by glucagon, vasoactive intestinal peptide, gastric inhibitory peptide, and 8-cholecystokinin in the perfused rat pancreas

Pancreastatin is a 49-amino acid straight chain molecule isolated from porcine pancreatic extracts. In the perfused rat pancreas, this peptide has been shown to inhibit unstimulated insulin release and the insulin responses to glucose, arginine, and tolbutamide. To further explore the influence of pancreastatin on islet cell secretion, the effect of synthetic porcine pancreastatin (a 2-micrograms priming dose, followed by constant infusion at a concentration of 15.7 nmol/L) was studied on the insulin, glucagon, and somatostatin responses to 1 nmol/L vasoactive intestinal peptide (VIP), 1 nmol/L gastric inhibitory peptide (GIP), and 1 nmol/L 26 to 33 octapeptide form of cholecystokinin (8-CCK). The effect of pancreastatin on the insulin and somatostatin secretion elicited by glucagon (20 nmol/L) was also examined. Pancreastatin infusion consistently reduced the insulin responses to VIP, GIP, and 8-CCK without modifying glucagon or somatostatin release. It also inhibited the insulin release but not the somatostatin output induced by glucagon. These observations broaden the spectrum of pancreastatin as an inhibitor of insulin release. The finding that pancreastatin does not alter glucagon or somatostatin secretion supports the concept that it influences the B cell directly, and not through an A cell or D cell paracrine effect.

Production of GAWK (chromogranin-B 420-493)-like immunoreactivity by endocrine tumors and its possible diagnostic value

GAWK (chromogranin-B 420-493) is a 74 amino acid peptide recently isolated from human pituitaries. Using two different antibodies (directed against GAWK [1-17] and [20-38] fragments) GAWK-LI was measured in tumors from 194 patients and in the plasma of 434 patients by RIA. The highest tissue concentrations of GAWK-LI were found in pheochromocytoma (GAWK [1-17]-LI, 18,173 +/- 3,915; GAWK [20-38]-LI, 17,852 +/- 2,763 [mean +/- SEM] pmol/g wet wt tissue; n = 9), which were at least ten times higher than any other tumors producing GAWK-LI. High concentrations of GAWK-LI were also found in other types of endocrine tumors including carcinoid, medullary carcinoma of thyroid, pancreatic, and ACTH-producing lung tumors. On the other hand, low concentrations of GAWK-LI were found in nonendocrine tumors. Plasma concentrations of GAWK-LI were found to be elevated in patients with endocrine tumor, but more so in those with pancreatic tumors than with pheochromocytomas. Plasma concentrations returned to normal after successful tumor removal. Chromatographic profiles of GAWK-LI in extracts of pheochromocytomas and normal adrenals showed high molecular weight peaks that were absent in the extracts of other endocrine tumors and normal pancreas, suggesting differential tissue-specific processing. Thus GAWK-LI is produced by a variety of endocrine tumors and may serve as a plasma tumor marker, especially in patients with pancreatic endocrine tumors.

Bioactivity of human pancreastatin and its localization in pancreas

Synthetic human pancreastatin and its C-terminal fragment were first evaluated with respect to the biological activity on the insulin secretion in the isolated rat islets. Both these pancreastatins inhibited glucose-stimulated insulin secretion at a concentration of 100 nM. The relative molar potency of human pancreastatin compared to that of porcine pancreastatin was equivalent. The pancreastatin-reactive cells were widely located in the islets of Langerhans, and not observed in exocrine acinar cells by immunocytochemistry using human pancreastatin C-terminal specific antibody. These results suggest that human pancreastatin may modulate endocrine function of the pancreas, especially insulin secretion.

Bioactivity of synthetic human pancreastatin on exocrine pancreas

A biological activities of synthetic human pancreastatin (1-52) and its C-terminal fragment (24-52) were evaluated for the first time in the conscious rats. Both pancreastatins inhibited CCK-stimulated pancreatic secretion in a range of 20-200 pmol/kg/h with the same potency, indicating that the C-terminal portion of this peptide has a full biological activity. The relative molar potency of this substance compared to that of porcine pancreastatin was equivalent. This study suggests that human pancreastatin has the same biological activity as that of porcine, and plays a biological action in the exocrine pancreas.

Isolation and primary structure of tumor-derived peptides related to human pancreastatin and chromogranin A

Using an antiserum raised against a synthetic C-terminal peptide of porcine pancreastatin, we detected pancreastatin-like immunoreactivity (PLI) in human pancreatic islets, adrenal medulla, and endocrine tumors. From a carcinoid liver metastasis, human PLI was extracted and purified by HPLC. Two C-terminally amidated peptides were isolated and characterized by sequence analysis. The first peptide, hCgA-210-301, consists of 92 amino acid residues with glycinamide as C terminus. It is identical to the cDNA-derived sequence of human chromogranin A, positions 210-301, which is preceded by two basic residues indicating a putative processing site. The C-terminal part, positions 250-301, shows 70% sequence identity to porcine pancreastatin and represents the human pancreastatin-like sequence. The second peptide, hCgA-273-301, represents a C-terminally amidated fragment of the human pancreastatin sequence, generated by an Asp-Pro cleavage at the N terminus. Peptide hCgA-273-301 was synthesized to confirm the structure of the natural peptide. Two other peptides derived from human chromogranin A were isolated and partially characterized. They are generated by proteolytic cleavage after dibasic amino acids Lys-Arg (positions 338-339) and after Trp-376 of the human chromogranin A sequence, respectively. These results indicate that chromogranin A may represent the precursor for pancreastatin-related and possibly other yet-unidentified peptides of unknown physiological function.

The occurrence of pancreastatin in tumours of the diffuse neuroendocrine system

We have reported previously the localization of the 49 amino acid peptide pancreastatin to all identifiable endocrine cells of porcine gut, pancreas and adrenal, thyroid and pituitary glands. In this study, we have investigated the occurrence of pancreastatin in a series of human neuroendocrine tumours using an antibody to whole synthetic porcine pancreastatin. The most consistent immunostaining for pancreastatin was found in carcinoid tumours of ileum (four out of six), rectum (four out of six), ovary (two out of two) and lung (nine out of 10). Radioimmunoassay of tumour extracts showed that the concentrations of pancreastatin in ileal carcinoids were very high (mean 71.6, range 31.0-184.0 pmol g-1). The high rate of positivity in lung carcinoids contrasted sharply with the results of 10 pulmonary small cell carcinomas which displayed no immunoreactivity and contained minimal concentrations of pancreastatin (mean 2.0, range 0-6.0 pmol g-1). Extra-adrenal paragangliomas also contained pancreastatin (seven out of 10), but although radioimmunoassay detected peptide in phaeochromocytomas (mean 29.8, range 8.0-69.0 pmol g-1), immunocytochemistry did not. Porcine pancreastatin shows structural homology with bovine chromogranin A, an observation which has led to suggestions that chromogranin is a precursor for the peptide. More recently, a sequence homologous to porcine pancreastatin has been identified in the human chromogranin A molecule. In this study, immunostaining with an antiserum to human chromogranin gave positive results in most cases of each tumour type except the small cell carcinomas. The lack of consistent relationships between chromogranin and pancreastatin immunoreactivities may reflect the fact that the antiserum to pancreastatin was raised against the porcine peptide. When antibodies to human pancreastatin become available, the peptide may prove to be a more consistent marker for neuroendocrine tumours.