Chromostatin, a chromogranin A-derived bioactive peptide, is present in human pancreatic insulin (beta) cells

Role and function of granin proteins in diabetes mellitus

The granin glycoprotein family consists of nine acidic proteins; chromogranin A (CgA), chromogranin B (CgB), and secretogranin II–VIII. They are produced by a wide range of neuronal, neuroendocrine, and endocrine cells throughout the human body. Their major intracellular function is to sort peptides and proteins into secretory granules, but their cleavage products also take part in the extracellular regulation of diverse biological processes. The contribution of granins to carbohydrate metabolism and diabetes mellitus is a recent research area. CgA is associated with glucose homeostasis and the progression of type 1 diabetes. WE-14, CgA_10-19, and CgA_43-52 are peptide derivates of CgA, and act as CD4⁺ or CD8⁺ autoantigens in type 1 diabetes, whereas pancreastatin (PST) and catestatin have regulatory effects in carbohydrate metabolism. Furthermore, PST is related to gestational and type 2 diabetes. CgB has a crucial role in physiological insulin secretion. Secretogranins II and III have angiogenic activity in diabetic retinopathy (DR), and are novel targets in recent DR studies. Ongoing studies are beginning to investigate the potential use of granin derivatives as drugs to treat diabetes based on the divergent relationships between granins and different types of diabetes.

The Emerging Roles of Chromogranins and Derived Polypeptides in Atherosclerosis, Diabetes, and Coronary Heart Disease

Chromogranin A (CgA), B (CgB), and C (CgC), the family members of the granin glycoproteins, are associated with diabetes. These proteins are abundantly expressed in neurons, endocrine, and neuroendocrine cells. They are also present in other areas of the body. Patients with diabetic retinopathy have higher levels of CgA, CgB, and CgC in the vitreous humor. In addition, type 1 diabetic patients have high CgA and low CgB levels in the circulating blood. Plasma CgA levels are increased in patients with hypertension, coronary heart disease, and heart failure. CgA is the precursor to several functional peptides, including catestatin, vasostatin-1, vasostatin-2, pancreastatin, chromofungin, and many others. Catestatin, vasostain-1, and vasostatin-2 suppress the expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in human vascular endothelial cells. Catestatin and vasostatin-1 suppress oxidized low-density lipoprotein-induced foam cell formation in human macrophages. Catestatin and vasostatin-2, but not vasostatin-1, suppress the proliferation and these three peptides suppress the migration in human vascular smooth muscles. Chronic infusion of catestatin, vasostatin-1, or vasostatin-2 suppresses the development of atherosclerosis of the aorta in apolipoprotein E-deficient mice. Catestatin, vasostatin-1, vasostatin-2, and chromofungin protect ischemia/reperfusion-induced myocardial dysfunction in rats. Since pancreastatin inhibits insulin secretion from pancreatic β-cells, and regulates glucose metabolism in liver and adipose tissues, pancreastatin inhibitor peptide-8 (PSTi8) improves insulin resistance and glucose homeostasis. Catestatin stimulates therapeutic angiogenesis in the mouse hind limb ischemia model. Gene therapy with secretoneurin, a CgC-derived peptide, stimulates postischemic neovascularization in apolipoprotein E-deficient mice and streptozotocin-induced diabetic mice, and improves diabetic neuropathy in db/db mice. Therefore, CgA is a biomarker for atherosclerosis, diabetes, hypertension, and coronary heart disease. CgA- and CgC--derived polypeptides provide the therapeutic target for atherosclerosis and ischemia-induced tissue damages. PSTi8 is useful in the treatment of diabetes.

Chromogranin A - unspecific neuroendocrine marker. Clinical utility and potential diagnostic pitfalls

Chromogranin A, despite a number of limitations, is still the most valuable marker of neuroendocrine tumors (NETs). Granins belong to the family of acidic proteins that constitute a major component of secretory granules of various endocrine and neuroendocrine cells, which are components of both the classical endocrine glands and the diffuse neuroendocrine system. These cells are a potential source of transformation into neuroendocrine tumors. The awareness of potential causes influencing the false results of its concentrations simplifies diagnosis and treatment. One of the disadvantages of this marker is its non-specificity and the existence of a number of pathological processes leading to an increase in its concentration, which often results in confusion and diagnostic difficulties. The molecular structure is characterized by a number of sites susceptible to the proteolytic activity of enzymes, resulting in the formation of a number of biologically active peptides. Presumably they act as precursors of active proteins. Chromogranin expression correlates with the amount of secretory vesicles in neuroendocrine cells. The peptide chain during biochemical changes becomes a precursor of biologically active proteins with a wide range of activities. There are a number of commercially available kits for the determination of chromogranin A, which differ in methodology. We present the evaluation of chromogranin A as a marker of neuroendocrine tumors in clinical practice and the possible factors that may affect the outcome of its concentration.

Mapping Mammalian Cell-type-specific Transcriptional Regulatory Networks Using KD-CAGE and ChIP-seq Data in the TC-YIK Cell Line

Mammals are composed of hundreds of different cell types with specialized functions. Each of these cellular phenotypes are controlled by different combinations of transcription factors. Using a human non islet cell insulinoma cell line (TC-YIK) which expresses insulin and the majority of known pancreatic beta cell specific genes as an example, we describe a general approach to identify key cell-type-specific transcription factors (TFs) and their direct and indirect targets. By ranking all human TFs by their level of enriched expression in TC-YIK relative to a broad collection of samples (FANTOM5), we confirmed known key regulators of pancreatic function and development. Systematic siRNA mediated perturbation of these TFs followed by qRT-PCR revealed their interconnections with NEUROD1 at the top of the regulation hierarchy and its depletion drastically reducing insulin levels. For 15 of the TF knock-downs (KD), we then used Cap Analysis of Gene Expression (CAGE) to identify thousands of their targets genome-wide (KD-CAGE). The data confirm NEUROD1 as a key positive regulator in the transcriptional regulatory network (TRN), and ISL1, and PROX1 as antagonists. As a complimentary approach we used ChIP-seq on four of these factors to identify NEUROD1, LMX1A, PAX6, and RFX6 binding sites in the human genome. Examining the overlap between genes perturbed in the KD-CAGE experiments and genes with a ChIP-seq peak within 50 kb of their promoter, we identified direct transcriptional targets of these TFs. Integration of KD-CAGE and ChIP-seq data shows that both NEUROD1 and LMX1A work as the main transcriptional activators. In the core TRN (i.e., TF-TF only), NEUROD1 directly transcriptionally activates the pancreatic TFs HSF4, INSM1, MLXIPL, MYT1, NKX6-3, ONECUT2, PAX4, PROX1, RFX6, ST18, DACH1, and SHOX2, while LMX1A directly transcriptionally activates DACH1, SHOX2, PAX6, and PDX1. Analysis of these complementary datasets suggests the need for caution in interpreting ChIP-seq datasets. (1) A large fraction of binding sites are at distal enhancer sites and cannot be directly associated to their targets, without chromatin conformation data. (2) Many peaks may be non-functional: even when there is a peak at a promoter, the expression of the gene may not be affected in the matching perturbation experiment.

Guanylin and functional coupling proteins in the hepatobiliary system of rat and guinea pig

Guanylin, a bioactive intestinal peptide, is involved in the cystic fibrosis transmembrane conductance (CFTR)-regulated electrolyte/water secretion in various epithelia. In the present work we report on the expression and cellular localization of guanylin and its affiliated signaling and effector proteins, including guanylate cyclase C (Gucy2c), Proteinkinase GII (Pkrg2), CFTR and the solute carrier family 4, anion exchanger, member 2 (Slc4a2) in the hepatobiliary system of rat and guinea pig. Localization studies in the liver and the gallbladder revealed that guanylin is located in the secretory epithelial cells of bile ducts of the liver and of the gallbladder, while Gucy2c, Pkrg2, CFTR, and Slc4a2 are confined exclusively to the apical membrane of the same epithelial cells. Based on these findings, we assume that guanylin is synthesized as an intrinsic peptide in epithelial cells of the hepatobiliary system and released luminally into the hepatic and cystic bile to regulate electrolyte secretion by a paracrine/luminocrine signaling pathway.

Pancreatic beta cells synthesize neuropeptide Y and can rapidly release peptide co-transmitters

Background

In addition to polypeptide hormones, pancreatic endocrine cells synthesize a variety of bioactive molecules including classical transmitters and neuropeptides. While these co-transmitters are thought to play a role in regulating hormone release little is known about how their secretion is regulated. Here I investigate the synthesis and release of neuropeptide Y from pancreatic beta cells.

Methodology/Principal Findings

NPY appears to be an authentic co-transmitter in neonatal, but not adult, beta cells because (1) early in mouse post-natal development, many beta cells are NPY-immunoreactive whereas no staining is observed in beta cells from NPY knockout mice; (2) GFP-expressing islet cells from an NPY(GFP) transgenic mouse are insulin-ir; (3) single cell RT-PCR experiments confirm that the NPY(GFP) cells contain insulin mRNA, a marker of beta cells. The NPY-immunoreactivity previously reported in alpha and delta cells is therefore likely to be due to the presence of NPY-related peptides. INS-1 cells, a beta cell line, are also NPY-ir and contain NPY mRNA. Using the FMRFamide tagging technique, NPY secretion was monitored from INS-1 beta cells with high temporal resolution. Peptide release was evoked by brief depolarizations and was potentiated by activators of adenylate cyclase and protein kinase A. Following a transient depolarization, NPY-containing dense core granules fused with the cell membrane and discharged their contents within a few milliseconds.

Conclusions

These results indicate that after birth, NPY expression in pancreatic islets is restricted to neonatal beta cells. The presence of NPY suggests that peptide co-transmitters could mediate rapid paracrine or autocrine signaling within the endocrine pancreas. The FMRFamide tagging technique may be useful in studying the release of other putative islet co-transmitters in real time.

Pancreatic expression of DOG1: a novel gastrointestinal stromal tumor (GIST) biomarker

The cDNA microarray gene profile of gastrointestinal stromal tumors (GISTs) revealed that DOG1 (TMEM16A) gene was mostly expressed in these neoplasms. Immunohistochemically, DOG1 protein was found positive in a significant proportion of GISTs. However, normal tissues' expression of DOG1 is not yet completely studied. Our study intended to identify the DOG1 protein expression in normal adult and fetal tissues, in comparison with that of GISTs, using an anti-DOG1 polyclonal serum. Fourteen CD117/CD34-positive GIST cases were tested for DOG1. Tissue samples from autopsies of 15 human fetuses and 11 adults were tested immunohistochemically on simple or double staining with antibodies raised against: DOG1, insulin, glucagon, somatostatin, NK1, PGP9.5, chromogranin A, and synaptophysin. All the tested GISTs were positive for DOG1, with a membranous and cytoplasmic location. The normal tissues showed a distinct positivity for DOG1 only in the endocrine pancreas, in both fetal and adult ones. The other tissues tested showed a weak or negative reaction. The DOG1 staining pattern in the pancreas islets was granular, like that of neuroendocrine markers. The location of DOG1 expression in pancreatic islets was partly similar to neuroendocrine markers chromogranin A, PGP9.5, and synaptophysin. The positive cells were situated centrally, in the vicinity of insulin-bearing cells as seen on double staining. DOG1 positivity in fetal and adult pancreatic islets suggests the strong antibody affinity for neuroendocrine cells. Before making a final conclusion regarding the suitability of DOG1 as a new neuroendocrine marker, a large survey of neuroendocrine lesions must be undertaken, including carcinoid tumors of various sites and pancreatic endocrine tumors. To the best of our knowledge, this particular localization has not been reported yet for DOG1.

Direct visualisation of peptide hormones in cultured pancreatic islet alpha- and beta-cells by intact-cell mass spectrometry

The application of intact-cell mass spectrometry (ICM) by matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry to achieve direct protein-profiling of bacterial species is now well established. However, this methodology has not to our knowledge been applied to the analysis of mammalian cells in routine culture. Here, we describe a novel application of ICM by which we have identified proteins in intact cells from two lines representative of pancreatic islet alpha- and beta-cells. Adherent alphaTC1 clone 9 and betaTC6 F7 cells were harvested into phosphate-buffered saline (PBS) using enzyme-free dissociation buffer before 1 microL of cell suspension was spotted onto MALDI plates. Cells were overlaid with sinapinic acid then washed with pure water before application of a final coat of sinapinic acid. Data in the 2000-20,000 m/z range were acquired in linear mode on a Voyager DE-Pro mass spectrometer. The proteins which ionised were composed in large part of peptide hormones (e.g. insulin and glucagon) known to be packaged into the secretory granules of the beta- and alpha-cells respectively. However, in addition to visualising the peptides expected to be associated with these cells, a mass consistent with oxyntomodulin was identified in the cultured alpha-cells, a finding not previously reported to our knowledge. In summary, this paper describes, for the first time, a rapid and direct method useful for identifying secretory products in intact endocrine cells.

Secretory granules of hypophyseal and pancreatic endocrine cells contain proteins of the neuronal postsynaptic density

The PDZ domain-containing protein Shank is a master scaffolding protein of the neuronal postsynaptic density and directly or indirectly links neurotransmitter receptors and cell adhesion molecules to the actin-based cytoskeleton. ProSAP/Shank proteins have recently also been detected in several non-neuronal cells in which they are mostly concentrated in the apical subplasmalemmal cytoplasm. In contrast, we have previously reported a more widespread cytoplasmic immunostaining pattern for the ProSAP1/Shank2 protein in endocrine cells at the light-microscopic level. Therefore, in the present study, we have determined the ultrastructural localization of ProSAP1/Shank2 and the ProSAP/Shank-interacting proteins ProSAPiP1 and IRSp53 in pancreatic islet and adenohypophyseal cells by using immunogold staining techniques. Dense immunolabeling of secretory granules including the granule core in cells such as hypophyseal somatotrophs and pancreatic B-cells indicates the unexpected presence of ProSAP/Shank and ProSAP/Shank-interacting proteins in the hormone-storing compartment of endocrine cells. Thus, ProSAP/Shank and certain ProSAP/Shank-interacting proteins exhibit distinct subcellular localizations in the different cell types, raising the possibility that the function of ProSAP/Shank proteins is more diverse than has been envisaged to date.

The normal cellular prion protein (PrPc) is strongly expressed in bovine endocrine pancreas

Expression of the cellular prion protein (PrP(c)) has been shown to be crucial for the development of transmissible spongiform encephalopathies and for the accumulation of the disease-associated conformer (PrP(sc)) in the brain and other tissues. One of the emerging hypotheses is that the conversion phenomenon could take place at the site where the infectious agent meets PrP(c). In this work we have studied whether PrP(c), a protein found predominantly in neurons, could also exist in pancreatic endocrine cells since neuroectoderm-derived cells and pancreatic islet cells share a large number of similarities. For this purpose we have examined the expression of PrP(c) in a series of fetal and postnatal bovine pancreatic tissue by immunohistochemistry and RT-PCR. Using immunostained serial sections and specific antibodies against bovine PrP(c), insulin, glucagon, somatostatin, chromogranin A and chromogranin B we found that PrP(c) is highly expressed in all endocrine cells of fetal and adult pancreatic islets with a particular strong expression in A-cells. Moreover it became evident that the PrP(c) gene-neighbour chromogranin B as well as chromogranin A are coexpressed together with PrP(c). The selective expression of PrP(c) in the bovine endocrine pancreas is of particular importance regarding possible iatrogenic transmission routes and demonstrates also that bovine pancreatic islet cells could represent an interesting model to study the control of PrP-gene expression.

Association between endocrine pancreas and ductal system. More than an epiphenomenon of endocrine differentiation and development?

Traditional histological descriptions of the pancreas distinguish between the exocrine and the endocrine pancreas, as if they were two functionally distinct glands. This view has been proven incorrect and can be considered obsolete. Interactions between acinar and islet tissues have been well established through numerous studies that reveal the existence of anatomical and functional relationships between these compartments of the gland. Less attention, however, has traditionally been paid to the relationships occurring between the endocrine pancreas and the ductal system. Associations between islet tissue and ducts are considered by most researchers as only a transient epiphenomenon of endocrine development. This article reviews the evidence that has emerged in the last 10 years demonstrating the existence of stable, close, and systematic relationships between these two pancreatic compartments. Functional and pathophysiological implications are considered, and the existence of an "acinar-duct-islet" axis is put forward. The pancreas appears at present to be an integrated organ composed of three functionally related components of well-orchestrated endocrine and exocrine physiological responses.

Guanylin and functional coupling proteins in the human salivary glands and gland tumors : expression, cellular localization, and target membrane domains

Cystic fibrosis transmembrane conductance regulator (CFTR)-mediated secretion of an electrolyte-rich fluid is a major but incompletely understood function of the salivary glands. We provide molecular evidence that guanylin, a bioactive intestinal peptide involved in the CFTR-regulated secretion of electrolyte/water in the gut epithelium, is highly expressed in the human parotid and submandibular glands and in respective clinically most relevant tumors. Moreover, in the same organs we identified expression of the major components of the guanylin signaling pathway, ie, guanylin-receptor guanylate cyclase-C, cGKII, and CFTR, as well as of the epithelial Cl(-)/HCO(3)(-) anion exchanger type 2 (AE2). At the cellular level, guanylin is localized to epithelial cells of the ductal system that, based on its presence in the saliva, is obviously released into the salivary gland ducts. The guanylin-receptor guanylate cyclase-C, cGKII, CFTR, and AE2 are all confined exclusively to the apical membrane of the same duct cells. These findings implicate guanylin as intrinsic regulator of electrolyte secretion in the salivary glands. We assume that duct epithelial cells synthesize and release guanylin into the saliva to regulate electrolyte secretion in the ductal system by an intraductal luminocrine signaling pathway. Moreover, the high expression of guanylin in pleomorphic adenoma and Warthin tumors (cystadenolymphoma), the most common neoplasms of salivary glands, predicts guanylin as a significant marker in tumor pathology.

Structural and biological characterization of chromofungin, the antifungal chromogranin A-(47-66)-derived peptide

Vasostatin-I, the natural fragment of chromogranin A-(1-76), is a neuropeptide able to kill a large variety of fungi and yeast cells in the micromolar range. We have examined the antifungal properties of synthetic vasostatin-I-related peptides. The most active shortest peptide, named chromofungin, corresponds to the sequence Arg(47)-Leu(66). Extensive (1)H NMR analysis revealed that it adopts a helical structure. The biophysical mechanism implicated in the interaction of chromofungin with fungi and yeast cells was studied, showing the penetration of this peptide with different lipid monolayers. In order to examine thoroughly the antifungal activity of chromofungin, confocal laser microscopy was used to demonstrate the ability of the rhodamine-labeled peptide to interact with the fungal cell wall, to cross the plasma membrane, and to accumulate in Aspergillus fumigatus, Alternaria brassicola, and Candida albicans. Our present data reveal that chromofungin inhibits calcineurin activity, extending a previous observation that the N-terminal region of chromogranin A interacts with calmodulin in the presence of calcium. Therefore, the destabilization of fungal wall and plasma membrane, together with the possible intracellular inhibition of calmodulin-dependent enzymes, is likely to represent the mechanism by which vasostatin-I and chromofungin exert antifungal activity.

The cortactin-binding postsynaptic density protein proSAP1 in non-neuronal cells

Proline-rich synapse-associated protein-1 (ProSAP1) is a neuronal PDZ domain-containing protein that has recently been identified as an essential element of the postsynaptic density. Via its interaction with the actin-binding protein cortactin and its integrative function in the organization of neurotransmitter receptors, ProSAP1 is believed to be involved in the linkage of the postsynaptic signaling machinery to the actin-based cytoskeleton, and may play a role in the cytoskeletal rearrangements that underlie synaptic plasticity. As a result of our ongoing studies on the distribution and function of this novel PDZ domain protein, we now report that the expression of ProSAP1 is restricted neither to neurons and interneuronal junctions nor to the nervous system. Using immunohistochemical techniques in conjunction with specific antibodies, we found that, in the CNS, ProSAP1 can be detected in certain glial cells, such as ependymal cells, tanycytes, subpial/radial astrocytes, and in the choroid plexus epithelium. Moreover, our immunohistochemical analyses revealed the presence of ProSAP1 in endocrine cells of the adenohypophysis and of the pancreas, as well as in non-neuronal cell types of other organs. In the pancreas, ProSAP1 immunoreactivity was also localized in the duct system of the exocrine parenchyma. Our findings demonstrate that, in addition to neurons, ProSAP1 is present in various non-neuronal cells, in which it may play a crucial role in the dynamics of the actin-based cytoskeleton. (J Histochem Cytochem 49:639-648, 2001)

Mechanisms underlying neuronal death induced by chromogranin A-activated microglia

The neurotoxic effects of activated microglia in neurodegenerative diseases are well established. We recently provided evidence that chromogranin A (CGA), a multifunctional protein localized in dystrophic neurites and in senile plaques, induces an activated phenotype and secretion of neurotoxins by rat microglia in culture. In the present study, we focused on the mechanisms underlying neuronal degeneration triggered by CGA-activated microglia. We found that neuronal death exhibits apoptotic features, characterized by the externalization of phosphatidylserine and the fragmentation of DNA. Microglial neurotoxins markedly stimulate the phosphorylation and activity of neuronal p38 mitogen-activated protein kinase and provoke the release of mitochondrial cytochrome c, which precedes apoptosis. Inhibition of p38 kinase with SB 203580 partially protects neurons from death induced by CGA-activated microglia. Furthermore, neurons are also protected by Fas-Fc, which antagonizes the interactions between the death receptor Fas and its ligand FasL and by cell-permeable peptides that inhibit caspases 8 and 3. Thus, CGA triggers the release of microglial neurotoxins that mobilize several death-signaling pathways in neurons. Our results further support the idea that CGA, which is up-regulated in many neuropathologies, represents a potent endogeneous inflammatory factor possibly responsible for neuronal degeneration.

Selective processing of chromogranin A in the different islet cells in human pancreas

We studied the immunoreactivity of 12 different region-specific antibodies to the chromogranin A (CgA) molecule in the four major neuroendocrine cell types of the human pancreas by using double immunofluorescence techniques. The antibodies raised to the N-terminal and midportions of CgA showed, on the whole, stronger immunoreactivity than did the C-terminal antibodies, with a few exceptions. Often the immunoreactivity was stronger in glucagon cells. Insulin cells expressed immunoreactivity to all region-specific antibodies, but glucagon cells were nonreactive to two antibodies. Somatostatin cells reacted only with the C-terminal antibodies (amino acid sequences CgA 411-424), while PP cells were stained with four CgA region-specific antibodies between amino acid sequences 63-195. The cause of these differences may be that the CgA molecule is cleaved, partly masked, or partly translated from CgA mRNA. Microwave treatment improved only the staining with the CgA 361-372 antibodies, which indicates that masking is not the sole or entire cause. Our findings may indicate that the CgA molecule is cleaved in different ways in the various pancreatic endocrine cell types, giving rise to a variety of biologically functional fragments.

Granin proteins (chromogranin A and secretogranin II C23-3 and C26-3) in the endocrine pancreas of reptiles

The endocrine pancreas of four reptile species belonging to the turtles, lizards and snakes was investigated immunohistochemically for the occurrence and cellular distribution of chromogranin A (CgA) and of two synthetic secretonin II (SgII)-peptides (C23-3 and C26-3). CgA-immunoreactivity was found only in the turtle pancreas, whereas that for SGIIC23-3 appeared both in the turtle and snake. None of the species studied displayed immunoreactivity for SgIIC26-3. The two detected granins showed different distributions in relation to the endocrine cell types. Conspicuous variations of the immunostaining density for either granin in the same endocrine cell population and even complete lack of the immunoreaction were recorded. The findings suggest that, despite the restricted presence in the endocrine pancreas of the reptiles investigated, the granins are relatively well conserved during phylogeny; they do not confirm, however, the previously accepted usefulness of the granin protein family as common markers of neuroendocrine cells.

Granin proteins (chromogranin A and secretogranin II C23-3 and C26-3) in the intestine of reptiles

The occurrence, distribution and the possible cellular co-localizations of chromogranin A (CgA) and of two synthetic secretogranin II-peptides (SgIIC23-3 and SgIIC26-3) with several enteric neuropeptides and serotonin have been investigated immunohistochemically in turtles, lizards and snakes. The distribution of CgA-immunoreactivity was restricted only to the enteroendocrine cells in all the reptiles studied. SgII-immunoreactivity--absent in turtle--revealed nerve cells and fibers, besides enteroendocrine cells in lizard and snake guts. Moreover, the two antisera (C23-3 and C26-3) raised against the different regions of the SgII-molecule yielded distinct distribution patterns of immunoreactivity both in the lizard and snake organs. Small amounts of enteric serotonin cells co-stored CgA or SgIIC23-3 in lizards and snakes and only SgIIC26-3-peptide in snakes. CgA was found co-stored with somatostatin in a few enterocytes of the turtle duodenum. In the same gut segment of lizards and throughout the snake organ, neurotensin and the SgIIC23-3-peptide co-existed in a small number of endocrine cells. The pancreatic polypeptide-containing cells were devoid of immunoreactivity both for CgA and SgII. Bombesin immunopositive cells were absent throughout the intestines of the reptiles investigated. The above findings entirely support the heterogenous distribution of granins in neuroendocrine organs and tissues and also within the same neuroendocrine cell population. They further support the concept of a good conservation of granins during phylogeny.

Phosphorylation and O-glycosylation sites of human chromogranin A (CGA79-439) from urine of patients with carcinoid tumors

Because of their water-soluble properties, chromogranins (CGs) and chromogranin-derived fragments are released together with catecholamines from adrenal chromaffin cells during stress situations and can be detected in the blood by radiochemical and enzyme assays. It is well known that chromogranins can serve as immunocytochemical markers for neuroendocrine tissues and as a diagnostic tool for neuroendocrine tumors. In 1993, large CGA-derived fragments have been shown to be excreted into the urine in patients with carcinoid tumors and the present study deals with the characterization of the post-translational modifications (phosphorylation and O-glycosylation) located along the largest natural CGA-derived fragment CGA79-439. Using mild proteolysis of peptidic material, high performance liquid chromatography, sequencing, and mass spectrometry analysis, six post-translational modifications were detected along the C-terminal CGA-derived fragment CGA79-439. Three O-linked glycosylation sites were located in the core of the protein on Thr163, Thr165, and Thr233, consisting in di-, tri-, and tetrasaccharides. Three phosphorylation sites were located in the middle and C-terminal domain, on serine residues Ser200, Ser252, and Ser315. These modified sites were compared with sequences of others species and discussed in relation with the post-translational modifications that we have reported previously for bovine CGA.

Granin proteins (chromogranin A and secretogranin II C23-3 and C26-3) in the intestine of amphibians

The occurrence, distribution and possible cellular colocalizations of chromogranin A (CgA) and of two synthetic secretogranin II peptides (SgIIC23-3 and SgIIC26-3) with serotonin, somatostatin, neurotensin, pancreatic polypeptide and bombesin have been investigated immunohistochemically in the amphibian gut. CgA or SgIIC26-3-immunostained enterocytes were found throughout along the frog intestine, while no immunoreaction for any of the tested antisera against granins was seen in the same organ of newts. Variable amounts of serotonin-immunoreactive cells co-storing CgA or SgIIC26-3, but never both granins, were encountered in all intestinal segments of the frogs investigated. In addition, CgA was co-localized with somatostatin in a few endocrine cells of the frog (genus Rana) duodenum and small intestine. In the duodenum of another frog (genus Xenopus) several enterocytes co-stored SgIIC26-3 and neurotensin. Pancreatic polypeptide- and bombesin-immunoreactive cells, the latter detected only in the duodenum of Xenopus, did not contain and granin. The results suggest that, in spite of their relatively restricted occurrence in the intestine of frogs and even of their absence in that of newts, the granins are well conserved during phylogeny. On the other hand, the heterogeneous distributions of these anionic glycoproteins, related to the entero-endocrine cell types, make their previously assigned usefulness as markers of all neuro-endocrine cells unlikely.

Chromogranin A induces a neurotoxic phenotype in brain microglial cells

Chromogranin A (CGA) belongs to a multifunctional protein family widely distributed in secretory vesicles in neurons and neuroendocrine cells. Within the brain, CGA is localized in neurodegenerative areas associated with reactive microglia. By using cultured rodent microglia, we recently described that CGA induces an activated phenotype and the generation of nitric oxide. These findings led us to examine whether CGA might affect neuronal survival, expression of neurofilaments, and high affinity gamma-aminobutyric acid uptake in neurons cultured in the presence or absence of microglial cells. We found that CGA was unable to exert a direct toxic effect on neurons but provoked neuronal injury and degeneration in the presence of microglial cells. These effects were observed with natural and recombinant CGA and with a recombinant N-terminal fragment corresponding to residues 1-78. CGA stimulated microglial cells to secrete heat-stable diffusible neurotoxic agents. CGA also induced a marked accumulation of nitric oxide and tumor necrosis factor-alpha by microglia, but we could not establish a direct correlation between the levels of nitric oxide and tumor necrosis factor-alpha and the neuronal damage. The possibility that CGA represents an endogenous factor that triggers the microglial responses responsible for the pathogenesis of neuronal degeneration is discussed.

A comparative immunohistochemical study of pancreatic islets in laboratory animals (rats, dogs, minipigs, nonhuman primates)

The aim of the present study was to distinguish and describe the patterns of distribution of pancreatic islets within the pancreas of four species of laboratory animals, including rats, dogs, minipigs and monkeys, and furthermore, to identify immunohistochemically various islet cell types and characterize their content. Histopathological examinations were performed on sections stained with hematoxylin and eosin (H&E) and immunostained using rabbit polyclonal antibodies (pAb) against insulin, glucagon, pancreatic polypeptide (PP), somatostatin, chromogranin A, keratin, bombesin and gastrin, or mouse monoclonal antibodies (mAb) against synaptophysin, Leu-7 and proliferating cell nuclear antigen (PCNA) in three-step rabbit immunoperoxidase (PAP) and streptavidin/peroxidase (StreptABC/HRP) reactions. Positive immunohistochemical reactions were observed in the pancreatic islets of all animal species with all antibodies, except with anti-bombesin and anti-gastrin antibodies. Our results revealed that: 1) there is species specific regional arrangement of islets in the pancreas, 2) each species presents a characteristic distribution of cells producing different hormones. 3) immunoreactivity with immunohistochemical markers varies between species and/or age. The present comparative immunohistochemical study could be helpful for answering questions which are important for understanding some of the intricate mechanisms that govern the integrated function of the endocrine pancreas.

Tertiary hypothyroidism and hyperglycemia in mice with targeted disruption of the thyrotropin-releasing hormone gene

Thyrotropin-releasing hormone (TRH) is a brain hypothalamic hormone that regulates thyrotropin (TSH) secretion from the anterior pituitary and is ubiquitously distributed throughout the brain and other tissues including pancreas. To facilitate studies into the role of endogenous TRH, we have used homologous recombination to generate mice that lack TRH. These TRH-/- mice are viable, fertile, and exhibit normal development. However, they showed obvious hypothyroidism with characteristic elevation of serum TSH level and diminished TSH biological activity. Their anterior pituitaries exhibited an apparent decrease in TSH immunopositive cells that was not due to hypothyroidism. Furthermore, this decrease could be reversed by TRH, but not thyroid hormone replacement, suggesting a direct involvement of TRH in the regulation of thyrotrophs. The TRH-/- mice also exhibited hyperglycemia, which was accompanied by impaired insulin secretion in response to glucose. These findings indicate that TRH-/- mice provide a model of exploiting tertiary hypothyroidism, and that TRH gene abnormalities cause disturbance of insulin secretion resulting in marked hyperglycemia.

Pancreastatin secretion by pituitary adenomas and regulation of chromogranin B mRNA expression

Pancreastatin, a carboxyl-terminal amidated peptide derived from chromogranin (Cg)A, inhibits secretion of insulin and parathyroid hormone. Our recent studies found significant amounts of immunoreactive pancreastatin in all pituitary adenomas except prolactin adenomas. To analyze the effects of pancreastatin on pituitary cell function, 17 cultured pituitary adenomas were examined for immunoreactive pancreastatin and pancreastatin secretion by the tumors. The effects of pancreastatin on pituitary hormone secretion and on pituitary hormone (follicle-stimulating hormone and prolactin), CgA, and CgB mRNA levels were also examined. Immunoreactive pancreastatin and CgA were present diffusely in gonadotroph and null cell adenomas, but only a few prolactin adenoma cells expressed pancreastatin or CgA. When cells were treated with hypothalamic peptides, gonadotroph adenomas were the only group that released increased amounts of pancreastatin in response to gonadotropin-releasing hormone (10(-7) mol/L). Pancreastatin (10(-7) mol/L) treatment did not stimulate pituitary hormone secretion significantly. In situ hybridization analyses showed that gonadotropin-releasing hormone and pancreastatin treatment led to significant increases in CgB and follicle-stimulating hormone mRNAs in gonadotroph adenomas, whereas CgA mRNA levels did not change significantly. These results show that there is a differential distribution of pancreastatin secretion in pituitary adenomas and that the hypothalamic hormone gonadotropin-releasing hormone and the CgA-derived peptide pancreastatin can regulate CgB mRNA in gonadotroph adenomas, suggesting an autocrine effect of pancreastatin on pituitary tumor function.

Loss of GLUT2 glucose transporter expression in pancreatic beta cells from diabetic Chinese hamsters

The diabetic Chinese hamster is a well-established animal model for NIDDM with a defective glucose-induced insulin secretory response. In the pancreas of nondiabetic hamsters, the GLUT2 glucose transporter was localized in the plasma membrane of insulin-positive beta cells. At variance with the rat, immunoreactivity was also detected in the cytoplasm. Other islet cell types were not GLUT2 positive. GLUT2 immunoreactivity was already significantly reduced in beta cells from mildly diabetic animals in spite of a normal insulin immunoreactivity. In severely diabetic animals the majority of the beta cells had lost GLUT2 immunostaining. This observation was confirmed in a Western blot analysis of the GLUT2 protein in isolated pancreatic islets. Only beta cells that were densely immunostained for insulin were still GLUT2 positive. However, around 40% of the beta cells devoid of GLUT2 immunoreactivity were still insulin immunoreactive. Thus, the loss of GLUT2 immunoreactivity, which is an important component of the glucose recognition apparatus of the pancreatic beta cell, is an early indicator of beta cell dysfunction before the development of degenerative lesions or the loss of insulin immunoreactivity. GLUT2 loss may be important in the deterioration of glucose-induced insulin secretion in the diabetic Chinese hamster.

Immunohistochemical detection of secretoneurin, a novel neuropeptide endoproteolytically processed from secretogranin II, in normal human endocrine and neuronal tissues

An antiserum raised against a synthetic peptide derived from the primary amino sequence of rat secretogranin II (chromogranin C) was used for immunological (quantitative radioimmunoassay analysis) and immunohistochemical studies of normal human endocrine and nervous tissues. This antibody recognized a novel and biologically active neuropeptide which was coined as secretoneurin. In endocrine tissues, secretoneurin was mainly co-localized with chromogranin A and B with some exceptions (e.g., parathyroid gland). Secretoneurin was demonstrated immunohistochemically in the adrenal medulla, thyroid C cells, TSH- and FSH/LH-producing cells of the anterior pituitary, A and B cells of pancreatic islets, in endocrine cells of the gastrointestinal tract and the bronchial mucosa, and the prostate. Immunoreactivity determined by radioimmunoassay analysis revealed high secretoneurin levels in the anterior and posterior pituitary and lower levels in pancreatic and thyroid tissue. A strong secretoneurin immunoreactivity was also found in ganglion cells of the submucosal and myenteric plexus of the gastrointestinal tract, and in ganglionic cells of dorsal root ganglia, peripheral nerves, and ganglion cells of the adrenal medulla. Thus, secretoneurin may serve as a useful marker of gangliocytic/neuronal differentiation.

Analysis of the chromogranin A post-translational cleavage product pancreastatin and the prohormone convertases PC2 and PC3 in normal and neoplastic human pituitaries

Several members of the chromogranin/secretogranin (Cg/Sg) family are post-translationally processed in neuroendocrine cells and tumors to smaller peptides, some of which are biologically active. For example, CgA is processed to pancreastatin, parastatin, and other peptides. We analyzed the distribution of pancreastatin and CgA proteins in normal and neoplastic pituitaries as well as the prohormone convertases PC2 and PC3/1 (PC3), the putative processing enzymes for the Cg/Sg family, in 35 pituitary adenomas and 4 non-neoplastic pituitaries by immunohistochemistry and immunoblotting with highly specific antisera. CgA and CgB mRNAs were also examined. Pancreastatin was present in all subtypes of pituitary tumors, although prolactin-secreting adenomas expressed this peptide less frequently than did other tumor types. CgA protein and CgA mRNA expression were also restricted in prolactin adenomas and in normal prolactin cells, as shown by combined in situ hybridization and immunostaining. The prohormone convertases PC2 and PC3 were present in pituitary tumors and in non-neoplastic pituitaries. Immunoblot analysis and immunostaining showed a principal approximately 69-kd PC3 band and a approximately 68-kd PC2 band. Adrenocorticotrophic hormone-secreting adenomas expressed mainly PC3 as determined by immunoblotting and immunohistochemistry, whereas all other adenoma groups expressed predominantly PC2. These results indicate that the enzymes capable of processing CgA and other members of the Cg/Sg family to peptides with biological activity such as pancreastatin are widely expressed in human pituitary adenomas and in non-neoplastic pituitaries, with adrenocorticotrophic hormone tumors expressing predominantly PC3 and other adenomas expressing mainly PC2. The infrequent expression of CgA protein and pancreastatin peptides in normal and neoplastic prolactin cells suggests a unique role of CgA in these tumors.

Immunohistochemical Localization of Chromostatin and Pancreastatin, Chromogranin A-Derived Bioactive Peptides, in Normal and Neoplastic Neuroendocrine Tissues

Despite the widespread distribution of chromogranin A (CgA) in neuroendocrine tissues, the biological function of CgA has not yet been elucidated. The primary amino acid sequence of CgA, elucidated by cDNA analysis, has been revealed to include several pairs of basic amino acid residues that are homologous to the bioactive peptides, such as pancreastatin (PST) and chromostatin (CST). Using antibodies for human PST and CST, the immunohistochemical localization of these peptides was investigated in neuroendocrine tissues, including human pituitary glands, pancreas, adrenal medulla, various types of neuroendocrine neoplasms (13 pheochromocytomas, 10 medullary thyroid carcinomas, 11 pancreatic endocrine tumors, and 19 carcinoid tumors), and the cell line QGP-1N derived from human somatostatin-producing pancreatic endocrine tumor. Variable immunoreactive intensities of PST and CST were seen, but both peptides were detectable in all neuroendocrine tissues and in most of the neoplasms. Immunoreactivity for both PST and CST was observed in 100 and 73%, respectively, of pancreatic endocrine tumors, all pheochromocytomas, and 80 and 40%, respectively, of medullary thyroid carcinomas, as well as all nonrectal carcinoid tumors. In rectal carcinoids, cells immunoreactive for PST and CST were sparse. The distribution of PST and CST was similar to that of CgA, and it is considered that these peptides are simultaneously processed from CgA, and may play roles in autocrine and paracrine regulation on various hormones in addition to their previously known functions.

Immunocytochemical and ultrastructural heterogeneities of normal and glibenclamide stimulated pancreatic beta cells in the rat

When studied morphologically in semi-thin sections in the rat in vivo, pancreatic beta cells displayed heterogeneous immunoreactivities for insulin and amylin, depending on the islet size and the intra islet position of the beta cells. In larger islets, cortical beta cells (beta cells with contacts with all islet cell types and with the exocrine parenchyma) which are located in the periphery were more densely immunostained for insulin and amylin than medullary beta cells (beta cells with contacts only with other beta cells) which are located in the centre of the islet. Ultrastructurally, these findings were accompanied by differences in the number of secretory granules and mitochondria. Beta cells in small islets and at extra-islet sites exhibited a dense immunoreactivity. After administration of glibenclamide, immunoreactivities for insulin and amylin were diminished in a time-dependent manner, decreasing first in medullary and thereafter in cortical beta cells of larger islets. Ultrastructurally, the beta cells exhibited the typical signs of stimulation. A minority of beta cells in small islets and all beta cells in extra-islet locations remained unchanged. Thus pancreatic beta cells under basal and stimulatory conditions in vivo exhibit heterogeneity in hormone content and in ultrastructural features. These differences may represent the basis for a functional heterogeneity of the insulin secretory response of the individual beta cell both in vivo and in vitro in states of normal and impaired insulin secretion. As heterogeneity was observed only among beta cells in islets, while single beta cells surrounded by acinar cells exhibited no changes in insulin immunoreactivity, interactions between beta cells as well as between beta cells and other endocrine cells may be critical for expression of heterogeneity within the beta cell population.

Expression of chromogranin A and B and secretoneurin immunoreactivity in neoplastic and nonneoplastic pancreatic alpha cells

In the endocrine pancreas, chromogranins A and B as well as secretoneurin (a biologically active peptide processed endoproteolytically from secretogranin II) are most intensely expressed in alpha (glucagon) cells. We examined whether the functional status of neoplastic and nonneoplastic human alpha cells is reflected in the expression patterns of chromogranins/secretogranins. Neoplastic alpha cells were analysed immunocytochemically in six functioning glucagonomas and 37 nonfunctioning neuroendocrine tumours (29 with alpha cells) for their immunoreactivity to chromogranin A and B, as well as secretoneurin. There was no difference in the staining intensity for either peptide between glucagonomas and nonfunctioning, alpha cell containing tumours. Nonneoplastic alpha cells from patients with a functioning glucagonoma showed a decreased glucagon immunoreactivity, whereas the expression of chromogranin A (but not chromogranin B and secretoneurin) was as intense as in alpha cells not associated with glucagonoma syndrome. These results suggest that the expression of chromogranins/secretogranins in neoplastic alpha cells of the pancreas may be independently regulated from the cells' functional status. In nonneoplastic alpha cells there seems to be an association between glucagon production and chromogranin B and secretoneurin expression.

Enterochromaffin cells of the digestive system: cellular source of guanylin, a guanylate cyclase-activating peptide

Guanylin, a bioactive peptide, has recently been isolated from the intestine; this peptide activates intestinal guanylate cyclase (i.e., guanylate cyclase C) and thus is potentially involved in the regulation of water/electrolyte transport in the gastrointestinal mucosa. As yet, the cells involved in synthesis, storage, or secretion of guanylin have not been identified by immunocytochemistry. We raised antisera against guanylin and investigated the entire gastrointestinal tract of guinea pigs by light and electron microscopical immunocytochemistry. Extracts of various intestinal segments and plasma analyzed on a Western blot revealed a peptide band corresponding to the molecular mass of guanylin. Localization studies in the entire digestive tract showed that guanylin is exclusively confined to enterochromaffin (EC) cells. Remarkably, most EC cells contacted the gut lumen by cell processes that were highly immunoreactive for guanylin. In addition to the well known secretion in an endocrine fashion, EC cells by circumstantial evidence may release guanylin into the gut lumen to activate guanylate cyclase C that is immediately located on the brush border of adjacent enterocytes. The unique localization of guanylin in EC cells may indicate that these cells are involved in the regulation of fluid secretion in the gastrointestinal mucous membrane.