Chromogranin A is present in and released by fish endocrine tissue

The Chromogranin A-derived sympathomimetic serpinin depresses myocardial performance in teleost and amphibian hearts

Chromogranin A (CgA) is an acidic protein co-stored with catecholamines, hormones and neuropeptides in the secretory granules of endocrine, neuronal and other cell types (including cardiomyocytes). Proteolytic cleavage in the C terminus of CgA generates a 2.9kDa peptide named serpinin (Serp; Ala26Leu) that can be modified at its N terminus to form a pyroglutamate residue (pGlu-Serp). In the rat heart, both peptides increase contractility and relaxation through a β-adrenergic-like action mechanism. Accordingly, Serp and pGlu-Serp were proposed as novel myocardial sympatho-adrenergic modulators in mammals. On a comparative basis, here we report the actions of Serp and pGlu-Serp on myocardial contractility in three poikilotherm vertebrate species: the eel (Anguilla anguilla), the goldfish (Carassius auratus) and the frog (Rana esculenta). Using isolated working heart preparations, we show that pGlu-Serp reduces stroke volume in all species tested, while Serp reduces contractility in the frog heart, but is uneffective in eel and goldfish hearts. In the goldfish and frog hearts, pGlu-Serp activates the Nitric Oxide/cGMP pathway involving Endothelin-1 B receptors (frog) and β₃ adrenergic receptors (goldfish). pGlu-Serp-treated hearts from goldfish and frog show increased cGMP content. Moreover, the exposure of the frog heart to pGlu-Serp is accompanied by an increased expression of activated eNOS and Akt. In conclusion, this first report showing that pGlu-Serp inhibits mechanical cardiac performance in teleost and amphibians supports an evolutionary role of the CgA system, and particularly its serpinin component, in the sympatho-adrenergic control of the vertebrate heart.

Catecholamines, cardiac natriuretic peptides and chromogranin A: evolution and physiopathology of a 'whip-brake' system of the endocrine heart

In the past 50 years, extensive evidence has shown the ability of vertebrate cardiac non-neuronal cells to synthesize and release catecholamines (CA). This formed the mindset behind the search for the intrinsic endocrine heart properties, culminating in 1981 with the discovery of the natriuretic peptides (NP). CA and NP, co-existing in the endocrine secretion granules and acting as major cardiovascular regulators in health and disease, have become of great biomedical relevance for their potent diagnostic and therapeutic use. The concept of the endocrine heart was later enriched by the identification of a growing number of cardiac hormonal substances involved in organ modulation under normal and stress-induced conditions. Recently, chromogranin A (CgA), a major constituent of the secretory granules, and its derived cardio-suppressive and antiadrenergic peptides, vasostatin-1 and catestatin, were shown as new players in this framework, functioning as cardiac counter-regulators in 'zero steady-state error' homeostasis, particularly under intense excitatory stimuli, e.g. CA-induced myocardial stress. Here, we present evidence for the hypothesis that is gaining support, particularly among human cardiologists. The actions of CA, NP and CgA, we argue, may be viewed as a hallmark of the cardiac capacity to organize 'whip-brake' connection-integration processes in spatio-temporal networks. The involvement of the nitric oxide synthase (NOS)/nitric oxide (NO) system in this configuration is discussed. The use of fish and amphibian paradigms will illustrate the ways that incipient endocrine-humoral agents have evolved as components of cardiac molecular loops and important intermediates during evolutionary transitions, or in a distinct phylogenetic lineage, or under stress challenges. This may help to grasp the old evolutionary roots of these intracardiac endocrine/paracrine networks and how they have evolved from relatively less complicated designs. The latter can also be used as an intellectual tool to disentangle the experimental complexity of the mammalian and human endocrine hearts, suggesting future investigational avenues.

New insights into granin-derived peptides: evolution and endocrine roles

The granin protein family is composed of two chromogranin and five secretogranin members that are acidic, heat-stable proteins in secretory granules in cells of the nervous and endocrine systems. We report that there is little evidence for evolutionary relationships among the granins except for the chromogranin group. The main granin members, including chromogranin A and B, and secretogranin II are moderately conserved in the vertebrates. Several small bioactive peptides can be generated by proteolysis from those homologous domains existing within the granin precursors, reflecting the conservation of biological activities in different vertebrates. In this context, we focus on reviewing the distribution and function of the major granin-derived peptides, including vasostatin, bovine CgB(1-41) and secretoneurin in vertebrate endocrine systems, especially those associated with growth, glucose metabolism and reproduction.

New biological aspects of Chromogranin A-derived peptides: Focus on vasostatins

Chromogranin A (CgA), one component of the granin family, represents the major soluble protein co-stored and co-released with catecholamines, within chromaffin cells secretory granules. It is considered a diagnostic and prognostic marker of several diseases, including a variety of tumours and cardiac heart failure. It also represents a precursor of biologically active fragments, generated after proteolytic cleavage at the level of the multiple pairs of dibasic sites which enrich its sequence. CgA, and its derived fragments show an old evolutionary history being ubiquitously present throughout the animal word, from mammals to invertebrates. Their biological functions include control of hormone production, and several paracrine and autocrine actions mainly attributed to its derived peptides. Two N-terminal fragments, named vasostatins 1 (VS-1: CgA(1-76)) and vasostatin 2 (VS-2: CgA(1-113)) due to their ability to dilate pre-constricted vessels, exert a large spectrum of homeostatic actions, including antifungal and antimicrobial effect, modulation of cell adhesion, and inhibition of parathyroid hormone secretion. Recently, on isolated heart preparations from eel, frog and rat they were shown to act as negative inotropic agents able to counteract the effects of beta-adrenergic stimulation. This short note introduces the abstracts of the contributions at the "International Workshop on Vasostatins and Chromogranin A-derived peptides" (Island of Capri, Italy; September 2005). The Workshop was focused on recent findings on the role of vasostatins (VSs) in cardiovascular and gastrointestinal systems, extracellular fluids composition, and innate immunity. Particular attention has been given to the still elusive mechanism of action of these peptides.

The granin family of uniquely acidic proteins of the diffuse neuroendocrine system: comparative and functional aspects

The chromogranins A (CgA) and B (CgB) and secretogranin II (SgII) constitute the main members of a family of uniquely acidic secretory proteins in elements of the diffuse neuroendocrine system. These genetically distinct proteins, CgA, CgB, SgII and the less well known secretogranins III-VII are collectively referred to as 'granins' and characterised by numerous pairs of basic amino acids as potential cleavage sites for processing by the co-stored prohormone converting enzymes PC 1/3 and PC2. This review is directed towards comparative and functional aspects of the granins with emphasis on their phylogenetically conserved sequences. Recent developments provide ample evidence of widely different effects and targets for the intact granins and their derived peptides, intracellularly in the directed trafficking of storage components during granule maturation and extracellularly in autocrine, paracrine and endocrine interactions. Most of the effects assigned to the granin derived peptides fit into patterns of direct or indirect inhibitory modulations of major functions. So far, peptides derived from CgA (vasostatins, chromacin, pancreastatin, WE-14, catestatin and parastatin), CgB (secretolytin) and SgII (secretoneurin) are the most likely candidates for granin-derived regulatory peptides, of postulated relevance not only for homeostatic processes, but also for tissue assembly and repair, inflammatory responses and the first line of defence against invading microorganisms.

Chromogranin A-immunoreactive cells in the olfactory system of anuran amphibians

Chromogranin A (CgA) is a member of the granin family of acidic proteins that are present in the secretory granules of many endocrine and neuroendocrine cells. The specific function(s) of these proteins is not known, but they seem to be the precursors of biologically active peptides, and they may act as helper proteins in the sorting and packaging of peptide hormones and neuropeptides. Using indirect immunohistochemistry, we have found CgA immunoreactivity in the primary olfactory epithelia, the vomeronasal epithelia, the olfactory nerves, and the olfactory bulbs of tadpoles of the American toad, Bufo americanus, and the green frog, Rana clamitans. CgA immunoreactivity was present in the early stages of larval development in toads but was not detected in toad tadpoles after the hindlimb buds formed or in toadlets or adults. In green frog tadpoles, CgA-immunoreactive cells were found in pre- and prometamorphic stages but not in late climax. CgA immunoreactivity was also absent in froglets, but it was detected in the vomeronasal epithelium but not the olfactory epithelium of adult green frogs.

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.

Immunohistochemical localization of chromogranin A and B in the endocrine cells of the alimentary tract of the green frog, Rana esculenta

Novel monoclonal antibodies to human chromogranin A (CgA) and chromogranin B (CgB) were used to investigate the presence of immunoreactive (-IR) elements in the alimentary tract of the green frog Rana esculenta. Numerous CgA-IR and a few CgB-IR endocrine cells were found within the gut mucosa, from the oesophagus to the cloaca, with some local differences in density. Co-localization studies demonstrated that they were co-stored in almost all the serotonin-IR, the amylin-IR or islet amyloid polypeptide-IR cells and in the peptide tyrosine tyrosine-IR cells located proximal to the pylorus, but not in those located in more caudal tracts. No other co-localization was demonstrated; substances investigated included somatostatin, substance P, gastrin/cholecystokinin, glucagon, glycentin, bombesin, secretin and neurotensin. CgA-IR and CgB-IR cells nearly always displayed argyrophilia with the Grimelius silver method.

Phylogenetic aspects of pancreastatin- and chromogranin-like immunoreactive cells in the gastro-entero-pancreatic neuroendocrine system of vertebrates

Using a battery of region-specific antisera raised against different amino acid sequences of pancreastatin (Pst) (Pst-1-6, Pst-1-17, Pst-14-49, Pst-33-49) as well as two antisera raised against chromogranin (Cg) A and CgA/B and the biotin-avidin technique, the phylogenetic distribution of Pst-immunoreactive (-IR) and Cg-IR cells was studied in the gastroentero-pancreatic (GEP) neuroendocrine system. The investigation was carried out with representatives of all vertebrate classes as well as with the protochordates Branchiostoma lanceolatum and Ciona intestinalis. The study revealed the presence of Pst-IR and Cg-IR cells in the gastro-intestinal mucosal epithelium as well as in the islet parenchyma of all vertebrates studied with the only exception found in rat. In the rat GEP system unequivocal immunoreactions were obtained only by the use of antiserum CgA/B. In the gastro-intestinal tract of the deuterostomian invertebrates no Pst-IR or Cg-IR cells could be observed with any of our antisera. Whether this might indicate that Pst-like or Cg-like peptides are characteristic for vertebrates or, more likely, whether similar proteins/peptides might be present in the alimentary tract of protochordates which do not react with the antisera at hand, remains to be clarified. Thouh pronounced interspecies and some intraspecies differences were found, several general conclusions can be drawn. In all vertebrate species, the Pst-IR and Cg-IR cells observed in the mucosal epithelium of the gastro-intestinal tract showed an endocrine structure and were of the so-called open type. The Pst and the Cg antisera which gave immunoreactions with parenchymal cells in the islets of Langerhans also reacted with cells in the epithelium of the pancreatic ducts. Comparative analysis of the reaction properties of the region-specific antisera used indicated that the Pst-like material in the islet cells of the cartilaginous fish species studied seems to be "mammalian-like," whereas it appears to be different in the other (phylogenetically younger) submammalian vertebrates. In addition, the Pst-like peptides in the gastro-intestinal mucosal epithelium and in those in the islets seem to differ in most submammalians. Finally, in the pyloric-duodenal junction of the quail (Coturnix c. japonica) the presence of a so far unknown peptide of the Cg family is presumed. In general, our results seem to indicate that the phylogeny of Pst-like and Cg-like peptides is not as "straight" as those which have been demonstrated for several other neurohormonal peptides.(ABSTRACT TRUNCATED AT 400 WORDS)

Fragmentation of bovine chromogranin A by plasma kallikrein

Chromogranin A has been reported to be processed in vivo by an as yet undefined proteinase(s) suggesting that it is a precursor of biologically active peptides such as pancreastatin. In this study, plasma kallikrein was used as a model proteinase to identify the cleavage sites exposed in bovine parathyroid chromogranin A. Purified bovine parathyroid chromogranin A was digested with human plasma kallikrein. The proteolytic fragments produced were isolated by HPLC and chemically characterized by amino acid composition and sequence analysis. The combined results indicate that the enzyme has preference for specific single Arg residues, cutting C-terminal to this amino acid, although certain pairs of basic sites were also cleaved. The characterized fragments were released in a selective manner from the whole molecule with rapid production of the fragments covering positions 1-247 and 352-358.

Immunohistochemical localization of chromogranin A in normal tissues from laboratory animals

To analyze the distribution of Chromogranin A in endocrine cells of various species of laboratory animals (dog, gerbil, guinea pig, hamster, monkey, mouse, and fetal, neonatal, and adult rats), normal tissues were stained immunohistochemically with polyclonal anti-bovine Chromogranin A antiserum (SP-1). Selected tissues (pituitary, adrenal, thyroid, parathyroid, pancreas, brain, peripheral nerve, stomach, small and large intestine, bone marrow, spleen, thymus, lymph node, and liver) from these species and from the rabbit were stained with two monoclonal anti-human Chromogranin A antibodies (LK2H10 and PHE5) to compare the immunoreactivities of the monoclonal antibodies and polyclonal antiserum. Staining with the polyclonal antiserum (SP-1) resulted in a broader spectrum of immunoreactivity but had more nonspecific background staining than either monoclonal antibody. Immunoreactivity and staining intensity with SP-1 varied between species, but most endocrine tissues (pituitary cells in the anterior and intermediate lobes, thyroid "C" cells, adrenal medulla, parathyroid, pancreatic islets, and enterochromaffin cells) from most species stained positively. In some species, pancreatic alpha cells stained more intensely, and two populations of adrenal medullary cells with different staining intensities were observed. Sciatic nerve (axonal area) was immunoreactive with monoclonal antibodies and/or the polyclonal antiserum in several species. The spectrum of immunoreactive tissues from fetal and neonatal rats increased with age. There was good cross-reactivity between species with SP-1, but not with either LK2H10 or PHE5. These results indicate that many endocrine cells with secretory granules in laboratory animals express Chromogranin A and that a polyclonal antiserum, such as SP-1, is more sensitive in detecting this protein in various species than monoclonal antibodies such as LK2H10 or PHE5.

Biochemistry of the chromogranin A protein family

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Effect of secretagogues on chromogranin A synthesis in bovine cultured chromaffin cells. Possible regulation by protein kinase C

Chromogranin A is a major component of storage granules in many different secretory cell types. After [35S]methionine labelling of proteins from cultured bovine chromaffin cells, chromogranin A was immunoprecipitated with specific antibodies, and the radioactivity incorporated into chromogranin A was determined and used as an index of its synthesis rate. Depolarization of cells with nicotine or high K+ evoked a Ca2+-dependent increase in chromogranin A synthesis, whereas muscarine, which does not evoke significant Ca2+ influx from bovine chromaffin cells, had no effect on chromogranin A synthesis. Forskolin, an activator of adenylate cyclase, affected neither the basal nor the nicotine-stimulated rate of chromogranin A synthesis. In contrast, 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, significantly enhanced the incorporation of radioactivity into chromogranin A. Sphingosine, an inhibitor of protein kinase C, abolished both nicotine-stimulated and TPA-induced chromogranin A synthesis. In addition, long-term treatment of chromaffin cells with TPA decreased protein kinase C activity and inhibited the nicotine-stimulated chromogranin A synthesis. These results suggest that protein kinase C may play an important role in the control of chromogranin A synthesis.

The effects of forskolin and calcium ionophore A23187 on secretion and cytoplasmic RNA levels of Chromogranin-A and calcitonin

We have studied the regulation of the secretion and cytoplasmic RNA levels of calcitonin (CT) and Chromogranin-A (CgA) to determine if the biosynthesis and secretion of these two substances are controlled in a coordinated fashion. The studies were conducted in two cell lines, a medullary thyroid carcinoma (MTC) cell line and a lung tumor (BEN) cell line. Both cell types secrete CT and CgA. Forskolin treatment resulted in a significant increase in the secretion of CT and CgA in each cell line and in CT-specific cytoplasmic RNA in the MTC cell line. Treatment with calcium ionophore A23187 resulted in significantly increased secretion of both substances in the lung tumor cells but not in the medullary thyroid carcinoma cells. A significant increase in CT-specific or CgA-specific cytoplasmic RNA was not seen in either cell line. We conclude that the secretion of CT and CgA are regulated in a coordinated fashion in these cell lines through processes that are calcium-mediated and processes that involve cyclic AMP-dependent protein kinase A. However, each of these regulatory pathways is not always operative in a given tissue. The coordinate regulation of the secretion of CT and CgA supports the hypothesis that CgA participates in the secretory process of its associated hormones.

Demonstration of Chromogranin A in human neuroendocrine cell lines by immunohistology and immunoassay

We have used immunohistology and radioimmunoassay procedures to study Chromogranin A (CgA) in human neuroendocrine tumor cell lines, especially small cell lung cancers (SCLC). By immunohistology, CgA could be detected in 11 of 18 classical SCLC cell lines, in a medullary thyroid carcinoma (MTC) cell line, and in only one of 13 variant- or non-SCLC cell lines. By radioimmunoassay, CgA could be detected in the cells and culture media of all of the classical SCLC cell lines tested. Many of the classical SCLC cell lines also produced calcitonin (CT). These studies demonstrate that CgA production is a common feature of SCLC cell lines, especially those with neuroendocrine characteristics.

Phylogenetic distribution of peptides related to chromogranins A and B

The presence of chromogranin-related peptides in a wide range of species was investigated by one and two-dimensional electrophoresis followed by immunoblotting. Antisera against bovine chromogranins A and B and the peptide WE-14 (chromogranin A316-329) were used. Chromogranins were identified by their heat stability, by their electrophoretic behavior, and by immunological cross-reaction with antisera. In all species investigated ranging from mammals to birds, amphibians, fish, and arthropods, chromogranin A- and B-like proteins could be demonstrated. For all species, there was an immunological cross-reaction with antisera against bovine chromogranins. The molecular sizes and isoelectric points of the chromogranins were similar in all species. The antiserum against WE-14 cross-reacted with pig, rat, and chicken chromogranins. It is concluded that the chromogranins A and B have a widespread phylogenetic distribution with a significant conservation of molecular size, isoelectric points, and immunological epitopes. This is consistent with the concept that these peptides have a specific function.