Structure-activity relationships of chromogranin A in cell adhesion. Identification of an adhesion site for fibroblasts and smooth muscle cells

A novel bioengineered fragment peptide of Vasostatin-1 exerts smooth muscle pharmacological activities and anti-angiogenic effects via blocking VEGFR signalling pathway

Chromogranin A (CgA) is a hydrophilic glycoprotein released by post-ganglionic sympathetic neurons. CgA consists of a single peptide chain containing numerous paired basic residues, which are typical cleavage sites in prohormones to generate bioactive peptides. It is recognized as a diagnostic and prognostic serum marker for neuroendocrine tumours. Vasostatin-1 is one of the most conserved regions of CgA and has diverse inhibitory biological activities. In this study, a novel peptide fragment that contains three typical functional structures of Vasostatin-1 was synthesized. This unique bioengineered Vasostatin-1 Derived Peptide (named V1DP) includes a highly conserved domain between vertebrate species in its N-terminal region, comprising a disulphide bridge formed by two cysteine residues at amino acid positions 17 and 38, respectively. Besides, V1DP contains two significant tripeptide recognition sequences: the amino acid triplets, RGD and KGD. Our data demonstrated that V1DP could induce a dose-dependent relaxation of rat arterial smooth muscle and also increase the contraction activity of rat uterus smooth muscle. More importantly, we found that V1DP inhibits cancer cell proliferation, modulate the HUVEC cell migration, and exhibit anti-angiogenesis effect both in vitro and in vivo. We further investigated the actual mechanism of V1DP, and our results confirmed that V1DP involves inhibiting the vascular endothelial growth factor receptor (VEGFR) signalling. We docked V1DP to the apo structures of VEGFR2 and examined the stability of the peptide in the protein pockets. Our simulation and free energy calculations results indicated that V1DP can bind to the catalytic domain and regulatory domain pockets, depending on whether the conformational state of the protein is JM-in or JM-out. Taken together, our data suggested that V1DP plays a role as the regulator of endothelial cell function and smooth muscle pharmacological homeostasis. V1DP is a water-soluble and biologically stable peptide and could further develop as an anti-angiogenic drug for cancer treatment.

Circulating Chromogranin A Is Cleaved Into Vasoregulatory Fragments in Patients With Pancreatic Ductal Adenocarcinoma

Chromogranin A (CgA), a secretory protein released in the blood by the neuroendocrine system, consists of a mixture of full-length molecules and fragments endowed of vasoregulatory activity. The extent and the role of CgA fragmentation were investigated in patients with locally advanced or metastatic pancreatic ductal adenocarcinoma (PDAC, n=172). Multivariate analysis showed that full-length CgA was associated with better progression free and overall survival, whereas CgA C-terminal fragmentation was associated with worse prognosis. In vitro studies showed that PDAC cells can promote the cleavage of CgA C-terminal region by activating plasminogen to plasmin. Limited digestion of full-length CgA with plasmin abolished its anti-angiogenic activity and generated pro-angiogenic molecules. The fragmentation of CgA C-terminal region was increased also in murine models of PDAC. In these models, the inhibition of CgA fragmentation with aprotinin, an inhibitor of plasmin and other serine proteases, or the blockade of pro-angiogenic fragments with specific antibodies inhibited the growth of PDAC implanted subcutaneously in mice. Finally, administration of full-length CgA to mice bearing orthotopic PDAC reduced tumor perfusion, as measured by contrast-enhanced ultrasound. These findings suggest that PDAC can promote the cleavage of circulating CgA C-terminal region to generate fragments that regulate the tumor vascular biology and that may represent new potential therapeutic targets.

Physiological levels of chromogranin A prevent doxorubicin-induced cardiotoxicity without impairing its anticancer activity

The clinical use of doxorubicin (Doxo), a widely used anticancer chemotherapeutic drug, is limited by dose-dependent cardiotoxicity. We have investigated whether chromogranin A (CgA), a cardioregulatory protein released in the blood by the neuroendocrine system and by the heart itself, may contribute to regulation of the cardiotoxic and antitumor activities of Doxo. The effects of a physiologic dose of full-length recombinant CgA on Doxo-induced cardiotoxicity and antitumor activity were investigated in rats using in vivo and ex vivo models and in murine models of melanoma, fibrosarcoma, lymphoma, and lung cancer, respectively. The effect of Doxo on circulating levels of CgA was also investigated. In vivo and ex vivo mechanistic studies showed that CgA can prevent Doxo-induced heart inflammation, oxidative stress, apoptosis, fibrosis, and ischemic injury. On the other hand, CgA did not impair the anticancer activity of Doxo in all the murine models investigated. Furthermore, we observed that Doxo can reduce the intracardiac expression and release of CgA in the blood (i.e., an important cardioprotective agent). These findings suggest that administration of low-dose CgA to patients with low levels of endogenous CgA might represent a novel approach to prevent Doxo-induced adverse events without impairing antitumor effects.-Rocca, C., Scavello, F., Colombo, B., Gasparri, A. M., Dallatomasina, A., Granieri, M. C., Amelio, D., Pasqua, T., Cerra, M. C., Tota, B., Corti, A., Angelone, T. Physiological levels of chromogranin A prevent doxorubicin-induced cardiotoxicity without impairing its anticancer activity.

Spatiotemporal Regulation of Tumor Angiogenesis by Circulating Chromogranin A Cleavage and Neuropilin-1 Engagement

The unbalanced production of pro- and antiangiogenic factors in tumors can lead to aberrant vasculature morphology, angiogenesis, and disease progression. In this study, we report that disease progression in various murine models of solid tumors is associated with increased cleavage of full-length chromogranin A (CgA), a circulating vasoregulatory neurosecretory protein. Cleavage of CgA led to the exposure of the highly conserved PGPQLR site, which corresponds to residues 368-373 of human CgA_1-373, a fragment that has proangiogenic activity. Antibodies against this site, unable to bind full-length CgA, inhibited angiogenesis and reduced tumor perfusion and growth. The PGPQLR sequence of the fragment, but not of the precursor, bound the VEGF-binding site of neuropilin-1; the C-terminal arginine (R₃₇₃) of the sequence was crucial for binding. The proangiogenic activity of the CgA_1-373 was blocked by anti-neuropilin-1 antibodies as well as by nicotinic acetylcholine receptor antagonists, suggesting that these receptors, in addition to neuropilin-1, play a role in the proangiogenic activity of CgA_1-373. The R₃₇₃ residue was enzymatically removed in plasma, causing loss of neuropilin-1 binding and gain of antiangiogenic activity. These results suggest that cleavage of the R₃₇₃R₃₇₄ site of circulating human CgA in tumors and the subsequent removal of R₃₇₃ in the blood represent an important "on/off" switch for the spatiotemporal regulation of tumor angiogenesis and may serve as a novel therapeutic target. SIGNIFICANCE: This work reveals that the interaction between fragmented chromogranin A and neuropilin-1 is required for tumor growth and represents a novel potential therapeutic target.

Catestatin regulates vesicular quanta through modulation of cholinergic and peptidergic (PACAPergic) stimulation in PC12 cells

We have previously shown that the chromogranin A (CgA)-derived peptide catestatin (CST: hCgA_352-372) inhibits nicotine-induced secretion of catecholamines from the adrenal medulla and chromaffin cells. In the present study, we seek to determine whether CST regulates dense core (DC) vesicle (DCV) quanta (catecholamine and chromogranin/secretogranin proteins) during acute (0.5-h treatment) or chronic (24-h treatment) cholinergic (nicotine) or peptidergic (PACAP, pituitary adenylyl cyclase activating polypeptide) stimulation of PC12 cells. In acute experiments, we found that both nicotine (60 μM) and PACAP (0.1 μM) decreased intracellular norepinephrine (NE) content and increased ³H-NE secretion, with both effects markedly inhibited by co-treatment with CST (2 μM). In chronic experiments, we found that nicotine and PACAP both reduced DCV and DC diameters and that this effect was likewise prevented by CST. Nicotine or CST alone increased expression of CgA protein and together elicited an additional increase in CgA protein, implying that nicotine and CST utilize separate signaling pathways to activate CgA expression. In contrast, PACAP increased expression of CgB and SgII proteins, with a further potentiation by CST. CST augmented the expression of tyrosine hydroxylase (TH) but did not increase intracellular NE levels, presumably due to its inability to cause post-translational activation of TH through serine phosphorylation. Co-treatment of CST with nicotine or PACAP increased quantal size, plausibly due to increased synthesis of CgA, CgB and SgII by CST. We conclude that CST regulates DCV quanta by acutely inhibiting catecholamine secretion and chronically increasing expression of CgA after nicotinic stimulation and CgB and SgII after PACAPergic stimulation.

Vasostatin-1: A novel circulating biomarker for ileal and pancreatic neuroendocrine neoplasms

Background

Chromogranin A (CgA) is a plasma biomarker widely used in the follow-up of patients with neuroendocrine neoplasms (NENs). However, its accuracy as a tumor biomarker is relatively low because plasma CgA can increase also in patients with other diseases or in subjects treated with proton-pump inhibitors (PPIs), a class of widely-used drugs.

Methods

In the attempt to identify a more reliable biomarker for NENs, we investigated, by ELISA, the circulating levels of full-length CgA (CgA_1-439) and of various CgA-derived fragments in 17 patients with ileal or pancreatic NENs, 10 healthy controls, and 21 healthy volunteers before and after treatment with PPIs.

Results

Patients with ileal or pancreatic NENs showed increased plasma levels of total-CgA and CgA_1-76 fragment (vasostatin-1, VS-1) compared to controls [median (25^th-75^th-percentiles); total-CgA: 1.85 nM (1.01–4.28) vs 0.75 nM (0.52–0.89), p = 0.004; VS-1: 2.76 nM (1.09–7.10) vs 0.29 nM (0.26–0.32), p<0.001, respectively], but not of CgA_1-439 or CgA_1-373 fragment. VS-1 positively correlated with total-CgA (r = 0.65, p<0.001). The Receiver Operating Characteristic area under the curve was 0.9935 for VS-1 and 0.8824 for total-CgA (p = 0.067). Treatment of patients with somatostatin analogues decreased both total-CgA and VS-1. In contrast, administration of PPIs increased the plasma levels of total-CgA, but not of VS-1.

Conclusion

These findings suggest that plasma VS-1 is a novel biomarker for ileal and pancreatic NENs. Considering that VS-1 is a well-defined fragment not induced by proton-pump inhibitors, this polypeptide might represent a biomarker for NENs diagnosis and follow-up more accurate and easier to standardize than CgA.

Regulation of tumor growth by circulating full-length chromogranin A

Chromogranin A (CgA), a neuroendocrine secretory protein, and its fragments are present in variable amounts in the blood of normal subjects and cancer patients. We investigated whether circulating CgA has a regulatory function in tumor biology and progression. Systemic administration of full-length CgA, but not of fragments lacking the C-terminal region, could reduce tumor growth in murine models of fibrosarcoma, mammary adenocarcinoma, Lewis lung carcinoma, and primary and metastatic melanoma, with U-shaped dose-response curves. Tumor growth inhibition was associated with reduction of microvessel density and blood flow in neoplastic tissues. Neutralization of endogenous CgA with antibodies against its C-terminal region (residues 410-439) promoted tumor growth. Structure-function studies showed that the C-terminal region of CgA contains a bioactive site and that cleavage of this region causes a marked loss of anti-angiogenic and anti-tumor potency. Mechanistic studies showed that full-length CgA could induce, with a U-shaped dose-response curve, the production of protease nexin-1 in endothelial cells, a serine protease inhibitor endowed of anti-angiogenic activity. Gene silencing or neutralization of protease nexin-1 with specific antibodies abolished both anti-angiogenic and anti-tumor effects of CgA. These results suggest that circulating full-length CgA is an important inhibitor of angiogenesis and tumor growth, and that cleavage of its C-terminal region markedly reduces its activity. Pathophysiological changes in CgA blood levels and/or its fragmentation might regulate disease progression in cancer patients.

Inhibition of chronic lymphocytic leukemia progression by full-length chromogranin A and its N-terminal fragment in mouse models

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of leukemic B cells in peripheral blood, bone marrow (BM) and lymphoid tissues, and by their recirculation between these compartments. We observed that circulating chromogranin A (CgA) and its N-terminal fragment (called vasostatin-1, CgA_1-76), two neuroendocrine secretory polypeptides that enhance the endothelial barrier function, are present in variable amounts in the blood of CLL patients. Studies in animal models showed that daily administration of full-length human CgA_1-439 (0.3 μg, i.v., or 1.5 μg/mouse, i.p.) can reduce the BM/blood ratio of leukemic cells in Eμ-TCL1 mice, a transgenic model, and decrease BM, lung and kidney infiltration in Rag2^−/−γc^−/− mice engrafted with human MEC1 CLL cells, a xenograft model. This treatment also reduced the loss of body weight and improved animal motility. In vitro, CgA enhanced the endothelial barrier integrity and the trans-endothelial migration of MEC1 cells, with a bimodal dose-response curve. Vasostatin-1, but not a larger fragment consisting of N-terminal and central regions of CgA (CgA_1-373), inhibited CLL progression in the xenograft model, suggesting that the C-terminal region is crucial for CgA activity and that the N-terminal domain contains a site that is activated by proteolytic cleavage. These findings suggest that circulating full-length CgA and its fragments may contribute to regulate leukemic cell trafficking and reduce tissue infiltration in CLL.

Chromogranin A regulates vesicle storage and mitochondrial dynamics to influence insulin secretion

Chromogranin A (CgA) is a prohormone and a granulogenic factor that regulates secretory pathways in neuroendocrine tissues. In β-cells of the endocrine pancreas, CgA is a major cargo in insulin secretory vesicles. The impact of CgA deficiency on the formation and exocytosis of insulin vesicles is yet to be investigated. In addition, no literature exists on the impact of CgA on mitochondrial function in β-cells. Using three different antibodies, we demonstrate that CgA is processed to vasostatin- and catestatin-containing fragments in pancreatic islet cells. CgA deficiency in Chga-KO islets leads to compensatory overexpression of chromogranin B, secretogranin II, SNARE proteins and insulin genes, as well as increased insulin protein content. Ultrastructural studies of pancreatic islets revealed that Chga-KO β-cells contain fewer immature secretory granules than wild-type (WT) control but increased numbers of mature secretory granules and plasma membrane-docked vesicles. Compared to WT control, CgA-deficient β-cells exhibited increases in mitochondrial volume, numerical densities and fusion, as well as increased expression of nuclear encoded genes (Ndufa9, Ndufs8, Cyc1 and Atp5o). These changes in secretory vesicles and the mitochondria likely contribute to the increased glucose-stimulated insulin secretion observed in Chga-KO mice. We conclude that CgA is an important regulator for coordination of mitochondrial dynamics, secretory vesicular quanta and GSIS for optimal secretory functioning of β-cells, suggesting a strong, CgA-dependent positive link between mitochondrial fusion and GSIS.

Nanoprecipitated catestatin released from pharmacologically active microcarriers (PAMs) exerts pro-survival effects on MSC

Catestatin (CST), a fragment of Chromogranin-A, exerts angiogenic, arteriogenic, vasculogenic and cardioprotective effects. CST is a very promising agent for revascularization purposes, in "NOOPTION" patients. However, peptides have a very short half-life after administration and must be conveniently protected. Fibronectin-coated pharmacologically active microcarriers (FN-PAM), are biodegradable and biocompatible polymeric microspheres that can convey mesenchymal stem cell (MSCs) and therapeutic proteins delivered in a prolonged manner. In this study, we first evaluated whether a small peptide such as CST could be nanoprecipitated and incorporated within FN-PAMs. Subsequently, whether CST may be released in a prolonged manner by functionalized FN-PAMs (FN-PAM-CST). Finally, we assessed the effect of CST released by FN-PAM-CST on the survival of MSCs under stress conditions of hypoxia-reoxygenation. An experimental design, modifying three key parameters (ionic strength, mixing and centrifugation time) of protein nanoprecipitation, was used to define the optimum condition for CST. An optimal nanoprecipitation yield of 76% was obtained allowing encapsulation of solid CST within FN-PAM-CST, which released CST in a prolonged manner. In vitro, MSCs adhered to FN-PAMs, and the controlled release of CST from FN-PAM-CST greatly limited hypoxic MSC-death and enhanced MSC-survival in post-hypoxic environment. These results suggest that FN-PAM-CST are promising tools for cell-therapy.

Granin-derived peptides

The granin family comprises altogether 7 different proteins originating from the diffuse neuroendocrine system and elements of the central and peripheral nervous systems. The family is dominated by three uniquely acidic members, namely chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). Since the late 1980s it has become evident that these proteins are proteolytically processed, intragranularly and/or extracellularly into a range of biologically active peptides; a number of them with regulatory properties of physiological and/or pathophysiological significance. The aim of this comprehensive overview is to provide an up-to-date insight into the distribution and properties of the well established granin-derived peptides and their putative roles in homeostatic regulations. Hence, focus is directed to peptides derived from the three main granins, e.g. to the chromogranin A derived vasostatins, betagranins, pancreastatin and catestatins, the chromogranin B-derived secretolytin and the secretogranin II-derived secretoneurin (SN). In addition, the distribution and properties of the chromogranin A-derived peptides prochromacin, chromofungin, WE14, parastatin, GE-25 and serpinins, the CgB-peptide PE-11 and the SgII-peptides EM66 and manserin will also be commented on. Finally, the opposing effects of the CgA-derived vasostatin-I and catestatin and the SgII-derived peptide SN on the integrity of the vasculature, myocardial contractility, angiogenesis in wound healing, inflammatory conditions and tumors will be discussed.

[Changes in serum chromogranin A and urotensin II levels in children with chronic heart failure]

OBJECTIVE

To examine the changes in serum chromogranin A (CgA) and urotensin II (U II) levels in children with chronic heart failure (CHF) and their clinical significance.

METHODS

A total of 58 children with CHF, among whom 17 had endocardial fibroelastosis (EFE) and 41 had dilated cardiomyopathy (DCM), were selected as CHF group, and 20 healthy children were selected as control group. Serum levels of CgA and U II were measured using enzyme-linked immunosorbent assay, and the level of N-terminal pro-brain natriuretic peptide (NT-proBNP) was determined by bi-directional lateral flow immunoassay. Ventricular remodeling indices were measured using echocardiography. The correlation between serum CgA and U II levels and ventricular remodeling was evaluated by Pearson correlation or Spearman's rank correlation analysis.

RESULTS

There were no significant differences in serum CgA and NT-proBNP levels between children with grade II heart function and the control group (P>0.05). However, the serum CgA and NT-proBNP levels gradually increased as the heart function grade increased, and were significantly higher in grade III and IV children compared to those in the control group (P<0.05). U II levels were lower in children with grade II, III, or IV heart function than those in the control group (P<0.05), and significantly decreased with the aggravation of CHF (P<0.05). There were no significant differences in CgA and U II levels between patients with EFE and DCM (P>0.05). Serum CgA concentration was positively correlated with left ventricular mass index (LVMI), NT-proBNP, and cardiac function classification (r=0.279, 0.649, and 0.778 respectively; P<0.05), but was negatively correlated with left ventricular ejection fraction (LVEF), left ventricular fractional shortening (LVFS), and U II (r=-0.369, -0.322, and -0.718 respectively; P<0.05). Serum U II concentration was negatively correlated with NT-proBNP and cardiac function classification (r=-0.472 and -0.591 respectively; P<0.05), but was not correlated with LVMI, LVEF, and LVFS (P>0.05).

CONCLUSIONS

CgA may play a role in ventricular remodeling in children with CHF. Serum CgA and U II may serve as a reference for the diagnosis and functional classification of heart failure.

Association of serum HMGB2 level with MACE at 1 mo of myocardial infarction: Aggravation of myocardial ischemic injury in rats by HMGB2 via ROS

High-mobility group box (HMGB) family is related to inflammatory diseases. We investigated whether serum HMGB2 levels are related to myocardial infarction (MI) severity and major adverse cardiac events (MACE) during MI. We included 432 consecutive patients with ST-segment elevation myocardial infarction and 312 controls. Serum HMGB2 levels were significantly higher in MI patients than in controls. Increased HMGB2 levels were associated with MACE and negatively with ejection fraction in MI patients. HMGB2 was an independent determinant of MACE in logistic regression analysis. HMGB2 protein (10 μg) or saline was injected intramyocardially in MI rats, with or without coadministration of the NADPH oxidase inhibitor apocynin. After 72 h, pathological, echocardiographic, and hemodynamic examinations showed that HMGB2 increased infarct size and worsened cardiac function in MI rats. Moreover, HMGB2 administration enhanced reactive oxygen species (ROS) production, cell apoptosis, inflammation, and autophagosome clearance impairment, which were attenuated by coadministration of apocynin or knock down of receptor for advanced glycation end products (RAGE). In conclusion, increased serum HMGB2 levels are associated with MI severity and MACE at 1 mo. HMGB2 promotes myocardial ischemic injury in rats and hypoxic H9C2 cell damage via ROS provoked by RAGE.

NEW & NOTEWORTHY We demonstrate that serum high-mobility group box 2 is associated with major adverse cardiac events at 1 mo in myocardial infarction patients. Mechanistically, high-mobility group box 2 promotes reactive oxygen species production via receptor for advanced glycation end products signaling in ischemic myocardium, thereby aggravating cell apoptosis, inflammation, and autophagosome clearance impairment. This study reveals that high-mobility group box 2 is a novel factor enhancing ischemic injury in myocardial infarction.

Muscle injury, impaired muscle function and insulin resistance in Chromogranin A-knockout mice

Chromogranin A (CgA) is widely expressed in endocrine and neuroendocrine tissues as well as in the central nervous system. We observed CgA expression (mRNA and protein) in the gastrocnemius (GAS) muscle and found that performance of CgA-deficient Chga-KO mice in treadmill exercise was impaired. Supplementation with CgA in Chga-KO mice restored exercise ability suggesting a novel role for endogenous CgA in skeletal muscle function. Chga-KO mice display (i) lack of exercise-induced stimulation of pAKT, pTBC1D1 and phospho-p38 kinase signaling, (ii) loss of GAS muscle mass, (iii) extensive formation of tubular aggregates (TA), (iv) disorganized cristae architecture in mitochondria, (v) increased expression of the inflammatory cytokines Tnfα, Il6 and Ifnγ, and fibrosis. The impaired maximum running speed and endurance in the treadmill exercise in Chga-KO mice correlated with decreased glucose uptake and glycolysis, defects in glucose oxidation and decreased mitochondrial cytochrome C oxidase activity. The lack of adaptation to endurance training correlated with the lack of stimulation of p38MAPK that is known to mediate the response to tissue damage. As CgA sorts proteins to the regulated secretory pathway, we speculate that lack of CgA could cause misfolding of membrane proteins inducing aggregation of sarcoplasmic reticulum (SR) membranes and formation of tubular aggregates that is observed in Chga-KO mice. In conclusion, CgA deficiency renders the muscle energy deficient, impairs performance in treadmill exercise and prevents regeneration after exercise-induced tissue damage.

Chromogranin A Is Preferentially Cleaved into Proangiogenic Peptides in the Bone Marrow of Multiple Myeloma Patients

Angiogenesis has been postulated to be critical for the pathogenesis of multiple myeloma, a neoplastic disease characterized by abnormal proliferation of malignant plasma cells in the bone marrow (BM). Cleavage of the N- and C-terminal regions of circulating chromogranin A (CgA, CHGA), classically an antiangiogenic protein, can activate latent antiangiogenic and proangiogenic sites, respectively. In this study, we investigated the distribution of CgA-derived polypeptides in multiple myeloma patients and the subsequent implications for disease progression. We show that the ratio of pro/antiangiogenic forms of CgA is altered in multiple myeloma patients compared with healthy subjects and that this ratio is higher in BM plasma compared with peripheral plasma, suggesting enhanced local cleavage of the CgA C-terminal region. Enhanced cleavage correlated with increased VEGF and FGF2 BM plasma levels and BM microvascular density. Using the Vk*MYC mouse model of multiple myeloma, we further demonstrate that exogenously administered CgA was cleaved in favor of the proangiogenic form and was associated with increased microvessel density. Mechanistic studies revealed that multiple myeloma and proliferating endothelial cells can promote CgA C-terminal cleavage by activating the plasminogen activator/plasmin system. Moreover, cleaved and full-length forms could also counter balance the pro/antiangiogenic activity of each other in in vitro angiogenesis assays. These findings suggest that the CgA-angiogenic switch is activated in the BM of multiple myeloma patients and prompt further investigation of this CgA imbalance as a prognostic or therapeutic target. Cancer Res; 76(7); 1781–91. ©2016 AACR.

Biological function and clinical relevance of chromogranin A and derived peptides

Chromogranin A (CgA (CHGA)) is the major soluble protein co-stored and co-released with catecholamines and can function as a pro-hormone by giving rise to several bioactive peptides. This review summarizes the physiological functions, the pathogenic implications, and the recent use of these molecules as biomarkers in several pathological conditions. A thorough literature review of the electronic healthcare databases MEDLINE, from January 1985 to September 2013, was conducted to identify articles and studies concerned with CgA and its processing. The search strategies utilized keywords such as chromogranin A, vasostatins 1 and 2, chromofungin, chromacin, pancreastatin, catestatin, WE14, chromostatin, GE25, parastatin, and serpinin and was supplemented by the screening of references from included papers and review articles. A total of 209 English-language, peer-reviewed original articles or reviews were examined. The analysis of the retrospective literature suggested that CgA and its several bioactive fragments exert a broad spectrum of regulatory activities by influencing the endocrine, the cardiovascular, and the immune systems and by affecting the glucose or calcium homeostasis. As some peptides exert similar effects, but others elicit opposite responses, the regulation of the CgA processing is critical to maintain homeostasis, whereas an unbalanced production of peptides that exert opposing effects can have a pathogenic role in several diseases. These clinical implications entail that CgA and its derived peptides are now used as diagnostic and prognostic markers or to monitor the response to pharmacological intervention not only in endocrine tumors, but also in cardiovascular, inflammatory, and neuropsychiatric diseases.

Full-length human chromogranin-A cardioactivity: myocardial, coronary, and stimulus-induced processing evidence in normotensive and hypertensive male rat hearts

Plasma chromogranin-A (CgA) concentrations correlate with severe cardiovascular diseases, whereas CgA-derived vasostatin-I and catestatin elicit cardiosuppression via an antiadrenergic/nitric oxide-cGMP mediated mechanism. Whether these phenomena are related is unknown. We here investigated whether and to what extent full-length CgA directly influences heart performance and may be subjected to stimulus-elicited intracardiac processing. Using normotensive and hypertensive rats, we evaluated the following: 1) direct myocardial and coronary effects of full-length CgA; 2) the signal-transduction pathway involved in its action mechanism; and 3) CgA intracardiac processing after β-adrenergic [isoproterenol (Iso)]- and endothelin-1(ET-1)-dependent stimulation. The study was performed by using a Langendorff perfusion apparatus, Western blotting, affinity chromatography, and ELISA. We found that CgA (1-4 nM) dilated coronaries and induced negative inotropism and lusitropism, which disappeared at higher concentrations (10-16 nM). In spontaneously hypertensive rats (SHRs), negative inotropism and lusitropism were more potent than in young normotensive rats. We found that perfusion itself, Iso-, and endothelin-1 stimulation induced intracardiac CgA processing in low-molecular-weight fragments in young, Wistar Kyoto, and SHR rats. In young normotensive and adult hypertensive rats, CgA increased endothelial nitric oxide synthase phosphorylation and cGMP levels. Analysis of the perfusate from both Wistar rats and SHRs of untreated and treated (Iso) hearts revealed CgA absence. In conclusion, in normotensive and hypertensive rats, we evidenced the following: 1) full-length CgA directly affects myocardial and coronary function by AkT/nitric oxide synthase/nitric oxide/cGMP/protein kinase G pathway; and 2) the heart generates intracardiac CgA fragments in response to hemodynamic and excitatory challenges. For the first time at the cardiovascular level, our data provide a conceptual link between systemic and intracardiac actions of full-length CgA and its fragments, expanding the knowledge on the sympathochromaffin/CgA axis under normal and physiopathological conditions.

A new chromogranin A-dependent angiogenic switch activated by thrombin

Angiogenesis, the formation of blood vessels from pre-existing vasculature, is regulated by a complex interplay of anti and proangiogenic factors. We found that physiologic levels of circulating chromogranin A (CgA), a protein secreted by the neuroendocrine system, can inhibit angiogenesis in various in vitro and in vivo experimental models. Structure-activity studies showed that a functional anti-angiogenic site is located in the C-terminal region, whereas a latent anti-angiogenic site, activated by cleavage of Q76-K77 bond, is present in the N-terminal domain. Cleavage of CgA by thrombin abrogated its anti-angiogenic activity and generated fragments (lacking the C-terminal region) endowed of potent proangiogenic activity. Hematologic studies showed that biologically relevant levels of forms of full-length CgA and CgA1-76 (anti-angiogenic) and lower levels of fragments lacking the C-terminal region (proangiogenic) are present in circulation in healthy subjects. Blood coagulation caused, in a thrombin-dependent manner, almost complete conversion of CgA into fragments lacking the C-terminal region. These results suggest that the CgA-related circulating polypeptides form a balance of anti and proangiogenic factors tightly regulated by proteolysis. Thrombin-induced alteration of this balance could provide a novel mechanism for triggering angiogenesis in pathophysiologic conditions characterized by prothrombin activation.

Chromogranin A binds to αvβ6-integrin and promotes wound healing in mice

Chromogranin A (CgA), a secretory protein expressed by many neuroendocrine cells, neurons, cardiomyocytes, and keratinocytes, is the precursor of various peptides that regulate the carbohydrate/lipid metabolism and the cardiovascular system. We have found that CgA, locally administered to injured mice, can accelerate keratinocyte proliferation and wound healing. This biological activity was abolished by the Asp(45)Glu mutation. CgA and its N-terminal fragments, but not the corresponding Asp(45)Glu mutants, could selectively recognize the αvβ6-integrin on keratinocytes (a cell-adhesion receptor that is up-regulated during wound healing) and regulate keratinocyte adhesion, proliferation, and migration. No binding was observed to other integrins such as αvβ3, αvβ5, αvβ8, α5β1, α1β1, α3β1, α6β4, α6β7 and α9β1. Structure-activity studies showed that the entire CgA(39-63) region is crucial for αvβ6 recognition (K(i) = 7 nM). This region contains an RGD site (residues CgA(43-45)) followed by an amphipathic α-helix (residues CgA(47-63)), both crucial for binding affinity and selectivity. These results suggest that the interaction of the RGD/α-helix motif of CgA with αvβ6 regulates keratinocyte physiology in wound healing.

The N-terminal fragment of chromogranin A, vasostatin-1 protects mice from acute or chronic colitis upon oral administration

BACKGROUND

Vasostatin-1 (VS-1), the N-terminal fragment of chromogranin A (CgA), decreases the permeability of endothelial cells in vitro and in vivo.

AIMS

Here, we investigated whether a similar effect could be observed also on intestinal epithelial cells (IECs) in vitro and whether VS-1 could have favorable effects on animal models of acute or chronic colitis, which are characterized by increased permeability of the intestinal epithelium.

METHODS

In vitro, VS-1 was tested on IEC monolayers showing increased permeability, on mechanically injured IEC monolayers, and on the production of the chemokine IL-8/KC by lipopolysaccharide (LPS)-stimulated IECs. In vivo, VS-1 was tested in animal models of dextran sodium salt (DSS)-induced acute or chronic colitis.

RESULTS

In vitro, VS-1 inhibited increased permeability of IECs induced by interferon-γ and tumor necrosis factor-α. Moreover, VS-1 promoted healing of mechanically injured IEC monolayers, most likely through stimulation of cell migration, rather than cell proliferation. Eventually, VS-1 inhibited LPS-induced production of IL-8. In vivo, VS-1 exerted protective effects in animal models of acute or chronic colitis upon oral, but not systemic administration.

CONCLUSIONS

VS-1 is therapeutically active in animal models of acute or chronic, DSS-induced colitis. The mechanisms underlying this effect are likely to be multiple, and may include inhibition of enhanced intestinal permeability, repair of injured intestinal mucosae, and inhibition of the production of IL-8/KC and possibly other inflammatory cytokines.

Chromogranin A regulates tumor self-seeding and dissemination

Cancer progression involves the seeding of malignant cells in circulation and the colonization of distant organs. However, circulating neoplastic cells can also reinfiltrate the tumor of origin. This process, called "tumor-self seeding," can select more aggressive cells that may contribute to cancer progression. Here, using mouse mammary adenocarcinoma models, we observed that both tumor self-seeding and organ colonization were inhibited by chromogranin A (CgA), a protein present in variable amounts in the blood of cancer patients. Mechanism studies showed that CgA inhibited the shedding of cancer cells in circulation from primary tumors, as well as the reinfiltration of tumors and the colonization of lungs by circulating tumor cells. CgA reduced gap formation induced by tumor cell-derived factors in endothelial cells, decreased vascular leakage in tumors, and inhibited the transendothelial migration of cancer cells. Together, our findings point to a role for circulating CgA in the regulation of tumor cell trafficking from tumor-to-blood and from blood-to-tumor/normal tissues. Inhibition of the multidirectional trafficking of cancer cells in normal and neoplastic tissues may represent a novel strategy to reduce cancer progression.

Chromogranin A restricts drug penetration and limits the ability of NGR-TNF to enhance chemotherapeutic efficacy

NGR-TNF is a derivative of TNF-α that targets tumor blood vessels and enhances penetration of chemotherapeutic drugs. Because of this property, NGR-TNF is being tested in combination with chemotherapy in various phase II and III clinical trials. Here we report that chromogranin A (CgA), a protein present in variable amounts in the blood of normal subjects and cancer patients, inhibits the synergism of NGR-TNF with doxorubicin and melphalan in mouse models of lymphoma and melanoma. Pathophysiologically relevant levels of circulating CgA blocked NGR-TNF-induced drug penetration by enhancing endothelial barrier function and reducing drug extravasation in tumors. Mechanistic investigations done in endothelial cell monolayers in vitro showed that CgA inhibited phosphorylation of p38 MAP kinase, disassembly of VE-cadherin-dependent adherence junctions, paracellular macromolecule transport, and NGR-TNF-induced drug permeability. In this system, the N-terminal fragment of CgA known as vasostatin-1 also inhibited drug penetration and NGR-TNF synergism. Together, our results suggest that increased levels of circulating CgA and its fragments, as it may occur in certain cancer patients with nonneuroendocrine tumors, may reduce drug delivery to tumor cells particularly as induced by NGR-TNF. Measuring CgA and its fragments may assist the selection of patients that can respond better to NGR-TNF/chemotherapy combinations in clinical trials.

The chromogranin A- derived N-terminal peptide vasostatin-I: In vivo effects on cardiovascular variables in the rabbit

This study is the first to report on vascular effect of the chromogranin A derived Vasostatin-I (CgA(1-76)) in vivo. Cardiovascular parameters were recorded in 29 rabbits with sympathetically decentralized right carotid vascular bed. The recombinant human STA CgA(1-78) (VS-1) was infused at 480 μg/kg over 25 min. Group I was kept awake while groups II-V were anesthetized with Ketamine-xylazine. VS-1 was given alone in groups I-II while in presence of either phentolamine, phentolamine plus propranolol or hexamethonium in groups III-V. Serum VS-1 peaked at 2 μg/ml (200 nM) before onset of vascular effects and declined rapidly to ~200 ng/ml within 30 min. In all groups but III and IV VS-1 induced a brief vasoconstriction, being larger in intact than in sympathetically decentralized beds. The VS-1 induced vasoconstriction was not altered by hexamethonium but was abolished by phentolamine. In presence of the α-adrenergic blocker a long lasting vasodilatation, unaffected by propranolol, was apparent on both innervated and decentralized sides. In conclusion, VS-1 induced an α-adrenoceptor-mediated vasoconstriction presumably brought about by noradrenaline release from sympathetic nerves when infused at a dose giving an initial serum concentration of ~200 nM. This initial vasoconstriction masked a persistent adrenoceptor-independent vasodilatation, consistent with previous reports from in vitro models.

VEGFR-2 expression in carcinoid cancer cells and its role in tumor growth and metastasis

Carcinoid tumors are slow growing and highly vascular neuroendocrine neoplasms that are increasing in incidence. Previously, we showed that carcinoid tumors express vascular endothelial growth factor receptor 2 (VEGFR-2) in the epithelial compartment of carcinoid tumor sections; yet, its role is not completely understood. The purpose of our study was to: (i) assess the expression of VEGFR-2 in the novel human carcinoid cell line BON, (ii) to determine the role of PI3K/Akt signaling on VEGFR-2 expression and (iii) to assess the effect of VEGFR-2 on BON cell invasion, migration and proliferation. We found that, although VEGFR-2 is expressed in BON cells, reduction in VEGFR-2 expression actually enhanced proliferation, invasion, and migration of the BON cell line. Also, expression of VEGFR-2 was inversely related to PI3K signaling. Carcinoid liver metastases in mice demonstrated decreased VEGFR-2 expression. Furthermore, the expression of a truncated, soluble form of VEGFR-2 (sVEGFR-2), a protein demonstrated to inhibit cell growth, was detected in BON cells. The presence of VEGFR-2 in the epithelial component of carcinoid tumors and in the BON cell line suggests an alternate role for VEGFR-2, in addition to its well-defined role in angiogenesis. The expression of sVEGFR-2 may explain the inverse relationship between VEGFR-2 expression and PI3K/Akt signaling and the inhibitory effect VEGFR-2 has on BON cell proliferation, migration and invasion.

Effects of chromogranin A deficiency and excess in vivo: biphasic blood pressure and catecholamine responses

OBJECTIVE

The phenotype of the chromogranin A (Chga) null (knockout) mouse is hypertensive. However, hypertensive humans and spontaneously hypertensive rats display elevated CHGA expression. This study addresses the paradox that both ablation and elevation of CHGA result in hypertension.

METHODS

Mice with varying copy number of the CHGA gene were generated. In these mice CHGA, catecholamine and blood pressure (BP) were measured. Also a cohort of healthy human individuals was stratified into tertiles based on plasma CHGA expression and phenotyped for characteristics including their BP response to environmental (cold) stress.

RESULTS

The mice displayed a direct CHGA gene dose-dependent (0-4 copies/genome) activation of CHGA expression in both plasma and adrenal gland, yet the BP dependence of CHGA gene dose was U-shaped, maximal at 0 and four copies of the gene, whereas minimal at two copies (i.e., the wild-type gene dosage). Plasma catecholamine showed a parallel U-shaped dose/response in mice, whereas adrenal epinephrine exhibited a reciprocal (inverted) U-shaped response, suggesting dysregulated neurotransmission at both extremes of CHGA expression. The human individuals also showed a nonlinear relationship between CHGA expression and pressor responses to environmental (cold) stress, that were maximal in the highest and lowest tertiles, though basal BPs did not differ among the groups. The human CHGA tertiles also differed in epinephrine secretion as well as degree of CHGA processing to catestatin (catecholamine release-inhibitory peptide derived from CHGA processing).

CONCLUSION

Thus, across mammalian species, an optimal amount of CHGA may be required to establish appropriate catecholamine storage and release, and hence BP homeostasis.

Chromogranin A and the tumor microenvironment

Chromogranin A (CgA) is an acidic glycoprotein belonging to a family of regulated secretory proteins stored in the dense core granules of the adrenal medulla and of many other neuroendocrine cells and neurons. This protein is frequently used as a diagnostic and prognostic serum marker for a range of neuroendocrine tumors. Circulating CgA is also increased in patients with other diseases, including subpopulations of patients with non-neuroendocrine tumors, with important prognostic implications. A growing body of evidence suggests that CgA is more than a diagnostic/prognostic marker for cancer patients. Indeed, results of in vitro experiments and in vivo studies in animal models suggest that this protein and its fragments can affect several elements of the tumor microenvironment, including fibroblasts and endothelial cells. In this article, recent findings implicating CgA as a modulator of the tumor microenvironment and suggesting that abnormal secretion of CgA could play important roles in tumor progression and response to therapy in cancer patients are reviewed and discussed.

Novel biomarkers in heart failure: an overview

Heart failure is a complex systemic syndrome resulting from significant impairment of cardiac function. A vast array of biological pathways is now known to be involved in heart failure, including deleterious pathways promoting its development and progression, as well as compensatory cardioprotective pathways. Some of the components of these pathways are now recognized as biomarkers of this condition, and can aid diagnosis, prognostication and guide management. As the understanding of the pathophysiology of heart failure progresses, further candidate biomarkers are being identified. This article reviews the literature regarding the more recently identified biomarkers and outlines areas requiring further study.

Role of vasostatin-1 C-terminal region in fibroblast cell adhesion

Fibroblast adhesion can be modulated by proteins released by neuroendocrine cells and neurons, such as chromogranin A (CgA) and its N-terminal fragment vasostatin-1 (VS-1, CgA(1-78)). We have investigated the mechanisms of the interaction of VS-1 with fibroblasts and of its pro-adhesive activity and have found that the proadhesive activity of VS-1 relies on its interaction with the fibroblast membrane via a phospholipid-binding amphipathic alpha-helix located within residues 47-66, as well as on the interaction of the adjacent C-terminal region 67-78, which is structurally similar to ezrin-radixin-moesin-binding phosphoprotein 50 (a membrane-cytoskeleton adapter protein), with other cellular components critical for the regulation of cell cytoskeleton.

The chromogranin A-derived peptides vasostatin-I and catestatin as regulatory peptides for cardiovascular functions

A range of inflammatory conditions is associated with pathologically high levels of circulating chromogranin A (CgA). This prohormone belongs to the family of uniquely acidic proteins co-stored and co-secreted with other hormones and peptides from the diffuse neuroendocrine system. Two highly conserved, CgA-derived peptides, vasostatin-I and catestatin, have been implicated as modulators of a wide range of cells and tissues, including those of the cardiovascular system. This review focuses on links between elevated circulating CgA and cardiovascular dysfunctions in inflammatory conditions in relation to potential beneficial effects of vasostatin-I and catestatin. Characteristic membrane-penetrating properties have been assigned to both peptides, and pertussis toxin sensitivity is shared by a number of their responses, notably in the vascular and cardiac endothelium. Pertussis toxin-sensitive, receptor-independent activation via heterotrimeric G proteins and Galphai/o subunits will be discussed as possible mechanisms for inhibitory effects of vasostatin-I and catestatin on vascular and cardiac responses. The accumulated evidence provides convincing support for vasostatin-I and catestatin as regulatory peptides for the cardiovascular system, converging on alleviation of significant dysfunctions as part of several inflammatory conditions.

Chromogranins A and B and secretogranin II as prohormones for regulatory peptides from the diffuse neuroendocrine system

Chromogranin A (CgA), chromogranin B (CgB), and secretogranin II (SgII) belong to a family of uniquely acidic secretory proteins in elements of the diffuse neuroendocrine system. These "granins" are characterized by numerous pairs of basic amino acids as potential sites for intra- and extragranular processing. In response to adequate stimuli, the granins are coreleased with neurotransmitters and hormones and appear in the circulation as potential modulators of homeostatic processes. This review is directed towards functional aspects of the secreted CgA, CgB, and SgII and their biologically active sequences. Widely different effects and targets have been reported for granin-derived peptides. So far, the CgA peptides vasostatin-I, pancreastatin, and catestatin, the CgB peptides CgB(1-41) and secretolytin, and the SgII peptide secretoneurin are the most likely candidates for granin-derived regulatory peptides. Most of their effects fit into patterns of direct or indirect modulations of major functions, in particular associated with inflammatory conditions.

Long human CHGA flanking chromosome 14 sequence required for optimal BAC transgenic "rescue" of disease phenotypes in the mouse Chga knockout

Chromogranin A (CHGA) plays a catalytic role in formation of catecholamine storage vesicles and also serves as precursor to the peptide fragment catestatin, a catecholamine secretory inhibitor whose expression is diminished in the hypertensive individuals. We previously reported the hypertensive, hyperadrenergic phenotype of Chga-/- knockout (KO) mice and rescue by the human ortholog. In the present study, we compare two humanized CHGA mouse models. Into the Chga null background, by bacterial artificial chromosome transgenesis human CHGA transgene has been introduced. Both lines have the complete approximately 12 kbp CHGA gene integrated stably in the genome but have substantial differences in CHGA expression, as well as consequent sympathochromaffin biochemistry and physiology. A mouse model with longer-insert HumCHGA31 displays integration encompassing not only CHGA but also long human flanking sequences. This is in contrast to mouse model HumCHGA19 with limited flanking human sequence co-integrated. As a consequence, HumCHGA19 mice have normal though diminished pattern of spatial expression of CHGA, and 14-fold lower circulating CHGA, with failure to rescue KO phenotypes to normalcy. In the longer-insert HumCHGA31 mice, catecholamine secretion, exaggerated responses to environmental stress, and hypertension were all alleviated. Promoter regions of the transgenes in both HumCHGA19 and HumCHGA31 display minimal CpG methylation, weighing against differential "position effects" of integration, and thus suggesting that lack of cis elements required for optimal CHGA expression occurs in HumCHGA19 mice. Such "humanized" CHGA mouse models may be useful in probing the physiological consequences of variation in CHGA expression found in humans, with consequences for susceptibility to hypertension and cardiovascular disease.

The antimicrobial peptides derived from chromogranin/secretogranin family, new actors of innate immunity

Chromogranins/secretogranins are members of the granin family present in secretory vesicles of nervous, endocrine and immune cells. In chromaffin cells, activation of nicotinic cholinergic receptors induces the release, with catecholamines, of bioactive peptides resulting from a natural processing. During the past decade, our laboratory has characterized new antimicrobial chromogranin-derived peptides in the secretions of stimulated bovine chromaffin cells. They act at the micromolar range against bacteria, fungi, yeasts, and are non-toxic for the mammalian cells. They are recovered in several biological fluids involved in defence mechanisms (human serum, neutrophil secretions and saliva). These new antimicrobial peptides demonstrate the major role of the adrenal medulla in innate immunity. In this review we focus on the antimicrobial peptides derived from human and bovine chromogranin A (CGA), chromogranin B (CGB) and secretogranin II (SGII) emphasizing their direct action against pathogens and their effects on immune cells.

Cytoskeleton mediates negative inotropism and lusitropism of chromogranin A-derived peptides (human vasostatin1-78 and rat CgA₁₋₆₄) in the rat heart

Cytoskeleton scaffold in cardiac myocytes provides structural support and compartmentalization of intracellular components. It is implicated in cardiac pathologies including hypertrophy and failure, playing a key role in the determinism of contractile and diastolic dysfunctions. Chromogranin A (CgA) and its derived peptides have revealed themselves as novel cardiovascular modulators. In humans, normal CgA levels considerably increase in several pathologies, including heart failure. Recent data have shown on the unstimulated rat heart that human recombinant Vasostatin-1 (hrVS-1) and rat chromogranin A 1-64 (rCgA₁₋₆₄) induce negative inotropic and lusitropic effects counteracting the β-adrenergic-dependent positive inotropism with a functional non-competitive antagonism. This study investigates, on the isolated Langendorff perfused rat heart, whether cardiac cytoskeleton is involved in the modulation of contractility and relaxation exerted by hrVS-1 and rCgA₁₋₆₄. Cytoskeleton impairment by either cytochalasin-D (actin polymerization inhibitor), BDM (myosin ATP-ase antagonist) or wortmannin (inhibitor of PI3-K/Akt transduction cascade), or W-7 (calcium-calmodulin antagonist) abolished hrVS-1 and rCgA₁₋₆₄-mediated inotropism and lusitropism. Using fluorescent phalloidin, we showed on rat cardiac H9C2 cells that hrVS-1 (10 nM÷10 µM) stimulates actin polymerization. Taken together these data indicate that in the rat heart, the actin cytoskeletal network strongly contributes to the cardiotropic action of CgA-derived peptides.

Regulatory peptides from chromogranin A and secretogranin II: putative modulators of cells and tissues involved in inflammatory conditions

Chromogranin A (CgA) and secretogranin II (SgII) of the granin family of uniquely acidic proteins secreted from elements of the diffuse neuroendocrine system are also produced by cells involved in inflammation. CgA and the CgA-derived peptides vasostatin-I and catestatin are products of polymorphonuclear neutrophils accumulating at sites of injury or infections while SgII and the Sg II-derived secretoneurin may contribute to neurogenic inflammation when released from sensory nerve terminals. This review is directed towards vasostatin-I, catestatin and secretoneurin as modulators of cells and tissues associated with inflammatory conditions. The accumulated literature indicates that concerted effects of vasostatin-I and catestatin may be relevant for the first-line host-defence against invading microorganisms, contrasting the apparent lack of antibacterial potencies in secretoneurin. Oppositely directed effects of vasostatin-I and secretoneurin on endothelial permeability and transendothelial extravasation are particularly striking. While vasostatin-I protects the integrity of the endothelial barrier against the disruptive effects of proinflammatory agents, secretoneurin activates transendothelial extravasation, chemotaxis and migration of leukocytes. Oppositely directed effects of vasostatin-I and secretoneurin on formation of blood vessels are also indicated, vasostatin-I inhibiting angiogenetic parameters while secretoneurin activates not only angiogenesis but also vascularization.

Neuroendocrine carcinoma of the liver and gallbladder in a cow

A 15-year-old Limousin-cross cow was presented for examination with neurological signs and serum biochemical changes consistent with liver disease. Necropsy revealed enlargement of the liver with multifocal firm, depressed, pale, circumscribed lesions throughout the parenchyma. Within the gallbladder there were exophytic and villiform mucosal masses. Microscopically, hepatic structure was displaced by neoplastic cells forming trabeculae, nests and rosettes. There was transmural infiltration of the gallbladder by similar cells. The histological pattern of growth of the neoplastic cells, the presence of silver-stained cytoplasmic granules within these cells and the immunohistochemical demonstration of chromogranin A supported the diagnosis of neuroendocrine carcinoma. Bovine liver and gallbladder neuroendocrine carcinomas are rare and this is the first detailed documentation of the disease in the United Kingdom.

Chromogranins A and B and secretogranin II: evolutionary and functional aspects

Chromogranins/secretogranins or granins are a class of acidic, secretory proteins that occur in endocrine, neuroendocrine, and neuronal cells. Granins are the precursors of several bioactive peptides and may be involved in secretory granule formation and neurotransmitter/hormone release. Characterization and analysis of chromogranin A (CgA), chromogranin B (CgB), and secretogranin II (SgII) in distant vertebrate species confirmed that CgA and CgB belong to related monophyletic groups, probably evolving from a common ancestral precursor, while SgII sequences constitute a distinct monophyletic group. In particular, selective sequences within these proteins, bounded by potential processing sites, have been remarkably conserved during evolution. Peptides named vasostatin, secretolytin and secretoneurin, which occur in these regions, have been shown to exert various biological activities. These conserved domains may also be involved in the formation of secretory granules in different vertebrates. Other peptides such as catestatin and pancreastatin may have appeared late during evolution. The function of granins as propeptide precursors and granulogenic factors is discussed in the light of recent data obtained in various model species and using knockout mice strains.

The vasostatin-I fragment of chromogranin A inhibits VEGF-induced endothelial cell proliferation and migration

A growing body of evidence suggests that chromogranin A (CgA), a secretory protein released by many neuroendocrine cells and frequently used as a diagnostic and prognostic serum marker for a range of neuroendocrine tumors, is a precursor of several bioactive fragments. This work was undertaken to assess whether the N-terminal fragment CgA(1-76) (called vasostatin I) can inhibit the proangiogenic activity of vascular endothelial growth factor (VEGF), a factor involved in tumor growth. The effect of recombinant human vasostatin I (VS-1) on VEGF-induced human umbilical endothelial cells (HUVEC) signaling, proliferation, migration, and organization has been investigated. We have found that VS-1 (3 microg/ml; 330 nM) can inhibit VEGF-induced ERK phosphorylation, as well as cell migration, proliferation, morphogenesis, and invasion of collagen gels in various in vitro assays. In addition, VS-1 could inhibit the formation of capillary-like structures in Matrigel plugs in a rat model. VS-1 could also inhibit basal ERK phosphorylation and motility of HUVEC, leading to a more quiescent state in the absence of VEGF, without inducing apoptotic or necrotic effects.

CONCLUSION

These findings suggest that vasostatin I may play a novel role as a regulator of endothelial cell function and homeostasis.

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.

Human recombinant chromogranin A-derived vasostatin-1 mimics preconditioning via an adenosine/nitric oxide signaling mechanism

The acidic protein chromogranin A (CgA) is the precursor of several regulatory peptides generated by specific proteolytic processes. Human recombinant CgA NH(2)-terminal fragment STA-CgA(1-78) (hrSTA-CgA(1-78)), containing vasostatin-1 (CgA(1-76)) domain, exerts a negative inotropic effect and counteracts the beta-adrenergic positive inotropic effect on the rat heart. We hypothesized an involvement of nitric oxide (NO)-dependent pathway in both cardiodepression and cardioprotection by hrSTA-CgA(1-78). We also hypothesized an involvement of adenosine A(1) receptor and protein kinase C (PKC) in cardioprotection by hrSTA-CgA(1-78). Therefore, we evaluated whether 1) the cardioinhibition mediated by hrSTA-CgA(1-78) involves the G(i/o) proteins/NO-dependent signal transduction cascade, 2) hrSTA-CgA(1-78) induces ischemic preconditioning-like protective effects on the myocardium, and 3) inhibition of NO synthase (NOS), adenosine A(1) receptor, or PKC affects hrSTA-CgA(1-78) protection. Using the isolated rat heart, we found that the reduction of left ventricular pressure (LVP), rate-pressure product, and maximal values of the first derivative of LVP elicited by hrSTA-CgA(1-78) at 33 nM is abolished by blocking G(i/o) proteins with pertussis toxin, scavenging NO with hemoglobin, and blocking NOS activity with N(G)-monomethyl-l-arginine or N(5)-(iminoethyl)-l-ornithine, soluble guanylate cyclase with 1H-[1,2,4]oxadiazole-[4,4-a]quinoxalin-1-one, and protein kinase (PKG) with KT5823. Data suggest the involvement of the G(i/o) proteins/NO-cGMP-PKG pathway in the hrSTA-CgA(1-78)-dependent cardioinhibition. When given before 30 min of ischemia, hrSTA-CgA(1-78) significantly reduced the size of the infarct from 64 +/- 4 to 32 +/- 3% of the left ventricular mass. This protective effect was abolished by either NOS inhibition or PKC blockade and was attenuated, but not suppressed, by the blockade of A(1) receptors. These results suggest that hrSTA-CgA(1-78) activity triggers two different pathways: one of these pathways is mediated by A(1) receptors, and the other is mediated by NO release. As with repeated brief preconditioning ischemia, hrSTA-CgA(1-78) may be considered a stimulus strong enough to trigger both pathways, which may converge on PKC.

Relaxation induced by N-terminal fragments of chromogranin A in mouse gastric preparations

A definitive role for chromogranin A (CGA)-derived fragments in the control of the gastrointestinal smooth muscle contractility has not been yet established. The purpose of the present study was to evaluate, in vitro, the effects of the recombinant vasostatin 1-78 (VS-1), CGA 7-57 and CGA 47-66 on the mouse gastric mechanical activity, recording the changes of intraluminal pressure. VS-1, CGA 7-57 and CGA 47-66 produced concentration-dependent relaxations. Mouse anti-vasostatin-1 monoclonal antibody 5A8, recognising the region 53-57, abolished the relaxation induced by VS-1, indicating the specificity of the effect. The relaxation was significantly reduced by tetrodotoxin (TTX), blocker of neuronal voltage-dependent Na(+) channels, l-NAME, inhibitor of nitric oxide (NO) synthase, or apamin, blocker of small conductance Ca(2+)-dependent K(+) channels. The joint application of TTX and l-NAME did not show any additive effects, whereas TTX plus apamin abolished the VS-1 response. The results suggest that the N-terminal CGA-derived peptides are able to relax mouse gastric muscle and, therefore, they point out an inhibitory role of vasostatin I in the gastrointestinal tract. The relaxation is mediated in part by neural mechanisms through NO production and in part by non-neural mechanisms involving the opening of small conductance Ca(2+)-dependent K(+) channels.

Crucial role of cytoskeleton reorganization in the negative inotropic effect of chromogranin A-derived peptides in eel and frog hearts

Vasostatins (VSs), i.e. the main biologically active peptides generated by the proteolytic processing of chromogranin A (CGA) N-terminus, exert negative inotropism in vertebrate hearts. Here, using isolated working eel (Anguilla anguilla) and frog (Rana esculenta) heart preparations, we have studied the role of the cytoskeleton in the VSs-mediated inotropic response. In both eel and frog hearts, VSs-mediated-negative inotropy was abolished by treatment with inhibitors of cytoskeleton reorganization, such as cytochalasin-D (eel: 10 nM; frog: 1 nM), an inhibitor of actin polymerisation, wortmannin (0.01 nM), an inhibitor of PI3-kinase (PI3-K)/protein kinase B (Akt) signal-transduction cascade, butanedione 2-monoxime (BDM) (eel: 100 nM; frog: 10 nM), an antagonist of myosin ATPase, and N-(6-aminohexil)-5-chloro-1-naphthalenesulfonamide (W7) (eel: 100 nM; frog: 1 nM), a calcium-calmodulin antagonist. These results demonstrate that changes in cytoskeletal dynamics play a crucial role in the negative inotropic influence of VSs on eel and frog hearts.

Human Recombinant Vasostatin-1 May Interfere with Cell-Extracellular Matrix Interactions

Vasostatin-1 (VS-1), the N-terminal fragment derived from the cleavage of chromogranin A (CgA), has been shown to exert several biological activities on several tissues and organs. Recently, it has been reported that human recombinant VS-1 (STA-CGA1-78) may alter myocardial contractility in eel, frog, and rat hearts. In this article we have explored if STA-CGA1-78 can induce intracellular cascades interacting both with adhesion molecules and/or extracellular matrix (ECM), components, that is, involvement of the heat shock protein 90 (HSP90) and the endothelial NOS (eNOS), known to be implicated in signal transduction mechanisms affecting myocardial contractility. We used 3D cultured adult rat cardiomyocytes cultivated over fibronectin or fibroblasts or embedded in matrigel or collagen type I. Aurion-conjugated VS-1 (Au-STA-CGA1-78) has been used to identify possible sites of interaction of this molecule with the cell membrane. We found that in our 3D culture, cell-ECM interactions played a crucial role in the cellular localization of HSP90 as well as in the expression of eNOS. VS-1 appeared to modulate cell-ECM interactions, thereby remarkably leading to a different cellular localization of HSP90. Moreover, Au-STA-CGA1-78 was never detected inside the cell nor overlapping the plasma membrane, but nearby the outer side of the cardiomyocyte plasmalemma, at a particular distance, typical of integrins. On the whole, these data suggest that VS-1 does not have a classic receptor on the membrane but that integrins may represent a nonconventional VS-1 receptor modulating eNOS signaling pathway.

The chromogranin A peptide vasostatin-I inhibits gap formation and signal transduction mediated by inflammatory agents in cultured bovine pulmonary and coronary arterial endothelial cells

The proinflammatory agent tumour necrosis factor alpha (TNFalpha) is one of several agents causing vascular leakage. The N-terminal domain of CgA, vasostatin-I (CgA1-76), has recently been reported to inhibit TNFalpha induced gap formation in human umbilical venous endothelial cells. Here we report on the effect of recombinant human CgA1-78, vasostatin-I, on TNFalpha induced gap formation in two model systems of vascular leakage in arterial endothelial cells of bovine pulmonary (BPAEC) and coronary (BCAEC) origin. Vasostatin-I inhibited the TNFalpha induced gap formation in both models, being inactive in the unstimulated cells. The phosphorylation of p38MAP kinase in TNFalpha activated BPAEC was markedly attenuated in the presence of vasostatin-I and the inhibitory effect corresponded to that of the specific p38MAPK inhibitor SB203580. Vasostatin-I also inhibited the phosphorylation of p38MAPK induced by both thrombin and pertussis toxin in these cells. The results demonstrate that vasostatin-I has inhibitory effects on TNFalpha-induced disruption of confluent layers of cultured pulmonary and coronary arterial endothelial cells. This suggests that vasostatin-I may affect endothelial barrier dysfunction also in arterial vascular beds. Furthermore, the inhibitory activity of vasostatin-I may be associated with the p38MAPK signalling cascade via a pertussis toxin sensitive, presumably Galphai coupled mechanism.

Interactions of chromogranin A-derived vasostatins and monolayers of phosphatidylserine, phosphatidylcholine and phosphatidylethanolamine

Vasostatin-I (CgA1-76) is a naturally occurring and biologically active N-terminal peptide derived from chromogranin A (CgA), produced and secreted at high concentrations by neuroendocrine tissues and also from a range of neuroendocrine tumors. This study aims to examine the hypothesis that in the absence of classical protein receptors CgA1-76 may, like its two derived peptides CgA1-40 and CgA47-66, perturb the lipid microenvironment of other membrane receptors, as a basis for the largely inhibitory activities of these CgA peptides. The nature of the interactions between phospholipids and vasostatin-derived fragments was studied in the Langmuir film balance apparatus at 37 degrees C. The synthetic peptides CgA1-40 and CgA47-66 and a recombinant fragment (VS-I) containing vasostatin-I (Ser-Thr-Ala-CgA1-78) were compared for their effects on monolayers of phosphatidylcholine and phosphatidylethanolamine from pig brain and defined species of phosphatidylserine. Marked differences in surface pressure-area isotherms and phase-transition plateaus were apparent with the three classes of phospholipids on VS-I, CgA1-40 and CgA47-66 in physiological buffer or pure water. The results indicate that VS-I and CgA47-66 at 5-10 nM concentrations may engage in electrostatic as well as hydrophobic interactions with membrane-relevant phospholipids at physiological conditions, VS-I in particular enhancing the fluidity of saturated species of phosphatidylserine.

Chromogranin A-derived peptides: interaction with the rat posterior cerebral artery

Chromogranin A (CgA), an acidic granule protein of the regulated secretory pathway in the diffuse neuroendocrine system, is postulated to serve as a prohormone for regulatory peptides. Betagranin (rCgA(1-128)), the first N-terminal cleavage product of rat CgA, is 87% homologous to the bovine vasostatin I (bCgA(1-76)), previously shown to be vasoinhibitory in bovine resistance arteries. In this study the vasoactivity of homologous rat and bovine peptides was investigated in the rat posterior cerebral artery. Firstly, we examined the interaction of rhodamine (Rh)-labelled bCgA(7-40) and bCgA(47-70) with elements of the arterial wall by fluorescence microscopy. Secondly, rCgA(7-57), bCgA(1-40), bCgA(7-40) and bCgA(47-66) (chromofungin) were studied for effects on arterial tone and intracellular calcium as function of pressure in an arteriograph. Although without dilator or constrictor responses at 60-150 mm Hg, the rat peptide (rCgA(7-57)) evoked a significant delay in the onset of forced dilatation at 170 mm Hg, in contrast to the bovine peptides bCgA(1-40), bCgA(7-40) and bCgA(47-66) (chromofungin). Neither Rh-bCgA(7-40) nor Rh-bCgA(47-70) stained the endothelial layer, while Rh-bCgA(47-70) but not Rh-bCgA(7-40) stained the smooth muscle compartment. Analogously, bCgA(47-66) but not bCgA(7-40) reduced intracellular calcium, however without modifying the myogenic response. Thus, the betagranin peptide rCgA(7-57) and the two bovine chromofungin-containing peptides, highly homologous to the corresponding sequence (rCgA(47-66)), affected the rat cerebral artery without vasodilator effects, indicating significant species differences in vasoactivity of the N-terminal domain of CgA.

Recombinant N-terminal fragments of chromogranin-A modulate cardiac function of the Langendorff-perfused rat heart

In this study we tested the hypothesis that vasostatins could act as myocardial modulators in the mammalian heart. Using the Langendorff-perfused rat heart, the cardiac effects of the two recombinant human CGA N-terminal fragments STA-CGA1-78 and STA-CGA1-115, containing the vasostatin-1 (CGA 1-76) and vasostatin-2 (CGA 1-113) sequences, respectively, were evaluated at concentrations of 11 / 165 nM. Cardiac performance was evaluated by analyzing left ventricular pressure (LVP) and the rate pressure product (RPP: HR x LVP), used as indexes of contractile activity and cardiac work, respectively. Under basal conditions, STA-CGA1-78 at all concentrations tested elicited a dose-dependent negative inotropism (LVP variations ranging from -9.6% +/- 2 to -23% +/- 2.9) without affecting coronary pressure (CP). In contrast, STA-CGA1-115 increased CP at 110 and 165 nM without affecting inotropism. Both STA-CGA1-78 and STA-CGA1-115 counteracted the cardio-stimulatory effects of isoproterenol (ISO). The ISO-dependent positive chronotropism was unaffected by STA-CGA1-78, while being reduced by STA-CGA1-115. Both peptides abolished the ISO-induced positive inotropism without modifying either the beta-adrenergic-dependent coronary dilation or the ouabain-induced positive inotropism. The analysis of the percentage of variations of RPP in terms of EC50 values of ISO alone (-8.5 +/- 0.3; r2 = 0.88) and in presence of STA-CGA1-78 (11, or 33, or 65 nM: -7.7 +/- 0.15, r2 = 0.97; -7.7 +/- 0.15, r2 = 0.97; -7.8 +/- 0.78, r2 = 0.55, respectively) revealed a non-competitive type of antagonism of STA-CGA1-78. Taken together, these data suggest vasostatins as novel cardioregulatory peptides in mammals.

Peptide microarrays for the characterization of antigenic regions of human chromogranin A

Microarraying peptides is a powerful proteomics technique for studying molecular recognition events. Since peptides have small molecular mass, they are not easily accessible when adsorbed onto solid supports. Moreover, peptides can lack a well-defined three-dimensional structure, and therefore a correct orientation is essential to promote the interaction with their target. In this work, we investigated the suitability as a peptide array substrate of a glass slide coated with a copolymer of N,N-dimethylacrylamide, N,N-acryloyloxysuccinimide, and [3-(methacryloyl-oxy)propyl]trimethoxysilyl. This polymeric surface was used as substrate for peptides in the characterization of linear antigenic sites of human chromogranin A, a useful tissue and serum marker for neuroendocrine tumors and a precursor of many biologically active peptides. The microarray support provided sufficient accessibility of the ligand, with no need for a spacer, as the polymer chains prevent interaction of immobilized peptides with substrate. In addition, the polymeric surface constitutes an aqueous micro-environment in which linear epitopes are freely exposed despite peptide random orientation. The results reported in this article are in accordance with those obtained in conventional ELISA assays using biotinylated and non-biotinylated peptides.

Inhibitory influence of chromogranin A N-terminal fragment (vasostatin-1) on the spontaneous contractions of rat proximal colon

Very little is known about the role played by CGA and its fragments in the gastrointestinal physiology. We have studied the role of CGA N-terminal fragments in the regulation of intestinal smooth muscle contractility by measuring the influence of recombinant CGA 1-78 (VS-1) and synthetic CGA 7-57 peptides on the spontaneous mechanical activity of rat proximal colon in vitro. The mechanical activity was recorded as changes in the intraluminal pressure. VS-1 (0.1-30 nM) and CGA 7-57 (10-300 nM) produced concentration-dependent inhibitory effects, characterized by a progressive decrease in the mean amplitude of circular muscle spontaneous contractions, without affecting the resting tone. The response to VS-1 was antagonised by anti-CGA monoclonal antibodies (mAb5A8, B4E11, 7D1 or 4D5) but not by an irrelevant antibody, indicating that the effect was specific. The inhibitory responses to VS-1 and to CGA 7-57 were significantly reduced by pre-treatment of the preparations with N(omega)-nitro-l-arginine methyl ester (l-NAME) (300 microM), 1H-(1,2,4) oxadiazolo-(4,3-a) quinoxalin-1-one (ODQ) (10 microM), apamin (0.1 microM) or tetrodotoxin (TTX) (1 microM). The results suggest that VS-1 plays an inhibitory modulatory role on spontaneous contractions rat colon circular muscle, through mechanisms involving in part neural release of nitric oxide.

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.