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

Prospective Study of Chromogranin A as a Predictor of Progression in Patients with Pancreatic, Small-Intestinal, and Unknown Primary Neuroendocrine Tumors

BACKGROUND

Retrospective studies are conflicting but most of them report that an increase in plasma chromogranin A (CgA) predicts tumor progression in neuroendocrine tumor (NET) patients. Prospectively, we investigated if a change in plasma CgA is associated with tumor burden changes in NET patients with disseminated disease.

METHODS

We included 239 patients treated at 5 NET centers from December 2010 to December 2013. CgA was measured within 6 weeks of a CT or MRI in a patient undergoing at least 2 scan examinations performed over a period of 1-24 months. In a post hoc analysis, CgA measured 3-6 months prior to the CT/MRI was analyzed. Changes in tumor size were evaluated by RECIST1.1. A 25% change in CgA was chosen to discriminate between increased, decreased, or unchanged levels.

RESULTS

In 671 events (2 CT/MRI scans and 2 corresponding CgA measurements), we found a weak positive correlation between the RECIST 1.1 responses and change in plasma CgA from baseline (Spearman's rank correlation coefficient: 0.15; p < 0.05). Of 304 events in the post hoc analysis, 58 showed progression, 228 showed stable disease, and 18 showed regression, with a median change in CgA of 19% (IQR: 57 to -20%), -12% (23 to -38%), and -73% (-55 to -83%), respectively. The correlation coefficient for all sites was 0.17 (p = 0.003), and it was 0.16 (p = 0.07), 0.18 (p = 0.04), and 0.20 (p = 0.21) for small-intestinal (n = 137), pancreatic (n = 123), and unknown primary NET (n = 40), respectively. In the 58 patients showing tumor progression, the sensitivity and specificity of an increased CgA concentration were 36 and 82%, respectively, with positive and negative predictive values of 32 and 85%.

CONCLUSIONS

In this prospective study of gastroenteropancreatic NET patients, we observed only a weak association between a change in plasma CgA and changes in tumor burden. CgA as a single biomarker was thus inadequate to predict tumor progression.

A Review of Selected Studies That Determine the Physical and Chemical Properties of Saliva in the Field of Dental Treatment

Physiological whole saliva is a unique body fluid constantly washing the mucous membranes of the mouth, throat, and larynx. Saliva is a clear, slightly acidic mucinous-serous secretion, composed of various electrolytes, small organic substances, proteins, peptides, and polynucleotides. There are many ways to use saliva as a biological fluid (biofluid). The significant advantages of saliva as a unique diagnostic material are its availability and the noninvasive method of collection. The aim of this review is to emphasize the diagnostic value of saliva as a research material in the configuration of its structure and secretion disorders. The data were obtained using the MEDLINE (PubMed) search engine, as well as an additional manual search. The analysis covered 77 articles selected from a group of 1986 publications and initially qualified for devising. The results were evaluated and checked for the correctness of qualifying in accordance with inclusion and exclusion criteria. The diagnostic use of saliva has attracted the attention of many researchers due to its noninvasive nature and relative simplicity of collection. In addition, it should be noted that the determination of chemical and physical saliva parameters can be effectively performed in the patient's presence in the dental office.

Chromogranin A as a valid marker in oncology: Clinical application or false hopes?

Chromogranin A, due to its primary expression throughout the neuroendocrine system, is a widely accepted biomarker for the assessment of neuro-endocrine tumors. It has been traditionally used in the management of patients with tumors of gastro-enteropancreatic origin. Lately, it has also been implicated in various conditions and diseases, both benign and malignant. However, the paucity of data of adequate strength, as well as its relation with common physiologic conditions and its interaction with commonly prescribed medications, limit its clinical use in only a narrow spectrum. Herein, we present a thorough review to the most frequent conditions where its levels are affected, focusing specifically on its potential use as a prognostic and predictive biomarker in oncology.

Differential Reovirus-Specific and Herpesvirus-Specific Activator Protein 1 Activation of Secretogranin II Leads to Altered Virus Secretion

Viruses utilize host cell machinery for propagation and manage to evade cellular host defense mechanisms in the process. Much remains unknown regarding how the host responds to viral infection. We recently performed global proteomic screens of mammalian reovirus TIL- and T3D-infected and herpesvirus (herpes simplex virus 1 [HSV-1])-infected HEK293 cells. The nonenveloped RNA reoviruses caused an upregulation, whereas the enveloped DNA HSV-1 caused a downregulation, of cellular secretogranin II (SCG2). SCG2, a member of the granin family that functions in hormonal peptide sorting into secretory vesicles, has not been linked to virus infections previously. We confirmed SCG2 upregulation and found SCG2 phosphorylation by 18 h postinfection (hpi) in reovirus-infected cells. We also found a decrease in the amount of reovirus secretion from SCG2 knockdown cells. Similar analyses of cells infected with HSV-1 showed an increase in the amount of secreted virus. Analysis of the stress-activated protein kinase (SAPK)/Jun N-terminal protein kinase (JNK) pathway indicated that each virus activates different pathways leading to activator protein 1 (AP-1) activation, which is the known SCG2 transcription activator. We conclude from these experiments that the negative correlation between SCG2 quantity and virus secretion for both viruses indicates a virus-specific role for SCG2 during infection.

IMPORTANCE

Mammalian reoviruses affect the gastrointestinal system or cause respiratory infections in humans. Recent work has shown that all mammalian reovirus strains (most specifically T3D) may be useful oncolytic agents. The ubiquitous herpes simplex viruses cause common sores in mucosal areas of their host and have coevolved with hosts over many years. Both of these virus species are prototypical representatives of their viral families, and investigation of these viruses can lead to further knowledge of how they and the other more pathogenic members of their respective families interact with the host. Here we show that secretogranin II (SCG2), a protein not previously studied in the context of virus infections, alters virus output in a virus-specific manner and that the quantity of SCG2 is inversely related to amounts of infectious-virus secretion. Herpesviruses may target this protein to facilitate enhanced virus release from the host.

Obligatory role for endothelial heparan sulphate proteoglycans and caveolae internalization in catestatin-dependent eNOS activation

The chromogranin-A peptide catestatin modulates a wide range of processes, such as cardiovascular functions, innate immunity, inflammation, and metabolism. We recently found that the cardiac antiadrenergic action of catestatin requires a PI3K-dependent NO release from endothelial cells, although the receptor involved is yet to be identified. In the present work, based on the cationic properties of catestatin, we tested the hypothesis of its interaction with membrane heparan sulphate proteoglycans, resulting in the activation of a caveolae-dependent endocytosis. Experiments were performed on bovine aortic endothelial cells. Endocytotic vesicles trafficking was quantified by confocal microscopy using a water-soluble membrane dye; catestatin colocalization with heparan sulphate proteoglycans and caveolin 1 internalization were studied by fluorimetric measurements in live cells. Modulation of the catestatin-dependent eNOS activation was assessed by immunofluorescence and immunoblot analysis. Our results demonstrate that catestatin (5 nM) colocalizes with heparan sulphate proteoglycans and induces a remarkable increase in the caveolae-dependent endocytosis and caveolin 1 internalization, which were significantly reduced by both heparinase and wortmannin. Moreover, catestatin was unable to induce Ser¹¹⁷⁹ eNOS phosphorylation after pretreatments with heparinase and methyl-β-cyclodextrin. Taken together, these results highlight the obligatory role for proteoglycans and caveolae internalization in the catestatin-dependent eNOS activation in endothelial cells.

In-depth characterization of the cerebrospinal fluid (CSF) proteome displayed through the CSF proteome resource (CSF-PR)

In this study, the human cerebrospinal fluid (CSF) proteome was mapped using three different strategies prior to Orbitrap LC-MS/MS analysis: SDS-PAGE and mixed mode reversed phase-anion exchange for mapping the global CSF proteome, and hydrazide-based glycopeptide capture for mapping glycopeptides. A maximal protein set of 3081 proteins (28,811 peptide sequences) was identified, of which 520 were identified as glycoproteins from the glycopeptide enrichment strategy, including 1121 glycopeptides and their glycosylation sites. To our knowledge, this is the largest number of identified proteins and glycopeptides reported for CSF, including 417 glycosylation sites not previously reported. From parallel plasma samples, we identified 1050 proteins (9739 peptide sequences). An overlap of 877 proteins was found between the two body fluids, whereas 2204 proteins were identified only in CSF and 173 only in plasma. All mapping results are freely available via the new CSF Proteome Resource (http://probe.uib.no/csf-pr), which can be used to navigate the CSF proteome and help guide the selection of signature peptides in targeted quantitative proteomics.

Chromogranins can be measured in samples from cats and dogs

BACKGROUND

Methods for objective evaluation of stress in animals are important, but clinically difficult. An alternative method to study the sympathetic activity may be to investigate Chromogranin A (CGA), Chromogranin B (CGB) and Secretogranin II (SG2). The aim of this study was to investigate the cross-reactivity of CGA, CGB and SG2 between man, cat and dog and to explore possibilities to measure these proteins in samples from cats and dogs.

RESULTS

Adrenal gland extracts from feline and canine species were measured by region-specific radioimmunoassays in different dilution steps to explore possible inter species cross reactivity. High cross reactivity was found for cats in the CGA17-38, CGA324-337, CGA361-372, CGB and SG2 assays. High cross reactivity was found for dogs in the CGA17-38, CGA361-372, CGB and SN assays. The method measuring the intact CGA was not useful for measurements in cats and dogs.

CONCLUSIONS

Region-specific assays measuring defined parts of CGA, CGB and SG2 can be used for measurements in samples from cats and dogs. These results are promising and will allow for further studies of these proteins as possible clinical biomarkers in cats and dogs.

Plasma chromogranin A is a marker of death in elderly patients presenting with symptoms of heart failure

Cardiovascular risk assessment remains difficult in elderly patients. We examined whether chromogranin A (CgA) measurement in plasma may be valuable in assessing risk of death in elderly patients with symptoms of heart failure in a primary care setting. A total of 470 patients (mean age 73 years) were followed for 10 years. For CgA plasma measurement, we used a two-step method including a screening test and a confirmative test with plasma pre-treatment with trypsin. Cox multivariable proportional regression and receiver-operating curve (ROC) analyses were used to assess mortality risk. Assessment of cardiovascular mortality during the first 3 years of observation showed that CgA measurement contained useful information with a hazard ratio (HR) of 5.4 (95% CI 1.7-16.4) (CgA confirm). In a multivariate setting, the corresponding HR was 5.9 (95% CI 1.8-19.1). WHEN ADDING N-TERMINAL PROBNP (NT-PROBNP) TO THE MODEL, CGA CONFIRM STILL POSSESSED PROGNOSTIC INFORMATION (HR: 6.1; 95% CI 1.8-20.7). The result for predicting all-cause mortality displayed the same pattern. ROC analyses in comparison to NT-proBNP to identify patients on top of clinical variables at risk of cardiovascular death within 5 years of follow-up showed significant additive value of CgA confirm measurements compared with NT-proBNP and clinical variables. CgA measurement in the plasma of elderly patients with symptoms of heart failure can identify those at increased risk of short- and long-term mortality.

MicroRNA-22 and promoter motif polymorphisms at the Chga locus in genetic hypertension: functional and therapeutic implications for gene expression and the pathogenesis of hypertension

Hypertension is a common hereditary syndrome with unclear pathogenesis. Chromogranin A (Chga), which catalyzes formation and cargo storage of regulated secretory granules in neuroendocrine cells, contributes to blood pressure homeostasis centrally and peripherally. Elevated Chga occurs in spontaneously hypertensive rat (SHR) adrenal glands and plasma, but central expression is unexplored. In this report, we measured SHR and Wistar-Kyoto rat (control) Chga expression in central and peripheral nervous systems, and found Chga protein to be decreased in the SHR brainstem, yet increased in the adrenal and the plasma. By re-sequencing, we systematically identified five promoter, two coding and one 3'-untranslated region (3'-UTR) polymorphism at the SHR (versus WKY or BN) Chga locus. Using HXB/BXH recombinant inbred (RI) strain linkage and correlations, we demonstrated genetic determination of Chga expression in SHR, including a cis-quantitative trait loci (QTLs) (i.e. at the Chga locus), and such expression influenced biochemical determinants of blood pressure, including a cascade of catecholamine biosynthetic enzymes, catecholamines themselves and steroids. Luciferase reporter assays demonstrated that the 3'-UTR polymorphism (which disrupts a microRNA miR-22 motif) and promoter polymorphisms altered gene expression consistent with the decline in SHR central Chga expression. Coding region polymorphisms did not account for changes in Chga expression or function. Thus, we hypothesized that the 3'-UTR and promoter mutations lead to dysregulation (diminution) of Chga in brainstem cardiovascular control nuclei, ultimately contributing to the pathogenesis of hypertension in SHR. Accordingly, we demonstrated that in vivo administration of miR-22 antagomir to SHR causes substantial (∼18 mmHg) reductions in blood pressure, opening a novel therapeutic avenue for hypertension.

The extended granin family: structure, function, and biomedical implications

The chromogranins (chromogranin A and chromogranin B), secretogranins (secretogranin II and secretogranin III), and additional related proteins (7B2, NESP55, proSAAS, and VGF) that together comprise the granin family subserve essential roles in the regulated secretory pathway that is responsible for controlled delivery of peptides, hormones, neurotransmitters, and growth factors. Here we review the structure and function of granins and granin-derived peptides and expansive new genetic evidence, including recent single-nucleotide polymorphism mapping, genomic sequence comparisons, and analysis of transgenic and knockout mice, which together support an important and evolutionarily conserved role for these proteins in large dense-core vesicle biogenesis and regulated secretion. Recent data further indicate that their processed peptides function prominently in metabolic and glucose homeostasis, emotional behavior, pain pathways, and blood pressure modulation, suggesting future utility of granins and granin-derived peptides as novel disease biomarkers.

Subjective food hypersensitivity: assessment of enterochromaffin cell markers in blood and gut lavage fluid

BACKGROUND

Food hypersensitivity is commonly suspected, but seldom verified. Patients with subjective food hypersensitivity suffer from both intestinal and extraintestinal health complaints. Abnormalities of the enterochromaffin cells may play a role in the pathogenesis. The aim of this study was to investigate enterochromaffin cell function in patients with subjective food hypersensitivity by measuring serum chromogranin A (CgA) and 5-hydroxytryptamine (5-HT, serotonin) in gut lavage fluid.

METHODS

Sixty-nine patients with subjective food hypersensitivity were examined. Twenty-three patients with inflammatory bowel disease and 35 healthy volunteers were included as comparison groups. CgA was measured in serum by enzyme-linked immunosorbent assay. Gut lavage fluid was obtained by administering 2 L of polyethylene glycol solution intraduodenally. The first clear fluid passed per rectum was collected and 5-HT was analyzed by liquid chromatography tandem mass spectrometry.

RESULTS

Serum levels of CgA were significantly lower in patients with subjective food hypersensitivity than in healthy controls (P = 0.04). No differences were found in 5-HT levels in gut lavage fluid between patients with subjective food hypersensitivity and the control groups. There was no correlation between serum CgA and gut lavage 5-HT.

CONCLUSION

Decreased blood levels of CgA suggest neuroendocrine alterations in patients with subjective food hypersensitivity. However, 5-HT levels in gut lavage fluid were normal.

Systematic polymorphism discovery after genome-wide identification of potential susceptibility loci in a hereditary rodent model of human hypertension

Genetic strategies such as linkage analysis and quantitative trait locus (QTL) mapping have identified a multitude of loci implicated in the pathogenesis of hypertension in the spontaneously hypertensive rat (SHR). While several candidate genetic regions have been identified in the SHR and its control, the Wistar-Kyoto rat (WKY), systematic follow-up of candidate identification with polymorphism discovery has not been widespread. In the current report, we develop a data-mining strategy to identify candidate genes for hypertension in the SHR, and then sequence each gene in the SHR and WKY strains. We integrate blood pressure QTL data, microarray data and data-mining methods. First, we determined the set of genes differentially expressed in SHR and WKY adrenal glands. Next, the chromosomal position of all differentially expressed genes was compared with peak marker position of all reported SHR blood pressure QTLs. We also identified the set of differentially expressed genes with the most extreme fold-change. Finally, the QTL positional candidates and the genes with extreme differential expression were proposed as candidate genes if they had biologically plausible roles in hypertensive pathology. We identified seven candidate genes that merit resequencing (catechol-O-methyltransferase [Comt], chromogranin A [Chga], dopamine beta-hydroxylase [Dbh], electron transferring flavoprotein dehydrogenase [Etfdh], endothelin receptor type B [Ednrb], neuropeptide Y [Npy] and phenylethanolamine-N-methyltransferase [Pnmt]), and then discovered polymorphism in four of these seven candidate genes. Chga is proposed as the strongest candidate for additional functional investigation. Our method for candidate gene identification is portable and can be applied to microarray data from any tissue, in any disease model with a QTL database.

Cutting edge: vasostatin-1-derived peptide ChgA29-42 is an antigenic epitope of diabetogenic BDC2.5 T cells in nonobese diabetic mice

Mechanistic and therapeutic insights in autoimmune diabetes would benefit from a more complete identification of relevant autoantigens. BDC2.5 TCR transgenic NOD mice express transgenes for TCR Vα1 and Vβ4 chains from the highly diabetogenic BDC2.5 CD4(+) T cell clone, which recognizes pancreatic β cell membrane Ags presented by NOD I-A(g7) MHC class II molecules. The antigenic epitope of BDC2.5 TCR is absent in β cells that do not express chromogranin A (ChgA) protein. However, characterization of the BDC2.5 epitope in ChgA has given inconclusive results. We have now identified a ChgA29-42 peptide within vasostatin-1, an N-terminal natural derivative of ChgA as the BDC2.5 TCR epitope. Having the necessary motif for binding to I-A(g7), it activates BDC2.5 T cells and induces an IFN-γ response. More importantly, adoptive transfer of naive BDC2.5 splenocytes activated with ChgA29-42 peptide transferred diabetes into NOD/SCID mice.

Regulatory peptides from chromogranin A and secretogranin II

This commentary is focusing on novel aspects on the secreted CgA- and SgII-derived peptides, vasostatin-I (bovine and human CgA_1–76, VS-I), WE-14 (CgA_316–329), catestatin (bovine CgA_344–366, human CgA_352–372, Cts) and the SgII-derived secretoneurin (SgII_180–204) as significant regulators of inflammatory reactions.

Substrate specificity of human carboxypeptidase A6

Carboxypeptidase A6 (CPA6) is an extracellular matrix-bound metallocarboxypeptidase (CP) that has been implicated in Duane syndrome, a neurodevelopmental disorder in which the lateral rectus extraocular muscle is not properly innervated. Consistent with a role in Duane syndrome, CPA6 is expressed in a number of chondrocytic and nervous tissues during embryogenesis. To better characterize the enzymatic function and specificity of CPA6 and to compare this with other CPs, CPA6 was expressed in HEK293 cells and purified. Kinetic parameters were determined using a panel of synthetic carboxypeptidase substrates, indicating a preference of CPA6 for large hydrophobic C-terminal amino acids and only very weak activity toward small amino acids and histidine. A quantitative peptidomics approach using a mixture of peptides representative of the neuropeptidome allowed the characterization of CPA6 preferences at the P1 substrate position and suggested that small and acidic P1 residues significantly inhibit CPA6 cleavage. Finally, a comparison of available kinetic data for CPA enzymes shows a gradient of specificity across the subfamily, from the very restricted specificity of CPA2 to the very broad activity of CPA4. Structural data and modeling for all CPA/B subfamily members suggests the structural basis for the unique specificities observed for each member of the CPA/B subfamily of metallocarboxypeptidases.