Identification of the secretogranin II-derived peptide EM66 in pheochromocytomas as a potential marker for discriminating benign versus malignant tumors

Identification of an immune gene-associated prognostic signature in patients with bladder cancer

A deeper understanding of the interaction between tumor cell and the immune microenvironment in bladder cancer may help select predictive and prognostic biomarkers. The current study aims to construct a prognostic signature for bladder cancer by analysis of molecular characteristics, as well as tumor-immune interactions. RNA-sequencing and clinical information from bladder cancer patients were downloaded from the TCGA database. The single sample Gene Sets Enrichment Analysis (ssGSEA) and Cell type Identification by Estimating Relative Subsets of RNA Transcripts (CIBERSORT) were employed to separate the samples into two clusters. Lasso Cox regression was performed to construct an immune gene signature for bladder cancer. The correlation between key target genes of immune checkpoint blockade and the prognostic signature was also analyzed. Dataset from Gene Expression Omnibus (GEO) was retrieved for validation. Two immunophenotypes and immunological characteristics were identified, and a 17-immune gene signature was constructed to provide an independent prognostic signature for bladder cancer. The signature was verified through external validation and correlated with genomic characteristics and clinicopathologic features. Finally, a nomogram was generated from the clinical characteristics and immune signature. Our study reveals a tumor-immune microenvironment signature useful for prognosis in bladder cancer. The results provide information on the potential development of treatment strategies for bladder cancer patients. Prospective studies are warranted to validate the prognostic capability of this model, but these data highlight the role of the microenvironment in the clinical outcome of patients.

Differential Expression of Secretogranins II and III in Canine Adrenal Chromaffin Cells and Pheochromocytomas

Secretogranin II (SgII) and III (SgIII) function within peptide hormone-producing cells and are involved in secretory granule formation. However, their function in active amine-producing cells is not fully understood. In this study, we analyzed the expression profiles of SgII and SgIII in canine adrenal medulla and pheochromocytomas by immunohistochemical staining. In normal adrenal tissues, the intensity of coexpression of these two secretogranins (Sgs) differed from each chromaffin cell, although a complete match was not observed. The coexpression of vesicular monoamine transporter 2 (VMAT2) with SgIII was similar to that with chromogranin A, but there was a subpopulation of VMAT2-expressing cells that were negative or hardly detectable for SgII. These results are the first to indicate that there are distinct expression patterns for SgII and SgIII in adrenal chromaffin cells. Furthermore, the expression of these two Sgs varied in intensity among pheochromocytomas and did not necessarily correlate with clinical plasma catecholamine levels in patients. However, compared with SgIII, the expression of SgII was shown to be strong at the single-cell level in some tumor tissues. These findings provide a fundamental understanding of the expression differences between SgII and SgIII in normal adrenal chromaffin cells and pheochromocytomas.

Identification of a prognostic gene signature based on an immunogenomic landscape analysis of bladder cancer

Cancer immune plays a critical role in cancer progression. Tumour immunology and immunotherapy are one of the exciting areas in bladder cancer research. In this study, we aimed to develop an immune‐related gene signature to improve the prognostic prediction of bladder cancer. Firstly, we identified 392 differentially expressed immune‐related genes (IRGs) based on TCGA and ImmPort databases. Functional enrichment analysis revealed that these genes were enriched in inflammatory and immune‐related pathways, including in ‘regulation of signaling receptor activity’, ‘cytokine‐cytokine receptor interaction’ and ‘GPCR ligand binding’. Then, we separated all samples in TCGA data set into the training cohort and the testing cohort in a ratio of 3:1 randomly. Data set GSE13507 was set as the validation cohort. We constructed a prognostic six‐IRG signature with LASSO Cox regression in the training cohort, including AHNAK, OAS1, APOBEC3H, SCG2, CTSE and KIR2DS4. Six IRGs reflected the microenvironment of bladder cancer, especially immune cell infiltration. The prognostic value of six‐IRG signature was further validated in the testing cohort and the validation cohort. The results of multivariable Cox regression and subgroup analysis revealed that six‐IRG signature was a clinically independent prognostic factor for bladder cancer patients. Further, we constructed a nomogram based on six‐IRG signature and other clinicopathological risk factors, and it performed well in predict patients' survival. Finally, we found six‐IRG signature showed significant difference in different molecular subtypes of bladder cancer. In conclusions, our research provided a novel immune‐related gene signature to estimate prognosis for patients' survival with bladder cancer.

Genetic and epigenetic differences of benign and malignant pheochromocytomas and paragangliomas (PPGLs)

Pheochromocytomas and paragangliomas (PPGLs) are tumors arising from the adrenal medulla and sympathetic/parasympathetic paraganglia, respectively. According to Th e Cancer Genome Atlas (TCGA), approximately 40% of PPGLs are due to germ line mutations in one of 16 susceptibility genes, and a further 30% are due to somatic alterations in at least seven main genes (VHL, EPAS1, CSDE1, MAX, HRAS, NF1, RET, and possibly KIF1B). Th e diagnosis of malignant PPGL was straight forward in most cases as it was defined as presence of PPGL in non-chromaffin tissues. Accordingly, there is an extreme need for new diagnostic marker(s) to identify tumors with malignant prospective. Th e aim of this study was to review all suggested genetic and epigenetic alterations that are remarkably different between benign and malignant PPGLs. It seems that more than two genetic mutation clusters in PPGLs and other genetic and methylation biomarkers could be targeted for malignancy discrimination in different studies.

Intricacies of the Molecular Machinery of Catecholamine Biosynthesis and Secretion by Chromaffin Cells of the Normal Adrenal Medulla and in Pheochromocytoma and Paraganglioma

The adrenal medulla is composed predominantly of chromaffin cells producing and secreting the catecholamines dopamine, norepinephrine, and epinephrine. Catecholamine biosynthesis and secretion is a complex and tightly controlled physiologic process. The pathways involved have been extensively studied, and various elements of the underlying molecular machinery have been identified. In this review, we provide a detailed description of the route from stimulus to secretion of catecholamines by the normal adrenal chromaffin cell compared to chromaffin tumor cells in pheochromocytomas. Pheochromocytomas are adrenomedullary tumors that are characterized by uncontrolled synthesis and secretion of catecholamines. This uncontrolled secretion can be partly explained by perturbations of the molecular catecholamine secretory machinery in pheochromocytoma cells. Chromaffin cell tumors also include sympathetic paragangliomas originating in sympathetic ganglia. Pheochromocytomas and paragangliomas are usually locally confined tumors, but about 15% do metastasize to distant locations. Histopathological examination currently poorly predicts future biologic behavior, thus long term postoperative follow-up is required. Therefore, there is an unmet need for prognostic biomarkers. Clearer understanding of the cellular mechanisms involved in the secretory characteristics of pheochromocytomas and sympathetic paragangliomas may offer one approach for the discovery of novel prognostic biomarkers for improved therapeutic targeting and monitoring of treatment or disease progression.

Characterization of the EM66 Biomarker in the Pituitary and Plasma of Healthy Subjects With Different Gonadotroph Status and Patients With Gonadotroph Tumor

Granins and their derived-peptides are useful markers of secretion from normal and tumoral neuroendocrine cells. The need to identify new diagnostic markers for neuroendocrine tumors, including pituitary tumors prompted us to determine plasma levels of the secretogranin II-derived peptide EM66 in healthy volunteers with different gonadotroph status and to evaluate its usefulness as a circulating marker for the diagnosis of gonadotroph tumor. Using a radioimmunoassay, we determined plasma EM66 concentrations in healthy men and women volunteers in different physiological conditions in relation with the gonadotroph function. Our results revealed that in men, in women with or without contraception, in pregnant or post-menopausal women, plasma EM66 concentrations are not significantly different, and did not show any correlation with gonadotropin levels. In addition, stimulation or inhibition tests of the gonadotroph axis had no effect on EM66 levels, whatever the group of healthy volunteers investigated while gonadotropin levels showed the expected variations. Immunohistochemical experiments and HPLC analysis showed the occurrence of EM66 in pituitary gonadotroph, lactotroph and corticotroph tumors but not in somatotroph tumor. In patients with gonadotroph or lactotroph tumor, plasma EM66 levels were 1.48 (0.82-4.38) ng/ml and 2.49 (1.19-3.54) ng/ml, respectively. While median value of EM66 was significantly lower in patients with gonadotroph tumor compared to healthy volunteers [2.59 (0.62-4.95) ng/ml], plasma EM66 concentrations were in the same range as normal values and did not show any correlation with gonadotropin levels. These results show that plasma EM66 levels are independent of the activity of the gonadotroph axis in healthy volunteers and, while EM66 levels are reduced in gonadotroph tumors, plasma EM66 does not provide a helpful marker for the diagnosis of these tumors.

Mysterious inhibitory cell regulator investigated and found likely to be secretogranin II related

In the context of a hunt for a postulated hormone that is tissue-mass inhibiting and reproductively associated, there is described probable relatedness to a granin protein. A 7–8 kDa polypeptide candidate (gels/MS) appeared in a bioassay-guided fractionation campaign involving sheep plasma. An N-terminal sequence of 14 amino acids was obtained for the polypeptide by Edman degradation. Bioinformatics and molecular biology failed to illuminate any ovine or non-ovine protein which might relate to this sequence. The N-terminal sequence was synthesized as the 14mer EPL001 peptide and surprisingly found to be inhibitory in an assay in vivo of compensatory renal growth in the rat and modulatory of nematode fecundity, in line with the inhibitory hormone hypothesis. Antibodies were raised to EPL001 and their deployment upheld the hypothesis that the EPL001 amino acid sequence is meaningful and relevant, notwithstanding bioinformatic obscurity. Immunohistochemistry (IHC) in sheep, rodents and humans yielded staining of seeming endocrine relevance (e.g. hypothalamus, gonads and neuroendocrine cells in diverse tissues), with apparent upregulation in certain human tumours (e.g. pheochromocytoma). Discrete IHC staining in Drosophila melanogaster embryo brain was seen in glia and in neuroendocrine cells, with staining likely in the corpus cardiacum. The search for the endogenous antigen involved immunoprecipitation (IP) followed by liquid chromatography and mass spectrometry (LC–MS). Feedstocks were PC12 conditioned medium and aqueous extract of rat hypothalamus—both of which had anti-proliferative and pro-apoptotic effects in an assay in vitro involving rat bone marrow cells, which inhibition was subject to prior immunodepletion with an anti-EPL001 antibody—together with fruit fly embryo material. It is concluded that the mammalian antigen is likely secretogranin II (SgII) related. The originally seen 7–8 kDa polypeptide is suggested to be a new proteoform of secretogranin II of ∼70 residues, SgII-70, with the anti-EPL001 antibody seeing a discontinuous epitope. The fly antigen is probably Q9W2X8 (UniProt), an uncharacterised protein newly disclosed as a granin and provisionally dubbed macrogranin I (MgI). SgII and Q9W2X8 merit further investigation in the context of tissue-mass inhibition.

Establishment and evaluation of a novel biomarker-based nomogram for malignant phaeochromocytomas and paragangliomas

OBJECTIVE

No single histological or molecular marker is diagnostic for malignant phaeochromocytomas and paragangliomas (PPGLs). This study aimed to establish and evaluate a prognostic nomogram to improve the prediction of metastatic probability in individual PPGL patients.

METHODS

Three hundred and 47 consecutive PPGL patients from January 2002 through December 2014 were randomly divided into a training set (n=208) and a validation set (n=139). A multivariate logistic regression analysis of selected prognostic features was performed, and a nomogram to predict metastasis was constructed. Discrimination and calibration were employed to evaluate the performance of the nomogram. Clinical usefulness was calculated using decision curve analysis.

RESULTS

The overall metastatic rate was 10.6%. Primary tumour size, primary tumour location, vascular invasion, ERBB-2 overexpression, SDHB mutation and catecholamine type were associated with malignancy in the logistic analysis and were included in the nomogram. The nomogram showed an area under the receiver operating characteristic curve (AUC) of 0.872 (95% confidence interval [CI], 0.819-0.914) in the training set. The validation set showed good discrimination, with an AUC of 0.870 (95% CI, 0.803-0.921). The nomogram was well calibrated, with no significant difference between the predicted and the observed probabilities (Hosmer-Lemeshow test: P=.510 for the training set; .314 for the validation set). Decision curve analysis revealed that molecular markers (ERBB-2 overexpression and SDHB mutation) could increase the clinical benefit of the nomogram.

CONCLUSION

Our results support the use of the present biomarker-based nomogram, which has good discriminative ability, to predict the metastatic probability of PPGLs.

A potential role for the secretogranin II-derived peptide EM66 in the hypothalamic regulation of feeding behaviour

EM66 is a conserved 66-amino acid peptide derived from secretogranin II (SgII), a member of the granin protein family. EM66 is widely distributed in secretory granules of endocrine and neuroendocrine cells, as well as in hypothalamic neurones. Although EM66 is abundant in the hypothalamus, its physiological function remains to be determined. The present study aimed to investigate a possible involvement of EM66 in the hypothalamic regulation of feeding behaviour. We show that i.c.v. administration of EM66 induces a drastic dose-dependent inhibition of food intake in mice deprived of food for 18 hours, which is associated with an increase of hypothalamic pro-opiomelanocortin (POMC) and melanocortin-3 receptor mRNA levels and c-Fos immunoreactivity in the POMC neurones of the arcuate nucleus. By contrast, i.c.v. injection of EM66 does not alter the hypothalamic expression of neuropeptide Y (NPY), or that of its Y1 and Y5 receptors. A 3-month high-fat diet (HFD) leads to an important decrease of POMC and SgII mRNA levels in the hypothalamus, whereas NPY gene expression is not affected. Finally, we show that a 48 hours of fasting in HFD mice decreases the expression of POMC and SgII mRNA, which is not observed in mice fed a standard chow. Taken together, the present findings support the view that EM66 is a novel anorexigenic neuropeptide regulating hypothalamic feeding behaviour, at least in part, by activating the POMC neurones of the arcuate nucleus.

Characterization and plasma measurement of the WE-14 peptide in patients with pheochromocytoma

Granins and their derived peptides are valuable circulating biological markers of neuroendocrine tumors. The aim of the present study was to investigate the tumoral chromogranin A (CgA)-derived peptide WE-14 and the potential advantage to combine plasma WE-14 detection with the EM66 assay and the existing current CgA assay for the diagnosis of pheochromocytoma. Compared to healthy volunteers, plasma WE-14 levels were 5.4-fold higher in patients with pheochromocytoma, but returned to normal values after surgical resection of the tumor. Determination of plasma CgA and EM66 concentrations in the same group of patients revealed that the test assays for these markers had an overall 84% diagnostic sensitivity, which is identical to that determined for WE-14. However, we found that WE-14 measurement improved the diagnostic sensitivity when combined with the results of CgA or EM66 assays. By combining the results of the three assays, the sensitivity for the diagnosis of pheochromocytoma was increased to 95%. In fact, the combination of WE-14 with either CgA or EM66 test assays achieved 100% sensitivity for the diagnosis of paragangliomas and sporadic or malignant pheochromocytomas if taken separately to account for the heterogeneity of the tumor. These data indicate that WE-14 is produced in pheochromocytoma and secreted into the general circulation, and that elevated plasma WE-14 levels are correlated with the occurrence of this chromaffin cell tumor. In addition, in association with other biological markers, such as CgA and/or EM66, WE-14 measurement systematically improves the diagnostic sensitivity for pheochromocytoma. These findings support the notion that granin-processing products may represent complementary tools for the diagnosis of neuroendocrine tumors.

Molecular and therapeutic advances in the diagnosis and management of malignant pheochromocytomas and paragangliomas

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare catecholamine-secreting tumors derived from chromaffin cells originating in the neural crest. These tumors represent a significant diagnostic and therapeutic challenge because the diagnosis of malignancy is frequently made in retrospect by the development of metastatic or recurrent disease. Complete surgical resection offers the only potential for cure; however, recurrence can occur even after apparently successful resection of the primary tumor. The prognosis for malignant disease is poor because traditional treatment modalities have been limited. The last decade has witnessed exciting discoveries in the study of PCCs and PGLs; advances in molecular genetics have uncovered hereditary and germline mutations of at least 10 genes that contribute to the development of these tumors, and increasing knowledge of genotype-phenotype interactions has facilitated more accurate determination of malignant potential. Elucidating the molecular mechanisms responsible for malignant transformation in these tumors has opened avenues of investigation into targeted therapeutics that show promising results. There have also been significant advances in functional and radiological imaging and in the surgical approach to adrenalectomy, which remains the mainstay of treatment for PCC. In this review, we discuss the currently available diagnostic and therapeutic options for patients with malignant PCCs and PGLs and detail the molecular rationale and clinical evidence for novel and emerging diagnostic and therapeutic strategies.

Differential expression and processing of secretogranin II in relation to the status of pheochromocytoma: implications for the production of the tumoral marker EM66

We have previously demonstrated that measurement of tissue concentrations of the secretogranin II (SgII or SCG2 as listed in the HUGO database)-derived peptide EM66 may help to discriminate between benign and malignant pheochromocytomas and that EM66 represents a sensitive plasma marker of pheochromocytomas. Here, we investigated the gene expression and protein production of SgII in 13 normal adrenal glands, and 35 benign and 16 malignant pheochromocytomas with the goal to examine the molecular mechanisms leading to the marked variations in the expression of EM66 in tumoral chromaffin tissue. EM66 peptide levels were 16-fold higher in benign than in malignant pheochromocytomas and had an area under the receiver-operating characteristic curve of 0.95 for the distinction of benign and malignant tumors. Q-PCR experiments indicated that the SgII gene was significantly underexpressed in malignant tumors compared with benign tumors. Western blot analysis using antisera directed against SgII and SgII-derived fragments revealed lower SgII protein and SgII-processing products in malignant tumors. Western blot also showed that low p-cAMP-responsive element-binding (CREB) concentrations seemed to be associated with the malignant status. In addition, the prohormone convertase PC1 and PC2 genes and proteins were overexpressed in benign pheochromocytomas compared with malignant pheochromocytomas. Low concentrations of EM66 found in malignant tumors are associated with reduced expression and production of SgII and SgII-derived peptides that could be ascribed to a decrease in SgII gene transcription, probably linked to p-CREB down-regulation, and to lower PC levels. These findings highlight the mechanisms leading to lower concentrations of EM66 in malignant pheochromocytoma and strengthen the notion that this peptide is a suitable marker of this neuroendocrine tumor.

Diagnostic tests and biomarkers for pheochromocytoma and extra-adrenal paraganglioma: from routine laboratory methods to disease stratification

The laboratory workup of patients with pheochromocytoma and extra-adrenal paraganglioma (PPGLs) has traditionally focused on biochemical measurements of tumor secretory products or their metabolites, with ultimate diagnosis resting on routine histopathology and immunohistochemistry. While such testing remains important, the needs to distinguish potentially metastatic from benign tumors and to identify tumors with a hereditary basis have stimulated searches for additional means to stratify patients according to risk of metastasis or presence of a particular mutation. Biomarkers based on traditional biochemical tests, such as profiles of catecholamine metabolites and granin-derived peptides, provide utility for both purposes, while novel biomarkers are being identified by proteomic and transcriptomic studies, the latter including microRNA expression profiling. Histopathological scoring methods for predicting metastatic potential, such as the Pheochromocytoma of the Adrenal Gland Scaled Score (PASS), are limited by poor interobserver concordance, discrepant results between studies and incomplete knowledge of how scores relate to genotype. Immunohistochemical staining for succinate dehydrogenase (SDH) subunit B to triage patients for genetic testing of SDH subunit genes illustrates the growing importance of pathology as an adjunct to genetic testing for disease stratification. Although considerable effort has been expended on microarray-based platforms to identify biomarkers of malignancy, as yet, none of those proposed have been demonstrated to reliably discriminate malignant from benign disease any better than the PASS. Because of the heterogeneity of PPGLs and variable time between first appearance of tumors and identification of metastases, any prospective study to establish prognostic efficacy requires large numbers of patients and extended follow-up.

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.

Granins and their derived peptides in normal and tumoral chromaffin tissue: Implications for the diagnosis and prognosis of pheochromocytoma

Pheochromocytomas are rare catecholamine-secreting tumors that arise from chromaffin tissue within the adrenal medulla and extra-adrenal sites. Typical clinical manifestations are sustained or paroxysmal hypertension, severe headaches, palpitations and sweating resulting from hormone excess. However, their presentation is highly variable and can mimic many other diseases. The diagnosis of pheochromocytomas depends mainly upon the demonstration of catecholamine excess by 24-h urinary catecholamines and metanephrines or plasma metanephrines. Occurrence of malignant pheochromocytomas can only be asserted by imaging of metastatic lesions, which are associated with a poor survival rate. The characterization of tissue, circulating or genetic markers is therefore crucial for the management of these tumors. Proteins of the granin family and their derived peptides are present in dense-core secretory vesicles and secreted into the bloodstream, making them useful markers for the identification of neuroendocrine cells and neoplasms. In this context, we will focus here on reviewing the distribution and characterization of granins and their processing products in normal and tumoral chromaffin cells, and their clinical usefulness for the diagnosis and prognosis of pheochromocytomas. It appears that, except SgIII, all members of the granin family i.e. CgA, CgB, SgII, SgIV-SgVII and proSAAS, and most of their derived peptides are present in adrenomedullary chromaffin cells and in pheochromocytes. Moreover, besides the routinely used CgA test assays, other assays have been developed to measure concentrations of tissue and/or circulating granins or their derived peptides in order to detect the occurrence of pheochromocytomas. In most cases, elevated levels of these entities were found, in correlation with tumor occurrence, while rarely discriminating between benign and malignant neoplasms. Nevertheless, measurement of the levels of granins and derived peptides improves the diagnostic sensitivity and may therefore provide a complementary tool for the management of pheochromocytomas. However, the existing data need to be substantiated in larger groups of patients, particularly in the case of malignant disease.

Granins and granin-related peptides in neuroendocrine tumours

This review focus on neuroendocrine tumours (NETs), with special reference to the immunohistochemical analysis of granins and granin-related peptides and their usefulness in identifying and characterizing the great diversity of NET types. Granins, their derived peptides, and complex protein-processing enzyme systems that cleave granins and prohormones, have to some extent cell-specific expression patterns in normal and neoplastic NE cells. The marker most commonly used in routine histopathology to differentiate between non-NETs and NETs is chromogranin (Cg) A, to some extent CgB. Other members of the granin family may also be of diagnostic value by identifying special NET types, e.g. secretogranin (Sg) VI was only found in pancreatic NETs and phaeochromocytomas. SgIII has recently arisen as an important NET marker; it was strongly expressed in NETs, with some exceptions--phaeochromocytomas expressed few cells and parathyroid adenomas none. Some expression patterns of granin-related peptides seem valuable in differentiating between some benign and malignant NETs, some may also provide prognostic information, among which: well-differentiated NET types expressed more CgA epitopes than the poorly differentiated ones, except insulinomas, where the opposite was noted; medullary thyroid carcinomas containing few cells immunoreactive to a CgB antibody were related to a bad prognosis; C-terminal secretoneurin visualized a cell type related to malignancy in phaeochromocytomas. Further research will probably establish new staining patterns with marker functions for granins in NETs which may be of histopathological diagnostic value.

Pheochromocytoma and paraganglioma

Pheochromocytoma is a very special kind of tumor full of duplicity. On the one hand it represents its own microworld with unique clinical, biochemical and pathological features, while on the other it constitutes a tremendously significant part of whole body system, playing a vital role for practically every organ system. It has a very special character - sometimes like a child it can be sweet and predictable, while at times it can behave like a deadly wild beast, crashing and tearing everything on its path in a fierce rage. It also consists of the amazingly intelligent neuroendocrine cells that possess a magical ability to make miraculous substances of many kinds. But most of all, it is a system that is able to drive our curiosity and the itch of "Cogito, ergo sum" to limitless depths and year by year it still amazes us with new and unexpected discoveries that move our understanding of multiple pathways and metabolic events closer to the ultimate truth. Recent discoveries of succinate dehydrogenase (SHD) and prolyl hydroxylase (PHD) mutations, for example, propelled our understanding of neuroendocrine tumorigenesis as a whole, as well as physiology of mitochondrial respiratory chain and phenomenon of pseudohypoxia in particular. Good old discoveries make their way from dusty repositories to shine with new meaning, appropriate for the current level of knowledge. This acquired wisdom makes us better physicians - knowing the specific expression makeup of catecholamine transporters, GLUTs and SRIFs allows for better tailored imaging and therapeutic manipulations. There are still long ways to go, keeping in mind that pheochromocytoma is but so very special, and we are optimistic and expect many great things to come.

Granin-derived peptides as diagnostic and prognostic markers for endocrine tumors

Chromogranin A-like immunoreactivity (CgA-LI) has been, and remains, the most widely used diagnostic and prognostic marker for endocrine tumors. The availability of assay kits combined with moderately high sensitivity and specificity has meant that there has been no great incentive to develop alternative markers. However, circulating concentrations of CgA-LI are elevated in several non-neoplastic diseases and in patients receiving acid-suppression therapy which may lead to false positive diagnosis. Additionally, certain endocrine tumors, such as rectal carcinoids, do not express the CgA gene so that there is a need for additional markers to complement CgA measurements. Plasma concentrations of the CgA-derived peptide, pancreastatin, measured with antisera of defined regional specificity, have a prognostic value in patients with metastatic midgut carcinoid tumors receiving somatostatin analog therapy or hepatic artery chemoembolization. Other CgA-derived peptides with potential as tumor markers are vasostatin-1, WE-14, catestatin, GE-25, and EL-35 but their value has yet to be fully assessed. Circulating concentrations of chromogranin B-like immunoreactivity (CgB-LI) are not elevated in non-neoplastic diseases and measurements of CCB, the COOH-terminal fragment of CgB, may be useful as a biochemical marker for neuroendocrine differentiation in lung tumors. Antisera to the secretogranin II-derived peptide, secretoneurin detects carcinoid tumors of the appendix with greater frequency than antisera to CgA and are of value in identifying therapy-resistant carcinoma of the prostate (clinical stage D3). Measurement of concentrations of a second secretogranin II-derived peptide, EM-66 in tumor tissue has been used to differentiate between benign and malignant pheochromocytoma. These examples point to a limited although potentially valuable role for granin-derived peptides as tumor markers.

[Biological diagnosis of pheochromocytomas and paragangliomas]

Pheochromocytomas and/or paragangliomas are rare, heterogeneous tumors of the chromaffin cells. Thirty percent of the patients presented with these diseases in a hereditary context. The biological diagnosis relies on the identification of excessive secretion of the metanephrines which are more sensitive and specific than those of catecholamines The published recommendations give the opportunity to choose between the free metanephrines and the fractionated metanephrines in sera or urines. The concentrations of the free plasmatic metanephrines reflect the ongoing production of tumor. They are little sensitive to the renal failure. The assay of the vanillylmandelic acid should be dropped because of its inefficiency. The assay of the chromogranin A in serum should be used in association with those of metanephrines in the diagnosis but also in the follow-up. Its role still has to be precised.

Genetic markers for the diagnosis and prognosis of pheochromocytoma

The last 5 years have witnessed important advances in understanding the mechanisms of tumorigenesis of chromaffin cells. Large-scale microarray analyses of pheochromocytomas have identified two distinct gene-expression profiles encompassing all hereditary and sporadic tumors. Gene-expression profiling of benign and malignant pheochromocytomas is providing a better understanding of the mechanisms of metastasis. Such studies hold promise for the development of new prognostic markers for early detection of malignant pheochromocytoma and for the identification of novel targets for therapeutic intervention.

Molecular cloning, mapping, and polymorphism of the porcine SCG2 gene

The secretogranin II (SCG2) gene is associated with the synthesis and secretion of follicle-stimulating hormone and luteinizing hormone. In the present study, we have determined the complete cDNA sequence of pig SCG2, which was submitted to GenBank with accession no. AY870646. Its complete open reading frame of 1,851 nucleotides encodes 616 amino acids. The predicted protein shares 80-87% identity with mouse, human, and bovine SCG2 proteins, and all four species share almost complete identity in the secretoneurin and EM66 domains. Pig SCG2 is a protein of 589 amino acids and 68,132 Da, preceded by a signal peptide of 27 residues. It contains nine pairs of dibasic residues, which are used as potential cleavage sites for generation of physiologically active peptides. Analysis of the SCG2 gene across the INRA-Minnesota porcine radiation hybrid panel indicates close linkage with microsatellite marker SW2608, located on Sus scrofa chromosome 15 (SSC15) q25, which harbors several QTL for ovulation rate and meat quality. Comparative sequencing and EST analysis revealed nine SNPs in porcine SCG2 cDNA, including seven SNPs in the coding region and two SNPs in the 3' UTR. Four nonsynonymous SNPs (G622A, G1671T, C1718T, and A1790C) resulted in amino acid substitutions of Ala-->Thr, Glu-->Asp, Pro-->Leu, and Asn-->Thr, respectively.

Recently identified a novel neuropeptide manserin colocalize with the TUNEL-positive cells in the top villi of the rat duodenum

We recently isolated a novel 40 amino acid neuropeptide designated manserin from the rat brain. Manserin is derived from secretogranin II, a member of granin acidic secretory protein family by proteolytic processing, as previously reported secretoneurin and EM66. Manserin peptide are localized in the endocrine cells of the pituitary. In this study, we further investigated the manserin localization in the digestive system by immunohistochemical analysis using antimanserin antibody. In the duodenum, manserin immunostaining was exclusively observed in the nuclei of top villi instead of cytosol as observed in neurons in our previous study. Interestingly, manserin-positive cells in the duodenum are colocalized with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) positive cells, the cells whose DNA was damaged. Since the top villi of duodenum epithelial cells are known to undergo spontaneous apoptosis during epithelial cell turn over, and since other peptides such as secretoneurin and EM66 derived from SgII have been reported to be cancer-related, these results indicated that manserin peptide may have a role in apoptosis and/or cancer pathogenesis in the digestive organ.

Development of differential diagnosis for benign and malignant pheochromocytomas

Unlike common malignant tumors, malignant pheochromocytomas cannot be definitely diagnosed using histological features. This unique nature of pheochromocytomas provides a valuable model that may promote the investigation of the mechanism of other common malignant tumors where similar frameworks are not available. Studies on malignant pheochromocytomas should benefit not only the individuals with pheochromocytomas but those with other tumors. A review on the development of differentiating diagnosis between malignant and benign pheochromocytomas in imaging studies, biological fluid examinations, pathological examinations, molecular markers and genome studies, was updated in the hopes of guiding the next studies of pheochromcytomas.

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.

Clinical review: Current treatment of malignant pheochromocytoma

CONTEXT

Pheochromocytomas are rare tumors of predominantly adrenal origin that often produce and secrete catecholamines. Malignancy occurs in a variable percentage of cases depending on genetic background and tumor location. Definitive diagnosis relies on the detection of distant metastases. Treatments for malignant pheochromocytoma include surgical debulking, pharmacological control of hormone-mediated symptoms, targeted methods such as external irradiation, and systemic antineoplastic therapy. Different agents and protocols for this purpose are reviewed, and their therapeutic potential is discussed.

EVIDENCE ACQUISITION

Literature on antineoplastic therapies for malignant pheochromocytoma was identified by searching the PubMed database with restriction to articles published in English during the past 30 yr.

EVIDENCE SYNTHESIS

Because of the rarity of the condition, no randomized clinical trials concerning the treatment of malignant pheochromocytoma have been performed. The strategy established best is [131I]meta-iodobenzylguanidine (MIBG) therapy, which is well tolerated. Similar to cytotoxic chemotherapy with cyclophosphamide, vincristine, and dacarbazine, MIBG can induce remission for a limited period in a significant proportion of patients. Octreotide as a single agent seems to be largely ineffective.

CONCLUSIONS

MIBG radiotherapy and cyclophosphamide, vincristine, and dacarbazine chemotherapy are comparable with respect to response rate and toxicity. It is unclear whether combining both can improve the outcome. Future developments may include new multimodal concepts with focus on inhibition of angiogenetic factors and heat shock protein 90. Any present or new therapeutic approach must take into account the highly variable natural course of the disease.

Immunohistochemical distribution of the secretogranin II-derived peptide EM66 in the rat hypothalamus: A comparative study with jerboa

EM66 is a 66-amino acid peptide derived from secretogranin II, a member of granin acidic secretory protein family, by proteolytic processing. EM66 has been previously characterized in the jerboa (Jaculus orientalis) hypothalamus and its potential implication in the neuroendocrine regulation of feeding behaviour has been demonstrated. In the present study, an immunohistochemical analysis of the localization of EM66 within hypothalamic structures of rat was performed and compared to the distribution of EM66 in the jerboa hypothalamus. In the rat hypothalamus, as in the jerboa, EM66 immunostaining was detected in the parvocellular paraventricular, preoptic and arcuate nuclei, as well as the lateral hypothalamus which displayed an important density of EM66-producing neurones. However, unlike jerboa, the suprachiasmatic and supraoptic nuclei of the rat hypothalamus were devoid of cellular EM66-immunolabeling. Thus, the novel peptide EM66 may exert common neuroendocrine activities in rat and jerboa, e.g. control of food intake, and species-specific roles in jerboa such as the regulation of biological rhythms and hydromineral homeostasis. These results suggest the existence of differences between jerboas and rats in neuroendocrine regulatory mechanisms involving EM66.

Malignant pheochromocytoma: state of the field with future projections

The prevalence of malignant pheochromocytoma is about 10%, and is somewhat higher for paraganglioma. A problem for clinical follow-up is that patients with "benign" histopathologic findings may develop metastatic disease. At the first international symposium on pheochromocytoma in Bethesda (2005) experts from different disciplines and patients shared their experiences, and the present knowledge of this rare disease was updated. The discussion related to future strategies for better clinical/histopathologic diagnosis and understanding of different geno- and phenotypes. Curative surgery can only seldom be performed because of multiple metastases. The main therapeutic goal is therefore often tumor reduction and control of hypertension. To date the best adjunct to surgery is radionuclide therapy using 131I-MIBG, but the background information for optimal treatment is still incomplete. Certain patients may benefit from 131I-MIBG combined with radiotherapy via somatostatin receptors expressed by the tumor, or the combination with chemotherapy. The need for future multicenter studies was emphasized. In experimental models the work on enhanced expression of amine transporters critical for radiotherapy is continued. Ongoing microarray studies will reveal novel intracellular pathways of importance for proliferation/cell cycle control, which can be inhibited by pharmacologic tools.

Development of novel tools for the diagnosis and prognosis of pheochromocytoma using peptide marker immunoassay and gene expression profiling approaches

Pheochromocytomas (PHEOs) are rare catecholamine-producing neoplasias that arise from chromaffin cells of the adrenal medulla or from extra-adrenal locations. These neuroendocrine tumors are usually benign, but may also present as or develop into a malignancy. There are currently no means to predict or to cure malignant tumors which have a poor prognosis. We have recently validated several assays for the measurement of peptides derived from chromogranin A (CgA) and secretogranin II (SgII) in order to determine whether these secreted neuroendocrine products could provide useful, complementary markers for the diagnosis and prognosis of PHEOs. Both the CgA-derived peptide WE14 and the SgII-derived peptide EM66 proved to be sensitive circulating markers for the diagnosis of PHEO. In addition, much higher EM66 levels were measured in benign than in malignant tumoral tissues, suggesting that this peptide could represent a valuable tool for the prognosis of PHEO. We have also initiated a comparative microarray study of benign and malignant PHEOs, which allowed the identification of a set of about 100 genes that were differentially expressed and best discriminated the two types of tumors. A large majority of these genes were expressed at lower levels in the malignant disease and were associated with various characteristics of chromaffin cells, such as hormone secretion signaling and machinery, peptide maturation, and cellular morphology. Altogether, these studies provide novel tools for the management of PHEO, and new insights for the understanding of tumorigenesis in chromaffin cells, which may offer potential therapeutic strategies.

Expression and processing of the neuroendocrine protein secretogranin II in benign and malignant pheochromocytomas

The aim of the present study was to compare the expression levels of secretogranin II (SgII), prohormone convertases (PC)1 and PC2, and the proteolytic processing of SgII in benign versus malignant pheochromocytomas. Quantitative (Q)-PCR experiments indicated that SgII, PC1, and PC2 mRNAs were overexpressed in pheochromocytoma compared to non-tumoral chromaffin cells (P<0.001) and in benign compared to malignant tumors (P<0.01). Western blot analysis using a human SgII antiserum revealed the occurrence of a 97-kDa band corresponding to the expected size of SgII, with significantly higher quantities in benign than in malignant tumors (P<0.05). Using antisera directed against sequential regions of SgII (N-terminal, secretoneurin [SN], EM66, internal, and C-terminal sequences), we observed distinct processing profiles between benign and malignant pheochromocytomas. In contrast, using PC1 and PC2 antisera no differences between the two types of tumors were found. RIA measurement showed that EM66 median values between benign and malignant chromaffin cell tumors were significantly different (128.5 vs. 6.3 ng/mg protein, respectively; P<0.001). Taken together, these results indicate that, in pheochromocytoma, malignancy is associated with reduced PC1, PC2, and SgII mRNA expression and decreased levels of processing products of SgII, in line with the low concentrations of EM66 that occur in malignant tumors. These data support the notion that SgII-processing products, such as EM66, could represent prognostic markers of pheochromocytomas.

Involvement of multiple signaling pathways in PACAP-induced EM66 secretion from chromaffin cells

Secretoneurin (SN) and EM66 are two highly conserved peptides that derive from the processing of secretogranin II (SgII), one of the major constituents of chromaffin cell secretory vesicles. It has been shown that PACAP regulates SgII gene transcription and SN release in bovine adrenochromaffin cells. The aim of the present study was to localize and characterize EM66 in the bovine adrenal gland, and to examine the signaling pathways activated by PACAP to regulate the secretion of EM66 from cultured chromaffin cells. Double immunohistochemical labeling showed an intense EM66-immunoreactive (EM66-IR) signal in TH-positive medullary chromaffin cells of the adrenal gland. HPLC analysis combined with RIA detection revealed, in adrenal medulla extracts and cultured chromaffin cell media, the presence of a major EM66-IR peak co-eluting with the recombinant peptide. PACAP dose-dependently stimulated EM66 release from chromaffin cells (ED(50)=4.8 nM). The effect of PACAP on EM66 secretion was observed after 6 h of treatment and increased to reach a 2.6-fold stimulation at 48 h. The nonselective calcium channel blocker NiCl(2), the cytosolic calcium chelator BAPTA-AM and the L-type calcium channel blocker nimodipine significantly inhibited the stimulatory effect of PACAP on EM66 release. The secretory response to PACAP was also significantly lowered by the protein kinase A inhibitor H89 and by the protein kinase C inhibitor chelerythrine. Concomitant administration of chelerythrine, H89, NiCl(2) and BAPTA totally abolished PACAP-stimulated EM66 secretion. The MAPK inhibitors U0126 and SB203580 respectively decreased by 63% and 72% PACAP-evoked EM66 release. These results indicate that, in bovine adrenal medulla, SgII is processed to generate the EM66 peptide and that PACAP activates multiple signaling pathways to regulate EM66 release from chromaffin cells, suggesting that EM66 may act downstream of the trans-synaptic stimulation of the adrenal medulla by neurocrine factors.

Circulating EM66 is a highly sensitive marker for the diagnosis and follow-up of pheochromocytoma

We have previously demonstrated that measurement of tissue concentration of the novel secretogranin II-derived peptide EM66 may help to discriminate between benign and malignant pheochromocytomas. The aim of the present study was to characterize EM66 in plasma and urine of healthy volunteers and pheochromocytoma patients, in order to further evaluate the usefulness of this peptide as a circulating marker for the management of the tumors. HPLC analysis of plasma and urine samples demonstrated that the EM66-immunoreactive material coeluted with the recombinant peptide. In healthy volunteers, plasma and urinary EM66 levels were, respectively, 2.6 (1.9-3.7) ng/ml and 2.9 (1.9-4.6) ng/ml. In patients with pheochromocytoma, plasma EM66 levels were 10-fold higher than those of healthy volunteers (26.9 (7.3-44) ng/ml), and returned to normal values after removal of the tumor. In contrast, urinary EM66 levels were not significantly different from those of healthy volunteers (3.2 (2.2-3.9) ng/ml). Measurement of total or free plasma metanephrines and 24 hr urinary metanephrines in our series of patients revealed that these tests, taken separately, are less sensitive than the EM66 determination. Pheochromocytes in primary culture secreted high levels of EM66, suggesting that the chromaffin tumor was actually responsible for the increased plasma peptide concentrations in the patients. These data indicate that EM66 is secreted in the general circulation and that elevated plasma EM66 levels are correlated with the occurrence of pheochromocytoma. Thus, EM66 is a sensitive plasma marker that should be considered as a complementary tool in the management of pheochromocytoma.

Melanotrope cells as a model to understand the (patho)physiological regulation of hormone secretion

Regulation of hormone secretion is a complex process that comprises the sequential participation of numerous subcellular mechanisms. Hormone secretion is dictated by extracellular stimuli that are transduced intracellularly into activation/deactivation of different mechanisms, such as hormone expression, processing and exocytosis, which will ultimately determine the precise availability of hormone to be secreted. Malfunction in any of these steps may result in deficient or excessive hormone release and the subsequent appearance of endocrine disorders. Given the complexity of this system, it is difficult to find appropriate cellular models wherein to investigate the multiple components of the secretory process in a physiologically relevant, experimentally manipulable setting. In this review, we present recent evidence on the use of the intermediate lobe (IL) of the pituitary as a powerful tool to understand different aspects of the regulated secretory pathway. IL is composed of a single endocrine cell type, alpha-melanocyte stimulating hormone (alpha-MSH)-producing melanotropes, a fact that greatly facilitates its study. Furthermore, melanotropes can be separated using classic cell separation techniques into two cell subtypes showing opposite morphophysiological phenotypes of hypo- and hypersecretory cells. Comparison of their gene expression fingerprints has unveiled the existence of certain genes preferentially expressed in each melanotrope subtype. Because of their direct participation in the secretory pathway, we postulate that characterization of these gene products in an endocrine cell type may represent novel and useful markers for reliably determining the general secretory status in an endocrine gland, as well as a valuable new tool to further investigate this complex process.

Biochemical characterisation and immunohistochemical localisation of the secretogranin II-derived peptide EM66 in the hypothalamus of the jerboa (Jaculus orientalis): modulation by food deprivation

The neuroendocrine protein secretogranin II is the precursor of several neuropeptides, including secretoneurin and a novel 66-amino acid peptide, EM66, the sequence of which has been highly conserved across the vertebrae phylum. The presence of EM66 has been detected in the adult and fetal human adrenal gland, as well as the rat pituitary and adrenal glands. The present study aimed to explore a possible neuroendocrine role of EM66 by analysing its occurrence and distribution within the jerboa hypothalamus, and its potential implication in the control of feeding behaviour. High-performance liquid chromatography analysis of jerboa hypothalamic extracts combined with a radioimmunoassay of EM66 revealed a single peak of immunoreactive material exhibiting the same retention time as recombinant EM66. Immunocytochemical labelling showed that EM66-producing neurones are widely distributed in several hypothalamic regions, including the preoptic area, the suprachiasmatic, supraoptic, parvocellular paraventricular and arcuate nuclei, and the lateral hypothalamus. Food deprivation for 5 days induced a significant increase in the number of EM66-containing neurones within the arcuate nucleus (105% increase) and the parvocellular aspect of the paraventricular nucleus (115% increase), suggesting that EM66 could be involved in the control of feeding behaviour and/or the response to stress associated with fasting. Altogether, these data reveal the physiological plasticity of the EM66 system in the hypothalamus and implicate this novel peptide in the regulation of neuroendocrine functions.

Pheochromocytoma and functional paraganglioma

PURPOSE

Pheochromocytomas and paragangliomas are rare tumors of chromaffin cell origin. Their identification is likely increasing owing to the increased use of radiographic images detecting incidental adrenal masses.

RECENT FINDINGS

The pathophysiology of hypertension induced by the release of catecholamines and newly discovered peptides has been shown to be more complex than the concept of episodic catecholamine release.

SUMMARY

This review looks at the most recent advances in the physiology and molecular basis of these tumors.