Molecular basis of neuroendocrine cell type-specific expression of the chromogranin B gene: Crucial role of the transcription factors CREB, AP-2, Egr-1 and Sp1

The molecular basis of neuroendocrine-specific expression of chromogranin B gene (Chgb) has remained elusive. Utilizing wild-type and mutant Chgb promoter/luciferase reporter constructs, this study established a crucial role for the cAMP response element (CRE) box at -102/-95 bp in endocrine [rat pheochromocytoma (chromaffin) cell line (PC12) and rat pituitary somatotrope cell line (GC)] and neuronal [rat dorsal root ganglion/mouse neuroblastoma hybrid cell line (F-11), cortical and hippocampal primary neurons] cells. Additionally, G/C-rich domains at -134/-127, -125/-117 and -115/-110 bp played especially important roles for endocrine-specific expression of the Chgb gene. Co-transfection of expression plasmids for CREB, activator protein-2 (transcription factor) (AP-2), early growth response protein (transcription factor) (Egr-1) or specificity protein 1 (transcription factor) (Sp1) with the Chgb promoter constructs trans-activated expression of the Chgb gene. Nuclear extracts from either PC12 or F-11 cells formed specific complexes with the Chgb (-110/-87 bp) (CRE) oligonucleotide, which were either supershifted or disrupted by anti-CREB antibodies. In addition PC12 nuclear extracts also formed a specific complex with a Chgb (-140/-104-bp) oligonucleotide containing three G/C-rich regions, which was dose-dependently disrupted by anti-AP-2, anti-Egr-1 or anti-Sp1 antibodies; indeed, any one of these three antibodies completely abolished the complex, suggesting that all three factors bind the region simultaneously, at least in vitro. Chromatin immunoprecipitation assays documented the binding of the transcription factors CREB, AP-2, Egr-1 and Sp1 to the chromosomal Chgb gene promoter in vivo in PC12 cells within the context of chromatin. We conclude that the neuroendocrine-specific expression of Chgb is mediated by the CRE and G/C boxes in cis and the transcription factors CREB, AP-2, Egr-1 and Sp1 in trans.

First localization and biochemical identification of chromogranin B- and secretoneurin-like immunoreactivity in the fetal human vagal/nucleus solitary complex

The human vagal/nucleus solitary complex is a primary visceral relay station and an integrative brain stem area which displays a high density of chromogranin B- and secretoneurin-like immunoreactivity. In this study, we localized and biochemically identified these proteins during prenatal development. At prenatal week 11, 15, 20 and 37, we performed a chromatographic analysis to identify the molecular forms of PE-11, a peptide within the chromogranin B sequence, and secretoneurin, a peptide within secretogranin II. Their localization was studied with immunocytochemistry, and was compared to that of substance P which is well established as a functional neuropeptide in the vagal/nucleus solitary complex. At prenatal week 11, chromogranin B-, secretoneurin- and substance P-like immunoreactivities were detected consisting of varicosities, varicose fibers and single cells. At the same time, PE-11 and secretoneurin appeared as a single peak in chromatographic analysis. Prohormone convertases PC1- and PC2-like immunoreactivities were also present at week 11. In general, the density for each peptide increased during later fetal stages with the highest density at week 37. These results demonstrate that each chromogranin peptide is expressed during human fetal life in neurons of the vagal/nucleus solitary complex indicating that these peptides could be important during prenatal development.

Role of nuclear chromogranin B in inositol 1,4,5-trisphosphate-mediated nuclear Ca2+ mobilization

Recently, secretory granule Ca(2+) storage protein chromogranin B (CGB) was shown to be present in the nucleoplasm proper in a complex structure that consists of the inositol 1,4,5-trisphosphate receptor (IP(3)R)/Ca(2+) channels and the phospholipids. Further, the amounts of IP(3)Rs present in the nucleus of bovine chromaffin cells were shown to be comparable to that of the endoplasmic reticulum. Therefore, we investigated here the potential contribution of nuclear CGB on the IP(3)-dependent Ca(2+) mobilization in the nucleus, using both neuroendocrine PC12 and nonneuroendocrine NIH3T3 cells. Chromogranin A (CGA) expression in the NIH3T3 cells, which do not contain intrinsic chromogranins, increased the IP(3)-induced Ca(2+) releases in the nucleus by 45%, while CGB expression in the same cells increased the IP(3)-induced Ca(2+) releases in the nucleus by 80%. Microinjection of IP(3) into the nucleus of CGB-expressing NIH3T3 cells increased the IP(3)-dependent nuclear Ca(2+) mobilization approximately 3-fold, whereas in CGA-expressing cells it remained the same as that of control cells. In contrast, inhibition of CGA expression in PC12 cells by siRNA treatment decreased the IP(3)-induced Ca(2+) releases in the nucleus by 17%, while inhibition of CGB expression decreased the IP(3)-induced Ca(2+) releases in the nucleus by 55%. Microinjection of IP(3) into the nucleus of siCGB-treated PC12 cells decreased the IP(3)-dependent nuclear Ca(2+) mobilization by approximately 75%, whereas in siCGA-treated cells it remained the same as that of control cells. Given the presence of CGB in the nucleus, these results further highlight the critical contribution of nuclear CGB in the IP(3)-induced Ca(2+) release in the nucleus.

A panel of 13 region-specific radioimmunoassays for measurements of human chromogranin B

INTRODUCTION

The primary structure of human chromogranin B (CgB) contains 15 pairs of basic amino acids, which are potential cleavage sites for specific endogenous proteases, but also other sites in the molecule can be subjected to cleavage. Several CgB-related peptides have been identified in tissue extracts.

MATERIALS AND METHODS

Peptides homologous to defined parts of the human CgB molecule were selected and synthesized. Antibodies were raised and 13 specific radioimmunoassays were developed. Plasma samples from 19 patients with neuroendocrine tumors were collected and measured in all assays.

RESULTS

All region-specific assays measured circulating levels of CgB-related peptides. Only five of the assays measured high concentrations of circulating CgB and two of them correlated with that of intact chromogranin A (CgA).

CONCLUSION

The assays presented allow measurements of defined regions of CgB and will thus become important tools for further studies of the processing of CgB. One of the assays merit further investigations as a new marker for neuroendocrine tumors.

Association between chromogranin b gene polymorphisms and schizophrenia in the Japanese population

BACKGROUND

We found in previous work a significant association between schizophrenia and D20S95 on chromosome 20p12.3. In this study, we analyzed 10 microsatellite markers and found an association of schizophrenia with D20S882 and D20S905 that flank D20S95. The chromogranin B gene (CHGB) is 30 kb from D20S905. The chromogranin B (secretogranin I) belongs to a series of acidic secretory proteins that are widely expressed in endocrine and neuronal cells, and its cerebrospinal fluid levels have been reported to decrease in patients with chronic schizophrenia.

METHODS

We screened for polymorphisms in CHGB with polymerase chain reaction direct sequencing methods in 24 Japanese schizophrenic patients and identified a total of 22 polymorphisms. Allelic and genotypic distributions of detected polymorphisms were compared between unrelated Japanese schizophrenic patients (n = 192) and healthy control subjects (n = 192).

RESULTS

Statistically significant differences in the allelic distributions were found between schizophrenic patients and control subjects for 1058C/G (A353G) (corrected p = 7.7 x 10(-5)) and 1104A/G (E368E) (corrected p = 8.1 x 10(-6)). The 1058C/G and 1104A/G alleles were in almost complete linkage disequilibrium and were in linkage disequilibrium with D20S95.

CONCLUSIONS

Results suggest that the CHGB variations are involved in the susceptibility to schizophrenia in our study population.

Genome-wide linkage analysis of chromogranin B expression in the CEPH pedigrees: implications for exocytotic sympathochromaffin secretion in humans

Chromogranin B (CgB), a major member of the chromogranin/secretogranin family of catecholamine storage vesicle secretory proteins, plays both intracellular (vesiculogenic) and extracellular (prohormone) roles in the neuroendocrine system, and its biosynthesis and release are under the control of efferent sympathetic nerve traffic ("stimulus-transcription coupling"). To explore the role of heredity in control of CgB, we conducted a genome-wide linkage analysis of CgB release in 12 extended CEPH (Centre d'Etude du Polymorphisme Humain) pedigrees. Region-specific radioimmunoassays were used to measure five CgB fragments in plasma: CgB1-16, CgB312-331, CgB439-451, CgB568-577, and CgB647-657. Substantial heritability, as measured by h2r, was observed for three of the fragment concentrations, CgB312-331, CgB439-451, and CgB568-577, which yielded h2r estimates ranging from 0.378 (P = 0.002) to 0.910 (P < 0.0000001). Variance-component genome-wide linkage analysis with 654 microsatellite markers at 5 cM spacing identified a major quantitative trait locus for CgB312-331 on chromosome 11q24-q25 with a maximum multipoint LOD score of 5.84. Significant allelic associations between markers in the region and CgB levels were also observed. Although the 2-LOD confidence interval for linkage did not include the CgB locus itself, known trans-activators of the CgB gene promoter, or prohormone cleaving proteases, examination of positional candidate loci within this region yielded novel and plausible physiological candidates for further exploration. Allelic variation in this region may thus influence effects of sympathetic outflow on target organs in humans.

A Functional Interaction between Chromogranin B and the Inositol 1,4,5-Trisphosphate Receptor/Ca2+ Channel

Chromogranins A and B (CGA and CGB) are high capacity, low affinity calcium (Ca2+) storage proteins found in many cell types most often associated with secretory granules of secretory cells but also with the endoplasmic reticulum (ER) lumen of these cells. Both CGA and CGB associate with inositol 1,4,5-trisphosphate receptor (InsP3R) in a pH-dependent manner. At an intraluminal pH of 5.5, as found in secretory vesicles, both CGA and CGB bind to the InsP3R. When the intraluminal pH is 7.5, as found in the ER, CGA totally dissociates from InsP3R, whereas CGB only partially dissociates. To investigate the functional consequences of the interaction between the InsP3R and CGB monomers or CGA/CGB heteromers, purified mouse InsP3R type I were fused to planar lipid bilayers and activated by 2 microM InsP3. In the presence of luminal CGB monomers or CGA/CGB heteromers the InsP3R/Ca2+ channel open probability and mean open time increased significantly. The channel activity remained elevated when the pH was changed to 7.5, a reflection of CGB binding to the InsP3R even at pH 7.5. These results suggest that CGB may play an important modulatory role in the control of Ca2+ release from the ER. Furthermore, the difference in the ability of CGA and CGB to regulate the InsP3R/Ca2+ channel and the variability of CGA/CGB ratios could influence the pattern of InsP3-mediated Ca2+ release.

Chromogranin B-induced secretory granule biogenesis: comparison with the similar role of chromogranin A

The two major proteins of secretory granules of secretory cells, chromogranins A (CGA) and B (CGB), have previously been proposed to play key roles in secretory granule biogenesis. Recently, CGA was reported to play an on/off switch role for secretory granule biogenesis. In the present study we found CGB being more effective than CGA in inducing secretory granule formation in non-neuroendocrine NIH3T3 and COS-7 cells. The mean number of dense core granules formed/cell of CGA-transfected NIH3T3 cells was 2.51, whereas that of CGB-transfected cells was 4.02, indicating the formation of 60% more granules in the CGB-transfected cells. Similarly, there were 55% more dense core granules formed in the CGB-transfected COS-7 cells than in the CGA-transfected cells. Moreover, transfection of CGA- and CGB-short interfering RNA (siRNA) into neuroendocrine PC12 cells not only decreased the amount of CGA and CGB expressed but also reduced the number of secretory granules by 41 and 78%, respectively, further suggesting the importance of CGB expression in secretory granule formation.

Differential effects of phencyclidine application on secretogranin II expression in organotypic slices of rat prefrontal cortex

Phencyclidine (PCP) is a non-competitive NMDA glutamate receptor antagonist that induces psychotomimetic effects in humans and experimental animals. Chronic PCP exposure elicits signs of persistently altered frontal brain activity and related behaviors which are also seen in patients with schizophrenia. Secretogranin II (sg II) belongs to the chromogranin family of proteins that exist in large dense core vesicles in nervous tissue. In the brain, 90% of sg II is processed to the small peptide secretoneurin. We previously detected differential effects of single-dose and subchronic PCP administration on sg II expression in the rat prefrontal cortex (PFC). In the present study, we applied PCP to organotypic PFC slices. PCP application for 28 h induced decreased tissue and culture medium secretoneurin content. In contrast, incubation with the adenylate cyclase activator forskolin caused significantly increased secretoneurin levels after 8 h. PCP for 4 h followed by 24 h without PCP resulted in increased culture medium secretoneurin content but no change in tissue levels. sg II mRNA expression was decreased after 28 h PCP application in cortical neurons. Immunohistochemical and TUNEL staining profiles indicated that the alterations were not due to neurodegeneration. PCP for 5 days changed neither the secretoneurin tissue or culture medium levels, nor the sg II mRNA expression. These results demonstrate that PCP modulates sg II expression in PFC tissue in the absence of afferent inputs and that the nature of these changes is dependent upon the duration of exposure to and/or withdrawal from PCP.

Cellular expression and specific intragranular localization of chromogranin A, chromogranin B, and synaptophysin during ontogeny of pancreatic islet cells: an ultrastructural study

INTRODUCTION AND AIMS

To get more insight into the differentiation patterns of pancreatic islet neuroendocrine cells and granules during ontogeny, the expression and localization of chromogranin A (CgA), chromogranin B (CgB), synaptophysin, and insulin were ultrastructurally studied with the immunogold technique in porcine and human pancreatic islet neuroendocrine cells.

METHODOLOGY AND RESULTS

In porcine pancreas at early fetal stage, CgA was visualized throughout the immature granules in all neuroendocrine cells. Later, CgB also was expressed with the same pattern in most granules in all types of cells. In neonatal islets, CgA was localized in the periphery of immature alpha- and beta-cell granules and throughout the matrix of delta-cell granules; CgB was distributed throughout the matrix of these granules. In adult islets, alpha-cell granules stored CgA in the halo and CgB in both the core and the halo, beta-cell granules stored both CgA and CgB in their cores, and in delta-cell granules, both substances were mixed throughout the matrix. In all ontogenetic stages, synaptophysin was demonstrated in all cell types and granules. Insulin was expressed in early fetal cells of both pigs and humans, and colocalization with CgA, CgB, and synaptophysin was demonstrated.

CONCLUSION

The early expression of CgA and synaptophysin may reflect a role at early fetal stages, and the individual localization of CgA and CgB upon differentiation indicates individual functions.

Reduction of chromogranin B-like immunoreactivity in distinct subregions of the hippocampus from individuals with schizophrenia

Synaptic disturbances may play a key role in the pathophysiology of schizophrenia. This study was designed to further investigate possible synaptic alterations in the brains of chronic schizophrenic patients. Chromogranin B was applied as a marker for large dense core vesicles and synapsin I as a protein associated with the synaptic vesicle membrane. The distribution and density of chromogranin B-and synapsin I-like immunoreactivity in subregions of the hippocampus was compared between controls (n = 16) and patients with schizophrenia (n = 17). The overall distribution of hippocampal chromogranin B- and synapsin I-like immunoreactivity was similar in controls and in schizophrenic patients with the highest densities in the terminal field of mossy fibers and in the inner molecular layer of the dentate gyrus. In schizophrenic hippocampi, a significant reduction in the density of chromogranin B-like immunoreactivity was found in the CA4 and CA3 but not in the CA1 area of the dentate gyrus based on computerized image analysis. The loss of immunoreactivity was localized to mossy fibers and terminals surrounding hilar interneurons. Double-labelling immunohistochemistry revealed that synapsin I was co-expressed with chromogranin B in these neuronal structures and was also significantly reduced in schizophrenic hippocampi. The present study demonstrates an area-specific reduction of chromogranin B which is paralleled by a decrease of synapsin I. The loss of presynaptic proteins involved in distinct steps of exocytosis may cause complex synaptic disturbances in specific hippocampal subregions resulting in an imbalanced neurotransmitter availability in schizophrenic patients.

Region-specific antibodies to chromogranin B display various immunostaining patterns in human endocrine pancreas

Chromogranin (Cg) B is an acidic glycoprotein present in neuroendocrine tissue. The sequence shows several dibasic amino acid positions susceptible to proteolytic cleavage. The purpose of this study was to elucidate the expression of CgB epitopes in the human endocrine pancreas. Tissue sections of six human pancreata were immunostained with 16 different region-specific antibodies to the CgB molecule, using double immunofluorescence techniques. The CgB epitope pattern varied in the four major islet cell types. B (insulin)-cells expressed immunoreactivity to all region-specific antibodies. The antibodies to the N-terminal and mid-portions of CgB showed moderate immunoreactivity, the C-terminal antibodies weak. A (glucagon)-cells were reactive only to the N-terminal and mid-portion antibodies but, after microwave pretreatment, to all antibodies, whereas D (somatostatin)-cells expressed only the sequence CgB 244-255 and a subpopulation CgB 580-595. PP (pancreatic polypeptide) cells were immunostained with antibodies between CgB 1-417 and a few with CgB 580-593. The fragment CgB 244-255 was expressed in all four cell types. The cause of these differences may be cell-specific cleavage or masking of the molecule, but varying translation of CgB mRNA is also possible. The extent to which these epitopes reflect fragments having biological functions remains to be evaluated.

Presence of chromogranin-derived antimicrobial peptides in plasma during coronary artery bypass surgery and evidence of an immune origin of these peptides

Chromogranin A (CGA) and chromogranin B (CGB) are acidic proteins stored in secretory organelles of endocrine cells and neurons. In addition to their roles as helper proteins in the packaging of peptides, they may serve as prohormones to generate biologically active peptides such as vasostatin-1 and secretolytin. These molecules derived from CGA and CGB, respectively, possess antimicrobial properties. The present study demonstrates that plasmatic levels of both vasostatin-1 and secretolytin increase during surgery in patients undergoing cardiopulmonary bypass (CPB). Vasostatin-1 and secretolytin, initially present in plasma at low levels, are released just after skin incision. Consequently, they can be added to enkelytin, an antibacterial peptide derived from proenkephalin A, for the panoply of components acting as a first protective barrier against hypothetical invasion of pathogens, which may occur during surgery. CGA and CGB, more commonly viewed as markers for endocrine and neuronal cells, were also found to have an immune origin. RNA messengers coding for CGB were amplified by reverse transcription-polymerase chain reaction in human monocytes, and immunocytochemical analysis by confocal microscopy revealed the presence of CGA or CGB or both in monocytes and neutrophils. A combination of techniques including confocal microscopic analysis, mass spectrometry measurement, and antibacterial tests allowed for the identification of the positive role of interleukin 6 (IL-6) in the secretolytin release from monocytes in vitro. Because IL-6 release is known to be strongly enhanced during CPB, we suggest a possible relationship between IL-6 and the increased level of secretolytin in patients undergoing CPB.

Presence and release of SR-17 (chromogranin B(586-602)) in the porcine splenic nerve and its enzymatic degradation by CD26/dipeptidyl peptidase IV

Using the pig splenic nerve as a model, we investigated the proteolytic processing of porcine chromogranin B (CgB) during its axonal transport. An ELISA was developed for SR-17 (CgB(586-602)), a novel CgB-derived peptide, originally found in the adrenal medulla. The results demonstrate that CgB is processed in an early stage during its axonal transport. Immunohistochemical data, based on a rabbit anti-SR-17 antiserum, show that the spleen CgB/SR-17 is exclusively present in the nerve endings. No SR-17 immunoreactivity (IR) was found in splenocytes. We also provide evidence that SR-17 is co-released with noradrenaline (NA) upon electrical stimulation of the splenic nerve. Its release is frequency-dependent and strongly enhanced in the presence of the alpha-blocking agent phentolamine. In addition, we show that the new CgB-peptide can serve as a substrate for the lymphocyte surface glycoprotein CD26, also known as dipeptidyl peptidase IV (DPP IV), generating a new peptide ER-15 (CgB(588-602)).

Cellular localization of a chromogranin B-like derived peptides in leeches

Using immunocytochemistry techniques, we demonstrated specific immunostaining with antibodies rose against fragment (547-560) and (614-626) of bovine chromogranin B (CGB) at the level of brain and the tegument of the leech Theromyzon tessulatum. The used of these antibodies on leech sections revealed immunopositive labeling in neurons and glial cells of the central nervous system (CNS), and epidermal glandular cells of the tegument. Co-localization between two antibodies rose against different fragment of bovine CGB have been demonstrated in neurons and glial cells of leech CNS like in vertebrates. Finally, the whole of the data showed for the first time the presence in leeches of CGB like derived peptides.

N-terminal chromogranin-derived peptides as dilators of bovine coronary resistance arteries

N-terminal peptides of chromogranin A and B (CGA and CGB) were compared for dilator responses in isolated bovine coronary arteries (bCoA), measuring diameter changes as a function of pressure. bCoA developed and maintained myogenic tone (MYT) at approximately 20% from 50 to 150 mm Hg. In contrast to CGB(1-40), CGA(1-40) and CGA(1-76) (VS-I) both displayed significant intrinsic vasodilator effects. CGA(1-40) reduced myogenic reactivity from 70 to 150 mm Hg (p<0.05, n=6). At 75 mm Hg, CGA(1-40) showed a concentration-dependent dilatation at 0.1 nM-10 microM. The dilator effect of CGA(1-40) persisted at moderately elevated [K(+)](e) (8.4-16 mM). However, this effect was diminished by pertussis toxin (PTX) and abolished by antagonists to several subtypes of K(+) channels (tetraethylammonium, Ba(2+) and glibenclamide). These results demonstrate that the N-terminal domain of CGA has dilator effect in the myogenically active bCoA. We propose that CGA(1-40) and the naturally occurring vasostatin I are regulatory peptides of relevance for the coronary microcirculation and that a G(alphai) sub-unit and K(+) channel activation may be involved in the signal pathway.

Polymorphisms of chromogranin B gene associated with schizophrenia in Chinese Han population

Chromogranin is a widespread family of proteins in the neurosystem, whose function is guiding the sorting and secretion of neuropeptides. Using functional and positional evidences, chromogranin B was selected as a candidate gene for schizophrenia. We systematically screened all the promoter and exon regions of the gene and detected 15 single nucleotide polymorphisms (SNPs), among which four SNPs (including two non-synonymous SNPs) were selected for association analysis. In a cohort of Chinese Han schizophrenia cases and controls, the results of both the individual SNPs and the haplotypes of SNPs were significantly positive (P<0.01). Our results confirm the role of neuropeptides in the pathogenesis of schizophrenia.

Potential role in transcription control

Chromogranins A (CGA) and B (CGB) are two major Ca(2+) storage proteins of the secretory granules of neuroendocrine cells. Nevertheless, we found in the present study that CGB was also localized in the nucleus. In immunogold electron microscopy using bovine adrenal medullary chromaffin cells, it was found that the number of CGB-labeled gold particles localized per microm(2) of the nucleus was equivalent to 20% that of CGB-labeled gold particles localized per microm(2) of the secretory granules. Considering that CGB is estimated to exist in the 0.1-0.2-mm range in the secretory granules of bovine chromaffin cells, 20% of these amounts to 20-40 microm. In addition, transfection of CGA and CGB into nonneuroendocrine COS-7 and NIH3T3 cells repeatedly indicated the nuclear localization of CGB in addition to its usual localization in the cytoplasm. Moreover, immunoblot and immunogold electron microscopy analyses of neuroendocrine PC12 cells also showed the existence of endogenous CGB in both the cytosol and the nucleus. Nuclear routing of CGB did not appear to depend entirely upon the nuclear localization signal as some of the nuclear localization signal mutant CGB were still targeted to the nucleus. In gene array assay, CGB was shown to either induce or suppress transcription of many genes including those of transcription factors. Of these we have analyzed eight genes, four induced (zinc finger protein, MEF2C, hCRP2, abLIM) and four suppressed (hcKrox, T3-receptor, troponin C, integrin) using the quantitative reverse transcription-PCR method and spectrophotometry to determine the transcription levels of each mRNA. CGB was shown to increase the transcription of zinc finger protein, MEF2C, hCRP2, and abLIM by 2.5-5-fold while suppressing that of hcKrox, T3-receptor, troponin C, and integrin by 60-75%. Given that MEF2C and hcKrox genes are transcription factors, these results pointed to the transcription control role of CGB in the nucleus.

Synaptic proteins in Alzheimer's disease

Chromogranin A, chromogranin B, and secretogranin II are acidic proteins which are stored in large dense core vesicles of neurons. An antiserum, raised against a synthetic peptide (PE-11), present in the chromogranin B molecule, and an antiserum raised against secretoneurin contained in the secretogranin II sequence, was used to localize these peptides together with chromogranin A in the human hippocampal formation. The distribution of these peptides was investigated in Alzheimer's disease and compared to control subjects. Chromogranin A, chromogranin B, and secretogranin II are distinctly distributed with an overlap in their distribution patterns. They were only detected in neuronal structures. The highest density of immunoreactivity was found for chromogranin B. A layer specific distribution was especially obvious in the inner molecular layer of the dentate gyrus as secretoneurin-like immunoreactivity was restricted to its innermost part whereas that of chromogranin B was highly concentrated throughout the inner molecular layer. In Alzheimer's disease, about 10 to 20% of the amyloid-immunoreactive plaques contained either chromogranin A, chromogranin B or secretoneurin. The density of secretoneurin-and chromogranin B-like immunoreactivity was significantly reduced in the inner molecular layer of the dentate gyyrs, the CA1 area, the subiculum and in layers I, III and V of the entorhinal cortex. The present study demonstrates that chromogranin peptides are markers for human hippocampal pathways. Thee are particularly suitable to study nerve fibers, terminating at the inner molecular layer of the dentate gyrus. Chromogranin peptides have a potential as neuronal markers for synaptic degeneration in Alzheimer's disease.

Molecular characterization of frog chromogranin B reveals conservation of selective sequences encoding potential novel regulatory peptides

Chromogranin B (CgB) is a member of the granin family of neuroendocrine secretory proteins, which has been proposed to play a role in secretory granule biogenesis and as a precursor to bioactive peptides. The cloning of CgB in a phylogenetically distant vertebrate, the frog Rana ridibunda, reveals a modest overall homology (35-40%) with mammalian CgB. However, the sequences of the N- and C-terminal regions are more highly conserved (57-65% amino acid identity) and may give rise to novel regulatory peptides. In frog, intense expression of CgB mRNA was observed in particular structures of the brain and in the distal lobe of the pituitary.

Chromogranin A and chromogranin B in noninvasive and invasive breast carcinoma

Recent progress in the study of chromogranins has revealed that there are many novel peptides derived from chromogranin with their multiple pathophysiologic roles. To learn the possible roles of chromogranin in breast carcinoma, we immunohistochemically investigated tissue localization of chromogranin A (CgA) and chromogranin B (CgB) in 10 normal breast tissues, 23 noninvasive ductal carcinomas (NIDCs), and 169 invasive ductal carcinomas (IDCs) and compared their expression with estrogen receptor (ER), progesterone receptor (PR), and Ki67. CgA and CgB were sporadically detected in normal cells of the ducts, acini, and luminal secretion. The expression of CgA and CgB was higher in NIDCs than in IDCs: CgA = 70% of NIDC vs 22% of IDC and CgB = 65% of NIDC vs 30% of IDC. There was a statistical correlation between the expression of CgA and PR (p < 0.05) and CgB and ER (p < 0.05) in IDCs without lymph node metastasis. On the other hand, there was a significant correlation between expression of CgB and PR and an inverse correlation between CgA and Ki67 in IDCs of overall cases. The data suggest that CgA and CgB may play some role in the early phase of neoplastic progression.

Evidence that the chromogranin B fragment 368-417 extracted from a pheochromocytoma is phosphorylated

A rabbit antiserum was raised against a synthetic peptide corresponding to residues 403 to 417 of human chromogranin B. This peptide was chosen to match the potential C-terminal end of a putative proteolytic fragment of the protein located between dibasic doublets in positions 366-367 and in positions 418-419 of the precursor. A radioimmunoassay based on this antiserum was developed and used to detect the protein or a fragment thereof in a pheochromocytoma tumor extract. One fragment was purified to homogeneity by successive reverse-phase HPLC chromatographies. The N-terminal sequence established by automated Edman degradation, was N-Y-P-S-L-E-L-D-K-M-A-H-G-Y-G-E-E-S-E-E-E-R corresponding to the 368-389 sequence of human chromogranin B. Taking into account the specificity of the antiserum used for peptide identification and alignment with the precursor sequence, we deduced that the purified peptide was chromogranin B (368-417) and represented a new peptide generated by limited proteolysis of chromogranin B. Combining electrospray mass-spectrometry and enzymatic dephosphorylation, we demonstrated that this peptide was phosphorylated.

Differential regulation of chromogranin A, chromogranin B and secretogranin II in rat brain by phencyclidine treatment

Chromogranin A, chromogranin B and secretogranin II belong to the chromogranin family which consists of large protein molecules that are found in large dense core vesicles. Chromogranins are endoproteolytically processed to smaller peptides. This study was designed to elucidate the regulation of chromgranin expression by acute and subchronic phencyclidine administration. The behavioral syndrome produced by phencyclidine represents a pharmacological model for some aspects of schizophrenia [Jentsch and Roth (1999) Neuropsychopharmacology 20, 201-225]. Tissue concentrations of chromogranins were measured with specific radioimmunoassays. Alterations in secretogranin II gene expression were investigated by in situ hybridization. A single dose of phencyclidine (10mg/kg) led to a transient decrease in secretoneurin tissue levels in the prefrontal cortex after 4h followed by an increase in secretoneurin tissue levels after 12h. Repeated phencyclidine treatment (10mg/kg/day) for five days resulted in elevated secretoneurin levels in cortical areas whereas chromogranin A and chromogranin B tissue levels were unchanged. After the same treatment, a significant increase in the number of secretoneurin containing neurons was found in cortical layers II-III, and V-VI as revealed by immunocytochemistry. The increases in secretoneurin levels were paralleled by an increased number of secretogranin II messenger RNA containing neurons as well as by an increased expression of secretogranin II by individual neurons. The present study shows that secretoneurin II tissue concentration and secretogranin II messenger RNA expression is distinctly altered after acute and subchronic phencyclidine application. From these results we suggest that phencyclidine may induce synaptic alterations in specific brain areas and may contribute to a better understanding of synaptic dysfunction which may also occur in schizophrenia.

Proteomic analysis of proteins in PC12 cells before and after treatment with nerve growth factor: increased levels of a 43-kDa chromogranin B-derived fragment during neuronal differentiation

Proteomic analysis is an important approach to characterizing the proteome and studying protein function in the post-genomic era. It is also a powerful screening method for detecting unexpected alterations in protein expression that may be missed by conventional biochemical techniques. The aim of this study was to perform a preliminary proteomic analysis of PC12 cells in order to investigate the effect of nerve growth factor (NGF) on protein expression in PC12 cells during neurite outgrowth. PC12 cell proteins were separated by two-dimensional electrophoresis (2DE) and visualized by silver staining, then certain proteins were identified by N-terminal amino acid microsequencing and a homology search of a protein sequence database. Over 400 proteins were detected, 10% of which showed a significant (greater than 30%) increase or decrease in expression during NGF-induced neuronal differentiation. Seven proteins in the 2DE map were identified; the levels of five of these were unaffected by NGF treatment, whereas the levels of the other two, beta-tubulin and a novel 43-kDa chromogranin B-derived fragment, were significantly increased by more than 30 and 200%, respectively. Our results suggest that chromogranin B processing is enhanced in PC12 cells during NGF-induced neuronal differentiation. In addition, since this increase in the levels of the chromogranin B-derived fragment was specifically blocked by PD98059, we suggest that the increased processing can be ascribed to activation of the MAP kinase pathway, and that the 43-kDa chromogranin B-derived fragment can serve as a new marker of neuronal differentiation for proteomic studies.

Identification and characterization of novel chromogranin B-derived peptides from porcine chromaffin granules by liquid chromatography/electrospray tandem MS

Chromogranin B (CgB) is a regulated secretory protein that is stored in endocrine and neuroendocrine cells. It can be processed proteolytically to small peptide fragments. In the present study three proteolytic products of porcine CgB were obtained after size-exclusion, immunoaffinity, and reversed-phase chromatography, and then identified by electrospray tandem MS. One novel peptide was identified as S586-R602 (SR-17) and is phosphorylated at one or two serine residues. Another novel peptide H603-Q636 (HQ-34), with molecular mass 3815.56 Da, was found to be oxidized at the methionine residue. In addition, a secretolytin-like peptide fragment (KR-11), which is two amino acids shorter than the bovine secretolytin, was found. This is the first report that the C-terminal region of CgB, the homologue of human CCB, is proteolytically processed further into three small peptide fragments.

Neuroendocrine cell type-specific and inducible expression of the chromogranin B gene: crucial role of the proximal promoter

Chromogranin B, a soluble acidic secretory protein, is widely distributed in neuroendocrine and neuronal cells, although not in other cell types. To identify the elements governing such widespread, yet selective, expression of the gene, we characterized the isolated mouse chromogranin B promoter. 5'-Promoter deletions localized neuroendocrine cell type-specific expression to the proximal chromogranin B promoter (from -216 to -91 bp); this region contains an E box (at [-206 bp]CACCTG[-201 bp]), four G/C-rich regions (at [-196 bp]CCCCGC[-191 bp], [-134 bp]CCGCCCGC[-127 bp], [-125 bp]GGCGCCGCC[-117 bp], and [-115 bp]CGGGGC[-110 bp]), and a cAMP response element (CRE; at [-102 bp]TGACGTCA[-95 bp]). A 60-bp core promoter region, defined by an internal deletion from - 134 to -74 bp upstream of the cap site and spanning the CRE and three G/C-rich regions, directed tissue-specific expression of the gene. The CRE motif directed cell type-specific expression of the chromogranin B gene in neurons, whereas three of the G/C-rich regions played a crucial role in neuroendocrine cells. Both the endogenous chromogranin B gene and the transfected chromogranin B promoter were induced by preganglionic secretory stimuli (pituitary adenylyl cyclase-activating polypeptide, vasoactive intestinal peptide, or a nicotinic cholinergic agonist), establishing stimulus-transcription coupling for this promoter. The adenylyl cyclase activator forskolin, nerve growth factor, and retinoic acid also activated the chromogranin B gene. Secretagogue-inducible expression of chromogranin B also mapped onto the proximal promoter; inducible expression was entirely lost upon internal deletion of the 60-bp core (from 134 to -74 bp). We conclude that CRE and G/C-rich domains are crucial determinants of both cell type-specific and secretagogue-inducible expression of the chromogranin B gene.

Distribution of chromogranin B-like immunoreactivity in the human hippocampus and its changes in Alzheimer's disease

Synapse loss is crucially involved in cognitive decline in Alzheimer's disease (AD). This study was performed to investigate the distribution and density of chromogranin B-like immunoreactivity in the hippocampus of control compared to AD brain. Chromogranin B is a large precursor molecule found in large dense-core vesicles. For immunocytochemistry we used an antiserum raised against a synthetic peptide (PE- 11) present in the chromogranin B molecule. Chromogranin B-like immunoreactivity was concentrated in the terminal field of mossy fibers, the inner molecular layer of the dentate gyrus and in layer II of the entorhinal cortex. In AD, chromogranin B was detected in neuritic plaques. The density of chromogranin B-like immunoreactivity was significantly reduced in the inner molecular layer of the dentate gyrus and in layers II, III and V of the entorhinal cortex in AD brains. The present study demonstrates that chromogranin B is a marker for human hippocampal pathways. It is particularly suitable for studying nerve fibers terminating at the inner molecular layer of the dentate gyrus. It is present in neuritic plaques, and its density is reduced in a layer-specific manner.

Characterisation of N-terminal chromogranin A and chromogranin B in mammals by region-specific radioimmunoassays and chromatographic separation methods

Chromogranin A (CgA) and chromogranin B (CgB) are acidic proteins stored in and released from hormone granules in endocrine and neuroendocrine tissue. The chromogranins are postulated to serve as pro-hormones to generate biologically active peptides, which may influence hormonal release and vascular functions or have antibacterial functions. Although N-terminal and C-terminal regions show some species amino acid homology, the chromogranins as a whole display considerable interspecies differences, which prevents their use in comparative studies of biological functions. We present four new radioimmunoassays for the measurement of defined N-terminal regions of CgA and CgB. A new radioimmunoassay for measurement of intact bovine CgA has also been developed. With these assays and two previously published ones, we have compared the cross-reactivity of chromogranins from man, cattle, sheep, goat, pig and horse and compared adrenomedullar content and serum levels of CgA from these species. We have also studied the influence of peptide concentrations and the ionic strength of the mobile phase on molecular weight estimations. Assays with antibodies directed against the N-terminal parts of CgA and CgB showed sufficient interspecies cross-reactivity to allow comparative quantification of the circulating levels in man, cattle, sheep, goat, pig and horse. Assays measuring the intact human or bovine CgA were not suitable for comparative purposes in samples from sheep, goat, pig and horse. Molecular interactions between vasostatin immunoreactive material and intact bovine CgA were demonstrated in gel permeation studies, suggesting that conclusions about the degree of N-terminal processing from elution profiles should be made with caution. Reliable interspecies comparison of chromogranins is difficult, but measurements with region-specific assays may be helpful to study concentrations of chromogranins and chromogranin-related peptides.

Chromogranin-B regulation of IAPP and insulin secretion

In the endocrine pancreas, chromogranin-A and pancreastatin have been suggested to inhibit islet insulin secretion, whereas chromogranin-B has not been studied in this context. Furthermore, a putative effect by chromogranins on IAPP secretion is unknown. We aimed to elucidate the endogenous effect of chromogranin-A, pancreastatin and chromogranin-B on islet insulin and IAPP secretion from pancreatic NMRI mouse islets. In acute experiments, there was a tendency towards an increase in insulin release, which became more manifest after a 48-h exposure. Moreover, 48 h exposure to chromogranin-B antiserum resulted in a significant increase in (pro)insulin synthesis. Neither antibodies against chromogranin-A nor pancreastatin had any effect on islet hormone secretion. None of the antibodies tested had any effect on islet IAPP or insulin content. We suggest that chromogranin-B released from islets may have an autocrine inhibitory effect on islet IAPP and insulin secretion. Our data imply a regulatory role of chromogranin-B in islet IAPP and insulin secretion.

Co-distribution patterns of chromogranin B-like immunoreactivity with chromogranin A and secretoneurin within the human brainstem

As members of the chromogranin family, chromogranin A, chromogranin B, and secretogranin II are acidic proteins found in large, dense core vesicles. They are endoproteolytically processed to smaller peptides and released after neuronal stimulation. Using immunocytochemistry, this study closely examines chromogranin B-like immunoreactivity within the human brainstem and then takes a comparative view of co-distribution patterns by chromogranin B, chromogranin A, and secretogranin II. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. Secretogranin II was localized with an antiserum against secretoneurin, a 33 amino acid peptide, found within the secretogranin II precursor. Like chromogranin A and secretoneurin, chromogranin B is expressed through all levels of the human brainstem. Chromogranin B was exclusively detected in neuronal structures. The medial part of the substantia nigra pars reticulata, the nucleus interpeduncularis, the area of the central gray, and the raphe complex displayed a high density of PE-11-like immunoreactivity. Furthermore, a prominent staining was found in the medial, dorsal and gelatinous subnuclei of the solitary tract and the dorsal motor nucleus of vagus. The substantia gelatinosa of the caudal trigeminal nucleus and spinal cord were also very strongly PE-11-immunopositive. In conclusion, chromogranin B and secretogranin II showed similar distributions while neuronal localization typically differed from chromogranin A aside from a few exceptions. These findings may provide a framework for future research in revealing a functional role of chromogranin peptides in the human brainstem.

PE-11, a peptide derived from chromogranin B, in the human brain

This study was performed to investigate the distribution of chromogranin B in the human central nervous system. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. PE-11-like immunoreactivity was characterized by molecular size exclusion and reversed-phase high-performance liquid chromatography. Its localization was studied using immunocytochemistry. Only the free peptide and an N-terminally elongated peptide were detected by molecular size exclusion high-performance liquid chromatography, indicating that proteolytic processing of chromogranin B is quite extensive. PE-11-like immunoreactivity was present in differently shaped fibers, varicosities and neurons, but not in glial cells. Its density varied throughout the brain. An especially high density was observed in the bed nucleus of the stria terminalis, the central and cortical nuclei of the amygdala, the hypothalamus, the hippocampus, the raphe complex, the nucleus interpeduncularis, the nucleus of the solitary tract, and laminae I and II of the spinal cord. This study demonstrates a significant processing of chromogranin B and indicates that chromogranin B constitutes a precursor for smaller peptides which are derived by endoproteolytic processing. It provides the neuroanatomical basis to investigate the chromogranin B molecule as a widespread component of large dense-core vesicles in the human central nervous system.

The disulfide-bonded loop of chromogranin B mediates membrane binding and directs sorting from the trans-Golgi network to secretory granules

The disulfide-bonded loop of chromogranin B (CgB), a regulated secretory protein with widespread distribution in neuroendocrine cells, is known to be essential for the sorting of CgB from the trans-Golgi network (TGN) to immature secretory granules. Here we show that this loop, when fused to the constitutively secreted protein alpha1-antitrypsin (AT), is sufficient to direct the fusion protein to secretory granules. Importantly, the sorting efficiency of the AT reporter protein bearing two loops (E2/3-AT-E2/3) is much higher compared with that of AT with a single disulfide-bonded loop. In contrast to endogenous CgB, E2/3-AT-E2/3 does not undergo Ca2+/pH-dependent aggregation in the TGN. Furthermore, the disulfide-bonded loop of CgB mediates membrane binding in the TGN and does so with 5-fold higher efficiency if two loops are present on the reporter protein. The latter finding supports the concept that under physiological conditions, aggregates of CgB are the sorted units of cargo which have multiple loops on their surface leading to high membrane binding and sorting efficiency of CgB in the TGN.

Chromogranin B (secretogranin I), a neuroendocrine-regulated secretory protein, is sorted to exocrine secretory granules in transgenic mice

Chromogranin B (CgB, secretogranin I) is a secretory granule matrix protein expressed in a wide variety of endocrine cells and neurons. Here we generated transgenic mice expressing CgB under the control of the human cytomegalovirus promoter. Northern and immunoblot analyses, in situ hybridization and immunocytochemistry revealed that the exocrine pancreas was the tissue with the highest level of ectopic CgB expression. Upon subcellular fractionation of the exocrine pancreas, the distribution of CgB in the various fractions was indistinguishable from that of amylase, an endogenous constituent of zymogen granules. Immunogold electron microscopy of pancreatic acinar cells showed co-localization of CgB with zymogens in Golgi cisternae, condensing vacuoles/immature granules and mature zymogen granules; the ratio of immunoreactivity of CgB to zymogens being highest in condensing vacuoles/immature granules. CgB isolated from zymogen granules of the pancreas of the transgenic mice aggregated in a mildly acidic (pH 5.5) milieu in vitro, suggesting that low pH-induced aggregation contributed to the observed concentration of CgB in condensing vacuoles. Our results show that a neuroendocrine-regulated secretory protein can be sorted to exocrine secretory granules in vivo, and imply that a key feature of CgB sorting in the trans-Golgi network of neuroendocrine cells, i.e. its aggregation-mediated concentration in the course of immature secretory granule formation, also occurs in exocrine cells although secretory protein sorting in these cells is thought to occur largely in the course of secretory granule maturation.

Essential role of the disulfide-bonded loop of chromogranin B for sorting to secretory granules is revealed by expression of a deletion mutant in the absence of endogenous granin synthesis

Sorting of regulated secretory proteins in the TGN to immature secretory granules (ISG) is thought to involve at least two steps: their selective aggregation and their interaction with membrane components destined to ISG. Here, we have investigated the sorting of chromogranin B (CgB), a member of the granin family present in the secretory granules of many endocrine cells and neurons. Specifically, we have studied the role of a candidate structural motif implicated in the sorting of CgB, the highly conserved NH2-terminal disulfide- bonded loop. Sorting to ISG of full-length human CgB and a deletion mutant of human CgB (Deltacys-hCgB) lacking the 22-amino acid residues comprising the disulfide-bonded loop was compared in the rat neuroendocrine cell line PC12. Upon transfection, i.e., with ongoing synthesis of endogenous granins, the sorting of the deletion mutant was only slightly impaired compared to full-length CgB. To investigate whether this sorting was due to coaggregation of the deletion mutant with endogenous granins, we expressed human CgB using recombinant vaccinia viruses, under conditions in which the synthesis of endogenous granins in the infected PC12 cells was shut off. In these conditions, Deltacys-hCgB, in contrast to full-length hCgB, was no longer sorted to ISG, but exited from the TGN in constitutive secretory vesicles. Coexpression of full-length hCgB together with Deltacys-hCgB by double infection, using the respective recombinant vaccinia viruses, rescued the sorting of the deletion mutant to ISG. In conclusion, our data show that (a) the disulfide-bonded loop is essential for sorting of CgB to ISG and (b) the lack of this structural motif can be compensated by coexpression of loop-bearing CgB. Furthermore, comparison of the two expression systems, transfection and vaccinia virus-mediated expression, reveals that analyses under conditions in which host cell secretory protein synthesis is blocked greatly facilitate the identification of sequence motifs required for sorting of regulated secretory proteins to secretory granules.

Proteolytic processing of chromogranin B and secretogranin II by prohormone convertases

Two experimental approaches were used to study the processing of chromogranin B and secretogranin II by prohormone convertases. In GH3 cells various prohormone convertases were overexpressed together with the substrate chromogranin B by use of a vaccinia virus infection system. PC1 appeared to be by far the most active enzyme and converted chromogranin B to several smaller molecules, including the peptide PE-11. In brain this peptide is cleaved physiologically from chromogranin B. Some processing of chromogranin B and formation of free PE-11 were also observed with PC2 and PACE4. Furin produced larger fragments, whereas PC5-A and PC5-B had negligible effects. As a second model, PC12 cells were stably transfected with PC1 or PC2 to investigate the processing of endogenous chromogranins. Both enzymes effectively cleaved chromogranin B and secretogranin II, liberating the peptides PE-11 and secretoneurin, respectively. However, in transfection experiments the ability to generate the free peptides was more pronounced with PC2 than with PC1. The extent of proprotein processing achieved by prohormone convertases apparently differed depending on the experimental system applied. This suggests that in vivo mechanisms to support and fine-tune the activity of the processing enzymes exist, which might be overlooked by using only one methodological approach.

Chromogranin A and chromogranin B are sensitive circulating markers for phaeochromocytoma

Specific assays for measurements of circulating chromogranin (Cg) A, CgB, CgC and pancreastatin (Ps) have recently been developed. The aim of the present study was to investigate the usefulness of these markers in diagnosing and following the effects of treatment of patients with phaeochromocytoma, and to compare the results with those concerning other biochemical markers. CgA was elevated in 19/21 (90%), CgB in 17/21 (81%), Ps in 9/21 (43%) and neuropeptide Y in 9/21 (43%) of the patients. Urinary noradrenaline was increased in 19/21 (90%) and urinary adrenaline in 17/19 (89%) of the patients. All patients had increased levels of either urinary catecholamines or plasma chromogranins. In one patient levels of CgA, CgB and Ps were measured at frequent intervals before, during and after surgery. The CgA level fell to normal shortly after the tumour was removed, whereas the CgB level decreased towards normal over the course of several days. Significant correlation was observed between the contents of CgA and CgB in the tumour tissue and the plasma levels of CgA and CgB respectively. We conclude that CgA and CgB are sensitive circulating markers for phaeochromocytoma and that measurements of both urinary catecholamines and plasma chromogranins improve the diagnostic sensitivity. Furthermore, measurements of CgA may be useful in assessing the radicality of surgery in the early postoperative period.

Rat brain: distribution of immunoreactivity of PE-11, a peptide derived from chromogranin B

An antiserum was raised against the peptide PE-11 whose sequence is present in the chromogranin B molecule. The antiserum reacts only with the free C-terminal end of this peptide. PE-11 immunoreactivity in brain was characterized by molecular size exclusion high performance liquid chromatography. Only the free peptide and a N-terminally elongated peptide were detected, indicating that proteolytic processing of chromagranin B in brain is quite extensive. In immunohistochemistry PE-11 immunoreactivity was found in varicosities, fibres and perikarya throughout the brain. Strong staining was detected in the shell sector of the nucleus accumbens, in the lateral septum, in subregions of the extended amygdala, in some areas of the hippocampus and of the hypothalamus, in the locus coeruleus, in the Purkinje cells of the cerebellum and in the dorsal horn of the spinal cord. Our results, which demonstrate significant processing of chromogranin B in brain and its widespread distribution, can be taken as an indication that chromogranin B represents a precursor of peptides with functional relevance for this organ.

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

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

Chromogranin B (secretogranin I) promotes sorting to the regulated secretory pathway of processing intermediates derived from a peptide hormone precursor

Chromogranin B (CgB, secretogranin I) is a widespread constituent of neuroendocrine secretory granules whose function is unknown. To determine whether CgB affects the sorting of peptide hormone and neuropeptide precursors to secretory granules, we overexpressed CgB in AtT-20 cells, which exhibit an only moderate capacity to sort proopiomelanocortin and proteolytic fragments derived therefrom. In mock-transfected AtT-20 cells, a substantial proportion of newly synthesized proopiomelanocortin and its two primary proteolytic products generated in the trans-Golgi network, the N-terminal 23-kDa fragment containing adrenocorticotropin and the C-terminal beta-lipotropin fragment, was secreted via the constitutive pathway. Two- to three-fold overexpression of CgB markedly reduced the constitutive secretion of the 23-kDa fragment, but not beta-lipotropin and tripled the amount of adrenocorticotropin generated and stored in secretory granules. Our results indicate the existence of neuroendocrine-specific helper proteins which promote the sorting from the trans-Golgi network to secretory granules of certain processing intermediates derived from peptide hormone and neuropeptide precursors and demonstrate that CgB functions as such.

Differential storage of prolactin, granins (Chromogranin B and secretogranin II), and constitutive secretory markers in rat pituitary GH4C1 cells

The rat pituitary cell line GH4C1 secretes granins (chromogranin B and secretogranin II) and prolactin by the regulated secretory pathway. The intracellular storage of prolactin is preferentially induced by hormone treatment with estradiol, insulin, and epidermal growth factor. The goal of this study was to determine the effect of hormone treatment on storage of granins and constitutive secretory markers. The granins were efficiently stored in both hormone-treated and -untreated cells (17% of total secreted in 4 h). Secreted alkaline phosphatase (SEAP), a truncated membrane protein that would not be expected to enter secretory granules, and glycosaminoglycan, a marker for the constitutive secretory pathway, exhibited 70 80% secretion under both conditions. In comparison, the relative prolactin secretion was 31 and 68% from hormone-treated and -untreated cells, respectively. Phorbol ester and KCl stimulated prolactin secretion 2.3-fold from untreated cells and 5. 5-fold from hormone-treated cells. In contrast, SEAP secretion was stimulated 1.5-fold from both treated and untreated cells, consistent with secretion by the constitutive secretory pathway. Stimulated secretion of granins was detected from both hormone-treated and -untreated cells. These results suggest that granin and prolactin storage are differentially regulated and that the constitutive secretory pathway is not affected by hormone treatment.

Antibacterial activity of secretolytin, a chromogranin B-derived peptide (614-626), is correlated with peptide structure

Amongst the chromogranin B (CGB) derived fragments naturally generated in bovine chromaffin granules and detected in the extracellular space, we recently identified a major peptide corresponding to the 614-626 sequence of CGB. This peptide, named secretolytin, shared an interesting sequence homology with the lytic domain of cecropins and displayed a potent antibacterial activity. The aim of the present study was to determine the structural features of secretolytin necessary for this biological activity. Our results suggest that an alpha-helical amphipathic structure common to secretolytin, cecropins and pig myeloid antibacterial peptide may account for the antibacterial activity.

Calcitonin and calcitonin gene-related peptide mRNA detection in a population of hyperplastic parathyroid cells also expressing chromogranin B

BACKGROUND

In contrast to chromogranin A, chromogranin B is found only in small amounts in parathyroid tissue. We have recently shown that hyperplastic parathyroid glands occasionally show a pronounced focal chromogranin B expression. The aim of the present study was to further investigate the properties of these chromogranin B-positive cells by means of immunohistochemistry and in situ hybridization.

EXPERIMENTAL DESIGN

Routinely processed tissues from 22 normal, 86 hyperplastic, and 36 neoplastic parathyroid glands were immunohistochemically investigated with Ab against parathyroid hormone (PTH), chromogranin A and B, calcitonin, and calcitonin gene-related peptide (CGRP). Additionally, six hyperplastic glands with focal chromogranin immunoreactivity as well as chromogranin B-negative normal, hyperplastic, and neoplastic (two cases each) glands were used for in situ hybridization studies for the demonstration of calcitonin and CGRP mRNA.

RESULTS

All normal, hyperplastic, and neoplastic parathyroids were immunohistochemically PTH- and chromogranin A-positive. Twelve of 86 hyperplastic glands showed a focal chromogranin B immunoreactivity; in 10 out of these 12 cases, calcitonin could be colocalized with chromogranin B, chromogranin A, and PTH. CGRP was found in a fraction of calcitonin-positive cells in four cases. In hyperplastic glands, calcitonin mRNA was detected in areas with immunohistochemical calcitonin and chromogranin B positivity. CGRP mRNA was demonstrated only in a few cells.

CONCLUSIONS

The results from this study demonstrate that calcitonin and CGRP may be synthesized and stored in PTH-producing hyperplastic parathyroid cells. The calcitonin-positive cells also strongly express chromogranin B, which is immunohistochemically not detectable in normal parathyroid cells. The functional significance of these findings remains to be elucidated.

Identification of secretolytin, the endogenous C-terminal fragment of residues 614-626 with antibacterial activity

Chromogranins constitute a family of acidic soluble proteins widely distributed in endocrine cells and neurons. Chromogranin A, the major soluble component in bovine adrenal medullary secretory granules in chromaffin cells, has been shown to be actively processed to peptide fragments [Metz-Boutigue, M. H., Garcia-Sablone, P., Hogue-Angeletti, R. & Aunis, D. (1993) Eur. J. Biochem. 217, 247-257]. In the present paper, the structural features of the proteolytic degradation mechanism of chromogranin B/secretogranin I have been characterized with regard to the possible function of this protein as a precursor of biologically active peptides. Chromogranin-B-derived fragments present in bovine chromaffin granules were identified by microsequencing after separation by two-dimensional gel electrophoresis or high-performance liquid chromatography. A similar approach was performed to characterize chromogranin-B-derived fragments released into the extracellular space from depolarized bovine cultured chromaffin cells. In chromogranin B, 18 cleavage sites were identified along the protein chain and chromogranin B/secretogranin I fragments were generated by proteolytic attack at both the N-terminus and C-terminus. A major fragment corresponding to residues 614-626 of the C-terminal sequence, was identified in the extracellular space; this peptide was found to share sequence and structural similarities with the lytic domain of cecropins and, as expected from this similarity, to display potent antibacterial properties. Endogenous and synthetic peptides were active on Micrococus luteus, killing bacteria in the micromolar concentration range. The synthetic peptide slows the growth of Bacillus megaterium and was inactive towards Escherichia coli. In addition, the synthetic peptide was unable to induce hemolytic activity. This antibacterial function might be of biological significance in the neuroendocrine system of living organisms. We propose to name this peptide secretolytin.

Measurements of chromogranin A, chromogranin B (secretogranin I), chromogranin C (secretogranin II) and pancreastatin in plasma and urine from patients with carcinoid tumours and endocrine pancreatic tumours

Chromogranins and/or secretogranins constitute a family of water-soluble acidic glycoproteins that are present in almost all endocrine, neuroendocrine and neuronal tissue. Antibodies against chromogranins have been widely used for immunohistochemical staining of endocrine tissue and tumours of neuroendocrine origin. Furthermore, measurements of circulating chromogranin A have been used as a reliable marker for neuroendocrine tumour growth. In this study, we describe the development of specific antibodies against chromogranin A, chromogranin B (secretogranin I), chromogranin C (secretogranin II) and pancreastatin. The antibodies were used for immunohistochemical staining of normal and neoplastic neuroendocrine tissue and development of reliable radioimmunoassays for chromogranin A, chromogranin B, chromogranin C and pancreastatin. In 44 patients with carcinoid tumours, 17 patients with sporadic endocrine pancreatic tumours and 11 patients with endocrine pancreatic tumours and the multiple endocrine neoplasia 1 syndrome, plasma measurements revealed elevated chromogranin A levels in 99%, elevated chromogranin B in 88%, elevated chromogranin C in 6% and elevated pancreastatin in 46% of the patients. Urinary measurements revealed elevated levels in 39%, 15%, 14% and 33% of the patients respectively. Gel permeation chromatography of plasma and urine showed that circulating chromogranin A, and immunoreactive fragments of chromogranin A, had a higher molecular weight distribution than the chromogranin A fragments excreted to the urine. Furthermore, it was noted that most of the patients excreting chromogranin A fragments to the urine had previously been treated with streptozotocin, a cytotoxic agent known to induce renal tubular dysfunction. The antibodies raised proved useful for immunohistochemical staining and visualised endocrine cells in pancreatic islets, adrenal medulla and the small intestine as well as in endocrine pancreatic tumours, pheochromocytoma and midgut carcinoid tumours. In conclusion, the antibodies raised were useful for both immunohistochemical staining of normal tissue and endocrine tumours as well as development of specific radioimmunoassays for plasma measurements of the different chromogranins. Furthermore, we show that plasma measurements of chromogranin A and B were superior to measurements of chromogranin C and pancreastatin and plasma measurements of the different chromogranins were more reliable as markers for tumour growth than the corresponding urine measurements.

Identification of a new chromogranin B fragment (314-365) in endocrine tumors

A rabbit antiserum was raised against the fragment (350-365) of human chromogranin B corresponding to the C-terminal end of a putative proteolytic fragment generated by the cleavage of a dibasic doublet located in position 366-367 of the precursor. A radioimmunoassay was developed. Chromatographic analysis of 10 endocrine tumor extracts (one liver metastasis of a gastrinoma, one liver metastasis of a medullary carcinoma of the thyroid, one VIPoma, one insulinoma, one nonsecreting pancreatic endocrine tumor, one local recurrence of a gut carcinoid, two pituitary gonadotropinoma, and two non-secreting pituitary adenomas) revealed the presence of two forms of immunoreactive material. The most abundant form had an apparent molecular weight of 4500 and was purified to homogeneity by successive reverse-phase HPLC chromatographies and partially sequenced. The N-terminal sequence of the peptide, established by automated Edman degradation, was A-S-E-E-E-P-E-Y-G-E-E-I-K-G-Y-P-V-Q and corresponded to the 314-332 sequence of human chromogranin B. Taking into account the specificity of the antiserum used for peptide identification, we deduced that the purified peptide was chromogranin B(314-365) and represented a new form generated by limited proteolysis of chromogranin B.