Chromogranin B Research Articles

Quantifying the Effects of Renal Impairment on Plasma Concentrations of the Neuroendocrine Neoplasia Biomarkers Chromogranin A, Chromogranin B, and Cocaine- and Amphetamine-Regulated Transcript

To the Editor: Neuroendocrine neoplasia (NEN)1 accounts for 2% of all malignancies (1). Patients with NEN often present with nonspecific symptoms and thus represent a major diagnostic challenge. There are several circulating NEN biomarkers, and chromogranin A (CgA) is regarded as the gold standard (2). Chromogranin B (CgB) has been found to be a useful diagnostic addition to CgA measurements (3). The peptide product of cocaine- and amphetamine-regulated transcript (CART) is also increased in patients with NENs, particularly in those with pancreatic NENs (4). Renal impairment or failure can increase circulating concentrations of CgA (2) and CART (4); however, CgB may be unaffected by mild renal impairment and is increased only in severe renal failure (3). The population most likely to be affected by NEN is also susceptible to renal impairment: Chronic kidney disease (CKD) occurs in approximately 10% of the population between 50 and 60 years of age, and the mean age of patients with a NEN diagnosis is 61 years (1, 5). We therefore examined the effect of varying degrees of renal impairment/failure on plasma concentrations of CgA, CgB, and CART in patients without NEN. Ethics approval for this study was obtained from the Hammersmith and Queen Charlotte's and Chelsea Hospitals Research Ethics Committee (04/Q0406/80). After informed written consent was obtained, 5 mL of blood was collected from 40 healthy volunteers. In addition, samples from 107 patients with different stages of renal impairment were obtained and irreversibly anonymized as per Royal College of Pathology, UK, guidelines (D035, September 2007). All blood samples were collected into EDTA-containing tubes and centrifuged at 10 000 g for …

Differential Responses of Genes for Neurosecretory Granules in the Rat Adrenal Medulla to Acute and Repeated Stress

With acute stress, release of adrenomedullary catecholamines is important for handling the emergency situation. However, when chronic or repeated, stress leads to development or worsening of wide range of diseases. To clarify the mechanism, we studied changes in components of neurosecretory granules in adrenal medulla of male Sprague Dawley rats exposed to immobilization stress for 2 h once (1xIMO) or for 6 days (6xIMO). While vesicular monoamine transporter 1 (VMAT1) was expressed in all chromaffin cells, VMAT2, which has greater affinity for catecholamines, and higher turnover number than VMAT1, was expressed only in the NE‐cells under basal conditions. 1xIMO elevated VMAT2 mRNA, and after 6xIMO, this was reflected in nearly 3‐fold rise in VMAT2 protein, and expression in many Epi‐synthesizing cells. With 6xIMO, not only was VMAT2 mRNA still elevated, but chromogranin A (CgA) and chromogranin B (CgB) mRNAs were also increased 2–3 fold. The elevation of CgA, CgB and VMAT2 are each expected to increase the quantal size. This can facilitate more efficient use of the well characterized heightened catecholamine levels. To investigate a possible role of the HPA axis in induction of VMAT2, PC12 cells were treated with dexamethasone, which elevated VMAT2 mRNA expression. In contrast, the rise in Egr1 and P‐CREB may mediate the induction of CgA and CgB with repeated IMO stress.American Heart Association 10GRNT4420001

Stress triggered changes in expression of genes for neurosecretory granules in adrenal medulla.

With acute stress, the release of adrenomedullary catecholamines is important for handling the emergency situation. However, when chronic or repeated, stress alters the allostatic load and leads to a hyperadrenergic state, resulting in the development or worsening of a wide range of diseases. To help elucidate the mechanism, we examined the effects of single and repeated immobilization stress on gene expression of components of neurosecretory vesicles in the adrenal medulla. Male Sprague-Dawley rats were exposed to immobilization stress once for 2h (1× IMO) or daily for six consecutive days (6× IMO). Compared to unstressed controls, 1× IMO elevated gene expression of vesicular monoamine transporter 2 (VMAT2). In response to 6× IMO, not only was VMAT2 mRNA still elevated, but chromogranin A (CgA) and chromogranin B (CgB) mRNAs were also increased two to three-fold above basal levels. To investigate the possible role of the hypothalamic-pituitary-adrenal axis in the induction of VMAT2, PC12 cells were treated with the synthetic glucocorticoid dexamethasone, which was found to elevate VMAT2 mRNA expression. The findings suggest that following repeated stress, elevations of various components of neurosecretory vesicles in the adrenal can facilitate more efficient utilization of the well-characterized heightened catecholamine levels.

C-terminal Domain of Chromogranin B Regulates Intracellular Calcium Signaling

The versatility of intracellular calcium as a second messenger is seen in its ability to mediate opposing events such as neuronal cell growth and apoptosis. A leading hypothesis used to explain how calcium regulates such divergent signaling pathways is that molecules responsible for maintaining calcium homeostasis have multiple roles. For example, chromogranin B (CGB), a calcium binding protein found in secretory granules and in the lumen of the endoplasmic reticulum, buffers calcium and also binds to and amplifies the activity of the inositol 1,4,5-trisphosphate receptor (InsP(3)R). Previous studies have identified two conserved domains of CGB, an N-terminal domain (N-CGB) and a C-terminal domain (C-CGB). N-CGB binds to the third intraluminal loop of the InsP(3)R and inhibits binding of full-length CGB. This displacement of CGB decreases InsP(3)R-dependent calcium release and alters normal signaling patterns. In the present study, we further characterized the role of N-CGB and identified roles for C-CGB. The effect of N-CGB on calcium release depended upon endogenous levels of cellular CGB, whereas the regulatory effect of C-CGB was apparent regardless of endogenous levels of CGB. When either full-length CGB or C-CGB was expressed in cells, calcium transients were increased. Additionally, the calcium signal initiation site was altered upon C-CGB expression in neuronally differentiated PC12 and SHSY5Y cells. These results show that CGB has numerous regulatory roles and that CGB is a critical component in modulating InsP(3)R-dependent calcium signaling.

Chromogranin B in Calpain-Mediated Hypertrophic Signaling—The Chicken, the Egg, or Even Both…?

To the Editor: It was with great interest that we read this focused review by Patterson and colleagues on the role of calpains in cardiac hypertrophy. Succinctly, the authors provide a comprehensive overview on the current body of evidence of how calpains are believed to be implicated in the regulation of the development of cardiac, specifically ventricular, hypertrophy and go further on to discuss potential therapeutic strategies.1 In 2008, we studied the mechanism by which angiotensin II (Ang II) activates nuclear factor (NF)-κB in cardiomyocytes to drive the hypertrophic signaling pathway and showed that this activation depends on calcium release by the inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R).2 Importantly, we identified the calcium storage protein chromogranin B (CGB) to be of crucial importance in shaping this InsP3-dependent release of calcium. Our in vitro results were supported by in vivo experiments that showed …

Catecholamine Storage Vesicles: Role of Core Protein Genetic Polymorphisms in Hypertension

Hypertension is a complex trait with deranged autonomic control of the circulation. The sympathoadrenal system exerts minute-to-minute control over cardiac output and vascular tone. Catecholamine storage vesicles (or chromaffin granules) of the adrenal medulla contain remarkably high concentrations of chromogranins/secretogranins (or “granins”), catecholamines, neuropeptide Y, adenosine triphosphate (ATP), and Ca2+. Within secretory granules, granins are co-stored with catecholamine neurotransmitters and co-released upon stimulation of the regulated secretory pathway. The principal granin family members, chromogranin A (CHGA), chromogranin B (CHGB), and secretogranin II (SCG2), may have evolved from shared ancestral exons by gene duplication. This article reviews human genetic variation at loci encoding the major granins and probes the effects of such polymorphisms on blood pressure, using twin pairs to probe heritability and individuals with the most extreme blood pressure values in the population to study hypertension.

Neuronal over‐expression of chromogranin A accelerates disease onset in a mouse model of ALS

Recent studies provided evidence that chromogranins can interact with mutant superoxide dismutase 1 (SOD1) and that chromogranin B (CgB) may act as a susceptibility gene and modifier of onset in amyotrophic lateral sclerosis (ALS). To further investigate the role of chromogranins in ALS pathogenesis, we generated SOD1(G37R) mice that over-express CgA under the control of Thy1 promoter. Here, we report that neuronal over-expression of CgA in SOD1(G37R) mice caused acceleration of onset of motor impairment and exacerbation of motor neuron degeneration. The use of monoclonal antibody specific to misfolded mutant SOD1 demonstrated a higher level of misfolded SOD1 species in double transgenic mice compared to SOD1(G37R) mice, suggesting a stabilization of pathogenic SOD1 species by excess CgA. These results suggest a role of chromogranins as modulators of disease onset in ALS pathogenesis.

Isoprostane, an “Intermediate Phenotype” for Oxidative Stress: Heritability, Risk Trait Associations, and the Influence of Chromogranin B Polymorphism

The purpose of this study is to understand whether isoprostane, a biomarker of oxidative stress, is subject to heritable control; whether it shares heritability with other cardiometabolic risk traits; and finally whether genetic variation at a specific candidate locus contributes to isoprostane variability. Isoprostane marks oxidative stress, and elevated isoprostane excretion might be involved in cardiovascular target organ damage. Here we used the classical twin pair method to probe the role of heredity in generating the isoprostane trait. Trait heritability (h(2)) and shared genetic determination among traits (pleiotropy, genetic covariance, ρ(G)) were estimated by variance components in twin pairs. Because the isoprostane and Chromogranin B (CHGB) traits shared ρ(G), we examined the CHGB locus for effects on the traits. Urinary isoprostane excretion was substantially heritable (h(2) = 65.8 ± 4.3%), and the isoprostane trait aggregated with multiple traits (CHGB, catecholamines, autonomic/baroreceptor, and renal function), including several features of the metabolic syndrome (body mass index, insulin resistance, dyslipidemia). Isoprostane excretion also aggregated with systemic hypertension. Twin studies demonstrated genetic covariance (pleiotropy) for the isoprostane and CHGB traits (ρ(G) = 0.27), and therefore we investigated the CHGB locus for trait effects. A common variant in the 3'-UTR of CHGB (C+84A) associated with plasma CHGB as well as isoprostane excretion. The C+84A disrupted an A/U-rich messenger ribonucleic acid stability element, and in transfected luciferase/3'-UTR plasmids, the C+84 and +84A alleles differed markedly in reporter expression in chromaffin and neuroblastoma cells, whereas site-directed mutagenesis confirmed the importance of this variant within the context of the A/U-rich motif. Isoprostane excretion is substantially heritable and shares joint genetic determination with CHGB as well as multiple features of the metabolic syndrome. A common polymorphism in the 3'-UTR (C+84A) of CHGB, which disrupts an A/U-rich messenger ribonucleic acid stability element, associates with not only CHGB secretion but also excretion of isoprostane. We propose a chain of events whereby CHGB genetic variation results in oxidative stress, with isoprostane formation. The results suggest novel links among the catecholaminergic system, oxidative pathways, and systemic hypertension.

Chromogranin B in Heart Failure

Background— Chromogranin B (CgB) is a member of the granin protein family. Because CgB is often colocalized with chromogranin A (CgA), a recently discovered cardiac biomarker, we hypothesized that CgB is regulated during heart failure (HF) development. Methods and Results— CgB regulation was investigated in patients with chronic HF and in a post–myocardial infarction HF mouse model. Animals were phenotypically characterized by echocardiography and euthanized 1 week after myocardial infarction. CgB mRNA levels were 5.2-fold increased in the noninfarcted part of the left ventricle of HF animals compared with sham-operated animals ( P <0.001). CgB mRNA level in HF animals correlated closely with animal lung weight ( r =0.74, P =0.04) but not with CgA mRNA levels ( r =0.20, P =0.61). CgB protein levels were markedly increased in both the noninfarcted (110%) and the infarcted part of the left ventricle (70%) but unaltered in other tissues investigated. Myocardial CgB immunoreactivity was confined to cardiomyocytes. Norepinephrine, angiotensin II, and transforming growth factor-β increased CgB gene expression in cardiomyocytes. Circulating CgB levels were increased in HF animals (median levels in HF animals versus sham, 1.23 [interquartile range, 1.03 to 1.93] versus 0.98 [0.90 to 1.04] nmol/L; P =0.003) and in HF patients (HF patients versus control, 1.66 [1.48 to 1.85] versus 1.47 [1.39 to 1.58] nmol/L; P =0.007), with levels increasing in proportion to New York Heart Association functional class ( P =0.03 for trend). Circulating CgB levels were only modestly correlated with CgA ( r =0.31, P =0.009) and B-type natriuretic peptide levels ( r =0.27, P =0.014). Conclusions— CgB production is increased and regulated in proportion to disease severity in the left ventricle and circulation during HF development.

P413L CHGB is not associated with ALS susceptibility or age at onset in a Dutch population

Gros-Louis and colleagues (1) performed a classical candidate gene case-control study on Chromogranin B (CHGB) variations in ALS patients of French, French-Canadian, and Scandinavian origin. They found a significant association between a missense variation in exon 4 (rs742710) and ALS susceptibility conferring an ≈3.3-fold increased risk of ALS in the French/French-Canadian population studied. This missense variation is comparable to the APOE-e4 allele in Alzheimer's disease (2). In addition, this P413L CHGB variant also acts as a modifier of disease onset by decreasing the median age at onset by 7 years in patients with sporadic ALS and by as much as 11 years in familial ALS.

Common Functional Genetic Variants in Catecholamine Storage Vesicle Protein Promoter Motifs Interact to Trigger Systemic Hypertension

The purpose of this study is to understand whether naturally occurring genetic variation in the promoter of chromogranin B (CHGB), a major constituent of catecholamine storage vesicles, is functional and confers risk for cardiovascular disease. CHGB plays a necessary (catalytic) role in catecholamine storage vesicle biogenesis. Previously, we found that genetic variation at CHGB influenced autonomic function, with association maximal toward the 5' region. Here we explored transcriptional mechanisms of such effects, characterizing 2 common variants in the proximal promoter, A-296C and A-261T, using transfection/cotransfection, electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP). We then tested the effects of promoter variation on cardiovascular traits. The A-296C disrupted a c-FOS motif, exhibiting differential mobility shifting to chromaffin cell nuclear proteins during EMSA, binding of endogenous c-FOS on ChIP, and differential response to exogenous c-FOS. The A-261T disrupted motifs for SRY and YY1, with similar consequences for EMSA, endogenous factor binding, and responses to exogenous factors. The 2-SNP CHGB promoter haplotypes had a profound (p=3.16E-20) effect on blood pressure (BP) in the European ancestry population, with a rank order of CT<AA<<CA<AT on both systolic blood pressure (SBP) and diastolic blood pressure (DBP), accounting for approximately 2.3% to approximately 3.4% of SBP/DBP variance; the haplotype effects on BP in vivo paralleled those on promoter activity in cella. Site-by-site interactions at A-296C and A-261T yielded highly nonadditive effects on SBP/DBP. The CHGB haplotype effects on BP were also noted in an independent (African ancestry) sample. In normotensive twins, parallel effects were noted for a pre-hypertensive phenotype, BP response to environmental stress. The common CHGB promoter variants A-296C and A-261T, and their consequent haplotypes, alter binding of specific transcription factors to influence gene expression in cella as well as BP in vivo. Such variation contributes substantially to risk for human hypertension. Involvement of the sex-specific factor SRY suggests a novel mechanism for development of sexual dimorphism in BP.

Proteolytic Fragments of Chromogranins A and B Represent Major Soluble Components of Chromaffin Granules, Illustrated by Two-Dimensional Proteomics with NH2-Terminal Edman Peptide Sequencing and MALDI-TOF MS

Neuroendocrine chromaffin granules of adrenal medulla represent regulated secretory vesicles that secrete neuropeptides and catecholamines which mediate cell-cell communication for physiological functions. This study addressed the identification of the major proteins in these secretory vesicles that provide dynamic storage and secretion of bioactive molecules. Proteins of the soluble compartment of the vesicles were separated by two-dimensional gels and subjected to NH(2)-terminal Edman sequencing for identification and determination of NH(2)-termini. Results showed that proteolytic fragments of chromogranin A (CgA) and chromogranin B (CgB) represent the major proteins of these secretory vesicles. These fragments resulted from cleavage of their respective precursor proteins at dibasic and monobasic sites, which is consistent with the known cleavage specificities of prohormone processing enzymes. MALDI-TOF MS analyses of protein spots similar in molecular weight that possessed a range of pI values were represented by molecular forms of CgA and CgB proteins. These findings indicate the high prevalence of endogenous CgA and CgB proteolytic fragments that function in chromaffin secretory vesicles for release of bioactive molecules for cell-cell communication.

Aspects of the neuroendocrine cerebellum: expression of secretogranin II, chromogranin A and chromogranin B in mouse cerebellar unipolar brush cells

Morphologically distinct neuron classes can be subdivided in sublineages by differential chemical phenotypes that correlate with functional diversity. Here we show by immunocytochemistry that chromogranin A (CgA) chromogranin B (CgB) and secretogranin II (SgII), the principal granins situated in neuronal secretory granules and large dense-core vesicles, are widely but differentially expressed in cells of the mouse cerebellum and terminals of cerebellar afferents. While CgA and CgB were nearly panneuronal, SgII was more restricted in distribution. The cells most intensely immunoreactive for SgII were a class of small, excitatory interneurons enriched in the granular layer of the vestibulocerebellum, the unipolar brush cells (UBCs), although larger neurons likely to be a subset of the Golgi–Lugaro–globular cell population were also distinctly immunopositive; by contrast, Purkinje cells and granule cells were, at best, faintly stained and, stellate, basket cells were unstained. SgII was also present in subsets of mossy fibers, climbing fibers and varicose fibers. Neurons in the cerebellar nuclei and inferior olive were distinctly positive for the three granins. Double-labeling with subset-specific cell class markers indicated that, while both CgA and CgB were present in most UBCs, SgII immunoreactivity was present in the calretinin (CR)-expressing subset, but lacked in metabotropic glutamate receptor 1alpha (mGluR1α)-expressing UBCs. Thus, we have identified an additional cell class marker, SgII, which serves to study subtype properties in the UBC population. The abundance of SgII in only one of the two known subsets of UBCs is remarkable, as its expression in other neurons of the cortex was moderate or altogether lacking. The data suggest that the CR-positive UBCs represent a unique neuroendocrine component of the mammalian cerebellar cortex, presumably endowed with transynaptically regulated autocrine or paracrine action/s. Because of the well-known organization of the cerebellar system, several of its neuron classes may represent valuable cellular models to analyze granin functions in situ, in acute slices and in dissociated cell and organotypic slice cultures.

A C-terminal Fragment of Chromogranin B Amplifies Inostiol (1,4,5)-Trisphohsphate Receptor Mediated Signaling

Chromogranin B (CGB) is a low affinity, high capacity calcium binding protein belonging to the granin family. It is located in the lumen of the endoplasmic reticulum (ER) and is also found in secretory granules. Addition of CGB amplifies calcium release from ER stores and increases the activity of the inostiol (1,4,5)-trisphohsphate receptor (InsP3R). We previously demonstrated that CGB is non-uniformly distributed within neurons, and its spatial localization is cell type specific. We also showed that stimulation of the InsP3R in neurons leads to initiation of intracellular calcium release where the concentration of CGB is highest. When we expressed the N-terminal region of CGB, which binds to the third intralumenal loop of the InsP3R, the functional interaction between CGB and the InsP3R was disrupted and the initiation site of calcium release was altered. We now report that a 20 amino acid fragment of the C-terminal region plays a critical role in regulating calcium transients from the InsP3R. Addition of the C-terminal region of CGB increased the activity of single InsP3R currents in lipid bilayers. When intracellular calcium transients were monitored in 3T3 cells lacking CGB, InsP3R dependent calcium release was markedly amplified after expression of full length CGB or expression of the C-terminal region. In contrast, expression of the N-terminal region was unable to amplify the intracellular calcium transients. In SHSY5Y cells with endogenous CGB, expression of the C-terminal region induced a prolonged response to extracelluar agonists compared to native cells whereas expression of the N-terminal region depressed calcium signaling and altered the signal initiation site. These effects of CGB on calcium transients in neuronal cells indicate its importance in physiological processes and will guide investigation into pathophysiological processes.

Autonomic Function in Hypertension

Background— Hypertension is a complex trait, with deranged autonomic control of circulation. Chromogranin B ( CHGB ) is the most abundant core protein in human catecholamine secretory vesicles, playing an important role in their biogenesis. Does common interindividual variation at the CHGB locus contribute to phenotypic variation in CHGB and catecholamine secretion, autonomic stability of circulation, or blood pressure (BP) in the population? Methods and Results— To probe interindividual variability in CHGB , we systematically studied polymorphism across the locus by resequencing CHGB (≈6 kbp footprint spanning the promoter, 5 exons, exon/intron borders, untranslated regions) in 160 subjects (2n=320 chromosomes) of diverse biogeographic ancestries. We identified 53 single-nucleotide polymorphisms, of which 22 were common. We then studied 1182 subjects drawn from the most extreme BP values in the population (highest and lowest 5th percentiles), typing 4 common polymorphisms spanning the ≈14 kbp locus. Sliding-window haplotype analysis indicated BP associations peaking in the 5′/promoter region, most prominent in men, and a peak effect in the proximal promoter at variant A-261T (A&gt;T), accounting for ≈8/≈6 mmHg BP in males. The promoter allele (A-261) that was a predictor of higher diastolic BP and systolic BP was also associated with lower circulating/plasma CHGB concentration (CHGB 439 to 451 epitope) in twin pairs. In twins, the same CHGB variants that were predictors of lower basal CHGB secretion were also associated with exaggerated catecholamine secretion and BP response to environmental (cold) stress; likewise, women displayed increased plasma CHGB 439 to 451 but decreased catecholamine secretion as well as BP response to environmental stress. The effect of A-261T on CHGB expression was confirmed in chromaffin cells by site-directed mutagenesis on transfected CHGB promoter/luciferase reporter activity, and the allelic effects of A-261T on gene expression were directionally coordinate in cella and in vivo. To confirm these clinical associations experimentally, we undertook targeted homozygous (−/−) ablation of the mouse CHGB gene; knockout mice displayed substantially increased BP, by ≈20/≈18 mmHg, confirming the mechanistic basis of our findings in humans. Conclusion— Common genetic variation at the CHGB locus, especially in the proximal promoter, influences CHGB expression and later catecholamine secretion and the early heritable responses to environmental stress, eventuating in changes in resting/basal BP in the population. Both the early (gene expression) and late (population BP) consequences of CHGB variation are sex dependent. These results point to new molecular strategies for probing autonomic control of circulation and, ultimately, the susceptibility to and pathogenesis of cardiovascular disease states such as hypertension.

Chromogranin B Regulates Calcium Signaling, Nuclear Factor κB Activity, and Brain Natriuretic Peptide Production in Cardiomyocytes

Altered regulation of signaling pathways can lead to pathologies including cardiac hypertrophy and heart failure. We report that neonatal and adult cardiomyocytes express chromogranin B (CGB), a Ca(2+) binding protein that modulates Ca(2+) release by the inositol 1,4,5-trisphosphate receptor (InsP(3)R). Using fluorescent Ca(2+) indicator dyes, we found that CGB regulates InsP(3)-dependent Ca(2+) release in response to angiotensin II, an octapeptide hormone that promotes cardiac hypertrophy. ELISA experiments and luciferase reporter assays identified angiotensin II as a potent inducer of brain natriuretic peptide (BNP), a hormone that recently emerged as an important biomarker in cardiovascular disease. CGB was found to regulate angiotensin II-stimulated and basal secretion, expression and promoter activity of BNP that depend on the InsP(3)R. Moreover, we provide evidence that CGB acts via the transcription activity of nuclear factor kappaB in an InsP(3)/Ca(2+)-dependent manner but independent of nuclear factor of activated T cells. In vivo experiments further showed that cardiac hypertrophy induced by angiotensin II, a condition characterized by increased ventricular BNP production, is associated with upregulation of ventricular CGB expression. Overexpression of CGB in cardiomyocytes, in turn, induced the BNP promoter. The evidence presented in this study identifies CGB as a novel regulator of cardiomyocyte InsP(3)/Ca(2+)-dependent signaling, nuclear factor kappaB activity, and BNP production.

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.

Inositol 1,4,5 trisphosphate receptor and chromogranin B are concentrated in different regions of the hippocampus

Calcium (Ca(2+)) release from intracellular stores plays a crucial role in many cellular functions in the brain. These intracellular signals have been shown to be transmitted within and between cells. We report a non-uniform distribution of proteins essential for Ca(2+) signaling in acutely prepared brain slice preparations and organotypic slice cultures, both made from rat hippocampus. The Type I inositol-1,4,5 trisphosphate receptor (InsP(3)R1) is the main InsP(3)R subtype in neurons. Immunohistochemistry experiments showed a prominent expression of InsP(3)R1 in the CA1 region of the hippocampus whereas the CA3 region and dentate gyrus (DG) showed only moderate immunoreactivity. In contrast, chromogranin B (CGB), a protein binding to the InsP(3)R1 on the luminal side of the endoplasmic reticular membrane was enriched in the CA3 region whereas DG and the CA1 region showed only faint CGB signals. The neuronal kinases leading to the formation of inositol-1,4,5 trisphosphate (InsP(3)), phosphatidylinositol-4-kinase (PI4K), and phosphatidylinositol-4-phosphate-5-kinase (PIPK), showed strong immunoreactivity throughout all hippocampal cell fields with differences in the subcellular distribution. Moreover, a distinct band of strong CGB and PIPK immunoreactivity was observed in the CA3 region that coincides with the mossy fiber tract (stratum lucidum). These data show differential expression of the components of the signaling toolkit leading to InsP(3)-mediated Ca(2+) release in cells of the hippocampus. The regulation of these differences may play an important role in various neuropathologic conditions such as Alzheimer's disease, epilepsy, or schizophrenia.

Further evidence that the chromogranin B gene confers predisposition to schizophrenia: a family-based association study in Chinese

The Chromogranin B (CHGB) gene has been proposed as a candidate gene for predisposition to schizophrenia due to its location on the genome, the evidence of genetic studies, and its functional role in schizophrenia. To investigate its association with schizophrenia using case-control analysis, we genotyped eight single nucleotide polymorphisms (SNPs) and performed transmission disequilibrium tests (TDT) using 192 Han Chinese trios. The G allele of IVS4 + 808A > G showed a trend of over-transmission from heterozygous parents to affected offspring (P = 0.06), although no significant over-transmission was found for individual markers. Furthermore, a significant transmission was observed for the common haplotype G-G-A-G-C (P = 0.0018). Overall, our results suggest that at least one locus in or close to the CHGB gene confers risk of the disorder and strengthen the evidence that CHGB is a promising susceptibility gene for schizophrenia in Chinese population.

Presence of a Putative Vesicular Inositol 1,4,5-Trisphosphate-Sensitive Nucleoplasmic Ca2+ Store

The inositol 1,4,5-trisphosphate receptors (IP(3)Rs) are widely localized in both the heterochromatin and euchromatin regions. We found recently the presence of nucleoplasmic complexes that are composed of phospholipids, IP(3)R/Ca(2+) channels, and Ca(2+) storage protein chromogranin B (CGB). Close examination and 3D image reconstruction of these complexes revealed numerous vesicular structures with an average diameter of approximately 50 nm that are primarily interspersed between the heterochromatins. IP(3) rapidly released Ca(2+) from these structures, but other inositol phosphates, inositol 1,4-bisphosphate, inositol 1,3,4-trisphosphate, and inositol 1,3,4,5-tetrakisphosphate, failed to release Ca(2+). Addition of heparin or IP(3)R antibody blocked the IP(3)-induced Ca(2+) releases, indicating the release of Ca(2+) through the IP(3)R/Ca(2+) channels. Given the presence of the IP(3)R/Ca(2+) channels and Ca(2+) storage protein CGB in these vesicular structures, we postulate that these vesicles are the IP(3)-sensitive nucleoplasmic Ca(2+) stores. Abundance of the vesicular Ca(2+) stores between the heterochromatins appeared to imply critical roles these vesicular Ca(2+) stores play in controlling the Ca(2+) concentrations of the chromosomes.