Recombinant human chromogranin A: expression, purification and characterization of the N-terminal derived peptides

Accuracy and Clinical Correlates of Two Different Methods for Chromogranin A Assay in Neuroendocrine Tumors

Measurement of chromogranin A (CgA) plays a major role in the management of neuroendocrine tumors (NET); however, reliable assaying of CgA is made difficult by the rapid hydrolysis following its release into the bloodstream. This study was aimed at the assessment of two assays for CgA in NET patients. CgA was measured in 93 patients by means of an enzyme-linked immunosorbent assay (ELISA) and an immunoradiometric assay (IRMA). The specificity and sensitivity of CgA were evaluated in relation to tumor histology. The clinical accuracy of the two assays was evaluated by receiver-operating characteristic (ROC) curve analysis. Regression analysis demonstrated different immunoreactivity for CgA of the antibodies used in the two kits (r=0.61). The two assays had different accuracy also in classifying patients according to their clinical condition (91% vs 64% specificity and 79% vs 79% sensitivity for the ELISA and IRMA assay, respectively) and tumor histology (81% vs 85% sensitivity for the ELISA and IRMA assays, respectively, in carcinoids; 92% vs 67% sensitivity for the ELISA and IRMA assays, respectively, in pancreatic islet cell tumors). The different clinical accuracy of the two assays was confirmed by the ROC analysis (AUC=0.90 vs AUC=0.87 for the ELISA and IRMA assays, respectively). In conclusion, because of the poor standardization of the commercially available measurement tools the clinical accuracy of CgA measurement depends on the assay used. This makes it difficult to compare CgA values measured with different kits and affects the clinical accuracy of the different assays for CgA.

Targeting Neuroinflammation to Treat Alzheimer's Disease

Over the past few decades, research on Alzheimer's disease (AD) has focused on pathomechanisms linked to two of the major pathological hallmarks of extracellular deposition of beta-amyloid peptides and intra-neuronal formation of neurofibrils. Recently, a third disease component, the neuroinflammatory reaction mediated by cerebral innate immune cells, has entered the spotlight, prompted by findings from genetic, pre-clinical, and clinical studies. Various proteins that arise during neurodegeneration, including beta-amyloid, tau, heat shock proteins, and chromogranin, among others, act as danger-associated molecular patterns, that-upon engagement of pattern recognition receptors-induce inflammatory signaling pathways and ultimately lead to the production and release of immune mediators. These may have beneficial effects but ultimately compromise neuronal function and cause cell death. The current review, assembled by participants of the Chiclana Summer School on Neuroinflammation 2016, provides an overview of our current understanding of AD-related immune processes. We describe the principal cellular and molecular players in inflammation as they pertain to AD, examine modifying factors, and discuss potential future therapeutic targets.

Cathepsin L colocalizes with chromogranin a in chromaffin vesicles to generate active peptides

Chromogranin A (CgA), the major soluble protein in chromaffin granules, is proteolytically processed to generate biologically active peptides including the catecholamine release inhibitory peptide catestatin. Here we sought to determine whether cysteine protease cathepsin L (CTSL), a novel enzyme for proteolytic processing of neuropeptides, acts like the well-established serine proteases [prohormone convertase (PC)1/3 or PC2] to generate catestatin by proteolytic processing of CgA. We found that endogenous CTSL colocalizes with CgA in the secretory vesicles of primary rat chromaffin cells. Transfection of PC12 cells with an expression plasmid encoding CTSL directed expression of CTSL toward secretory vesicles. Deconvolution fluorescence microscopy suggested greater colocalization of CTSL with CgA than the lysosomal marker LGP110. The overexpression of CTSL in PC12 cells caused cleavage of full-length CgA. CTSL also cleaved CgA in vitro, in time- and dose-dependent fashion, and specificity of the process was documented through E64 (thiol reagent) inhibition. Mass spectrometry on CTSL-digested recombinant CgA identified a catestatin-region peptide, corresponding to CgA(360-373). The pool of peptides generated from the CTSL cleavage of CgA inhibited nicotine-induced catecholamine secretion from PC12 cells. CTSL processing in the catestatin region was diminished by naturally occurring catestatin variants, especially Pro370Leu and Gly364Ser. Among the CTSL-generated peptides, a subset matched those found in the catestatin region in vivo. These findings indicate that CgA can be a substrate for the cysteine protease CTSL both in vitro and in cella, and their colocalization within chromaffin granules in cella suggests the likelihood of an enzyme/substrate relationship in vivo.

The trans-Golgi proteins SCLIP and SCG10 interact with chromogranin A to regulate neuroendocrine secretion

Secretion of proteins and peptides from eukaryotic cells takes place by both constitutive and regulated pathways. Regulated secretion may involve interplay of proteins that are currently unknown. Recent studies suggest an important role of chromogranin A (CHGA) in the regulated secretory pathway in neuroendocrine cells, but the mechanism by which CHGA enters the regulated pathway, or even triggers the formation of the pathway, remains unclear. In this study, we used a transcriptome/proteome-wide approach, to discover binding partners for CHGA, by employing a phage display cDNA library method. Several proteins within or adjacent to the secretory pathway were initially detected as binding partners of recombinant human CHGA. We then focused on the trans-Golgi protein SCLIP (STMN3) and its stathmin paralog SCG10 (STMN2) for functional study. Co-immunoprecipitation experiments confirmed the interaction of each of these two proteins with CHGA in vitro. SCLIP and SCG10 were colocalized to the Golgi apparatus of chromaffin cells in vivo and shared localization with CHGA as it transited the Golgi. Downregulation of either SCLIP or SCG10 by synthetic siRNAs virtually abolished chromaffin cell secretion of a transfected CHGA-EAP chimera (expressing CHGA fused to an enzymatic reporter, and trafficked to the regulated pathway). SCLIP siRNA also decreased the level of secretion of endogenous CHGA and SCG2, as well as transfected human growth hormone, while SCG10 siRNA decreased the level of regulated secretion of endogenous CHGB. Moreover, a dominant negative mutant of SCG10 (Cys 22,Cys 24-->Ala 22,Ala 24) significantly blocked secretion of the transfected CHGA-EAP chimera. A decrease in the buoyant density of chromaffin granules was observed after downregulation of SCG10 by siRNA, suggesting participation of these stathmins in granule formation or maturation. We conclude that SCLIP and SCG10 interact with CHGA, share partial colocalization in the Golgi apparatus, and may be necessary for typical transmitter storage and release from chromaffin cells.

Proteolytic cleavage of human chromogranin a containing naturally occurring catestatin variants: differential processing at catestatin region by plasmin

The plasma level of chromogranin A (CgA) is elevated in genetic hypertension. Conversely, the plasma level of the CgA peptide catestatin is diminished in individuals with established hypertension and those with a genetic risk of this disease. Resequencing of the human CHGA gene identified three naturally occurring variants of catestatin (Gly364Ser, Pro370Leu, and Arg374Gln) that exhibit different potencies in inhibiting catecholamine secretion. Here, we have examined whether there is any differential processing of the three CHGA variants to catestatin by the endoproteolytic enzyme plasmin. Plasmin digestion of the purified CgA proteins generated a stable biologically active 14-amino acid peptide (human CgA(360-373)) from the wild-type, Gly364Ser, and Arg374Gln proteins despite the disruption of the dibasic site (Arg(373)Arg(374)) in the Arg374Gln variant. Unexpectedly, the action of plasmin in generating the catestatin peptide from the Pro370Leu protein was less efficient. The efficiency of cleavage at the dibasic Arg(373) downward arrowArg(374) site in synthetic human CgA(360-380) was 3- to 4-fold less in Pro370Leu CgA, compared with the wild type. Circular dichroism of the synthetic CgA(352-372) suggested a difference in the amount of alpha-helix and beta-sheet between the wild-type and Pro370Leu CgA peptides. Because the Pro(370) residue is in the P4 position, the local secondary structure in the vicinity of the cleavage site may enforce the specificity or accessibility to plasmin. The less efficient proteolytic processing of the Pro370Leu protein by plasmin, coupled with the strong association of this variant with ethnicity, suggests that the Pro370Leu CHGA gene variant may contribute to the differential prevalence of cardiovascular disease across ethnic groups.

Heredity of Endothelin Secretion

Background— Endothelial dysfunction predisposes to vascular injury in association with hypertension. Endothelin (ET-1) is a potent vasoactive peptide that is synthesized and released by the vascular endothelium and is a marker of endothelial function. Chromogranin A (CHGA) regulates the storage and release of catecholamines and may have direct actions on the microvasculature. CHGA , a candidate gene for intermediate phenotypes that contribute to hypertension, shows a pattern of single nucleotide polymorphism variations that alter the expression and function of this gene both in vivo and in vitro.

Methods and Results— In a study of twins (n=238 pairs), plasma ET-1 was 58±5% ( P <0.0001) heritable. Plasma ET-1 was both correlated and associated with chromogranin fragment levels, and the 2 were influenced by shared genetic determination (pleiotropy [ρ G ]; for the CHGA precursor, ρ G =0.318±0.105; P =0.0032). We therefore hypothesized that variation in the CHGA gene may influence ET-1 secretion. Carriers of the CHGA promoter −988G, −462A, and −89A minor alleles showed significantly higher mean plasma ET-1 than their major allele homozygote counterparts ( P =0.02, P =0.006, P =0.03, respectively). Analysis of a linkage disequilibrium block that spans these 3 single nucleotide polymorphisms showed a significant association between the GATACA haplotype and plasma ET-1 ( P =0.0075). In cultured human umbilical vein endothelial cells, CHGA caused dose-dependent secretion of ET-1 over a brief (<1 hour) time course at relatively low concentrations of CHGA (10 to 100 nmol/L) with a threshold concentration (10 nmol/L) in the range found circulating in humans in vivo.

Conclusions— These results suggest that common, heritable variation in expression of the human CHGA gene influences endothelial ET-1 secretion in vivo, explained by a CHGA stimulus/ET-1 secretion coupling in endothelial cells in vitro. The findings document a previously unsuspected interaction between the sympathochromaffin system and the endothelium and suggest novel genetic and cell biological approaches to the prediction, diagnosis, and mechanism of endothelial dysfunction in human disease.

Granulogenesis in Non-neuroendocrine COS-7 Cells Induced by EGFP-tagged Chromogranin A Gene Transfection: Identical and Distinct Distribution of CgA and EGFP

We examined whether an enhanced green fluorescent protein (EGFP)-tagged chromogranin A (CgA) gene construct could serve as a marker protein to follow the synthesis of CgA and the process of granulogenesis in non-neuroendocrine (NE) cells. We transfected a CgA-EGFP expression vector into non-NE COS-7 cells and investigated the localization of a chimeric CgA-EGFP protein using confocal laser scanning microscopy (CLSM). The fluorescent signal of CgA-EGFP was distributed granularly in the cytoplasm. An immunocytochemical study using anti-CgA antibody with a quantum dot (Qd)525 shows colocalization of fluorescent signal of chimeric CgA-EGFP and CgA-Qd525 signals in granular structures, particularly at the periphery of the cytoplasm. We interpreted granules that were immunoreactive to CgA in electron micrographs as secretory. Spectral analysis of EGFP fluorescence revealed distinct EGFP signals without CgA colocalization. This is the first report to show that a granular structure can be induced by transfecting the EGFP-tagged human CgA gene into non-NE cells. The EGFP-tagged CgA gene could be a useful tool to investigate processes of the regulatory pathway. A more precise analysis of the fluorescence signal of EGFP by combination with the Qd system or by spectral analysis with CLSM can provide insight into biological phenomena.

Secretory granule biogenesis in sympathoadrenal cells: identification of a granulogenic determinant in the secretory prohormone chromogranin A

Chromogranin A (CgA) may be critical for secretory granule biogenesis in sympathoadrenal cells. We found that silencing the expression of CgA reduced the number of secretory granules in normal sympathoadrenal cells (PC12), and we therefore questioned whether a discrete domain of CgA might promote the formation of a regulated secretory pathway in variant sympathoadrenal cells (A35C) devoid of such a phenotype. The secretory granule-forming activity of a series of human CgA domains labeled with a hemagglutinin epitope, green fluorescent protein, or embryonic alkaline phosphatase was assessed in A35C cells by deconvolution and electron microscopy and by secretagogue-stimulated release assays. Expression of CgA in A35C cells induced the formation of vesicular organelles throughout the cytoplasm, whereas two constitutive secretory pathway markers accumulated in the Golgi complex. The lysosome-associated membrane protein LGP110 did not co-localize with CgA, consistent with non-lysosomal targeting of the granin in A35C cells. Thus, CgA-expressing A35C cells showed electron-dense granules approximately 180-220 nm in diameter, and secretagogue-stimulated exocytosis of CgA from A35C cells suggested that expression of the granin may be sufficient to restore a regulated secretory pathway and thereby rescue the sorting of other secretory proteins. We show that the formation of vesicular structures destined for regulated exocytosis may be mediated by a determinant located within the CgA N-terminal region (CgA-(1-115), with a necessary contribution of CgA-(40-115)), but not the C-terminal region (CgA-(233-439)) of the protein. We propose that CgA promotes the biogenesis of secretory granules by a mechanism involving a granulogenic determinant located within CgA-(40-115) of the mature protein.

Chromogranin A transcription and gene expression in Folliculostellate (TtT/GF) cells inhibit cell growth

Folliculostellate (FS) cells are present in the anterior pituitary and have important regulatory functions including controlling hormone release from other anterior pituitary cells. FS cells do not usually express neuroendocrine genes such as chromogranin A (CgA). We analyzed transcriptional regulation and gene expression in the TtT/GF FS cell line to better understand the role of FS cells in anterior pituitary function. After transient transfection with a human (h) CgA promoter sequence linked to a luciferase reporter, there was basal level of transcriptional activity, which was two- to fourfold less than that observed in the anterior pituitary neuroendocrine cell lines HP75 and GH3. The transcriptional activity was decreased in all cell lines when a mutant hCgA promoter cyclic AMP response element (CRE) was used for transfection. Sodium butyrate treatment increased the transcriptional activity in all cell lines, but remained two- to fourfold higher in the HP75 and GH3 cell lines than in the TtT/GF cells. Stable transfection of a plasmid expressing bovine (b) CgA in the TtT/GF cells led to inhibition of cell growth as measured by 3H-thymidine incorporation, Ki-67 labeling index, and growth curve analysis. CgA protein and mRNA could be readily demonstrated in the cloned cells but not in the parental cell line or vector control cells. When the CgA expressing cloned cells were injected into SCID mice, there was a decrease in the rate of tumor growth compared to the vector control in vivo. These results indicate that the TtT/GF FS cells are fibroblast-like compared to the neuroendocrine anterior pituitary secretory cells when analyzed by transcriptional activity with a transiently transfected CgA promoter. In TtT/GF cells with a stably transfected bCgA plasmid, CgA has a direct regulatory effect on tumor cell proliferation.

Different chromogranin immunoreactivity between prion and a-beta amyloid plaque

Brain lesions in Creutzfeldt-Jakob disease (CJD) include spongiform change, neuronal loss, amyloid plaques, astrogliosis and microglial activation. Microglia are thought to play a key role in prion-induced neurodegeneration. However, the intermediate molecules supporting relationships between neurons and microglia are still unknown. Chromogranins (Cg) are soluble glycophosphoproteins that can activate microglial cells leading to a neurotoxic phenotype. The immunoreactive patterns of CgA and CgB were investigated in CJD and compared to those observed in Alzheimer's disease. We found that CgB, but not CgA, immunoreactivity was selectively associated with prion protein deposits, whereas CgA was only seen in Abeta plaques. This suggests a specific influence of the constitutive amyloid protein on chromogranin secretion and a role of CgB in the CJD neurodegenerative process.

Identification of a novel sorting determinant for the regulated pathway in the secretory protein chromogranin A

Chromogranin A (CgA) is the index member of the chromogranin/secretogranin (or 'granin') family of regulated secretory proteins that are ubiquitously distributed in amine- and peptide-containing secretory granules of endocrine, neuroendocrine and neuronal cells. Because of their abundance and such widespread occurrence, granins have often been used as prototype proteins to elucidate mechanisms of protein targeting into dense-core secretory granules. In this study, we used a series of full-length, point mutant or truncated CgA-green fluorescent protein (GFP) chimeras to explore routing of CgA in neuroendocrine PC12 cells. Using sucrose gradient fractionation and 3D deconvolution microscopy to determine the subcellular localization of the GFP chimeras, as well as secretagogue-stimulated release, the present study establishes that a CgA-GFP fusion protein expressed in neuroendocrine PC12 cells is trafficked to the dense core secretory granule and thereby sorted to the regulated pathway for exocytosis. We show that information necessary for such trafficking is contained within the N-terminal but not the C-terminal region of CgA. We find that CgA's conserved N-terminal hydrophobic Cys(17)-Cys(38) loop structure may not be sufficient for sorting of CgA into dense-core secretory granules, nor is its stabilization by a disulfide bond necessary for such sorting. Moreover, our data reveal for the first time that the CgA(77-115) domain of the mature protein may be necessary (though perhaps not sufficient) for trafficking CgA into the regulated pathway of secretion.

Relationship between renal function and blood level of chromogranin A

Chromogranin A (CGA) is a low MW (49,000) acidic hydrophilic protein. It is synthesized in the chromaffm granules of the neuroendocrine cells, and has been found circulating in the blood of healthy subjects. The aim of this study was to assess the relationship between serum levels of CGA and renal function. One hundred two renal patients (45 M and 57 F; age 14-76 years, mean 52) participated in the study. Glomerular filtration rate (GFR) was measured by the bladder cumulative method, using 99mTc-DTPA as a tracer. Blood CGA was determined by RIA. Plasma creatinine, beta2microglobulin (beta2m) and tumor associated trypsin inhibitor (TATI) were also determined. The reduction in renal function was associated with an increase in all of the above studied parameters. In patients with advanced renal failure (GFR <20 mL/min) CGA levels increased by 22-fold as compared to the patients with normal renal function (GFR> 100 mL/min). The other studied parameters were also increased but to a lesser degree, e.g., TATI 14-, beta2m 8- and creatinine 5-fold. The results of this study demonstrate that renal handling of the CGA is similar to other low MW proteins, and it accumulates in the blood in renal failure.

Formation of the catecholamine release-inhibitory peptide catestatin from chromogranin A. Determination of proteolytic cleavage sites in hormone storage granules

The catestatin fragment of chromogranin A is an inhibitor of catecholamine release, but its occurrence in vivo has not yet been verified, nor have its precise cleavage sites been established. Here we found extensive processing of catestatin in chromogranin A, as judged by catestatin radioimmunoassay of size-fractionated chromaffin granules. On mass spectrometry, a major catestatin form was bovine chromogranin A(332-364); identity of the peptide was confirmed by diagnostic Met(346) oxidation. Further analysis revealed two additional forms: bovine chromogranin A(333-364) and A(343-362). Synthetic longer (chromogranin A(332-364)) and shorter (chromogranin A(344-364)) versions of catestatin each inhibited catecholamine release from chromaffin cells, with superior potency for the shorter version (IC(50) approximately 2.01 versus approximately 0.35 microm). Radioimmunoassay demonstrated catestatin release from the regulated secretory pathway in chromaffin cells. Human catestatin was cleaved in pheochromocytoma chromaffin granules, with the major form, human chromogranin A(340-372), bounded by dibasic sites. We conclude that catestatin is cleaved extensively in vivo, and the peptide is released by exocytosis. In chromaffin granules, the major form of catestatin is cleaved at dibasic sites, while smaller carboxyl-terminal forms also occur. Knowledge of cleavage sites of catestatin from chromogranin A may provide a useful starting point in analysis of the relationship between structure and function for this peptide.

Antibacterial and antifungal activities of vasostatin-1, the N-terminal fragment of chromogranin A

Vasostatin-1, the natural N-terminal 1-76 chromogranin A (CGA)-derived fragment in bovine sequence, has been purified from chromaffin secretory granules and identified by sequencing and matrix-assisted laser desorption time-of-flight mass spectrometry. This peptide, which displays antibacterial activity against Gram-positive bacteria at micromolar concentrations, is also able to kill a large variety of filamentous fungi and yeast cells in the 1-10 microM range. We have found that the C-terminal moiety of vasostatin-1 is essential for the antifungal activity, and shorter active peptides have been synthesized. In addition, from the comparison with the activity displayed by related peptides (human recombinant and rat synthetic fragments), we could determine that antibacterial and antifungal activities have different structural requirements. To assess for such activities in vivo, CGA and CGA-derived fragments were identified in secretory material released from human polymorphonuclear neutrophils upon stimulation. Vasostatin-1, which is stored in a large variety of cells (endocrine, neuroendocrine, and neurons) and which is liberated from stimulated chromaffin and immune cells upon stress, may represent a new component active in innate immunity.

Chromogranin A alters ductal morphogenesis and increases deposition of basement membrane components by mammary epithelial cells in vitro

The extracellular function of chromogranin A (CgA), a glycoprotein widely distributed in secretory vesicles of neurons and neuroendocrine cells, has not been clearly established. To examine whether CgA might modulate the biological properties of epithelial cells, we used an in vitro model of ductal morphogenesis in which mammary epithelial (TAC-2) cells are grown in three-dimensional collagen gels. Whereas under control conditions TAC-2 cells formed thin, branched cords with pointed ends, in the presence of CgA they formed thicker cords with bulbous extremities, reminiscent of growing mammary ducts in vivo. Immunofluorescence analysis demonstrated that CgA increases the deposition of three major basement membrane components, i.e., collagen type IV, laminin, and perlecan, around the surface of the duct-like structures. Similar effects were observed with CgA partially digested with endoproteinase Lys-C, suggesting that one or more fragments of CgA are endowed with the same activity. These findings reveal a hitherto unsuspected activity for CgA, i.e., the ability to alter ductal morphogenesis and to promote basement membrane deposition in mammary epithelial cells.

A new human chromogranin A (CgA) immunoradiometric assay involving monoclonal antibodies raised against the unprocessed central domain (145-245)

Chromogranin A (CgA), a major protein of chromaffin granules, has been described as a potential marker for neuroendocrine tumours. Because of an extensive proteolysis which leads to a large heterogeneity of circulating fragments, its presence in blood has been assessed in most cases either by competitive immunoassays or with polyclonal antibodies. In the present study, 24 monoclonal antibodies were raised against native or recombinant human CgA. Their mapping with proteolytic peptides showed that they defined eight distinct epitopic groups which spanned two-thirds of the C-terminal part of human CgA. All monoclonal antibodies were tested by pair and compared with a reference radioimmunoassay (RIA) involving CGS06, one of the monoclonal antibodies against the 198-245 sequence. It appears that CgA C-terminal end seems to be highly affected by proteolysis and the association of C-terminal and median-part monoclonal antibodies is inadequate for total CgA assessment. Our new immunoradiometric assay involves two monoclonal antibodies, whose contiguous epitopes lie within the median 145-245 sequence. This assay allows a sensitive detection of total human CgA and correlates well with RIA because dibasic cleavage sites present in the central domain do not seem to be affected by degradation. It has been proved to be efficient in measuring CgA levels in patients with neuroendocrine tumours.

Chromogranin A induces a neurotoxic phenotype in brain microglial cells

Chromogranin A (CGA) belongs to a multifunctional protein family widely distributed in secretory vesicles in neurons and neuroendocrine cells. Within the brain, CGA is localized in neurodegenerative areas associated with reactive microglia. By using cultured rodent microglia, we recently described that CGA induces an activated phenotype and the generation of nitric oxide. These findings led us to examine whether CGA might affect neuronal survival, expression of neurofilaments, and high affinity gamma-aminobutyric acid uptake in neurons cultured in the presence or absence of microglial cells. We found that CGA was unable to exert a direct toxic effect on neurons but provoked neuronal injury and degeneration in the presence of microglial cells. These effects were observed with natural and recombinant CGA and with a recombinant N-terminal fragment corresponding to residues 1-78. CGA stimulated microglial cells to secrete heat-stable diffusible neurotoxic agents. CGA also induced a marked accumulation of nitric oxide and tumor necrosis factor-alpha by microglia, but we could not establish a direct correlation between the levels of nitric oxide and tumor necrosis factor-alpha and the neuronal damage. The possibility that CGA represents an endogenous factor that triggers the microglial responses responsible for the pathogenesis of neuronal degeneration is discussed.

Production and structure characterisation of recombinant chromogranin A N-terminal fragments (vasostatins) -- evidence of dimer-monomer equilibria

Vasostatins (VS) are vasoinhibitory peptides derived from the N-terminal domain of chromogranin A, a secretory protein present in the electron-dense granules of many neuroendocrine cells. In this work we describe a method for the production in Escherichia coli of large amounts of recombinant vasostatins, corresponding to chromogranin A residues 1-78 (VS-1), and 1-115 (VS-2), and the use of these materials for structure characterisation. The masses of both products were close to the expected values, by SDS/PAGE and mass spectrometry analysis. However, their hydrodynamic behaviours in size-exclusion chromatography corresponded to that of proteins with a larger size. SDS/PAGE analysis of VS-1 and VS-2 after cross-linking with disuccinimidyl suberate indicated that both polypeptides form dimers. VS-2 was almost entirely dimeric at > 4 microM, but rapidly converted to monomer after dilution to 70 nM. The rapid dimer-monomer transition of VS-2 after dilution could be part of a mechanism for regulating its activity and localising its action. Immunological studies of VS-1 have shown that residues 37-70 constitute a highly antigenic region characterised by an abundance of linear epitopes efficiently mimicked by synthetic peptides. The recombinant products and the immunological reagents developed in this work could be valuable tools for further investigating the structure and the function of chromogranin A and its fragments.

Isolation and identification of intact chromogranin A and two N-terminal processing products, vasostatin I and II, from bovine adrenal medulla chromaffin granules by chromatographic and mass spectrometric methods

Chromogranin A (CGA) is the most abundant protein of the bovine adrenal medulla and plays an important role as precursor protein of several peptides that act as modulators for endocrine cell secretory activity. Furthermore, it is presumed to play a role in the targeting of peptide hormones and neurotransmitters to granules of the regulated pathway. However, its complete primary structure and proteolytic processing have not yet been identified. This study describes a rapid and efficient procedure for the high yield isolation of bovine CGA and its N-terminal processing products, vasostatin I and II. Using the lysate from bovine adrenal medulla chromaffin granules, the soluble proteins were purified by three consecutive HPLC steps, thereby avoiding the use of buffer solutions. The protein fractions were isolated and characterized by SDS-PAGE and Western blot analysis as well as by mass spectrometry. In the latter analysis, the efficiency of matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) was demonstrated, enabling the unequivocal and sensitive characterization of proteins from crude mixtures. Sufficient amounts of pure protein were obtained by the present procedure to form the basis for detailed structural studies by spectroscopic methods and X-ray crystallography.

Human pheochromocytoma: different patterns of catecholamines and chromogranins in the intact tumour, urine and serum in clinically unsuspected cases

Clinically unsuspected pheochromocytoma is usually discovered either at autopsy or during surgical intervention for unrelated conditions, despite often enormous neoplastic masses producing and storing catecholamine (CA). In order to assess whether these tumours share some common features we have compiled data for six patients admitted to hospital without previous diagnosis of their pheochromocytoma. The clinical variables and the morphological and immunohistochemical characteristics of the tumours revealed that these cases represented quite different expressions of adrenomedullary neoplasms. They differed not only with respect to nuclear ploidity and overall cytoplasmic morphology but also in catecholamine storage and expression of immunoreactive chromogranin A sequences in the intact tissue. In two of the patients hypertension had been overlooked as a diagnostic indicator of their CA-producing tumours. There was no clear relationship between the mean arterial pressure, the tumour content of CA and the serum levels of CA. Processed chromogranin A dominated in the serum of the two hypertensive cases. The 24-h urine values of CA and its main metabolite (vanillin mandelic acid) were, together with the serum values of chromogranin A and B, proportional to tumour mass and provided the most reliable diagnostic indicators for the non-hypertensive as well as the hypertensive cases.

Chromogranin A triggers a phenotypic transformation and the generation of nitric oxide in brain microglial cells

Chromogranin A is an ubiquitous 48,000 mol. wt secretory protein stored and released from many neuroendocrine cells and neurons. In human brain, chromogranin A is a common feature of regions that are known to be affected by various neurodegenerative pathologies such as Alzheimer's, Parkinson's and Pick's diseases. Brain degenerative areas are generally infiltrated by activated microglial cells, the resident macrophage cell population within the central nervous system. Here, we report that both recombinant human chromogranin A and chromogranin A purified from bovine chromaffin granules trigger drastic morphological changes in rat microglial cells maintained in culture. Microglial cells exposed to chromogranin A adopted a flattened amoeboid shape and, this change was associated with an accumulation of actin in the subplasmalemmal region, as observed by immunocytochemistry and confocal laser microscopy. In single microglial cells loaded with indo-1, chromogranin A elicited a rapid and transient increase in [Ca2+]i which preceded the reorganization of actin cytoskeleton. The activity of nitric oxide synthase was estimated by measuring the accumulation of nitrite in the culture medium. Both recombinant human chromogranin A and bovine chromogranin A triggered an important accumulation of nitrite comparable to that induced by lipopolysaccharide, a well-known activator of microglia. The effect of chromogranin A was dose dependent, inhibited by N omega-nitro-L-arginine methyl ester, a competitive inhibitor of nitric oxide synthase, and by cycloheximide, an inhibitor of protein synthesis. These findings suggest that chromogranin A induces an activated phenotype of microglia, and thus may have a role in the pathogenesis of neuronal degeneration in the brain.