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Research Notes: Genes - Secretogranin II (Chromogranin C, SCG2)
Biol Rev Camb Philos Soc. 2004 Nov. The chromogranins A (CgA) and B (CgB) and secretogranin II (SgII) constitute the main members of a family of uniquely acidic secretory proteins in elements of the diffuse neuroendocrine system. These genetically distinct proteins, CgA, CgB, SgII and the less well known secretogranins III-VII are collectively referred to as 'granins' and characterised by numerous pairs of basic amino acids as potential cleavage sites for processing by the co-stored prohormone converting enzymes PC 1/3 and PC2. This review is directed towards comparative and functional aspects of the granins with emphasis on their phylogenetically conserved sequences. Recent developments provide ample evidence of widely different effects and targets for the intact granins and their derived peptides, intracellularly in the directed trafficking of storage components during granule maturation and extracellularly in autocrine, paracrine and endocrine interactions. Most of the effects assigned to the granin derived peptides fit into patterns of direct or indirect inhibitory modulations of major functions. So far, peptides derived from CgA (vasostatins, chromacin, pancreastatin, WE-14, catestatin and parastatin), CgB (secretolytin) and SgII (secretoneurin) are the most likely candidates for granin-derived regulatory peptides, of postulated relevance not only for homeostatic processes, but also for tissue assembly and repair, inflammatory responses and the first line of defence against invading microorganisms. Hum Mol Genet. 2003 Oct 15. Although uniparental disomy often results from the postzygotic rescue of a meiotic non-disjunction event, mosaicism is usually confined to the placenta. We describe a girl with Prader-Willi syndrome (PWS) who is mosaic for normal cells and cells with maternal uniparental disomy 15 [upd(15)mat] in blood and skin. Somatic mosaicism was confirmed by cloning and genotyping of skin fibroblasts. X inactivation studies indicated that upd occurred prior to X inactivation. RNA samples from the cloned cells were used in DNA microarray experiments to study the effect of upd(15)mat on the gene expression pattern of fibroblasts. Proof of principle was obtained by detecting several chromosome 15 genes known to be imprinted. We did not obtain any evidence for novel 15q genes showing imprinted expression in fibroblasts. Differentially expressed genes on other chromosomes are candidates for downstream genes regulated by an imprinted gene and may play a role in the pathogenesis of PWS. The finding of strongly reduced mRNA levels in upd(15)mat cells of the gene encoding secretogranin II (SCG2), which is a precursor of the dopamine releasing factor secretoneurin, raises the question whether hyperphagia in patients with PWS might be due to a defect in dopamine-modulated food reward circuits. J Rheumatol. 2000 Oct. OBJECTIVE: Secretoneurin (SN) is a neuropeptide that is chemotactic for mononuclear cells and it has been suggested to be involved in the mediation of pain; there is also evidence that SN is involved in the inflammation process. As secretogranin II (SGII) is the precursor of SN, we investigated expression of SGII mRNA and SN protein in the synovium of patients with rheumatoid arthritis (RA) and osteoarthritis (OA). METHODS: Snap frozen synovial tissue specimens from 12 patients with RA and 11 patients with OA were examined. RNA was isolated and cDNA copied by reverse transcription. The expression of SGII was determined by polymerase chain reaction and in situ hybridization (ISH). SGII expressing cells were compared with CD68 positive cells stained by immunohistochemistry. SN protein was also detected by immunohistochemistry. RESULTS: A 524 bp SGII-specific fragment could be amplified by PCR from the cDNA of all specimens. ISH showed scattered expression of SGII in both RA and OA synovial tissue; its expression pattern was characterized by positive staining for SGII in both the lining and the sublining layer. Immunohistochemical double labeling with anti-CD68 antibodies revealed expression of SGII in CD68 negative, fibroblast-like cells, whereas CD68 positive macrophages did not. In RA and OA, the SGII staining by ISH was positive with a diffuse staining throughout the entire synovial tissue. SN protein expression was scattered in RA but more intense in OA synovium. CONCLUSION: The expression of SGII mRNA in RA and OA synovial fibroblasts clearly supports the hypothesis that SN is involved in the synovial tissue inflammation in both diseases. The significant lower SN expression in RA could be due to an inhibitory mechanism with respect to the SN levels in synovial fluid. SN might be involved in the modulation of afferent nerve transmission and therefore might play a role in the sensation of pain, especially in patients with OA. Virchows Arch. 1994. In the endocrine pancreas, chromogranins A and B as well as secretoneurin (a biologically active peptide processed endoproteolytically from secretogranin II) are most intensely expressed in alpha (glucagon) cells. We examined whether the functional status of neoplastic and nonneoplastic human alpha cells is reflected in the expression patterns of chromogranins/secretogranins. Neoplastic alpha cells were analysed immunocytochemically in six functioning glucagonomas and 37 nonfunctioning neuroendocrine tumours (29 with alpha cells) for their immunoreactivity to chromogranin A and B, as well as secretoneurin. There was no difference in the staining intensity for either peptide between glucagonomas and nonfunctioning, alpha cell containing tumours. Nonneoplastic alpha cells from patients with a functioning glucagonoma showed a decreased glucagon immunoreactivity, whereas the expression of chromogranin A (but not chromogranin B and secretoneurin) was as intense as in alpha cells not associated with glucagonoma syndrome. These results suggest that the expression of chromogranins/secretogranins in neoplastic alpha cells of the pancreas may be independently regulated from the cells' functional status. In nonneoplastic alpha cells there seems to be an association between glucagon production and chromogranin B and secretoneurin expression. Endocrinology. 1992 Jun. The granins are a family of tyrosine-sulfated secretory proteins. Two members of this family, chromogranin-B (CgB) and secretogranin-II (SgII), are found in GH4C1 cells, a pituitary cell line that secretes PRL and GH. We have compared the spontaneous and regulated secretion of CgB and SgII with that of PRL in GH4C1 cells and have assessed the importance of granin sulfation on granin and PRL processing and secretion. CgB and SgII were identified by metabolic labeling with [35S]SO4, which was predominantly incorporated into two bands of 105,000 (CgB) and 84,000 (SgII) mol wt. The secretion of [35S]SgII and [35S]PRL from GH4C1 cells simultaneously labeled with 35S-labeled SO4 and methionine showed similar kinetics over 60 min, suggesting that the two proteins are similarly processed. CgB, SgII, and PRL were released in parallel after 10-min treatment with secretagogues (high K+ and BAY K8644, 8-bromo-cAMP, a phorbol ester, and TRH). Hypertonicity and substitution of chloride with isethionate, which inhibit stimulated PRL release, reduced the amount of CgB and SgII released in response to secretagogues, but not basally. Cells were labeled with [35S]SO4 with or without 10 mM chlorate, which inhibits sulfation by more than 90%, and media and cells were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, autoradiography, and immunoblotting using an antibody directed against the N-terminus of SgII. Chlorate reduced [35S]SO4 labeling of CgB and SgII, but had little effect on immunoreactive SgII in cells or media. Inhibiting sulfation with chlorate did not change the amount of PRL or GH synthesized and secreted by GH4C1 cells, basally or in response to secretagogues, or the induction of PRL storage by insulin, estrogen, and epidermal growth factor. The results show that granins are released from GH4C1 cells in parallel with GH and PRL under basal and stimulated conditions, and that sulfation is not essential for normal packaging and processing of these secretory proteins. The data suggest a model in which PRL, CgB, and SgII are sorted to the regulated pathway and released from this pathway basally as well as under stimulated conditions. From the full text article: The granins are a family of highly acidic proteins found as prominent components of the secretory granules of neuronal and endocrine cells. The granin family comprises chromogranin-A (CgA), chromogranin-B (CgB), secretogranin-II (SgII), as well as other proteins that share similar physicochemical properties and tissue specific expression (1). The granins are found in cells of the anterior pituitary gland, where they have been shown to colocalize with glycoprotein hormones in secretory granules (2). The granins are subject to extensive posttranslational modification including 0-glycosylation, phosphorylation on serine residues, and sulfation on sugars and/or tyrosine residues (3). Both CgB and SgII are sulfated on tyrosine, a posttranslational modification carried out in the trans-Golgi apparatus. Tyrosine sulfation is a rare protein modification found selectively, although not exclusively, on secretory proteins (4). Tyrosine protein sulfotransferase transfers sulfate from 3’-phosphoadenosine 5’-monophosphate to tyrosines. Sequences around sites of tyrosine sulfation are characterized by a high density of acidic residues (5). Sulfation contributes to the overall acidity of the granins and may be important to normal transit and packaging. The granins also contain multiple dibasic sites and are candidates for posttranslational proteolytic cleavage. CgA, CgB, and SgII have all been shown to be processed to smaller mol wt fragments (6-8). Histochemistry. 1986. Antibodies specific for chromogranin A, B or C have been used to detect immunohistochemically these three anionic proteins. Pancreatic A, B and PP cells, gut argentaffin EC, argyrophil ECL and gastrin G cells, thyroid C cells, parathyroid cells, adrenal medullary cells, pituitary TSH, FSH and LH cells as well as some axons of visceral nerves have been found to react with chromogranin A antibodies. Pancreatic A, gut EC and G, adrenal medullary and pituitary cells as well as some gut nerve fibers showed chromogranin B immunoreactivity. Chromogranin C immunoreactivity has been detected in pancreatic A, pyloric D1, intestinal L, thyroid C, adrenal medullary and pituitary cells, as well as in some gut neurons and nerve fibers. No crossreactivity has been found in immunohistochemical tests between chromogranins A, B or C and costored monoamines or peptide hormones/prohormones, from which chromogranins can be separated by selective extraction during fixation. On both morphological and chemical grounds a relationship seems to exist between chromogranin A and Grimelius' argyrophilia. Sialooligosaccharide chains of chromogranin A and, possibly, chromogranins' phosphoserine/phosphothreonine groups, seem to interact with guanidyl, amino, and/or imidazole groups of non-chromogranin components to form silver complexing sites accounting for granules' argyrophilia, which can be removed or blocked without affecting chromogranin immunoreactivities. The abundant anionic groups of the three proteins should contribute substantially to granules' basophilia, the partly "masked" pattern of which supports the existence of a close interaction of such groups with other components of secretory granules, including monoamines and peptide hormones or prohormones. Chromogranins could play a rôle in hormone postranslational biosynthesis and intragranular packaging. |