Chromogranin A: Its Role in Endocrine Function and As an Endocrine and Neuroendocrine Tumor Marker*

Home , Chromogranin A

0163-769X/91/1202-0181$03.00/0 Endocrine Reviews Vol. 12, No. 2 Copyright <$ 1991 by The Endocrine Society Printed in U.S.A.

Chromogranin A: Its Role in Endocrine Function and as an Endocrine and Neuroendocrine Tumor Marker*

L. J. DEFTOS Department of Medicine, University of California San Diego and the San Diego Veterans Administration

Medical Center, La Jolla, California 92161 Downloaded from https://academic.oup.com/edrv/article/12/2/181/2548640 by guest on 27 September 2021

I. Introduction low isoelectric points. The abundance of acidic amino acid residues results in an anomalous electrophoretic HROMOGRANIN A (CgA) is a 49 kilodalton pro- mobility for CgA (3). There is considerable structural tein that is produced exclusively by endocrine and C homology among the CgAs, especially at their amino- neuroendocrine cells (1-3). CgA was originally discovered and carboxy termini (Fig. 1). Each species has a hydro- in the chromaffin granules of the adrenal medulla, hence phobic leader sequence, a 17,38 disulfide bridge, and an its name (1-3). The adrenal gland is the main organ internal homology at residues 250-301 to pancreastatin source of CgA, where it is the major soluble protein of (22). Nine serine sites are conserved in CgA, some of catecholamine secretory granules (2, 4). Furthermore, CgA is found in a variety of endocrine and neuroendo- which are potential sites for cAMP-dependent phos- crine cells and tissues that have electron-dense core phorylation and consequent modification of biological secretory granules and is absent in such tissues that do activity; however, the importance of phosphorylation for not; however, CgA is not present in exocrine cells (1-5). CgA has not been established. An RGD sequence is CgA has also been demonstrated in human neurons and present at residues 43-45 in the bovine, human, and in the central nervous system (1, 5, 6) and is present in porcine species but is not conserved at the same site in submammalian species (7, 8). CgA is costored and cose- rat CgA, although an RGD moiety is present at residues creted with the resident hormones of these secretory 399-401 in this species (Fig. 1). Thus, it is unlikely that granules, such as catecholamines and calcitonin (CT) (9, the RGD moiety has an important membrane binding 10). In these other endocrine sites, as in the adrenal function for CgA, especially since it is primarily a cyto- medulla and thyroid C cells, CgA is in the same secretory solic protein. Sites for glycosylation are present in essen- granule as the associated hormones (9-11). The gene for tially all CgAs, and O-glycosylation produces a protein CgA has been localized to chromosome 14 (12). Although that contains approximately 3-5% carbohydrate (3). All the function of CgA is not known, it can serve as a tissue of the CgAs contain many dibasic residues, potential and serum marker for a variety of endocrine cells and cleavage and peptide processing sites, and seven of these tumors (9-15). Thus, the identification of CgA by im- dibasic sites are conserved in all CgA species (Figs. 1 and munohistology and the measurement of CgA by immu- 2). Processing at these sites can lead to the release of noassay represent new diagnostic tools for the endocri- peptides with unique biological effects, as discussed be- nologist (9, 16). low. Several oligoglutamic regions are present in the CgAs, with conservation at the 220-224 site. Three pu- tative binding domains for calcium have been postulated II. Biochemistry for CgA based on respective homologies to s-100 /3- The amino acid sequence of CgA has been deduced protein, intestinal calcium-binding protein, and rat on- from the nucleotide sequence of the protein in several comodulin (23-27). Although CgA does bind calcium in species, namely human, bovine, porcine, and rat (17-21); vitro, the binding affinity is low compared to other au- CgA is found in fish as well as mammalian endocrine thentic calcium-binding proteins, so the physiological glands (7, 13). All species of CgA are hydrophilic with relevance of this observation is unclear (3,25,26). Never- theless, the presence of multiple potential calcium-bind- Address requests for reprints to: Dr Leonard J. Deftos, Department ing sites in CgA, even though of moderate affinity, may of Medicine, San Diego Veterans Administration Medical Center, 3350 confer significant binding activity to the entire molecule La Jolla Village Drive, San Deigo, California 92161. (3, 27). * Supported by the National Institutes of Health, the National Cancer Institute, and the Department of Veterans Affairs. CgA has been likened to several other high molecular 181 182 DEFTOS Vol. 12, No. 2

CHROMOGRANIN A

-18 +1 hCgA MRSAAVLALLLCAGQVTALPVNSPMNKGDTEVMKCIVEVISDTLSKPSPMPVSQECFETLRGDERILSILRHQNLLKELQDLALQGAKERA HQQKKHSGFEDELSEVLENQSSQAELK bCgA -T SY KPND—P- pCgA I S Q-SY ND rCgA —S-A F- T—-K----VL S P--L—Q—-V QQQQQQQQQQQQQQQQ--QQ F—-PA-KIIG 101 hCgA EAVEEPSSKDVMEKREDSKEAEKS.. GEATDGARPQALPEPMQESKAEGNNQAPGEEEEEEEEATNTHPPASLPSQKYPGPQAEGDSE.GLS. QGLVDREKGLS 200 bCgA -VT--V AA—0 V D-DS--D S-GLGPGP-V-ED APS-A--L P KE— .-P-.--PAS pCgA _GT--A AA—G N... .-A—K—SL--P.XXXEA--.-T--. K-R--A H-..--. P- rCgA D-AS-AP—TV DKGQQDAFEGT-E-P FP--K—SMM--S-S-- -DT-N--QS-T EHGI--TT-G--R—A-QQ-RKA-QEE 201 hCgA AEPGWQAKREEEEEEEEEAEAGEEAVPEEE..GPTVVLNPHPSLGYKEI.RK..GESRSEALAVDGAGKPGAEEAQDPEGKGEQEHSQQKEEEEE.MAVVPQ 300 bCgA --Q-R-TE KW R-K .SP-AAFK-P—-N--TQ-AAP-WPE H KP WA--R-.-—. .--RA-- pCgA —-P-A A-. .G-RSE--DS M--... —. .QAP-M T AR .— -. .T-G— rCgA K-EEEEE-E K-I G-K-..V—-.SSS-FYS—K--KDDD-QS--Q..--N..--T--S--VPS L E-DG-A--GP- 301 hCgA GLFRGGK SGELEQE.EE.RLSKEWEDSKRWSKMDQLAKELTAEKRLEG.. .QEEEED... .NRDSSMKLSrRARAYGFRGPGPQLRRGWRPSSREDSLEAGLPL 400 bCgA V--H— —PK-.. .-.Q A .E—-E... .DP-R-R G L N-Q—V Downloaded from https://academic.oup.com/edrv/article/12/2/181/2548640 by guest on 27 September 2021 pCgA R-PA-.-E—E—NA R Q-...E EEEEEDP-R P L V rCgA —P—GQELERKQQ-E-E-.--R--.R R - — D 401 hCgA QVRGYPEEKKEEEEGSANRRPEDQELESLSAIEAELEKVAHQLQALRRG 439 bCgA EE pCgA ..X—L P—S rCgA ..--DF A FIG. 1. Amino acid sequence of human chromogranin A (hCgA) compared to the bovine (bCgA), porcine (pCgA), and rat (rCgA) forms. Alignments are made to demonstrate homologies. The pancreastatin region for hCgA is residues 250-231. Potential dibasic cleavage sites for hCgA are summarized in Fig. 2. [Adapted from Refs. 17-21.]

(77) (114) (200) (248) (322)(335)(373)(400)(409)(437) V100V 200V V 300 VV V VV V CgA 1-L J-439 PEPTIDE rzi EFFECT

CT 0 + CGRP + 0 0

PTH -

PTHrP

Insulin — FIG. 2. The effect of CgA-derived peptides on the secretion of its coresident peptide hormones. The linear sequence of human CgA is represented along with the location (V) of dibasic sites of potential processing. The effect of the CgA-derived peptides CgA 1-40, CgA 250-301 (pancreastatin sequence), and CgA 403-428 on the secretion of hormones is summarized: +, stimulation of secretion; -, inhibition of secretion; 0, no effect; absence of a symbol indicates that testing was not done. In addition to these data, an inhibition of catecholamine secretion is produced by an unidentified cleavage product of CgA (32), and preliminary work has reported the inhibition of ACTH and somatostatin by CgA-derived peptides (36). [Data from Refs. 32-36.] weight proteins found in neuroendocrine and endocrine Despite these structural similarities among CgA, CgB, tissues and variably named as CgB (Secretogranin I), and CgC, one can only speculate about any functional CgC (Secretogranin II), and 0-granin (3, 28). There is similarities among this group of proteins based on cur- considerable homology between CgA and CgB at their rent evidence (3, 27-29). Many of the structural homol- respective amino-terminal disulfide-bonded loops and at ogies are either weak or not conserved among the various their carboxy termini, as there is between /3-granin and species of the CgAs that have been studied. Although the amino terminus of CgA. CgC also has significant CgA, CgB, and CgC have some common tissue and cell- homologies to the carboxy-terminal sequences of CgA ular locations, CgA has the widest tissue distribution and and CgB, but CgC lacks cysteine residues (28). The significance of these sequence homologies is generally is present in some cells that do not express CgB and CgC unknown, although it has been postulated that, like (3, 28). Furthermore, these other chromogranins acquire pancreastatin, discussed later, /?-granin is a cleavage posttranslational modifications, such as tyrosine sulfa- product of CgA (3, 29). In fact, CgA, CgB, and CgC each tion, that are not present in CgA (3). Nevertheless, there contain multiple dibasic residues that are potential sites are enough common features among these molecules to for proteolytic processing to smaller peptides (3, 17-21). postulate that they are members of a family (3, 27). This May, 1991 CHROMOGRANIN A 183 view is further supported by the presence of these pro- (3, 30). Support for this view regarding the functional teins in the same secretory vesicles in some tissues (3). implications of this property of CgA has come from The most consistent and striking homology among the several observations. CgAs is the presence of a large number of dibasic sites In the bovine adrenal, proteolytic cleavage of native for potential cleavage and processing, ranging up to 10 CgA has been reported to inhibit the secretion of cate- in the human species (17-21). The number of dibasic cholamines, whereas the native molecule itself has no sites far exceeds that observed for any other family of such effect (32). This was one of the first observations proteins (Figs. 1 and 2). This observation, along with the to suggest that processing of CgA was necessary before conservation of seven of these dibasic sites, is consistent it exerted biological effects. In the pancreas, the peptide with one of the most widely articulated and studied pancreastatin, the structure of which is compatible with hypotheses regarding CgA's function, i.e. that it is a proteolytic processing of CgA at residues 250-301, inhibits the secretion of insulin (20, 22). The pancreastatin precursor molecule for biologically active peptides, as Downloaded from https://academic.oup.com/edrv/article/12/2/181/2548640 by guest on 27 September 2021 discussed below. sequence is conserved among the various CgA species (Figs. 1 and 2). In addition to its inhibitory effects on insulin secretion, pancreastatin has also been reported III. Function to inhibit the secretion of PTH (33). Furthermore, CgA- Although the biological role of CgA is not known, derived peptides variably modulate the secretion of cal- theories regarding its function have been derived from citonin (CT)-gene products and PTH-related protein studies of its structure and secretion (Table 1). Thus, (PTHrP). Specifically, the amino-terminal peptide of CgA has been postulated to be a calcium-binding protein CgA, CgA 1-40, stimulates the secretion of CGRP (CT- because of its homologies with other calcium-binding gene related-peptide) and inhibits the secretion of proteins and to participate in the exocytotic secretory PTHrP and CT; both effects occur in a dose-dependent manner (34, 35). These studies demonstrate a secretory process because of its association with other hormones effect of CgA-derived peptides on all of the calcium- (1-5). None of these hypotheses has received conclusive regulating peptide hormones; furthermore, there is a experimental support. The most compelling hypothesis differential effect on two of the products of the CT gene, to date regarding the biological function of CgA is that CT itself and CGRP (Fig. 3). Preliminary studies report it is a precursor molecule for biologically active peptides. an inhibition of CgA-derived peptides on the secretion Similar to POMC, CgA may be processed in a tissue- of ACTH and somatostatin (36). Although analogies can specific manner at its dibasic sites to peptides that have be drawn between proteolytic processing of POMC and distinct biological properties. Such tissue-specific pro- CgA, little is known about the enzymes that might proc- cessing has been observed for CgA, and distinct forms of ess CgA. Furthermore, little distinction has been noted the molecule thought to represent processed peptides between CgA processing in normal and malignant tissue. have been demonstrated among different endocrine cell It is the aggregate of these observations that has led types (30, 31). The processing seems to occur primarily to the hypothesis that CgA is processed by its resident at the amino- and carboxy-terminal sites of the molecule, endocrine glands to biologically active peptides that reg- the regions most highly conserved among the CgA species ulate the function of those glands (Fig. 2). This hypothesis is supported by these studies of the effects on cores- TABLE 1. Postulated functions of CgA ident hormone secretion of CgA peptides derived from the most conserved regions of the protein. However, it is I. Regulation of secretory granule function A. Stabilize secretory granule important to note that secretion has been defined in 1. Buffering hydrogen ions most of these studies as release of CgA by cells or tissue 2. Binding calcium and ATP into culture medium; other mechanisms of regulation 3. Binding coresident hormones have not yet been investigated and may exist. Neverthe- 4. Osmotic regulation less, these data support a paracrine function for CgA at B. Modulate secretion of coresident hormones these tissues sites. Second, there is also evidence that 1. Regulate calcium fluxes CgA-related peptides are present in the peripheral cir- 2. Regulate packaging and processing of the hormones culation and thus, an endocrine role for them is also 3. Regulate peptide-processing enzymes II. Regulation of secretion of coresident hormones possible (9, 37). Third, a role for CgA in the secretory A. Chaperone hormones through the secretory pathway process could also constitute an autocrine or intracrine B. Target hormones to intracellular compartments function for the protein (38). C. Exert these actions through derived peptides III. Precursor of biologically active peptides with: IV. Clinical Utility A. Endocrine function B. Paracrine function A. Immunohistology C. Autocrine function Even though the biological function of CgA has not D. Intracrine function been established, its clinical value as a marker for en- 184 DEFTOS Vol. 12, No. 2

FlG. 3. Top, Inhibition of phorbol-stimulated PTHrP secretion i by CgA 1-40. PTHrP was measured after overnight incubations with CgA peptides and phorbol-12-myristate-13-acetate in the BEN neuroendocrine cell line (36). The open columns represent the phorbol (10 nM)-stimulated PTHrP concentration, and the hatched columns represent basal PTHrP (means ± SE). Significant (P < 0.05) inhibition was achieved by 10~8 M CgA 1-40. Bottom, T CgA 1-40 inhibits the secretion of phorbol-stimulated (100 nM) CT {left) and stimulates the secretion of CGRP (right). CT and

CGRP were measured after 18 h incubations (the same cells as Downloaded from https://academic.oup.com/edrv/article/12/2/181/2548640 by guest on 27 September 2021 above) with CgA 1-40 and phorbol. The open columns represent the phorbol-stimulated concentrations, and the hatched columns represent the basal concentrations of CT and CGRP (means ± SE). CgA 1-40 produced a decline in phorbol-stimulated CT concentration that reached significance (P < 0.05) at 10~8 M and an increase in basal CGRP concentration that reached significance (P < 0.05) at a concentration of 10~9 M. [Data from Refs. 35 and 36.1

LOG CgA 1-40

docrine and neuroendocrine tumors is becoming well- distinction between a neuroendocrine and nonneuroen- established (9) (Table 2). In tissue studies, immunohis- docrine tumor can have implications for chemotherapy tological procedures for CgA help to identify the endo- (39). Furthermore, classical endocrine tumors that are crine and neuroendocrine nature of tumors. This can be hormone negative can sometimes be identified by their useful where such assignment can be clinically impor- CgA content (40,41). However, CgA is absent in exocrine tant, as in some types of lung cancer in which the glands and in some tumors with neuroendocrine elements such as melanoma. It should be noted that the presence TABLE 2. Endocrine and neuroendocrine tumors in which CgA is of CgA in endocrine and neuroendocrine tumors gener- marker for the neoplasia ally correlates with its presence in the corresponding normal endocrine tissues and cells (3, 16, 42). CgA has Pheochromocytoma Lung cancers Medullary thyroid carcinoma Small cell also been detected in some tumors that are not clearly Parathyroid neoplasia Non-small cell endocrine or neuroendocrine, such as certain breast can- Adenoma Small cell tumors cers, uterine cancers, and stomach adenocarcinomas (3). Hyperplasia Lung These latter observations are difficult to evaluate be- Carcinoma Prostate cause of their rarity and because of the technical prob- Anterior pituitary tumors Uterus Pancreaticoduodenal tumors Bladder lems that can confound immunochemical studies. Islet cell carcinoma Carcinoid tumors Insulinoma Stomach B. Immunoassay Gastrinoma Small intestine Somatostatinoma Large intestine In addition to immunohistological procedures, immu- Vipoma Lung Glucagonoma Middle ear noassay procedures have been developed for CgA (9, 37, Neural tumors Ovary 39-41, 43, 44). These assays utilize either human or Neuroblastoma Prostate bovine CgA as tracer and standards. Both polyclonal- Paraganglioma Thymus and monoclonal-based procedures have been developed Ganglioneuroblastoma Liver and, consistent with the structural similarities between Ganglioneuroma Aortic body tumors Medulloblastoma Merkel cell tumors these two forms of CgA, there is considerable cross- Hormone-negative tumors reactivity of antibodies to human and bovine CgA (1, 3). Pituitary adenomas Most immunochemical systems identify multiple size Islet cell carcinomas forms of CgA in tissue and serum (9, 31). These obser- Medullary thyroid carcinoma vations are consistent with cellular processing of CgA, May, 1991 CHROMOGRANIN A 185 although degradation of the hormone, especially in serum CgA and catecholamines, with variation in the serum, may also account for some of these size forms (9, latter accounting for only 15% of the former (1, 5, 43, 37). These theoretical considerations notwithstanding, 45). In the basal state, there is little if any correlation the practical import of the immunochemical heteroge- between catecholamines and CgA, and it is likely that neity of CgA is the need for each immunoassay system other tissue sources, along with the sympathochromaffin to have its own well defined normal range. Existing assay system, account for circulating levels of CgA under these systems are sufficiently sensitive to measure CgA in circumstances (9, 43, 45). Furthermore, the correlation normal subjects (9, 37, 39, 43, 44). For most CgA-pro- between plasma CgA and catecholamines may not be ducing tumors, the circulating CgA levels are well above precise because of the presence, at least in some experi- the corresponding normal ranges, and false-positives and mental animals, of a lymphatic (thoracic duct) transport false-negatives do not appear to be common problems system for CgA (49).

(9). However, in patients with renal failure, CgA may be Because of these characteristics of CgA production, Downloaded from https://academic.oup.com/edrv/article/12/2/181/2548640 by guest on 27 September 2021 spuriously elevated as is the case with many immunoas- increases in serum CgA greater than 2-fold above normal sayable substances (9, 37). This phenomenon represents usually mean overproduction of the protein by one of its the most common false-positive measurement of CgA. tissue sources. This forms the basis of CgA's role as a Even under intense sympatheticoadrenal stimulation, serum marker for endocrine tumors (9, 38-40, 44, 47). serum CgA levels do not increase more than 2-fold However, it should be reemphasized that, as is true with whereas the levels associated with tumors are usually many secreted products, CgA can be increased in renal markedly increased above normal (9, 43-46). There do failure because of its retention in serum (37). This can not appear to be any correlations between tumor type confound immunoassay analysis in the patient with renal and serum CgA concentrations (9). However, within a disease. Within these limitations, serum measurements tumor type, there is a correlation between tumor burden of CgA are useful for the clinical management of patients and serum CgA (47, 48). No methods other than immu- with endocrine tumors in several circumstances. nochemical have been reported for the measurement of CgA. Although not yet widely available, CgA immunoas- C. Diagnostic applications says are now performed by several laboratories, and commercial availability should increase (9, 39, 44, 47). 1. Tumors with known secretory products. CgA is a serum In serum studies in which CgA measurements by im- marker for many tumors of endocrine and neuroendo- munoassay are helpful in endocrine tumor diagnosis, it crine tissues that secrete the protein (Table 2). These is important to note that a variety of tissue sources may include classical endocrine tissues such as pheochromo- contribute to circulating CgA levels (9, 43, 45). Thus, cytoma, a tumor of CgA-producing cells, and tumors of whereas the adrenal medulla is the major organ source the diffuse neuroendocrine system, such as small cell of serum CgA normally, near normal levels of the protein lung cancer (9, 39). For pituitary tumors, CgA has been circulate in adrenalectomized subjects (45). In the adre- coidentified with the cell types that produce ACTH, GH, nal medulla, CgA secretion is specific for the exocytotic and FSH, LH, and TSH (3, 41, 50). By contrast most process (1). Thus, the release of catecholamines by a studies have not demonstrated CgA in prolactinomas, nonexocytotic process is not accompanied by an increase whereas some null cell pituitary tumors have been dem- in serum CgA levels. During intense activation of the onstrated to contain and secrete CgA (41, 50). These sympathochromaffin system, plasma CgA levels come observations generally correspond to the location of CgA primarily from the exocytotic release, along with epi- in normal pituitary cells. In pancreatic tumors, CgA has nephrine and norepinephrine, of chromaffin cells in the been demonstrated in essentially all hormone-producing adrenal medulla and from sympathetic postganglionic cell types, although less consistently in pancreatic poly- neurons (43-46). Intense stimulation of the adrenal me- peptide cells, again consonant with its distribution in dulla by, for example, hypoglycemia induced by insulin, normal pancreatic cells (3,42). However, in patients with or of the sympathetic nerves by, for example, vigorous gastrinomas, the increased CgA activity may come from exercise, will increase plasma CgA along with serum the tumor or from gastrin-stimulated neuroendocrine catecholamines (45). Adreno-medullary stimulation cells (enterochromaffin cells) in the vicinity of the tumor causes a much higher increase than sympathetic neu- (51). CgA has also been reported in tumor and serum of ronal stimulation, consistent with the higher concentra- apparently nonfunctioning islet cell carcinomas (40). tion of CgA in the adrenal medulla than in sympathetic Many of these CgA-producing tumors are not classical axons (1, 45). Serum CgA correlates with norepinephrine endocrine tumors but share a neural crest origin or have during sympathetic stimulation and with epinephrine neuroendocrine characteristics (3, 52). For example, during adreno-medullary stimulation (45, 46). Under less small cell lung cancers and enterochromaffin intestinal intense stimulation, there is less correlation between tumors can produce and secrete CgA (39, 53). Addition- 186 DEFTOS Vol. 12, No. 2 ally, it is notable that most of the tumors involved in the serum may provide another index of the activity of that multiple endocrine neoplastic disorders, namely adrenal, endocrine cell type (30-33). pancreas, parathyroid, pituitary, and thyroidal C cell, can be marked by abnormal CgA production (9, 10, 40, V. Summary 47,53). For one of the signal hormones of these disorders, CgA is a 49 kilodalton protein that is present in the CT, there is a general association between its secretory secretory granules of most endocrine and many neuroen- regulation and that of CgA (54). However, there can be docrine cells. Detection of CgA in cells by immunocyto- dissociation of secretion of CgA and its coresident hor- chemistry and measurement of CgA in serum by immu- mones (3, 55). Thus, reliable provocative tests for CgA noassay can serve as tissue and serum markers for CgA- secretion have not yet been developed for CgA-producing producing tumors. CgA is of diagnostic value in classical tumors (3, 9). endocrine tumors, in hormone-negative tumors, and in 2. Tumors with no or unknown secretory products. Al- endocrine tumors in which other diagnostic procedures Downloaded from https://academic.oup.com/edrv/article/12/2/181/2548640 by guest on 27 September 2021 though the classical identifying feature of endocrine tu- have their limitations. Although the biological function mors is production of their resident hormones, a small of CgA is yet unknown, it may serve as a precursor but significant percentage of such tumors is hormone- molecule, like POMC, for a family of biologically active negative in that they either do not produce a hormone peptides (3, 44). CgA is an important new tool for the or the methods used to study the tumors fail to identify endocrinologist in the diagnosis and management of any hormonal product (40). Perhaps one of the more patients with endocrine and neuroendocrine tumors. important clinical uses for CgA is its value in identifying such nonfunctioning endocrine tumors (40, 41, 50). This has now been demonstrated for three types of endocrine Acknowledgments tumors, in which a hormonal product could not be iden- The following individuals contributed to this manuscript: Cheryl tified, but abnormal amounts of CgA could be demon- Chalberg, Kathy Smith, Su Tu, Douglas Burton, Estralita Martin, strated in both tumor and in the patient's blood: med- Debbie Hussong, and Dr. D. T. O'Connor. ullary thyroid carcinoma, pituitary adenoma, and pancreatic islet cell carcinoma (40). It is likely that the list of hormone-negative, CgA-positive endocrine tumors will References increase with wider application of CgA detection in 1. O'Connor DT, Takiyyuddin MA, Parmer RJ, Cervenka JH, Bar- cancer. bosa JA, Hsiao RJ, Chang YM 1990 Sympathoadrenal catecholamine storage and release in man: insights from the study of chromogranin A. In: Brown MB, Hisser C, Korb G (eds) Neurobiology 3. Tumors with secretory products of limiting clinical and Neuroendocrinology of Stress. Marcel Decker, New York, value. For some tumors for which other diagnostic tests Chapter 11, p 217 are available, CgA has additional clinical value. For 2. Angeletti RH 1986 Chromogranins and neuroendocrine secretion. Lab Invest 55:387 example, for neuroblastomas CgA can be more specific 3. Weidenmann B, Huttner WB 1989 Synaptophysin and chromo- and even more sensitive than other procedures such as granins/secretogranins: widespread constitutes of distinct types of neuroendocrine vesicles and new tools in tumor diagnosis. Vir- neuron-specific enolase, and serum CgA has been re- chows Arch [Cell Pathol] 58:95 ported to give a sufficiently accurate assessment of tumor 4. Winkler H, Apps DK, Fischer-Colbrie R 1986 The molecular burden so that therapy for this tumor can be monitored function of adrenal chromaffin granules: established facts and unresolved topics. Neuroscience 18:261 (48). Similarly, serum CgA measurements are useful in 5. O'Connor DT, Parmer RJ, Deftos LJ 1984 Chromogranin A: stud- monitoring the response to therapy of carcinoid tumors, ies in the endocrine system. Trans Assoc Am Physicians 97:242 6. Muiios DG, Kobylinski L, Henry DD, George DH 1990 Chromo- in which 5-hydroxyindolacetic acid measurements can granin-A-like immunoreactivity in the human brain: distribution sometimes be negative and where serum serotonin levels in bulbar medulla and cerebral cortex. Neuroscience 34:533 may not reflect tumor burden (53). In addition, CgA 7. Deftos LJ, Bjornsson BTh, Burton DW, O'Connor DT, Copp DH 1987 Chromogranin is present in and released by fish endocrine measurements are especially useful for those tumors for tissue. Life Sci 40:2133 which there is no reliable and convenient serum test, 8. Davis WL, Schmid KO, Huettner JW, Farmer GR, Jacoby BH, Goodman DBP 1990 Immunolocalization of secretory protein-I or such as nonfunctioning tumors and carcinoid tumors (40, chromogranin A in amphibian urinary bladder granular cell gran- 53). And CgA can serve as a single test for the multiple ules. Cell Biol Int Rep 14:601 endocrine neoplasia syndromes, where it identifies many 9. O'Connor DT, Deftos LJ 1986 Secretion of chromogranin A by peptide-producing endocrine neoplasms. N Engl J Med 493:379 of the tumor components of these disorders (9). The 10. Silver MM, Hearn SA, Lines LD, Troster M 1988 Calcitonin and serum assay for CgA is also useful in pheochromocytomas chromogranin A localization in medullary carcinoma of the thyroid by immunoelectron microscopy. J Histochem Cytochem 46:1031 in which catecholamines do not provide a useful reliable 11. Deftos LJ, Woloszczuk W, Krisch I, Horvat G, Ulrich W, Neuhold serum test (47). Finally, if CgA is processed to peptides N, Braun O, Reiner A, Srikanta S, Krisch K 1988 Medullary thyroid carcinomas express chromogranin A and a novel neuroen- in a tissue-specific manner in endocrine cells and if these docrine protein recognized by monoclonal antibody HISL-19. Am peptides are secreted, their specific measurement in J Med 85:780 May, 1991 CHROMOGRANIN A 187

12. Murray SS, Deaven LL, Burton DW, O'Connor DT, Mellon PL, protein-I) processing, inhibits secretion from porcine parathyroid Deftos LJ 1987 The gene for human chromogranin A is located on cells in culture. Endocrinology 125:1617 chromosome 14. Biochem Biophys Res Commun 142:141 34. Deftos LJ, Hogue-Angeletti R, Chalberg C, Tu S 1989 PTHrP 13. Lloyd RV, Wilson BS 1983 Specific endocrine tissue marker de- secretion is stimulated by calcitonin and inhibited by chromogranin fined by a monoclonal antibody. Science 222:628 A peptides. Endocrinology 125:563 14. Steiner H-J, Weiler R, Ludescher C, Schmid KW, Winkler H 1990 35. Deftos LJ, Hogue-Angeletti R, Chalberg C, Tu S 1991 A chromo- Chromogranins A and B are co-localized with atrial natriuretic granin A-derived peptide differentially regulates the secretion of peptides in secretory granules of rat heart. J Histochem Cytochem calcitonin gene products. J Bone Mineral Res 5:989 38:845 36. 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