Chromogranin a Expression in Normal and Malignant Human Tissues Lee J
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Chromogranin A Expression in Normal and Malignant Human Tissues Lee J. Helman, Adi F. Gazdar, Jae-Gahb Park, Pamela S. Cohen, James D. Cotelingam, and Mark A. Israel Pediatric Branch, Naval Medical Oncology Branch, National Cancer Institute, Bethesda, Maryland 20892; and Department ofPathology, Bethesda Naval Hospital, Bethesda, Maryland 20814 Abstract tion and progressive increases during the first year of life (un- published observations). Immunoreactivity of this 71 -kD We used a recombinant cDNA probe for human chromogranin acidic protein has now been extensively characterized and A to measure the expression of mRNA encoded by this gene in shown to be specifically present in normal and malignant cells a variety of normal human tissues and tumor specimens using of the diffuse neuroendocrine system (3-8). 81% of patients Northern blot and in situ hybridization analysis. With few ex- with neuroendocrine tumors have an elevation in serum cga ceptions, the expression of chromogranin A mRNA appears to levels, and serum cga is now used as a marker for neuroendo- be restricted to normal tissues and tumors of neuroendocrine crine tumors (8). In addition, an elevation in serum cga levels lineage. However, we have detected mRNA expression of this may be a useful marker for small cell lung carcinoma disease gene in 1 of 14 cell lines and 2 of 13 tumor specimens of colon activity (9). In this study, we have used nucleic acid hybridiza- adenocarcinoma. The finding of chromogranin A expression in tion analysis to characterize the expression of cga in a variety some colon carcinomas suggests that a previously unrecog- of human tissues and we have identified a number of adeno- nized subgroup of these tumors has neuroendocrine features. carcinomas ofthe colon that unexpectedly express cga. The detection of this subgroup demonstrates the potential for improving tumor classification through the use of techniques and reagents developed by recombinant DNA technology. Methods Northern blot analysis. Total RNA was extracted from human tissues Introduction and cell lines using guanidine thiocyanate (10), and RNA concentra- tion was determined by ultraviolet spectroscopy at 260 nm. Northern Molecular genetics affords the opportunity to examine tissue blot analysis was performed as previously described (11). Briefly, specimens in a uniquely specific manner at the level of either 10-30 uig oftotal RNA was size fractionated on 1% agarose/formalde- gene structure or RNA expression. Furthermore, such evalua- hyde gels. The positions of the 28S and 18S ribosomal RNA were tions do not require either an antibody or a functional assay determined by ultraviolet irradiation ofethidium bromide stained gels, for the protein product of the gene that is being studied. The and the RNA was then transferred to Nytran (Schleicher & Schuell ability to examine human tumors in this manner may both Inc., Keene, NH). The membrane was hybridized according to the permit the subclassification of tumors into increasingly spe- manufacturer's recommendations. To confirm that all lanes contained cific disease entities as well as give insight into the molecular intact RNA at the expected concentration, the blots were stripped in We to evaluate 50% formamide/l X standard saline citrate (SSC) (1X SSC = 0.15 M mechanisms underlying tumorigenesis. sought sodium chloride/0.015 M sodium citrate) and rehybridized to an in the application ofmolecular analysis to tumor classification by vitro isotopically labeled actin probe (12) (data not shown). examining various tissues for the expression of chromogranin In situ hybridization studies. In situ hybridization was performed A (cga),' a marker for tissues with neuroendocrine features. To as previously described (13, 14) with the following modifications. Cul- measure cga RNA expression in normal and malignant human tured cells or adrenal tissue sections (8 Mum diam) were placed on tissues, we used a molecular probe that recognizes the mRNA polylysine-coated silanated slides, which were activated by treatment that encodes cga in Northern blot and in situ hybridization with 2.5% glutaraldehyde and 0.1 M sodium periodate (15). After analyses. fixation with periodate-lysine-paraformaldehyde-glutaraldehyde and Cga was originally isolated as the major secretory protein digestion with 0.2 N HCl and 10 Ag/ml proteinase K, samples were of adrenal medulla chromaffin granules and accounts for acetylated as previously described (16), and prehybridized in 50% about one half of the soluble protein content within the gran- formamide, 2X SSC, 50 mM Tris pH 7.4, 1 mM EDTA, 0.02% Ficoll, 0.02% polyvinylpyrrolidone, 1 mg/ml BSA, and 33 Mg/ml yeast tRNA ules (1). While the precise function of cga is unknown, recent at 650C for 3 h. Samples were hybridized at 650C for 16 h in 12 M1 data suggest that it may play a critical role in the maturation of reaction mixtures containing 50% formamide, 10% dextran, 50 mM secretory granules (2). In addition, the expression of this pro- Tris pH 7.4, 1 mM EDTA, IX Denhardt's, 10 nM DTT, 500 Mg/ml tein appears to be developmentally regulated in human chro- yeast tRNA, 500 Mg/ml sheared salmon sperm DNA and 5 X 1O' cpm maffin tissue with levels being first detected at 8 wk of gesta- IIS-labeled cga RNA. Slides were washed once briefly in 2X SSC at 20'C, once in 50% formamide, 2X SSC at 20C for 15 min, three times in 2X SSC, 0.1% SDS at 650C for 15 min, and once at 370C in 0.3 M Address all correspondence to Dr. Helman, Pediatric Branch, National NaCl, 10 mM Tris pH 7.4 containing 40 Mg/ml RNase A and 5 Mg/ml Cancer Institute, Building 10, Room 13N240, Bethesda, MD 20892. RNase TI. These washes were followed by 15 min washes first in 2X Received for publication 13 August 1987 and in revised form I SSC and 0.1X SDS, and then in 0.lX SSC and, 0.1% SDS at 650C. March 1988. Slides were then dehydrated through graded alcohols. Autoradiogra- phy was performed as previously described (13, 14), and slides were 1. Abbreviations used in this paper: cga, chromogranin A. stained with hematoxylin and eosin by standard techniques. Probes. A 2.1-kb Pst I fragment containing the entire coding se- The Journal of Clinipal Investigation, Inc. quence for human cga cloned into pUC9, pHCGA, was used in Volume 82, August 1988, 686-690 Northern blot hybridizations (Helman, L. J., T. G. Ahn, M. A. Levine, 686 Helman, Gazdar, Park, Cohen, Cotelingam, and Israel A. Allison, P. S. Cohen, M. J. Cooper, D. V. Cohn, and M. A. Israel, ficity of hybridization to adrenal medullary cells. A Northern manuscript submitted for publication). The plasmid was in vitro la- blot analysis of adrenal gland tissues (Fig. 2) confirms this beled with DNA polymerase using [32P]dCTP to a specific activity of pattern of reactivity, which demonstrates the presence of cga > 1 X 108 cpm/,gg. mRNA in the adrenal medulla but not in the adrenal cortex. A Hind III/Eco RI fragment of pHCGA containing the entire 2.1- Northern blot analysis of tumor specimens for cga expres- kb Pst I fragment was subcloned into pGEM3 (Promega Biotec, Madi- the presence of the 2.1-kb chromogranin son, WI). RNA was prepared using T7 polymerase according to the sion demonstrates manufacturer's recommendations (Promega Biotec) using a Pvu II-di- message in representative neuroendocrine tumors (Fig. 3, gested template yielding a 500 bp RNA fragment that was labeled with lanes 3, 7, 8, and 13) but not in carcinomas, sarcomas, and 35S-UTP to a specific activity of I09 cpm/gg and then it was used as a lymphoid tumors (Fig. 3, lanes 1, 2, 4-6, 9-12). Tables I and II molecular probe for in situ hybridization. summarize our Northern blot evaluation of cga expression in 111 human tissues and demonstrates that expression of this Results gene can be detected in normal neuroendocrine tissues and neuroendocrine tumors but not in normal nonneuroendocrine Distribution of cga expression in normal and malignant tissues or most nonneuroendocrine tumors. The experiments human tissue and cell lines. To demonstrate the specificity of reported in Table II indicate that the expression ofcga message hybridization analysis for the characterization of cga expres- in cell lines is concordant with the pattern ofexpression seen in sion in neuroendocrine cells, we examined the pattern of cga fresh normal tissues and tumor specimens. Each human neu- expression in human adrenal glands using in situ hybridiza- roendocrine tumor cell line examined expressed high levels of tion. As shown in Fig. 1, a hybridization signal identifying the cga. With a single exception, tumor cell lines from sarcomas, presence ofcga mRNA is found exclusively in the neuroendo- carcinomas, lymphomas, and gliomas do not express detect- crine adrenal medulla and not in the endocrine adrenal cortex. able levels of this gene. A of this figure shows a bright field examination in which the The observation of cga expression in this exception, a hybridization signal appears as dark grains that are readily colon carcinoma cell line, complements the data in Table 1, visible only at higher magnification (see below). B shows the which indicates that 2 out of 13 colon adenocarcinoma tumor identical section of adrenal gland in dark field, which demon- specimens also express cga. Fig. 4 A shows a Northern blot that strates the hybridization of the cDNA probe to the central demonstrates the 2.1-kb cga mRNA in a colon adenocarci- adrenal medulla while the surrounding cortex shows no hy- noma tumor specimen (lane 7). While the level of expression bridization. C shows a close-up bright field of the framed area in the tumor is clearly less than the level ofexpression seen in a from A in which the junction between the adrenal cortex and pheochromocytoma tumor specimen (lane 1), it is easily dis- the central adrenal medulla is shown to demonstrate the speci- tinguishable from the six other colon adenocarcinomas exam- Figure 1.