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Human Cancer Biology |
Authors' Affiliations: 1 Center for Cancer Research, National Cancer Institute; 2 National Institute of Allergy and Infectious Diseases, Bethesda Maryland; 3 Walter Reed Army Medical Center, Washington, District of Columbia; and 4 Department of Obstetrics and Gynecology/Division of Gynecologic Oncology and the Duke Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina
Requests for reprints: John Ian Risinger, Memorial Health University Medical Center, Curtis and Elizabeth Anderson Cancer Institute, 4700 Waters Avenue, Savannah, GA 31404. Phone: 912-350-0960; Fax: 912-350-8199; E-mail: risinJo1{at}memorialhealth.com.
| Abstract |
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Experimental Design: We queried the expression of known and putative CT gene transcripts (representing 79 gene loci) using whole genome gene expression arrays. Specifically, the global gene expressions of uterine cancers (n = 122) and normal uteri (n = 10) were determined using expression data from the Affymetrix HG-U133A and HG-U133B chips. Additionally, we also examined the brother of the regulator of imprinted sites (BORIS) transcript by reverse transcription-PCR and quantitative PCR because its transcript was not represented on the array.
Results: Global microarray analysis detected many CT genes expressed in various uterine cancers; however, no individual CT gene was expressed in more than 25% of all cancers. The expression of the two most commonly expressed CT genes on the arrays, MAGEA9 (24 of 122 cancers and 0 of 10 normal tissues) and Down syndrome critical region 8 (DSCR8)/MMA1 (16 if 122 cancers and 0 of 10 normal tissues), was confirmed by reverse transcription-PCR methods, validating the array screening approach. In contrast to the relatively low incidence of expression of the other CT genes, BORIS expression was detected in 73 of 95 (77%) endometrial cancers and 24 of 31 (77%) uterine mixed mesodermal tumors.
Conclusions: These data provide the first extensive survey of multiple CT genes in uterine cancers. Importantly, we detected a high frequency of BORIS expression in uterine cancers, suggesting its potential as an immunologic or diagnostic target for these cancers. Given the high incidence of BORIS expression and its possible regulatory role, an examination of BORIS function in the etiology of these cancers is warranted.
7,350 of these women will die (1). It is therefore important to develop novel strategies for early detection, diagnosis, and treatments for these cancers. Of particular interest, immunotherapy that targets antigens specifically expressed in cancer cells but not in normal tissues is one such possibility. Cancer/testis (CT) genes offer an appealing class of targets. In normal tissues, CT genes are predominantly expressed in the germ cells of the testis, placenta, or ovary but are often aberrantly expressed in various cancers. CT genes have recently been expertly reviewed (24). Some of these gene products are immunogenic in cancer patients, designated CT antigens, and are promising vaccine targets in cancer therapy (2). Additionally, these genes encode products that are possible targets for small moleculebased drugs. Only limited studies on the expression incidence of various known CT genes in uterine cancers are reported. Resnick et al. examined the expression of MAGEA4 and NY-ESO-1 in a variety of uterine cancers and observed that a high proportion of uterine carcinosarcomas (91%) and papillary serous cancers (63%) expressed these antigens (5). In contrast Chitale et al. evaluated NY-ESO-1 by immunohistochemistry and found that only 6% of endometrial carcinomas expressed the gene (6). Various other CT genes have been evaluated in endometrial cancers, including MAGEA4, MAGEA3, MAGE-C1 (CT7), SSX, and CAGE (68). To more comprehensively examine this topic, we did a screen for CT genes using the gene expression data obtained from microarray analysis of 122 uterine cancers and also from 10 normal uteri. A similar screen identifying germ line genes was recently reported (9). In addition, we used individually tailored reverse transcription-PCR (RT-PCR)/real-time quantitative RT-PCR assays to confirm findings from the array data as well as to examine CT genes not present on the array chips. The goal of these screens was to identify those CT genes with the highest incidence of expression in uterine cancers.
| Materials and Methods |
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Gene expression array. We studied gene expressions using Affymetrix Human Genome HG-U133A and HG-U133B Gene Chip expression arrays (45,000 array features covering >28,000 UniGene clusters). Five micrograms of total RNA from each sample were labeled using the bioarray high-yield transcript kit according to manufacturer's conditions (ENZO, Farmingdale, NY). Labeled RNAs were hybridized and washed according to manufacturer's recommendations (Affymetrix, Inc., Santa Clara, CA). Initial gene expression data analysis was done using Microarray Suite 5.0 software (Affymetrix 2001). All arrays were normalized to a trimmed mean transcript signal level of 500 counts (absent and present call procedure). Expression values for each sample for each element of the filter are contained in the Supplementary Material.
Statistical calculations. All statistical calculations were done on the logarithmic values of signals or ratios. The expression ratios of MAGEA9 and DSCR8 to ß-actin are shown for mixed mesodermal tumor, papillary serous cancer, and endometrioid cancer. Comparison of the geometric mean expression values of Taqman data indicates that mixed mesodermal tumors are 8-fold higher than endometrioid cancers, and that papillary serous cancers are 19-fold higher than endometrioid cancers. The statistical significance of these differences was tested using two-tailed Student's t tests. MAGEA9 expression is found to be significantly different in papillary serous cancers compared with endometrioid cancers at P < 0.03 (papillary serous/endometrioid = 16.7), whereas all other comparisons indicated Ps > 0.05 (MAGEA9: mixed mesodermal tumor/endometrioid = 8.5, P = 0.127; DSCR8: mixed mesodermal tumor/endometrioid = 19.0, P = 0.056; papillary serous/endometrioid = 11.7, P = 0.1). Similarly, BORIS expression is higher in mixed mesodermal tumor and papillary serous cancers compared with endometrioid cancers with the geometric mean ratios of mixed mesodermal tumor/endometrioid = 132 and papillary serous/endometrioid = 18, respectively. Both mixed mesodermal tumor and papillary serous cancers are found to be significantly different from endometrioid cancers, with P values of 2.8 x 108 and 0.0018, respectively, whereas mixed mesodermal tumor is not significantly different from papillary serous cancers, although the mixed mesodermal tumor/papillary serous ratio is 7.1. Examination of endometrioid cancers indicated progressive increase in BORIS expression with grade, although the differences among grades 1, 2, and 3 are not statistically significant (P
0.1).
CT antigen filter. We created a list of potential CT genes based on an examination of the literature and gene databases. Although many genes described in the literature have been described as CT genes, few have had a thorough examination of their expression in a wide variety of fetal and adult tissues. In addition, many have not been described in the literature as being expressed aberrantly in cancer but rather show strong sequence homology to other known CT genes. We therefore queried the data from the gene arrays for both expression in cancers and also in 10 normal uteri. Potential CT genes were excluded when expression was detected in one or more normal uteri. Genes contained in this filter are contained in Supplementary Table S1.
Real-time PCR and RT-PCR. Total RNA from each sample was used to make first-strand cDNA using a commercial kit (Invitrogen). The quality of all cDNAs was assured by confirmed expression of the housekeeping genes ß-actin (ACTB) and GAPDH. ß-Actin and GAPDH assays were obtained from ABI (Foster City, CA). First-strand cDNA was used to assess BORIS expression using quantitative real-time PCR. The relative concentration of BORIS was determined using ACTB as a reference, as described by Vatolin et al. (10). BORIS real-time PCR primers and probe with corresponding position in the reference sequence (NM_080618) were forward primer, CCCATTGTGCCACCATCA (1374-1391) and reverse primer, AGCATGCAAGTTGCGCATAT (1438-1418). Taqman MGB probe, FAM-ACGGAAAAGCGACCTAC (1396-1412). BORIS real-time results were confirmed by conventional RT-PCR using primers described in a subset of samples (11). Similarly, relative levels of MAGEA9 and DSCR8 were determined using commercially available probe and primer sets (Applied Biosystems, Foster City, CA). Primers used for detection of NY-ESO-1 and LAGE have been described (12). Normal human testis RNA (Clontech, Palo Alto, CA) served as positive control for all reverse transcription-PCR. Samples from normal human tissues were obtained from Clontech. In addition to the 10 normal uterine biopsy RNAs, commercially available RNA from uterus was also used as negative control (Clontech).
| Results |
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Determination of CT genes expressed in uterine cancers by gene expression arrays. Our group has previously completed gene expression analysis of 122 uterine cancers and 10 normal uteri using the Affymetrix HG-U133A and HG-U133B gene chips (16, 17). These samples included 63 endometrioid endometrial cancers, 24 papillary serous cancers, 29 mixed mesodermal tumor of the uterus, 2 clear cell cancers, and 1 mucinous cancer. These expression data were analyzed using the potential CT gene list to identify those transcripts present in some subset of tumors but not in normal uteri. We applied stringent criteria in our selection of genes by using the Affymetrix absent/present call in making this determination. Although this analysis feature has the potential to exclude some genes that are truly expressed at low levels, it provides strong evidence for true gene expression. Initially, we examined those transcripts that were expressed in the normal uteri samples and excluded any that were given present calls. We used the most stringent cutoff and excluded the gene even if it was found expressed in only one of the 10 normal uteri. These data are depicted in Fig. 1 , and data are contained in Supplementary Table S1. The genes involving the greatest numbers of cancers as detected by this screen were MAGEA9 (24 of 122), PNMA3 (17 of 122), and DSCR8 (also called MMA1; 16 of 122).
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BORIS transcript expression in normal and malignant uterine tissues. We examined the newly described BORIS CT gene for which probes were not present on the array chips. The recently described BORIS was found expressed in a variety of cancer cell types (in vitro cell lines and primary tumors) and may play a role in the etiology of these cancers (11, 21). We examined BORIS expression using both conventional RT-PCR as well as quantitative real-time PCR in the same set of cancers that were examined by microarray as well as four additional tumors. Interestingly, we found a very high incidence of expression of BORIS in these cancers (Fig. 3A ). Specifically, 73 of 95 endometrial cancers and 27 of 31 mixed mesodermal tumors expressed BORIS transcript. Importantly, we found no expression of BORIS in normal endometrial samples, or in 20 benign uterine leiomyomas and their matched normal myometrium (Supplementary Fig. S1).
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| Discussion |
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Somewhat surprising were the results for NY-ESO-1 (CTAG1) and MAGEA4. Only two cancers exhibited NY-ESO-1 expression, and only 14 cancers expressed MAGEA4 based on our microarray data. This finding is in contrast to results obtained by Resnick et al. who observed higher incidence of expression using immunohistochemistry (5). However, our data are in concordance with another report that found only 6% of endometrial cancers expressed NY-ESO-1, and 23% expressed MAGEA4 (6). We chose to re-evaluate NY-ESO-1 expression in our cancers by conventional non-quantitative reverse transcription-PCR. These data tracked our microarray findings, as we confirmed expression in these 2 cancers but not 20 others that were negative by array (data not shown). MAGEA family members share very high amino acid homology yet contain considerable variation at the nucleotide level. The differences in this previous report may be due to differences in methodology (immunohistochemistry versus oligonucleotide array) or in specificity. Our data were obtained from oligonucleotide array that has the ability to distinguish between family members. Alternatively, low levels of transcript undetectable by array technologies may not be reflective of highly stable and abundant protein detected by immunohistochemistry.
Several interesting genes with a high incidence of expression in cancers were excluded from our analysis due to low levels of expression in several normal samples. Among these was the PRAME antigen, excluded due to low but reliably detected expression in normal uterine samples. PRAME was highly expressed in many of the endometrial cancers, and unlike the other CT genes that tended to be expressed in more aggressive serous and mixed mesodermal tumor histologic types, PRAME showed a high incidence and level of expression in many early-stage endometrioid cancers as well as serous and mixed mesodermal tumor types. Furthermore, PRAME was identified as a cancer biomarker based on its increased level of expression in a comparison of normal endometrium and endometrial cancer.6 This expression in the most common histologic type of endometrial cancer deserves further investigation, including analysis of the relative levels of transcript and protein in normal and malignant uterine tissue. Recent progress in the understanding of the role of PRAME in modulating tumor progression through retinoic acid signaling further highlights the need for more study in this area (23).
Importantly, we identify for the first time a high incidence of expression of the BORIS gene. BORIS was expressed in the majority of uterine cancers examined and was not found expressed in normal uterine samples. These expression data are consistent with other evidence in the literature that BORIS is a true CT gene in which expression occurs only in testis and malignancies and not other tissues (11). The fact that BORIS expression was frequently detected in cancers and not in normal adult female tissues raises the possibility that BORIS represents a novel target for immunotherapy of endometrial cancers. Additionally, BORIS expression could be used as a potential screening marker for presence of malignant uterine disease or for monitoring treatment response in patients with endometrial cancer.
Although the normal function of most CT genes is unknown, BORIS contains an almost identical 11 zinc-finger region present in the CTCF transcription factor. Based on this homology, BORIS would be predicted to bind similar DNA elements as CTCF (11, 21). CTCF functions in the cell are numerous, including regulation of many epigenetically regulated loci, such that promoter competitions might disrupt the normal expression of many genes (2427).
Indeed, recent data indicate that BORIS can modulate the expression of several CT genes in normal human dermal fibroblasts as well as lung cancer cells (10, 28). Specifically, Vatolin et al. found that ectopic BORIS expression could de-repress a variety of CT genes in neonatal dermal fibroblasts (10). Similarly, Hong et al. described the ability of BORIS to de-repress the NY-ESO-1 CT gene in lung cancer cells (28). Functionally, BORIS was found to replace the CTCF transcription factor on CT gene promoters normally necessary for maintaining these loci in a silenced state. Although some of these data were obtained from in vitro cell culture models, it is possible that BORIS can aberrantly modulate the expression of a variety of genes (not just CT genes) normally regulated by CTCF in cancers and influence the carcinogenic process. Further examination of this concept is warranted.
In addition, to the BORIS gene, our data identified a variety of CT genes that are expressed in uterine cancers. Of these, we identify for the first time expression of MAGEA9 in any cancer tissue. MAGEA9 was originally identified based on homology to other MAGEA family members, but to date, no evidence existed as to its expression in cancers. Of the CT genes other than BORIS, MAGEA9 was expressed in the most uterine cancers with highest incidence in the mixed mesodermal tumors (11 of 29, 38%) and papillary serous cancers (7 of 24, 29%). This report verifies this MAGE family member as a true CT gene frequently expressed in these histologic types of uterine cancer with unfavorable prognosis.
| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/).
5 http://www.cancerimmunity.org/CTdatabase/#Ctlist ![]()
6 G.V.R. Chandramouli and J.I. Risinger, unpublished data. ![]()
Received 11/23/05; revised 5/25/06; accepted 11/29/06.
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