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J Thorac Cardiovasc Surg 2008;135:255-260
© 2008 The American Association for Thoracic Surgery
General Thoracic Surgery |
a Department of Pathology, Mount Sinai Medical Center, New York, NY
b Division of Thoracic Surgery, Department of Cardiothoracic Surgery, Mount Sinai Medical Center, New York, NY
c Heart, Lung and Esophageal Surgery Institute, University of Pittsburgh Medical Center, Pittsburgh, Pa
Received for publication May 4, 2007; revisions received August 12, 2007; accepted for publication August 15, 2007. * Address for reprints: Virginia R. Litle, MD, Division of Thoracic Surgery, Mount Sinai Medical Center, 1190 Fifth Ave, Box 1028, New York, NY 10029. (Email: virginia.litle{at}mountsinai.org).
| Abstract |
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Methods: MicroRNA was isolated from 35 frozen specimens (10 adenocarcinoma, 10 squamous cell carcinoma, 9 normal epithelium, 5 Barrett esophagus, and 1 high-grade dysplasia). MicroRNA expression was analyzed with Ambion bioarrays (Ambion, Austin, Tex) containing 328 human microRNA probes.
Results: Unsupervised hierarchic clustering resulted in four major branches corresponding with four histologic groups. One branch consisted of 7 normal epithelium samples and 1 squamous cell carcinoma sample. The second branch consisted of 7 squamous cell carcinoma samples and 1 normal epithelium sample. The third branch contained 4 Barrett esophagus samples and 1 squamous cell carcinoma sample. The fourth contained all the adenocarcinoma samples and 1 sample each of Barrett esophagus, normal epithelium, squamous cell carcinoma, and high-grade dysplasia. Supervised classification with principal component analysis determined that the normal epithelium samples were more similar to the squamous cell carcinoma tumors, whereas the Barrett esophagus samples were more similar to adenocarcinoma. Pairwise comparisons between sample types revealed microRNAs that may be markers of tumor progression. Both mir_203 and mir_205 were expressed 2- to 10-fold lower in squamous cell carcinoma and adenocarcinomas than in normal epithelium. The mir_21 expression was 3- to 5-fold higher in both tumors than in normal epithelium. Prediction analysis of microarray classified 3 Barrett esophagus samples as Barrett esophagus, 1 as adenocarcinoma, and 1 as normal epithelium.
Conclusion: Expression profiles of miRNA distinguish esophageal tumor histology and can discriminate normal tissue from tumor. MicroRNA expression may prove useful for identifying patients with Barrett esophagus at high risk for progression to adenocarcinoma.
| Introduction |
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Dysplasia alone as a marker of malignant progression is marred by pathologists' differential interpretation of degrees of dysplasia.20
Because only a subset of dysplastic lesions progress to cancer, the challenge lies in substratification of biopsy samples according to the probability of malignancy development. If molecular markers of premalignancy can be identified on small pieces of esophageal tissue obtained endoscopically, this could lead to improved early detection and provide objective criteria for selection of patients who might benefit from aggressive surgical treatment.
MicroRNAs (miRNAs), a class of small, noncoding RNA molecules first reported on in 1993,21
are posttranscriptional regulators of gene expression that have been shown to be involved in cell differentiation, proliferation, and apoptosis. Furthermore, it has recently been demonstrated that some miRNAs may function as either oncogenes or tumor suppressor genes (oncomirs).22
Altered expression of oncomirs has now been found in a variety of human tumors including lung, breast, and prostate cancers,23-27
and recent reports demonstrate a role for miRNA expression in disease progression and outcome.24,26
Although protein-coding gene expression studies have shown differences between normal squamous epithelium (NSE) in the esophagus and BE and between BE and AC,28,29
only one recent report on 7 patients has determined miRNA expression in esophageal lesions.30
We hypothesized that unique miRNA expression profiles exist to distinguish normal esophagus, BE, esophageal dysplasia, and esophageal cancer. Furthermore, because miRNA expression is associated with differentiation, specific miRNAs may become deregulated in the progression from BE to dysplasia to AC. Identification of these differences in miRNA expression could then discriminate patients who have a high risk for progression to cancer and who therefore need to be followed up more closely or treated more aggressively.
| Materials and Methods |
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Thirty-five frozen specimens were chosen for analysis. There were 10 AC specimens, 10 SCC specimens, 5 BE specimens, 1 HGD lesion specimen, and 9 NSE specimens. NSE specimens were obtained from patients undergoing esophagectomy for HGD or cancer and were taken from as far from the malignancy as possible.
Isolation of miRNA
Enriched miRNA was isolated from tissue specimens with the mirVana miRNA Isolation Kit (Ambion Inc, Austin, Tex), which allows capture of both enriched miRNA and larger RNA species separately. Both the enriched miRNA and large RNA were quantified with a NanoDrop spectrophotometer (NanoDrop Technology, Wilmington, Del), and integrity of the large RNA fraction was determined with an Agilent Bioanalyzer (Agilent Technologies, Palo Alto, Calif) as a surrogate for miRNA quality control. The miRNA samples were only used in microarray experiments if the RNA integrity number for the large RNA from the same specimen was at least 6.
Labeling and Hybridization of miRNA, Scanning, and Data Processing
Samples of miRNA from 35 esophageal specimens were labeled with the mirVana miRNA Labeling Kit (Ambion) according to the manufacturer protocol. The Cy5-labeled miRNA was then hybridized at 42°C for 16 hours on mirVana miRNA Bioarrays (Ambion), which contain 796 probes representing duplicate spots for each of 287 human miRNAs, 65 mouse and rat miRNAs, 33 Ambion-predicted miRNAs, and 4 positive controls (20 replicate spots for each positive control). The slides were then washed and scanned with an Axon 4000B (Molecular Devices Corporation, Sunnyvale, Calif) scanner at 100% power and a photomultiplier tube gain of 750. The microarray images were analyzed with Genepix PRO (version 5.1; Molecular Devices), and normalization was performed with CyclicLoess31
in R program downloaded from the Bioconductor open source project (http://www.bioconductor.org). Unsupervised hierarchic clustering, differentially expressed gene analysis among the groups, and prediction analysis of microarray (PAM) were performed with the National Cancer Insitute BRB-ArrayTools Version 3.4 (BRB-ArrayTools Version 3.4; Biometrics Research Branch, National Cancer Institute, Bethesda, Md). For differentially expressed gene analysis among four histologic types (AC, SCC, NSE, BE), class comparison between groups of arrays was performed with a random-variance F test. Genes were considered statistically significant if their P value was less than .001. A stringent significance threshold was used to limit the number of false-positive findings. This tool also used the multivariate permutation test to provide 90% confidence that the false discovery rate was less than 10%. The false discovery rate is the proportion of the list of genes claimed to be differentially expressed that are expected to be false positives. For PAM, 10-fold cross validation was performed with samples of four histologic types (AC, SCC, NSE, and BE). The comparison of PAM with histologic examination was facilitated by transforming the continuous PAM output into binary data with a probability of 0.5 as the cut off. Principal component analysis was performed with Partek Genomics Suite software (Partek, Inc, St Louis, Mo).
| Results |
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Sample Classification With PAM
PAM identified a set of miRNAs, the expression of which was able to classify samples accurately according to histologic type. All 10 AC and 10 SCC samples were accurately classified into the correct histologic groups, whereas 2 NSE samples were classified incorrectly, 1 as BE and 1 as SCC. Of the 5 BE samples, 3 were classified as BE, 1 was called AC, and the other was classified as NSE. With the same miRNA classifier, the single HGD sample was determined to be more similar to AC than to the other three histologic types. These data are shown in
Table 2.
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| Discussion |
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Global gene expression (messenger RNA) profiling of BE and esophageal cancer has previously been used to identify differentially expressed genes in BE relative to esophageal AC.33
In nonesophageal tissues, miRNA expression profiling has been shown to provide more accurate classification of tissue and tumor types than global messenger RNA expression profiles.23,34
For example, differential miRNA expression has been used to discriminate lung cancer from benign lung tissue, lung AC from SCC,26
and malignant from benign tissues in the prostate and thyroid.27,35
In addition, miRNA plays a role in lineage-specific tissue differentiation and as such is particularly good at identifying the source of poorly differentiated tumors of unknown origin.23
We therefore hypothesized that (1) tumor-specific miRNA expression profiles exist for malignant and normal esophageal tissues and (2) miRNA expression profiles may be associated with progression from BE to AC.
To test our hypotheses, we used miRNA expression arrays from Ambion to determine the miRNA profiles for esophageal NSE, BE, an HGD lesion, and the two primary types of esophageal cancer, AC and SCC. In this series we demonstrated that miRNA expression profiles distinguish different esophageal tissue types and also discriminate malignant from normal esophageal tissue. Furthermore, the NSE and SCC samples were much more similar to each other than to the AC samples. Similarly, BE and AC miRNA expression profiles were more similar to each other than to tissues of squamous origin (either benign or malignant). In light of our current understanding of the development of esophageal AC, this makes good biologic sense, because AC is believed to arise from Barrett columnar epithelium and not from squamous epithelium.
In addition to identifying differential expression of particular miRNAs in NSE, BE, AC, and SCC of the esophagus, we also used the miRNA data to predict into which groups the BE specimens would be genotyped on the basis of miRNA expression rather than histologic examination. This analysis identified possible subtypes of miRNA expression within the 5 BE samples: 1 with a "normal" profile, 1 with an "AC" profile, and 3 with BE-specific miRNA expression. These results support future studies in a larger sample of patients with BE undergoing cancer follow-up to examine the hypothesis that miRNA expression may distinguish a subgroup of BE patients most likely to have esophageal cancer develop.
Finally, there are reports in the literature associating some of the differentially expressed miRNAs reported on here with other cancers. For example, miR_21 is upregulated in both esophageal AC and SCC, and this has also been reported in tumors of the breast, lung, prostate, colon and stomach, as well as in glioblastomas.25,26,35,36
In addition, miR_192 and miR_203 expressions were upregulated in lung cancer tissue relative to normal lung,36
and inhibition of miR_192 has been shown to downregulate cell growth in a lung AC cell line.38
In our data, we saw higher expression of miR_192 in esophageal AC but lower expression of miR_203 in both cancer types relative to NSE of the esophagus.
| Conclusions |
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| Acknowledgments |
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| References |
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