1Laboratory of Medical Genetics, Institute for Medical Sciences, Korea. 2Department of Hematology-Oncology, Ajou University School of Medicine, Suwon, Korea.
ABSTRACT
PURPOSE: There are only a few cytogenetic studies in gastric cancer and so far no consistent specific chromosomal abnormalities have been described. In this study, we have used comparative genomic hybridization (CGH), a powerful molecular cytogenetic technique for detecting changes of the copy number throughout the genome, to screen for genetic alterations in gastric cancer cell lines. The CGH results were compared with those derived from G-banding and chromosome painting.
MATERIALS AND METHODS: Conventional cytogenetic analysis was performed on five human gastric cancer cell lines, AGS, SNU-1, SNU-16, SNU-620, and SNU-719, by a G-banding staining technique. In CGH, equal amounts of differently labeled DNA from the cell lines and normal reference DNA were hybridized simultaneously to normal metaphase chromosomes. They were visualized by different fluorochromes, and the signal intensities were quantitated separately as gray levels along the single chromosomes. The over- and under- represented DNA segments were determined by computation of ratio images and average ratio profiles. To confirm the CGH results, fluorescence in situ hybridization (FISH) with chromosome specific painting was performed using indirectly labeled chromosome specific paints.
RESULTS: Complex unbalanced chromosomal aberrations that could not be identified reliably by conventional cytogenetics in gastric cancer cell lines were successfully resolved by CGH analysis. CGH results were validated by using FISH with chromosome specific probes. In gastric cancer cell lines, gains of DNA copy number were more common than losses. Gains were detected on 1p, 1q, 2p, 3q, 6p, 7q, 10q, 11p, and 19q, and losses were observed on 4p, 4q, 5q, 12p, 12q, and 18q. Interestingly, all the five gastric cancer cell lines tested showed gain of DNA copy number on the chromosome 20, suggesting an existence of oncogene.
CONCLUSION: Conventional cytogenetics, CGH, and FISH using painting probes represent complementary approaches that, when employed in combination, could greatly facilitate the comprehensive analysis of chromosomal imbalances in gastric cancer cell lines. Our results suggest the existence of an oncogene or oncogenes on chromosome 20 that play a role in the development and/or the progression of gastric carcinogenesis.
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