Chromosomal Alterations in Hepatocellular Carcinoma Cell Lines Detected by Comparative Genomic Hybridization

There have only been a few cytogenetic studies of hepatocellular carcinoma (HCC), and so far, no consistent specific chromosomal abnormalities have been described. Here, 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 HCC cell lines. The CGH results were compared with those derived from G-banding and chromosome painting. MATERIALS AND METGODS: Conventional cytogenetic analyses were performed on five HCC cell lines, SNU-354, SNU-368, SNU-387, SNU-449 and SNU-475, using 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 quantified 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, florescence in situ hybridization (FISH), with chromosome specific painting, was performed using indirectly labeled chromosome specific paints.

Complex unbalanced chromosomal aberrations, which could not be identified reliably by conventional cytogenetics in HCC cell lines, were successfully resolved by CGH analysis. CGH results were validated using FISH with chromosome specific probes. In HCC cell lines, gains in DNA copy number were more common than losses. The most prominent changes were gains of 1q12- qter (80% of cases), 1q41-qter (100%), 7 (80%), 8q12-qter (60%), 8q23-qter (80%) and 20q12-qter (60%). Recurrent losses were mapped on 4q13-qter (60%), 16q12-qter (60%), 16q21-qter (80%), 13q12-q14.2 (60%) and Yq11.2 (100%). All four male HCC cell lines showed loss or rearrangement of the Y chromosome.

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 HCC cell lines. Our results suggest the existence of an oncogene, or protooncogenes, on chromosome 1q41-qter, and the tumor suppressor genes on Yq11.2, that play a role in the development and/or progression of hepatocellular carcinogenesis.