Establishment of two distinct human hepatocellular carcinoma cell lines from a single nodule showing clonal dedifferentiation of cancer cells.

Hepatocellular carcinomas often contain tumor cells of more than one histological grade. The clonal relationship and biological behavior of hepatocellular carcinoma cells in histologically heterogeneous areas have not been fully explored. We established two distinct human hepatocellular carcinoma cell lines (HAK-1A and 1B) from a single nodule showing a three-layered structure with a different histological grade in each layer. Morphologically, HAK-1A and 1B resembled well-differentiated hepatocellular carcinoma cells in the outer layer of the original tumor and poorly differentiated ones in the inner layer, respectively. HAK-1B appeared less differentiated morphologically and more aggressive biologically than HAK-1A; HAK-1B had a shorter doubling time, higher tumorigenicity and an aneuploid DNA index. Chromosome analysis revealed many different abnormalities in the two cell lines, in which, however, two identical structural abnormalities (2q+ and 17p+) were identified. Moreover, sequence analysis of the p53 gene showed identical mutations at codon 242 in both cell lines. These findings suggest that the two cell lines are of clonal origin and that hepatocellular carcinomas consisting of cancerous tissues of more than one histological grade may reflect clonal dedifferentiation in the tumor. Furthermore, we predict that a clonal, morphologically less differentiated subpopulation such as HAK-1B is more aggressive in proliferation and may be closely related to subsequent tumor progression in hepatocellular carcinoma.