Spontaneous neoplastic transformation of WB-F344 rat liver epithelial cells

Several studies have shown that cultured rat liver epithelial cells transfo rm spontaneously after chronic maintenance in a confluent state in vitro. i n the present study, multiple independent lineages of low-passage WB-F344 r at Liver epithelial stem-like cells were initiated and subjected in paralle l to selection for spontaneous transformation to determine whether spontane ous acquisition of tumorigenicity was the result of events (genetic or epig enetic) that occurred independently and stochastically, or reflected the ex pression of a pre-existing alteration within the parental WB-F344 cell line . Temporal analysis of the spontaneous acquisition of tumorigenicity by WB- F344 cells demonstrated lineage-specific differences in the time of first e xpression of the tumorigenic phenotype, frequencies and latencies of tumor formation, and tumor differentiations. Although spontaneously transformed W B-F344 cells produced diverse tumor types (including hepatocellular carcino mas, cholangiocarcinomas, hepatoblastomas, and osteogenic sarcomas), indivi dual Lineages yielded tumors with consistent and specific patterns of diffe rentiation. These results provide substantial evidence that the stochastic accumulation of independent transforming events during the selection regime n in vitro were responsible for spontaneous neoplastic transformation of WB -F344 cells. Furthermore, cell lineage commitment to a specific differentia tion program was stable with time in culture and with site of transplantati on. This is the first report of a cohort of related, but independent, rat L iver epithelial cell Lines that collectively produce a spectrum of tumor ty pes but individually reproduce a specific tumor type. These cell Lines will provide valuable reagents for investigation of the molecular mechanisms in volved in the differentiation of hepatic stem-like cells and for examinatio n of potential causal relationships in spontaneously transformed rat Liver epithelial cell lines between molecular/cellular alterations and the abilit y to produce tumors in syngeneic animals.