GENOMIC FLUIDITY IS A NECESSARY EVENT PRECEDING THE ACQUISITION OF TUMORIGENICITY DURING SPONTANEOUS NEOPLASTIC TRANSFORMATION OF WB-F344 RAT-LIVER EPITHELIAL-CELLS

The genomic evolution of a cohort of WB-F344 rat liver epithelial cell lineages undergoing spontaneous neoplastic transformation was followe d to define the mechanistic relationship between genomic instability a nd progression to the neoplastic phenotype. Eighteen independent popul ations of WB-F344 cells (initiated from a single diploid-founding popu lation) were subjected to 12 cycles of selective growth at confluent c ell density, and cellular DNA contents were measured after each select ion cycle. Flow cytometry demonstrated significant gains in the amount of G(1) DNA after selection cycles 3, 6, and 7 in 44% (8 of 18), 89% (16 of 18), and 39% (7 of 18) of the cell populations, respectively Al l populations subsequently lost DNA and returned to a diploid or pseud o-diploid DNA content within 1 to 2 selection cycles after the appeara nce of an increased DNA content. Additionally, appearance and subseque nt disappearance of aneuploid or tetraploid subpopulations was observe d in 11% (2 of 18) and 83% (15 of 18) of the experimental lineages, re spectively Although perturbations of G1 DNA content were apparent as e arly as selection cycle 3, at least 8 cycles of selective growth were required for the acquisition of tumorigenicity, While the independent lineages demonstrated significant fluctuations in G1 DNA content betwe en selection cycles 3 and 8, the majority (11 of 13) of the population s contained a diploid or pseudodiploid DNA content at the time tumorig enicity was expressed. Genomic instability preceded the acquisition of tumorigenic potential in rat liver epithelial cells subjected to sele ctive growth conditions of maintenance at influence, and may be requir ed for its expression.