Telomere shortening, telomerase expression, and chromosome instability in rat hepatic epithelial stem-like cells

Telomeres, which are specialized structures consisting of T(2)AG(3) repeats and proteins at the ends of chromosomes, may be essential for genomic stab ility. To test whether telomere length maintenance preserves genomic stabil ity in rats (Rattus rattus and Fischer 344), we assayed telomerase activity and telomere length in the rat hepatic epithelial stem-like cell line WB-F 344 during aging in vitro and in tumor-derived lines. Telomerase activity i n the parental WB-F344 line was repressed at low and intermediate passage l evels in vitro and reexpressed at high passages. Southern blot hybridizatio n and quantitative fluorescence in situ hybridization analyses demonstrated that telomeres were significantly eroded at intermediate passage levels, w hen telomerase was repressed, and at high passage levels, when telomerase w as expressed. Fluorescence in situ hybridization analysis also revealed int erstitial telomeric sequences in rat chromosomes. Tumor-derived WB-F344 cel l lines that express telomerase had variably shortened telomeres. Cytogenet ic analyses performed on WB-F344 cells at low, intermediate, and high passa ges demonstrated that chromosome instability was most severe in the interme diate passage cells. These data suggest that telomere shortening during agi ng of rat hepatic epithelial stem-like WB-F344 cells in vitro and during se lection of tumorigenic lines in vivo may destabilize chromosomes. Expressio n of telomerase in high passage cells appeared to partially stabilize chrom osomes. Mol. Carcinog. 24:209-217, 1999. (C) 1999 Wiley-Liss. Inc.