Genomic fluidity is a necessary event preceding the acquisition of tumorigenicity during spontaneous neoplastic transformation of WB-F344 rat liver epithelial cells

Beyond the oncogene paradigm: understanding complexity in cancerogenesis

In the past decades, an enormous amount of precious information has been collected about molecular and genetic characteristics of cancer. This knowledge is mainly based on a reductionistic approach, meanwhile cancer is widely recognized to be a 'system biology disease'. The behavior of complex physiological processes cannot be understood simply by knowing how the parts work in isolation. There is not solely a matter how to integrate all available knowledge in such a way that we can still deal with complexity, but we must be aware that a deeply transformation of the currently accepted oncologic paradigm is urgently needed. We have to think in terms of biological networks: understanding of complex functions may in fact be impossible without taking into consideration influences (rules and constraints) outside of the genome. Systems Biology involves connecting experimental unsupervised multivariate data to mathematical and computational approach than can simulate biologic systems for hypothesis testing or that can account for what it is not known from high-throughput data sets. Metabolomics could establish the requested link between genotype and phenotype, providing informations that ensure an integrated understanding of pathogenic mechanisms and metabolic phenotypes and provide a screening tool for new targeted drug.

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

Telomeres, which are specialized structures consisting of T2AG3 repeats and proteins at the ends of chromosomes, may be essential for genomic stability. To test whether telomere length maintenance preserves genomic stability in rats (Rattus rattus and Fischer 344), we assayed telomerase activity and telomere length in the rat hepatic epithelial stem-like cell line WB-F344 during aging in vitro and in tumor-derived lines. Telomerase activity in the parental WB-F344 line was repressed at low and intermediate passage levels in vitro and reexpressed at high passages. Southern blot hybridization and quantitative fluorescence in situ hybridization analyses demonstrated that telomeres were significantly eroded at intermediate passage levels, when telomerase was repressed, and at high passage levels, when telomerase was expressed. Fluorescence in situ hybridization analysis also revealed interstitial telomeric sequences in rat chromosomes. Tumor-derived WB-F344 cell lines that express telomerase had variably shortened telomeres. Cytogenetic analyses performed on WB-F344 cells at low, intermediate, and high passages demonstrated that chromosome instability was most severe in the intermediate passage cells. These data suggest that telomere shortening during aging of rat hepatic epithelial stem-like WB-F344 cells in vitro and during selection of tumorigenic lines in vivo may destabilize chromosomes. Expression of telomerase in high passage cells appeared to partially stabilize chromosomes.