Hepatoselüler karsinogenez belirteci olarak yaşlanma ve ölümsüzlük genleri

Cellular senescence is a tumor-suppression mechanism, and immortalizationfacilitates neoplastic transformation. Both mechanisms may be highly relevantto hepatocellular carcinoma (HCC) development. We worked on two ma jor as-pects of cellular senescence and immortality in HCC. First, we analyzed the roleof ZEB2 (Smad-interacting protein SIP1, ZFXH1) gene for a senescence-relatedrole in HCC. Then, we extended our work on the identi ? cation and analysis ofa senescence and immortality gene network (SIGN) in relation to hepatocellularcarcinogenesis. ZEB2 is a transcriptional repressor of E-cadherin, and inducesepithelial-mesenchymal transition (EMT), a key process involved in tumor metas-tasis and progression. However, ZEB2 is also a repressor of telomerase reversetranscriptase (TERT) gene, which encodes a key enzyme required for telomeremaintenance and tumor cell immortality. We performed in-vivo, in-silico andin-vitro studies to explore potential implications of ZEB2 in hepatocellular carci-noma (HCC). Tissue expression of ZEB2 transcripts displayed stepwise decreasesin HCC lesions, as compared to liver cirrhosis. This inverse correlation suggestedthat sustained ZEB2 expression is not compatible with HCC progression. Next,we studied in vitro e ? ects of ZEB2 knockdown and overexpression in HCC cells.Huh7 clones stably transfected with a speci ? c ZEB2-shRNA expression vectordisplayed increased colony formation and increased proliferation. Conversely,Hep3B cells stably transfected with ZEB2 expression vector displayed permanentcell cycle arrest associated with increased senescence-associated ß -galactosidaseactivity. ZEB2-induced senescence arrest was correlated with the repression ofTERT expression and concomitant upregulation of cyclin-dependent kinase in-hibitor p21Cip1 . Transient expression of ZEB2 did not induce p21Cip1 expression,suggesting an indirect mechanism. Finally, ZEB2 overexpression was not com-patible with in vitro survival of cancer cells, as ZEB2-overexpressing Hep3B andA431 clones depleted progressively during in vitro culture and expansion. Theseobservations suggest that the ZEB2 gene, aside from its role in EMT, also playsa negative role in HCC cell growth and survival.In the other study, we integrated gene expression data from senescence pro-grammed and immortal HCC cells with the data from cirrhosis and HCC tissuesto generate a SIGN signature. The SIGN signature accurately classi ? ed nor-mal liver, cirrhosis, dysplasia and HCC lesions, and indicated that senescence-to-immortality conversion ? rst occured during dysplasia-to-early HCC transi-tion. Senescence-to-immortality conversion contributed also to tumor progres-sion. This conversion was accompanied by hepatic dedi ? erentiation and increasedexpression of cell proliferation, chromosome modi ? cation and DNA damage re-sponse genes. Thus, HCC immortalization is closely associated with the ac-quisition of stem/progenitor-like features. Finally, we identi ? ed a large set ofupregulated DNA damage checkpoint and DNA repair genes that showed signif-icant associations with tumor initiation and progression. These genes may serveas potential targets for HCC prevention and therapy.