The β-catenin driven expression of hTERT (human telomerase RT-component) indicates tumor stell cells in colorectal adenocarcinomas

4530 Introduction: Tumor stem cells have been shown to be the biologically relevant fraction of tumor cells in leukemias, mamma carcinomas, and glioblastomas. Therefore, we wanted to characterize the potential fraction of tumor stem cells in human colorectal adenocarcinomas (hCRC) on the basis of their nuclear expression of β-catenin and hTERT (human telomerase RT component) which are both markers for adult intestinal stem cells. Experimental Procedures: The localisation of β-catenin and hTERT was investigated using immunohistochemistry (IHC) of hCRC applying specific monoclonal antibodies for β-catenin or hTERT respectively. Binding of β-catenin or TCF-4 to the promoter enhancer of the hTERT gene was analysed using Electric Mobility Shift Assays (EMSA) and chromatin immuneprecipitations (ChIP). The β-catenin/TCF-4 driven transcriptional activation of the hTERT gene was investigated applying luciferase-reporter assays and knockingdown β-catenin using siRNA as functional tests. Data: Nuclear co-expresion of β-catenin and hTERT was found in tumor cells located in the zone of the invasion front of 25 well differentiated hCRC using IHC specific for β-catenin and hTERT. Moreover, the expression of hTERT is regulated by β-catenin/TCF-4 on the level of transcription. For the hTERT promoter/enhancer harbours four consensus binding sites for TCF-4 (TBE) which specifically bind recombinant TCF-4 or endogenous β-catenin using EMSAs or ChIPs respectively. Additionally, the transcription of the hTERT gene depends on β-catenin/TCF-4 as mutating the TBEs of the hTERT promoter/enhancer results in a lowered activity of the hTERT promoter/enhancer using luciferase-reporter assays. Moreover, a reduction in the hTERT expression was induced in colorectal tumor cell lines knockingdown β-catenin by applying β-catenin specific siRNA. Conclusions: Tumor cells might exist also in hCRC. They resemble a tiny fraction of the whole tumors and are located at their invasion fronts. The tumor stem cells are characterized by the nuclear expression of β-catenin and hTERT. Moreover, β-catenin drives the expression of hTERT supporting the role of β-catenin as an inductor of stemness in intestinal cells. The functional testing of the stemness of this fraction of cells has now to be shown.