Attenuation of telomerase activity by a hammerhead ribozyme targeting the template region of telomerase RNA in endometrial carcinoma cells.

Telomerase activity is found in almost all carcinoma cells but not in most somatic cells, suggesting that telomerase is an excellent target for cancer therapy. We designed hammerhead ribozymes against human telomerase RNA and studied their possible use as a tool for cancer therapy. Three ribozymes targeting the 3' end of the GUC sequence at 33-35 (the template region), 168-170, and 313-315 from the 5' end of telomerase RNA were designed. In a cell-free system, these three hammerhead ribozymes efficiently cleaved the RNA substrate. When these ribozyme RNAs were introduced into Ishikawa cells, which are endometrial carcinoma cells, only a ribozyme targeting the RNA template region could diminish the telomerase activity. Next we subcloned the ribozyme sequence into an expression vector and introduced this into AN3CA cells, which are endometrial carcinoma cells. The clones that were obtained showed reduced telomerase activity and telomerase RNA with expression of the ribozyme. These data suggest that the ribozyme against the RNA template region is a good tool to repress telomerase activity in cancer cells.