**3.4 Human telomerase reverse transcriptase**

Human telomerase reverse transcriptase (hTERT) is a rate-limiting enzyme maintaining the activity of telomerase. However, it is found that hTERT not only maintains telomerase but stabilizes cell genomes, promotes cell proliferation, inhibits cell apoptosis, and plays a role in regulating intracellular signaling pathways. A recent study(de Souza Nascimento *et al,*  2006)transfected Hela with shRNA expressing carrier-encoded target shRNA, and found that short telomerase-related hTERT mRNA was reduced dramatically, cell growth was inhibited, and cell apoptosis was accelerated. A similar study(Gandellini *et al,* 2007)showed that transfection of hTERT specific siRNA with lipofectamine 2000 could inhibit the expression of hTERT for a prolonged time, thus affecting the proliferation and tumorigenesis of prostate cancer PC-3 cells.
