Acta Pharmacologica Sinica 2006 February; 27 (2): 242-248; doi: 10.1111/j.1745-7254.2006.00247.x

Aim: RNA interference (RNAi) has been proposed as a potential treatment for cancer, but the lack of cellular targets limits its use in cancer gene therapy. No current technology has achieved direct tumor-specific gene silencing using RNAi. In the present study we attempt to develop a tumor-specific RNAi system using the human telomerase reverse transcriptase (hTERT) promoter; furthermore, we analyzed its inhibitive effect on Bcl-2 expression.

Methods: The vectors containing a small hairpin RNA (shRNA) to target exogenous reporters [firefly luciferase and enhanced green fluorescent protein (EGFP)] and endogenous gene (Bcl-2) were constructed. Luciferase expression was determined by dual luciferase assay. Reverse transcription-polymerase chain reaction (RT-PCR), fluorescence microscopy and fluorescence-activated cell sorting (FACS) were used to measure EGFP expression. Inhibition of Bcl-2 was evaluated by RT-PCR and Western blotting. Cell proliferation and viability were measured by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H -tetrazolium bromide (MTT) assay. FACS was used to analyze the cell cycle distribution profile.

Results: We showed that with the hTERT promoter directly driving shRNA transcription, expression of the exogenous reporters (LUC and EGFP) in tumor cells, but not normal cells, was specifically inhibited in vitro. The hTERT promoter-driven shRNA also depressed the expression of Bcl-2. Inhibition of Bcl-2 did not affect cell proliferation, but increased the chemosensitivity of HeLa cells to 5-fluorouracil.

Conclusion: The present study describes an efficient RNAi system for gene silencing that is specific to tumor cells using the hTERT promoter. Suppression of Bcl-2 by using this system sensitized HeLa cells to 5-fluorouracil. This system may be useful for RNAi therapy.

Keywords: RNA interference; telomerase; promoter regions (Genetics); Bcl-2; fluorouracil; gene therapy