3. Results
3.1. siRNA and shRNA-mediated knockdown of hTERT expression in cancer
cells
Transient knockdown methods can reveal the silencing of target
gene and it also helps to understand the associated changes in immediate
early gene expression profile. To investigate the immediate early effects
of siRNA against hTERT, HeLa cells were transfected with 80 pmol
siRNA and harvested 72 h posttransfection. The sense and anti-sense sequences
of siRNA are shown in Fig. 1A. In parallel, equimolar concentrations
of siRNA against GAPDH and scrambled siRNA were used as
controls. Real Time PCR using hTERT specific primers showed 60% reduction
of hTERT transcript level in cells transfected with siRNA against
hTERT (Fig. 1B). HeLa cells transfected with hTERT siRNA showed no
morphological changes (Fig. 1C).
To further assess the potential of shRNA targeting different target
sites of hTERT, the duplex representing the shRNA along with miRNA
loop was constructed in pPRIME vector under a Tet regulated promoter
(Fig. 2A). Schematic representation of predicted RNA folds for simple
stem-loop and miR-30–based hTERT shRNA is shown in Fig. 2B. As reported
earlier, the miR30 loop can increase the processivity and knockdown
efficiency by presenting silencing RNAs in its natural format. In
addition, the transfected shRNA can be monitored with GFP expression
(Fig. 2C). HeLaTet-On cell lines were transfected with shRNA mirhTERT
constructwith Dox and 80% reduction in the hTERT levelswas observed
(Fig. 2D). The silencing efficiency of siRNA and shRNA was comparable
and the latter was used in subsequent experiments.