Objective: To examine the selective killing effects of pEGFP-C1-mediated double suicide gene system driven by the hTERT promoter (hTERT-CDglyTK) on hepatic carcinoma cells.
Methods: The hTERT promoter and gene fragments SV40, yCD and TKgly were amplified by PCR (polymerase chain reaction) and then inserted into pEGFP-C1. And the constructs of pEGFP-hTERT-CD, pEGFP-hTERT-TK and pEGFP-hTERT-CDglyTK were transfected to SMMC 7721 or HL7702 respectively. The transfection effects were observed and the cellular expressions of suicide genes detected by RT-PCR (reverse transcription-polymerase chain reaction), QPCR (quantitative polymerase chain reaction) and Western blot. The transfected cells were treated with 5-fluorocytosine and ganciclovir at different concentrations and the cell-killing and bystander effects evaluated by the method of MTT (3-(4,5)-dimethyl thiadiazole (-z-y1)-3,5-di-phenytetrazoliumromide). The activity of cell telomerase was detected by the method of TRAP-argentation and the apoptotic rates analyzed by flow cytometry. All results of double and single gene systems were analyzed.
Results: The fragments of enzyme digestion corresponded to the expectations. RT-PCR, QPCR and Western blot demonstrated the expressions of CD, TK and CDglyTK. pEGFP-hTERT-CD, pEGFP-hTERT-TK and pEGFP-hTERT-CDglyTK showed the similar transfection efficiencies in SMMC7721 (74.5%, 76.3%, 76.9%). More sensitive to the prodrugs (P = 0.020, P = 0.015), higher apoptotic rates (P = 0.023, P = 0.017) and bystander effects (P = 0.012, P = 0.001)and lower telomerase activities (P = 0.045, P = 0.038) were observed in double gene system versus those in single gene system. However, the transfection and growth of HL7702 cell could not be infected by this double suicide gene.
Conclusion: The plasmid of CDglyTK fusion gene system driven by hTERT promoter has been successfully constructed. It has demonstrated highly specific killing effects on hepatic carcinoma cells.