The effect of Bcl-2 gene silencing on the sensitivity of cell line A549 to chemotherapeutic drugs

Abstract

To investigate the effects of miRNA-mediated down-regulation of the Bcl-2 gene on the chemotherapeutic sensitivities and mRNA transcriptions of sensitivity associated genes in human lung adenocarcinoma cell line A549 cells, and therefore to provide experimental data for improving the chemotherapeutic effects on non-small cell lung cancer (NSCLC). The miRNA recombinant plasmid targeting to human Bcl-2 gene was designed, synthesized and stably transferred into A549 cells by lipofectin technique as the experiment group. The transcription of Bcl-2 mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR) by agarose gel electrophoresis, real-time PCR, and the protein level of Bcl-2 was measured by Western blot to confirm the function of miRNA plasmid. The cell proliferation was examined by methyl thiazolyl tetrazolium (MTT) assay. Cell cycle was measured by flow cytometry. Drug sensitivities of A549 cells to etoposide, 5-fluorouracil, cisplatin, adriamycin, vincristine, paclitaxel and navelbine were analyzed by MTT assay. The mRNA expressions of excision repair cross-complementing gene 1 (ERCC1), thymidylate synthase (TYMS), Class III β-tubulin, topoisomerase 2 alpha (TOP2α) genes were detected by RT-PCR and real-time PCR. The recombinant miRNA plasmid was successfully synthesized and stably transferred into A549 cells. The transcription of Bcl-2 mRNA dramatically decreased by 98.1% in the experiment group (RQ = 0.002 ± 0.001) compared to that in the negative control group (RQ = 0.104 ± 0.003) by real-time PCR (t = 98.70, P < 0.05); and the protein level of Bcl-2 in the experiment group decreased by 57.6% by Western blot (t = 7.66, P < 0.05). The cell cycle profile showed that the low expression of Bcl-2 gene led to A549 cell cycle arrest at G1-phase. The results of MTT showed that the growth of A549 cells in the experiment group was markedly inhibited. The sensitivities of A549 cells to etoposide, cisplatin, paclitaxel, and navelbine were significantly enhanced [IC₅₀ values in the experiment group were (107.3 ± 0.1) mg/L, (7.7 ± 0.6) mg/L, (11.5 ± 1.9) mg/L and (10.8 ± 1.6) mg/L; IC₅₀ values in the negative control group were (145.8 ± 0.1) mg/L, (60.7 ± 1.4) mg/L, (80.6 ± 1.7) mg/L and (20.6 ± 1.7) mg/L], the respective t values being 655.33, 108.04, 82.16 and 12.48, all P < 0.05. The mRNA level of ERCC1, TYMS, and TOP2α genes in the experiment group decreased by 99.6%, 92.9% and 96.1% respectively, but Class III β-tubulin mRNA increased by 122% compared to the negative control group (1.154 ± 0.008, 0.520 ± 0.009), the respective t values being 689.79, 689.37, 768.04 and 160.07, all P < 0.05. Targeting to inhibit antiapoptotic mitochondrial gene Bcl-2 expression in A549 cells specifically decreased the mRNA of ERCC1, TYMS, and TOP2α genes, and significantly increased the sensitivities of A549 cells to chemotherapeutic agents such as etoposide, cisplatin, paclitaxel and navelbine.