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The present study investigated the mechanism of selective killing of liver cancer cells of melanoma differentiation associated gene-7 (MDA-7, also called IL-24α) in order to provide a theoretical basis for gene therapy of liver cancer. A recombinant eukaryotic expression vector (pcDNA3-MDA-7) containing human MDA-7 gene was constructed, which was then delivered to liver cancer cell line HepG2 and normal liver cell line L02. The positive cell clone was screened by G418. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was performed to confirm the occurrence of MDA-7 transcription in the transfected cells. The protein expression of MDA-7 was determined by western blot analysis. The effects of MDA-7 on liver cancer cell proliferation and apoptosis were investigated through MTT assay and flow cytometry by Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) double-staining. The mitochondrial protein was extracted from the normal liver cell line L02 and liver cancer cell line HepG2 at 3 day post-culture, in which the alterations of anti-apoptotic B-cell lymphoma-2 (Bcl-2), pro-apoptotic Bcl-2 associated X protein (Bax), mitochondria-released cytochrome c and caspase 9 were determined by western blot analysis. pcDNA3-MDA-7 mediated the expression of foreign gene MDA-7 in HepG2 and L02 cells. MDA-7 promoted liver cancer cell apoptosis and inhibited cell proliferation; while no effect was exerted on normal liver cells, as determined by the MTT assay and flow cytometry. Relative to the L02 cells, the protein expression of Bcl-2 was downregulated in the HepG2 cells, while that of Bax, cytochrome c and caspase 9 were upregulated. In the study, the eukaryotic expression vector pcDNA3-MDA-7 was successfully constructed, it can mediate the expression of MDA-7 in human liver cancer cells and normal liver cells and inhibits the proliferation of human liver cancer cells through the restored expression of mitochondrial pro-apoptotic Bcl-2.

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