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Objective: To investigate the effect of over-expression of paired related homoeobox 1 (PRRX1) on apoptosis of hepatocellular carcinoma SMMC7721 cells, and to explore its detailed mechanism. Methods： ：Lentivirus-mediated PRRX1 over-expression vector (pGMLV-PRRX1) and empty vector (Vector) were respectively infected into SMMC7721 cells, and the mRNA and protein expression levels of PRRX1 in infected cells were detected by qPCR and WB. The effect of PRRX1 over-expression on the cell proliferation and apoptosis of SMMC7721 cells were assessed by CCK-8 assay and Annexin-V FITC/PI double staining flow cytometry assay, respectively. The change of mitochondrial membrane potential of SMMC7721 cells was detected by mitochondrial membrane potential assay kit (JC-10 staining assay). The enzymatic activities of caspase-8 and caspase-9 in infected cells were detected by using caspase activity assay kit (spectrophotometric method). The protein expression levels of p53, Bcl-2, Bax, Fas, Cleaved-caspase-3 and Cty C expressed in mitochondria and cytosol were evaluated by WB. Results： ：PRRX1 over-expressed SMMC7721 cell line was successfully constructed, and the protein and mRNA expression levels of PRRX1 were significantly increased in lentivirus infected cells (all P< 0.01). Compared with control group and vector group, over-expression of PRRX1 significantly inhibited cell proliferation, weakened mitochondrial membrane potential, but increased the rate of apoptosis, elevated the shear level of caspase-3, promoted the release of Cyt C protein from mitochondrial into cytosol and increased the enzymatic activity of caspase-9 (all P<0.05 or P<0.01). In addition, over-expression of PRRX1 also promoted the protein expressions of p53 and Bax but inhibited the protein expression of Bcl-2 (all P< 0.05 or P<0.01); however,it had no significant effect on the expression of Fas protein and the enzymatic activity of caspase-8 (all P＞ 0.05). Conclusion： ：Over-expression of PRRX1 induces apoptosis in hepatocellular carcinoma SMMC7721 cells, which may be related to the activation of p53-mediated mitochondrial apoptotic pathway