Multimolecular complex of Par-4 and E2F1 binding to Smac promoter contributes to glutamate-induced apoptosis in human- bone mesenchymal stem cells.

Neural cells undergo glutamate-induced apoptosis in ischaemic brain tissue, in which prostate apoptosis response-4 gene (Par-4) is involved. Human-bone mesenchymal stem cells can be utilized as an effective therapy for ischemic brain injury. In this study, we found that glutamate could induce apoptosis in human-bone mesenchymal stem cells, accompanied by increased expression of Par-4 gene and Smac release from mitochondria. Repressing Par-4 expression attenuated the glutamate-induced apoptosis. Both Par-4 protein and E2F1 protein could bind to E2F1-binding BS3 site on Smac promoter and participated in the formation of a proteins-DNA complex. Moreover, in the complex, E2F1, not Par-4, was found to be directly bound to the Smac promoter, suggesting that Par-4 exerted indirectly its transcriptional control on the Smac gene though interacting with E2F1. Expression of full-length Par-4 in human-bone mesenchymal cells resulted in increased activity of the Smac promoter. In addition, the indirect transcripional regulation of Par-4 on Smac depended on its COOH terminus-mediated interaction between Par-4 and E2F1. We conclude that the formation of proteins-DNA complex, containing Par-4 protein, E2F1 protein and the Smac promoter, contributes to the pro-apoptotic effect on glutamate-treated human-bone mesenchymal stem cells.

[Effects of Par-4 gene silencing induced by siRNA on the expression of Smac gene, activity of caspase-3, and apoptosis of human bone marrow mesenchymal stem cells].

OBJECTIVE: To investigate the effects of Par-4 gene silencing induced by siRNA on the expression of Smac gene, activity of caspase-3, and apoptosis of human bone marrow mesenchymal stem cells (hBMSCs). METHODS: Bone marrow was obtained from a healthy young man and hBMSCs were isolated and cultured. Two siRNAs (Par-4-siRNA-1 and -2) targeting Par-4 gene were chemically synthesized. Eukaryocytic expression vectors containing these Par-4 siRNA sequences were established and transfected into the hBMSCs. The hBMSCs were divided into 4 groups: non-transfected hBMSCs (normal control group), blank Pae-4 plasmid transfected hBMSCs (Par4 control group), Par4-siRNA-1 transfected hBMSCs, and Par-4-siRNA-2 transfected hBMSCs. The expression of Par-4 mRNA was detected by real-time PCR. Another hBMSCs were inoculated in DMEM and divided into 4 groups: non-transfected normal hBMSCs, glutamate (an apoptosis inducer) + non-transfected hBMSC group, glutamine + Par-4-siRNA-1 hBMSC group, and glutamate + Par4-SiRNS-2 hBMSC group. Flow cytometry was used to detect the apoptotic rate. The relative activity of caspase-3 was determined by colorimetric assay. Western blotting was used to detect the Smac protein expression. RESULTS: The relative mRNA expression levels of Par-4 gene of the Par-4-siRNA-1 hBMSCs, Par-4 SiENA-2 hBMSCs, and Par-4 control hBMSCs were 0.12 +/- 0.03, 0.33 +/- 0.09, and 0.97 +/- 0.02 respectively, decreased by 88%, 67%, and 3% respectively compared with that of the normal control. The percentages of apoptotic cells of the glutamate + Par-4-siRNA-1 hBMSCs was (37.2 +/- 6.3)%, significantly lower than that of the glutamate + non-transfected hBMSC group [(58.9 +/- 8. 9)%, F = 58.26, P < 0.01). The Smac protein expression level of the glutamate + non-transfected hBMSC group was significantly higher than that of the normal control group (P < 0.01); however, the Smac protein expression level of the Par-4-siRNA-1 hBMSC group was significantly lower than that of the glutamate + non-transfected hBMSC group (P < 0.01). The caspase-3 activity of the glutamate + Par-4-siRNA-1 hBMSC group was significantly lower than that of the glutamate + non-transfected BMSC group (P < 0.01). CONCLUSION: Par-4-siRNA-1 inhibits markedly the apoptosis of the hBMSCs induced by glutamate. Par-4 gene silencing induced by siRNA inhibits the apoptosis of hBMSCs. The mechanism of the inhibition may be closely related to suppression of the up-regulation of Smac gene expression and caspase-3 activity.

[Effects of small interfering RNA (siRNA) against Par-4 gene on the apoptosis of human bone marrow mesenchymal stem cells].

OBJECTIVE: The prostate apoptosis response factor-4 (Par-4) gene was originally identified by differential screening for genes that are up-regulated when prostate cells are induced to undergo apoptosis. Par-4 was found to possess potent apoptotic activity in various cellular systems in response to numerous stimuli. The aim of this study was to explore the effects of small interfering RNA (siRNA) against Par-4 gene on the apoptosis of human bone marrow mesenchymal stem cells (hBMSCs) exposed to glutamate. METHODS: Primary culture of hBMSCs was carried out and siRNAs targeted Par-4 gene (Par-4-SiRNA) were chemically synthesized. Eukaryocytic expression vector was built and were transfected into hBMSCs with liposome. After selecting with G418, the stable cell clones were treated with glutamate. The expression of Par-4 mRNA was determined by real-time PCR. The apoptosis of hBMSCs was quantified by flow cytometry. Western blotting was used to detect the protein levels of phosphorylated Akt1 (Thr308). Relative Caspase-3 activity was determined by colorimetric assay. RESULTS: The Par-4-SiRNA-1 and Par-4-siRNA-2 could markedly down-regulate the mRNA levels of Par-4 gene in hBMSCs. With the transfections of Par-4-SiRNA-1 and Par-4-SiRNA-2, the levels of Par-4 mRNA were respectively decreased by 88% and 67%. Both Par-4-SiRNA-1 and Par-4-SiRNA-2 inhibited significantly the apoptosis of hBMSCs induced by glutamate, in which the percentages of apoptotic cells were respectively decreased to 38.80% +/- 3.97% (P < 0.01) and 45.49% +/- 4.32% (P < 0.01) from 60.30% +/- 6.82%. Western blot assays demonstrated that, glutamate down-regulated the expression of phosphorylated Akt1 proteins in hBMSCs (89.07 +/- 6.42 and 28.30 +/- 5.65, respectively, P < 0.01). However, Par-4-SiRNA-1 and Par-4-SiRNA-2 could markedly recover the down-regulation of Akt1 proteins induced by glutamate (63.56 +/- 6.75 and 45.59 +/- 4.88, respectively, P < 0.01). And the relative Caspase-3 activity which was enhanced by the treatment with glutamate (0.1428 +/- 0.0495 and 0.8616 +/- 0.1051, P < 0.01), was suppressed by Par-4-SiRNA-1 and Par-4-SiRNA-2 (0.8616 +/- 0.1051 and 0.6581 +/- 0.0555, respectively, P < 0.01). CONCLUSION: SiRNA against Par-4 gene could inhibit the apoptosis of hBMSCs induced by glutamate, and its inhibitory effects may be mediated by the up-regulation of phosphorylated Akt1 and the suppression of the relative Caspase-3 activity.