Singh Pankaj Kumar, Kumar Raj, Sharma Ashok, Arora Rajesh, Jain Swatantra Kumar, Sharma Rakesh Kumar
Division of Radiation Biology and Radioprotection, Institute of Nuclear Medicine and Allied Sciences (INMAS), Delhi-110 054, India.
Biotechnol Appl Biochem. 2009 Jul 9;54(1):53-64. doi: 10.1042/BA20080250.
Inhibition of the tumour suppressor p53 by PFT (pifithrin-alpha) promotes p53-mediated apoptosis and protects against doxorubicin-induced apoptosis. The present study was carried out to evaluate the effect of PFT on the radioprotective potential of Podophyllum hexandrum fraction (REC-2006) in HepG2 (p53++) cell line. REC-2006 (10-5 microg/ml) treatment at 2 h before irradiation (10 Gy) rendered 80+/-3% protection in HepG2 cells, whereas PFT debilitated the radioprotective potential of REC-2006. REC-2006 increased the expression of Hsp70 (heat-shock protein 70), HSF1 (heat-shock factor 1) and Bcl-2 in irradiated HepG2 cells, whereas PFT when treated with REC-2006 decreased the expression of Hsp70, HSF1 and Bcl-2 in HepG2 cells. REC-2006 facilitated post-irradiation DNA repair by pausing cell-cycle progression at G1- and G2-phase, whereas no such cell-cycle arrest was observed in irradiated HepG2 cells pretreated with PFT in irradiated HepG2 cells. No change was observed in Mdm2 (murine double minute 2) and Ras-GAP (Ras-GTPase-activating protein) expression with or without PFT treatment. Decrease in the expression of caspase 3 and Bax was observed in HepG2 cells when REC-2006 treatment was given 2 h before irradiation; however, PFT treatment increased the expression of Bax leading to apoptosis. It can be concluded that p53 expression plays a major role in the REC-2006-mediated protection against acute irradiation in HepG2 cells. PFT treatment reduced the radioprotective efficacy of REC-2006 by inhibiting the expression of HSF1 and Hsp70 and thereby the expression of Bcl-2, by up-regulating the cell-cycle-regulatory proteins and therefore reducing the span of time for DNA repair and also by inducing Bax-mediated apoptosis. PFT did not, however, show any effect on p53 regulating protein (Mdm2) and pro-survival protein (Ras-GAP).
PFT（pifithrin-α）对肿瘤抑制因子p53的抑制作用可促进p53介导的细胞凋亡，并抵御阿霉素诱导的细胞凋亡。本研究旨在评估PFT对鬼臼六叶提取物（REC-2006）在HepG2（p53++）细胞系中的辐射防护潜力的影响。在照射（10 Gy）前2小时用REC-2006（10-5微克/毫升）处理，可使HepG2细胞获得80±3%的保护，而PFT削弱了REC-2006的辐射防护潜力。REC-2006增加了受照射HepG2细胞中Hsp70（热休克蛋白70）、HSF1（热休克因子1）和Bcl-2的表达，而当PFT与REC-2006一起处理时，HepG2细胞中Hsp70、HSF1和Bcl-2的表达降低。REC-2006通过使细胞周期进程在G1期和G2期暂停来促进照射后DNA修复，而在用PFT预处理的受照射HepG2细胞中未观察到这种细胞周期阻滞。无论有无PFT处理，Mdm2（小鼠双微体2）和Ras-GAP（Ras鸟苷三磷酸酶激活蛋白）的表达均未发生变化。在照射前2小时给予REC-2006处理时，HepG2细胞中caspase 3和Bax的表达降低；然而，PFT处理增加了Bax的表达，导致细胞凋亡。可以得出结论，p53表达在REC-2006介导的HepG2细胞急性辐射防护中起主要作用。PFT处理通过抑制HSF1和Hsp70的表达，从而抑制Bcl-2的表达，上调细胞周期调节蛋白，因此减少DNA修复的时间跨度，并诱导Bax介导的细胞凋亡，降低了REC-2006的辐射防护功效。然而，PFT对p53调节蛋白（Mdm2）和促生存蛋白（Ras-GAP）没有任何影响。
