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Pifithrin‐α decreases the radioprotective efficacy of a Podophyllum hexandrum (Himalayan mayapple) fraction (REC‐2006) in HepG2 cells
Author(s) -
Singh Pankaj Kumar,
Kumar Raj,
Sharma Ashok,
Arora Rajesh,
Jain Swatantra Kumar,
Sharma Rakesh Kumar
Publication year - 2009
Publication title -
biotechnology and applied biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.468
H-Index - 70
eISSN - 1470-8744
pISSN - 0885-4513
DOI - 10.1042/ba20080250
Subject(s) - podophyllum , apoptosis , hsp70 , cell cycle , hsf1 , cell cycle checkpoint , microbiology and biotechnology , biology , chemistry , cancer research , heat shock protein , podophyllotoxin , biochemistry , gene , stereochemistry
Inhibition of the tumour suppressor p53 by PFT (pifithrin‐α) 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 μg/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 G 1 ‐ and G 2 ‐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).