Transfection of p27kip1 enhances radiosensitivity induced by 60Co γ-irradiation in hepatocellular carcinoma HepG2 cell line

Variation of gene expression profile linked to p27 (Kip1) Ser(10) phosphorylation status in MCF-7 cell line

Ser(10) was the major phosphorylation site in p27(Kip1) (here after referred to as p27), accounting for 70% of the total phosphorylation of this protein, due to cytoplasmic shuttling. To further elucidate the mechanism for Ser(10)-mediated dysfunction of p27 during breast cancer progression. Affymetrix Human Genome U133A Array was used to identify differentially regulated genes between MCF-7 breast cancer cell lines stably-transfected with wild type and Ser(10) mutant (substitution of Ser(10) with Ala, S10A), alternatively. Then to confirm by RT-PCR then western blot partly. Microarray analysis showing that S10A, then abrogation of Ser(10) phosphorylation, result in important changes in a large number of genes involved in the control of cell cycle, cell differentiation, metabolism, immune response and signal transduction. S10A induced cell cycle G(0) phase arrest by FACS method. And cell growth inhibition and abrogation of cytoplasmic translation. Our data indicate that abrogation of phosphorylation of Ser(10) resulted in significant changes in gene expression profiles which mediate cell cycle redistribution, sub-cellular localization.

The reduction of cell death and proliferation by p27(Kip1) minimizes DNA damage in an experimental model of genotoxicity

Hepatocellular carcinoma (HCC) is the fifth most commonly occurring cancer worldwide. The expression of p27 has been related to reduced severity of tumor grade and recurrence of HCC. The study assessed the role of p27 on the cell proliferation and death, and DNA mutagenesis in experimental genotoxicity induced by aflatoxin B1 (AFB(1)) in cultured hepatocytes obtained from control and p27(Kip1) deficient mice. The overexpression of p27 was assessed with wild type p27(Kip1) expression vector in HepG2 cells. The expression of p27, p21 and p53 was assessed in well and poorly-differentiated liver tumors. DNA damage and cell death induced by AFB(1) were related to a reduction of p27 and p21 expression in cultured hepatocytes. AFB(1)-induced nuclear phosphorylated (Ser 10) p27 degradation was related to a rise of nuclear KIST, Rsk-1 and Rsk-2 expression and cytoplasm phosphorylated (Thr 198) p27 expression. The overexpression of p27 reduced cell proliferation, cell death and DNA damage in AFB(1)-treated hepatocytes. The enhanced survival of patients with well differentiated compared to poorly-differentiated tumors was related to high expression of p27, p21 and p53 in liver sections. The study showed that the p27 reduced cell proliferation and death, as well as the accumulation of DNA damage in hepatocarcinogenesis.

Pifithrin-alpha decreases the radioprotective efficacy of a Podophyllum hexandrum Himalayan mayapple fraction REC-2006 in HepG2 cells

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).