Differential regulation of survivin by p53 contributes to cell cycle dependent apoptosis

Abstract

Recent studies indicate that cell-cycle checkpoints are tightly correlated with the regulation of apoptosis, in which p53 plays an important role. Our present works show that the expression of E6/E7 oncogenes of human papillomavirus in HeLa cells is inhibited in the presence of anti-tumor reagent tripchlorolide (TC), which results in the up-regulation of p53 in HeLa cells. Interestingly, under the same TC-treatment, the cells at the early S-phase are more susceptible to apoptosis than those at the middle S-phase although p53 protein is stabilized to the same level in both situations. Significant difference is exhibited between the two specified expression profiles. Further analysis demonstrates that anti-apoptotic gene survivin is up-regulated by p53 in the TC-treated middle-S cells, whereas it is down-regulated by p53 in the TC-treated early-S cells. Taken together, the present study indicates that the differential p53-regulated expression of survivin at different stages of the cell cycle results in different cellular outputs under the same apoptosis-inducer.

p53-independent pRB degradation contributes to a drug-induced apoptosis in AGS cells

“…Several reports showed that TC inhibited the proliferation of peripheral blood mononuclear cells [26], mesangial cells [27] and spermatocytes [28]. It was also reported that TC could induce apoptosis of cells in both p53-dependent and p53-independent manner [29,30]. Moreover, our group showed that TC caused DNA damage in CHO cells and induced the degradation of c-Myc protein [31].…”

“…6A and 6D). To address whether the activated p53 involved in the degradation of pRB in the TC treated AGS cells, an AGS-derivative cell line, AER, containing the p53 dominant-negative was constructed (see Materials and methods) [30]. When the cells were administrated with 20 ng/ml TC for the indicated times, there was the pRB reduction of the TC-treated AER cells in a time-dependent manner (Fig.…”

“…Since our previous data reported that TC could induce apoptosis of HeLa S3 cells in a p53 dependent manner [30], we analyzed the apoptosis of AER cells containing the p53 dominant-negative under the TC-treatment. The results showed the significant reduction of the apoptotic population observed in the TC treated AER cells (Fig.…”

“…DNA-damaging agents are used frequently in cancer therapy. Our previous works showed that TC could induce apoptosis by degrading c-Myc protein [31] or via p53-dependent apoptotic pathway [30] in different cell lines. In the present study, we revealed the p53-independent degradation of pRB might be one of the causations of TCinduced apoptosis of AGS cells, which suggests a novel mechanism of action that TC exhibits its antineoplastic activity.…”

“…For the stable cell line AER, AGS cells was transfected with pEGFP-cgTP53, an EGFP fused p53 dominant-negative construct [30], by Lipofectamine TM 2000 system. AER was further selected in the presence of 500 µg/ml G418.…”