Wild-type p53 Expression Overcomes p21-mediated G1 Arrest and Induces Apoptosis in Cancer Cells Expressing Bax

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Tumor suppression by p53 is deficient in the majority of human cancers. Previous studies have suggested that expression of p53 in human cancer cells can result in either growth arrest or apoptosis. The biological and genetic de-terminants that dictate which of these two pathway - apoptosis or arrest - will be chosen by a particular cell following p53 expression are largely un-known. To investigate the basis of this difference, we evaluated the role of p21, a mediator of p53-induced growth arrest. We generated a replication-deficient adenoviral recombinant which expresses p21 and com-pared its tumor suppressive abilities with Ad-p53. Infection with Ad-p21 re-sulted in high levels of p21 expression and suppressed the growth of human cancer cells, through the Gl arrest of the cell cycle. We then examined the effects of combined infection with Ad-p21 and Ad-p53 to investigate which of these molecules had the dominant function. Introduction of exogenous p53 in RERF-LC-OK, BT549 and ZR-75-1 cells overcame p21-mediated cell cycle arrest at G1 and induced apoptosis, suggesting that this affect is a general event among human cancer cell lines. We then evaluated the role of Bax/Bcl-2 in the response to p53. A Significantly greater amount of Bax protein was pre-sent in cell lines undergoing apoptosis than in cells with arrested growth,suggesting that Bax might be an important component of the p53-mediated apoptosis of cancer cells.
札幌医科大学の論文