TIS21 shifts p53-induced response of EJ bladder carcinoma cells from senescence to apoptosis

Abstract

It has been known that wild type p53 mediates senescence phenotypes and cell death in response to DNA damage signals both in human and animals. TIS21BTG2/PC3 has been known as a p53 target gene and functions as a tumor suppressor in carcinogenesis of thymus, prostate, kidney, and liver. Bladder carcinoma EJ cells contain both oncogenic H-ras and non-functional p53 tumor suppressor due to mutation in its exon 5, possibly contributing to conferring EJ cells cancer characteristic. In normal primary fibroblast cells, over-expression of H-ras activates p53 pathway and induces cellular senescence.

Employing adenoviral vectors carrying p53 (Ad-p53) or TIS21 (Ad-TIS21) gene, I evaluated the effect of TIS21 on the p53-induced senescence phenotypes in EJ cells. Adenoviral transfer with wild-type p53 significantly induced senescent phenotypes of EJ cells characterized by increase in size, flattened morphology and an increase in SA-？？-galactosidase activity. p53 increased expression of paxillin which regulated senescent morphology localizing at the edge of cell membrane. EJ cells co-expressing p53 plus TIS21 significantly reduced the expression paxillin, which was induced by p53 expression.

The effect in cells infected with p53 plus TIS21 was quite distinct from that of the p53 alone. Expression of the tumor suppressors clearly reduced cell size, SA-？？-galactosidase activity and expression of paxillin. Expressions of p53 plus TIS21 significantly induced cell death of the cells, as demonstrated by staining with EthD-1 and Annexin V. Moreover, the expression of TIS21 increased apoptosis-associated acetylation of p53 molecule at lysine residues and its accumulation in the nuclei.

Based on the evidences presented herein, I conclude that TIS21 directs p53-induced senescence towards apoptosis in EJ bladder carcinoma cells.