Induction and alternative splicing of the Bax gene mediated by p53 in a transformed endothelial cell line

Overexpression of the normal p53 protein in tumor cell lines is known to induce apoptosis and a potential mediator of this response is the apoptotic inducer, Bax. The expression of Bax mRNA products were investigated in the ECV-304 endothelial cell tumor line and primary human umbilical vein endothelial cells (HUVEC) that were induced to overexpress the p53 protein. Induction of p53 in ECV-304 and HUVEC cells was mediated by infection with a p53 recombinant adenovirus (AdCMV-p53). The expression of Bax transcripts in p53-induced cells was investigated by reverse-transcription polymerase chain reaction (RT-PCR). The Bax alpha mRNA species was detected in both ECV-304 and HUVEC cells. Surprisingly, Bax alpha expression was reduced several-fold in ECV-304 endothelial cells overproducing p53 and no change in Bax alpha was detected in HUVEC cells after induction of p53. However, the Bax delta spliced transcript was observed to be induced by p53 in the ECV-304 tumor cell line. Bax alpha was the predominant species expressed in normal human endothelial cells but, in contrast to the immortalized ECV-304 endothelial cell line, induction of p53 failed to alter the expression of Bax alpha or to induce any other Bax transcripts. HUVEC cells were more resistant to p53, since at least 80% of the HUVEC cell population survived the overexpression of p53 after 24 h of infection with AdCMV-p53. An ECV-304-derived cell line (DECV) resistant to p53-mediated apoptosis did not show any changes in expression of Bax mRNA products, even in the presence of high levels of p53. ECV-304 endothelial cells that expressed the Bax delta species underwent apoptosis much more rapidly and more extensively after induction of p53, suggesting that the Bax delta species enhances p53-mediated apoptosis.