97 Cisplatin-induced apoptosis in malignant pleural mesothelioma cells involves p53 but not p14ARF

Abstract

Background: Malignant pleural mesothelioma (MPM) tumours often contain homozygous deletions in the INK4A locus that encodes p14ARF, a tumour suppressor protein that promotes p53 stability by blocking the p53 inhibitor MDM2. It has been suggested that p53 is inactive in MPM due to the absence of p14ARF expression. Methods and Results: We investigated p53 activation in p14ARF negative MPM cells or primary cultures after cisplatin treatment and found increased levels of phospho-p53 (serine-15), total p53 protein and p53 specific DNAbinding activity in the majority of cell lines. In addition, the expression levels of p53-positively controlled genes p21WAF, Bax, pig3 and MDM2 increased on incubation with cisplatin, whereas levels of the negatively regulated p53 target gene survivin decreased. Cisplatin-induced apoptosis was detected in p14ARF-deficient cells expressing wild type p53 but not in a p53 mutant cell line. Knockdown of wild type p53 with siRNA rendered MPM cells more resistant to cisplatin-induced apoptosis. Over-expression of p14ARF in p53 wild type MPM cells by transient transfection did not increase their sensitivity to cisplatininduced apoptosis, however, pre-incubation with antisense oligonucleotides targeting the inhibitor of apoptosis protein survivin lead to p53 activation and increased apoptosis sensitivity to cisplatin. Conclusions: These results suggest that p53 is functional in MPM in the absence of p14ARF, and that therapies that target the inhibitor of apoptosis protein survivin are worthy of investigation in MPM.