p53-Induced Apoptosis Occurs in the Absence of p14ARF in Malignant Pleural Mesothelioma

Abstract

Malignant pleural mesotheliomas (MPMs) are usually wild type for the p53 gene but contain homozygous deletions in the INK4A locus that encodes p14(ARF), an inhibitor of p53-MDM2 interaction. Previous findings suggest that lack of p14(ARF) expression and the presence of SV40 large T antigen (L-Tag) result in p53 inactivation in MPM. We did not detect SV40 L-Tag mRNA in either MPM cell lines or primary cultures, and treatment of p14(ARF)-deficient cells with cisplatin (CDDP) increased both total and phosphorylated p53 and enhanced p53 DNA-binding activity. On incubation with CDDP, levels of positively regulated p53 transcriptional targets p21(WAF), PIG3, MDM2, Bax, and PUMA increased in p14(ARF)-deficient cells, whereas negatively regulated survivin decreased. Significantly, p53-induced apoptosis was activated by CDDP in p14(ARF)-deficient cells, and treatment with p53-specific siRNA rendered them more CDDP-resistant. p53 was also activated by: 1) inhibition of MDM2 (using nutlin-3); 2) transient overexpression of p14(ARF); and 3) targeting of survivin using antisense oligonucleotides. However, it is noteworthy that only survivin downregulation sensitized cells to CDDP-induced apoptosis. These results suggest that p53 is functional in the absence of p14(ARF) in MPM and that targeting of the downstream apoptosis inhibitor survivin can sensitize to CDDP-induced apoptosis.

Upregulated p53 expression activates apoptotic pathways in wild-type p53-bearing mesothelioma and enhances cytotoxicity of cisplatin and pemetrexed

“…13,14 It is however currently unknown about a precise mechanism of phosphorylation of p53 induced under no apparent DNA damage as Ad infection itself, as demonstrated with Ad-LacZ, did not increase endogenous p53 expression or the phosphorylation. Overexpressed p53 was not always associated with the phosphorylation, 9 but increased p53 expression can augment activities of p53-phosphorylating kinases and consequently result in p53 activation.…”

“…9 Ad-p14 transduction thus did not initiate the entire p53-mediated pathways or p14 may negatively affect apoptotic pathways induced by DNA-damaging agents. In contrast, Ad-p53 transduction enhanced CDDP-induced cytotoxicity as well as PEMmediated cell killing with a synergistic manner in most of the cells tested.…”

“…Moreover, Yang et al 18 showed that Ad-p16 did not increase CDDP-mediated cytotoxicity as well as Ad-p14. 9 Interestingly, co-transduction with Ad-14 and Ad-p16 was less effective than Ad-p16 alone, but the underlying mechanism remains unknown. 18 A combinatorial use of Ad-p53 and Ad-p16 needs to be tested to clarify whether restoration of the p53 and the pRb pathways may compete in terms of cytotoxicity in mesothelioma.…”

“…Forced expression of p16 or p14 with adenovirus vectors (Ad-p16, Ad-p14) in fact inhibited proliferation of mesothelioma cells through dephosphorylation of pRb and restoration of the p53 pathways. [5][6][7][8] Expressed p14 however did not fully activate the p53-mediated signal transduction, 9 and Ad-p14-mediated anti-tumor effects required intact p53 downstream pathways. 6 Reactivation of p53 by Ad-p53 can therefore be a more direct way to reconstitute all the p53 signal pathways and can dephosphorylate pRb through p53-induced upregulation of p21.…”

The Molecular Basis of Cisplatin Resistance in Bladder Cancer Cells

“…Survivin, one of the members of the IAP family, is activated by cisplatin, which in part protects cells from cisplatin-induced apoptosis (Belyanskaya et al, 2005). An associated between survivin levels and cisplatin resistance has been reported for a number of cell lines derived from various cancer tissues including thyroid, lung and colon (Tirro et al, 2006) (Belyanskaya et al, 2005, Hopkins-Donaldson et al, 2006, Pani et al, 2007. Bladder cancer cell lines showed a high expression of survivin compared to non-cancerous uro-epithelial cells (Yang et al, 2010).…”