Inability of p53-reactivating compounds Nutlin-3 and RITA to overcome p53 resistance in tumor cells deficient in p53Ser46 phosphorylation

• Published in: Biochemical and biophysical research communications 2012-01, Vol.417 (3), p.931-937
• Main Authors: Ma, Teng, Yamada, Shumpei, Ichwan, Solachuddin J.A., Iseki, Sachiko, Ohtani, Kiyoshi, Otsu, Megumi, Ikeda, Masa-Aki
• Format: Article
• Language: English
• Subjects: Apoptosis; Apoptosis - drug effects; Apoptosis - genetics; Caspase 3; Cell Line, Tumor; Furans - pharmacology; Genes, p53; Humans; Imidazoles - pharmacology; Nutlin-3; p53; p53 resistance; Phosphorylation; Phosphorylation - drug effects; Phosphorylation - genetics; Piperazines - pharmacology; Poly(ADP-ribose) Polymerases - metabolism; RITA; Serine - genetics; Serine - metabolism; Transduction, Genetic; Tumor Suppressor Protein p53 - genetics; Tumor Suppressor Protein p53 - metabolism
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2011.11.161

► Nutlin-3 and RITA activate p53 without genotoxic stress. ► Phosphorylation of p53Ser46 plays critical roles in p53-mediated apoptosis. ► Nutlin-3 and RITA failed to induce apoptosis in the phosphorylation-deficient cells. ► They did not restore p53Ser46 phosphorylation in the phosphorylation-deficient cells. ► Thus, Ser46 phosphorylation is crucial for Nutlin-3- and RITA-mediated apoptosis. The p53 tumor suppressor protein plays key roles in protecting cells from tumorigenesis. Phosphorylation of p53 at Ser46 (p53Ser46) is considered to be a crucial modification regulating p53-mediated apoptosis. Because the activity of p53 is impaired in most human cancers, restoration of wild-type p53 (wt-p53) function by its gene transfer or by p53-reactivating small molecules has been extensively investigated. The p53-reactivating compounds Nutlin-3 and RITA activate p53 in the absence of genotoxic stress by antagonizing the action of its negative regulator Mdm2. Although controversial, Nutlin-3 was shown to induce p53-mediated apoptosis in a manner independent of p53 phosphorylation. Recently, RITA was shown to induce apoptosis by promoting p53Ser46 phosphorylation. Here we examined whether Nutlin-3 or RITA can overcome resistance to p53-mediated apoptosis in p53-resistant tumor cell lines lacking the ability to phosphorylate p53Ser46. We show that Nutlin-3 did not rescue the apoptotic defect of a Ser46 phosphorylation-defective p53 mutant in p53-sensitive tumor cells, and that RITA neither restored p53Ser46 phosphorylation nor induced apoptosis in p53Ser46 phosphorylation-deficient cells retaining wt-p53. Furthermore, treatment with Nutlin-3 or RITA together with adenoviral p53 gene transfer also failed to induce apoptosis in p53Ser46 phosphorylation-deficient cells either expressing or lacking wt-p53. These results indicate that neither Nutlin-3 nor RITA in able to induce p53-mediated apoptosis in the absence of p53Ser46 phosphorylation. Thus, the dysregulation of this phosphorylation in tumor cells may be a critical factor that limits the efficacy of these p53-based cancer therapies.