The Cancer-associated K351N Mutation Affects the Ubiquitination and the Translocation to Mitochondria of p53 Protein

Background:Stress-induced monoubiquitination of p53 is a crucial event forthe nuclear-cytoplasm-mitochondria trafficking and transcription-independentpro-apoptotic functions of p53. Although an intact ubiquitination pathway and afunctional Nuclear Export Sequence (NES) are required for p53 nuclear export,the role of specific residues within this region in regulating both processesremains largely unknown.Materials and Methods:Here we characterize the mechanisms accounting forthe nuclear accumulation of a new point mutation (Lys 351 to Asn) in the NESof p53 identified in a cisplatin-resistant ovarian carcinoma cell line (A2780CIS). In particular we evaluated the ubiquitination stauts of p53 K351N, itstanslocation to mitochondria and mitochondria-dependent apoptosis.Results:We found that K351N substitution abrogates the monoubiquitinationof p53 induced by both Mdm2 and MSL2 E3-ligases. As a consequence,cells expressing p53 K351N mutant showed defects in cisplatin-inducedtranslocation of p53 to mitochondria, Bax oligomerization and mitochondrialmembrane depolarization.Conclusion:These data identify K351N as a critical mutation of p53 thatcontributes to the development and maintenance of resistance to cisplatin.