Identification of RKIP as a differentially tyrosine-phosphorylated protein in nasopharyngeal carcinoma and normal nasopharyngeal epithelial tissues by phosphoproteomic approach

Aims To screen for differentially tyrosine-phosphorylated proteins between nasopharyngeal carcinoma (NPC) and normal nasopharyngeal epithelial tissues (NNET) to provide a basis for elucidate the molecular mechanisms of NPC carcinogenesis. Methods Two-dimensional (2-D) electrophoresis was applied to separate proteins from NPC and NNET, respectively, and 2-D Western blotting was performed to detect tyrosine-phosphorylated proteins using antiphosphotyrosine antibody. Differentially tyrosine-phosphorylated proteins were identified by electrospray ionization-quadrupole time-of-flight MS (ESI-Q-TOF MS). NetPhos software was used to predict the tyrosine-phosphorylation sites of the identified proteins, and Western blotting was used to detect the tyrosine-phosphorylated levels of RKIP in NPC and NNET. Results Twenty-five differentially tyrosine-phosphorylated proteins in the two types of tissues were found, 13 of which were identified by ESI-Q-TOF MS. Among the 13 identified proteins, tyrosine-phosphorylated levels of 7 proteins were increased, and those of 6 proteins were decreased in NPC compared with NNET. NetPhos software prediction showed that all the 13 identified proteins contained tyrosine phosphorylation sites, and the differentially tyrosine-phosphorylated level of RKIP in NPC and NNET was confirmed. Conclusion The 13 differentially tyrosine-phosphorylated proteins may be involved in the development and progression of NPC.