The role of nucleophosmin/B23 in radiation-induced chromosomal instability in human lymphoblastoid cells of different p53 genotypes.

Purpose: To investigate the role of nucleophosmin (NPM/B23) in radiation-induced chromosomal instability and apoptosis in human lymphoblastoid cells with different protein 53 (p53) status. Materials and methods: Wild type (wt) p53 TK6 and mutant type (mt) p53 WTK1 with or without short hairpin RNA (shRNA)-mediated silencing of NPM, TK6 with or without short interfering RNA (siRNA)-mediated silencing of p53 (p53i and NEGi) were irradiated with 4 Gy gamma-rays. Six to 48 h after irradiation, the index of apoptosis, chromosome aberration, cell cycle distribution and the levels of total NPM and phosphorylated-threonine 199 (pThr199) NPM proteins were measured. Cells in some dishes were treated with 10 μM Olomoucine (OLO) for 3 h before irradiation and remained in the medium after irradiation. Results: The rates of radiation-induced apoptosis in TK6 and TK6/NEGi were about 2-fold of those in WTK1 and TK6/p53i, while the frequencies of polyploidy in TK6 and TK6/NEGi were obviously lower than those in WTK1 and TK6/p53i. Moreover, after irradiation, pThr199 NPM levels increased significantly in WTK1 and TK6/p53i, and slightly increased in TK6 and TK6/NEGi, indicating that the increased level of pThr199 NPM was related to p53 status. When Thr199 hyperphosphorylation of NPM was inhibited by OLO or when NPM was knocked down, we found that radiation-induced apoptosis was more pronounced and polyploidy formation was reduced as compared with negative control while the magnitude of these changes in TK6 was obviously higher than that in WTK1, indicating that NPM has an antagonistic interaction with wt p53. Conclusions: NPM/B23 plays an important role in protecting cells from radiation-induced apoptosis and increasing polyploidy formation via either a p53 or non-p53 pathway. [ABSTRACT FROM AUTHOR]