Abstract
Human T-cell leukemia cell line MOLT-4 is highly radiosensitive and shows typical apoptotic cell death after irradiation. p53 is a well-studied transcription factor associated with the cell death. Previous studies by us and others have demonstrated that overexpressing p53 shRNA or dominant negative form of p53 in MOLT-4 cells results in resistance to radiation-induced apoptosis. On the other hand, several researchers have reported a novel apoptotic function of p53, i.e., transcription-independent apoptogenic role of p53 in mitochondria. Moreover, recent studies have shown that codon 72 polymorphic variants of p53 show different sensitivities to apoptosis. Arg72 variant of p53 has more potent apoptosis-inducing activity in mitochondria than Pro72 variant.
In this study, we initially investigated the codon 72 polymorphism of p53 in MOLT-4 cells. Immunoblotting analysis of p53 in 10 Gy-gamma-irradiated MOLT-4 and Nalm-6 cells revealed that the radiation-induced p53 in Nalm-6 cell showed mostly same electrophoretic mobility as Pro72 p53 from SaOs-2 transfectant, and MOLT-4 cell's p53 showed different mobility. The altered mobility of MOLT-4 p53 suggested the possibility that the p53 was Arg72 variant. Therfore, we next analyzed p53 exon4 genomic DNA sequences encoding codon 72. As expected, MOLT-4 was homozygous with respect to the allele encoding Arg72. The relative contribution of Arg 72 variant in irradiated MOLT-4 transcription-dependent/independent apoptosis would be examined and presented.
