Transcriptional Responses to Ionizing Radiation Reveal That p53R2 Protects Against Radiation-induced Mutagenesis in Human Lymphoblastoid Cells

抄録

The p53 protein has been implicated in multiple cellular responses related to DNA damage. Alterations in any of these cellular responses could be related to increased genomic instability. Our previous study has shown that mutations in p53 lead to hypermutability to ionizing radiation. To investigate further how p53 is involved in regulating mutational processes, we used 8K cDNA microarrays to compare the patterns of gene expression among three closely related human cell lines with different p53 status. Template-based clustering analyses of gene expression profiles among these three cell lines revealed distinct patterns. Furthermore, we found several genes associated with DNA repair namely p53R2, DDB2, XPC, PCNA, BTG2 and MSH2 that were highly induced in TK6 compared to WTK1 and NH32. p53R2, which is regulated by p53, is a small subunit of ribonucleotide reductase. To determine whether it is involved in radiation induced mutagenesis, p53R2 protein was inhibited by siRNA in TK6 cells and followed by 2 Gy radiation. The background mutation frequencies at the TK locus of siRNA transfected TK6 cells were about three times higher than those seen in TK6 cells. The mutation frequencies of siRNA transfected TK6 cells after 2 Gy radiation were significantly higher than the irradiated TK6 cells without p53R2 knock down. These results indicate that p53R2 was induced by p53 protein and is involved in protecting against radiation-induced mutagenesis.