Shuji Ohtsu

Increase in hypoxanthine-guanine phosphoribosyl transferase gene mutations by exposure to high-density 50-Hz magnetic fields

Exposure to extremely low frequency magnetic field (ELFMF) of 50 Hz and 400 mT induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene of human melanoma MeWo cells. The mutant frequency was enhanced both by increasing the exposure period and the induced current intensity. Mutations induced by X-rays were enhanced by ELFMF exposure. No significant increase in mutant frequency occurred when DNA replication was inhibited during ELFMF exposure. DNA replication error is suspected of causing the mutations produced by ELFMF exposure.

Increased Radiosensitivity of p16 Gene-deleted Human Glioma Cells after Transfection with Wild-type p16 Gene

The A1235 and T98 cell lines derived from human gliomas have homozygous deletions in their p16 genes and are radiosensitive and radioresistant, respectively, with respect to other established glioma cell lines. These differences in radiosensitivity may be due to variations to some extent among cell lines, rather than genetically defined resistance or sensitivity. We examined the effect on radiation sensitivity of introducing a wild‐type p16 gene into both p16‐deficient glioma cell lines. The plasmid pOPMTS containing human wild‐type plfi cDNA and a neomycin resistance gene, or the control plasmid pOPRSV1, were transfected into these cells. Clones from both cell lines, which expressed wild‐type p16 mRNA constitutively after transfection with pOPMTS, were more radiosensitive than the parental cells and clones obtained after transfection with the negative control plasmid.