Human osteosarcoma cells (transfected with inducible wild type p53) were compared in the mutant frequency of hypoxanthine-guanine phosphoribosyl transferase gene (induction of the 6-thioguanine resistent mutation in the hyphxanthine-guanine phosphoribosyl transferease gene) and the mutant spectrum (e.g. transition, deletion, insertion).
The hypoxanthine-guanine phosphoribosyl transferase (HPRT) is an enzyme in the purine (for example guanine) synthesis pathway. HPRT-negative cells are not able to use guanine for GTP synthesis und thus, they have to synthesize the base de novo. Using the guanine analog 6-thioguanine HPRT-positive cells use 6-thioguanine for nucleotide synthesis. However, integration of 6-thioguanine leads to DNA and RNA damage and it is lethal for these cells. In contrast, HPRT-negative cells are not able to utilize 6-thioguanine and survive.
The HPRT gene mutation assay is a well-established mutagenicity assay based on the selection of clones resistant to the purine analog 6-thioguanine. I.e. for determination of the induction of 6-thioguanine resistant mutation in the HPRT gene exposed cells are plated in a medium containing 6-thioguanine.
The experiments were repeated three times.
|Exposure room||An acrylic CO2 incubator was installed in the inner space between cores which housed the annular plates.|
|Setup||magnetic cores (silicon steel plates) 240 x 340 mm, 40 mm apart; 2 copper coils penetrating through them|
|Sham exposure||A sham exposure was conducted.|
The exposure of human osteosarcoma cells to high-density extremely low frequency magnetic fields induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene.
The mutation in the cells was suppressed by expression of the introduced wild type p53 gene during 400 mT extremely low frequency magnetic fields exposure.
No marked difference in the mutation spectrum was observed among the exposed p53 induced, exposed p53 not-induced and sham exposed cells.
Our findings suggest that wild type p53 has a function in suppression of DNA replication errors and/or in maintenance of genomic stability after high-density extremely low frequency magnetic field exposure.