Transcriptionally active and inactive genes are similarly modified by chemical carcinogens or X-ray in normal human fibroblasts

Abstract

Chemical carcinogens and ionizing radiation induce DNA modifications and strand breaks in cells. This damage is reported to be affected by chromatin proteins or chromatin of a higher structure order. To compare the sensitivity of transcriptionally active and inactive genes on chromatin toward DNA-damaging agents, we treated normal human fibroblasts (WI-38) cells in N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), X-ray, 4-hydroxyaminoquinoline 1-oxide or N-acetoxy-2-acetylaminofluorene, and high molecular weight DNA was isolated. After digestion with EcoRI to completion, the DNA was electrophoresed on an alkaline agarose gel, blotted on a nitrocellulose filter and hybridized with a transcriptionally active gene probe (human type I(alpha 2) procollagen gene) or an inactive gene probe (human beta-globin gene). The results show that both genes are similarly modified by these agents. Repair of DNA damage caused by MNNG also occurred similarly in collagen and beta-globin genes after removal of MNNG.