Analysis of mammalian-cell mutagenesis and DNA repair using in-vitro selected CHO cell mutants

In the Chinese hamster ovary (CHO) cell line, mutants that have defects in DNA repair processes were isolated. One class of mutants was obtained on the basis of hypersensitivity to killing by far uv radiation and is comprised of 5 genetic complementation groups. Mutants from each group have similar uv sensitivity as measured by killing and mutation induction, show < 10% of the normal level of DNA incision after uv exposure, and exhibit hypersensitivity to chemicals that form bulky DNA adducts. These properties resemble those of cells from xeroderma pigmentosum (XP) patients. However, mutants from two of the CHO complementation groups are extremely sensitive to killing by DNA cross-linking agents, a property commonly associated with Fanconi's anemia rather than XP. Conditions have been devised to test for genetic complementation between the cross-link-sensitive CHO mutants and human diploid fibroblasts. A second class of CHO mutants (represented by strain EM9) appears to differ from the cellular phenotypes of human genetic diseases that affect repair. The properties of this mutant include: (1) greatly elevated (12-fold) baseline frequency of sister-chromatid exchange, (2) delayed rejoining of DNA strand breaks after x rays or simple alkylation damage, and (3) increased sensitivity to killing by DNA strand-breakingmore » agents.« less