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Use of rhek-1 immortalized human keratinocytes for detection of induced mutation at the hypoxanthine-Guanine phosphoribosyltransferase locus.

We report here the use of a nontumorigenic, immortalized human keratinocyte line, RHEK-1, for the detection of rare mutations induced at the hypoxanthine-guanine phosphoribosyltransferase locus. RHEK-1 keratinocytes were used as a prototype to determine mutagen treatment conditions, plating density, and phenotypic expression time for maximum recovery of thioguanine-resistant mutants. Mutation frequency was measured after exposure to ionizing radiation or to polycyclic aromatic hydrocarbons. 7,12-Dimethylbenz[a]-anthracene and benzo[a]pyrene caused almost no cytotoxicity, but induced thioguanine-resistant mutants at frequencies as much as 30 to 40-fold higher than the median spontaneous frequency of 7 x 10(-6). X-irradiation was also an efficient mutagen in RHEK-1 keratinocytes. The mutants were aminopterin-sensitive and possessed no measurable hypoxanthine-guanine phosphoribosyltransferase activity. The RHEK-1 human epithelial cell line is therefore useful for the study of induced mutation at a defined genetic locus as well as being an important model for the investigation, of molecular, cellular and genetic mechanisms of neoplastic transformation in human stratified squamous epithelia.