CHARACTERIZATION OF NICKEL-INDUCED MUTATIONS

A Chinese hamster ovary cell line (designated AS52) has been used to t est the mutagenicity of nickel compounds. This line lacks the endogeno us gene for hypoxanthine phosphoribosyl transferase (HPRT) but contain s an inserted bacterial gene coding for the enzyme guanine-hypoxanthin e phosphoribosyl transferase (gpt) which is the targeted locus for sel ection. Isolated mutants were clonally expanded and analysed utilizing the polymerase chain reaction (PCR) following exposure to ethyl metha nesulfonate (EMS), Ni3S2, Ni(OH)2, NiSO4, and control conditions. Ampl ification of the gpt locus in normal AS52 cells results in the generat ion of two distinct bands, both of which have been characterized by re striction enzyme analysis and nucleotide sequencing. The smaller band represents the gpt gene. The larger band contains a large insert of ba cterial origin and is non-functional. Analysis of mutants revealed thr ee distinct patterns: (1) both PCR bands remain intact; (2) the smalle r DNA band is deleted; (3) both bands are deleted. Mutant analysis was performed with two unique sets of DNA amplification primers with iden tical results. When compared to spontaneous or EMS induced mutants, th ose generated by exposure to nickel compounds exhibited an increase in gene deletions relative to point mutations; the extent of which was c ompound specific: NiSO4 > Ni(OH)2 > Ni3S2. These results clearly sugge st that a variety of genotoxicological mechanisms are involved in the mutagenic activity of nickel compounds