GGT to GTT Transversions in Codon 12 of the K-ras Oncogene in Rat Renal Sarcomas Induced with Nickel Subsulfide or Nickel Subsulfide/Iron Are Consistent with Oxidative Damage to DNA¹

Nickel is a toxic, mutagenic, and carcinogenic metal of significant occupational and environmental concern. Although several cellular targets of nickel have been identified, considerable evidence suggests that it can act indirectly upon DNA by inducing the formation of oxidized purines or pyrimidines that constitute promutagenic lesions. In this study, we examined nickel subsulfide (Ni₃S₂)- or Ni₃S₂/iron-induced renal sarcomas in F344 rats for the presence of transforming mutations in the K-ras oncogene. Selective oligonucleotide hybridization analysis of K-ras gene sequences amplified by polymerase chain reaction revealed that 1 of 12 primary tumors induced with Ni₃S₂ and 7 of 9 primary tumors induced with Ni₃S₂/iron contained exclusively GGT to GTT activating mutations in codon 12. These mutations are consistent with the known ability of nickel, in the presence of an oxidizing agent, to catalyze formation of 8-hydroxydeoxyguanosine, which in turn promotes misincorporation of dATP opposite the oxidized guanine residue. The presence of GGT to GTT transversions was confirmed by direct sequencing of the polymerase chain reaction products. Sequencing also revealed that there were no transforming mutations in codons 13 or 59–61. Additionally, a direct correlation between shortened tumor latency and the presence of activating ras mutations was noted. These results show that, in rat kidney, Ni₃S₂ can induce transforming mutations that are consistent with the ability of nickel to produce oxidative lesions and that iron, which exacerbates the extent of cellular oxidative damage, can enhance the frequency of these transforming mutations.