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.