Complete cDNA sequence of the Ki-ras proto-oncogene in the liver of wild English sole (Pleuronectes vetulus) and mutation analysis of hepatic neoplasms and other toxicopathic liver lesions

A complete copy of Ki-ras b cDNA from English sole (Pleuronectes vetulus), a benthic marine flatfish, was cloned and sequenced. The percent identity b etween the predicted amino acid sequence of English sole and human Ki-ras b was 97%, whereas the percent identity between the English sole gene and ra inbow trout or Rivulus Ki-ras b was 98%. Areas of amino-acid sequence conse rvation included codons 12, 13, and 61, the positions in which mutations ar e observed in ras cellular oncogenes in other species. The 5' untranslated region (UTR), consisting of 217 nt, was not highly GC rich but contained fo ur ATG start codons upstream of the major open reading frame. The 3' UTR, c ontaining 26 nt, was AU rich. Analysis of Ki-ras mutations was performed on a variety of necrotic, preneoplastic, and neoplastic lesions in livers fro m 13 English sole collected from contaminated waterways in Puget Sound, WA. Despite reports of Ki-ras mutations in hepatic tumors from other fish, no mutations in codons 12, 13, or 61 were found in hepatic lesions from Englis h sole by direct DNA sequencing of polymerase chain reaction-amplified geno mic DNA. Although mutations could exist at levels below the detection limit s of this analysis, the results suggest that Ki-ras has a role in river car cinogenesis that varies according to the fish species or carcinogen. Furthe rmore, future studies of the etiology of chemically induced cancer in feral English sole should consider mutations in other cancer-related genes, such asp53, Ha-ras, and N-ras. (C) 1998 Wiley-Liss. Inc.