Analysis of ras gene mutations in rainbow trout liver tumors initiated by aflatoxin B1.
The suspect human hepatocarcinogen aflatoxin B1 (AFB1) is a well-known potent initiator of hepatic tumors in rainbow trout (Oncorhynchus mykiss). Both hepatocellular carcinomas and mixed hepatocellular/cholangiocellular carcinomas are induced by AFB1 in trout, with the mixed form predominating. We previously isolated two c-ras genes from trout liver cDNA, and in the present study we analyzed DNA from 14 AFB1-induced trout liver tumors for point mutations in exon 1 of both genes. Using the polymerase chain reaction (PCR) and oligonucleotide hybridization methods, a high proportion (10/14) of the AFB1-initiated tumor DNAs showed evidence of activating point mutations in the trout c-Ki-ras gene. Of the 10 mutant ras genotypes, seven were codon 12 GGA----GTA transversions, two were codon 13 GGT----GTT transversions, and one was codon 12 GGA----AGA transition. Nucleotide sequence analysis of cloned PCR products from four of these tumor DNAs provided definitive evidence for two codon 12 GGA----GTA mutations, one codon 12 GGA----AGA mutation, and one codon 13 GGT----GTT mutation, in complete agreement with the oligonucleotide hybridization results. No mutations were detected in exon 1 of a second trout ras gene also expressed in liver, nor in DNA from control livers. This is the first report of experimentally induced ras gene point mutations in a lower vertebrate fish model. The results indicate that the hepatocarcinogen AFB1 induces c-Ki-ras gene mutations in trout similar to those in rat liver tumors.
Chang
Y J
YJ
Department of Biochemistry, Oregon State University, Corvallis 97331-6603.
Mathews
C
C
Mangold
K
K
Marien
K
K
Hendricks
J
J
Bailey
G
G
D002759:Adenoma, Bile Duct / Q000139:chemically induced / Q000235:genetics*; D016604:Aflatoxin B1; D000348:Aflatoxins / Q000633:toxicity*; D000483:Alleles; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D005091:Exons; D005786:Gene Expression Regulation / Q000187:drug effects; D011905:Genes, ras / Q000187:drug effects*; D008113:Liver Neoplasms / Q000139:chemically induced / Q000235:genetics*; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009693:Nucleic Acid Hybridization; D015345:Oligonucleotide Probes; D010957:Plasmids; D016133:Polymerase Chain Reaction / Q000379:methods; D013045:Species Specificity; D014337:Trout
D000348:Aflatoxins; D015345:Oligonucleotide Probes; D016604:Aflatoxin B1