Identification of a c-Ki- ras oncogene in a neoplasm isolated from winter flounder

Abstract

It has been shown that a high incidence of hepatomas are present in winter flounder ( Pseudopleuronectes americanus) obtained from Boston Harbor. It has been suggested that this may be a consequence of locally high levels of polycyclic aromatic hydrocarbons found in the sediment. The purpose of this study was to determine whether transforming DNA sequences (oncogenes) could be identified in liver neoplasms isolated from feral fish and to study their relationship to their corresponding proto-oncogenes. The ultimate aim of this study is to characterize novel mutations in oncogenes derived from these hepatomas to correlate these genetic changes with chemical exposure history. Genomic DNA was isolated from liver neoplasms and transfected into NIH3T3 mouse fibroblasts to assay for the formation of transformed foci. DNA was prepared from transformed foci and analyzed by Southern blot hybridization to viral DNA probes specific for c-Ki- ras and c-Ha- ras DNA sequences. A c-Ki- ras oncogene was identified in a transformant derived from one of the two tumors assayed. Comparison of c-Ki- ras DNA sequences of tumor and tumor-derived transformants indicate that the activated oncogene in the transformant is of flounder origin. We are currently analyzing the flounder oncogene for activating point mutations by primer-directed enzymatic amplification and direct sequence analysis.