Early Detection of ras Oncogenes Activated by Chemical Carcinogentreatment

Abstract

Molecular analysis of H-ras oncogenes induced by a single dose of nitrosomethylurea (NMU) in pubescent rats revealed their consistent activation by G→A transitions, the type of mutation preferentially induced by NMU. These results suggested that NMU is directly responsible for the malignant activation of ras oncogenes during initiation of carcinogenesis. We have now modified this experimental system to examine’ the precise mechanisms by which ras oncogenes contribute to carcinogenesis. Our results suggest that although ras oncogenes may become activated during the carcinogenic insult, they require specific cooperation with normal developmental programs to exert their carcinogenic properties. Definitive demonstration of this hypothesis requires identification of activated ras oncogenes in the putative target cells prior to the manifestation of the neoplastic phenotype. In an attempt to reach the sensitivity levels necessary to verify this hypothesis, we have optimized the detection of ras DNA sequences amplified by the polymerase chain reaction (PCR) technique and have succeeded in identifying ras oncogenes at the single-cell level.