Cellular ras protooncogene expression in human mammary explant cultures. A potential marker for chemical carcinogenesis.

The major findings of the present study can be summarized as follows: 1. The newly developed assay for quantitative determination of ras protooncogene expression which utilizes affinity labeling of ras p21 with [alpha-32P]GTP can effectively demonstrate the presence of ras protooncogene expression in explant cultures of human mammary tissues. 2. The prototype chemical carcinogens NMU and BP induce amplified expression of ras protooncogene in benign (noninvolved) human mammary TDLU. 3. The specific enhancement of ras expression by BP in TDLU (target tissue) but not in MF (nontarget tissue) for tumorigenesis indicates that the constitutive levels of ras protooncogene in the target tissue are responsive to carcinogenic insult. 4. The relative extent of ras protooncogene expression may constitute a sensitive marker for target tissue susceptibility to chemical carcinogenesis.