Expression of the c-Ha-ras and neu oncogenes in DMBA-induced, anti-estrogen-treated rat mammary tumors.

Dimethylbenzanthracene (DMBA)-induced rat mammary tumors were analyzed for the structure and expression of the oncogenes c-Ha-ras and neu and the effects of anti-estrogen treatment. Tumor samples were divided into 3 groups, the first consisting of untreated tumors, the second of anti-estrogen (toremifene)-treated unresponsive (growing) tumors, and the third of toremifene-treated responsive (regressing) tumors. DNA and RNA derived from normal tissues of the same experimental animals were also analyzed. In Southern blot analysis of genomic DNAs, 2 tumors out of 23 contained new Xbal site in the Ha-ras gene, indicating a point mutation in the second nucleotide of codon 61. Both of these tumors belonged to the group that had not received toremifene. No amplifications of the Ha-ras or the neu genes were observed. Although greatly variable, the levels of Ha-ras mRNA were highest in untreated tumors, lower in toremifene-treated, unresponsive tumors and even lower in toremifene-treated, regressing tumors, corresponding approximately to the levels detected in normal liver and uterus of untreated animals. Expression of the neu mRNA was variable and considerably lower than that of Ha-ras mRNA. It was similar in all 3 groups and somewhat elevated than in several non-malignant control tissues. Localization of c-Ha-ras expression by in situ hybridization revealed a relatively even distribution of the mRNA throughout the mammary tissue. The results suggest that mechanisms other than activation of the c-Ha-ras or neu genes are important for progression and regression of DMBA-induced rat mammary carcinomas.