Effect of actidione (cycloheximide) on estrogen-induced biochemical changes in R3230AC mammary tumors, uteri, and mammary glands.

Abstract

Summary The R3230AC mammary adenocarcinoma responds to estrogen treatment by increased glucose-6-phosphate dehydrogenase, malate dehydrogenase (decarboxylating), and phosphoglucomutase activities. Various doses of actidione (cycloheximide), an antibiotic reported to inhibit protein synthesis in mammalian systems without inhibiting RNA synthesis, were employed to determine their effect on the estrogen-induced alterations in enzyme activities in this neoplasm as well as in the uteri and mammary glands of the tumor-bearing animal. Actidione caused a decrease in the activities of glucose-6-phosphate dehydrogenase, malate dehydrogenase (decarboxylating), and phosphoglucomutase in the carcinoma. The antibiotic, at certain doses, completely prevented the estrogen-induced elevations in the activities of these enzymes in the neoplasm and prevented the estrogen-induced decrease in isocitrate dehydrogenase (decarboxylating) activity in the tumor. Although actidione did not prevent the uterotropic response to estrogen, the antibiotic did block the estrogen-induced elevations of glucose-6-phosphate dehydrogenase, malate dehydrogenase (decarboxylating), glucosephosphate isomerase, and glutamate dehydrogenase activities in the uterus. Actidione, administered alone or with estrogen, produced an increase in the RNA concentration and RNA/DNA ratios in the tumors and uteri and had no significant effect on the concentration of DNA in these tissues. The activities of most of these enzymes in the mammary gland were not notably elevated by estrogen treatment under these experimental conditions, and both malate dehydrogenase (decarboxylating) and α-glycerolphosphate dehydrogenase activities were significantly reduced. Actidione treatment, either alone or with estrogen, produced a dose-related decrease in the activities of these enzymes in the mammary gland. The estrogen-induced decrease in α-glycerolphosphate dehydrogenase activity was prevented at only the lowest dose of actidione employed. Protein and RNA synthesis were estimated by determining the amount of leucine- 14 C and uridine-5- 3 H incorporated into these substances in the neoplasm and uteri. Estrogen treatment produced a 2- to 3-fold increased in both the total activity and specific activity of both radioactive substrates in the carcinoma in vivo and actidione treatment prevented this estrogen-induced response. Similar results were obtained in the uteri of these tumor-bearing animals. These data, together with results of our earlier experiments employing actinomycin D, suggest that the estrogen-induced elevations of enzyme activities in the R3230AC mammary adenocarcinoma are dependent on protein synthesis.