Protein content and enzyme levels of cultured chick embryo cells treated with camptothecin and actinomycin D

Abstract

The alkaloid camptothecin uncouples the growth and division of chick embryo cells. At a moderate dose (0.5 μg/ml) it inhibits the incorporation of thymidine but not of uridine and leucine and the cell protein content increases and reaches twice that of control after 4 days of treatment. Twelve hours after addition of the drug, the activities per cell of the mitochondrial enzymes poly A hydrolase (EC 3.1.4.21), cytochrome c oxidase (EC 1.9.3.1), and succinate dehydrogenase (EC 1.3.99.1) are greater than that of the control and keep increasing for at least 96 h. The increase in the activities of the mitochondrial enzymes precede that of NADPH-cytochrome c reductase (EC 1.6.2.4) and cytidine triphosphatase (EC 3.6.1.15), which are microsomal and plasma membranes enzymes respectively. Actinomycin D (0.01 μg/ml) also inhibits the multiplication of the chick cells and the synthesis of DNA. The protein content of the actinomycin D treated cells decreases to 70% of the control by day 2. Nevertheless, the activities of the mitochondrial enzymes increase over that of the control but to a smaller extent than with camptothecin. The activities of the enzymes of the other organelles are not stimulated. Camptothecin at a higher dose (5.0 μg/ml) induces effects similar to those of actinomycin D.