Factors regulating cellular DNA synthesis induced by adenovirus infection. I. The effects of actinomycin D on G1-arrested BHK21 cells abortively infected with type 12 adenovirus of stimulated by serum.

Abstract

Abstract The effect of actinomycin D (AMD) on induction of cellular DNA synthesis in G1-arrested BHK21 cells by type 12 adenovirus (Ad12) and serum has been studied. Three-hundredths microgram of AMD/ml inhibited by 98 to 99% the induction of both RNA and DNA synthesis by Ad12, while the frequency of cells synthesizing Ad12 T antigen was unaffected. Serum-induced DNA synthesis was inhibited by 99% at only 0.01 μg of AMD/ml, indicating a greater sensitivity to the drug. Overall protein synthesis in both systems was inhibited by 80% at 0.03 μg/ml. Addition of AMD to serum-stimulated or Ad12-infected cells by 5 or 7 hr, respectively, before initiation of S completely blocked entry into S. When the drug was added to a culture in which cells were less than 5 to 7 hr from the beginning of their S period, or to randomly growing cultures, cells continued to enter S for approximately 6 hr after drug addition. Furthermore, addition of AMD to cells already in S produced a decrease in the rate of synthesis, but not a total arrest. At much higher doses of AMD (up to 4 μg/ml), more rapid and more complete inhibition of ongoing DNA synthesis was observed. Protein synthesis was affected more slowly than DNA synthesis at either high or low AMD concentration. These results are interpreted to indicate that AMD can interfere with induction of cellular DNA synthesis by at least two mechanisms: 1) blocking of a highly AMD-sensitive function which in untreated cells occurs at 5 to 7 hr before S would normally begin, and which is required for the transition from G1 to S; and 2) blocking of a relatively drug-insensitive function which is directly involved in the continuation of DNA synthesis.