Studies on the induction of DNA polymerase during transformation of human lymphocytes

Abstract

The addition of phytohemagglutinin to cultures of human peripheral lymphocytes initiates a series of metabolic alterations leading to DNA replication and cell division. DNA polymerase activity increases immediately before the onset of thymidine incorporation and thereafter both increase proportionally. Addition of actinomycin D in the first 2 hr after phytohemagglutinin is added completely prevents the increase in DNA polymerase activity. However, the earliest increase in DNA polymerase activity is detected only after 18 to 20 hr in culture. This may be an example of translational delay. Actinomycin D added at 6 hr after phytohemagglutinin slows and limits the increase in DNA polymerase activity by only 50%. Subsequently, the increase in DNA polymerase activity becomes increasingly less sensitive to the effect of actinomycin D. Induction of DNA polymerase activity thus appears to be programmed by an actinomycin D-sensitive product made early during lymphocyte transformation. However, there appears to be no delay between the synthesis of polymerase and the appearance of activity, since the addition of either puromycin or cycloheximide (inhibitors of protein synthesis) to cultures of stimulated lymphocytes prevents further increases in DNA polymerase activity and thymidine incorporation.