DNA polymerase and DNA replication during lymphocyte transformation

Abstract

The initiation of DNA synthesis in human peripheral blood lymphocytes is coincident with the induction of DNA polymerase activity. Phytohemagglutinin was added to cultures of lymphocytes, and, at sequential times thereafter, incorporation of thymidine into DNA and various enzymatic activities in the DNA synthetic pathway were determined. An increase of 30- to 150- fold in DNA polymerase activity paralleled in time and magnitude the ability of the cells to synthesize DNA. An increase in DNase activity also paralleled DNA synthesis and the rise in polymerase. The activities of thymidine kinase and thymidine monophosphate kinase multiplied about 2− to 10−fold. In contrast, kinase such as deoxyguanosine monophosphate kinase and guanosine monophosphate kinase, which were present in greater activity, were not increased by phytohemagglutinin. The induction of these enzyme activities by phytohemagglutinin appears to require RNA synthesis. Actinomycin D in sufficient amounts abolished the phytohemagglutinin-mediated increases in RNA and DNA synthesis, enzyme activities, and lymphocyte transformation. Smaller amounts of actinomycin prevented the induction of DNA polymerase, thymidine kinase, and thymidine monophosphate kinase, as well as the increase in RNA and DNA synthesis, but did not hinder lymphocyte transformation. Accordingly, the morphological changes characterizing lymphocyte transformation do not require DNA replication or increases in enzyme activities associated with this replication. In contrast, the stimulation of DNA synthesis is rigidly dependent on the induction of DNA polymerase.