Inhibition of poly(ADP-ribosyl)ation does not prevent lymphocyte entry into the cell cycle

The enzyme poly(ADP-ribosyl)transferase (ADPRT) becomes activated soon after a mitogenic stimulus is applied to lymphocyte cultures. It has also been reported that ADPRT inhibitors prevent cell proliferation when added to cultures at the same time as the mitogen. While this has been ascribed to the need to seal physiologically present DNA strand breaks before cells enter S phase, the presence of DNA strand breaks in quiescent human lymphocytes has been recently questioned. We demonstrate here that non-toxic concentrations of ADPRT inhibitors do not affect lymphocyte blastization and proliferation, as measured by thymidine incorporation and cytofluorimetry. We therefore suggest that ADPRT activation is required for late functions which are not needed for cell cycle progression.