Poly (ADP-Ribosyl)ation is implicated in the G0-G1 transition of resting cells.

Poly(ADP-ribosyl)ation, catalysed by a family of poly(ADP-ribose) polymerases (PARPs), plays an important role in a large variety of physiological processes, including cell proliferation, but its role in cell cycle progression is not yet completely defined. As reported here, the examination of early times following serum stimulation of quiescent fibroblasts suggests that poly(ADP-ribosyl)ation is necessary for the transition from the G0 to the G1 phase. We show that PARP activity is involved in this step through the regulation of immediate early response genes, such as c-Fos and c-Myc. This is supported by the finding that exogenous Myc expression substantially restores cell cycle reactivation in the absence of polymer synthesis. Furthermore, using RNA interference, we show that PARP-1 is the PARP family member playing the most prominent role in the up-regulation of c-Fos and c-Myc during G0/G1 transition. We report that also in lectin-stimulated PBMC the inhibition of PARP activity interferes with the up-regulation of immediate early genes and delays the induction of proliferation, suggesting a general role for PARP-1 in linking growth factor signaling with cell cycle entry.