PARP1 Deficiency Reduces Tumour Growth by Decreasing E2F1 Hyperactivation: A Novel Mechanism Beyond PARP Enzymatic Inhibition in the Treatment of Cancer

In recent years, poly (ADP-ribose) polymerase (PARP) inhibitors have heen evaluated for treating homologous recombination-deficient tumors, taking advantage of synthetic lethality. However, increasing evidence indicates that PARP proteins exert several cellular functions unrelated with their role on DNA repair, including function as a co-activators of transcription through protein-protein interaction with E2F1. Since the RB/E2F1 pathway is among the most frequently mutated in many tumours types, we investigated whether the absence of PARP activity could counteract the consequences of E2F1 hyperactivation. Our results demonstrate that genetic ablation of Parp1 extends the survival of Rb-null embryos, while genetic inactivation of Parp1 results in reduced development of pRb-dependent tumors. Our results demonstrate that PARP1 plays a key role as a transcriptional co-activator of the transcription factor E2F1, an important component of the cell cycle regulation. Furthermore, impairment of PARP results in a reduction of tumor growth, that is not depending of the activity of PARP on DNA repair. Considering that most oncogenic processes are associated with cell cycle deregulation, the disruption of this PARP1-E2F1 interaction could provide a new therapeutic target of great interest and a wide spectrum of indications.