Role of the tumour suppressor PML in DNA damage response and cellular senescence after genotoxic stress

The promyelocytic leukemia protein (PML) is a tumour suppressor. It has been reported that PML interaction with the p53 protein is involved in the activation of cell cycle checkpoints and, when persistent, may lead to the premature onset of cellular senescence. Cellular senescence is a state of permanent cell growth arrest that is associated with characteristic morphological and metabolic changes and persistent DNA damage signalling. Importantly, PML nuclear bodies coassociate with persistent DNA damage foci in senescent cells; however, the role of this interaction is still obscure. My goal was to characterize the role of PML in DNA damage response (DDR) and the induction of premature cellular senescence after genotoxic stress, namely X-radiation, using both siRNA-mediated PML knock down (PML KD) and complete PML knock out (PML KO) in human cells. The dynamics of DNA damage foci, levels of various proteins involved in DDR, and proliferation rate were measured in both PML KD and KO cells. No significant changes in the formation of DNA damage foci, activated DDR (p53 and Chk2), activated p21CIP1/WAF1 cyclin-dependent kinase inhibitor, senescent morphology, and SA-β-galactosidase activity in PML KO cells were observed. However, PML KO cells displayed higher levels of retinoblastoma protein (Rb) and..