p53 acts to prevent the formation of pathological R-loops during epigenetic stress
5-Azacytidine (Aza) and 5-Aza-2’-deoxycytidine (Dac) are the two primary therapeutics for the treatment of Acute Myeloid Leukaemia and some myelodysplastic syndromes. The two are frequently used interchangeably, surprisingly as their selectivity of de-methylation is unique from the other, however there remains very few studies which compare them directly. R-loops are three stranded nucleic acid structures that form during transcription and have known physiological roles in influencing their surrounding epigenetic environment. Despite these physiological roles, R-loops are also implemented in inducing DNA damage, with their formation frequently enriched in cancers. Using Aza and Dac to induce DNA hypomethylation, data from DRIPc-Seq, Immunostaining, RNA-Seq and Mass spectrometry was combined with epigenetic analysis to uncover unique cellular responses following Aza and Dac treatment, with a particular focus on how treatment with these drugs differentially influences R-loop formation. From these data it was uncovered that a key player in the different cellular responses to these drugs was the activation of p53. p53 was activated upon treatment with Aza but not Dac. Furthermore, p53 was found to be critical in preventing R-loop-driven genomic instability in Aza treated cells. This effect was both abolished by the removal of p53, and reversed through its’ rescue. In contrast, Dac treatment induced global chromatin modification and increased markers of genomic instability, independently of p53 activation. Collectively, these insights further our knowledge of how cells recognise and respond to methylation changes and uncovered a potentially unidentified role for p53 in the modulation of the epigenome to prevent aberrant R-loop formation. The newly identified differences between these two chemotherapy drugs on R-loop formation could also help research into better understanding the occurrence of chemo-resistance associated with these drugs.
Acute Myeloid Leukaemia, Azacytidine, Epigenetics, p53, R-loops
Networked Digital Library of Theses and Dissertations