The regulation of microRNA activity by ATM in the DNA damage response

Postdoc Assoc Ther Radiology
15 York St, New Haven, CT 06510-3221

The temporal and spatial expression of microRNAs proceed through several regulatory checkpoints mainly, transcription and precursor processing by Drosha and Dicer. Previous work indicates that miR-34 expression is induced at the transcriptional level in a P53-dependent manor following DNA damage, and protect cells against apoptosis by targeting a number of critical genes required for cell cycle progression. However, data from several laboratories (including our own) suggests that there is a pool of P53 and DNA damage-independent miR-34 in cells, the role of which is not understood. To study this, we established a luciferase reporter assay to measure miR-34 gene silencing activity. Here we show that the pre-existing pool of miR-34 is inactive, but can be rapidly activated by ionizing radiation (IR) and this occurs before P53-mediated transcription. Systematic knockdown of genes involved in microRNA processing, indicates that IR-induced miR-34 activation occurs independently of both transcription and processing. Concomitant with this observation we found that the inactive miR-34 is not bound by Ago2 (an
effector protein required for microRNA gene silencing), whereas after IR miR-34 is bound by Ago2. To determine which DNA damage sensory pathway miR-34
activation by be occurring through we chose to knockdown ATR, ATM, and P53.Our results showed that while ATR is not required for miR-34 activity, ATM is
required for early activation whereas P53 is required for late activation. Interestingly we found that ATM activates the pool of miR-34 by phosphorylating the 5’-end of miR-34. Our work has uncovered a novel mechanism for the regulation of microRNA activity.