ATM activation by DNA single-strand breaks

Project Summary/Abstract
As the most common form of DNA lesions, DNA single-strand breaks (SSBs) are derived from
environmental toxins and chemotherapy drugs as well as endogenous resources such as intermediate
DNA repair products in oxidative stress, and have been implicated in association with cancer and
neurodegenerative disorders. Whereas it is widely accepted that ATM is essential for the repair and
signaling of DNA double-strand breaks (DSBs), it remains unknown whether and how SSBs trigger ATM
activation, and how SSB-induced ATM activation maintains genome stability at the molecular level. Our
substantial preliminary data using biochemical, structure and function analyses suggest that ATM-
mediated DNA damage response (DDR) pathway is activated by the defined SSB structure in Xenopus
egg extracts and that such SSB-induced ATM activation is earlier than ATR activation. Notably, further
mechanistic studies suggest that a critical upstream regulator is implicated in the SSB-induced ATM
activation. Thus, we will dissect the molecular mechanisms of SSB-induced ATM activation in genome
integrity via two Specific Aims: (1) determine whether and how ATM-mediated DDR pathway is activated
by defined SSB structures in Xenopus egg extracts and reconstitution system with purified proteins, and
(2) determine the mechanism of how this upstream regulator contributes to the SSB-induced ATM
activation. Anticipated results from this NIH R21 project will provide direct evidence that ATM is activated
by defined SSB structures and how SSB-induced ATM activation is regulated and coordinated. Thus, our
studies will provide novel avenues for potential cancer therapies through the modulation of distinct
regulatory mechanisms of SSB-induced ATM activation in genome integrity and cancer etiology.