Pharmacological inhibition of ATM by KU55933 stimulates ATM transcription

Abstract

Ataxia-telangiectasia mutated (ATM) kinase is a component of a signalling mechanism that determines the process of decision-making in response to DNA damage and involves the participation of multiple proteins. ATM is activated by DNA double-strand breaks (DSBs) through the Mre11–Rad50–Nbs1 (MRN) DNA repair complex, and orchestrates signalling cascades that initiate the DNA damage response. Cells lacking ATM are hypersensitive to insults, particularly genotoxic stress, induced through radiation or radiomimetic drugs. Here, we investigate the degree of ATM activation during time-dependent treatment with genotoxic agents and the effects of ATM on phospho-induction and localization of its downstream substrates. Additionally, we have demonstrated a new cell-cycle-independent mechanism of ATM gene regulation following ATM kinase inhibition with KU5593. Inhibition of ATM activity causes induction of ATM protein followed by oscillation and this mechanism is governed at the transcriptional level. Furthermore, this autoregulatory induction of ATM is also accompanied by a transient upregulation of p53, pATR and E2F1 levels. Since ATM inhibition is believed to sensitize cancer cells to genotoxic agents, this novel insight into the mechanism of ATM regulation might be useful for designing more precise strategies for modulation of ATM activity in cancer therapy.

NRF2 inhibition causes repression of ATM and ATR expression leading to aberrant DNA Damage Response

“…Finally, we looked at γ-H2AX levels in these cells. γ-H2AX is a biomarker of DNA damage [35] and we used it to assess the degree of DNA damage sustained in the cell lines. Again, we found higher basal and induced levels of γ-H2AX in PEO1 cell line as compared to PEO4 possibly explained by higher cell death seen in Fig.…”

“…Once activated, the ATM and ATR protein kinases phosphorylate and in turn activate their downstream substrates P53, checkpoint kinases (CHK1, CHK2) and H2AX [32][33][34]. Checkpoint proteins arrest the cell cycle transiently, P53 activation links the repair responses with cell cycle progression and apoptotic pathway, while H2AX focus formation at the DNA lesion recruits important repair enzymes at the damaged site [35][36][37]. Checkpoint arrest could also activate enzymes involved in apoptosis, permanently leading to cell senescence or cell death [32].…”

Reverse engineering of drug induced DNA damage response signalling pathway reveals dual outcomes of ATM kinase inhibition

“…In this micro-environment, the effect of inhibiting ATM protein is not fully predictable in terms of signalling consequences and the associated cellular response, especially owing to the fact that ATM function can contribute in both cell cycle arrest to allow for DNA repair [24,25], as well as in apoptosis [125,30]. Prediction is further complicated by the finding that ATM may self-regulate its own protein levels [75,117]. In this complex and unpredictable situation, the efficacy of potential ATM inhibitors would have to be assessed in terms of the effects it exerts, not only on ATM activity and its immediate substrates e.g.…”

“…This is consistent with the typical protective function of ATM whereby it is known to exert cell cycle arrest and promote DNA repair in order to ensure cell survival at a repairable scale of DNA damage. This is through its phosphorylation of P53 which exerts CIP/KIP mediated cell cycle arrest by sequestering E2F1 activities [23][24][25], as well as its activation of checkpoint kinases Chk1 and Chk2, which phosphorylate and inhibit phosphatase activities of Cdc25 [75] stopping the cell cycle progression. While ATM is also implicated in apoptosis induction [26], it could be inferred from fig.…”

What's Your Poison? Impact of Individual Repair Capacity on the Outcomes of Genotoxic Therapies in Cancer. Part I—Role of Individual Repair Capacity in the Constitution of Risk for Late-Onset Multifactorial Disease

“…Usually, these strategies are based on inactivation of a key protein acting in induction of cell cycle arrest and repair of damage in actively dividing cells. Among the common target proteins are, for example, ATM (inactivated by compounds such as KU-55933 and KU59403) (42,43) and cyclin-dependent kinases (targeted by R-roscovitine [seliciclib], flavopiridol, difluoromethylornitine, and others) (7,29).…”