Marriott, Andrew S. and Copeland, Nikki and Cunningham, Ryan and Wilkinson, Mark C. and McLennan, Alexander G. and Jones, Nigel J. (2015) Diadenosine 5′, 5′′′-P1,P4-tetraphosphate (Ap4A) is synthesized in response to DNA damage and inhibits the initiation of DNA replication. DNA Repair, 33. pp. 90-100. ISSN 1568-7864
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Abstract
The level of intracellular diadenosine 5, 5-P1,P4-tetraphosphate (Ap4A) increases several fold in mammalian cells treated with non-cytotoxic doses of interstrand DNA-crosslinking agents such as mitomycinC. It is also increased in cells lacking DNA repair proteins including XRCC1, PARP1, APTX and FANCG,while >50-fold increases (up to around 25 M) are achieved in repair mutants exposed to mitomycin C.Part of this induced Ap4A is converted into novel derivatives, identified as mono- and di-ADP-ribosylatedAp4A. Gene knockout experiments suggest that DNA ligase III is primarily responsible for the synthesisof damage-induced Ap4A and that PARP1 and PARP2 can both catalyze its ADP-ribosylation. Degrada-tive proteins such as aprataxin may also contribute to the increase. Using a cell-free replication system,Ap4A was found to cause a marked inhibition of the initiation of DNA replicons, while elongation wasunaffected. Maximum inhibition of 70–80% was achieved with 20 M Ap4A. Ap3A, Ap5A, Gp4G and ADP-ribosylated Ap4A were without effect. It is proposed that Ap4A acts as an important inducible ligand inthe DNA damage response to prevent the replication of damaged DNA.