Ataxia-telangiectasia mutated (ATM) is an apical regulator of responses to DNA double-strand breaks (DSB). Using two complementary unbiased proteomic screens, we identified the cohesin complex proteins PDS5A, PDS5B, RAD21, NIPBL, and WAPL as apparent novel ATM interactors and substrates. ATM-dependent phosphorylation of PDS5A on Ser1278 following treatment with ionizing radiation is required for optimal cell survival, cell-cycle checkpoint activation, and chromosomal stability. Using a system that introduces site-specific DNA breaks, we found that ATM phosphorylation of cohesin proteins SMC1A, SMC3, and PDS5A are all required for repression of both RNA transcription and DNA replication within the vicinity of a DSB, the latter insight based on development of a novel localized S-phase cell-cycle checkpoint assay. These findings highlight the significance of interactions between ATM and cohesin in the regulation of DNA metabolic processes by altering the chromatin environment surrounding a DSB.

Implications:

Multiple members of the cohesin complex are involved in the regulation of DNA replication and transcription in the vicinity of DNA double-strand breaks and their role(s) are regulated by the ATM kinase.

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