Immediate-Early, Early, and Late Responses to DNA Double Stranded Breaks

Abstract

Loss or rearrangement of genetic information can result from incorrect responses to DNA double strand breaks (DSBs). The cellular responses to DSBs encompass a range of highly coordinated events designed to detect and respond appropriately to the damage, thereby preserving genomic integrity. In analogy with events occurring during viral infection, we appropriate the terms Immediate-Early, Early, and Late to describe the pre-repair responses to DSBs. A distinguishing feature of the Immediate-Early response is that the large protein condensates that form during the Early and Late response and are resolved upon repair, termed foci, are not visible. The Immediate-Early response encompasses initial lesion sensing, involving poly (ADP-ribose) polymerases (PARPs), KU70/80, and MRN, as well as rapid repair by so-called ‘fast-kinetic’ canonical non-homologous end joining (cNHEJ). Initial binding of PARPs and the KU70/80 complex to breaks appears to be mutually exclusive at easily ligatable DSBs that are repaired efficiently by fast-kinetic cNHEJ; a process that is PARP-, ATM-, 53BP1-, Artemis-, and resection-independent. However, at more complex breaks requiring processing, the Immediate-Early response involving PARPs and the ensuing highly dynamic PARylation (polyADP ribosylation) of many substrates may aid recruitment of both KU70/80 and MRN to DSBs. Complex DSBs rely upon the Early response, largely defined by ATM-dependent focal recruitment of many signalling molecules into large condensates, and regulated by complex chromatin dynamics. Finally, the Late response integrates information from cell cycle phase, chromatin context, and type of DSB to determine appropriate pathway choice. Critical to pathway choice is the recruitment of p53 binding protein 1 (53BP1) and breast cancer associated 1 (BRCA1). However, additional factors recruited throughout the DSB response also impact upon pathway choice, although these remain to be fully characterised. The Late response somehow channels DSBs into the appropriate high-fidelity repair pathway, typically either ‘slow-kinetic’ cNHEJ or homologous recombination (HR). Loss of specific components of the DSB repair machinery results in cells utilising remaining factors to effect repair, but often at the cost of increased mutagenesis. Here we discuss the complex regulation of the Immediate-Early, Early, and Late responses to DSBs proceeding repair itself.

Multi-Level Control of the ATM/ATR-CHK1 Axis by the Transcription Factor E4F1 in Triple-Negative Breast Cancer

“…Of note, the E4F1 depletion did not impact on the formation of 53BP1 foci in response to Gemcitabine. The preservation of this marker of the early phase of the DNA damage-response, suggest that the early steps of this response, upstream of the ATM/ATR-CHK1 signaling, might still be functional in the E4F1-depleted cells ( Figure 6 ) [ 47 ].

Figure 5 E4F1-depletion impacts on ATM/ATR-CHK1 signaling in response to CT drugs Gemcitabine and Cisplatin.

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BTApep-TAT peptide inhibits ADP-ribosylation of BORIS to induce DNA damage in cancer

“…Genome instability is a hallmark of cancer. The inappropriate responses to DNA damage or DNA repair disorders are linked to rearrangement of the genome, microsatellite instability, chromosome instability, and tumorigenesis [ 61 , 62 ]. We found that BORIS was ADP-ribosylated within 30 min after stimulation with single- and double-strand DNA, and BORIS facilitated the recruitment of Ku70.…”

DNA Damage Response Regulation by Histone Ubiquitination

“…Accumulated ATM phosphorylates H2AX, but DNA-dependent protein kinase catalytic subunit (DNA-PKcs), ataxia telangiectasia, and Rad3-related (ATR) also phosphorylate H2AX [ 15 , 16 , 17 ]. Additionally, increased levels of γH2AX on either side of the DSB further promote chromatin decondensation and DSB repair [ 18 ]. Chromatin structure is a key determinant of DSB repair pathway choice.…”