The molecular basis and regulation of the DNA damage-induced nuclear export of the human MacroD2 protein

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Cells rapidly respond to DNA damage by activating vital signaling and repair pathways. The orchestration of cellular events often involves the modulation of protein traffic between nucleus and cytoplasm by post-translational modifications. Phosphorylation and poly-ADP-ribosylation (PARylation) constitute major signaling pathways regulating protein function upon DNA damage. Significantly, PARylation is an important regulator of double-strand break repair choice between homologous recombination and non-homologous end-joining. While this crosstalk is of clinical relevance, its molecular basis is poorly understood. MacroD2, one of the newly identified terminal ADP-ribosylhydrolases fully reversing protein PARylation, emerges as an important regulator of the crosstalk between phosphorylation and PARylation. MacroD2 rapidly recruits to damage sites upon PARylation and removes the terminal ADP-ribose unit from proteins, but is exported from the nucleus in response to activation of DNA damage response (DDR) kinases (PIKKs). Using a combination of live-cell imaging, biochemical assays and high-content siRNA-based screening, the proposed project will identify the molecular basis and regulation of this novel DNA damage-induced export mechanism. Furthermore, we will elucidate the dynamic regulatory connections between PARylation and phosphorylation networks upon DNA damage. In particular, we will identify the export motif and the export carrier of MacroD2 and establish the connection between MacroD2 export and the regulation of the DNA damage response.