The human Exonuclease-1 interactome and phosphorylation sites

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA double-strand breaks are critical lesions repaired by homologous recombination (HR).
• Exonuclease-1 (EXO1) and DNA2/BLM are essential for DNA end resection, generating 3'-overhangs crucial for HR.
• Understanding the regulation of EXO1 function is vital for comprehending DNA repair fidelity.

Purpose of the Study:

• To identify novel protein interactors of Exonuclease-1 (EXO1).
• To investigate the role of EXO1-interacting proteins in DNA damage response (DDR).
• To analyze the phosphorylation status of EXO1 under various conditions.

Main Methods:

• Affinity purification of EXO1 followed by Orbitrap mass spectrometry.
• Depletion of identified interacting proteins using RNA interference.
• Assessment of DNA damage response markers (e.g., γ-H2AX foci) and cellular resistance.
• Mass spectrometry-based phosphoproteomic analysis of EXO1.

Main Results:

• Identification of novel EXO1 interacting partners involved in RNA processing and X-linked disorders.
• Depletion of specific EXO1 interactors, including PDCD11/ALG-4, diminished the DNA damage response.
• PDCD11 depletion decreased γ-H2AX foci and DDR signaling, conferring increased cellular resistance to DNA damage.
• Identification of 26 differentially phosphorylated EXO1 residues under basal and DNA-damaged conditions.

Conclusions:

• PDCD11/ALG-4 is a novel regulator of DNA damage response pathways involving EXO1.
• EXO1 phosphorylation sites are dynamically regulated during DNA repair.
• These findings provide insights into the complex regulatory network governing homologous recombination and DNA repair.