ETAA1 acts at stalled replication forks to maintain genome integrity

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• The ATR (Ataxia Telangiectasia and Rad3-related) kinase is a key regulator of cellular responses to DNA replication stress.
• While budding yeast have multiple Mec1 (ATR orthologue) activators, only TOPBP1 was known to activate ATR in vertebrates.

Purpose of the Study:

• To identify novel proteins involved in the replication stress response in vertebrates.
• To elucidate the mechanism by which ATR is activated during replication stress.

Main Methods:

• Proteomic screening to identify replication stress response proteins.
• Cellular assays to assess DNA damage, genome instability, and replication fork stability in ETAA1-deficient cells.
• Biochemical experiments to determine ETAA1's interaction with ATR/ATRIP and other DNA damage response proteins.

Main Results:

• ETAA1 was identified as a replication stress response protein.
• ETAA1-deficient cells exhibit hallmarks of genome instability, including double-strand breaks and sister chromatid exchanges, and are hypersensitive to replication stress.
• ETAA1 localizes to stalled replication forks and directly activates ATR/ATRIP, functioning in parallel to the TOPBP1 pathway.

Conclusions:

• ETAA1 is a novel, direct activator of ATR kinase in vertebrate cells.
• ETAA1 plays a critical role in maintaining genome stability by regulating the ATR pathway during replication stress.
• Vertebrate cells possess at least two distinct ATR-activating proteins, ETAA1 and TOPBP1.