Ca²⁺-Stimulated AMPK-Dependent Phosphorylation of Exo1 Protects Stressed Replication Forks from Aberrant Resection

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Replication fork instability due to nucleases causes genomic instability and cell death.
• Cellular mechanisms controlling nucleases during replication stress are not fully understood.

Purpose of the Study:

• To elucidate the signaling pathway regulating exonuclease activity during replication stress.
• To identify how cells prevent aberrant processing of stressed replication forks.

Main Methods:

• Investigated the role of intracellular calcium ([Ca2+]i), CaMKK2, and AMPK in regulating Exo1.
• Utilized biochemical assays and cellular studies to examine Exo1 phosphorylation and recruitment to replication forks.

Main Results:

• Replication stress increases [Ca2+]i, activating CaMKK2 and AMPK.
• AMPK phosphorylates Exo1 at serine 746, promoting 14-3-3 binding and inhibiting its recruitment to stressed forks.
• Disrupting this pathway leads to excessive single-stranded DNA (ssDNA), chromosomal instability, and sensitivity to replication stress.

Conclusions:

• A novel Ca2+-CaMKK2-AMPK signaling pathway safeguards replication fork structure.
• This pathway inhibits Exo1 activity to prevent genomic instability during replication stress.
• This finding links calcium signaling to the replication stress response and genome maintenance.