Functional interactions between BRCA1 and the checkpoint kinase ATR during genotoxic stress

Area of Science:

• Molecular Biology
• Cellular Biology
• Genetics

Background:

• The BRCA1 gene is a tumor suppressor frequently mutated in familial breast cancers.
• BRCA1 protein is crucial for DNA damage response, with phosphorylation and recruitment to nuclear foci upon DNA damage.
• The ataxia-telangiectasia-mutated (ATM) kinase regulates BRCA1 phosphorylation after gamma-irradiation (IR).

Purpose of the Study:

• To investigate the kinases responsible for BRCA1 phosphorylation beyond ATM.
• To elucidate the role of ATR in BRCA1 phosphorylation and DNA damage response.
• To determine if ATR and BRCA1 function within the same genotoxic stress pathway.

Main Methods:

• Assessed BRCA1 phosphorylation in response to IR, UV light, hydroxyurea (HU), and aphidicolin (APH).
• Investigated the role of ATR using increased ATR expression and a kinase-inactive ATR mutant.
• Examined ATR and BRCA1 localization in nuclear foci following DNA damage.

Main Results:

• BRCA1 phosphorylation is only partially ATM-dependent upon IR and ATM-independent upon UV, HU, or APH treatment.
• ATR directly phosphorylates BRCA1 on multiple residues, including Ser 1423, in vitro and in vivo.
• ATR forms distinct nuclear foci at stalled replication forks and these foci overlap with BRCA1 foci.

Conclusions:

• ATR, similar to ATM, controls BRCA1 phosphorylation in response to genotoxic stress.
• ATR directly phosphorylates BRCA1, indicating they are part of the same DNA damage response pathway.
• ATR relocalization to sites of DNA damage suggests a mechanism for regulating substrate phosphorylation.