Constitutive Association of BRCA1 and c-Abl and Its ATM-Dependent Disruption after Irradiation

Abstract

BRCA1 plays an important role in mechanisms of response to double-strand breaks, participating in genome surveillance, DNA repair, and cell cycle checkpoint arrests. Here, we identify a constitutive BRCA1-c-Abl complex and provide evidence for a direct interaction between the PXXP motif in the C terminus of BRCA1 and the SH3 domain of c-Abl. Following exposure to ionizing radiation (IR), the BRCA1-c-Abl complex is disrupted in an ATM-dependent manner, which correlates temporally with ATM-dependent phosphorylation of BRCA1 and ATM-dependent enhancement of the tyrosine kinase activity of c-Abl. The BRCA1-c-Abl interaction is affected by radiation-induced modification to both BRCA1 and c-Abl. We show that the C terminus of BRCA1 is phosphorylated by c-Abl in vitro. In vivo, BRCA1 is phosphorylated at tyrosine residues in an ATM-dependent, radiation-dependent manner. Tyrosine phosphorylation of BRCA1, however, is not required for the disruption of the BRCA1-c-Abl complex. BRCA1-mutated cells exhibit constitutively high c-Abl kinase activity that is not further increased on exposure to IR. We suggest a model in which BRCA1 acts in concert with ATM to regulate c-Abl tyrosine kinase activity.

We thank J. Feunteun (Institut Gustave-Roussy, Villejuif, France) for stimulating discussions in the initial steps of this work. We thank R. Scully and D. Livingston (Dana Farber Institute, Boston, Mass.) and P.-A. Briand for kindly providing GST-BRCA1 and GST-c-Abl fusion constructs, respectively. We are grateful to A. Chompret and B. Bressac (Institut Gustave-Roussy) for fruitful discussions and Jeannine Cabannes (Institut Gustave-Roussy), F. Mégnin-Chanet, N. Giocanti, M. Fernet, and C. Reis (Institut Curie, Orsay, France) for skillful help.

N.F. is the recipient of a Fondation de la Recherche Médicale and an A.R.C. postdoctoral fellowship. D.P. was supported by the Swiss National Science Foundation and the Canton de Genève. This work was supported by the Fondation de la Recherche Médicale, Electricité de France (Comité de Radioprotection), the Ligue Nationale Contre le Cancer and the A.R.C. Work in the P.J. laboratory contributing to this study was supported by the Leukemia Research Fund.