tBRCT Interactome Analysis Uncovers DNA Damage Response Components

BRCA1 C-terminal (BRCT) domains are modules that can recognize peptide motifs phosphorylated after DNA damage and thus are commonly found in proteins with roles in the DNA damage response (DDR). Some proteins contain tandem BRCT (tBRCT) domains, which act as a single unit to form a recognition pocket for phosphopeptides. To gain insight into the cellular processes regulated by such proteins, Woods and colleagues used literature curation, yeast two-hybrid screens, and tandem affinity purification coupled to mass spectrometry (TAP-MS) to generate a protein interaction network for 7 tBRCT-containing proteins. Interestingly, only 1.9% of the interactions identified experimentally by yeast two-hybrid and TAP-MS had been previously reported. Although the vast majority of these specific interactions remain to be validated with endogenous proteins, these results suggest that our current understanding of DDR components is far from complete. One unexpected observation was that multiple tBRCTs bound copper metabolism Murr1 domain 1 (COMMD1), a protein involved in copper homeostasis with no known DDR links. COMMD1 abundance increased in human cells after ionizing radiation, and knockdown of COMMD1 sensitized breast cancer cells to the DNA-damaging agents cisplatin and doxorubicin, indicating that COMMD1 plays a role in the DDR. Another surprising finding was that the BRCA1 tBRCT specifically interacted with Rictor, a component of mTOR complex 2 (mTORC2), particularly in response to DNA damage or serum starvation. The BRCA1 tBRCT inhibited mTORC2-dependent phosphorylation of AKT in vitro and promoted the dissociation of mTOR from mTORC2, suggesting a potential mechanism to explain the previous observation that BRCA1 inhibits AKT signaling. These findings thus illustrate the potential of the tBRCT interactome to reveal protein–protein interactions that mediate the integration of DDR signaling with other cellular activities.

Woods NT, Mesquita RD, Sweet M, Carvalho MA, Li X, Liu Y, et al. Charting the landscape of tandem BRCT domain-mediated protein interactions. Sci Signal 2012;5:rs6.