BRCA1 Is Required for Common-Fragile-Site Stability via Its G₂/M Checkpoint Function

Abstract

Common fragile sites are loci that form chromosome gaps or breaks when DNA synthesis is partially inhibited. Fragile sites are prone to deletions, translocations, and other rearrangements that can cause the inactivation of associated tumor suppressor genes in cancer cells. It was previously shown that ATR is critical to fragile-site stability and that ATR-deficient cells have greatly elevated fragile-site expression (A. M. Casper, P. Nghiem, M. F. Arlt, and T. W. Glover, Cell 111:779-789, 2002). Here we demonstrate that mouse and human cells deficient for BRCA1, due to mutation or knockdown by RNA interference, also have elevated fragile-site expression. We further show that BRCA1 functions in the induction of the G₂/M checkpoint after aphidicolin-induced replication stalling and that this checkpoint function is involved in fragile-site stability. These data indicate that BRCA1 is important in fragile-site stability and that fragile sites are recognized by the G₂/M checkpoint pathway, in which BRCA1 plays a key role. Furthermore, they suggest that mutations in BRCA1 or interacting proteins could lead to rearrangements at fragile sites in cancer cells.

This work was supported by NIH grant CA43222 to T.W.G. Support for B.X. was provided by a grant from the Department of Defense (DAM17-03-1-0709) and by the Cancer Association of Greater New Orleans. M.B.K. was supported by grants from the NIH (CA86861, CA71387, and CA21765) and by the American Lebanese Syrian Associated Charities (ALSAC) of the St. Jude Children's Research Hospital.

We thank Shannon Callens for her technical support and Sara Hamon for her assistance with the statistical analysis. Mouse cell lines were kindly provided by Phang-Lang Chen and Wen-Hwa Lee. We thank J. Moran and M. Ljungman for helpful discussions.