The C-terminal proteolytic fragment of the breast cancer susceptibility type 1 protein (BRCA1) is degraded by the N-end rule pathway

The breast cancer susceptibility type 1 gene product (BRCA1) is cleaved by caspases upon the activation of apoptotic pathways. After proteolysis the C-terminal fragment has been reported to translocate to the cytoplasm and promote cell death. Here we report that the C-terminal fragment is unstable in cells as it is targeted for degradation by the N-end rule pathway. The data reveals that mutating the wild type N-terminal aspartate, of the C-terminal fragment, to valine stabilizes the fragment. If the N terminus is mutated to another N-terminal destabilizing residue, like arginine, the C-terminal fragment remains unstable in cells. Last, the C-terminal fragment of BRCA1 is stable in cells lacking ATE1, a component of the N-end rule pathway.