Potential role of BRCA2 in a mitotic checkpoint after phosphorylation by hBUBR1

BRCA2, a gene responsible for inherited susceptibility to breast cancer in a number of families, is thought to be critical for replication and repair of DNA during S-phase, To elucidate the physiological functions of BRCA2, w e used a yeast two-hybrid system to screen for proteins that could associat e with BRCA2. Here we report interaction of BRCA2 with a mitotic checkpoint protein, hBUBR1, and its phosphorylation by hBUBR1 irt vitro. After cotran sfection of BRCA2 and hBUBR1 expression vectors into the COS7 cell line, bo th proteins were stained together in the nuclei of cells whose spindle fibe rs were disrupted, but not in undamaged cells. Treatment with vincristine, which disrupts microtubules, significantly increased expression of both hBU BR1 and BRCA2 in the MCF7 cells. The results suggest that BRCA2 protein mig ht be involved in a mitotic checkpoint in vivo after it has been phosphoryl ated by hBUBR1.