Analysis for a new mechanism of neoplastic cell transformation through the centrosome control with MT1-MMP

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BRCA2 is a multifunctional tumor suppressor protein with critical roles in DNA repair, replication, centrosome amplification, and cytokinesis. We previously identified the complexes of BRCA2 and membrane type-1 matrix metalloproteinase (MT1-MMP). In addition, we found the cleaved BRCA2 by MT1-MMP in cancer cells. To examine the role of the cleaved BRCA2 fragments, we generated cleavage-site-directed antibodies, which specifically recognize each of the fragments of BRCA2 (N-BRCA2 or C-BRCA2). Immunofluorescence analysis revealed that C-BRCA2 localizes to discrete nuclear foci. We measured the fluorescence intensity of the wild-type BRCA2 and C-BRCA2 nuclear foci in HeLa cells exposed to 10 Gy of ionizing radiation at several time points after irradiation. Interestingly, the intensity of wild-type BRCA2 foci was stronger near thenuclear envelope compared with the central part, but the intensity of cleaved C-BRCA2 foci was distributed evenly in the nucleus after irradiation. We suggest that BRCA2 is a cleavage target of MT1-MMP and that cleaved C-BRCA2 may play an important role in HRand breast oncogenesis.