ANALYSIS OF TUMOR SUPPRESSOR GENE USING MOLECULAR IMAGING FOR PERSONALIZED MEDICINE

Abstract

Breast cancer susceptibility gene 1 (BRCA1) is a prominent gene responsible for hereditary breast and ovarian cancers. Although increasing evidences indicate that BRCA1 participates in multiple cellular processes, its precise mechanisms in these processes remain unclear. To elucidate the molecular function of BRCA1 as a tumor suppressor gene, we analyzed the various functions of BRCA1, such as apoptosis, DNA repair, and cell cycle regulation. We recently analyzed the cellular responses of BRCA1 to various DNA damages using a molecular imaging technique. In particular, we examined the in situ response of BRCA1 accumulation at laser micro-irradiation– induced double-strand breaks (DSBs) and single-strand breaks (SSBs). BRCA1 accumulated at DSBs via its amino (N)and carboxyl (C)-termini. N-terminal BRCA1 rapidly accumulated at DSBs in a Ku80-dependent manner. In contrast, BRCA1 accumulated at SSBs via its C-terminus and with different kinetics from its accumulation at DSBs. BRCA1 accumulation at SSBs was abolished by caffeine treatment of the cells, which inhibits the PI3-kinases ataxia telangiectasis mutated (ATM) and ataxia telangiectasis mutated-related (ATR). To analyze the response of BRCA1 to UV irradiation, we generated local UV irradiation in cell nuclei using an isopore membrane filter. Interestingly, BRCA1 accumulation was dependent on a protein that is involved in the nucleotide excision repair pathway. Furthermore, BRCA1 immediately accumulated at the locally UV-irradiated sites in a transcription-dependent manner. These results suggest that BRCA1 is involved in the transcription-coupled repair (TCR) process for UV irradiation–induced DNA damage. Furthermore, we have identified a new BRCA1associated protein by proteomics, and are analyzing the properties of this protein. These precise analyses of BRCA1 and its related proteins will contribute to the development of novel molecular diagnoses and therapies for the personalized medicine of breast and ovarian cancers.