RACK1 regulates centriole duplication by controlling localization of BRCA1 to the centrosome in mammary tissue-derived cells.

Breast cancer gene 1 (BRCA1) is a tumor suppressor that is associated with hereditary breast and ovarian cancer. BRCA1 functions in DNA repair and centrosome regulation together with BRCA1-associated RING domain protein (BARD1), a heterodimer partner of BRCA1. Obg-like ATPase 1 (OLA1) was identified as a protein that interacts with BARD1. OLA1 regulates the centrosome by binding to and collaborating with BRCA1 and BARD1. We identified receptor for activated C kinase (RACK1) as a protein that interacts with OLA1. RACK1 directly bound to OLA1, the N-terminal region of BRCA1, and γ-tubulin, associated with BARD1, and localized the centrosomes throughout the cell cycle. Knockdown of RACK1 caused abnormal centrosomal localization of BRCA1 and abrogated centriole duplication. Overexpression of RACK1 increased the centrosomal localization of BRCA1 and caused centrosome amplification due to centriole overduplication. The number of centrioles in cells with two γ-tubulin spots was higher in cell lines derived from mammary tissue compared to those derived from other tissues. The effects of aberrant RACK1 expression level on centriole duplication were observed in cell lines derived from mammary tissue, but not in those derived from other tissues. Two BRCA1 variants, R133H and E143K, and a RACK1 variant, K280E, associated with cancer, which weakened the BRCA1-RACK1 interaction, interfered with the centrosomal localization of BRCA1 and reduced centrosome amplification induced by overexpression of RACK1. These results suggest that RACK1 regulates centriole duplication by controlling the centrosomal localization of BRCA1 in mammary tissue-derived cells and that this is dependent on the BRCA1-RACK1 interaction.