BRCA1 is associated with the centrosome during mitosis

Abstract

Centrosomes and their associated microtubules direct events during mitosis and control the organization of animal cell structures and movement during interphase. The centrosome replicates during the cell cycle, directs the assembly of bipolar mitotic spindles, and plays an important role in maintaining the fidelity of cell division. Recently, tumor suppressors such as p53 and retinoblastoma protein pRB have been localized to the centrosome in a cell cycledependent manner. Immunof luorescence microscopy and analysis of isolated centrosomes now provide evidence that BRCA1 protein, a suppressor of tumorigenesis in breast and ovary, also is associated with centrosomes during mitosis. Our results indicate that BRCA1 localizes with the centrosome during mitosis and coimmunoprecipitates with ␥-tubulin, a centrosomal component essential for nucleation of microtubules. Furthermore, ␥-tubulin associates preferentially with a hypophosphorylated form of BRCA1.Breast cancer affects one in eight women in the Western world, with genetic predisposition caused by BRCA1 accounting for͞3% of breast cancer cases. This gene is also responsible for a familial predisposition to ovarian cancer. Most of the mutations that have been identified in these families are frameshift, nonsense, or splice-site alterations, that generate truncated BRCA1 protein (1-3).

BRCA1 gene in breast cancer

“…These Brca1-defective MEFs showed centrosome amplification with multiple functional centrosomes, which led to unequal chromosome segregation and aneuploidy (Xu et al, 1999b). Consistent with this finding, an earlier study had shown that BRCA1 localizes to the centrosome during mitosis and associates with g-tubulin, a centrosomal protein necessary for the nucleation of microtubules (Hsu and White, 1998;Hsu et al, 2001). These studies suggest a role for BRCA1 in the regulation of centrosome duplication as a component of its function in maintaining genomic integrity.…”

PIBF (progesterone induced blocking factor) is overexpressed in highly proliferating cells and associated with the centrosome

“…The most prominent example is the best-characterized breast cancer susceptibility gene BRCA1 11,22 that is linked to the development of breast and ovarian cancers. Importantly, recent genetic studies indicated PIBF among the candidate genes for breast cancer predisposition and cancer progression.…”

“…11 Exponentially grown HEK 293 cells were incubated with culture medium containing 0.6 g/ml nocodazole and 1 g/ml cytochalasin D for 1 hr at 37°C, to depolymerize microtubule filaments and actin, respectively. The cells were harvested and resuspended in 1ml lysis buffer (1 mM HEPES pHϭ7.2, 0.5% NP-40, 0.5 mM MgCl 2 , 0.1% 2-mercaptoethanol, 1 mM phenylmethylsulfonyl fluoride and Complete™ EDTA free tablets).…”

“…11 The fractionation procedure involved treatment of cells with nocodazole at a reduced concentration (0.6 ␥g/ml) for 1 hr that allowed the separation of organelles but retained proteins loosely associated with centrosomes. Western blot analysis demonstrated that PIBF was among the proteins copurified with centrosomes, similarly to ␥-tubulin (Fig.…”

An ATM- and ATR-dependent checkpoint inactivates spindle assembly by targeting CEP63

“…Tumour suppressor proteins including BRCA1 and p53 have also been found to co-localize with centrosomes in mitosis, although how these proteins participate in centrosome regulation it is not known. It is also unknown if they impact on centrosome stability in the context of mitotic DNA damage (Hsu and White, 1998;Kais and Parvin, 2008;Shinmura et al, 2007;Fukasawa, 2007).…”