Mutations in tumor-suppressor gene BARD1 have been found in inherited and spontaneous breast, ovarian and
uterine cancers. BARD1 plays a critical role in DNA repair and ubiquitination as binding partner of BRCA1, with which it colocalizes to nuclear dots. Independently of BRCA1, BARD1 can induce p53-dependent apoptosis in response to genotoxic stress. Therefore, BARD1 or p53 might be defective in
cancer cells spared from apoptosis. We investigated BARD1 and p53 expression in ovarian, breast and non-small-cell
lung cancers. BARD1 expression was highly upregulated and cytoplasmic in most
cancer cells, while weak nuclear staining was observed in the surrounding normal tissue. Maximal BARD1 expression was associated with the most malignant
ovarian cancer, clear cell
carcinoma. In
breast cancer, BARD1 expression was correlated with poor differentiation and large
tumor size, established factors of poor prognosis, as well as short disease-free survival. In contrast to breast and
ovarian cancers, no correlation of BARD1 expression with either grade or stage could be determined for
lung cancer. RT-PCR, performed on 10
ovarian cancers, revealed absence of the 5' portion of the BARD1 transcript in 7
tumors, and sequencing of the remaining 3 identified a missense mutation (A1291G) resulting in an
amino acid change of
glutamine 406 to
arginine. These data suggest that genetic and epigenetic changes might lead to elevated cytoplasmic expression of BARD1 and that cytoplasmic BARD1 might be a poor prognostic factor for breast and
ovarian cancers.