from High-Risk Women Frequently Perturb Strongly Hydrophobic Amino Acids Conserved among Mammals

Inherited missense mutations in the tumor suppressor gene, BRCA-1, may predispose to breast or ovarian cancer, but the exact effects on the protein are generally unknown. The COOH-terminal region of BRCA-1 encodes two BRCT repeats, which are partially con-served in mammalian species (human, dog, rat, and mouse; 60 % amino acid identity). A bioinformatic analysis was conducted to evaluate 246 BRCT missense mutations from high-risk breast and/or ovarian cancer patients (reported in the NIH Breast Cancer Informa-tion Core database). It was hypothesized that amino acids conserved in evolution would be disproportion-ately targeted by the mutations and that conserved amino acids with strongly hydrophobic side chains would be disproportionately perturbed. A statistical model was developed, and C 2 tests were used to deter-mine whether missense mutations are randomly dis-tributed throughout the BRCT repeats or whether they disproportionately target certain amino acids. The results showed that missense mutations dispropor-tionately target amino acids that are identical in all four mammals (C 2 = 46.01, P < 0.001). In addition, mis-sense mutations disproportionately perturb conserved amino acids with strongly hydrophobic side chains (C 2 = 68.57, P < 0.001) and alter the strongly hydro-phobic property. The two most frequently observed known cancer-predisposing missense mutations in the BRCT repeats, M1775R and A1708E, conform to this pattern. These results suggest that missense mu-tations affecting highly conserved amino acids with strongly hydrophobic side chains can disturb impor-tant features of the BRCA-1 protein and may play a role in breast and ovarian cancer formation. (Cancer Epidemiol Biomarkers Prev 2004;13(6):1037–41