Functional analysis of BRCA1 C-terminal missense mutations identified in breast and ovarian cancer families

Germline mutations in the breast and ovarian cancer susceptibility gene BRC A1 are responsible for the majority of cases involving hereditary breast an d ovarian cancer, Whereas all truncating mutations are considered as functi onally deleterious, most of the missense variants identified to date cannot be readily distinguished as either disease-associated mutations or benign polymorphisms, The C-terminal domain of BRCA1 displays an intrinsic transac tivation activity, and mutations linked to disease predisposition have been shown to confer loss of such activity in yeast and mammalian cells. In an attempt to clarify the functional importance of the BRCA1 C-terminus as a t ranscription activator in cancer predisposition, we have characterized the effect of C-terminal germline variants identified in Scandinavian breast an d ovarian cancer families, Missense variants A1669S, C1697R, R1699W, R1699Q , A1708E, S1715R and G1738E and a truncating mutation, W1837X, were charact erized using yeast- and mammalian-based transcription assays. In addition, four additional missense variants (V1665M, D1692N, S1715N and D1733G) and o ne in-frame deletion (V1688del) were included in the study. Our findings de monstrate that transactivation activity may reflect a tumor-suppressing fun ction of BRCA1 and further support the role of BRCA1 missense mutations in disease predisposition, We also report a discrepancy between results from y east- and mammalian-based assays, indicating that it may not be possible to unambiguously characterize variants with the yeast assay alone. We show th at transcription-based assays can aid in the characterization of deleteriou s mutations in the C-terminal part of BRCA1 and may form the basis of a fun ctional assay.