Epidemiological, molecular and cellular studies of the function of BRCA1 in human breast and ovarian cancer

BRCA1 is a large and complex gene, causal for the early onset breast and ovarian cancer syndrome, of undetermined biochemical function. The protein is important both in development of mice and the progression of human breast and ovarian cancers, acting as a tumour suppressor protein. The function differs from that of other tumour suppressors as it is not classically mutated in any sporadic cancers. Animal models developed for the study of the function of the protein have been difficult to develop and do not provide a paradigm for human function. This work examines the importance of the gene in apparently sporadic cancers and develops human cell culture models for the study of the biochemical function. Studies of a group of breast cancer cases that presented with a second primary cancer allowed the identification of three novel and a fourth previously described mutation in patients with no profound family history of breast or ovarian cancer. I suggest that these mutations are acting as low penetrance germ line mutations. To determine the molecular basis of low penetrance BRCA1 mutations, I have developed a variety of ceil lines that have decreased levels of BRCA1 through antisense inhibition. I found that no differences in the growth rate or drug response could be detected in these cell lines, counter to other reports. I propose that these changes may be a reflection of the mechanism for lower penetrance mutations. Finally, to simplify the further study of BRCA1 function, I have developed prokaryotic expression systems for BRCA1 recombinant protein. This work demonstrates that lower penetrance mutations may be accounting for more sporadic breast cancer cases than previously thought. This manuscript also proposes biochemical mechanisms by which BRCA1 may mediate its variety of functions.