1. BRCA2: Breast Cancer Susceptibility Gene 2 Lindy Behrend March 4, 2003

2. Breast Cancer 2nd major cause of cancer death in women 1 in 8 women likely to develop breast cancer 5-10% hereditary: of these, 1/3 due to mutations in BRCA1, 1/3 due to mutations in BRCA2, and 1/3 due to mutations in other unknown/unidentified genes

3. Risk Factors exposure to chemicals high dose radiation other environmental exposures smoking and drinking childless first child after 30

4. BRCA2 Inherited mutations in BRCA2 can increase breast cancer risk by 90% and ovarian cancer risk by 15-20% Increased chance of developing these cancers at a young age Increased risk of lymphoma, melanoma, and cancers of the colon, pancreas, gall bladder, bile duct and stomach

5. BRCA2 Located on chromosome 13 A tumor suppressor gene Inherited in an autosomal dominant fashion

6. BRCA2 Interacts with RPA and RAD51 during homologous recombination to repair double-strand DNA breaks caused by ionizing radiation and DNA cross- linking

7. BRCA2 function determined by looking at its structure C-terminal region: highly conserved amino acid sequence often mutated in mouse, rat, and human tumors Contains 3 oligonucleotide binding folds that are present in most single-strand DNA- binding proteins Interact with DNA in same way as RPA

8. BRCA2 function determined by looking at its structure Tower domain: homologous to DNA- binding domains of bacterial recombinases that bind double stranded DNA 4 of 7 most common missense mutations in BRCA2 occur here

9. BRCA2 stimulates RAD51-mediated recombination During S phase, BRCA1, BRCA2, and RAD51 colocalize in nuclear dots and then disperse after the arrest of synthesis In response to ionizing radiation or cross-linked DNA, these nuclear dots reform smaller foci Mice lacking one of these three genes show proliferation defects and die in utero In vitro assays indicate strand pairing and exchange are strongly dependent on RPA BRCA2 not found to be a successful substitute for RPA Adding BRCA2 stimulates the reaction in proportion to the amount added

10. Homologous Recombination RPA coats strands RAD 51 binds, initiates recombination RAD52, RAD54-RAD57 are mediator proteins to keep RPA from binding so tightly it interferes with RAD51 BRCA2 stimulates strand transfer

11. Remaining Uncertainties What is the mechanism by which BRCA2 interacts with RAD51? Why are there no BRCA2 homologs in yeast, flies, or worms? Why do mutations in BRCA2 produce tumors in select tissues?