The Role of BRCA1 in Breast Cancer Ryan Allred Biol 445 Cancer Biology Spring 2009

1. The Role of BRCA1 in Breast Cancer Ryan Allred Biol 445 Cancer Biology Spring 2009

2. Breast Cancer • One in eight women will develop breast cancer. • 100 times more likely for a woman to develop breast cancer than a man • Sporadic form • ~90% of cases • No family history • Hereditary Form • 5-10% of cases • 25% of cases diagnosed before age 30 • Treatment • Mastectomy, radiation, chemotherapy, hormone therapy

3. How BRCA1 Was Found • Linkage analysis linked hereditary forms to the long (q) arm of chromosome 17 at position 21 • Positional Cloning Miki, Y et al, 1994.

4. Structure • 1863 amino acids • Carboxyl terminus contains two tandem BRCT repeats • Recognized in many DNA repair proteins • Could form DNA repair protein complex • RING finger domain  • Zinc finger which contains a Cys3HisCys4 amino acid motif which binds two zinc cations. • Involved with protein ubiquitination www.pdb.org Powell and Kachnic, 2003.

5. Knockout Mice • BRCA1 null embryos  Die in development • p53 growth arrest – associated with DNA damage • p53 inactivation partially rescues • Heterozygous mutants  normal • BRCA1 inactivation  late onset breast cancer • Frequent p53 mutations

6. Tumor Suppressor Paradox

7. We still need to figure out the function though. Let’s Irradiate

8. Homologous recombination • Ionizing Radiation Experiments • No BRCA1  fivefold reduction in homologous recombination • Correct BRCA1 function  normal

9. Nonhomologous End Joining • More irradiation. • Cells deficient in BRCA1 protein showed defects in the rejoining of fragmented DNA

10. Other Problems • After Ionizing Radiation in BRCA1 deficient cells • DNA synthesis checkpoint defect • G2/M checkpoint defect • Transcription coupled repair • Apoptosis • Ubiquitylation • Chromatin remodelling

11. Immunoflourescent microscopy

12. BRCA1 and it’s partners

13. Why Breast Cancer? ? • Estrogen • Progesterone • Estrogen Receptor Negative Cells? • Proposed - Surrounding cells send pro-survival signals BRCA1

14. Mutations • Penetrance of BRCA1 for carriers • Breast Cancer ~80% • Ovarian Cancer ~40% • Over 1,000 mutations • Loss of heterozygosity • Hypermethylation • Ring Domain • BRCT Narod et al, 2004.

15. The Big Picture • Defining the physiological function of BRCA1 has been very complicated • Important for Genomic Integrity • Forms complex that is involved with DNA repair Narod et al, 2004.

16. References • Miki, Y. et al. A strong candidate for the breast and ovarian cancer susceptibility gene BRCA1. Science 266, 66-71 (1994). • Hall, J.M. et al. Linkage of early-onset familial breast cancer to chromosome 17q21. Science 250, 1684-1689 (1990). • Narod, S.A. et al. BRCA1 and BRCA 2:1994 and beyond. Nature Reviews Vol. 4, 665-674 (2004) • Powell, S.N. et al. Roles of BRCA1 and BRCA2 in homologous recombination, DNA replication fidelity and the cellular response to ionizing radiation. Oncogene 22, 5784-5791 (2003). • Evers, B. et al. Mouse models of BRCA1 and BRCA2 deficiency: past lesson, current understanding and future prospects. Oncogene 25, 5885-5897 (2006). • Tapia T. et al. Promoter hypermethylation of BRCA1 correlates with absence of expression in hereditary breast cancer tumors. Epigenetics 3, 157-163 (2008). • Sankaran S. et al. Identification of domains of BRCA1 critical for the ubiquitin-dependent inhibition of centrosome function. Cancer Research 66, 4100-4107 (2006) • Weinberg R. The Biology of Cancer. Garland Science (2007).