Molecular Functions of BRCA2 and Its Interaction Partners in Suppression of Breast Cancer
Abstract
Several million women in the United States are diagnosed with or are undergoing therapy for breast cancer. The risk of breast cancer is about 1 in 8 during a woman s lifetime. Most breast cancers are sporadic, but about 10% have a well-defined genetic basis: about one-quarter of the genetically susceptible breast cancers are due to familial mutation of BRCA1 or BRCA2. Individuals with BRCA1/2 disease-causing mutations have an 80%-90% chance of developing breast cancer by age 70-80 (compared to ~8% in the general population). Hence, understanding the function of BRCA2, and its associated proteins, and why their mutations predispose affected individuals to cancer is essential for the development of new therapeutic strategies for these patients. It is now known that BRCA2 functions in a DNA maintenance pathway known as homologous recombination (HR). A role for BRCA2 in HR was established by its interaction with a key protein involved in HR, the RAD51 protein. DNA repair by HR is a very complex biological process involving well over 50 different proteins. BRCA2 itself interacts with many proteins in addition to RAD51; one such protein is PALB2 (Partner and Localizer of BRCA2). PALB2 is also a breast cancer suppressor protein; PALB2 also interacts with BRCA1. In addition to forming a complex with BRCA2, RAD51 – the central protein of HR – also interacts with many proteins, including a group of proteins known as the RAD51 paralogs. Of the RAD51 paralogs, four – RAD51B, RAD51C, RAD51D, and XRCC2 – are tumor suppressors linked to breast and ovarian cancer. Using biochemical, cellular, molecular, and single-molecule imaging approaches, we plan to uncover the molecular defects that underlie the cancer-causing mutations in BRCA2, PALB2, and the RAD51 paralog proteins. BRCA2 is an extremely large (3,418 amino acids) and complex protein. With previous support from the Department of Defense (DoD) Breast Cancer Research Program (BCRP) and 4 years of effort, we reported the purification of full-length human BRCA from human cells. This report received widespread international attention (e.g., Nature News & Views, a commentary in the Journal of the National Cancer Institute, a news highlight by the American Cancer Society, and inclusion as a “landmark paper” in the DoD BCRP and Ovarian Cancer Research Program Contributions to Advancement in BRCA timeline). We now understand much more about the molecular basis of BRCA2 function in genome maintenance and why its loss results in susceptibility to cancer. In individuals harboring BRCA2 mutations, disruption of this recombinational DNA repair process leads to chromosomal instability, and ultimately, cancer. DNA repair by HR is a fundamental biological process necessary for the maintenance of chromosomal integrity. A severed DNA molecule is a particularly difficult type of DNA damage to repair: the accurate repair breaks or gaps in DNA requires the use of a second copy of the DNA as a template to ensure that the breaks are rejoined properly and that missing information is replaced faithfully. It is now clear that the failure to maintain genomic integrity is a major source of predisposition to cancer. The research in this proposal will focus on specific molecular events essential for chromosomal maintenance by HR. Loss of HR function is now known to result not only in predisposition to cancers of the breast, ovary, and certain epithelial tissues, but also to hematological malignancies, bone marrow failure, and developmental abnormalities in Fanconi’s anemia. We plan to purify BRCA2, PALB2, and the RAD51 paralog proteins and to understand their biochemical activities. In addition, we use a novel visualization technique where we can literally see individual protein molecule “working” on a single-molecule of DNA. We will explore the effect of BRCA2 and the RAD51 paralogs on the ability of RAD51 protein to assemble into a filament on DNA. We expect that our experiments wi
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 29, 2018
- Source ID
- W81XWH1810730
Entities
People
- Stephen Kowalczykowski
Organizations
- United States Army
- University of California, Davis