GSBS Dissertations and Theses

Approval Date

February 2007

Document Type

Doctoral Dissertation

Department

Graduate School of Biomedical Sciences, Department of Cancer Biology

Subjects

DNA Damage; DNA Repair; Basic-Leucine Zipper Transcription Factors; Fanconi Anemia Complementation Group Proteins; Genes, BRCA1; BRCA Protein; Dissertations, UMMS; Academic Dissertations

Abstract

DNA damage response pathways are a complicated network of proteins that function to remove and/or reverse DNA damage. Following genetic insult, a signal cascade is generated, which alerts the cell to the presence of damaged DNA. Once recognized, the damage is either removed or the damaged region is excised, and the original genetic sequence is restored. However, when these pathways are defective the cell is unable to effectively mediate the DNA damage response and the damage persists unrepaired. Thus, the proteins that maintain the DNA damage response pathway are critical in preserving genomic stability.

One essential DNA repair protein is the Breast Cancer Associated gene, BRCA1. BRCA1 is essential for mediating the DNA damage response, facilitating DNA damage repair, and activating key cell cycle checkpoints. Moreover, mutations in BRCA1 lead to a higher incidence of breast and ovarian cancer, highlighting the importance of BRCA1 as a tumor suppressor. In an effort to better understand how BRCA1 carried out these functions, researchers sought to identify additional BRCA1 interacting proteins. This led to the identification of several proteins including the BRCA1 Associated C-terminal Helicase, BACH1. Due to the direct interaction of BACH1 with a region of BRCA1 essential for DNA repair and tumor suppression, it was speculated that BACH1 may help support these BRCA1 function(s). In fact, initial genetic screenings confirmed that mutations in BACH1 correlated not only with hereditary breast cancer, but also with defects in DNA damage repair processes.

The initial correlation between BACH1 and cancer predisposition was further confirmed when mutations in BACH1 were identified in the cancer syndrome Fanconi anemia (FA) (complementation group FA-J), thus giving BACH1 its new name FANCJ. These findings supported a previously established link between the FA and BRCA pathways and between FA and DNA repair. In particular, we demonstrated that similar to other FA/BRCA proteins, suppression of FANCJ lead to a substantial decrease in homologous recombination and enhanced both the cellular sensitivity to DNA interstrand cross-linking agents and chromosomal instability. What remained unknown was specifically how FANCJ functioned and whether these functions were dependent on its interaction with BRCA1 or other associated partners. In fact, we identified that FANCJ interacted directly with the MMR protein MLH1. Moreover, we found that the FANCJ/BRCA1 interaction was not required to correct the cellular defects in FA-J cells, but rather that the FANCJ/MLH1 interaction was required. Although both the FA/BRCA and MMR pathways undoubtedly mediate the DNA damage response, there was no evidence to suggest that these pathways were linked, until recently. Our findings not only indicate a physical link between these pathways by protein-protein interaction, but also demonstrated a functional link.

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