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Investigation of the Role Played by BRCA1 in the Activation of FANCD2 Following Chemotherapy Induced DNA Damage
Cells containing a mutation in one of the Fanconi Anemia (FA) genes or the BRCA1 gene show spontaneous chromosomal instability and a high level of sensitivity to the DNA crosslinking agents such as mitomycin C (MMC) or cisplatin that function by causing DNA replication arrest (1,2). Our lab has recently demonstrated that ATR specifically phosphorylates the FA protein FANCD2 at residues threonine 691 and serine 717 following treatment with these agents. Furthermore, we have demonstrated that ATR is required for efficient monoubiquitination and activation of the FANCD2 protein following DNA damage. We have also demonstrated that BRCA1 is required for the efficient monoubiquitination and subsequent subcellular relocalization of FANCD2 following DNA damage in human U2OS and HeLa cell lines. As BRCA1 has also been shown to be required for the activity and substrate specificity of ATR (3) we hypothesize that BRCA1 may be required for ATR-induced phosphorylation of FANCD2 which may then facilitate its subsequent monoubiquitination and the formation of DNA damage nuclear foci. To test this hypothesis we plan to investigate the effect of BRCA1 mutation in the HCC1937 cell line on FANCD2 phosphorylation, monoubiquitination and subsequent subcellular relocalization following DNA damage. To further relate the importance of ATR-mediated phosphorylation of FANCD2 to its subsequent activation we will individually mutate the FANCD2 phosphorylation sites and assess the monoubiquitination and relocalization of the mutant proteins following DNA damage. We will also investigate the effects of individually abrogating ATR and BRCA1 function with siRNA technology on FANCD2 phosphorylation, monoubiquitination and relocalization in a breast cancer cell line following DNA damage. Finally we will investigate the individual effects of abrogation of ATR and BRCA1 expression or loss of FANCD2 phosphorylation on cellular sensitivity to cytotoxic chemotherapy using cell cycle profiling and apoptotic assays. We hope that understanding the interactions between ATR, FANCD2 and BRCA1 will lead to better targeting of conventional chemotherapeutic agents and the development of novel therapeutic strategies that will prevent cytotoxic drug resistance.
Fanconi anemia (FA) and familial breast cancer are both diseases associated with failure to repair DNA damage. Recent evidence suggests that FANCD2 (a protein that is mutated in FA) and BRCA1 (a protein mutated in familial breast cancer) may function together in the response to DNA damage. In this study we plan to investigate how FANCD2 and BRCA1 interact following DNA damage and how this interaction activates DNA damage response pathways. In particular, we are interested in studying how loss of either BRCA1 or FANCD2 function makes cancer cells susceptible to DNA damaging chemotherapy commonly used in breast cancer treatment. Through these studies we hope to better understand how loss of BRCA1 or FANCD2 function results in genetic instability and subsequent cancer development. We also hope that a better understanding of BRCA1 and FANCD2 function will allow better targeting of conventional chemotherapy for breast cancer and lead to the development of new treatment strategies.