The BRCA1-GADD45 Pathway and Genomic Stability

University Of Pittsburgh At Pittsburgh, Pittsburgh PA

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Abstract

Breast cancer susceptibility gene, BRCA1, has been implicated in the maintenance of genomic integrity. However, the molecular mechanism(s) by which BRCA1 plays a role in maintenance of genomic fidelity remains to be defined. Interestingly, recent studies in our group and others have demonstrated that BRCA1 can regulate the GADD45, a p53-regulated stress inducible gene that plays an important role in cellular response to DNA damage. These results have evidently linked GADD45 to BRCA1 and raised the possibility that GADD45 might be a BRCA1-downstream effector and mediate BRCA1's role in maintenance of genomic stability. Therefore, this proposal seeks to define the biochemical mechanism(s) by which BRCA1 transactivates the GADD45 gene, and to define the role of the BRCA1-GADD45 pathway in the induction of apoptosis following genotoxic stress. The long-term objective described in this application will specifically focus on three key issues: (1). To characterize the GADD45 gene as a BRCA1's downstream effector. We will define the BRCA1-regulatory elements in the GADD45 promoter and identify the proteins that modulate the BRCA1 transactivation of the GADD45 promoter. (2). To define whether the GADD45 is an essential player in the BRCA1-induced apoptosis. We will analyze the induction of apoptosis following expression of GADD45 and BRCA1. We will also examine the alterations of the BRCA1-activated apoptosis and BRCA1-induced growth suppression in GADD45- deficient cells. (3). Our most recent studies demonstrated that BRCA1 is cleaved by caspase-3 during apoptosis induced by DNA damage. This DNA damage-activated cleavage results in an accumulated 90-kDa band of the BRCA1 C-terminus. Therefore, we will first determine whether the BRCA1 cleavage is required for BRCA1-activated apoptosis following DNA damaging agents. We will also determine the functional role of the cleaved 90-kDa band of the BRCA1 C-terminus in activation of apoptosis. Finally, we will analyze the role of this cleaved product in the BRCA1 transactivation of the GADD45 promoter. The studies proposed in this application would define a novel pathway (BRCA1-GADD45) controlling apoptosis following DNA damage and provide information regarding the biochemical mechanism by which BRCA1 regulates its targeted genes. Since apoptosis is closely associated with the therapeutic sensitivity, the perspective outcome will also provide insight into the development of therapeutic agents.