Abstract 2390: Identification of BRCA2 genetic interactors in an ES cell-based model

Mutations in breast cancer susceptible genes, BRCA1 and BRCA2 are the genetic factors conferring highest risk to develop breast cancer. Although BRCA proteins are known to maintain genomic stability mainly by homologous recombination-mediated DNA damage repair, detailed mechanisms of how BRCA loss induces tumorigenesis remain unclear. Interestingly, while inactivation of both alleles of BRCA1 or BRCA2 genes is necessary for tumor development, their loss in normal cells affects cell viability, indicating that cells lacking BRCA1 or 2 are able to survive and predisposed to tumorigenesis due to mutations in other genes such as those involved in cell cycle regulation or DNA damage response. In the current study, we identified some of the candidate genes using a mouse embryonic stem (mES) cell-based insertional mutagenesis screening. Overexpression of these genes rescued BRCA2 loss-induced lethality in mES cells. One candidate encodes a PDZ domain-containing protein, GIPC3. While overexpression of GIPC3 rescued BRCA2 loss efficiently, overexpression of its close homolog GIPC1 rescued much less efficiently. The GIPC3-rescued cells were hypersensitive to DNA damaging agents and exhibited an overall increase in genomic instability. Point mutation analysis showed several amino acids in the PDZ domain was critical for rescuing BRCA2 lethality, suggesting protein-protein interaction is responsible for the rescuing. We therefore performed IP-MS analysis and found that GIPC3 can interact with APPL1 and APPL2, two important mediators in AKT-mediated survival signal transduction pathway. We are now analyzing if these two molecules are potential down-stream factors of GIPC3 in rescuing BRCA2 loss-induced lethality. Meanwhile, we found that Gipc3 overxpression can partially rescue the lethality of Brca2ko/ko embryos. We are now also examining the expression of GIPC3 in human BRCA2-deficient tumors and we are monitoring tumorigenesis of GIPC3 transgenic mice in a K14-Cre;Brca2cko/cko mammary tumor model. Citation Format: Xia Ding, Shyam K. Sharan. Identification of BRCA2 genetic interactors in an ES cell-based model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2390. doi:10.1158/1538-7445.AM2014-2390