Abstract 5418: GATA3 zinc-finger mutation induces transcriptional reprogramming in breast cancer through gain and loss of function

Recent large-scale breast cancer genomic profiling identified frequent mutations in a pioneer transcription factor, GATA3. The expression of GATA3 is a prominent marker of luminal breast tumors, and loss of GATA3 expression is associated with aggressive tumor phenotypes. In addition, GATA3 mutations are frequently found in these luminal tumors. However, the clinical and molecular outcomes of GATA3 mutations are poorly understood. Our novel classification scheme of GATA3 mutations defines distinct clinical features of breast tumors with mutations in the second GATA3 zinc-finger (ZnFn2): frequent observation in luminal B subtype and worse prognosis than other GATA3 mutant cases. To dissect the molecular impacts of these ZnFn2 mutations, we generated a GATA3 mutant breast cancer cell clone by CRISPR-Cas9 gene editing. An engineered ZnFn2 mutant cell line manifested increased tumor growth as xenografts and more aggressive phenotypes in vitro. The ZnFn2 mutation led to loss of GATA3 binding and decreased expression at a subset of genes, including progesterone receptor (PR). The mutant cells also exhibited gain of GATA3 binding at other loci, correlated with increased expression of mesenchymal marker genes. Decreased expression of PR and impaired response to progesterone were crucial for cancer-promoting functions in GATA3 ZnFn2 mutant cells. Downregulation of PR and its downstream genes was also observed in the clinical gene expression data. These results illuminate tumor-promoting functions of GATA3 ZnFn2 mutations in breast cancer. Citation Format: Motoki Takaku, Sara A. Grimm, John D. Roberts, Kaliopi Chrysovergis, Page Myers, Charles M. Perou, Paul A. Wade. GATA3 zinc-finger mutation induces transcriptional reprogramming in breast cancer through gain and loss of function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5418.