GATA3 is a transcription factor expressed in luminal breast epithelial cells and is required for mammary gland development. Analysis of TCGA data reveals that somatic heterozygous mutations in GATA3 occur in up to 15% of estrogen receptor positive breast tumors, and that these tumors are diagnosed a median of eight years earlier than other estrogen receptor positive tumors, suggesting a more aggressive phenotype. These mutants have been proposed to be null alleles resulting in haploinsufficiency, however the mutation spectrum of GATA3 in breast cancer is in sharp contrast to that found in HDR syndrome, a true GATA3 haploinsufficiency disease. Based on this disparity, we propose that there is a selective pressure to mutate and retain a portion of the GATA3 in breast cancer. Here we focus on the GATA3 mutants which lack the second zinc finger which is responsible for GATA motif binding. Expression of these mutants accelerated xenograft tumor growth by ZR751 cells, and transgenic expression in mouse mammary glands promoted precocious lobuloalveolar development. We have used integrated gene expression and ChIP-Seq profiling to demonstrate that these zinc-finger deleted proteins retain the ability to associate with the genome by tethering to complexes associated with FOXA1 and AP-2gamma recognition motifs, where they modulate the expression of adjacent genes. These data support a model in which the GATA3 mutations recently observed in breast cancer encode for active transcription factors which elicit proliferative phenotypes in normal mammary epithelium and promote the growth of estrogen receptor positive breast cancer cell lines.

Citation Format: Kenny PA, Chandiramani N, Lofgren KA. Mutant GATA3 actively promotes the growth of normal and malignant mammary cells [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-08-02.