Abstract 4197: Mutant GATA3 drives precocious lobuloalveolar mammary development and promotes the growth of estrogen receptor positive xenograft tumors
Authors: Chandiramani Natasha , Peterson Esther A. , Jung Eric H. , Jenkins E. Charles , Kenny Paraic A. 
Published: August 2015

Abstract
The GATA3 transcription factor is expressed in luminal breast epithelial cells and is required for mammary gland development. Recent reports indicate that somatic mutations in GATA3 occur in up to 15% of estrogen receptor positive breast tumors. Our analysis of these published data demonstrates that the human breast tumors with GATA3 mutations are diagnosed 7 years earlier than other ER+ tumors, suggesting that these are more aggressive tumors.
Previously, these mutations were proposed to be null alleles that resulted in haploinsufficiency for GATA3 in breast cancer, however this interpretation currently lacks experimental support. We report that the mutation spectrum of GATA3 in breast cancer is in sharp contrast to HDR syndrome, a true GATA3 haploinsufficiency disease. In breast cancer, there is a striking enrichment of GATA3 mutations in exons 5 and 6 (amino acids 294-444) which encode the second of two DNA binding zinc fingers and the C-terminal amino acids. The absence of whole gene deletions or additional 5′ mutations in the open-reading frame, frequently found in HDR syndrome, suggests that there is a selective pressure to mutate and retain a portion of the GATA3 in breast cancer. We hypothesize that these GATA3 mutations do not result in null alleles but instead encode proteins with residual or neomorphic functions which actively contribute to breast cancer progression.
We have generated transgenic mice that express mammary-specific GATA3-336fs. Non-parous pubertal transgenic mice exhibit pronounced lobuloalveolar development compared to estrous-matched wildtype littermates. This indicates that expression of mutant GATA3 protein promotes aberrant mammary epithelial cell proliferation. We are currently testing the effect of mutant GATA3 on the kinetics of mammary tumorigenesis by crossing these mice with models of mammary cancer harboring mutant P53 and mutant PI3K.
We have generated ZR751 luminal breast cancer cell lines that stably express the hotspot GATA3 mutations that affect codons 309, 336 and 409. When xenografted into the mammary fat pads of nude mice, cells with GATA3-309* and GATA3-336fs have a growth advantage, while GATA3-409fs had slightly slower growth than the parental line. Genome wide ChIP-Seq analysis shows that GATA3-409fs has a similar binding profile to wildtype GATA3, with a significant enrichment at the GATA binding motif. The GATA3-309* and GATA3-336fs mutants bind fewer sites in the genome and are highly enriched at non-GATA motifs indicating an alternate mechanism of DNA binding for target gene regulation.
These data support a model in which the GATA3 mutations recently observed in breast cancer encode for dominantly-acting transcription factors. These mutations elicit proliferative phenotypes in normal mammary epithelium and promote the growth of estrogen receptor positive breast cancer cell lines.
Citation Format: Natasha Chandiramani, Esther A. Peterson, Eric H. Jung, E. Charles Jenkins, Paraic A. Kenny. Mutant GATA3 drives precocious lobuloalveolar mammary development and promotes the growth of estrogen receptor positive xenograft tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4197. doi:10.1158/1538-7445.AM2015-4197