GATA3 mutation disrupts a functional network governed by estrogen receptor, FOXA1 and GATA3

Estrogen receptors (ER) are part of the nuclear receptor superfamily of transcription factors and are activated by the steroid hormone 17β-estradiol. ER forms a regulatory network in conjunction with other transcription factors, such as FOXA1 and GATA3. GATA3 has been identified as one of the most frequently mutated genes in breast cancer and is capable of specifying chromatin localization of FOXA1 and ER. How GATA3 mutations impact this transcriptional network is unknown. Here we investigate the function of one of the recurrent patient-derived GATA3 mutations (R330fs) on this regulatory network. Genomic analysis indicates that the R330fs mutant can disrupt the cooperative action of ER, FOXA1, and GATA3, and induce a change in chromatin localization of these factors. Relocalization of ER and FOXA1 is associated with altered chromatin architecture, which leads to differential gene expression in GATA3 mutant cells. These results suggest an active role for GATA3 mutants in ER positive breast tumors.