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The pathophysiological function of the forkhead transcription factor FOXN3 remains to be explored. Here we report that FOXN3 is a transcriptional repressor that is physically associated with the SIN3A repressor complex in estrogen receptor–positive (ER+) cells. RNA immunoprecipitation–coupled high-throughput sequencing identified that NEAT1, an estrogen-inducible long noncoding RNA, is required for FOXN3 interactions with the SIN3A complex. ChIP-Seq and deep sequencing of RNA genomic targets revealed that the FOXN3-NEAT1-SIN3A complex represses genes including GATA3 that are critically involved in epithelial-to-mesenchymal transition (EMT). We demonstrated that the FOXN3-NEAT1-SIN3A complex promotes EMT and invasion of breast cancer cells in vitro as well as dissemination and metastasis of breast cancer in vivo. Interestingly, the FOXN3-NEAT1-SIN3A complex transrepresses ER itself, forming a negative-feedback loop in transcription regulation. Elevation of both FOXN3 and NEAT1 expression during breast cancer progression corresponded to diminished GATA3 expression, and high levels of FOXN3 and NEAT1 strongly correlated with higher histological grades and poor prognosis. Our experiments uncovered that NEAT1 is a facultative component of the SIN3A complex, shedding light on the mechanistic actions of NEAT1 and the SIN3A complex. Further, our study identified the ERα-NEAT1-FOXN3/NEAT1/SIN3A-GATA3 axis that is implicated in breast cancer metastasis, providing a mechanistic insight into the pathophysiological function of FOXN3.