Epithelial-to-mesenchymal transition (EMT) is an important process during embryonic development and tumor progression by which adherent epithelial cells acquire mesenchymal properties. Forkhead box protein A1 (FOXA1) is a transcriptional regulator preferentially expressed in epithelial breast cancer cells, and its expression is lost in mesenchymal breast cancer cells. However, the implication of this biased expression of FOXA1 in breast cancer is not fully understood. In this study, we analyzed the involvement of FOXA1 in EMT progression in breast cancer, and found that stable expression of FOXA1 in the mesenchymal breast cancer MDA-MB-231 cells strongly induced the epithelial marker E-cadherin at the mRNA and protein levels. Furthermore, stable expression of FOXA1 was found to reduce the mRNA and protein expression of Slug, a repressor of E-cadherin expression. FOXA1 knockdown in the epithelial breast cancer MCF7 cells reduced E-cadherin protein expression without decreasing its mRNA expression. In addition, FOXA1 knockdown in MCF7 cells up-regulated Slug mRNA and protein expression. Notably, similar to FOXA1 knockdown, stable expression of Slug in MCF7 cells reduced E-cadherin protein expression without decreasing its mRNA expression. Taken together, these results suggest that although FOXA1 can induce E-cadherin mRNA expression, it preferentially promotes E-cadherin expression at the protein level by suppressing Slug expression in epithelial breast cancer, and that the balance of this FOXA1-Slug axis regulates EMT progression.Key words epithelial-mesenchymal transition; E-cadherin; forkhead box protein A1; Slug; estrogen receptor Epithelial-to-mesenchymal transition (EMT) is a process that converts adherent epithelial cells to motile mesenchymal cells during embryonic development. 1) EMT is also involved in tumor progression through inducing metastasis and chemoresistance in tumor cells.2-4) Therefore, a better understanding of the molecular mechanisms underlying EMT in tumor cells is beneficial for development of novel antitumor agents.E-Cadherin is a crucial protein that mediates cell-cell adhesion in epithelial cells.1) E-Cadherin expression is dramatically reduced during EMT, which causes loss of cell-cell adhesion and gain of cell motility. Reduction in E-cadherin expression is mainly caused by the transcriptional repressors of E-cadherin gene (CDH1).2,5) A major transcriptional repressor of CDH1 is the zinc finger factor Slug. Slug binds to the E-box sequences present in the enhancer region of CDH1 and represses its expression. 6)Forkhead box A1 (FOXA1) is a member of the forkhead box family of transcription factors. FOXA1 contains the forkhead DNA-binding domain and the N-and C-terminal transactivation domains.7) FOXA1 regulates expression of many genes involved in the development of various tissues, including mammary gland, liver, midbrain, and lung. 8) FOXA1 is also known to function as a chromatin remodeling factor that opens closed chromatin and facilitates the recruitment of other transcription fa...

The pioneer transcription factor FoxA1 plays an important role in estrogen signaling by opening closed chromatin and promoting recruitment of the estrogen receptor to its target regions in DNA. In this study, we analyzed tyrosine phosphorylation of FoxA1 by the non-receptor-type tyrosine kinase c-Abl. c-Abl was shown to phosphorylate FoxA1 at multiple sites, especially in the N- and C-terminal regions. Tyr429 and Tyr464 were identified as the major phosphorylation sites in the FoxA1 C-terminal region. The phosphomimetic and nonphosphorylatable FoxA1 mutants were generated by glutamic acid and phenylalanine substitutions at these tyrosine residues, respectively. The phosphomimetic FoxA1 promoted the activation of estrogen signaling, whereas the nonphosphorylatable FoxA1 suppressed its activation. Stimulation with the epidermal growth factor, which activates c-Abl, enhanced the activation of estrogen signaling. In contrast, the c-Abl inhibitor imatinib reduced its activation. The phosphomimetic FoxA1 mutant showed a higher affinity toward histone H3 than the wild-type. These results suggest that c-Abl-mediated phosphorylation of FoxA1 promotes the activation of estrogen signaling by inducing its binding to histones. J. Cell. Biochem. 118: 1453-1461, 2017. © 2016 Wiley Periodicals, Inc.