Fra-1/AP-1 induces EMT in mammary epithelial cells by modulating Zeb1/2 and TGFβ expression

Abstract

Epithelial-to-mesenchymal transition (EMT) is essential for embryonic morphogenesis and wound healing and critical for tumour cell invasion and dissemination. The AP-1 transcription factor Fra-1 has been implicated in tumorigenesis and in tumour-associated EMT in human breast cancer. We observed a significant inverse correlation between Fra-1 mRNA expression and distant-metastasis-free survival in a large cohort of breast cancer patients derived from multiple array data sets. This unique correlation among Fos genes prompted us to assess the evolutionary conservation between Fra-1 functions in EMT of human and mouse cells. Ectopic expression of Fra-1 in fully polarized, non-tumourigenic, mouse mammary epithelial EpH4 cells induced a mesenchymal phenotype, characterized by a loss of epithelial and gain of mesenchymal markers. Proliferation, motility and invasiveness were also increased in the resulting EpFra1 cells, and the cells were tumourigenic and efficiently colonized the lung upon transplantation. Molecular analyses revealed increased expression of Tgfβ1 and the EMT-inducing transcription factors Zeb1, Zeb2 and Slug. Mechanistically, Fra-1 binds to the tgfb1 and zeb2 promoters and to an evolutionarily conserved region in the first intron of zeb1. Furthermore, increased activity of a zeb2 promoter reporter was detected in EpFra1 cells and shown to depend on AP-1-binding sites. Inhibiting TGFβ signalling in EpFra1 cells moderately increased the expression of epithelial markers, whereas silencing of zeb1 or zeb2 restored the epithelial phenotype and decreased migration in vitro and tumorigenesis in vivo. Thus Fra-1 induces changes in the expression of genes encoding EMT-related transcription factors leading to the acquisition of mesenchymal, invasive and tumorigenic capacities by epithelial cells. This study defines a novel function of Fra-1/AP-1 in modulating tgfb1, zeb1 and zeb2 expression through direct binding to genomic regulatory regions, which establishes a basis for future in vivo genetic manipulations and preclinical studies using mouse models. Epithelial-to-mesenchymal transition (EMT) is a complex biological programme that occurs in physiological processes during embryonic development and wound healing as well as in pathological conditions, such as organ fibrosis and carcinogenesis. During EMT, cells lose epithelial features and acquire mesenchymal characteristics. The acquisition of a mesenchymal state by malignant cancer cells is associated with decreased cell-cell adhesion, and increased migratory and invasive properties, which are crucial for metastasis. [1][2][3][4][5] The adherens junction (AJ) protein E-cadherin, encoded by cdh1, is a central determinant of the epithelial state and its downregulation is the hallmark of EMT. A number of molecular pathways converging on E-cadherin have been implicated in EMT. Transcription factors (TF) of the Snail, Zeb and Twist families, initially identified as regulators of epithelialmesenchymal plasticity during morphogenesis were shown to orchestrate EMT by...

MLK3 regulates FRA-1 and MMPs to drive invasion and transendothelial migration in triple-negative breast cancer cells

“…46 FRA-1 not only controls expression of genes involved in cell motility, epithelial-to-mesenchymal transition 13, 45, 47, 48 and cell invasion, 15, 17, 32, 49 but it also controls proliferation, 15, 50, 51 metastatic outgrowth 44 and the stem cell phenotype of cancer cells. 52 Several FRA-1-regulated genes 15, 17, 32, 49 have been demonstrated to facilitate cancer cell invasion including MMP-1, MMP-2 and MMP-9.…”

Therapeutic Activity of Anti-AXL Antibody against Triple-Negative Breast Cancer Patient-Derived Xenografts and Metastasis

“…Moreover, analysis of the genes correlated with AXL upregulation in basal-like breast tumors indicated that most of these genes are involved in cancer cell invasion and EMT, TGFb signaling, mesenchymal markers, stem cells, cytoskeleton, and ECM remodeling. Of note, the transcription factor FRA-1 induces EMT through TGFb modulation (42). AXL is also overexpressed in breast cancer stem cells (13) and EMT features are often associated with stemness (43).…”

The tumour suppressor OPCML promotes AXL inactivation by the phosphatase PTPRG in ovarian cancer

“…Further downstream in the signal cascade, MEK1, ERK and JNK demonstrated similar strongly induced phosphorylation status in SKOV3-Empty cells, which was abrogated by OPCML (Fig 3C), confirming the pERK dynamics observed above. FRA1 activity has been linked to the induction of the EMT transcription factors ZEB1, Slug and motility [26][27][28][29], and this could explain the Slug induction observed in control cells upon Gas6 stimulation of AXL [3,11,30,31] and its consequent abrogation upon OPCML expression. FRA1 activity has been linked to the induction of the EMT transcription factors ZEB1, Slug and motility [26][27][28][29], and this could explain the Slug induction observed in control cells upon Gas6 stimulation of AXL [3,11,30,31] and its consequent abrogation upon OPCML expression.…”