Sustained activation of SMAD3/SMAD4 by FOXM1 promotes TGF-β–dependent cancer metastasis

Abstract

A key feature of TGF-β signaling activation in cancer cells is the sustained activation of SMAD complexes in the nucleus; however, the drivers of SMAD activation are poorly defined. Here, using human and mouse breast cancer cell lines, we found that oncogene forkhead box M1 (FOXM1) interacts with SMAD3 to sustain activation of the SMAD3/SMAD4 complex in the nucleus. FOXM1 prevented the E3 ubiquitin-protein ligase transcriptional intermediary factor 1 γ (TIF1γ) from binding SMAD3 and monoubiquitinating SMAD4, which stabilized the SMAD3/SMAD4 complex. Loss of FOXM1 abolished TGF-β-induced SMAD3/SMAD4 formation. Moreover, the interaction of FOXM1 and SMAD3 promoted TGF-β/SMAD3-mediated transcriptional activity and target gene expression. We found that FOXM1/SMAD3 interaction was required for TGF-β-induced breast cancer invasion, which was the result of SMAD3/SMAD4-dependent upregulation of the transcription factor SLUG. Importantly, the function of FOXM1 in TGF-β-induced invasion was not dependent on FOXM1's transcriptional activity. Knockdown of SMAD3 diminished FOXM1-induced metastasis. Furthermore, FOXM1 levels correlated with activated TGF-β signaling and metastasis in human breast cancer specimens. Together, our data indicate that FOXM1 promotes breast cancer metastasis by increasing nuclear retention of SMAD3 and identify crosstalk between FOXM1 and TGF-β/SMAD3 pathways. This study highlights the critical interaction of FOXM1 and SMAD3 for controlling TGF-β signaling during metastasis.

TIF1γ Suppresses Tumor Progression by Regulating Mitotic Checkpoints and Chromosomal Stability

“…We and others have proposed that the tumor-suppressive function of TIF1g could result from its capacity to inhibit TGFb-induced epithelial-to-mesenchymal transition (EMT; refs. 17,26,30,31). However, we have also demonstrated in a transgenic mouse model of pancreatic cancer that the regulation of EMT by TIF1g could not fully explain its tumorsuppressive effect (30), thus indicating that TIF1g was able to regulate other oncosuppressive biologic functions.…”

“…At the molecular level, TIF1g is involved in chromatin remodeling and subsequent transcription modulation (3,7,10,13,14). Depending on the cellular context, TIF1g has been described as a potent modulator of the TGFb, acting either as a negative regulator (5,14,(15)(16)(17) or a positive regulator of the pathway (12,13,18).…”

“…Indeed, chromosomal rearrangements have been observed in the 1p13 locus containing TIF1g gene in carcinomas (19), in hematopoietic neoplasia (20), in embryonic tumors (21), in conjunctive tissue tumors (22), and in nervous central system tumors (23). Moreover, decreased TIF1g expression has been reported in different types of human tumors, including pancreatic ductal adenocarcinomas (24), breast tumors (17), non-small cell lung cancers (25), and hepatocellular carcinomas (HCC; ref. 26).…”

Association between transforming growth factor-β1 expression and the clinical features of triple negative breast cancer

“…Xue et al (17) confirmed that the TGF-β1-mediated Smad signaling pathway is involved in tumor recurrence and metastasis. Lang et al (14) demonstrated that TGF-β1 participates in the recurrence and metastasis of breast cancer via urokinase type plasminogen activator (uPA) and plasminogen activator inhibitor (PAI-1) activation.…”

miR-574-3p acts as a tumor promoter in osteosarcoma by targeting SMAD4 signaling pathway

“…In the present study, it was suggested that SMAD4 is a direct target of miR-574-3p and the associated genes CDKN1A, CDKN2B as well as ID3 were strongly suppressed by miR-574-3p transfection. SMAD4 is often mutated in numerous cancers and it acts as a tumor suppressor that is involved in the regulation of the TGF-β signal transduction pathway, which negatively regulates growth of epithelial cells and the extracellular matrix (28)(29)(30)(31). Therefore, the inhibition of SMAD4 and its downstream proteins may be an important part of the mechanism of miR-574-3p in osteosarcoma.…”