Jianfei Xue

FoxM1 Promotes β-Catenin Nuclear Localization and Controls Wnt Target-Gene Expression and Glioma Tumorigenesis

Wnt/β-catenin signaling is essential for stem cell regulation and tumorigenesis, but its molecular mechanisms are not fully understood. Here, we report that FoxM1 is a downstream component of Wnt signaling and is critical for β-catenin transcriptional function in tumor cells. Wnt3a increases the level and nuclear translocation of FoxM1, which binds directly to β-catenin and enhances β-catenin nuclear localization and transcriptional activity. Genetic deletion of FoxM1 in immortalized neural stem cells abolishes β-catenin nuclear localization. FoxM1 mutations that disrupt the FoxM1-β-catenin interaction or FoxM1 nuclear import prevent β-catenin nuclear accumulation in tumor cells. FoxM1-β-catenin interaction controls Wnt target gene expression, is required for glioma formation, and represents a mechanism for canonical Wnt signaling during tumorigenesis.

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

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 FOXM1s 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.

Tumour suppressor TRIM33 targets nuclear β-catenin degradation

Aberrant activation of β-catenin in the nucleus has been implicated in a variety of human cancers but the fate of nuclear β-catenin is unknown. Here we demonstrate that tripartite motif-containing protein 33 (TRIM33), acting as an E3 ubiquitin ligase, reduces the abundance of nuclear β-catenin protein. TRIM33-mediated β-catenin is destabilized and is GSK-3β or β-TrCP independent. TRIM33 interacts with and ubiquitylates nuclear β-catenin. Moreover, protein kinase Cδ, which directly phosphorylates β-catenin at Ser715, is required for the TRIM33–β-catenin interaction. The function of TRIM33 in suppressing tumour cell proliferation and brain tumour development depends on TRIM33-promoted β-catenin degradation. In human glioblastoma specimens, endogenous TRIM33 levels are inversely correlated with β-catenin. In summary, our findings identify TRIM33 as a tumour suppressor that can abolish tumour cell proliferation and tumorigenesis by degrading nuclear β-catenin. This work suggests a new therapeutic strategy against human cancers caused by aberrant activation of β-catenin.

Wnt‐induced deubiquitination FoxM1 ensures nucleus β‐catenin transactivation

A key step of Wnt signaling activation is the recruitment of β‐catenin to the Wnt target‐gene promoter in the nucleus, but its mechanisms are largely unknown. Here, we identified FoxM1 as a novel target of Wnt signaling, which is essential for β‐catenin/TCF4 transactivation. GSK3 phosphorylates FoxM1 on serine 474 which induces FoxM1 ubiquitination mediated by FBXW7. Wnt signaling activation inhibits FoxM1 phosphorylation by GSK3–Axin complex and leads to interaction between FoxM1 and deubiquitinating enzyme USP5, thereby deubiquitination and stabilization of FoxM1. FoxM1 accumulation in the nucleus promotes recruitment of β‐catenin to Wnt target‐gene promoter and activates the Wnt signaling pathway by protecting the β‐catenin/TCF4 complex from ICAT inhibition. Subsequently, the USP5–FoxM1 axis abolishes the inhibitory effect of ICAT and is required for Wnt‐mediated tumor cell proliferation. Therefore, Wnt‐induced deubiquitination of FoxM1 represents a novel and critical mechanism for controlling canonical Wnt signaling and cell proliferation.

Forkhead box M1 is essential for nuclear localization of glioma-associated oncogene homolog 1 in glioblastoma multiforme cells by promoting importin-7 expression

Background: The transcription factors GLI1 and FOXM1 play critical roles in cancer development and progression. Results: FOXM1 bound to the importin-7 promoter to up-regulate its expression; FOXM1 deficiency inhibited importin-7 expression and nuclear localization of GLI1. Conclusion: FOXM1 is essential for nuclear localization of GLI1 by promoting importin-7 expression. Significance: FOXM1 and GLI1 form a positive feedback loop that contributes to glioblastoma multiforme development. The transcription factors glioma-associated oncogene homolog 1 (GLI1), a primary marker of Hedgehog pathway activation, and Forkhead box M1 (FOXM1) are aberrantly activated in a wide range of malignancies, including glioma. However, the mechanism of nuclear localization of GLI1 and whether FOXM1 regulates the Hedgehog signaling pathway are poorly understood. Here we found that FOXM1 promotes nuclear import of GLI1 in glioblastoma multiforme cells and thus increases the expression of its target genes. Conversely, knockdown of FOXM1 expression with FOXM1 siRNA abrogated its nuclear import and inhibited the expression of its target genes. Also, genetic deletion of FOXM1 in mouse embryonic fibroblasts abolished nuclear localization of GLI1. We observed that FOXM1 directly binds to the importin-7 (IPO7) promoter and increases its promoter activity. IPO7 interacted with GLI1, leading to enhanced nuclear import of GLI1. Depletion of IPO7 by IPO7 siRNA reduced nuclear accumulation of GLI1. In addition, FOXM1 induced nuclear import of GLI1 by promoting IPO7 expression. Moreover, the FOXM1/IPO7/GLI1 axis promoted cell proliferation, migration, and invasion in vitro. Finally, expression of FOXM1 was markedly correlated with that of GLI1 in human glioblastoma specimens. These data suggest that FOXM1 and GLI1 form a positive feedback loop that contributes to glioblastoma development. Furthermore, our study revealed a mechanism that controls nuclear import of GLI1 in glioblastoma multiforme cells.

Gli1-induced deubiquitinase USP48 aids glioblastoma tumorigenesis by stabilizing Gli1

Aberrant activation of the Hedgehog (Hh) signaling pathway drives the tumorigenesis of multiple cancers. In this study, we screened a panel of deubiquitinases that may regulate the Hh pathway. We find that deubiquitinase USP48 activates Gli‐dependent transcription by stabilizing Gli1 protein. Mechanistically, USP48 interacts with Gli1 and cleaves its ubiquitin off directly. In glioblastoma cells, knockdown of USP48 inhibits cell proliferation and the expression of Gli1s downstream targets, which leads to repressed glioblastoma tumorigenesis. Importantly, USP48s effect on cell proliferation and tumorigenesis depends to some extent on Gli1. In addition, we find that the Sonic Hedgehog (SHH) pathway induces USP48 expression through Gli1‐mediated transcriptional activation, which forms thus a positive feedback loop to regulate Hh signaling. In human glioblastoma specimens, the expression levels of USP48 and Gli1 proteins are clinically relevant, and high expression of USP48 correlates with glioma malignancy. In summary, our study reveals that the USP48‐Gli1 regulatory axis is critical for glioma cell proliferation and glioblastoma tumorigenesis.

Abstract 5214: Functional interaction between foxm1 and β-catenin

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL The Wnt/β-catenin signaling pathway is aberrantly activated in human cancers and is critical for cancer formation, but its molecular mechanisms are not fully understood. In the current study, we found that FoxM1, which is also activated in most human tumors, is a novel downstream component of Wnt signaling and is critical for β-catenin transcriptional function in tumor cells. Wnt increases the level and nuclear translocation of FoxM1 through inhibition of FoxM1 protein degradation. FoxM1 binds directly to β-catenin and enhances β-catenin nuclear localization and transcriptional activity. Moreover, FoxM1, β-catenin and TCF-4 are mutually recruited to Wnt target-gene promoters, and FoxM1 promotes the assembly of the β-catenin-TCF transcription activation complex in the promoters hence the Wnt target gene expression. Furthermore, interaction of FoxM1 and β-catenin plays a critical role in glioma stem cell self-renewal and differentiation and is required for glioma formation. Finally, the expression levels of nuclear β-catenin in human GBM directly correlates with levels of nuclear FoxM1, supporting the critical role of FoxM1 in β-catenin activation in human GBM. Given the importance of FoxM1 and the Wnt/β-catenin signaling pathway in human cancers in general, our findings not only provide an improved understanding of the molecular mechanisms underlying Wnt/β-catenin activation and tumorigenesis but also suggest additional targets for therapeutic intervention. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5214. doi:1538-7445.AM2012-5214