Forkhead Transcription Factor FoxM1 Research Articles

Foxm1 regulates cardiomyocyte proliferation in adult zebrafish after cardiac injury.

The regenerative capacity of the mammalian heart is poor, with one potential reason being that adult cardiomyocytes cannot proliferate at sufficient levels to replace lost tissue. During development and neonatal stages, cardiomyocytes can successfully divide under injury conditions; however, as these cells mature their ability to proliferate is lost. Therefore, understanding the regulatory programs that can induce post-mitotic cardiomyocytes into a proliferative state is essential to enhance cardiac regeneration. Here, we report that the forkhead transcription factor Foxm1 is required for cardiomyocyte proliferation after injury through transcriptional regulation of cell cycle genes. Transcriptomic analysis of injured zebrafish hearts revealed that foxm1 expression is increased in border zone cardiomyocytes. Decreased cardiomyocyte proliferation and expression of cell cycle genes in foxm1 mutant hearts was observed, suggesting it is required for cell cycle checkpoints. Subsequent analysis of a candidate Foxm1 target gene, cenpf, revealed that this microtubule and kinetochore binding protein is also required for cardiac regeneration. Moreover, cenpf mutants show increased cardiomyocyte binucleation. Thus, foxm1 and cenpf are required for cardiomyocytes to complete mitosis during zebrafish cardiac regeneration.

Gain-of-function mutant p53 promotes the oncogenic potential of head and neck squamous cell carcinoma cells by targeting the transcription factors FOXO3a and FOXM1

Many mutant p53 proteins exert oncogenic gain-of-function (GOF) properties that promote cancer cell invasive growth and metastasis, yet the mechanisms mediating these functions still largely remain elusive. We show here that overexpression of the GOF mutant p53 G245D and other GOF p53 mutants enhances the invasive cell growth of p53-deficient head and neck squamous cell carcinoma (HNSCC) UM-SCC-1 cells both in in vitro three-dimensional culture and in an in vivo orthotopic nude mouse model of HNSCC through a novel transcription-independent mechanism. We demonstrate that the expression of the oncogenic forkhead transcription factor FOXM1 is upregulated by GOF mutant p53s. Moreover, we show that overexpression of GOF mutant p53 G245D decreases the AMP-activated protein kinase (AMPK)-mediated phosphorylation of FOXO3a, a tumor suppressive forkhead transcription factor, leading to its cytoplasmic accumulation. This downregulation of FOXO3a’s activity, in turn, leads to de-repression of FOXM1 expression. Importantly, we show that either overexpression of FOXO3a or downregulation of FOXM1 impairs both GOF mutant p53-mediated cell invasion in vitro and pulmonary metastases of UM-SCC-1 cells in vivo. Finally, not only do oral cancer patients with p53 mutations exhibit higher levels of FOXM1 expression than patients with wild-type p53, but also HNSCC patients with TP53 mutations and high levels of FOXM1 expression have the poorest survival outcomes. Given our prior demonstration that GOF mutant p53s inhibit AMPK, our current study, establishes and demonstrates a novel transcription-independent GOF mutant p53-AMPK-FOXO3a-FOXM1 signaling cascade that plays an important role in mediating mutant p53s’ gain-of-function activities in HNSCCs.

Abstract 73: Gain-of-function mutant p53 promotes the oncogenic potential of head and neck squamous cell carcinoma cell by targeting forkhead transcription factors FOXO3a and FOXM1

Abstract Many mutant p53 proteins exert oncogenic gain-of-function (GOF) properties in promoting cancer cell invasive growth and metastasis, but the mechanisms mediating these functions largely remain elusive. We show here that overexpression of the GOF mutant p53 G245D and other GOF p53 mutants enhances invasive cell growth of p53-deficient head and neck squamous cell carcinoma (HNSCC) UM-SCC-1 cells both in vitro 3D culture and in vivo orthotopic tumor mouse model. We demonstrate that the expression of the oncogenic forkhead transcription factor FOXM1 is upregulated by GOF mutant p53s in UM-SCC-1 cells and tumors. Moreover, we show that overexpression of GOF mutant p53 G245D decreases the inhibitory phosphorylation of FOXO3a, a tumor suppressive forkhead transcription factor, leading to its cytoplasmic accumulation. Consistent with the observation that FOXO3a negatively regulates FOXM1 expression, we demonstrate that overexpression FOXO3a decreases GOF mutant p53-mediated FOXM1 expression, whereas downregulation of FOXO3a partially restores decreased FOXM1 expression due to loss of GOF mutant p53. In support of the roles of FOXO3a-FOXM1 signaling axis in mutant p53's GOF signaling, we further show that overexpression of FOXO3a or downregulation of FOXM1 impairs GOF mutant p53-mediated cell invasion, whereas downregulation of FOXO3a, in part, rescues impaired cell invasion due to downregulated GOF mutant p53. Finally, given that AMP-activated protein kinase (AMPK) directly phosphorylates and promotes FOXO3a function, and that our prior demonstration that GOF mutant p53s inhibit AMPK, our current study establishes that GOF mutant p53-AMPK-FOX3a-FOXM1 signaling is one of important mechanisms through which mutant p53s gain oncogenic functions in HNSCCs. Citation Format: Noriaki Tanaka, Mei Zhao, Jiexin Zhang, Jing Wang, Ge Zhou, Jeffrey N. Myers. Gain-of-function mutant p53 promotes the oncogenic potential of head and neck squamous cell carcinoma cell by targeting forkhead transcription factors FOXO3a and FOXM1 [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr 73.

P2.01-037 Molecular Biology Underlying COPD and Lung Cancer Converge on FOXM1 Network

Chronic obstructive pulmonary disease (COPD) is a progressive, inflammatory lung disease associated with an up to 10-fold increased risk of lung cancer (LC). COPD and LC share common etiologies including genetic susceptibilities and risk factors, such as smoking. This study systematically characterizes the molecular overlap between COPD and LC. Small airway gene expression data was obtained from subjects with spirometry measures (n=267) (GSE37147). Genome-wide, multi-omics data for lung adenocarcinoma (LUAD) tumor and non-malignant lung tissues from two cohorts (TCGA, n=515; BCCA, n=90) was analyzed. Weighted correlation network analysis (WGCNA) was applied to identify clusters (modules) of highly correlated genes across airway expression profiles. Combined module expression (eigengene scores) were used to: 1) identify modules negatively associated with FEV1 and 2) calculate module preservation in lung tumors. Signaling network, pathway and gene ontology analyses were performed using IID, pathDIP, ClueGo and PARADIGM. Known and predicted protein-protein physical interactions (PPIs) were obtained from IID. Network analysis and visualization was performed in NAViGaTOR. A module of 31 genes significantly co-expressed across small airways was negatively associated with FEV1 and preserved in LUAD tumors. Genes in this module were enriched in functions associated with cell cycle progression, and known and/or predicted to physically interact in the protein complex critical to mediating G2/M progression. The forkhead transcription factor FOXM1 network was the most highly perturbed entity across 515 LUAD tumors. FOXM1 is an essential mitotic protein, known to regulate expression of genes involved in cell cycle progression, as well as stress response to ROS and DNA damage, angiogenesis and metastasis. COPD-related airway mRNA changes and genes highly altered at the DNA and mRNA level in LUAD tumors directly converge on the FOXM1 regulated mitotic complex proteins and/or FOXM1 transcription factor network. FOXM1 is overexpressed in multiple cancer types where it is correlated with poor prognosis and oncogenic transformation of epithelia through induction of genomic instability. The convergence of COPD and LUAD changes on this network may underlie increased LC risk in COPD patients, warranting further exploration as a target for COPD treatment and/or LC prevention or treatment.

FOXM1 and polo-like kinase 1 are co-ordinately overexpressed in patients with gastric adenocarcinomas.

BackgroundGastric cancers present late in life with advanced disease and carry a poor prognosis. Polo-like Kinase 1 (PLK1) is a mitotic kinase with regulatory functions during G2/M and mitosis in the cell cycle. In mammalian cells, there is an intricate co-regulatory relationship between PLK1 and the forkhead transcription factor FOXM1. It has been demonstrated that individually either PLK1 or FOXM1 expression predicts poorer survival. However, the co-expression of both of these markers in gastric adenocarcinomas has not been reported previously.MethodsWe aimed to assess the expression of PLK1 and FOXM1 in Gastric adenocarcinomas in a Western Population, to examine whether there is a relationship of PLK1 to FOXM1 in cancer samples. We assess both the protein and mRNA expression in this patient population by Tissue Microarray immunohistochemistry and RT-PCR.ResultsImmunohistochemistry was performed on biopsy samples from 79 patients with gastric cancer. Paired normal controls were available in 47 patients. FOXM1 expression was significantly associated with gastric adenocarcinoma (p = 0.001). PLK1 and FOXM1 co-expression was demonstrated in 6/8 (75 %) tumours when analysed by RT-PCR. FOXM1 is overexpressed in a large proportion of gastric carcinomas at the protein level and FOXM1 and PLK1 are concomitantly overexpressed at the mRNA level in this cancer type.ConclusionsThis study has demonstrated that FOXM1 and its target gene PLK1 are coordinately overexpressed in a proportion of gastric adenocarcinomas. This suggests that chemotherapeutic treatments that target this pathway may be of clinical utility.

OTUB1 inhibits the ubiquitination and degradation of FOXM1 in breast cancer and epirubicin resistance.

The forkhead transcription factor FOXM1 has a key role in DNA damage response, and its deregulated overexpression is associated with genotoxic drug resistance in breast cancer. However, little is known about the posttranslational mechanisms by which FOXM1 expression is regulated by genotoxic agents and how they are deregulated in resistant cells. Initial co-immunoprecipitation studies verified previous proteomic analysis finding that the OTUB1 is a novel FOXM1-interacting protein. Western blot analysis showed that both OTUB1 and FOXM1 expression reduced upon genotoxic agent treatment in MCF-7 cells, but remained relatively constant in resistant cells. FOXM1 expression reduced upon OTUB1 depletion by siRNA and increased with OTUB1 overexpression in MCF-7 cells, arguing that OTUB1 positively regulates FOXM1 expression. In agreement, co-immunoprecipitation experiments demonstrated that FOXM1 expression is associated with OTUB1 binding but inversely correlates with conjugation to the protein degradation-associated Lys-48-linked ubiquitin-chains. Overexpression of wild-type (WT) OTUB1, but not the OTUB1(C91S) mutant, disrupted the formation of Lys48-linked ubiquitin-conjugates on FOXM1. Importantly, knockdown of OTUB1 by siRNA resulted in an increase in turnover of FOXM1 in MCF-7 cells treated with the protein synthesis inhibitor cycloheximide, whereas overexpression of WT OTUB1, but not the OTUB1(C91S) mutant, significantly enhances the half-life of FOXM1. In addition, proliferative and clonogenic assays also show that OTUB1 can enhance the proliferative rate and epirubicin resistance through targeting FOXM1, as OTUB1 has little effect on FOXM1-deficient cells. The physiological relevance of the regulation of FOXM1 by OTUB1 is further underscored by the significant correlations between FOXM1 and OTUB1 expression in breast cancer patient samples. Cox-regression survival analysis indicates that OTUB1 overexpression is linked to poorer outcome in particular in patients treated with chemotherapy. Collectively, these data suggest that OTUB1 limits the ubiquitination and degradation of FOXM1 in breast cancer and has a key role in genotoxic agent resistance.

FOXM1 binds directly to non-consensus sequences in the human genome.

BackgroundThe Forkhead (FKH) transcription factor FOXM1 is a key regulator of the cell cycle and is overexpressed in most types of cancer. FOXM1, similar to other FKH factors, binds to a canonical FKH motif in vitro. However, genome-wide mapping studies in different cell lines have shown a lack of enrichment of the FKH motif, suggesting an alternative mode of chromatin recruitment. We have investigated the role of direct versus indirect DNA binding in FOXM1 recruitment by performing ChIP-seq with wild-type and DNA binding deficient FOXM1.ResultsAn in vitro fluorescence polarization assay identified point mutations in the DNA binding domain of FOXM1 that inhibit binding to a FKH consensus sequence. Cell lines expressing either wild-type or DNA binding deficient GFP-tagged FOXM1 were used for genome-wide mapping studies comparing the distribution of the DNA binding deficient protein to the wild-type. This shows that interaction of the FOXM1 DNA binding domain with target DNA is essential for recruitment. Moreover, analysis of the protein interactome of wild-type versus DNA binding deficient FOXM1 shows that the reduced recruitment is not due to inhibition of protein-protein interactions.ConclusionsA functional DNA binding domain is essential for FOXM1 chromatin recruitment. Even in FOXM1 mutants with almost complete loss of binding, the protein-protein interactions and pattern of phosphorylation are largely unaffected. These results strongly support a model whereby FOXM1 is specifically recruited to chromatin through co-factor interactions by binding directly to non-canonical DNA sequences.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0696-z) contains supplementary material, which is available to authorized users.

Changing partners: transcription factors form different complexes on and off chromatin.

The current knowledge on how protein–protein interactions regulate the function of transcription factors (TFs) has remained limited due to an incomplete knowledge of their interaction partners. In their recent work, Chen and colleagues (Li et al, 2015) analyse the interactome of 56 TFs and reveal distinct chromatin-associated and soluble TF complexes.

The forkhead transcription factor FOXM1 promotes endocrine resistance and invasiveness in estrogen receptor-positive breast cancer by expansion of stem-like cancer cells

IntroductionThe forkhead transcription factor FOXM1 coordinates expression of cell cycle-related genes and plays a pivotal role in tumorigenesis and cancer progression. We previously showed that FOXM1 acts downstream of 14-3-3ζ signaling, the elevation of which correlates with a more aggressive tumor phenotype. However, the role that FOXM1 might play in engendering resistance to endocrine treatments in estrogen receptor-positive (ER+) patients when tumor FOXM1 is high has not been clearly defined yet.MethodsWe analyzed FOXM1 protein expression by immunohistochemistry in 501 ER-positive breast cancers. We also mapped genome-wide FOXM1, extracellular signal-regulated kinase 2 and ERα binding events by chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq) in hormone-sensitive and resistant breast cancer cells after tamoxifen treatment. These binding profiles were integrated with gene expression data derived from cells before and after FOXM1 knockdown to highlight specific FOXM1 transcriptional networks. We also modulated the levels of FOXM1 and newly discovered FOXM1-regulated genes and examined their impact on the cancer stem-like cell population and on cell invasiveness and resistance to endocrine treatments.ResultsFOXM1 protein expression was high in 20% of the tumors, which correlated with significantly reduced survival in these patients (P = 0.003 by logrank Mantel-Cox test). ChIP-seq analyses revealed that FOXM1 binding sites were enriched at the transcription start site of genes involved in cell-cycle progression, maintenance of stem cell properties, and invasion and metastasis, all of which are associated with a poor prognosis in ERα-positive patients treated with tamoxifen. Integration of binding profiles with gene expression highlighted FOXM1 transcriptional networks controlling cell proliferation, stem cell properties, invasion and metastasis. Increased expression of FOXM1 was associated with an expansion of the cancer stem-like cell population and with increased cell invasiveness and resistance to endocrine treatments. Use of a selective FOXM1 inhibitor proved very effective in restoring endocrine therapy sensitivity and decreasing breast cancer aggressiveness.ConclusionsCollectively, our findings uncover novel roles for FOXM1 and FOXM1-regulated genes in promoting cancer stem-like cell properties and therapy resistance. They highlight the relevance of FOXM1 as a therapeutic target to be considered for reducing invasiveness and enhancing breast cancer response to endocrine treatments.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0436-4) contains supplementary material, which is available to authorized users.

Pregnancy-associated plasma protein A regulates mitosis and is epigenetically silenced in breast cancer.

Aberrant mitosis is a common feature of cancer, yet little is known about the altered genes causing mitotic defects. We screened human tumours for cells with morphological signatures of highly specific mitotic defects previously assigned to candidate genes in a genome-wide RNA interference screen carried out in HeLa cells (www.mitocheck.org). We discovered a striking enrichment of early mitotic configurations indicative of prophase/prometaphase delay in breast cancer. Promoter methylation analysis of MitoCheck candidate genes assigned to the corresponding 'mitotic delay' class linked this defect to epigenetic silencing of the gene encoding pregnancy-associated plasma protein-A (PAPPA), a secreted protease. PAPPA silencing was highly prevalent in precursor lesions and invasive breast cancer. Experimental manipulation of PAPPA protein levels in human mammary epithelial cells and in breast cancer cell lines demonstrates that progression through early mitosis is dependent on PAPPA function, and that breast cancer cells become more invasive after down-regulation of this protease. PAPPA regulates mitotic progression through modulating the IGF-1 signalling pathway resulting in activation of the forkhead transcription factor FoxM1, which drives a transcriptional cluster of essential mitotic genes. Our results show that PAPPA has a critical function in normal cell division and is targeted early in breast cancer development.

Kinetochore genes are coordinately up-regulated in human tumors as part of a FoxM1-related cell division program.

The key player in directing proper chromosome segregation is the macromolecular kinetochore complex, which mediates DNA-microtubule interactions. Previous studies testing individual kinetochore genes documented examples of their overexpression in tumors relative to normal tissue, leading to proposals that up-regulation of specific kinetochore genes may promote tumor progression. However, kinetochore components do not function in isolation, and previous studies did not comprehensively compare the expression behavior of kinetochore components. Here we analyze the expression behavior of the full range of human kinetochore components in diverse published expression compendia, including normal tissues and tumor samples. Our results demonstrate that kinetochore genes are rarely overexpressed individually. Instead, we find that core kinetochore genes are coordinately regulated with other cell division genes under virtually all conditions. This expression pattern is strongly correlated with the expression of the forkhead transcription factor FoxM1, which binds to the majority of cell division promoters. These observations suggest that kinetochore gene up-regulation in cancer reflects a general activation of the cell division program and that altered expression of individual kinetochore genes is unlikely to play a causal role in tumorigenesis.

Epidermal Growth Factor Receptor Signaling Promotes Pancreatic β-Cell Proliferation in Response to Nutrient Excess in Rats Through mTOR and FOXM1

The cellular and molecular mechanisms underpinning the compensatory increase in β-cell mass in response to insulin resistance are essentially unknown. We previously reported that a 72-h coinfusion of glucose and Intralipid (GLU+IL) induces insulin resistance and a marked increase in β-cell proliferation in 6-month-old, but not in 2-month-old, Wistar rats. The aim of the current study was to identify the mechanisms underlying nutrient-induced β-cell proliferation in this model. A transcriptomic analysis identified a central role for the forkhead transcription factor FOXM1 and its targets, and for heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF), a ligand of the EGF receptor (EGFR), in nutrient-induced β-cell proliferation. Phosphorylation of ribosomal S6 kinase, a mammalian target of rapamycin (mTOR) target, was increased in islets from GLU+IL–infused 6-month-old rats. HB-EGF induced proliferation of insulin-secreting MIN6 cells and isolated rat islets, and this effect was blocked in MIN6 cells by the EGFR inhibitor AG1478 or the mTOR inhibitor rapamycin. Coinfusion of either AG1478 or rapamycin blocked the increase in FOXM1 signaling, β-cell proliferation, and β-cell mass and size in response to GLU+IL infusion in 6-month-old rats. We conclude that chronic nutrient excess promotes β-cell mass expansion via a pathway that involves EGFR signaling, mTOR activation, and FOXM1-mediated cell proliferation.

Abstract P3-02-01: Pregnancy-associated plasma protein A regulates mitosis and is epigenetically silenced in breast cancer

Abstract Using Phosphohistone-H3, a marker of cells in mitosis, we identified mitotic delay in 95% of invasive breast cancers with a significant proportion of cells in prophase/prometaphase (58%). This delay was seen in breast cancer tissues only with other malignancies and normal tissues showing a normal mitotic phase distribution (23% of mitotic cells in prophase/prometaphase). We could detect a clear mitotic delay phenotype already in 80% (55 out of 69 evaluable patients) of precursor ductal carcinoma in situ (DCIS) lesions. This strong phenotype has been concealed for over a century because tinctorial stains routinely used in diagnostic practice do not allow cells in prophase or prometaphase to be distinguished from interphase cells. Promoter methylation analysis of candidate genes linked this defect to epigenetic silencing of the gene encoding Pregnancy-Associated Plasma Protein-A (PAPPA), a secreted protease. PAPPA silencing was highly prevalent in precursor lesions and invasive breast cancer. Experimental manipulation of PAPPA protein levels in human mammary epithelial cells and in breast cancer cell lines demonstrates that progression through early mitosis is dependent on PAPPA function, and that breast cancer cells become more invasive after PAPPA down regulation. We discovered that PAPPA regulates mitotic progression through its known role in modulating the IGF-1 signalling pathway, resulting in activation of the forkhead transcription factor FoxM1 which drives a transcriptional cluster of essential mitotic genes. Our results identify PAPPA as a candidate tumour suppressor in breast cancer. PAPPA loss is an early event in breast tumourigenesis increasing tumour cell invasiveness and may contribute to the transition from precursor lesions to invasive disease. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-02-01.

Epidermal Growth Factor Signalling Promotes Pancreatic Beta-Cell Proliferation in Response to Nutrient Excess in Rats Through MTOR And FOXM1

A compensatory increase in beta-cell mass occurs in several physiological and pathophysiological situations, such as pregnancy, obesity and insulin resistance. We have previously observed that a 72-hour co-infusion of glucose and Intralipid (GLU+IL) in 6-month-old (6-mo) rats causes insulin resistance and beta-cell dysfunction, despite a marked increase in beta-cell proliferation and mass. Interestingly, none of these effects were observed in 2-month-old (2-mo) animals despite similar levels of circulating glucose, fatty acids and insulin. Islet gene expression profiling in 6-mo GLU+IL rats identified a transcriptional network associated with beta-cell proliferation and a central role for the forkhead transcription factor FoxM1. Expression of the heparin binding EGF-like growth factor (HB-EGF), a ligand of the EGF receptor (EGFR), was significantly induced in response to GLU+IL. First, we confirmed by RT-PCR the increased expression of HB-EGF, FoxM1 and its direct targets in islets from GLU+IL-infused 6-mo, but not 2-mo rats. Second, we observed that the expression of HB-EGF correlates significantly and positively with the expression of FoxM1 and its direct targets. Third, co-infusion of either the EGFR inhibitor, AG1478 or the mTOR inhibitor, rapamycin, blocked the increase in expression of FoxM1 and its targets in response to GLU+IL in 6-mo rats. Finally, HB-EGF induces the proliferation of insulin-secreting MIN6 cells, and this effect was blocked by AG1478 or rapamycin. We conclude that insulin resistance induced by nutrient excess in aging rats promotes beta-cell proliferation via a pathway that involved HB-EGF binding to EGFR, mTOR activation and FoxM1-mediated cell division.

The Forkhead Transcription Factor FOXM1 Controls Cell Cycle-Dependent Gene Expression through an Atypical Chromatin Binding Mechanism

There are nearly 50 forkhead (FOX) transcription factors encoded in the human genome and, due to sharing a common DNA binding domain, they are all thought to bind to similar DNA sequences. It is therefore unclear how these transcription factors are targeted to specific chromatin regions to elicit specific biological effects. Here, we used chromatin immunoprecipitation followed by sequencing (ChIP-seq) to investigate the genome-wide chromatin binding mechanisms used by the forkhead transcription factor FOXM1. In keeping with its previous association with cell cycle control, we demonstrate that FOXM1 binds and regulates a group of genes which are mainly involved in controlling late cell cycle events in the G(2) and M phases. However, rather than being recruited through canonical RYAAAYA forkhead binding motifs, FOXM1 binding is directed via CHR (cell cycle genes homology region) elements. FOXM1 binds these elements through protein-protein interactions with the MMB transcriptional activator complex. Thus, we have uncovered a novel and unexpected mode of chromatin binding of a FOX transcription factor that allows it to specifically control cell cycle-dependent gene expression.

Genome-wide mapping of FOXM1 binding reveals co-binding with estrogen receptor alpha in breast cancer cells.

BackgroundThe forkhead transcription factor FOXM1 is a key regulator of the cell cycle. It is frequently over-expressed in cancer and is emerging as an important therapeutic target. In breast cancer FOXM1 expression is linked with estrogen receptor (ERα) activity and resistance to endocrine therapies, with high levels correlated with poor prognosis. However, the precise role of FOXM1 in ER positive breast cancer is not yet fully understood.ResultsThe study utilizes chromatin immunoprecipitation followed by high-throughput sequencing to map FOXM1 binding in both ERα-positive and -negative breast cancer cell lines. The comparison between binding site distributions in the two cell lines uncovered a previously undescribed relationship between binding of FOXM1 and ERα. Further molecular analyses demonstrated that these two factors can bind simultaneously at genomic sites and furthermore that FOXM1 regulates the transcriptional activity of ERα via interaction with the coactivator CARM1. Inhibition of FOXM1 activity using the natural product thiostrepton revealed down-regulation of a set of FOXM1-regulated genes that are correlated with patient outcome in clinical breast cancer samples.ConclusionsThese findings reveal a novel role for FOXM1 in ERα transcriptional activity in breast cancer and uncover a FOXM1-regulated gene signature associated with ER-positive breast cancer patient prognosis.

Role of the forkhead transcription factor FOXO-FOXM1 axis in cancer and drug resistance

The forkhead transcription factors FOXO and FOXM1 have pivotal roles in tumorigenesis and in mediating chemotherapy sensitivity and resistance. Recent research shows that the forkhead transcription factor FOXM1 is a direct transcriptional target repressed by the forkhead protein FOXO3a, a vital downstream effector of the PI3K-AKT-FOXO signaling pathway. Intriguingly, FOXM1 and FOXO3a also compete for binding to the same gene targets, which have a role in chemotherapeutic drug action and sensitivity. An understanding of the role and regulation of the FOXO-FOXM1 axis will impact directly on our knowledge of chemotherapeutic drug action and resistance in patients, and provide new insights into the design of novel therapeutic strategy and reliable biomarkers for prediction of drug sensitivity.

A Novel FoxM1-Caveolin Signaling Pathway Promotes Pancreatic Cancer Invasion and Metastasis

Caveolin-1 (Cav-1), a principal structural component of caveolar membrane domains, contributes to cancer development but its precise functional roles and regulation remain unclear. In this study, we determined the oncogenic function of Cav-1 in preclinical models of pancreatic cancer and in human tissue specimens. Cav-1 expression levels correlated with metastatic potential and epithelial-mesenchymal transition (EMT) in both mouse and human pancreatic cancer cells. Elevated levels in cells promoted EMT, migration, invasion, and metastasis in animal models, whereas RNA interference (RNAi)-mediated knockdown inhibited these processes. We determined that levels of Cav-1 and the Forkhead transcription factor FoxM1 correlated directly in pancreatic cancer cells and tumor tissues. Enforced expression of FoxM1 increased Cav-1 levels, whereas RNAi-mediated knockdown of FoxM1 had the opposite effect. FoxM1 directly bound to the promoter region of Cav-1 gene and positively transactivated its activity. Collectively, our findings defined Cav-1 as an important downstream oncogenic target of FoxM1, suggesting that dysregulated signaling of this novel FoxM1-Cav-1 pathway promotes pancreatic cancer development and progression.

Protein Phosphatase 2A (B55α) Prevents Premature Activation of Forkhead Transcription Factor FoxM1 by Antagonizing Cyclin A/Cyclin-dependent Kinase-mediated Phosphorylation

The forkhead transcription factor FoxM1 controls expression of a large number of genes that are specifically expressed during the G(2) phase of the cell cycle. Throughout most of the cell cycle, FoxM1 activity is restrained by an autoinhibitory mechanism, involving a repressor domain present in the N-terminal part of the protein. Activation of FoxM1 in G(2) is achieved by Cyclin A/Cyclin-dependent kinase (Cdk)-mediated phosphorylation, which alleviates autoinhibition by the N-terminal repressor domain. Here, we show that FoxM1 interacts with B55α, a regulatory subunit of protein phosphatase 2A (PP2A). B55α binds the catalytic subunit of PP2A, and this promotes dephosphorylation and inactivation of FoxM1. Indeed, we find that overexpression of B55α results in decreased FoxM1 activity. Inversely, depletion of B55α results in premature activation of FoxM1. The activation of FoxM1 that is observed upon depletion of B55α is fully dependent on Cyclin A/Cdk-mediated phosphorylation of FoxM1. Taken together, these data demonstrate that B55α acts to antagonize Cyclin A/Cdk-dependent activation of FoxM1, to ensure that FoxM1 activity is restricted to the G(2) phase of the cell cycle.

FoxM1 mediates the progenitor function of type II epithelial cells in repairing alveolar injury induced by Pseudomonas aeruginosa

The alveolar epithelium is composed of the flat type I cells comprising 95% of the gas-exchange surface area and cuboidal type II cells comprising the rest. Type II cells are described as facultative progenitor cells based on their ability to proliferate and trans-differentiate into type I cells. In this study, we observed that pneumonia induced by intratracheal instillation of Pseudomonas aeruginosa (PA) in mice increased the expression of the forkhead transcription factor FoxM1 in type II cells coincidentally with the induction of alveolar epithelial barrier repair. FoxM1 was preferentially expressed in the Sca-1(+) subpopulation of progenitor type II cells. In mice lacking FoxM1 specifically in type II cells, type II cells showed decreased proliferation and impaired trans-differentiation into type I cells. Lungs of these mice also displayed defective alveolar barrier repair after injury. Expression of FoxM1 in the knockout mouse lungs partially rescued the defective trans-differentiation phenotype. Thus, expression of FoxM1 in type II cells is essential for their proliferation and transition into type I cells and for restoring alveolar barrier homeostasis after PA-induced lung injury.