FOXM1 coming of age: time for translation into clinical benefits?

RNA-Seq Reveals Different Gene Expression in Liver-Specific Prohibitin 1 Knock-Out Mice

Prohibitin 1 (PHB1) is an evolutionarily conserved and ubiquitously expressed protein that stabilizes mitochondrial chaperone. Our previous studies showed that liver-specific Phb1 deficiency induced liver injuries and aggravated lipopolysaccharide (LPS)-induced innate immune responses. In this study, we performed RNA-sequencing (RNA-seq) analysis with liver tissues to investigate global gene expression among liver-specific Phb1^−/−, Phb1^+/−, and WT mice, focusing on the differentially expressed (DE) genes between Phb1^+/− and WT. When 78 DE genes were analyzed for biological functions, using ingenuity pathway analysis (IPA) tool, lipid metabolism-related genes, including insulin receptor (Insr), sterol regulatory element-binding transcription factor 1 (Srebf1), Srebf2, and SREBP cleavage-activating protein (Scap) appeared to be downregulated in liver-specific Phb1^+/− compared with WT. Diseases and biofunctions analyses conducted by IPA verified that hepatic system diseases, including liver fibrosis, liver hyperplasia/hyperproliferation, and liver necrosis/cell death, which may be caused by hepatotoxicity, were highly associated with liver-specific Phb1 deficiency in mice. Interestingly, of liver disease-related 5 DE genes between Phb1^+/− and WT, the mRNA expressions of forkhead box M1 (Foxm1) and TIMP inhibitor of metalloproteinase (Timp1) were matched with validation for RNA-seq in liver tissues and AML12 cells transfected with Phb1 siRNA. The results in this study provide additional insights into molecular mechanisms responsible for increasing susceptibility of liver injuries associated with hepatic Phb1.

NT5DC2 promotes leiomyosarcoma tumour cell growth via stabilizing unpalmitoylated TEAD4 and generating a positive feedback loop

5'-Nucleotidase Domain Containing 2 (NT5DC2) is a novel oncoprotein, the regulatory effects of which have not been well characterized. This study aimed to investigate the expression profile and functional regulation of NT5DC2 and its potential interplay with TEAD4 in leiomyosarcoma (LMS). Bioinformatic analysis was conducted using data from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) program. LMS cell lines SK-LMS-1 and SK-UT-1 were used for both in vitro and in vivo analysis. Results showed that NT5DC2 is aberrantly upregulated in LMS. Its overexpression was associated with unfavourable survival. Deletion of NT5DC2 significantly reduced the expression of cyclin B1, cyclin A2, cyclin E1 and CDK1 and increased G1 phase arrest in LMS cell lines, and suppressed their proliferation both in vitro and in vivo. NT5DC2 interacted with unpalmitoylated TEAD4, and this association reduced TEAD4 degradation via the ubiquitin-proteasome pathway. TRIM27 is a novel E3 ubiquitin ligase that induces K27/48-linked ubiquitination of unpalmitoylated TEAD4 at Lys278. TEAD4 inhibition significantly suppressed LMS cell growth both in vitro and in vivo. Dual-luciferase assay demonstrated that TEAD4 could bind to the NT5DC2 promoter and activate its transcription. Based on these findings, we infer that the NT5DC2-TEAD4 positive feedback loop plays an important role in LMS development and might serve as a potential therapeutic target.

FOXM1: A Multifunctional Oncoprotein and Emerging Therapeutic Target in Ovarian Cancer

Forkhead box M1 (FOXM1) is a member of the conserved forkhead box (FOX) transcription factor family. Over the last two decades, FOXM1 has emerged as a multifunctional oncoprotein and a robust biomarker of poor prognosis in many human malignancies. In this review article, we address the current knowledge regarding the mechanisms of regulation and oncogenic functions of FOXM1, particularly in the context of ovarian cancer. FOXM1 and its associated oncogenic transcriptional signature are enriched in >85% of ovarian cancer cases and FOXM1 expression and activity can be enhanced by a plethora of genomic, transcriptional, post-transcriptional, and post-translational mechanisms. As a master transcriptional regulator, FOXM1 promotes critical oncogenic phenotypes in ovarian cancer, including: (1) cell proliferation, (2) invasion and metastasis, (3) chemotherapy resistance, (4) cancer stem cell (CSC) properties, (5) genomic instability, and (6) altered cellular metabolism. We additionally discuss the evidence for FOXM1 as a cancer biomarker, describe the rationale for FOXM1 as a cancer therapeutic target, and provide an overview of therapeutic strategies used to target FOXM1 for cancer treatment.

Immune Cell-Associated Protein Expression Helps to Predict Survival in Muscle-Invasive Urothelial Bladder Cancer Patients after Radical Cystectomy and Optional Adjuvant Chemotherapy

Simple Summary

Adjuvant chemotherapy following radical cystectomy is a common therapy for muscle invasive bladder cancer (MIBC) patients. No applicable biomarkers exist to predict which patients will benefit from chemotherapy. Three immune cell markers, the chemokine CC motif ligand 2 (CCL2), the pan macrophage marker CD68, and the M2 macrophage marker CD163, were examined using immunohistochemistry to determine their predictive value for chemotherapy responses in different nodal stage and tumor stage subgroups. The presence of tumor-infiltrating immune cells, characterized by the markers CD68, CD163, and CCL2, was associated with a superior prognosis, and chemotherapy may not add an advantage for prognosis. However, a depleted immune microenvironment, here represented as a reduction or loss of macrophages, helped to predict the benefit of chemotherapy in N1 + 2 stage patients. Altogether, it is meaningful to consider the abundance of immune cells, such as macrophages, to better predict the response to chemotherapy for bladder cancer (BCa) patients after radical treatment.

Abstract

Bladder cancer (BCa) is the tenth most commonly diagnosed malignant cancer worldwide. Although adjuvant chemotherapy following radical cystectomy is a common therapy for muscle invasive bladder cancer patients, no applicable biomarkers exist to predict which patients will benefit from chemotherapy. In this study, we examined three immune cell markers, the chemokine CC motif ligand 2 (CCL2), the pan macrophage marker cluster of differentiation 68 (CD68) and the M2 macrophage marker cluster of differentiation 163 (CD163), using immunohistochemistry to determine their predictive value for the chemotherapy response in different nodal stage (pN0 vs. pN1 + 2) and tumor stage subgroups (pT2 vs. pT3 + 4). The prognosis was studied in terms of the overall survival (OS), disease-specific survival (DSS), and recurrence-free-survival (RFS) in 168 muscle invasive BCa patients. Chemotherapy was associated with a poorer prognosis in patients with a higher expression of the immune markers CCL2 (RFS), CD68 (DSS and RFS), and CD163 (DSS and RFS) in the N0 group and with poorer survival in patients with a higher expression of the immune markers CCL2 (OS, DSS, and RFS), CD68 (OS, DSS, and RFS), and CD163 (OS, DSS, and RFS) in the pT2 group when compared with treatments without chemotherapy. In contrast, chemotherapy was associated with a better prognosis in patients with a low expression of the immune markers CCL2 (DSS and RFS), CD68 (OS, DSS, and RFS), and CD163 (OS) in the N1 + 2 group. In addition, chemotherapy was associated with improved survival in patients with a low expression of the immune marker CD68 (OS and DSS) and there was a trend for a better prognosis in patients with a low expression of CD163 (OS) in the pT3 + 4 group compared to patients not treated with chemotherapy. Interestingly, CD68 appeared to be the most applicable immune marker to stratify patients by the outcome of chemotherapy in the nodal stage and tumor stage groups. Overall, we suggest that, in addition to the clinical factors of tumor stage and nodal stage, it is also meaningful to consider the abundance of immune cells, such as macrophages, to better predict the response to chemotherapy for BCa patients after radical treatment.

Circ-MMP2 (circ-0039411) induced by FOXM1 promotes the proliferation and migration of lung adenocarcinoma cells in vitro and in vivo

Numerous reports have stated the significance of cellular events such as proliferation, migration and EMT (epithelial-mesenchymal transition) for cancer development, but the related molecular mechanism remains elusive. FOXM1 (forkhead box transcription M1) is a nuclear co-activator participating in lung adenocarcinoma (LUAD). Thus, this study tried to explain the function of FOXM1 and its downstream molecular mechanism in LUAD. We uncovered FOXM1 upregulation in LUAD and demonstrated that FOXM1 facilitated β-catenin nuclear translocation to activate the transcription of downstream genes. Moreover, we discovered that FOXM1 transcriptionally activated circ0039411 which derived from matrix metallopeptidase 2 (MMP2) (also named as circ-MMP2), while MMP2 is a known downstream target of β-catenin. As for functional investigation, knockdown of circ-0039411 suppressed the proliferation, migration and EMT in LUAD cells and also hindered in vivo growth and metastasis of LUAD tumor. Mechanistically, circ-0039411 enhanced the stability of FOXM1 mRNA by recruiting IGF2BP3 (insulin like growth factor 2 mRNA binding protein 3), thus forming a positive feedback loop. In conclusion, this study revealed that FOXM1-induced circ-MMP2 (circ-0039411) contributes to malignant behaviors of LUAD cells via relying on FOXM1, potentially infusing inspirations for the search of new molecular targets for LUAD treatment.

FOXM 1 induces Vasculogenic mimicry in esophageal cancer through β-catenin /Tcf4 signaling

Objective

To investigate the role of FOXM1, β-catenin and TCF4 in esophageal cancer (EC) and their relationship to VM (Vasculogenic Mimicry).

Methods

CCK-8 were performed to examine EC cell proliferation in FOXM1 silenced cells. EC cell migration and invasion were investigated through wound healing and Transwell assays, respectively. The formation of pipe like structures were assessed in 3D cultures. The expression of Foxm1, β-catenin, Tcf4 and E-cadherin were investigated through western blot, RT-qPCR and immunohistochemistry (IHC) staining. The relationship between FOXM1 expression, clinic-pathological features, and overall survival (OS) were further analyzed.

Results

A loss of FOXM1 expression correlated with the OS of ESCC patients. FOXM1 silencing led to a loss of cell growth and suppressed cell migration and invasion in ESCC cells. VM structures were identified in ESCC tissues and human EC cell lines. Mechanistically, FOXM1 was found to promote tumorigenesis through the regulation of β-catenin, Tcf4, and E-cadherin in EC cells, leading to the formation of VM structures.

Conclusions

These findings highlight FoxM1 as a novel therapeutic target in ESCC.

High impact of miRNA-4521 on FOXM1 expression in medulloblastoma

Medulloblastoma, an embryonal tumor of the cerebellum/fourth ventricle, is one of the most frequent malignant brain tumors in children. Although genetic variants are increasingly used in treatment stratification, survival of high-risk patients, characterized by leptomeningeal dissemination, TP53 mutation or MYC amplification, is still poor. FOXM1, a proliferation-specific oncogenic transcription factor, is deregulated in various solid tumors, including medulloblastoma, and triggers cellular proliferation, migration and genomic instability. In tissue samples obtained from medulloblastoma patients, the significant upregulation of FOXM1 was associated with a loss of its putative regulating microRNA, miR-4521. To understand the underlying mechanism, we investigated the effect of miR-4521 on the expression of the transcription factor FOXM1 in medulloblastoma cell lines. Transfection of this microRNA reduced proliferation and invasion of several medulloblastoma cell lines and induced programmed cell death through activation of caspase 3/7. Further, downstream targets of FOXM1 such as PLK1 and cyclin B1 were significantly reduced thus affecting the cell cycle progression in medulloblastoma cell lines. In conclusion, a restoration of miRNA-4521 may selectively suppress the pathophysiological effect of aberrant FOXM1 expression and serve as a targeted approach for medulloblastoma therapy.

FOXM1 promotes the growth and metastasis of colorectal cancer via activation of β-catenin signaling pathway

Purpose

Our previous study proved that FOXM1 regulates colorectal cancer (CRC) cell metastasis through epithelial–mesenchymal transition program. The aim of this study is to further explore the underlying mechanism of FOXM1 in CRC.

Materials and methods

In this study, we detected the mRNA and protein expressions of FOXM1 and β-catenin in CRC tissues and their corresponding normal-appearing tissues (NATs) by quantitative reverse transcription-PCR and western blot analysis, respectively. Then the potential link between FOXM1 and β-catenin in CRC tissues was analyzed. Furthermore, we systematically analyzed the biological functions of FOXM1 in CRC cells after reconstitution of FOXM1 expression in vitro. Moreover, the mechanism of FOXM1-promoted CRC progression by improving β-catenin nuclear translocation was also discussed.

Results

Our data demonstrated that FOXM1 and β-catenin were upregulated in CRC tissues compared with the corresponding NATs (P<0.05). Clinicopathologic analysis revealed that increased FOXM1 (or β-catenin) expression positively correlated with some clinicopathologic features, such as tumor size, TNM stage, lymphatic metastasis, and distant metastasis (P<0.05). Meanwhile, the possible relationships between FOXM1 and β-catenin in CRC samples were evaluated using SPSS software, and a significant positive correlation was found (P<0.05). In vitro data demonstrate that elevated FOXM1 expression exerted oncogenic effects on CRC via activation of β-catenin signaling pathway. The inhibition of β-catenin by siRNAs significantly attenuates FOXM1-induced malignant activities.

Conclusion

The data suggested that FOXM1/β-catenin is critical for malignancy of CRC, which may constitute a potential therapeutic strategy for CRC.

High FOXM1 expression is a prognostic marker for poor clinical outcomes in prostate cancer

Purpose: We aimed to investigate the expression of FOXM1 and to determine the relationships between FOXM1 expression and clinicopathologic characteristics in patients with PCa. Furthermore, we reconfirmed the prognostic impact of FOXM1 in different cohorts using already published data. Patients and Methods: Formalin-fixed, paraffin-embedded tissues were collected from patients with low- (n=17), intermediate- (n=36), and high-risk (n=29) disease, from patients with CRPC (n=2) and from patients with BPH (n=28). To analyze FOXM1 expression, we performed IHC analyses. Also, we analyzed gene expression data from cBioPortal to evaluate the associations between FOXM1 alteration and prognosis of PCa. Results: FOXM1 expression measured using Allred score differed between patients with BPH, and low-, intermediate-, and high-risk PCa (0.3, 1.5, 4.8, and 6.2, respectively; p<0.001). Patients with high FOXM1 expression had higher preoperative PSA levels (p=0.023), more advanced tumor stages (p=0.047), and higher pathologic Gleason score (p<0.001) than those with low FOXM1 expression. ROC curve analysis indicated that FOXM1 expression was a useful marker for discriminating PCa from BPH (AUC 0.851, 95% CI 0.783-0.920) and for discriminating high-risk PCa from low- and intermediate-risk PCa (AUC 0.807, 95% CI 0.719-0.894). In multivariate analyses, high FOXM1 expression was an independent predictor of BCR. Finally, in the TCGA dataset, FOXM1 alteration was associated with poor overall (p=4.521e-4) and disease-free survival (p=0.0108). Conclusions: In patients with PCa, high FOXM1 expression was associated with advanced tumor stages, high Gleason score, and poor prognosis. These data suggest a role of FOXM1 in biologically and clinically aggressive PCa.

Drug resistance of bladder cancer cells through activation of ABCG2 by FOXM1

Recurrence is a serious problem in patients with bladder cancer. The hypothesis for recurrence was that the proliferation of drug-resistant cells was reported, and this study focused on drug resistance due to drug efflux. Previous studies have identified FOXM1 as the key gene for recurrence. We found that FOXM1 inhibition decreased drug efflux activity and increased sensitivity to Doxorubicin. Therefore, we examined whether the expression of ABC transporter gene related to drug efflux is regulated by FOXM1. As a result, ABCG2, one of the genes involved in drug efflux, has been identified as a new target for FOXM1. We also demonstrated direct transcriptional regulation of ABCG2 by FOXM1 using ChIP assay. Consequently, in the presence of the drug, FOXM1 is proposed to directly activate ABCG2 to increase the drug efflux activation and drug resistance, thereby involving chemoresistance of bladder cancer cells. Therefore, we suggest that FOXM1 and ABCG2 may be useful targets and important parameters in the treatment of bladder cancer. [BMB Reports 2018; 51(2): 98-103].

Immunotherapy based on dendritic cells pulsed with CTPFoxM1 fusion protein protects against the development of hepatocellular carcinoma

Application of dendritic cells (DCs) pulsed with tumor-associated antigens is considered attractive in immunotherapy for hepatocellular carcinoma (HCC). In order to efficiently prime tumor-associated antigens specific for cytotoxic T lymphocytes (CTLs), it is important that DCs present tumor-associated antigens on MHC class I. MHC class I generally present endogenous antigens expressed in the cytosol. In this study, we developed a new antigen delivery tool based on cross presentation of exogenous antigens in DCs by using cytoplasmic transduction peptide (CTP). CTP protein could transduce FoxM1 tumor antigen into the cytosol of DCs, and CTP-FoxM1 fusion protein could stimulate activation and maturation of DCs. DCs pulsed with CTP-FoxM1 could induce specific CTLs. More importantly, the immunity induced by DCs loaded with CTP-FoxM1 could significantly inhibit tumor growth and metastasis in HCC-bearing mice, which was more potent than that induced by DCs loaded with FoxM1 or CTP, alone. Our results indicate that DCs pulsed with CTP-FoxM1 might be a promising vaccine candidate for HCC therapy and provide new insight into the design of DC-based immunotherapy.

The Emerging Roles of Forkhead Box (FOX) Proteins in Osteosarcoma

Osteosarcoma is the most common bone cancer primarily occurring in children and young adults. Over the past few years, the deregulation of a superfamily transcription factors, known as forkhead box (FOX) proteins, has been demonstrated to contribute to the pathogenesis of osteosarcoma. Molecular mechanism studies have demonstrated that FOX family proteins participate in a variety of signaling pathways and that their expression can be regulated by multiple factors. The dysfunction of FOX genes can alter osteosarcoma cell differentiation, metastasis and progression. In this review, we summarized the evidence that FOX genes play direct or indirect roles in the development and progression of osteosarcoma, and evaluated the emerging role of FOX proteins as targets for therapeutic intervention.

CTLs相关的免疫疗法在肝癌治疗中的新前景

癌细胞内多种蛋白加工处理所产生的异常多肽通过主要组织相容性复合物Ⅰ类分子递呈, 激发肿瘤细胞毒性T淋巴细胞(cytotoxic T lymphocytes, CTLs), 从而对肿瘤产生免疫作用. 但受多因素影响, 肝癌组织中的CTLs功能受抑制或呈无功能状态, 影响其抑癌作用. 近年来, 在肝癌重新活化和增强CTLs功能的研究方面, 已取得不同程度的成果. 现就其新进展, 从强化抗原提呈及直接诱导两条途径, 作一综述.

A novel FOXM1 isoform, FOXM1D, promotes epithelial-mesenchymal transition and metastasis through ROCKs activation in colorectal cancer

Epithelial-mesenchymal transition (EMT) is a critical event in metastasis of colorectal cancer (CRC). Rho/ROCKs signaling has a pivotal role in orchestrating actin cytoskeleton, leading to EMT and cancer invasion. However, the underlying mechanisms for ROCKs activation are not fully understood. Here, we identified FOXM1D, a novel isoform of Forkhead box M1 (FOXM1) that has a pivotal role in ROCKs activation by directly interacting with coiled-coil region of ROCK2. FOXM1D overexpression significantly polymerizes actin assembly and impairs E-cadherin expression, resulting in EMT and metastasis in xenograft mouse model and knockdown of FOXM1D has the opposite effect. Moreover, a high FOXM1D level correlates closely with clinical CRC metastasis. FOXM1D-induced ROCKs activation could be abrogated by the ROCKs inhibitors Y-27632 and fasudil. These observations indicate that the FOXM1D-ROCK2 interaction is crucial for Rho/ROCKs signaling and provide novel insight into actin cytoskeleton regulation and therapeutic potential for CRC metastasis.

Depletion of FOXM1 via MET Targeting Underlies Establishment of a DNA Damage-Induced Senescence Program in Gastric Cancer

PURPOSE

Deregulated signaling via the MET receptor tyrosine kinase is abundant in gastric tumors, with up to 80% of cases displaying aberrant MET expression. A growing body of evidence suggests MET as a potential target for tumor radiosensitization.

EXPERIMENTAL DESIGN

Cellular proliferation and DNA damage-induced senescence were studied in a panel of MET-overexpressing human gastric cancer cell lines as well as in xenograft models after MET inhibition and/or ionizing radiation. Pathways activation and protein expression were assessed by immunoblotting and immunohistochemistry. Tumor tissue microarrays (91 gastric cancer patients) were generated and copy number alteration (178 patients) and gene expression (373 patients) data available at The Cancer Genome Atlas were analyzed to assess the coalterations of MET and FOXM1.

RESULTS

MET targeting administered before ionizing radiation instigates DNA damage-induced senescence (∼80%, P < 0.001) rather than cell death. MET inhibition-associated senescence is linked to the blockade of MAPK pathway, correlates with downregulation of FOXM1, and can be abrogated (11.8% vs. 95.3%, P < 0.001) by ectopic expression of FOXM1 in the corresponding gastric tumor cells. Cells with ectopic FOXM1 expression demonstrate considerable (∼20%, P < 0.001) growth advantage despite MET targeting, suggesting a novel clinically relevant resistance mechanism to MET inhibition as the copresence of both MET and FOXM1 protein (33%) and mRNA (30%) overexpression as well as gene amplification (24,7%) are common in patients with gastric cancer.

CONCLUSIONS

FOXM1, a negative regulator of senescence, has been identified as a key downstream effector and potential clinical biomarker that mediates MET signaling following infliction of DNA damage in gastric tumors. Clin Cancer Res; 22(21); 5322-36. ©2016 AACR.

Systematic transcriptome analysis reveals tumor-specific isoforms for ovarian cancer diagnosis and therapy

Tumor-specific molecules are needed across diverse areas of oncology for use in early detection, diagnosis, prognosis and therapy. Large and growing public databases of transcriptome sequencing data (RNA-seq) derived from tumors and normal tissues hold the potential of yielding tumor-specific molecules, but because the data are new they have not been fully explored for this purpose. We have developed custom bioinformatic algorithms and used them with 296 high-grade serous ovarian (HGS-OvCa) tumor and 1,839 normal RNA-seq datasets to identify mRNA isoforms with tumor-specific expression. We rank prioritized isoforms by likelihood of being expressed in HGS-OvCa tumors and not in normal tissues and analyzed 671 top-ranked isoforms by high-throughput RT-qPCR. Six of these isoforms were expressed in a majority of the 12 tumors examined but not in 18 normal tissues. An additional 11 were expressed in most tumors and only one normal tissue, which in most cases was fallopian or colon. Of the 671 isoforms, the topmost 5% (n = 33) ranked based on having tumor-specific or highly restricted normal tissue expression by RT-qPCR analysis are enriched for oncogenic, stem cell/cancer stem cell, and early development loci--including ETV4, FOXM1, LSR, CD9, RAB11FIP4, and FGFRL1. Many of the 33 isoforms are predicted to encode proteins with unique amino acid sequences, which would allow them to be specifically targeted for one or more therapeutic strategies--including monoclonal antibodies and T-cell-based vaccines. The systematic process described herein is readily and rapidly applicable to the more than 30 additional tumor types for which sufficient amounts of RNA-seq already exist.

Mammary glands exhibit molecular laterality and undergo left-right asymmetric ductal epithelial growth in MMTV-cNeu mice

Significant left-right (L-R) differences in tumor incidence and disease outcome occur for cancers of paired organs, including the breasts; however, the basis for this laterality is unknown. Here, we show that despite their morphologic symmetry, left versus right mammary glands in wild-type mice have baseline differences in gene expression that are L-R independently regulated during pubertal development, including genes that regulate luminal progenitor cell renewal, luminal cell differentiation, mammary tumorigenesis, tamoxifen sensitivity and chemotherapeutic resistance. In MMTV-cNeu(Tg/Tg) mice, which model HER2/Neu-amplified breast cancer, baseline L-R differences in mammary gene expression are amplified, sustained or inverted in a gene-specific manner and the mammary ductal epithelium undergoes L-R asymmetric growth and patterning. Comparative genomic analysis of mouse L-R mammary gene expression profiles with gene expression profiles of human breast tumors revealed significant linkage between right-sided gene expression and decreased breast cancer patient survival. Collectively, these findings are the first to demonstrate that mammary glands are lateralized organs, and, moreover, that mammary glands have L-R differential susceptibility to HER2/Neu oncogene-mediated effects on ductal epithelial growth and differentiation. We propose that intrinsic molecular laterality may have a role in L-R asymmetric breast tumor incidence and, furthermore, that interplay between the L-R molecular landscape and oncogene activity may contribute to the differential disease progression and patient outcome that are associated with tumor situs.

Increased FOXM1 expression can stimulate DNA repair in normal hepatocytes in vivo but also increases nuclear foci associated with senescence

OBJECTIVES

FOXM1 is a transcription factor that has been shown to promote cell proliferation in many tissues during early development and high cell turnover tissues in adults. In a number of tumour cell lines, enrichment of FOXM1 has been shown to reduce the DNA damage response (DDR) and induction of senescence by a range of DNA-damaging agents, suggesting a role for the protein in DNA repair. Endogenous FOXM1 is expressed at detectable levels in hepatocytes of mice up to 2 weeks of age, but not in older mice. The aim of this investigation has been to better understand the role of the protein in DDR in normal cells in vivo.

MATERIALS AND METHODS

Mice with artificially prolonged elevated FOXM1 expression in hepatocytes, were exposed to alkylating diethylnitrosamine.

RESULTS

FOXM1-enriched mice had dampened DDR after treatment with this alkylating agent, which was consistent with observed increase in expression of genes involved in DNA repair. Paradoxically, mice with FOXM1 expression, within weeks after exposure to the DNA-damaging agent, had increased levels of potentially senescent hepatocytes with large nuclear foci, containing 53BP1. Similarly, spontaneous accumulation of these cells seen with normal ageing in mice was increased with FOXM1 enrichment.

CONCLUSION

Despite its known abilities to promote proliferation and DNA repair, and to reduce ROS, enrichment of FOXM1, as with other oncoproteins, may cause increased persistent DNA lesions and/or senescence in normal murine hepatocytes.

The transcription factor FOXM1 (Forkhead box M1): proliferation-specific expression, transcription factor function, target genes, mouse models, and normal biological roles

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor, which stimulates cell proliferation and exhibits a proliferation-specific expression pattern. Accordingly, both the expression and the transcriptional activity of FOXM1 are increased by proliferation signals, but decreased by antiproliferation signals, including the positive and negative regulation by protooncoproteins or tumor suppressors, respectively. FOXM1 stimulates cell cycle progression by promoting the entry into S-phase and M-phase. Moreover, FOXM1 is required for proper execution of mitosis. Accordingly, FOXM1 regulates the expression of genes, whose products control G1/S-transition, S-phase progression, G2/M-transition, and M-phase progression. Additionally, FOXM1 target genes encode proteins with functions in the execution of DNA replication and mitosis. FOXM1 is a transcriptional activator with a forkhead domain as DNA binding domain and with a very strong acidic transactivation domain. However, wild-type FOXM1 is (almost) inactive because the transactivation domain is repressed by three inhibitory domains. Inactive FOXM1 can be converted into a very potent transactivator by activating signals, which release the transactivation domain from its inhibition by the inhibitory domains. FOXM1 is essential for embryonic development and the foxm1 knockout is embryonically lethal. In adults, FOXM1 is important for tissue repair after injury. FOXM1 prevents premature senescence and interferes with contact inhibition. FOXM1 plays a role for maintenance of stem cell pluripotency and for self-renewal capacity of stem cells. The functions of FOXM1 in prevention of polyploidy and aneuploidy and in homologous recombination repair of DNA-double-strand breaks suggest an importance of FOXM1 for the maintenance of genomic stability and chromosomal integrity.

Novel functions of FoxM1: from molecular mechanisms to cancer therapy

FoxM1 is a member of the forkhead family of transcription factors. Since its identification 15 year ago, numerous studies have progressively contributed to our current understanding on FoxM1 functions. Early work showed that FoxM1 regulates the transcriptional program of the G2 phase of the cell cycle, and is essential for proper mitotic progression and genomic stability. Moreover, FoxM1 was found to be overexpressed in many different types of human cancer, suggesting a role of FoxM1 in tumor proliferation. In the past years, a significant number of studies have formally demonstrated the involvement of FoxM1 in different aspects of tumorogenesis, including angiogenesis, invasion, and metastasis. In addition to this, recent studies have placed FoxM1 in DNA damage response and senescence pathways, two pathways relevant to tumor progression and the response to cancer therapies. Here, we review and discuss the molecular mechanisms through which FoxM1 executes these new roles, and the implications for the potential use of FoxM1 as a therapeutic target in cancer.

FOXM1b, which is present at elevated levels in cancer cells, has a greater transforming potential than FOXM1c

The forkhead box (FOX) M1 transcription factor is required to maintain the proliferation of cancer cells. Two transcriptionally active isoforms of FOXM1, FOXM1b and FOXM1c, have been identified, but their functional differences remain unclear. FOXM1c is distinguished from FOXM1b by an extra exon (exon Va) that contains an ERK1/2 target sequence. Based on a literature search and quantitative PCR analysis, we concluded that FOXM1b is the predominant isoform that is overexpressed in cancers. The further characterization of FOXM1b and FOXM1c revealed two interesting differences. First, FOXM1b exhibited a higher transforming ability than FOXM1c in a soft agar assay. Second, the transactivating activity of FOXM1c, but not that of FOXM1b, was sensitive to activation by RAF/MEK/MAPK signaling. Importantly, the MEK1 activation of FOXM1c was associated with proteolytic processing to generate short forms that might represent constitutively active forms missing the N-terminal inhibitory domain; in contrast, the proteolytic processing of FOXM1b did not require MEK1 activation. Our findings suggest that FOXM1b is functionally more active. These results provide novel insights into the regulation of FOXM1 activity and its role in tumorigenesis.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.