Foxm1 transcription factor is critical for proliferation and differentiation of Clara cells during development of conducting airways

CRISPR-Cas9 Genome Editing Allows Generation of the Mouse Lung in a Rat

Rationale: Recent efforts in bioengineering and embryonic stem cell (ESC) technology allowed the generation of ESC-derived mouse lung tissues in transgenic mice that were missing critical morphogenetic genes. Epithelial cell lineages were efficiently generated from ESC, but other cell types were mosaic. A complete contribution of donor ESCs to lung tissue has never been achieved. The mouse lung has never been generated in a rat. Objective: We sought to generate the mouse lung in a rat. Methods: Clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 genome editing was used to disrupt the Nkx2-1 gene in rat one-cell zygotes. Interspecies mouse-rat chimeras were produced by injection of wild-type mouse ESCs into Nkx2-1-deficient rat embryos with lung agenesis. The contribution of mouse ESCs to the lung tissue was examined by immunostaining, flow cytometry, and single-cell RNA sequencing. Measurements and Main Results: Peripheral pulmonary and thyroid tissues were absent in rat embryos after CRISPR-Cas9-mediated disruption of the Nkx2-1 gene. Complementation of rat Nkx2-1-/- blastocysts with mouse ESCs restored pulmonary and thyroid structures in mouse-rat chimeras, leading to a near-99% contribution of ESCs to all respiratory cell lineages. Epithelial, endothelial, hematopoietic, and stromal cells in ESC-derived lungs were highly differentiated and exhibited lineage-specific gene signatures similar to those of respiratory cells from the normal mouse lung. Analysis of receptor-ligand interactions revealed normal signaling networks between mouse ESC-derived respiratory cells differentiated in a rat. Conclusions: A combination of CRISPR-Cas9 genome editing and blastocyst complementation was used to produce mouse lungs in rats, making an important step toward future generations of human lungs using large animals as "bioreactors."

Transplantation of alveolar macrophages improves the efficacy of endothelial progenitor cell therapy in mouse model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a severe complication of preterm births, which develops due to exposure to supplemental oxygen and mechanical ventilation. Published studies demonstrated that the number of endothelial progenitor cells (EPC) is decreased in mouse and human BPD lungs and that adoptive transfer of EPC is an effective approach in reversing the hyperoxia-induced lung damage in mouse model of BPD. Recent advancements in macrophage biology identified the specific subtypes of circulating and resident macrophages mediating the developmental and regenerative functions in the lungs. Several studies reported the successful application of macrophage therapy in accelerating the regenerative capacity of damaged tissues and enhancing the therapeutic efficacy of other transplantable progenitor cells. In the present study, we explored the efficacy of combined cell therapy with EPC and resident alveolar macrophages (rAM) in hyperoxia-induced BPD mouse model. rAM and EPC were purified from neonatal mouse lungs and were used for adoptive transfer to the recipient neonatal mice exposed to hyperoxia. Adoptive transfer of rAM alone did not result in engraftment of donor rAM into the lung tissue but increased the mRNA level and protein concentration of proangiogenic CXCL12 chemokine in recipient mouse lungs. Depletion of rAM by chlodronate-liposomes decreased the retention of donor EPC after their transplantation into hyperoxia-injured lungs. Adoptive transfer of rAM in combination with EPC enhanced the therapeutic efficacy of EPC as evidenced by increased retention of EPC, increased capillary density, improved arterial oxygenation, and alveolarization in hyperoxia-injured lungs. Dual therapy with EPC and rAM has promise in human BPD.NEW & NOTEWORTHY Recent studies demonstrated that transplantation of lung-resident endothelial progenitor cells (EPC) is an effective therapy in mouse model of bronchopulmonary dysplasia (BPD). However, key factors regulating the efficacy of EPC are unknown. Herein, we demonstrate that transplantation of tissue-resident alveolar macrophages (rAM) increases CXCL12 expression in neonatal mouse lungs. rAM are required for retention of donor EPC in hyperoxia-injured lungs. Co-transplantation of rAM and EPC improves the efficacy of EPC therapy in mouse BPD model.

Injury-induced Foxm1 expression in the mouse kidney drives epithelial proliferation by a cyclin F-dependent mechanism

Acute kidney injury (AKI) strongly upregulates the transcription factor Foxm1 in the proximal tubule in vivo, and Foxm1 drives epithelial proliferation in vitro. Here, we report that deletion of Foxm1 either with a nephron-specific Cre driver or by inducible global deletion reduced proximal tubule proliferation after ischemic injury in vivo. Foxm1 deletion led to increased AKI to chronic kidney disease transition, with enhanced fibrosis and ongoing tubule injury 6 weeks after injury. We report ERK mediated FOXM1 induction downstream of the EGFR in primary proximal tubule cells. We defined FOXM1 genomic binding sites by cleavage under targets and release using nuclease (CUT&RUN) and compared the genes located near FOXM1 binding sites with genes downregulated in primary proximal tubule cells after FOXM1 knockdown. The aligned data sets revealed the cell cycle regulator cyclin F (CCNF) as a putative FOXM1 target. We identified 2 cis regulatory elements that bound FOXM1 and regulated CCNF expression, demonstrating that Ccnf is strongly induced after kidney injury and that Foxm1 deletion abrogates Ccnf expression in vivo and in vitro. Knockdown of CCNF also reduced proximal tubule proliferation in vitro. These studies identify an ERK/FOXM1/CCNF signaling pathway that regulates injury-induced proximal tubule cell proliferation.

Identification of endothelial and mesenchymal FOXF1 enhancers involved in alveolar capillary dysplasia

Mutations in the FOXF1 gene, a key transcriptional regulator of pulmonary vascular development, cause Alveolar Capillary Dysplasia with Misalignment of Pulmonary Veins, a lethal lung disease affecting newborns and infants. Identification of new FOXF1 upstream regulatory elements is critical to explain why frequent non-coding FOXF1 deletions are linked to the disease. Herein, we use multiome single-nuclei RNA and ATAC sequencing of mouse and human patient lungs to identify four conserved endothelial and mesenchymal FOXF1 enhancers. We demonstrate that endothelial FOXF1 enhancers are autoactivated, whereas mesenchymal FOXF1 enhancers are regulated by EBF1 and GLI1. The cell-specificity of FOXF1 enhancers is validated by disrupting these enhancers in mouse embryonic stem cells using CRISPR/Cpf1 genome editing followed by lineage-tracing of mutant embryonic stem cells in mouse embryos using blastocyst complementation. This study resolves an important clinical question why frequent non-coding FOXF1 deletions that interfere with endothelial and mesenchymal enhancers can lead to the disease.

The bone marrow of mouse-rat chimeras contains progenitors of multiple pulmonary cell lineages

Radiation-induced lung injury (RILI) is a common complication of anti-cancer treatments for thoracic and hematologic malignancies. Bone marrow (BM) transplantation restores hematopoietic cell lineages in cancer patients. However, it is ineffective in improving lung repair after RILI due to the paucity of respiratory progenitors in BM transplants. In the present study, we used blastocyst injection to create mouse-rat chimeras, these are artificial animals in which BM is enriched with mouse-derived progenitor cells. FACS-sorted mouse BM cells from mouse-rat chimeras were transplanted into lethally irradiated syngeneic mice, and the contribution of donor cells to the lung tissue was examined using immunostaining and flow cytometry. Donor BM cells provided long-term contributions to all lung-resident hematopoietic cells which includes alveolar macrophages and dendritic cells. Surprisingly, donor BM cells also contributed up to 8% in pulmonary endothelial cells and stromal cells after RILI. To identify respiratory progenitors in donor BM, we performed single-cell RNA sequencing (scRNAseq). Compared to normal mouse BM, increased numbers of hematopoietic progenitors were found in the BM of mouse-rat chimeras. We also identified unique populations of hemangioblast-like progenitor cells expressing Hes1, Dntt and Ebf1, along with mesenchymal stromal cells expressing Cpox, Blvrb and Ermap that were absent or ultra-rare in the normal mouse BM. In summary, by using rats as "bioreactors", we created a unique mouse BM cell transplant that contributes to multiple respiratory cell types after RILI. Interspecies chimeras have promise for future generations of BM transplants enriched in respiratory progenitor cells.

The Promise of Combination Therapies with FOXM1 Inhibitors for Cancer Treatment

Forkhead box M1 (FOXM1) is a transcription factor in the forkhead (FOX) family, which is required for cellular proliferation in normal and neoplastic cells. FOXM1 is highly expressed in many different cancers, and its expression is associated with a higher tumor stage and worse patient-related outcomes. Abnormally high expression of FOXM1 in cancers compared to normal tissue makes FOXM1 an attractive target for pharmacological inhibition. FOXM1-inhibiting agents and specific FOXM1-targeted small-molecule inhibitors have been developed in the lab and some of them have shown promising efficacy and safety profiles in mouse models. While the future goal is to translate FOXM1 inhibitors to clinical trials, potential synergistic drug combinations can maximize anti-tumor efficacy while minimizing off-target side effects. Hence, we discuss the rationale and efficacy of all previously studied drug combinations with FOXM1 inhibitors for cancer therapies.

Novel FOXF1-Stabilizing Compound TanFe Stimulates Lung Angiogenesis in Alveolar Capillary Dysplasia

Rationale: Alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV) is linked to heterozygous mutations in the FOXF1 (Forkhead Box F1) gene, a key transcriptional regulator of pulmonary vascular development. There are no effective treatments for ACDMPV other than lung transplant, and new pharmacological agents activating FOXF1 signaling are urgently needed. Objectives: Identify-small molecule compounds that stimulate FOXF1 signaling. Methods: We used mass spectrometry, immunoprecipitation, and the in vitro ubiquitination assay to identify TanFe (transcellular activator of nuclear FOXF1 expression), a small-molecule compound from the nitrile group, which stabilizes the FOXF1 protein in the cell. The efficacy of TanFe was tested in mouse models of ACDMPV and acute lung injury and in human vascular organoids derived from induced pluripotent stem cells of a patient with ACDMPV. Measurements and Main Results: We identified HECTD1 as an E3 ubiquitin ligase involved in ubiquitination and degradation of the FOXF1 protein. The TanFe compound disrupted FOXF1-HECTD1 protein-protein interactions and decreased ubiquitination of the FOXF1 protein in pulmonary endothelial cells in vitro. TanFe increased protein concentrations of FOXF1 and its target genes Flk1, Flt1, and Cdh5 in LPS-injured mouse lungs, decreasing endothelial permeability and inhibiting lung inflammation. Treatment of pregnant mice with TanFe increased FOXF1 protein concentrations in lungs of Foxf1+/- embryos, stimulated neonatal lung angiogenesis, and completely prevented the mortality of Foxf1+/- mice after birth. TanFe increased angiogenesis in human vascular organoids derived from induced pluripotent stem cells of a patient with ACDMPV with FOXF1 deletion. Conclusions: TanFe is a novel activator of FOXF1, providing a new therapeutic candidate for treatment of ACDMPV and other neonatal pulmonary vascular diseases.

FOXF1 Regulates Alveolar Epithelial Morphogenesis through Transcriptional Activation of Mesenchymal WNT5A

Mutations in the FOXF1 (forkhead box F1) gene, encoding the mesenchymal FOX (forkhead box) transcription factor, are linked to alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV), a severe congenital disorder associated with the loss of alveolar capillaries and lung hypoplasia. Although proangiogenic functions of FOXF1 have been extensively studied, the role of FOXF1 in mesenchymal-epithelial signaling during lung development remains uncharacterized. Herein, we used murine lung organoids to demonstrate that the S52F FOXF1 mutation (found in patients with ACDMPV) stimulates canonical WNT/β-catenin signaling in type 2 alveolar epithelial cells (AEC2s), leading to increased proliferation of AEC2s and decreased differentiation of AEC2s into type 1 alveolar epithelial cells (AEC1s). Alveolar organoids containing Foxf1WT/S52F lung fibroblasts and wild-type epithelial cells grew faster on Matrigel and exhibited AEC2 hyperplasia. AEC2 hyperplasia and loss of AEC1s were found in the lungs of Foxf1WT/S52F embryos, a mouse model of ACDMPV. Activation of canonical WNT/β-catenin signaling in AEC2s of lung organoids and Foxf1WT/S52F mice was associated with decreased expression of noncanonical WNT5A (Wnt family member 5A) ligand in lung fibroblasts. Mechanistically, FOXF1 directly activates the Wnt5a gene transcription through an evolutionarily conserved +6320/+6326 region located in the first intron of the Wnt5a gene. Site-directed mutagenesis of the +6320/+6326 region prevented the transcriptional activation of the Wnt5a enhancer by FOXF1. Treatment with exogenous WNT5A ligand inhibited the effects of the S52F FOXF1 mutation on canonical WNT/β-catenin signaling in alveolar organoids, preventing aberrant AEC2 expansion and restoring differentiation of AEC1s. Activation of either FOXF1 or WNT5A may provide an attractive strategy to improve lung function in patients with ACDMPV.

Pulmonary endogenous progenitor stem cell subpopulation: Physiology, pathogenesis, and progress

Lungs are structurally and functionally complex organs consisting of diverse cell types from the proximal to distal axis. They have direct contact with the external environment and are constantly at risk of various injuries. Capable to proliferate and differentiate, pulmonary endogenous progenitor stem cells contribute to the maintenance of lung structure and function both under homeostasis and following injuries. Discovering candidate pulmonary endogenous progenitor stem cell types and underlying regenerative mechanisms provide insights into therapeutic strategy development for lung diseases. In this review, we reveal their compositions, roles in lung disease pathogenesis and injury repair, and the underlying mechanisms. We further underline the advanced progress in research approach and potential therapy for lung regeneration. We also demonstrate the feasibility and prospects of pulmonary endogenous stem cell transplantation for lung disease treatment.

Endothelial progenitor cells stimulate neonatal lung angiogenesis through FOXF1-mediated activation of BMP9/ACVRL1 signaling

Pulmonary endothelial progenitor cells (EPCs) are critical for neonatal lung angiogenesis and represent a subset of general capillary cells (gCAPs). Molecular mechanisms through which EPCs stimulate lung angiogenesis are unknown. Herein, we used single-cell RNA sequencing to identify the BMP9/ACVRL1/SMAD1 pathway signature in pulmonary EPCs. BMP9 receptor, ACVRL1, and its downstream target genes were inhibited in EPCs from Foxf1WT/S52F mutant mice, a model of alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). Expression of ACVRL1 and its targets were reduced in lungs of ACDMPV subjects. Inhibition of FOXF1 transcription factor reduced BMP9/ACVRL1 signaling and decreased angiogenesis in vitro. FOXF1 synergized with ETS transcription factor FLI1 to activate ACVRL1 promoter. Nanoparticle-mediated silencing of ACVRL1 in newborn mice decreased neonatal lung angiogenesis and alveolarization. Treatment with BMP9 restored lung angiogenesis and alveolarization in ACVRL1-deficient and Foxf1WT/S52F mice. Altogether, EPCs promote neonatal lung angiogenesis and alveolarization through FOXF1-mediated activation of BMP9/ACVRL1 signaling.

In vivo generation of bone marrow from embryonic stem cells in interspecies chimeras

Generation of bone marrow (BM) from embryonic stem cells (ESCs) promises to accelerate the development of future cell therapies for life-threatening disorders. However, such approach is limited by technical challenges to produce a mixture of functional BM progenitor cells able to replace all hematopoietic cell lineages. Herein, we used blastocyst complementation to simultaneously produce BM cell lineages from mouse ESCs in a rat. Based on fluorescence-activated cell sorting analysis and single-cell RNA sequencing, mouse ESCs differentiated into multiple hematopoietic and stromal cell types that were indistinguishable from normal mouse BM cells based on gene expression signatures and cell surface markers. Receptor-ligand interactions identified Cxcl12-Cxcr4, Lama2-Itga6, App-Itga6, Comp-Cd47, Col1a1-Cd44, and App-Il18rap as major signaling pathways between hematopoietic progenitors and stromal cells. Multiple hematopoietic progenitors, including hematopoietic stem cells (HSCs) in mouse-rat chimeras derived more efficiently from mouse ESCs, whereas chondrocytes predominantly derived from rat cells. In the dorsal aorta and fetal liver of mouse-rat chimeras, mouse HSCs emerged and expanded faster compared to endogenous rat cells. Sequential BM transplantation of ESC-derived cells from mouse-rat chimeras rescued lethally irradiated syngeneic mice and demonstrated long-term reconstitution potential of donor HSCs. Altogether, a fully functional BM was generated from mouse ESCs using rat embryos as 'bioreactors'.

Dual Targeting with Cell Surface Electrical Charge and Folic Acid via Superparamagnetic Fe3O4@Cu2-xS for Photothermal Cancer Cell Killing

Simple Summary

There are two critical issues in cancer hyperthermia: (1) photothermal effect and (2) cancer cell targeting efficiency. While the former can be addressed by rendering the nano carriers with significant IR absorptions, the latter is dealt with using a novel dual-targeting strategy. In this study, the Fe₃O₄ nanoparticle was coated with a shell of Cu_2–xS; the resulting Fe₃O₄@Cu_2–xS exhibited strong IR absorption for enhanced photothermal cancer cell killing. The Fe₃O₄@Cu_2–xS nanoparticles are surface functionalized with amphiphilic polyethylenimine (LA-PEI) and Folic acid-TPGS (FA-TPGS) for two purposes: (1) the PEI surface coating renders the particles positively charged, enabling them to effectively bind with negatively-charged cancer cells for more intimate nano/bio contact resulting in much stronger cancer cell ablation; (2) the folic acid modification further increases the targeting efficiency via the folic receptors on the cancer cell surface. Dual-targeting with the surface electrical charge and the tumor-specific folic acid synergistically facilitates both passive and active targeting for significantly improved photothermal killing.

Abstract

A major challenge in cancer therapy is to achieve high cell targeting specificity for the highest therapeutic efficacy. Two major approaches have been shown to be quite effective, namely, (1) bio-marker mediated cell targeting, and (2) electrical charge driven cell binding. The former utilizes the tumor-specific moieties on nano carrier surfaces for active targeting, while the latter relies on nanoparticles binding onto the cancer cell surfaces due to differences in electrical charge. Cancer cells are known for their hallmark metabolic pattern: high rates of glycolysis that lead to negatively charged cell surfaces. In this study, the nanoparticles of Fe₃O₄@Cu_2–xS were rendered positively charged by conjugating their surfaces with different functional groups for strong electrostatic binding onto the negatively-charged cancer cells. In addition to the positively charged surfaces, the Fe₃O₄@Cu_2–xS nanoparticles were also modified with folic acid (FA) for biomarker-based cell targeting. The dual-targeting approach synergistically utilizes the effectiveness of both charge- and biomarker-based cell binding for enhanced cell targeting. Further, these superparamagnetic Fe₃O₄@Cu_2–xS nanoparticles exhibit much stronger IR absorptions compared to Fe₃O₄, therefore much more effective in photothermal therapy.

Generation of Pulmonary Endothelial Progenitor Cells for Cell-based Therapy Using Interspecies Mouse-Rat Chimeras

Rationale: Although pulmonary endothelial progenitor cells (EPCs) hold promise for cell-based therapies for neonatal pulmonary disorders, whether EPCs can be derived from pluripotent embryonic stem cells (ESCs) or induced pluripotent stem cells remains unknown.Objectives: To investigate the heterogeneity of pulmonary EPCs and derive functional EPCs from pluripotent ESCs.Methods: Single-cell RNA sequencing of neonatal human and mouse lung was used to identify the heterogeneity of pulmonary EPCs. CRISPR/Cas9 gene editing was used to genetically label and purify mouse pulmonary EPCs. Functional properties of the EPCs were assessed after cell transplantation into neonatal mice with S52F Foxf1 mutation, a mouse model of alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). Interspecies mouse-rat chimeras were produced through blastocyst complementation to generate EPCs from pluripotent ESCs for cell therapy in ACDMPV mice.Measurements and Main Results: We identified a unique population of EPCs, FOXF1⁺cKIT⁺ EPCs, as a subset of recently described general capillary cells (gCAPs) expressing SMAD7, ZBTB20, NFIA, and DLL4 but lacking mature arterial, venous, and lymphatic markers. FOXF1⁺cKIT⁺ gCAPs are reduced in ACDMPV, and their transcriptomic signature is conserved in mouse and human lungs. After cell transplantation into the neonatal circulation of ACDMPV mice, FOXF1⁺cKIT⁺ gCAPs engraft into the pulmonary vasculature, stimulate angiogenesis, improve oxygenation, and prevent alveolar simplification. FOXF1⁺cKIT⁺ gCAPs, produced from ESCs in interspecies chimeras, are fully competent to stimulate neonatal lung angiogenesis and alveolarization in ACDMPV mice.Conclusions: Cell-based therapy using donor or ESC/induced pluripotent stem cell-derived FOXF1⁺cKIT⁺ endothelial progenitors may be considered for treatment of human ACDMPV.

Therapeutic Potential of Endothelial Progenitor Cells in Pulmonary Diseases

Compromised alveolar development and pulmonary vascular remodeling are hallmarks of pediatric lung diseases such as bronchopulmonary dysplasia (BPD) and alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). Although advances in surfactant therapy, corticosteroids, and anti-inflammatory drugs have improved clinical management of preterm infants, still those who suffer with severe vascular complications lack viable treatment options. Paucity of the alveolar capillary network in ACDMPV causes respiratory distress and leads to mortality in a vast majority of ACDMPV infants. The discovery of endothelial progenitor cells (EPCs) in 1997 brought forth the paradigm of postnatal vasculogenesis and hope for promoting vascularization in fragile patient populations, such as those with BPD and ACDMPV. The identification of diverse EPC populations, both hematopoietic and nonhematopoietic in origin, provided a need to identify progenitor cell selective markers which are linked to progenitor properties needed to develop cell-based therapies. Focusing to the future potential of EPCs for regenerative medicine, this review will discuss various aspects of EPC biology, beginning with the identification of hematopoietic, nonhematopoietic, and tissue-resident EPC populations. We will review knowledge related to cell surface markers, signature gene expression, key transcriptional regulators, and will explore the translational potential of EPCs for cell-based therapy for BPD and ACDMPV. The ability to produce pulmonary EPCs from patient-derived induced pluripotent stem cells (iPSCs) in vitro, holds promise for restoring vascular growth and function in the lungs of patients with pediatric pulmonary disorders.

Blastocyst complementation reveals that NKX2-1 establishes the proximal-peripheral boundary of the airway epithelium

BACKGROUND

Distinct boundaries between the proximal conducting airways and more peripheral-bronchial regions of the lung are established early in foregut embryogenesis, demarcated in part by the distribution of SOX family and NKX2-1 transcription factors along the cephalo-caudal axis of the lung. We used blastocyst complementation to identify the role of NKX2-1 in the formation of the proximal-peripheral boundary of the airways in mouse chimeric embryos.

RESULTS

While Nkx2-1-/- mouse embryos form primordial tracheal cysts, peripheral pulmonary structures are entirely lacking in Nkx2-1-/- mice. Complementation of Nkx2-1-/- embryos with NKX2-1-sufficient embryonic stem cells (ESCs) enabled the formation of all tissue components of the peripheral lung but did not enhance ESC colonization of the most proximal regions of the airways. In chimeric mice, a precise boundary was formed between NKX2-1-deficient basal cells co-expressing SOX2 and SOX9 in large airways and ESC-derived NKX2-1+ SOX9+ epithelial cells of smaller airways. NKX2-1-sufficient ESCs were able to selectively complement peripheral, rather than most proximal regions of the airways. ESC complementation did not prevent ectopic expression of SOX9 but restored β-catenin signaling in Nkx2-1-/- basal cells of large airways.

CONCLUSIONS

NKX2-1 and β-catenin function in an epithelial cell-autonomous manner to establish the proximal-peripheral boundary along developing airways.

FOXM1 is required for small cell lung cancer tumorigenesis and associated with poor clinical prognosis

Small cell lung cancer (SCLC) continues to cause poor clinical outcomes due to limited advances in sustained treatments for rapid cancer cell proliferation and progression. The transcriptional factor Forkhead Box M1 (FOXM1) regulates cell proliferation, tumor initiation, and progression in multiple cancer types. However, its biological function and clinical significance in SCLC remain unestablished. Analysis of the Cancer Cell Line Encyclopedia and SCLC datasets in the present study disclosed significant upregulation of FOXM1 mRNA in SCLC cell lines and tissues. Gene set enrichment analysis (GSEA) revealed that FOXM1 is positively correlated with pathways regulating cell proliferation and DNA damage repair, as evident from sensitization of FOXM1-depleted SCLC cells to chemotherapy. Furthermore, Foxm1 knockout inhibited SCLC formation in the Rb1fl/flTrp53fl/flMycLSL/LSL (RPM) mouse model associated with increased levels of neuroendocrine markers, Ascl1 and Cgrp, and decrease in Yap1. Consistently, FOXM1 depletion in NCI-H1688 SCLC cells reduced migration and enhanced apoptosis and sensitivity to cisplatin and etoposide. SCLC with high FOXM1 expression (N = 30, 57.7%) was significantly correlated with advanced clinical stage, extrathoracic metastases, and decrease in overall survival (OS), compared with the low-FOXM1 group (7.90 vs. 12.46 months). Moreover, the high-FOXM1 group showed shorter progression-free survival after standard chemotherapy, compared with the low-FOXM1 group (3.90 vs. 8.69 months). Our collective findings support the utility of FOXM1 as a prognostic biomarker and potential molecular target for SCLC.

Epithelial Barrier Dysfunction in Chronic Respiratory Diseases

Mucosal surfaces are lined by epithelial cells, which provide a complex and adaptive module that ensures first-line defense against external toxics, irritants, antigens, and pathogens. The underlying mechanisms of host protection encompass multiple physical, chemical, and immune pathways. In the lung, inhaled agents continually challenge the airway epithelial barrier, which is altered in chronic diseases such as chronic obstructive pulmonary disease, asthma, cystic fibrosis, or pulmonary fibrosis. In this review, we describe the epithelial barrier abnormalities that are observed in such disorders and summarize current knowledge on the mechanisms driving impaired barrier function, which could represent targets of future therapeutic approaches.

Nanoparticle Delivery of STAT3 Alleviates Pulmonary Hypertension in a Mouse Model of Alveolar Capillary Dysplasia

BACKGROUND

Pulmonary hypertension (PH) is a common complication in patients with alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV), a severe congenital disorder associated with mutations in the FOXF1 gene. Although the loss of alveolar microvasculature causes PH in patients with ACDMPV, it is unknown whether increasing neonatal lung angiogenesis could prevent PH and right ventricular (RV) hypertrophy.

METHODS

We used echocardiography, RV catheterization, immunostaining, and biochemical methods to examine lung and heart remodeling and RV output in Foxf1^WT/S52F mice carrying the S52F Foxf1 mutation (identified in patients with ACDMPV). The ability of Foxf1^WT/S52F mutant embryonic stem cells to differentiate into respiratory cell lineages in vivo was examined using blastocyst complementation. Intravascular delivery of nanoparticles with a nonintegrating Stat3 expression vector was used to improve neonatal pulmonary angiogenesis in Foxf1^WT/S52F mice and determine its effects on PH and RV hypertrophy.

RESULTS

Foxf1^WT/S52F mice developed PH and RV hypertrophy after birth. The severity of PH in Foxf1^WT/S52F mice directly correlated with mortality, low body weight, pulmonary artery muscularization, and increased collagen deposition in the lung tissue. Increased fibrotic remodeling was found in human ACDMPV lungs. Mouse embryonic stem cells carrying the S52F Foxf1 mutation were used to produce chimeras through blastocyst complementation and to demonstrate that Foxf1^WT/S52F embryonic stem cells have a propensity to differentiate into pulmonary myofibroblasts. Intravascular delivery of nanoparticles carrying Stat3 cDNA protected Foxf1^WT/S52F mice from RV hypertrophy and PH, improved survival, and decreased fibrotic lung remodeling.

CONCLUSIONS

Nanoparticle therapies increasing neonatal pulmonary angiogenesis may be considered to prevent PH in ACDMPV.

Single-keratinocyte transcriptomic analyses identify different clonal types and proliferative potential mediated by FOXM1 in human epidermal stem cells

Autologous epidermal cultures restore a functional epidermis on burned patients. Transgenic epidermal grafts do so also in genetic skin diseases such as Junctional Epidermolysis Bullosa. Clinical success strictly requires an adequate number of epidermal stem cells, detected as holoclone-forming cells, which can be only partially distinguished from the other clonogenic keratinocytes and cannot be prospectively isolated. Here we report that single-cell transcriptome analysis of primary human epidermal cultures identifies categories of genes clearly distinguishing the different keratinocyte clonal types, which are hierarchically organized along a continuous, mainly linear trajectory showing that stem cells sequentially generate progenitors producing terminally differentiated cells. Holoclone-forming cells display stem cell hallmarks as genes regulating DNA repair, chromosome segregation, spindle organization and telomerase activity. Finally, we identify FOXM1 as a YAP-dependent key regulator of epidermal stem cells. These findings improve criteria for measuring stem cells in epidermal cultures, which is an essential feature of the graft.

In Vivo Generation of Lung and Thyroid Tissues from Embryonic Stem Cells Using Blastocyst Complementation

Rationale: The regeneration and replacement of lung cells or tissues from induced pluripotent stem cell- or embryonic stem cell-derived cells represent future therapies for life-threatening pulmonary disorders but are limited by technical challenges to produce highly differentiated cells able to maintain lung function. Functional lung tissue-containing airways, alveoli, vasculature, and stroma have never been produced via directed differentiation of embryonic stem cells (ESCs) or induced pluripotent stem cells. We sought to produce all tissue components of the lung from bronchi to alveoli by embryo complementation.Objectives: To determine whether ESCs are capable of generating lung tissue in Nkx2-1^-/- mouse embryos with lung agenesis.Methods: Blastocyst complementation was used to produce chimeras from normal mouse ESCs and Nkx2-1^-/- embryos, which lack pulmonary tissues. Nkx2-1^-/- chimeras were examined using immunostaining, transmission electronic microscopy, fluorescence-activated cell sorter analysis, and single-cell RNA sequencing.Measurements and Main Results: Although peripheral pulmonary and thyroid tissues are entirely lacking in Nkx2-1 gene-deleted embryos, pulmonary and thyroid structures in Nkx2-1^-/- chimeras were restored after ESC complementation. Respiratory epithelial cell lineages in restored lungs of Nkx2-1^-/- chimeras were derived almost entirely from ESCs, whereas endothelial, immune, and stromal cells were mosaic. ESC-derived cells from multiple respiratory cell lineages were highly differentiated and indistinguishable from endogenous cells based on morphology, ultrastructure, gene expression signatures, and cell surface proteins used to identify cell types by fluorescence-activated cell sorter.Conclusions: Lung and thyroid tissues were generated in vivo from ESCs by blastocyst complementation. Nkx2-1^-/- chimeras can be used as "bioreactors" for in vivo differentiation and functional studies of ESC-derived progenitor cells.

FOXF1 is required for the oncogenic properties of PAX3-FOXO1 in rhabdomyosarcoma

The PAX3-FOXO1 fusion protein is the key oncogenic driver in fusion positive rhabdomyosarcoma (FP-RMS), an aggressive soft tissue malignancy with a particularly poor prognosis. Identifying key downstream targets of PAX3-FOXO1 will provide new therapeutic opportunities for treatment of FP-RMS. Herein, we demonstrate that Forkhead Box F1 (FOXF1) transcription factor is uniquely expressed in FP-RMS and is required for FP-RMS tumorigenesis. The PAX3-FOXO1 directly binds to FOXF1 enhancers and induces FOXF1 gene expression. CRISPR/Cas9 mediated inactivation of either FOXF1 coding sequence or FOXF1 enhancers suppresses FP-RMS tumorigenesis even in the presence of PAX3-FOXO1 oncogene. Knockdown or genetic knockout of FOXF1 induces myogenic differentiation in PAX3-FOXO1-positive FP-RMS. Over-expression of FOXF1 decreases myogenic differentiation in primary human myoblasts. In FP-RMS tumor cells, FOXF1 protein binds chromatin near enhancers associated with FP-RMS gene signature. FOXF1 cooperates with PAX3-FOXO1 and E-box transcription factors MYOD1 and MYOG to regulate FP-RMS-specific gene expression. Altogether, FOXF1 functions downstream of PAX3-FOXO1 to promote FP-RMS tumorigenesis.

Nanoparticle Delivery Systems with Cell-Specific Targeting for Pulmonary Diseases

Respiratory disorders are among the most important medical problems threatening human life. The conventional therapeutics for respiratory disorders are hindered by insufficient drug concentrations at pathological lesions, lack of cell-specific targeting, and various biobarriers in the conducting airways and alveoli. To address these critical issues, various nanoparticle delivery systems have been developed to serve as carriers of specific drugs, DNA expression vectors, and RNAs. The unique properties of nanoparticles, including controlled size and distribution, surface functional groups, high payload capacity, and drug release triggering capabilities, are tailored to specific requirements in drug/gene delivery to overcome major delivery barriers in pulmonary diseases. To avoid off-target effects and improve therapeutic efficacy, nanoparticles with high cell-targeting specificity are essential for successful nanoparticle therapies. Furthermore, low toxicity and high degradability of the nanoparticles are among the most important requirements in the nanoparticle designs. In this review, we provide the most up-to-date research and clinical outcomes in nanoparticle therapies for pulmonary diseases. We also address the current critical issues in key areas of pulmonary cell targeting, biosafety and compatibility, and molecular mechanisms for selective cellular uptake.

Nanoparticle Delivery of Proangiogenic Transcription Factors into the Neonatal Circulation Inhibits Alveolar Simplification Caused by Hyperoxia

Rationale: Advances in neonatal critical care have greatly improved the survival of preterm infants, but the long-term complications of prematurity, including bronchopulmonary dysplasia (BPD), cause mortality and morbidity later in life. Although VEGF (vascular endothelial growth factor) improves lung structure and function in rodent BPD models, severe side effects of VEGF therapy prevent its use in patients with BPD.Objectives: To test whether nanoparticle delivery of proangiogenic transcription factor FOXM1 (forkhead box M1) or FOXF1 (forkhead box F1), both downstream targets of VEGF, can improve lung structure and function after neonatal hyperoxic injury.Methods: Newborn mice were exposed to 75% O2 for the first 7 days of life before being returned to a room air environment. On Postnatal Day 2, polyethylenimine-(5) myristic acid/polyethylene glycol-oleic acid/cholesterol nanoparticles containing nonintegrating expression plasmids with Foxm1 or Foxf1 cDNAs were injected intravenously. The effects of the nanoparticles on lung structure and function were evaluated using confocal microscopy, flow cytometry, and the flexiVent small-animal ventilator.Measurements and Main Results: The nanoparticles efficiently targeted endothelial cells and myofibroblasts in the alveolar region. Nanoparticle delivery of either FOXM1 or FOXF1 did not protect endothelial cells from apoptosis caused by hyperoxia but increased endothelial proliferation and lung angiogenesis after the injury. FOXM1 and FOXF1 improved elastin fiber organization, decreased alveolar simplification, and preserved lung function in mice reaching adulthood.Conclusions: Nanoparticle delivery of FOXM1 or FOXF1 stimulates lung angiogenesis and alveolarization during recovery from neonatal hyperoxic injury. Delivery of proangiogenic transcription factors has promise as a therapy for BPD in preterm infants.

Overexpression of FoxM1 promotes differentiation of bone marrow mesenchymal stem cells into alveolar type II cells through activating Wnt/β-catenin signalling

BACKGROUND

Acute respiratory distress syndrome (ARDS) becomes a serious challenge in critical care medicine due to the lack of effective therapy. As the damage of alveolar epithelium is a characteristic feature of ARDS, inducing mesenchymal stem cells (MSCs) to differentiate into alveolar epithelial cells turns out to be a promising therapy for ARDS, but the differentiation efficiency is yet to be improved. The study aimed to investigate the effect of overexpressing FoxM1 on MSCs' differentiation into alveolar epithelial cells.

METHODS

MSCs were isolated from mouse bone marrow, followed by transfected with lentivirus carrying the FoxM1 plasmid. Small airway epithelial cell growth medium was used as a culture system for inducing MSCs' differentiation into alveolar epithelial cells. Differentiation efficiency was assessed by detecting the expression levels of specific markers of alveolar epithelial cells mainly using quantitative reverse-transcription polymerase chain reaction and Western blot. To examine whether Wnt/β-catenin signalling was involved in the regulation mechanism, a specific inhibitor of the pathway XAV-939 was used and nuclear and cytoplasmic proteins were also analysed respectively. Co-immunoprecipitation was performed to examine the potential interaction between FoxM1 and β-catenin.

RESULTS

Overexpressing FoxM1 statistically significantly increased the expression levels of specific markers of type II alveolar epithelial cells prosurfactant protein C and surfactant protein B, which was partially reversed by XAV-939 treatment, while the expression levels of specific marker of type I alveolar epithelial cells aquaporin 5 did not change significantly. Overexpressing FoxM1 also increased the nuclear translocation of β-catenin and its transcriptional activity. A direct interaction between FoxM1 and β-catenin was found in co-immunoprecipitation assay.

CONCLUSION

Overexpression of FoxM1 could improve the efficiency of MSCs' differentiation into type II alveolar epithelial cells partly by activating Wnt/β-catenin signalling.

Molecular, cellular, and bioengineering approaches to stimulate lung regeneration after injury

The lung is susceptible to damage from a variety of sources throughout development and in adulthood. As a result, the lung has great capacities for repair and regeneration, directed by precisely controlled sequences of molecular and signaling pathways. Impairments or alterations in these signaling events can have deleterious effects on lung structure and function, ultimately leading to chronic lung disorders. When lung injury is too severe for the normal pathways to repair, or if those pathways do not function properly, lung regenerative medicine is needed to restore adequate structure and function. Great progress has been made in recent years in the number of regenerative techniques and their efficacy. This review will address recent progress in lung regenerative medicine focusing on pharmacotherapy including the expanding role of nanotechnology, stem cell-based therapies, and bioengineering techniques. The use of these techniques individually and collectively has the potential to significantly improve morbidity and mortality associated with congenital and acquired lung disorders.

Centromere protein F and Forkhead box M1 correlation with prognosis of non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the most common histological type of lung cancer. Altered expression of centromere protein F (CENPF), a transient kinetochore protein, has been found in a variety of human cancers. However, its clinical significance in NSCLC remains unknown. In the present study the results of quantitative PCR and western blot analyses demonstrated that CENPF and Forkhead box M1 (FOXM1) were significantly higher in NSCLC tissues than in the non-cancerous controls at both transcriptional and translational levels. Immunohistochemical staining results showed 58.7% (44/75) and 64.0% (48/75) of NSCLC tissues displayed high expression of CENPF and FOXM1, respectively. CENPF protein expression showed a positive correlation with tumor size (P=0.0179), vital status (P=0.0008) and FOXM1 expression (P=0.0013) in NSCLC. Poor overall survival was correlated with high levels of CENPF and FOXM1 in NSCLC patients as evaluated by Kaplan-Meier and log rank test. Multivariate analyses showed that CENPF expression was an independent prognostic factor for NSCLC. In conclusion, our study provides evidence of the prognostic function of CENPF in NSCLC.

Postnatal Alveologenesis Depends on FOXF1 Signaling in c-KIT+ Endothelial Progenitor Cells

Rationale: Disruption of alveologenesis is associated with severe pediatric lung disorders, including bronchopulmonary dysplasia (BPD). Although c-KIT+ endothelial cell (EC) progenitors are abundant in embryonic and neonatal lungs, their role in alveolar septation and the therapeutic potential of these cells remain unknown.Objectives: To determine whether c-KIT+ EC progenitors stimulate alveologenesis in the neonatal lung.Methods: We used single-cell RNA sequencing of neonatal human and mouse lung tissues, immunostaining, and FACS analysis to identify transcriptional and signaling networks shared by human and mouse pulmonary c-KIT+ EC progenitors. A mouse model of perinatal hyperoxia-induced lung injury was used to identify molecular mechanisms that are critical for the survival, proliferation, and engraftment of c-KIT+ EC progenitors in the neonatal lung.Measurements and Main Results: Pulmonary c-KIT+ EC progenitors expressing PECAM-1, CD34, VE-Cadherin, FLK1, and TIE2 lacked mature arterial, venal, and lymphatic cell-surface markers. The transcriptomic signature of c-KIT+ ECs was conserved in mouse and human lungs and enriched in FOXF1-regulated transcriptional targets. Expression of FOXF1 and c-KIT was decreased in the lungs of infants with BPD. In the mouse, neonatal hyperoxia decreased the number of c-KIT+ EC progenitors. Haploinsufficiency or endothelial-specific deletion of Foxf1 in mice increased apoptosis and decreased proliferation of c-KIT+ ECs. Inactivation of either Foxf1 or c-Kit caused alveolar simplification. Adoptive transfer of c-KIT+ ECs into the neonatal circulation increased lung angiogenesis and prevented alveolar simplification in neonatal mice exposed to hyperoxia.Conclusions: Cell therapy involving c-KIT+ EC progenitors can be beneficial for the treatment of BPD.

The S52F FOXF1 Mutation Inhibits STAT3 Signaling and Causes Alveolar Capillary Dysplasia

Rationale: Alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV) is a lethal congenital disorder causing respiratory failure and pulmonary hypertension shortly after birth. There are no effective treatments for ACDMPV other than lung transplant, and new therapeutic approaches are urgently needed. Although ACDMPV is linked to mutations in the FOXF1 gene, molecular mechanisms through which FOXF1 mutations cause ACDMPV are unknown.Objectives: To identify molecular mechanisms by which S52F FOXF1 mutations cause ACDMPV.Methods: We generated a clinically relevant mouse model of ACDMPV by introducing the S52F FOXF1 mutation into the mouse Foxf1 gene locus using CRISPR/Cas9 technology. Immunohistochemistry, whole-lung imaging, and biochemical methods were used to examine vasculature in Foxf1WT/S52F lungs and identify molecular mechanisms regulated by FOXF1.Measurements and Main Results: FOXF1 mutations were identified in 28 subjects with ACDMPV. Foxf1WT/S52F knock-in mice recapitulated histopathologic findings in ACDMPV infants. The S52F FOXF1 mutation disrupted STAT3-FOXF1 protein-protein interactions and inhibited transcription of Stat3, a critical transcriptional regulator of angiogenesis. STAT3 signaling and endothelial proliferation were reduced in Foxf1WT/S52F mice and human ACDMPV lungs. S52F FOXF1 mutant protein did not bind chromatin and was transcriptionally inactive. Furthermore, we have developed a novel formulation of highly efficient nanoparticles and demonstrated that nanoparticle delivery of STAT3 cDNA into the neonatal circulation restored endothelial proliferation and stimulated lung angiogenesis in Foxf1WT/S52F mice.Conclusions: FOXF1 acts through STAT3 to stimulate neonatal lung angiogenesis. Nanoparticle delivery of STAT3 is a promising strategy to treat ACDMPV associated with decreased STAT3 signaling.

The multifaceted roles of FOXM1 in pulmonary disease

Forkhead box M1 (FOXM1), a transcriptional regulator of G1/S and G2/M transition and M phase progression in the cell cycle, plays a principal role in many physiological and pathological processes. A growing number of studies have focused on the relationship between abnormal FOXM1 expression and pulmonary diseases, such as lung cancer, chronic obstructive pulmonary disease (COPD), asthma, acute lung injury (ALI), pulmonary fibrosis, and pulmonary arterial hypertension (PAH). These studies indicate that the FOXM1 regulatory network is a major predictor of poor outcomes, especially in lung cancer, and provide novel insight into various pulmonary diseases. For the first time, this review summarizes the mechanistic relationship between FOXM1 dysregulation and pulmonary diseases, the benefits of targeting abnormal FOXM1 expression, and the questions that remain to be addressed in the future.

The Forkhead box F1 transcription factor inhibits collagen deposition and accumulation of myofibroblasts during liver fibrosis

Hepatic fibrosis is the common end stage to a variety of chronic liver injuries and is characterized by an excessive deposition of extracellular matrix (ECM), which disrupts the liver architecture and impairs liver function. The fibrous lesions are produced by myofibroblasts, which differentiate from hepatic stellate cells (HSC). The myofibroblast's transcriptional networks remain poorly characterized. Previous studies have shown that the Forkhead box F1 (FOXF1) transcription factor is expressed in HSCs and stimulates their activation during acute liver injury; however, the role of FOXF1 in the progression of hepatic fibrosis is unknown. In the present study, we generated αSMACreER;Foxf1fl/fl mice to conditionally inactivate Foxf1 in myofibroblasts during carbon tetrachloride-mediated liver fibrosis. Foxf1 deletion increased collagen depositions and disrupted liver architecture. Timp2 expression was significantly increased in Foxf1-deficient mice while MMP9 activity was reduced. RNA sequencing of purified liver myofibroblasts demonstrated that FOXF1 inhibits expression of pro-fibrotic genes, Col1α2, Col5α2, and Mmp2 in fibrotic livers and binds to active repressors located in promotors and introns of these genes. Overexpression of FOXF1 inhibits Col1a2, Col5a2, and MMP2 in primary murine HSCs in vitro Altogether, FOXF1 prevents aberrant ECM depositions during hepatic fibrosis by repressing pro-fibrotic gene transcription in myofibroblasts and HSCs.

Building and Regenerating the Lung Cell by Cell

The unique architecture of the mammalian lung is required for adaptation to air breathing at birth and thereafter. Understanding the cellular and molecular mechanisms controlling its morphogenesis provides the framework for understanding the pathogenesis of acute and chronic lung diseases. Recent single-cell RNA sequencing data and high-resolution imaging identify the remarkable heterogeneity of pulmonary cell types and provides cell selective gene expression underlying lung development. We will address fundamental issues related to the diversity of pulmonary cells, to the formation and function of the mammalian lung, and will review recent advances regarding the cellular and molecular pathways involved in lung organogenesis. What cells form the lung in the early embryo? How are cell proliferation, migration, and differentiation regulated during lung morphogenesis? How do cells interact during lung formation and repair? How do signaling and transcriptional programs determine cell-cell interactions necessary for lung morphogenesis and function?

FOXF1 transcription factor promotes lung morphogenesis by inducing cellular proliferation in fetal lung mesenchyme

Organogenesis is regulated by mesenchymal-epithelial signaling events that induce expression of cell-type specific transcription factors critical for cellular proliferation, differentiation and appropriate tissue patterning. While mesenchymal transcription factors play a key role in mesenchymal-epithelial interactions, transcriptional networks in septum transversum and splanchnic mesenchyme remain poorly characterized. Forkhead Box F1 (FOXF1) transcription factor is expressed in mesenchymal cell lineages; however, its role in organogenesis remains uncharacterized due to early embryonic lethality of Foxf1^-/- mice. In the present study, we generated mesenchyme-specific Foxf1 knockout mice (Dermo1-Cre Foxf1^-/-) and demonstrated that FOXF1 is required for development of respiratory, cardiovascular and gastrointestinal organ systems. Deletion of Foxf1 from mesenchyme caused embryonic lethality in the middle of gestation due to multiple developmental defects in the heart, lung, liver and esophagus. Deletion of Foxf1 inhibited mesenchyme proliferation and delayed branching lung morphogenesis. Gene expression profiling of micro-dissected distal lung mesenchyme and ChIP sequencing of fetal lung tissue identified multiple target genes activated by FOXF1, including Wnt2, Wnt11, Wnt5A and Hoxb7. FOXF1 decreased expression of the Wnt inhibitor Wif1 through direct transcriptional repression. Furthermore, using a global Foxf1 knockout mouse line (Foxf1^-/-) we demonstrated that FOXF1-deficiency disrupts the formation of the lung bud in foregut tissue explants. Finally, deletion of Foxf1 from smooth muscle cell lineage (smMHC-Cre Foxf1^-/-) caused hyper-extension of esophagus and trachea, loss of tracheal and esophageal muscle, mispatterning of esophageal epithelium and decreased proliferation of smooth muscle cells. Altogether, FOXF1 promotes lung morphogenesis by regulating mesenchymal-epithelial signaling and stimulating cellular proliferation in fetal lung mesenchyme.

Smooth muscle cell-specific FoxM1 controls hypoxia-induced pulmonary hypertension

RATIONALE

Forkhead box M1 (FoxM1) is a transcription factor that promotes cell proliferation by regulating a broad spectrum of genes that participate in cell cycle regulation, such as Cyclin B, CDC25B, and Aurora B Kinase. We have shown that hypoxia, a well-known stimulus for pulmonary hypertension (PH), induces FoxM1 in pulmonary artery smooth muscle cells (PASMC) in a HIF-dependent pathway, resulting in PASMC proliferation, while the suppression of FoxM1 prevents hypoxia-induced PASMC proliferation. However, the implications of FoxM1 in the development of PH remain less known.

METHODS

We determined FoxM1 levels in the lung samples of idiopathic PAH (pulmonary arterial hypertension) (IPAH) patients and hypoxia-induced PH mice. We generated constitutive and inducible smooth muscle cell (SMC)-specific FoxM1 knockdown or knockout mice as well as FoxM1 transgenic mice which overexpress FoxM1, and exposed them to hypoxia (10% O₂, 90% N₂) or normoxia (Room air, 21% oxygen) for four weeks, and measured PH indices. We also isolated mouse PASMC (mPASMC) and mouse embryonic fibroblasts (MEF) from these mice to examine the cell proliferation and expression levels of SMC contractile proteins.

RESULTS

We showed that in hypertensive human lungs or mouse lungs, FoxM1 levels were elevated. Constitutive knockout of FoxM1 in mouse SMC caused early lethality, whereas constitutive knockdown of FoxM1 in mouse SMC prevented hypoxia-induced PH and PASMC proliferation. Inducible knockout of FoxM1 in SMC reversed hypoxia-induced pulmonary artery wall remodeling in existing PH. Overexpression of FoxM1 enhanced hypoxia-induced pulmonary artery wall remodeling and right ventricular hypertrophy in mice. Alteration of FoxM1 status did not affect hypoxia-induced hypoxia-inducible factor (HIF) activity in mice. Knockout of FoxM1 decreased PASMC proliferation and induced expression of SMC contractile proteins and TGF-β/Smad3 signaling.

CONCLUSIONS

Our studies provide clear evidence that altered FoxM1 expression in PASMC contributes to PH and uncover a correlation between Smad3-dependent signaling in FoxM1-mediated proliferation and de-differentiation of PASMC.

scEpath: energy landscape-based inference of transition probabilities and cellular trajectories from single-cell transcriptomic data

Motivation

Single-cell RNA-sequencing (scRNA-seq) offers unprecedented resolution for studying cellular decision-making processes. Robust inference of cell state transition paths and probabilities is an important yet challenging step in the analysis of these data.

Results

Here we present scEpath, an algorithm that calculates energy landscapes and probabilistic directed graphs in order to reconstruct developmental trajectories. We quantify the energy landscape using 'single-cell energy' and distance-based measures, and find that the combination of these enables robust inference of the transition probabilities and lineage relationships between cell states. We also identify marker genes and gene expression patterns associated with cell state transitions. Our approach produces pseudotemporal orderings that are-in combination-more robust and accurate than current methods, and offers higher resolution dynamics of the cell state transitions, leading to new insight into key transition events during differentiation and development. Moreover, scEpath is robust to variation in the size of the input gene set, and is broadly unsupervised, requiring few parameters to be set by the user. Applications of scEpath led to the identification of a cell-cell communication network implicated in early human embryo development, and novel transcription factors important for myoblast differentiation. scEpath allows us to identify common and specific temporal dynamics and transcriptional factor programs along branched lineages, as well as the transition probabilities that control cell fates.

Availability and implementation

A MATLAB package of scEpath is available at https://github.com/sqjin/scEpath.

Supplementary information

Supplementary data are available at Bioinformatics online.

HIF Oxygen Sensing Pathways in Lung Biology

Cellular responses to oxygen fluctuations are largely mediated by hypoxia-inducible factors (HIFs). Upon inhalation, the first organ inspired oxygen comes into contact with is the lungs, but the understanding of the pulmonary HIF oxygen-sensing pathway is still limited. In this review we will focus on the role of HIF1α and HIF2α isoforms in lung responses to oxygen insufficiency. In particular, we will discuss novel findings regarding their role in the biology of smooth muscle cells and endothelial cells in the context of hypoxia-induced pulmonary vasoconstriction. Moreover, we will also discuss recent studies into HIF-dependent responses in the airway epithelium, which have been even less studied than the HIF-dependent vascular responses in the lungs. In summary, we will review the biological functions executed by HIF1 or HIF2 in the pulmonary vessels and epithelium to control lung responses to oxygen fluctuations as well as their pathological consequences in the hypoxic lung.

Transcription factor FoxM1 is the downstream target of c-Myc and contributes to the development of prostate cancer

Background

Prostate cancer is a common malignancy and the second leading cause of cancer death in men. Elevated expression of the transcription factor FoxM1 and c-Myc has been identified in prostate cancer. However, the potential mechanism of elevated FoxM1 and c-Myc to the development of prostate cancer has not been identified.

Methods

In this report, the mRNA level of FoxM1 and c-Myc was detected in 30 prostate cancer and para-cancer tissues. Then, we detected the expression level of FoxM1 by real-time PCR and Western blot after disturbance of the expression level of c-Myc in PC-3 cells. Whether c-Myc could bind to FoxM1 promoter was identified by ChIP assay. Finally, the migratory, invasive, and proliferative abilities in FoxM1 overexpressing and silencing PC-3 cells were detected by wound healing, transwell assay, CCK-8 assays, and Ki-67 protein level.

Results

We found that the expression level of FoxM1 and c-Myc were both increased in prostate cancer samples compared with para-cancer samples. The expression level of FoxM1 was changed consistent with the protein level of c-Myc. ChIP assay detected the direct binding of c-Myc in FoxM1 gene promoter. Lastly, overexpression of FoxM1 increased the migratory, invasive, and proliferative abilities of PC-3 cells, and its downregulation significantly decreased the migratory, invasive, and proliferative abilities.

Conclusions

In conclusion, FoxM1 was significantly increased in prostate cancer samples, and it could regulate the proliferative and invasive ability of prostate cancer cells which might be a new target for prostate cancer. Besides, c-Myc could regulate the expression level of FoxM1 by directly binding to its gene promoter.

Transcription Factors Regulating Embryonic Development of Pulmonary Vasculature

Lung morphogenesis is a highly orchestrated process beginning with the appearance of lung buds on approximately embryonic day 9.5 in the mouse. Endodermally derived epithelial cells of the primitive lung buds undergo branching morphogenesis to generate the tree-like network of epithelial-lined tubules. The pulmonary vasculature develops in close proximity to epithelial progenitor cells in a process that is regulated by interactions between the developing epithelium and underlying mesenchyme. Studies in transgenic and knockout mouse models demonstrate that normal lung morphogenesis requires coordinated interactions between cells lining the tubules, which end in peripheral saccules, juxtaposed to an extensive network of capillaries. Multiple growth factors, microRNAs, transcription factors, and their associated signaling cascades regulate cellular proliferation, migration, survival, and differentiation during formation of the peripheral lung. Dysregulation of signaling events caused by gene mutations, teratogens, or premature birth causes severe congenital and acquired lung diseases in which normal alveolar architecture and the pulmonary capillary network are disrupted. Herein, we review scientific progress regarding signaling and transcriptional mechanisms regulating the development of pulmonary vasculature during lung morphogenesis.

FOXM1 activates AGR2 and causes progression of lung adenomas into invasive mucinous adenocarcinomas

Lung cancer remains one of the most prominent public health challenges, accounting for the highest incidence and mortality among all human cancers. While pulmonary invasive mucinous adenocarcinoma (PIMA) is one of the most aggressive types of non-small cell lung cancer, transcriptional drivers of PIMA remain poorly understood. In the present study, we found that Forkhead box M1 transcription factor (FOXM1) is highly expressed in human PIMAs and associated with increased extracellular mucin deposition and the loss of NKX2.1. To examine consequences of FOXM1 expression in tumor cells in vivo, we employed an inducible, transgenic mouse model to express an activated FOXM1 transcript in urethane-induced benign lung adenomas. FOXM1 accelerated tumor growth, induced progression from benign adenomas to invasive, metastatic adenocarcinomas, and induced SOX2, a marker of poorly differentiated tumor cells. Adenocarcinomas in FOXM1 transgenic mice expressed increased MUC5B and MUC5AC, and reduced NKX2.1, which are characteristics of mucinous adenocarcinomas. Expression of FOXM1 in KrasG12D transgenic mice increased the mucinous phenotype in KrasG12D-driven lung tumors. Anterior Gradient 2 (AGR2), an oncogene critical for intracellular processing and packaging of mucins, was increased in mouse and human PIMAs and was associated with FOXM1. FOXM1 directly bound to and transcriptionally activated human AGR2 gene promoter via the -257/-247 bp region. Finally, using orthotopic xenografts we demonstrated that inhibition of either FOXM1 or AGR2 in human PIMAs inhibited mucinous characteristics, and reduced tumor growth and invasion. Altogether, FOXM1 is necessary and sufficient to induce mucinous phenotypes in lung tumor cells in vivo.

FOXF1 transcription factor promotes lung regeneration after partial pneumonectomy

FOXF1, a member of the forkhead box family of transcription factors, has been previously shown to be critical for lung development, homeostasis, and injury responses. However, the role of FOXF1 in lung regeneration is unknown. Herein, we performed partial pneumonectomy, a model of lung regeneration, in mice lacking one Foxf1 allele in endothelial cells (PDGFb-iCre/Foxf1 ^fl/+ mice). Endothelial cell proliferation was significantly reduced in regenerating lungs from mice deficient for endothelial Foxf1. Decreased endothelial proliferation was associated with delayed lung regeneration as shown by reduced respiratory volume in Foxf1-deficient lungs. FACS-sorted endothelial cells isolated from regenerating PDGFb-iCre/Foxf1 ^fl/+ and control lungs were used for RNAseq analysis to identify FOXF1 target genes. Foxf1 deficiency altered expression of numerous genes including those regulating extracellular matrix remodeling (Timp3, Adamts9) and cell cycle progression (Cdkn1a, Cdkn2b, Cenpj, Tubb4a), which are critical for lung regeneration. Deletion of Foxf1 increased Timp3 mRNA and protein, decreasing MMP14 activity in regenerating lungs. ChIPseq analysis for FOXF1 and histone methylation marks identified DNA regulatory regions within the Cd44, Cdkn1a, and Cdkn2b genes, indicating they are direct FOXF1 targets. Thus FOXF1 stimulates lung regeneration following partial pneumonectomy via direct transcriptional regulation of genes critical for extracellular matrix remodeling and cell cycle progression.

Induction of Chromosome Instability by Activation of Yes-Associated Protein and Forkhead Box M1 in Liver Cancer

BACKGROUND & AIMS

Many different types of cancer cells have chromosome instability. The hippo pathway leads to phosphorylation of the transcriptional activator yes-associated protein 1 (YAP1, YAP), which regulates proliferation and has been associated with the development of liver cancer. We investigated the effects of hippo signaling via YAP on chromosome stability and hepatocarcinogenesis in humans and mice.

METHODS

We analyzed transcriptome data from 242 patients with hepatocellular carcinoma (HCC) to search for gene signatures associated with chromosomal instability (CIN); we investigated associations with overall survival time and cancer recurrence using Kaplan-Meier curves. We analyzed changes in expression of these signature genes, at mRNA and protein levels, after small interfering RNA-mediated silencing of YAP in Sk-Hep1, SNU182, HepG2, or pancreatic cancer cells, as well as incubation with thiostrepton (an inhibitor of forkhead box M1 [FOXM1]) or verteporfin (inhibitor of the interaction between YAP and TEA domain transcription factor 4 [TEAD4]). We performed co-immunoprecipitation and chromatin immunoprecipitation experiments. We collected liver tissues from mice that express a constitutively active form of YAP (YAP^S127A) and analyzed gene expression signatures and histomorphologic parameters associated with chromosomal instability. Mice were given injections of thiostrepton and livers were collected and analyzed by immunoblotting, immunohistochemistry, histology, and real-time polymerase chain reaction. We performed immunohistochemical analyses on tissue microarrays of 105 HCCs and 7 nontumor liver tissues.

RESULTS

Gene expression patterns associated with chromosome instability, called CIN25 and CIN70, were detected in HCCs from patients with shorter survival time or early cancer recurrence. TEAD4 and YAP were required for CIN25 and CIN70 signature expression via induction and binding of FOXM1. Disrupting the interaction between YAP and TEAD4 with verteporfin, or inhibiting FOXM1 with thiostrepton, reduced the chromosome instability gene expression patterns. Hyperplastic livers and tumors from YAP^S127A mice had increased CIN25 and CIN70 gene expression patterns, aneuploidy, and defects in mitosis. Injection of YAP^S127A mice with thiostrepton reduced liver overgrowth and signs of chromosomal instability. In human HCC tissues, high levels of nuclear YAP correlated with increased chromosome instability gene expression patterns and aneuploidy.

CONCLUSIONS

By analyzing cell lines, genetically modified mice, and HCC tissues, we found that YAP cooperates with FOXM1 to contribute to chromosome instability. Agents that disrupt this pathway might be developed as treatments for liver cancer. Transcriptome data are available in the Gene Expression Omnibus public database (accession numbers: GSE32597 and GSE73396).

The FOXM1 inhibitor RCM-1 suppresses goblet cell metaplasia and prevents IL-13 and STAT6 signaling in allergen-exposed mice

Goblet cell metaplasia and excessive mucus secretion associated with asthma, cystic fibrosis, and chronic obstructive pulmonary disease contribute to morbidity and mortality worldwide. We performed a high-throughput screen to identify small molecules targeting a transcriptional network critical for the differentiation of goblet cells in response to allergens. We identified RCM-1, a nontoxic small molecule that inhibited goblet cell metaplasia and excessive mucus production in mice after exposure to allergens. RCM-1 blocked the nuclear localization and increased the proteasomal degradation of Forkhead box M1 (FOXM1), a transcription factor critical for the differentiation of goblet cells from airway progenitor cells. RCM-1 reduced airway resistance, increased lung compliance, and decreased proinflammatory cytokine production in mice exposed to the house dust mite and interleukin-13 (IL-13), which triggers goblet cell metaplasia. In cultured airway epithelial cells and in mice, RCM-1 reduced IL-13 and STAT6 (signal transducer and activator of transcription 6) signaling and prevented the expression of the STAT6 target genes Spdef and Foxa3, which are key transcriptional regulators of goblet cell differentiation. These results suggest that RCM-1 is an inhibitor of goblet cell metaplasia and IL-13 signaling, providing a new therapeutic candidate to treat patients with asthma and other chronic airway diseases.

Forkhead transcription factor FoxF1 interacts with Fanconi anemia protein complexes to promote DNA damage response

Forkhead box F1 (Foxf1) transcription factor is an important regulator of embryonic development but its role in tumor cells remains incompletely understood. While 16 proteins were characterized in Fanconi anemia (FA) core complex, its interactions with cellular transcriptional machinery remain poorly characterized. Here, we identified FoxF1 protein as a novel interacting partner of the FA complex proteins. Using multiple human and mouse tumor cell lines and Foxf1^+/− mice we demonstrated that FoxF1 physically binds to and increases stability of FA proteins. FoxF1 co-localizes with FANCD2 in DNA repair foci in cultured cells and tumor tissues obtained from cisplatin-treated mice. In response to DNA damage, FoxF1-deficient tumor cells showed significantly reduced FANCD2 monoubiquitination and FANCM phosphorylation, resulting in impaired formation of DNA repair foci. FoxF1 knockdown caused chromosomal instability, nuclear abnormalities, and increased tumor cell death in response to DNA-damaging agents. Overexpression of FoxF1 in DNA-damaged cells improved stability of FA proteins, decreased chromosomal and nuclear aberrations, restored formation of DNA repair foci and prevented cell death after DNA damage. These findings demonstrate that FoxF1 is a key component of FA complexes and a critical mediator of DNA damage response in tumor cells.

Lethal lung hypoplasia and vascular defects in mice with conditional Foxf1 overexpression

FOXF1 heterozygous point mutations and genomic deletions have been reported in newborns with the neonatally lethal lung developmental disorder, alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). However, no gain-of-function mutations in FOXF1 have been identified yet in any human disease conditions. To study the effects of FOXF1 overexpression in lung development, we generated a Foxf1 overexpression mouse model by knocking-in a Cre-inducible Foxf1 allele into the ROSA26 (R26) locus. The mice were phenotyped using micro-computed tomography (micro-CT), head-out plethysmography, ChIP-seq and transcriptome analyses, immunohistochemistry, and lung histopathology. Thirty-five percent of heterozygous R26-Lox-Stop-Lox (LSL)-Foxf1 embryonic day (E)15.5 embryos exhibit subcutaneous edema, hemorrhages and die perinatally when bred to Tie2-cre mice, which targets Foxf1 overexpression to endothelial and hematopoietic cells. Histopathological and micro-CT evaluations revealed that R26Foxf1; Tie2-cre embryos have immature lungs with a diminished vascular network. Neonates exhibited respiratory deficits verified by detailed plethysmography studies. ChIP-seq and transcriptome analyses in E18.5 lungs identified Sox11, Ghr, Ednrb, and Slit2 as potential downstream targets of FOXF1. Our study shows that overexpression of the highly dosage-sensitive Foxf1 impairs lung development and causes vascular abnormalities. This has important clinical implications when considering potential gene therapy approaches to treat disorders of FOXF1 abnormal dosage, such as ACDMPV.

Role Of Hif2α Oxygen Sensing Pathway In Bronchial Epithelial Club Cell Proliferation

Oxygen-sensing pathways executed by the hypoxia-inducible factors (HIFs) induce a cellular adaptive program when oxygen supply becomes limited. However, the role of the HIF oxygen-sensing pathway in the airway response to hypoxic stress in adulthood remains poorly understood. Here we found that in vivo exposure to hypoxia led to a profound increase in bronchial epithelial cell proliferation mainly confined to Club (Clara) cells. Interestingly, this response was executed by hypoxia-inducible factor 2α (HIF2α), which controls the expression of FoxM1, a recognized proliferative factor of Club cells. Furthermore, HIF2α induced the expression of the resistin-like molecules α and β (RELMα and β), previously considered bronchial epithelial growth factors. Importantly, despite the central role of HIF2α, this proliferative response was not initiated by in vivo Vhl gene inactivation or pharmacological inhibition of prolyl hydroxylase oxygen sensors, indicating the molecular complexity of this response and the possible participation of other oxygen-sensing pathways. Club cells are principally involved in protection and maintenance of bronchial epithelium. Thus, our findings identify a novel molecular link between HIF2α and Club cell biology that can be regarded as a new HIF2α-dependent mechanism involved in bronchial epithelium adaptation to oxygen fluctuations.

FOXF1 maintains endothelial barrier function and prevents edema after lung injury

Multiple signaling pathways, structural proteins, and transcription factors are involved in the regulation of endothelial barrier function. The forkhead protein FOXF1 is a key transcriptional regulator of embryonic lung development, and we used a conditional knockout approach to examine the role of FOXF1 in adult lung homeostasis, injury, and repair. Tamoxifen-regulated deletion of both Foxf1 alleles in endothelial cells of adult mice (Pdgfb-iCreER/Foxf1(-/-)) caused lung inflammation and edema, leading to respiratory insufficiency and death. Deletion of a single Foxf1 allele made heterozygous Pdgfb-iCreER/Foxf1(+/-)mice more susceptible to acute lung injury. FOXF1 abundance was decreased in pulmonary endothelial cells of human patients with acute lung injury. Gene expression analysis of pulmonary endothelial cells with homozygous FOXF1 deletion indicated reduced expression of genes critical for maintenance and regulation of adherens junctions. FOXF1 knockdown in vitro and in vivo disrupted adherens junctions, enhanced lung endothelial permeability, and increased the abundance of the mRNA and protein for sphingosine 1-phosphate receptor 1 (S1PR1), a key regulator of endothelial barrier function. Chromatin immunoprecipitation and luciferase reporter assays demonstrated that FOXF1 directly bound to and induced the transcriptional activity of the S1pr1 promoter. Pharmacological administration of S1P to injured Pdgfb-iCreER/Foxf1(+/-)mice restored endothelial barrier function, decreased lung edema, and improved survival. Thus, FOXF1 promotes normal lung homeostasis and repair, in part, by enhancing endothelial barrier function through activation of the S1P/S1PR1 signaling pathway.

β-catenin and Kras/Foxm1 signaling pathway are critical to restrict Sox9 in basal cells during pulmonary branching morphogenesis

BACKGROUND

Lung morphogenesis is regulated by interactions between the canonical Wnt/β-catenin and Kras/ERK/Foxm1 signaling pathways that establish proximal-peripheral patterning of lung tubules. How these interactions influence the development of respiratory epithelial progenitors to acquire airway as compared to alveolar epithelial cell fate is unknown. During branching morphogenesis, SOX9 transcription factor is normally restricted from conducting airway epithelial cells and is highly expressed in peripheral, acinar progenitor cells that serve as precursors of alveolar type 2 (AT2) and AT1 cells as the lung matures.

RESULTS

To identify signaling pathways that determine proximal-peripheral cell fate decisions, we used the SFTPC gene promoter to delete or overexpress key members of Wnt/β-catenin and Kras/ERK/Foxm1 pathways in fetal respiratory epithelial progenitor cells. Activation of β-catenin enhanced SOX9 expression in peripheral epithelial progenitors, whereas deletion of β-catenin inhibited SOX9. Surprisingly, deletion of β-catenin caused accumulation of atypical SOX9-positive basal cells in conducting airways. Inhibition of Wnt/β-catenin signaling by Kras(G12D) or its downstream target Foxm1 stimulated SOX9 expression in basal cells. Genetic inactivation of Foxm1 from Kras(G12D) -expressing epithelial cells prevented the accumulation of SOX9-positive basal cells in developing airways.

CONCLUSIONS

Interactions between the Wnt/β-catenin and the Kras/ERK/Foxm1 pathways are essential to restrict SOX9 expression in basal cells. Developmental Dynamics 245:590-604, 2016. © 2016 Wiley Periodicals, Inc.

Club Cell Protein 16 (CC16) Augmentation: A Potential Disease-modifying Approach for Chronic Obstructive Pulmonary Disease (COPD)

INTRODUCTION

Club cell protein 16 (CC16) is the most abundant protein in bronchoalveolar lavage fluid. CC16 has anti-inflammatory properties in smoke-exposed lungs, and chronic obstructive pulmonary disease (COPD) is associated with CC16 deficiency. Herein, we explored whether CC16 is a therapeutic target for COPD.

AREAS COVERED

We reviewed the literature on the factors that regulate airway CC16 expression, its biologic functions and its protective activities in smoke-exposed lungs using PUBMED searches. We generated hypotheses on the mechanisms by which CC16 limits COPD development, and discuss its potential as a new therapeutic approach for COPD.

EXPERT OPINION

CC16 plasma and lung levels are reduced in smokers without airflow obstruction and COPD patients. In COPD patients, airway CC16 expression is inversely correlated with severity of airflow obstruction. CC16 deficiency increases smoke-induced lung pathologies in mice by its effects on epithelial cells, leukocytes, and fibroblasts. Experimental augmentation of CC16 levels using recombinant CC16 in cell culture systems, plasmid and adenoviral-mediated over-expression of CC16 in epithelial cells or smoke-exposed murine airways reduces inflammation and cellular injury. Additional studies are necessary to assess the efficacy of therapies aimed at restoring airway CC16 levels as a new disease-modifying therapy for COPD patients.

Transcriptome analysis in cardiomyocyte-specific differentiation of murine embryonic stem cells reveals transcriptional regulation network

The differentiation to cardiomyocytes is a prerequisite and an important part of heart development. A good understanding of the complicated cardiomyocyte differentiation process benefits cardiogenesis study. Embryonic stem cells (ESCs), cell lines with infinite ability to proliferate and to be differentiated into all cell types of the adult body, are important research tools for investigation of differentiation and meanwhile good models for developmental research. In the current study, genome-wide gene expression of ESCs is profiled through high throughput platform during cardiomyocyte-specific differentiation and maturation. Gene expression patterns of undifferentiated ESCs and ESC-derived cardiomyocytes provide a global overview of genes involved in cardiomyocyte-specific differentiation, whereas marker gene expression profiles of both ESC-related genes and cardiac-specific genes presented the expression pattern shift during differentiation in a pure ESC-derived cardiomyocyte cell culture system. The differentiation and maturation process was completed at day 19 after initiation of differentiation, according to our gene expression profile results. Functional analysis of regulated genes reveals over-represented biological processes, molecular functions and pathways during the differentiation and maturation process. Finally, transcription factor regulation networks were engineered based on gene expression data. Within these networks, the number of identified important regulators (Trim28, E2f4, Foxm1, Myc, Hdac1, Rara, Mef2c, Nkx2-5, Gata4) and possible key co-regulation modules (Nkx2-5 - Gata4 - Tbx5, Myc - E2F4) could be expanded. We demonstrate that a more comprehensive picture of cardiomyocyte differentiation and its regulation can be achieved solely by studying gene expression patterns. The results from our study contribute to a better and more accurate understanding of the regulation mechanisms during cardiomyocyte differentiation.

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.

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.