SLUG: a new target of lymphoid enhancer factor-1 in human osteoblasts

Targeting LEF1-mediated epithelial-mesenchymal transition reverses lenvatinib resistance in hepatocellular carcinoma

Acquired resistance is a significant hindrance to clinical application of lenvatinib in unresectable hepatocellular carcinoma (HCC). Further in-depth investigation of resistance mechanisms can help to develop additional therapeutic strategies to overcome or delay resistance. In our study, two lenvatinib-resistant (LR) HCC cell lines were established by treatment with gradient increasing concentration of lenvatinib, named Hep3B-LR and HepG2-LR. Interestingly, continuous lenvatinib treatment reinforced epithelial-mesenchymal transition (EMT), cell migration, and cell invasion. Gene set enrichment analysis (GSEA) enrichment analysis of RNA-sequencing from Hep3B-LR and corresponding parental cells revealed that activation of Wnt signaling pathway was involved in this adaptive process. Active β-catenin and its downstream target lymphoid enhancer binding factor 1 (LEF1) were significantly elevated in LR HCC cells, which promoted lenvatinib resistance through mediating EMT-related genes. Data analysis based on Gene Expression Omnibus (GEO) and the Cancer Genome Atlas Program (TCGA) databases suggests that LEF1, as a key regulator of EMT, was a novel molecular target linked to lenvatinib resistance and poor prognosis in HCC. Using a small-molecule specific inhibitor ICG001 and knocking down LEF1 showed that targeting LEF1 restored the sensitivity of LR HCC cells to lenvatinib. Our results uncover upregulation of LEF1 confers lenvatinib resistance by facilitating EMT, cell migration, and invasion of LR HCC cells, indicating that LEF1 is a novel therapeutic target for overcoming acquired lenvatinib resistance.

Combining Bevacizumab with knocked-down β-catenin reduces VEGF-A and Slug mRNA in HepG2 but not in Caco-2 cell lines

BACKGROUND

Bevacizumab (Bev) resistance is hypothesized to be overcome by combination with inhibitors of other signalling pathways.

OBJECTIVE

We aimed to study the effect of combining Bev with knocked down β-catenin (Bev-β-cat-siRNA) on the expression of VEGF-A, Slug, NFКB and its two target genes c-Flip and FasR in HepG2. Expression of VEGF-A and Slug was also studied in Caco-2 cells.

METHODS

Cultured cells were divided into six groups 1) cells treated with Bev only 2) cells treated with β-catenin-siRNA 3) cells treated with Bev-β-cat-siRNA 4) cells treated with negative control 5) cells treated with Bev-negative control and untreated cells. Expressions were assessed using qPCR and western blotting.

RESULTS

Bev-β-cat-siRNA significantly reduced the mRNA level of VEGF-A, which was initially increased in response to Bev alone in HepG2 but not in Caco-2. Additionally, Bev-β-cat-siRNA significantly decreased Slug mRNA level compared to Bev only treated HepG2 cells. In contrast, VEGF-A and Slug mRNA levels in Bev only group were remarkably lower than Bev-β-cat-siRNA in Caco-2 cells. Distinct β-catenin and Slug protein expressions were noticed in HepG2 and Caco-2 cells. On the other hand, Bev-β-cat-siRNA remarkably reduced the level of NFКB, FasR and c-Flip compared to Bev only treated HepG2 cells although the difference was not statistically significant.

CONCLUSION

We conclude that, combining Bevacizumab with knocked down β-catenin reduce the expression of VEGF-A and Slug in HepG2 but not in Caco-2 cells.

A Computational Model of the Endothelial to Mesenchymal Transition

Endothelial cells (ECs) form the lining of lymph and blood vessels. Changes in tissue requirements or wounds may cause ECs to behave as tip or stalk cells. Alternatively, they may differentiate into mesenchymal cells (MCs). These processes are known as EC activation and endothelial-to-mesenchymal transition (EndMT), respectively. EndMT, Tip, and Stalk EC behaviors all require SNAI1, SNAI2, and Matrix metallopeptidase (MMP) function. However, only EndMT inhibits the expression of VE-cadherin, PECAM1, and VEGFR2, and also leads to EC detachment. Physiologically, EndMT is involved in heart valve development, while a defective EndMT regulation is involved in the physiopathology of cardiovascular malformations, congenital heart disease, systemic and organ fibrosis, pulmonary arterial hypertension, and atherosclerosis. Therefore, the control of EndMT has many promising potential applications in regenerative medicine. Despite the fact that many molecular components involved in EC activation and EndMT have been characterized, the system-level molecular mechanisms involved in this process have not been elucidated. Toward this end, hereby we present Boolean network model of the molecular involved in the regulation of EC activation and EndMT. The simulated dynamic behavior of our model reaches fixed and cyclic patterns of activation that correspond to the expected EC and MC cell types and behaviors, recovering most of the specific effects of simple gain and loss-of-function mutations as well as the conditions associated with the progression of several diseases. Therefore, our model constitutes a theoretical framework that can be used to generate hypotheses and guide experimental inquiry to comprehend the regulatory mechanisms behind EndMT. Our main findings include that both the extracellular microevironment and the pattern of molecular activity within the cell regulate EndMT. EndMT requires a lack of VEGFA and sufficient oxygen in the extracellular microenvironment as well as no FLI1 and GATA2 activity within the cell. Additionally Tip cells cannot undergo EndMT directly. Furthermore, the specific conditions that are sufficient to trigger EndMT depend on the specific pattern of molecular activation within the cell.

Molecular regulation of Snai2 in development and disease

The transcription factor Snai2, encoded by the SNAI2 gene, is an evolutionarily conserved C2H2 zinc finger protein that orchestrates biological processes critical to tissue development and tumorigenesis. Initially characterized as a prototypical epithelial-to-mesenchymal transition (EMT) transcription factor, Snai2 has been shown more recently to participate in a wider variety of biological processes, including tumor metastasis, stem and/or progenitor cell biology, cellular differentiation, vascular remodeling and DNA damage repair. The main role of Snai2 in controlling such processes involves facilitating the epigenetic regulation of transcriptional programs, and, as such, its dysregulation manifests in developmental defects, disruption of tissue homeostasis, and other disease conditions. Here, we discuss our current understanding of the molecular mechanisms regulating Snai2 expression, abundance and activity. In addition, we outline how these mechanisms contribute to disease phenotypes or how they may impact rational therapeutic targeting of Snai2 dysregulation in human disease.

PM2.5, Fine Particulate Matter: A Novel Player in the Epithelial-Mesenchymal Transition?

Epithelial-mesenchymal transition (EMT) refers to the conversion of epithelial cells to mesenchymal phenotype, which endows the epithelial cells with enhanced migration, invasion, and extracellular matrix production abilities. These characteristics link EMT with the pathogenesis of organ fibrosis and cancer progression. Recent studies have preliminarily established that fine particulate matter with an aerodynamic diameter of less than 2.5 μm (PM_2.5) is correlated with EMT initiation. In this pathological process, PM_2.5 particles, excessive reactive oxygen species (ROS) derived from PM_2.5, and certain components in PM_2.5, such as ions and polyaromatic hydrocarbons (PAHs), have been implicated as potential EMT mediators that are linked to the activation of transforming growth factor β (TGF-β)/SMADs, NF-κB, growth factor (GF)/extracellular signal-regulated protein kinase (ERK), GF/phosphatidylinositol 3-kinase (PI3K)/Akt, wingless/integrated (Wnt)/β-catenin, Notch, Hedgehog, high mobility group box B1 (HMGB1)-receptor for advanced glycation end-products (RAGE), and aryl hydrocarbon receptor (AHR) signaling cascades and to cytoskeleton rearrangement. These pathways directly and indirectly transduce pro-EMT signals that regulate EMT-related gene expression in epithelial cells, finally inducing the characteristic alterations in morphology and functions of epithelia. In addition, novel associations between autophagy, ATP citrate lyase (ACLY), and exosomes with PM_2.5-induced EMT have also been summarized. However, some debates and paradoxes remain to be consolidated. This review discusses the potential molecular mechanisms underlying PM_2.5-induced EMT, which might account for the latent role of PM_2.5 in cancer progression and fibrogenesis.

Substrate elasticity regulates adipose-derived stromal cell differentiation towards osteogenesis and adipogenesis through β-catenin transduction

It is generally recognised that mesenchymal stem cells (MSCs) can differentiate into multiple lineages through guidance from the biophysical properties of the substrates. However, the precise biophysical mechanism that enables MSCs to respond to substrate properties remains unclear. In the current study, polydimethylsiloxane (PDMS) substrates with different stiffnesses were fabricated and the way in which the elastic modulus of the substrate regulated differentiation towards osteogenesis and adipogenesis in adipose-derived stromal cells (ASCs) was explored. Initially, a cell morphology change by SEM was observed between the stiff and soft substrates. The cytoskeleton stains including microfilament by F-actin and microtubule by α- and β-tubulin further showed a larger cell spreading area on the stiff substrate. Then the expression of vinculin, in charge for the linkage of adhesion molecules to the actin cytoskeleton, was enhanced on the stiff substrate. This change in focal adhesion plaque further triggered intracellular β-catenin signaling and promoted its nuclear translocation especially on the stiff substrate. The influence of β-catenin signaling on direct differentiation to osteogenic lineages was through direct binding between its downstream protein, Lef-1, and the osteogenic transcriptional factors, Runx2 and Osx, while on differentiation to adipogenic lineages was through modulating the expression of PPARγ. The imbalance of stiffness-induced β-catenin signaling finally induced a stronger osteogenesis and a weaker adipogenesis on the stiff substrate relative to those on the soft substrate. This study indicates the importance of stiffness on ASC differentiation and could help to increase understanding of the mechanism underlying molecular signal transduction from mechanosensing, mechanotransducing to stem cell differentiation.

STATEMENT OF SIGNIFICANCE

Mesenchymal stem cells can differentiate into multiple lineages, such as adipogenesis, myogenesis, neurogenesis, angiogenesis and osteogenesis, through influence of biophysical properties of the extracellular matrix. However, the precise bio-mechanism that triggers stem cell differentiation in response to matrix biophysical properties remains unclear. In the current study, we provide a series of experiments involving the characterization of cell morphology, microfilament, microtubule and adhesion capacity of adipose-derived stromal cells (ASCs) in response to substrate stiffness, and further elucidation of cytoplasmic β-catenin-dependent signal transduction, nuclear translocation and resultant promoter activation of transcriptional factors for osteogenesis and adipogenesis. This study provides an explanation on deeper understanding of bio-mechanism underlying substrate stiffness-triggered β-catenin signal transduction from active mechanosensing, mechanotransducing to stem cell differentiation.

Frequently rearranged and overexpressed δ-catenin is responsible for low sensitivity of prostate cancer cells to androgen receptor and β-catenin antagonists

The mechanism of prostate cancer (PCa) progression towards the hormone refractory state remains poorly understood. Treatment options for such patients are limited and present a major clinical challenge. Previously, δ-catenin was reported to promote PCa cell growth in vitro and its increased level is associated with PCa progression in vivo. In this study we show that re-arrangements at Catenin Delta 2 (CTNND2) locus, including gene duplications, are very common in clinically significant PCa and may underlie δ-catenin overexpression. We find that δ-catenin in PCa cells exists in a complex with E-cadherin, p120, and α- and β-catenin. Increased expression of δ-catenin leads to its further stabilization as well as upregulation and stabilization of its binding partners. Resistant to degradation and overexpressed δ-catenin isoform activates Wnt signaling pathway by increasing the level of nuclear β-catenin and subsequent stimulation of Tcf/Lef transcription targets. Evaluation of responses to treatments, with androgen receptor (AR) antagonist and β-catenin inhibitors revealed that cells with high levels of δ-catenin are more resistant to killing with single agent treatment than matched control cells. We show that combination treatment targeting both AR and β-catenin networks is more effective in suppressing tumor growth than targeting a single network. In conclusion, targeting clinically significant PCa with high levels of δ–catenin with anti-androgen and anti β-catenin combination therapy may prevent progression of the disease to a castration-resistant state and, thus, represents a promising therapeutic strategy.

Low-level overexpression of p53 promotes warfarin-induced calcification of porcine aortic valve interstitial cells by activating Slug gene transcription

The most frequently used oral anti-coagulant warfarin has been implicated in inducing calcification of aortic valve interstitial cells (AVICs), whereas the mechanism is not fully understood. The low-level activation of p53 is found to be involved in osteogenic transdifferentiation and calcification of AVICs. Whether p53 participates in warfarin-induced AVIC calcification remains unknown. In this study, we investigated the role of low-level p53 overexpression in warfarin-induced porcine AVIC (pAVIC) calcification. Immunostaining, quantitative PCR, and Western blotting revealed that p53 was expressed in human and pAVICs and that p53 expression was slightly increased in calcific human aortic valves compared with non-calcific valves. Terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling staining indicated that apoptosis slightly increased in calcific aortic valves than in non-calcific valves. Warfarin treatment led to a low-level increase of p53 mRNA and protein in both pAVICs and mouse aortic valves. Low-level overexpression of p53 in pAVICs via an adenovirus vector did not affect pAVIC apoptosis but promoted warfarin-induced calcium deposition and expression of osteogenic markers. shRNA-mediated p53 knockdown attenuated the pAVIC calcium deposition and osteogenic marker expression. Moreover, ChIP and luciferase assays showed that p53 was recruited to the slug promoter and activated slug expression in calcific pAVICs. Of note, overexpression of Slug increased osteogenic marker Runx2 expression, but not pAVIC calcium deposition, and Slug knockdown attenuated pAVIC calcification and p53-mediated pAVIC calcium deposition and expression of osteogenic markers. In conclusion, we found that p53 plays an important role in warfarin induced pAVIC calcification, and increased slug transcription by p53 is required for p53-mediated pAVIC calcification.

Wnt signaling pathway protein LEF1 in cancer, as a biomarker for prognosis and a target for treatment

Transcription factors are regulatory proteins that either activate or repress the transcription of genes via binding to DNA regulatory sequences and regulating recruitment of transcriptional complexes. Lymphoid enhancer-binding factor 1 (LEF1), a member of the T-cell Factor (TCF)/LEF1 family of high-mobility group transcription factors, is a downstream mediator of the Wnt/β-catenin signaling pathway, but can also modulate gene transcription independently. LEF1 is essential in stem cell maintenance and organ development, especially in its role in epithelial-mesenchymal transition (EMT) by activating the transcription of hallmark EMT effectors including N-Cadherin, Vimentin, and Snail. Aberrant expression of LEF1 is implicated in tumorigenesis and cancer cell proliferation, migration, and invasion. LEF1's activity in particular cancer cell types, such as chronic lymphocytic leukemia (CLL), Burkitt lymphoma (BL), acute lymphoblastic leukemia (ALL), oral squamous cell carcinoma (OSCC), and colorectal cancer (CRC), makes it a valuable biomarker in predicting patient prognosis. Additionally, due to aberrant LEF1 activity resulting in cancer progression, knockdown and inhibition treatments designed to target LEF1 have proven effective in alleviating cancer growth, migration, and invasion in CLL, CRC, glioblastoma multiforme (GBM), and renal cell carcinoma (RCC). In prostate cancer cells, LEF1 promotes androgen receptor expression and activity in an androgen-independent manner, ultimately increasing prostate cancer growth regardless of androgen ablation therapy. In this review, we review LEF1 regulation, its role in tumorigenesis in several cancer types, and its clinical value as a biomarker for predicting prognoses and as a target for treatment.

NOR1 Suppresses Cancer Stem-Like Cells Properties of Tumor Cells via the Inhibition of the AKT-GSK-3β-Wnt/β-catenin-ALDH1A1 Signal Circuit

Cancer stem cells (CSCs) play a key role in tumor radiotherapy and chemotherapy resistance, relapse, and metastasis, and are primarily maintained in a resting state in vivo. The failure of conventional therapies to target CSCs is the main cause of treatment failure. The discovery of CSCs in nasopharyngeal carcinoma (NPC) tumors is becoming more prevalent; however, the understanding of the mechanisms underlying the maintenance of tumor stemness is still limited. We previously cloned NOR1, a tumor suppressor gene downregulated in NPC cell lines and tissues. In this study, we demonstrate that Wnt/β-catenin and ALDH1A1 form a signal circuit and that NOR1 antagonizes the tumor stem cell-like phenotype in NPC cell lines: the ectopic overexpression of NOR1 reduced β-catenin and ALDH1A1 expression; β-catenin/TCF4 targeted the regulation of ALDH1A1 transcription in NPC cells; silencing ALDH1A1 reduced AKT (total and phosphorylated) and GSK-3β (phosphorylated) expression; and eventually feedback decreased β-catenin expression levels. We also found that NOR1 expression decreased cancer stem-like cell properties of NPC cells, reduced their ability to form tumor spheroids in vitro, reduced tumorigenicity in nude mice in vivo, and increased sensitivity to chemotherapy agents. Taken together, our findings illustrated a new function of NOR1 that suppresses cancer stem-like cell properties in tumor cells by inhibiting the AKT-GSK-3β-Wnt/β-catenin-ALDH1A1 signal circuit. The study suggests that NOR1 deletion expression in NPC cells may be a potential molecular target for cancer stem cell therapy. J. Cell. Physiol. 232: 2829-2840, 2017. © 2016 Wiley Periodicals, Inc.

The Emerging Roles of RUNX Transcription Factors in Epithelial-Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is an evolutionary conserved morphogenetic program necessary for the shaping of the body plan during development. It is guided precisely by growth factor signaling and a dedicated network of specialised transcription factors. These are supported by other transcription factor families serving auxiliary functions during EMT, beyond their general roles as effectors of major signaling pathways. EMT transiently induces in epithelial cells mesenchymal properties, such as the loss of cell-cell adhesion and a gain in cell motility. Together, these newly acquired properties enable their migration to distant sites where they eventually give rise to adult epithelia. However, it is now recognized that EMT contributes to the pathogenesis of several human diseases, notably in tissue fibrosis and cancer metastasis. The RUNX family of transcription factors are important players in cell fate determination during development, where their spatio-temporal expression often overlaps with the occurrence of EMT. Furthermore, the dysregulation of RUNX expression and functions are increasingly linked to the aberrant induction of EMT in cancer. The present chapter reviews the current knowledge of this emerging field and the common themes of RUNX involvement during EMT, with the intention of fostering future research.

Repression of Wnt/β-catenin response elements by p63 (TP63)

Submitted: TP63 (p63), a member of the tumor suppressor TP53 (p53) gene family, is expressed in keratinocyte stem cells and well-differentiated squamous cell carcinomas to maintain cellular potential for growth and differentiation. Controversially, activation of the Wnt/β-catenin signaling by p63 (Patturajan M. et al., 2002, Cancer Cells) and inhibition of the target gene expression (Drewelus I. et al., 2010, Cell Cycle) have been reported. Upon p63 RNA-silencing in squamous cell carcinoma (SCC) lines, a few Wnt target gene expression substantially increased, while several target genes moderately decreased. Although ΔNp63α, the most abundant isoform of p63, appeared to interact with protein phosphatase PP2A, neither GSK-3β phosphorylation nor β-catenin nuclear localization was altered by the loss of p63. As reported earlier, ΔNp63α enhanced β-catenin-dependent luc gene expression from pGL3-OT having 3 artificial Wnt response elements (WREs). However, this activation was detectable only in HEK293 cells examined so far, and involved a p53 family-related sequence 5' to the WREs. In Wnt3-expressing SAOS-2 cells, ΔNp63α rather strongly inhibited transcription of pGL3-OT. Importantly, ΔNp63α repressed WREs isolated from the regulatory regions of MMP7. ΔNp63α-TCF4 association occurred in their soluble forms in the nucleus. Furthermore, p63 and TCF4 coexisted at a WRE of MMP7 on the chromatin, where β-catenin recruitment was attenuated. The combined results indicate that ΔNp63α serves as a repressor that regulates β-catenin-mediated gene expression.

RCP induces Slug expression and cancer cell invasion by stabilizing β1 integrin

Rab coupling protein (RCP)-induced tumor cell migration has been implicated in tumor pathophysiology and patient outcomes. In the present study, we demonstrate that RCP stabilizes β1 integrin leading to increased β1 integrin levels and activation of a signaling cascade culminating in Slug induction, epithelial-to-mesenchymal transition and increased invasion. Ectopic expression of RCP induced Slug expression. Silencing β1 integrin efficiently inhibited RCP-induced Slug expression and subsequent cancer cell invasion. Conversely, ectopic expression of β1 integrin was sufficient to induce Slug expression. Pharmacological inhibition of integrin linked kinase (ILK), EGFR and NF-κB, as well as transfection of a dominant-negative mutant of Ras (RasN17), significantly inhibited RCP-induced Slug expression and cancer cell invasion. Strikingly, ectopic expression of RCP was sufficient to enhance metastasis of ovarian cancer cells to the lung. Collectively, we demonstrate a mechanism by which RCP promotes cancer cell aggressiveness through sequential β1 integrin stabilization, activation of an ILK/EGFR/Ras/NF-κB signaling cascade and subsequent Slug expression.

Glycyrrhizic acid attenuates stem cell-like phenotypes of human dermal papilla cells

BACKGROUND

Although the growth of unwanted hair or hirsutism is a harmless condition, many people find it bothersome and embarrassing. Maintaining stem cell features of dermal papilla cells is a critical biological process that keeps the high rate of hair growth. Glycyrrhizic acid has been reported to impair hair growth in some studies; however, its underlying mechanism has not yet been investigated.

PURPOSE

This study aimed to explore the effect and underlying mechanism of glycyrrhizic acid on stemness of human dermal papilla cells.

STUDY DESIGN/METHODS

The stem cell molecular markers, epithelial to mesenchymal markers and Wnt/β-catenin-associated proteins of human dermal papilla cell line and primary human dermal papilla cells were analysed by western blot analysis and immunocytochemistry.

RESULTS

The present study demonstrated that glycyrrhizic acid significantly depressed the stemness of dermal papilla cells in dose- and time-dependent manners. Clonogenicity and stem cell markers in the glycyrrhizic acid-treated cells were found to gradually decrease in the culture in a time-dependent manner. Our results demonstrated that glycyrrhizic acid exerted the stem cell suppressing effects through the interruption of ATP-dependent tyrosine kinase/glycogen synthase kinase3β-dependent mechanism which in turn down-regulated the β-catenin signalling pathway, coupled with decreased its down-stream epithelial-mesenchymal transition and self-renewal transcription factors, namely, Oct-4, Nanog, Sox2, ZEB1 and Snail. The effect of glycyrrhizic acid on the reduction of stem cell features was also observed in the primary dermal papilla cells directly obtained from human hair follicles.

CONCLUSION

These results revealed a novel molecular mechanism of glycyrrhizic acid in regulation of dermal papilla cells and provided the evidence supporting the use of this compound in suppressing the growth of unwanted hair.

Ciprofloxacin Improves the Stemness of Human Dermal Papilla Cells

Improvement in the expansion method of adult stem cells may augment their use in regenerative therapy. Using human dermal papilla cell line as well as primary dermal papilla cells as model systems, the present study demonstrated that ciprofloxacin treatment could prevent the loss of stemness during culture. Clonogenicity and stem cell markers of dermal papilla cells were shown to gradually decrease in the culture in a time-dependent manner. Treatment of the cells with nontoxic concentrations of ciprofloxacin could maintain both stem cell morphology and clonogenicity, as well as all stem cells markers. We found that ciprofloxacin exerted its effect through ATP-dependent tyrosine kinase/glycogen synthase kinase3β dependent mechanism which in turn upregulated β-catenin. Besides, ciprofloxacin was shown to induce epithelial-mesenchymal transition in DPCs as the transcription factors ZEB1 and Snail were significantly increased. Furthermore, the self-renewal proteins of Wnt/β-catenin pathway, namely, Nanog and Oct-4 were significantly upregulated in the ciprofloxacin-treated cells. The effects of ciprofloxacin in preserving stem cell features were confirmed in the primary dermal papilla cells directly obtained from human hair follicles. Together, these results revealed a novel application of ciprofloxacin for stem cell maintenance and provided the underlying mechanisms that are responsible for the stemness in dermal papilla cells.

Gene expression profiles induced by growth factors in in vitro cultured osteoblasts

Objectives

Effects of insulin-like growth factor 1 (IGF1), fibroblast growth factor 2 (FGF2) and bone morphogenetic protein 2 (BMP2) on the expression of genes involved in the proliferation and differentiation of osteoblasts in culture were analysed. The best sequence of growth factor addition that induces expansion of cells before their differentiation was sought.

Methods

Primary human osteoblasts in in vitro culture were treated with IGF1, BMP2 or FGF2 (10 ng/ml) for 24 hours (IGF1) or 48 hours (BMP2 and FGF2). Experiments were performed during the exponential growth phase with approximately 1e7 cells per 75 cm² flask. mRNA was reverse transcribed directly and analysed using RT-PCR Taqman assays. Expression levels of key genes involved in cell growth and differentiation (CDH11, TNFRSF11B, RUNX2, POSTN, ALP, WNT5A, LEF1, HSPA5, FOS, p21) were monitored using RT-PCR with gene-specific Taqman probes.

Results

Autocrine expression of BMP2 is stimulated by FGF2 and BMP2 itself. BMP2 and FGF2 act as proliferative factors as indicated by reduced expression of ALP and POSTN, whereas IGF1 exhibits a more subtle picture: the Wingless und Int-1 (Wnt) signalling pathway and the Smad pathway, but not p38 mitogen-activated protein (MAP) kinase signalling, were shown to be activated by IGF1, leading to proliferation and differentiation of the cells.

Conclusions

For future use of autologous bone cells in the management of bony defects, new treatment options take advantage of growth factors and differentiation factors. Thus, our results might help to guide the timely application of these factors for the expansion and subsequent differentiation of osteoblastic cells in culture.

Cite this article: Bone Joint Res 2014;3:236–40.

hRAD9 functions as a tumor suppressor by inducing p21-dependent senescence and suppressing epithelial-mesenchymal transition through inhibition of Slug transcription

Senescence and epithelial-mesenchymal transition (EMT) have opposing roles in tumor progression, in that, one is a barrier against tumorigenesis, whereas the other is required for invasive malignancies. Here, we report that the DNA damage response (DDR) protein hRAD9 contributes to induction of senescence and inhibition of EMT. Our data show that hRAD9 is frequently downregulated in breast and lung cancers. Loss of hRAD9 expression is associated with tumor stage in breast and lung cancers, as well as with acquisition of an invasive phenotype. Ectopic hRAD9 expression in highly invasive cancer cell lines, H1299 and MDA-MB 231, with low endogenous hRAD9 induced senescence by upregulation of nuclear p21, independent of the p53 status. Ectopic expression of hRAD9 also significantly attenuated cellular migration and invasion in vitro and tumor growth in a xenograft mouse model in vivo. In contrast, silencing hRAD9 in lower invasive cancer cell lines, A549 and MCF7, with high endogenous hRAD9 dramatically increased their migration and invasion abilities, and simultaneously activated EMT. Knockdown of hRAD9 increased, whereas ectopic expression of hRAD9 decreased, the expression of Slug. Moreover, hRAD9 directly bound to the promoter region of slug gene and repressed its transcriptional activity. Taken together, these results suggest that hRAD9 is a potential tumor suppressor in breast and lung cancers and that it is likely to function by upregulating p21 and inhibiting Slug to regulate tumorigenesis.

Compensatory regulation of the Snai1 and Snai2 genes during chondrogenesis

Endochondral bone formation is a multistep process during which a cartilage primordium is replaced by mineralized bone. Several genes involved in cartilage and bone development have been identified as target genes for the Snail family of zinc finger transcriptional repressors, and a gain-of-function study has demonstrated that upregulation of Snai1 activity in mouse long bones caused a reduction in bone length. However, no in vivo loss-of-function studies have been performed to establish whether Snail family genes have an essential, physiological role during normal bone development. We demonstrate here that the Snai1 and Snai2 genes function redundantly during embryonic long bone development in mice. Deletion of the Snai2 gene, or limb bud-specific conditional deletion of the Snai1 gene, did not result in obvious defects in the skeleton. However, limb bud-specific Snai1 deletion on a Snai2 null genetic background resulted in substantial defects in the long bones of the limbs. Long bones of the Snai1/Snai2 double mutants exhibited defects in chondrocyte morphology and organization, inhibited trabecular bone formation, and delayed ossification. Chondrocyte proliferation was markedly reduced, and transcript levels of genes encoding cell cycle regulators, such as p21(Waf1/Cip1) , were strikingly upregulated in the Snai1/Snai2 double mutants, suggesting that during chondrogenesis Snail family proteins act to control cell proliferation by mediating expression of cell-cycle regulators. Snai2 transcript levels were increased in Snai1 mutant femurs, whereas Snai1 transcript levels were increased in Snai2 mutant femurs. In addition, in the mutant femurs the Snai1 and Snai2 genes compensated for each other's loss not only quantitatively, but also by expanding their expression into the other genes' normal expression domains. These results demonstrate that the Snai1 and Snai2 genes transcriptionally compensate temporally, spatially, and quantitatively for each other's loss, and demonstrate an essential role for Snail family genes during chondrogenesis in mice.

IGF2BP1 promotes mesenchymal cell properties and migration of tumor-derived cells by enhancing the expression of LEF1 and SNAI2 (SLUG)

The oncofetal IGF2 mRNA-binding protein 1 (IGF2BP1) controls the migration and invasiveness of primary as well as tumor-derived cells in vitro. Whether the protein also modulates epithelial-mesenchymal-transition (EMT), a hallmark of tumor progression involved in tumor cell dissemination, remained elusive. In this study, we reveal that IGF2BP1 enhances mesenchymal-like cell properties in tumor-derived cells by promoting the expression of the transcriptional regulators LEF1 and SLUG (SNAI2). IGF2BP1 associates with LEF1 transcripts and prevents their degradation in a 3′-UTR-dependent manner resulting in an upregulation of LEF1 expression. LEF1 promotes transcription of the mesenchymal marker fibronectin by associating with the fibronectin 1 promoter. Moreover, LEF1 enforces the synthesis of the ‘EMT-driving’ transcriptional regulator SNAI2. Accordingly, IGF2BP1 knockdown causes MET-like (mesenchymal-epithelial-transition) morphological changes, enhances the formation of cell–cell contacts and reduces cell migration in various mesenchymal-like tumor-derived cells. However, in epithelial-like tumor-derived cells characterized by a lack or low abundance of IGF2BP1, the protein fails to induce EMT. These findings identify IGF2BP1 as a pro-mesenchymal post-transcriptional determinant, which sustains the synthesis of ‘EMT-driving’ transcriptional regulators, mesenchymal markers and enhances tumor cell motility. This supports previous reports, suggesting a role of IGF2BP1 in tumor cell dissemination.

The SNAI1 and SNAI2 proteins occupy their own and each other's promoter during chondrogenesis

Two Snail family genes, Snai1 and Snai2, encode E2 box-binding transcriptional repressors that are important for cartilage development during long bone formation in mice. We demonstrated previously that the Snai1 and Snai2 genes function redundantly, and compensate for each other's loss during mouse chondrogenesis in vivo. A prediction from this genetic data is that the SNAI1 and SNAI2 proteins can bind to each other's promoter to regulate gene expression. Here we demonstrate that expression of Snai1 and Snai2 RNA and protein is induced during chondrogenic differentiation of cultured mouse ATDC5 cells. Using chromatin immunoprecipitation assays, we then show that endogenous SNAI1 and SNAI2 proteins bind to a subset of E2 boxes in both their own and each other's promoter in differentiating ATDC5 cells. Together with our previous genetic data, these results support the model that expression of the Snai1 and Snai2 genes is negatively regulated by their protein products occupying each other's promoter during chondrogenesis, and help provide an explanation for the genetic redundancy observed in the mouse loss of function models.

Role of Slug transcription factor in human mesenchymal stem cells

The pathways that control mesenchymal stem cells (MSCs) differentiation are not well understood, and although some of the involved transcription factors (TFs) have been characterized, the role of others remains unclear. We used human MSCs from tibial plateau (TP) trabecular bone, iliac crest (IC) bone marrow and Wharton’s jelly (WJ) umbilical cord demonstrating a variability in their mineral matrix deposition, and in the expression levels of TFs including Runx2, Sox9, Sox5, Sox6, STAT1 and Slug, all involved in the control of osteochondroprogenitors differentiation program. Because we reasoned that the basal expression level of some TFs with crucial role in the control of MSC fate may be correlated with osteogenic potential, we considered the possibility to affect the hMSCs behaviour by using gene silencing approach without exposing cells to induction media. In this study we found that Slug-silenced cells changed in morphology, decreased in their migration ability, increased Sox9 and Sox5 and decreased Sox6 and STAT1 expression. On the contrary, the effect of Slug depletion on Runx2 was influenced by cell type. Interestingly, we demonstrated a direct in vivo regulatory action of Slug by chromatin immunoprecipitation, showing a specific recruitment of this TF in the promoter of Runx2 and Sox9 genes. As a whole, our findings have important potential implication on bone tissue engineering applications, reinforcing the concept that manipulation of specific TF expression levels may elucidate MSC biology and the molecular mechanisms, which promote osteogenic differentiation.

S100A4 regulates motility and invasiveness of human esophageal squamous cell carcinoma through modulating the AKT/Slug signal pathway

The involvement of S100A4 in modulating invasiveness of esophageal squamous cell carcinoma (ESCC) cell lines was explored. It was shown that S100A4 expression is positively correlated with the degree of invasiveness in human ESCC cells. The S100A4-rich EC-1 cells displayed higher migratory and invasive cell behavior while ET-1 cells with low S100A4 expression levels displayed lower migratory and invasive cell behavior. S100A4 silencing by small interfering (siRNA) in EC-1 cells induced E-cadherin expression, and overexpression of S100A4 in a lowly invasive TE-1 cells suppressed E-cadherin expression. It is suggested that S100A4 silencing inhibit invasion via E-cadherin upregulation, and overexpression of S100A4 promote invasion via E-cadherin downregulation in ESCC cells. Compared with the vector-transfected cells, S100A4 silencing in EC-1 cells showed reduced ability of migration and invasiveness, and overexpression of S100A4 in TE-1 cells showed increased ability of migration and invasiveness via wound-healing and Transwell assay, and pseudometastatic model assay. Furthermore, re-expression of S100A4 could increase the invasive phenotypes in S100A4 siRNA transfected EC-1 cells, and S100A4 silencing could decrease the invasive phenotypes in S100A4 circular DNA (cDNA) transfected TE-1 cells. It was found that Slug is downregulated in S100A4 siRNA transfected EC-1 cells, and Slug is upregulated in S100A4 cDNA transfected TE-1 cells. It was also discovered S100A4 cDNA induced protein kinase B (AKT) phosphorylation at Serine-473(phospho-AKT [p-AKT]) levels, followed by the Slug upregulation, and S100A4 siRNA decreases the phospho-AKT levels, followed by the Slug downregulation. The data suggested that S100A4 could regulate migratory and invasive behavior of human ESCC cells through modulating AKT/Slug pathway.

Hepatocyte growth factor activates Wnt pathway by transcriptional activation of LEF1 to facilitate tumor invasion

Hepatocyte growth factor (HGF) is a secretory protein that plays important roles in cancer growth and metastasis. Lymphoid-enhancing factor 1 (LEF1) is a transcription factor mediating Wnt/β-catenin signaling. Using microarray analysis, we found HGF induced expression of LEF1 in liver and breast cancer cell lines. HGF induced expression of LEF1 through phosphatidylinositol 3-kinase/Akt and nuclear factor-kappa B (NF-κB) signaling. Multiple NF-κB-binding sites were mapped within 3 kb upstream of LEF1 transcription initiation site. NF-κB binding to a site 2 kb upstream of LEF1 transcription initiation site was confirmed by chromatin immunoprecipitation assay. Knockdown of LEF1 inhibited the expression of Slug and Zinc finger E-box-binding homeobox 2 (ZEB2) and markedly attenuated HGF-induced tumor migration and invasion. Using immunohistochemical staining, we found LEF1 was frequently expressed in multiple types of carcinoma but not in the non-tumorous epithelial cells. Our finding suggest that transcriptional activation of LEF1 is a mechanism of cross talk between HGF/c-Met and Wnt/β-catenin pathways and is essential for HGF-induced tumor invasion.

Regulation of breast cancer metastasis by Runx2 and estrogen signaling: the role of SNAI2

Introduction

In contrast to its role in breast cancer (BCa) initiation, estrogen signaling has a protective effect in later stages, where estrogen receptor (ER)α loss associates with aggressive metastatic disease. We asked whether the beneficial effect of estrogen signaling in late-stage BCa is attributable to the recently reported estrogen-mediated antagonism of the pro-metastatic transcription factor Runx2.

Methods

MCF7/Rx2^dox breast cancer cells were engineered with a lentivirus expressing Runx2 in response to doxycycline (dox). Cells treated with dox and/or estradiol (E2) were subjected to genome-wide expression profiling, RT-qPCR analysis of specific genes, and Matrigel™ invasion assays. Knockdown of genes of interest was performed using lentiviruses expressing appropriate shRNAs, either constitutively or in response to dox. Gene expression in BCa tumors was investigated using a cohort of 557 patients compiled from publicly available datasets. Association of gene expression with clinical metastasis was assessed by dichotomizing patients into those expressing genes of interest at either high or low levels, and comparing the respective Kaplan-Meier curves of metastasis-free survival.

Results

Runx2 induced epithelial-mesenchymal transition (EMT) evidenced by acquisition of a fibroblastic morphology, decreased expression of E-cadherin, increased expression of vimentin and invasiveness. Runx2 stimulated SNAI2 expression in a WNT- and transforming growth factor (TGF)β-dependent manner, and knockdown of SNAI2 abrogated the pro-metastatic activities of Runx2. E2 antagonized the pro-metastatic activities of Runx2, including SNAI2 upregulation. In primary BCa tumors, Runx2 activity, SNAI2 expression, and metastasis were positively correlated, and SNAI2 expression was negatively correlated with ERα. However, the negative correlation between SNAI2 and ERα in bone-seeking BCa cells was weaker than the respective negative correlation in tumors seeking lung. Furthermore, the absence of ERα in primary tumors was associated with lung- and brain- but not with bone metastasis, and tumor biopsies from bone metastatic sites displayed the unusual combination of high Runx2/SNAI2 and high ERα expression.

Conclusions

E2 antagonizes Runx2-induced EMT and invasiveness of BCa cells, partly through attenuating expression of SNAI2, a Runx2 target required for mediating its pro-metastatic property. That ERα loss promotes non-osseous metastasis by unleashing Runx2/SNAI2 is supported by the negative correlation observed in corresponding tumors. Unknown mechanisms in bone-seeking BCa allow high Runx2/SNAI2 expression despite high ERα level

Wnt/β-catenin pathway forms a negative feedback loop during TGF-β1 induced human normal skin fibroblast-to-myofibroblast transition

BACKGROUND

Fibroblast-to-myofibroblast transition is a key event during wound healing and hypertrophic scar formation. Previous studies suggested Wnt/β-catenin signaling might be involved in the wound healing. However, its specific role in skin fibroblast-to-myofibroblast transition remains unclear.

OBJECTIVE

To investigate the specific role of β-catenin during the transforming growth factor-β1 induced normal skin myofibroblasts transition.

METHODS

By real-time quantitative polymerase chain reaction, Western-blot and immunocytochemistry, the activation of Wnt/β-catenin pathway in cultured human normal skin fibroblasts during TGF-β1 induced fibroblast-to-myofibroblast transition was investigated. The effects of β-catenin on myofibroblasts transition were also investigated when SB-216763, over-expression and siRNA of β-catenin were utilized. In addition, fibroblasts populated collagen lattices contraction assays were conducted to examine the effects of β-catenin on the contractility of the fibroblasts induced by TGF-β1. Furthermore, the effects of β-catenin on the expression of α-smooth muscle actin and collagen types I and III in hypertrophic scar derived fibroblasts were studied.

RESULTS

The expression of Wnts mRNA and β-catenin protein was up-regulated by TGF-β1 stimulation during the myofibroblasts transition. Both of SB-216763 and β-catenin over-expression was paralleled with decreased expression of α-smooth muscle actin, collagen types I and III, while siRNA targeting β-catenin leads to up-regulation of α-smooth muscle actin, collagen types I and III. The increased contractility and α-smooth muscle actin expression of the fibroblasts in the collagen lattices induced by TGF-β1 was inhibited by SB-216763. In addition, the expression levels of α-smooth muscle actin, collagen types I and III in hypertrophic scar derived fibroblasts were also down-regulated by SB-216763.

CONCLUSION

Specifically in normal skin fibroblasts, β-catenin might be involved in the myofibroblasts transition and negatively regulate the TGF-β1-induced myofibroblast transition.

Loss of EBP50 stimulates EGFR activity to induce EMT phenotypic features in biliary cancer cells

Scaffold proteins form multiprotein complexes that are central to the regulation of intracellular signaling. The scaffold protein ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50) is highly expressed at the plasma membrane of normal biliary epithelial cells and binds epidermal growth factor receptor (EGFR), a tyrosine kinase receptor with oncogenic properties. This study investigated EBP50-EGFR interplay in biliary cancer. We report that in a collection of 106 cholangiocarcinomas, EBP50 was delocalized to the cytoplasm of tumor cells in 66% of the cases. Ectopic expression of EBP50 was correlated with the presence of satellite nodules and with the expression of EGFR, which was at the plasma membrane, implying a loss of interaction with EBP50 in these cases. In vitro, loss of interaction between EBP50 and EGFR was mimicked by EBP50 depletion using a small interfering RNA approach in human biliary carcinoma cells co-expressing the two proteins at their plasma membrane, and in which interaction between EBP50 and EGFR was validated. EBP50 depletion caused an increase in EGFR expression at their surface, and a sustained activation of the receptor and of its downstream effectors (extracellular signal-regulated kinase 1/2, signal transducer and activator of transcription 3) in both basal and EGF-stimulated conditions. Cells lacking EBP50 showed epithelial-to-mesenchymal transition-associated features, including reduction in E-cadherin and cytokeratin-19 expression, induction of S100A4 and of the E-cadherin transcriptional repressor, Slug, and loss of cell polarity. Accordingly, depletion of EBP50 induced the disruption of adherens junctional complexes, the development of lamellipodia structures and the subsequent acquisition of motility properties. All these phenotypic changes were prevented upon inhibition of EGFR tyrosine kinase by gefitinib. These findings indicate that loss of EBP50 at the plasma membrane in tumor cells may contribute to biliary carcinogenesis through EGFR activation.

SLUG-induced elevation of D1 cyclin in breast cancer cells through the inhibition of its ubiquitination

UbcH5c, a member of the UbcH5 family of protein ubiquitin conjugase E2 enzymes, is a critical component of biological processes in human cells, being the initial ubiquitinating enzyme of substrates like IκB, TP53, and cyclin D1. We report here that the metastasis regulator protein SLUG inhibits the expression of UbcH5c directly through chromatin remodeling and thus, among other downstream effects, elevates the level of cyclin D1, thus enhancing the growth rates of breast cancer cells. Overexpression of SLUG in the SLUG-deficient breast cancer cells significantly decreased the levels of mRNA and protein of UbcH5c but only elevated the protein levels of cyclin D1. On the contrary, knockdown of SLUG in SLUG-high breast cancer cells elevated the levels of UbcH5c while decreasing the level of cyclin D1 protein. SLUG is recruited at the E2-box sequence at the UbcH5c gene promoter along with the corepressor CtBP1 and the effector HDAC1 to silence the expression of this gene. Knockdown of UbcH5c in the SLUG-deficient human breast cells elevated the level of cyclin D1 as well as the rates of proliferation and invasiveness of these cells. Whereas the growth rates of the cells are enhanced due to overexpression of SLUG or knockdown of UbcH5c in the breast cancer cells tested, ER(+) cells also acquire resistance to the anti-estrogen 4-hydroxytamoxifen due to the rise of cyclin D1 levels in these cells. This study thus implicates high levels of SLUG and low levels of UbcH5c as a determinant in the progression of metastatic breast cancer.