Slug gene expression supports human osteoblast maturation

Integrative transcriptomics analysis reveals convergent toxicological effects of perfluorooctanoic acid and perfluorooctane sulfonate on human liver: Evidence from multiple models

Perfluorooctanoic acid and perfluorooctane sulfonate are well-known eight-carbon per- and polyfluoroalkyl substances (8C-PFAS) potentially toxic for the human liver. However, direct experimental evidence demonstrating their toxicity on the human liver remains limited. Consequently, this study aimed to extrapolate the 8C-PFAS liver toxicity mechanisms by leveraging omics data to integrate mouse and human findings. Through integration analyses of nine datasets (one human, six murine, and two rat), we identified 199 genes with known biological functions that are commonly affected by 8C-PFAS across species. We delineated a comprehensive regulatory network of 8C-PFAS toxicity, demonstrating that 8C-PFAS may trigger fatty liver disease by up-regulating CD36 and PPARα pathway; dysregulate xenobiotic metabolism by disrupting CAR and CYP family genes; and induce cancer by dysregulating WNT, TGFβ, FGF21, and P53 pathways. We also identified ATF3, EGR1, ESR1, NFATC4, SNAI2, TP53, and EZH2 as transcriptionally regulated by 8C-PFAS, along with PPARα, RXRα, FGFR1, TCF3, and SMAD3 as potentially functionally impacted. Collectively, these factors account for over 90 % of 8C-PFAS-affected key genes. This study not only developed a novel method for extrapolating human toxicity risks by integrating scattered toxicity evidence based on transcriptomics data, but also proposes new mechanisms by which 8C-PFAS contributes to fatty liver disease and cancer.

Epithelial-to-mesenchymal transition transcription factors: New strategies for mesenchymal tissue regeneration

The epithelial-mesenchymal transition transcription factors (EMT-TFs)-ZEB, SNAI, and TWIST families-have been extensively studied in embryonic development and tumor metastasis, providing valuable insight into their roles in cell behavior and transformation. These EMT-TFs have garnered increasing attention in the context of mesenchymal tissue regeneration, potentially contributing an approach for cell therapy. Given that dysregulated EMT-TF expression can impair cell survival and lineage differentiation, controlled regulation of their expression could offer significant advantages for tissue regeneration. However, there is a lack of comprehensive reviews to summarize the influence of the EMT-TFs on mesenchymal tissue regeneration and potential molecular mechanisms. This review explores the regulatory roles of ZEB, SNAI, and TWIST in the regeneration of bone, adipose, cartilage, muscle, and other mesenchymal tissues, with a focus on the underlying molecular signaling mechanisms. Gaining a deeper understanding of how EMT-TFs regulate cell proliferation, apoptosis, migration, and differentiation may offer new insights into the management of mesenchymal tissue repair and open novel avenues for enhancing tissue regeneration.

miRNAs as potential game-changers in bone diseases: Future medicinal and clinical uses

MicroRNAs (miRNAs), short, highly conserved non-coding RNA, influence gene expression by sequential mechanisms such as mRNA breakdown or translational repression. Many biological processes depend on these regulating substances, thus changes in their expression have an impact on the maintenance of cellular homeostasis and result in the emergence of a variety of diseases. Relevant studies have shown in recent years that miRNAs are involved in many stages of bone development and growth. Additionally, abnormal production of miRNA in bone tissues has been closely associated with the development of numerous bone disorders, such as osteonecrosis, bone cancer, and bone metastases. Many pathological processes, including bone loss, metastasis, the proliferation of osteosarcoma cells, and differentiation of osteoblasts and osteoclasts, are under the control of miRNAs. By bringing together the most up-to-date information on the clinical relevance of miRNAs in such diseases, this study hopes to further the study of the biological features of miRNAs in bone disorders and explore their potential as a therapeutic target.

Osteopontin (OPN/SPP1), a Mediator of Tumor Progression, Is Regulated by the Mesenchymal Transcription Factor Slug/SNAI2 in Colorectal Cancer (CRC)

Simple Summary

Expression of the transcription factor Slug/SNAI2 is associated with the epithelial–mesenchymal transition (EMT) and is correlated with poorer disease-free survival in colorectal cancer (CRC). In order to decipher the basis for the Slug-mediated aggressive phenotype, we conducted RNAseq experiments with a panel of HT-29 CRC cells expressing different levels of Slug, both in vitro and in tumor models. Osteopontin (OPN), a mediator associated with tumor progression in different tumor types, was among the top upregulated genes in both cells and tumors and was the most overexpressed gene coding for a secreted protein. We further show that Slug is a direct regulator of osteopontin via binding to the OPN promoter. Interestingly, Slug expression and osteopontin secretion were correlated in vitro, as well as in tumor models, suggesting that liquid biopsies may be useful in estimating the aggressiveness phenotype of the tumor.

Abstract

In colorectal cancer (CRC), disease-related death is closely linked to tumor aggressiveness and metastasis. Gene expression profiling of patient tumors has suggested that a more mesenchymal phenotype, present in about one-fourth of all patients, is associated with increased aggressiveness. Accordingly, the mesenchymal transcription factor Slug/SNAI2 has been associated with decreased disease-free survival. To decipher the basis for the Slug-mediated phenotype, we conducted RNAseq experiments with a panel of HT-29 CRC cells expressing different levels of Slug, both in vitro and in tumor models. The results show that osteopontin, a secreted pleotropic protein involved in multiple steps of colorectal cancer progression, was highly upregulated by Slug in vitro, as well as in vivo. We further show that Slug is a direct regulator of osteopontin at the promoter level. The levels of secreted osteopontin were correlated with Slug expression, thereby linking the tumor phenotype to a biomarker available by liquid biopsies. The results also suggest that osteopontin neutralization may attenuate at least some of the Slug-mediated functions.

Analysis of crucial genes, pathways and construction of the molecular regulatory networks in vascular smooth muscle cell calcification

Vascular calcification (VC) accompanies the trans-differentiation of vascular smooth muscle cells (VSMCs) into osteo/chondrocyte-like cells and resembles physiological bone mineralization. However, the molecular mechanisms underlying VC initiation and progression have remained largely elusive. The aim of the present study was to identify the genes and pathways common to VSMC and osteoblast calcification and construct a regulatory network of non-coding RNAs and transcription factors (TFs). To this end, the Gene Expression Omnibus dataset GSE37558 including mRNA microarray data of calcifying VSMCs (CVSMCs) and calcifying osteoblasts (COs) was analyzed. The differentially expressed genes (DEGs) were screened and functionally annotated and the microRNA (miRNA/mRNA)-mRNA, TF-miRNA and long non-coding RNA (lncRNA)-TF regulatory networks were constructed. A total of 318 DEGs were identified in the CVSMCs relative to the non-calcified VSMCs, of which 43 were shared with the COs. The CVSMC-related DEGs were mainly enriched in the functional terms cell cycle, extracellular matrix (ECM), inflammation and chemotaxis-mediated signaling pathways, of which ECM was enriched by the DEGs for the COs as well. The protein-protein interaction network of CVSMCs consisted of 281 genes and 3,650 edges. There were 30 hub genes in this network, including maternal embryonic leucine zipper kinase (MELK), which potentially regulates the differentially expressed TF (DETF) forkhead box (FOX)M1 and is a potential target gene of Homo sapiens miR-485-3p and miR-181d. The TF-miRNA network included 251 TFs and 60 miRNAs, including 10 DETFs such as FOXO1 and snail family transcriptional repressor 2 (SNAI2). Furthermore, the lncRNAs H19 imprinted maternally expressed transcript (H19) and differentiation antagonizing non-protein coding RNA (DANCR) were predicted as the upstream regulators of FOXO1 and SNAI2 in the lncRNA-TF regulatory network. DANCR, MELK and FOXM1 were downregulated, and H19, FOXO1 and SNAI2 were upregulated in the CVSMCs. Taken together, the CVSMCs and COs exhibited similar molecular changes in the ECM. In addition, the MELK-FOXM1, H19/DANCR-FOXO1 and SNAI2 regulatory pathways likely mediate VSMC calcification.

Biochemical activity of magnesium ions on human osteoblast migration

Magnesium is well known as a biodegradable biomaterial that has been reported to promote bone remodeling in several studies; however, the underlying biological mechanism remains unclear. In the present study, the role of magnesium ions in the migration of U-2 OS cells, which are osteoblast-like cell lines, was investigated. Magnesium treatment did not significantly alter the global transcriptome of U-2 OS cells, but increased the protein expression level of SNAI2, an epithelial-mesenchymal transition (EMT) marker. In addition, it was confirmed that the junctional site localization of Zona-occludens 1 (ZO-1), a representative tight junction protein, was destroyed by magnesium treatment; furthermore, it was determined that cytoplasmic localization increased, and alkaline phosphatase (ALP) activity increased. The obtained results on the mechanism by which magnesium is involved in osteoblast migration, which is important for fracture healing, will contribute to the understanding of the bone-formation process in patients with osteoporosis and musculoskeletal injury.

Implication of the p53-Related miR-34c, -125b, and -203 in the Osteoblastic Differentiation and the Malignant Transformation of Bone Sarcomas

The formation of the skeleton occurs throughout the lives of vertebrates and is achieved through the balanced activities of two kinds of specialized bone cells: the bone-forming osteoblasts and the bone-resorbing osteoclasts. Impairment in the remodeling processes dramatically hampers the proper healing of fractures and can also result in malignant bone diseases such as osteosarcoma. MicroRNAs (miRNAs) are a class of small non-coding single-strand RNAs implicated in the control of various cellular activities such as proliferation, differentiation, and apoptosis. Their post-transcriptional regulatory role confers on them inhibitory functions toward specific target mRNAs. As miRNAs are involved in the differentiation program of precursor cells, it is now well established that this class of molecules also influences bone formation by affecting osteoblastic differentiation and the fate of osteoblasts. In response to various cell signals, the tumor-suppressor protein p53 activates a huge range of genes, whose miRNAs promote genomic-integrity maintenance, cell-cycle arrest, cell senescence, and apoptosis. Here, we review the role of three p53-related miRNAs, miR-34c, -125b, and -203, in the bone-remodeling context and, in particular, in osteoblastic differentiation. The second aim of this study is to deal with the potential implication of these miRNAs in osteosarcoma development and progression.

Reciprocal Regulation of TRPS1 and miR-221 in Intervertebral Disc Cells

Intervertebral disc (IVD), a moderately moving joint located between the vertebrae, has a limited capacity for self-repair, and treating injured intervertebral discs remains a major challenge. The development of innovative therapies to reverse IVD degeneration relies primarily on the discovery of key molecules that, occupying critical points of regulatory mechanisms, can be proposed as potential intradiscal injectable biological agents. This study aimed to elucidate the underlying mechanism of the reciprocal regulation of two genes differently involved in IVD homeostasis, the miR-221 microRNA and the TRPS1 transcription factor. Human lumbar IVD tissue samples and IVD primary cells were used to specifically evaluate gene expression and perform functional analysis including the luciferase gene reporter assay, chromatin immunoprecipitation, cell transfection with hTRPS1 overexpression vector and antagomiR-221. A high-level expression of TRPS1 was significantly associated with a lower pathological stage, and TRPS1 overexpression strongly decreased miR-221 expression, while increasing the chondrogenic phenotype and markers of antioxidant defense and stemness. Additionally, TRPS1 was able to repress miR-221 expression by associating with its promoter and miR-221 negatively control TRPS1 expression by targeting the TRPS1-3'UTR gene. As a whole, these results suggest that, in IVD cells, a double-negative feedback loop between a potent chondrogenic differentiation suppressor (miR-221) and a regulator of axial skeleton development (TRPS1) exists. Our hypothesis is that the hostile degenerated IVD microenvironment may be counteracted by regenerative/reparative strategies aimed at maintaining or stimulating high levels of TRPS1 expression through inhibition of one of its negative regulators such as miR-221.

Specific concentration of hyaluronan amide derivative induces osteogenic mineralization of human mesenchymal stromal cells: Evidence of RUNX2 and COL1A1 genes modulation

Hyaluronic acid (HA) is an ideal material for tissue regeneration. The aim of this study was to investigate whether a hyaluronan amide derivative (HAD) can enhance the mineralization of human mesenchymal stem cells (hMSCs). Osteogenically induced hMSCs cultured with or without HAD at different concentrations (0.5 mg/ml or 1 mg/ml) were analyzed for mineral matrix deposition, metabolic activity, cellular proliferation, and the expression of 14 osteogenic genes. Unmodified HA (HYAL) was used as control. We demonstrated that only cells treated daily until day 28 with 0.5 mg/ml HAD, but not with 1 mg/ml of HAD and HYAL, showed a significant induction of mineralization at day 14 compared to the osteogenic control group. HAD at both concentrations tested, significantly decreased the expression of the proliferating marker MKI67 at day 2. By contrast, increased metabolic activity was induced only by HYAL from day 14. HAD at both concentrations significantly down modulated SNAI2, DLX5, RUNX2, COL1A1, and IBSP genes, while significantly up regulated COL15A1. The induction of mineralization of 0.5 mg/ml of HAD at day 14 was significantly dependent on a specific modulation of RUNX2 and COL1A1. Our data demonstrate that only 0.5 mg/ml of HAD, but not HYAL, modulated hMSCs osteogenic differentiation, suggesting that the physicochemical features and concentration of HA products could differently affect osteogenic maturation.

Osteogenesis depends on commissioning of a network of stem cell transcription factors that act as repressors of adipogenesis

Mesenchymal (stromal) stem cells (MSCs) constitute populations of mesodermal multipotent cells involved in tissue regeneration and homeostasis in many different organs. Here we performed comprehensive characterization of the transcriptional and epigenomic changes associated with osteoblast and adipocyte differentiation of human MSCs. We demonstrate that adipogenesis is driven by considerable remodeling of the chromatin landscape and de novo activation of enhancers, whereas osteogenesis involves activation of preestablished enhancers. Using machine learning algorithms for in silico modeling of transcriptional regulation, we identify a large and diverse transcriptional network of pro-osteogenic and antiadipogenic transcription factors. Intriguingly, binding motifs for these factors overlap with SNPs related to bone and fat formation in humans, and knockdown of single members of this network is sufficient to modulate differentiation in both directions, thus indicating that lineage determination is a delicate balance between the activities of many different transcription factors.

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.

The expression of cystathionine gamma-lyase is regulated by estrogen receptor alpha in human osteoblasts

Hydrogen sulfide (H2S), generated in the osteoblasts predominantly via cystathionine-γ-lyase (CSE), is bone protective. Previous studies suggested that the onset of bone loss due to estrogen deficiency is associated to decreased levels of H2S and blunted gene expression of CSE. However, there are still a lot of unknowns on how H2S levels influence bone cells function. The present study aims to explore the mechanisms by which estrogen may regulate CSE expression, in particular the role of estrogen receptor alpha (ERα) in human osteoblasts (hOBs). Vertebral lamina derived hOBs were characterized and then assessed for CSE expression by western blot analysis in the presence or absence of ERα overexpression. Bioinformatic analysis, luciferase reporter assay and ChIP assay were performed to investigate ERα recruitment and activity on hCSE gene promoter. Three putative half Estrogen Responsive Elements (EREs) were identified in the hCSE core promoter and were found to participate in the ERα - mediated positive regulation of CSE expression. All osteoblast samples responded to ERα over-expression increasing the levels of CSE protein in a comparable manner. Notably, the ERα recruitment on the regulatory regions of the CSE promoter occurred predominantly in female hOBs than in male hOBs. The obtained results suggest that CSE/H2S system is in relation with estrogen signaling in bone in a gender specific manner.

Transcription factor ZNF25 is associated with osteoblast differentiation of human skeletal stem cells

Background

The differentiation of human bone marrow derived skeletal stem cells (known as human bone marrow stromal or mesenchymal stem cells, hMSCs) into osteoblasts involves the activation of a small number of well-described transcription factors. To identify additional osteoblastic transcription factors, we studied gene expression of hMSCs during ex vivo osteoblast differentiation.

Results

Clustering of gene expression, and literature investigation, revealed three transcription factors of interest – ZNF25, ZNF608 and ZBTB38. siRNA knockdown of ZNF25 resulted in significant suppression of alkaline phosphatase (ALP) activity. This effect was not present for ZNF608 and ZBTB38. To identify possible target genes of ZNF25, we analyzed gene expression following ZNF25 siRNA knockdown. This revealed a 23-fold upregulation of matrix metallopeptidase 1 and an 18-fold upregulation of leucine-rich repeat containing G protein-coupled receptor 5 and RAN-binding protein 3-like. We also observed enrichment in extracellular matrix organization, skeletal system development and regulation of ossification in the entire upregulated set of genes. Consistent with its function as a transcription factor during osteoblast differentiation of hMSC, we showed that the ZNF25 protein exhibits nuclear localization and is expressed in osteoblastic and osteocytic cells in vivo. ZNF25 is conserved in tetrapod vertebrates and contains a KRAB (Krueppel-associated box) transcriptional repressor domain.

Conclusions

This study shows that the uncharacterized transcription factor, ZNF25, is associated with differentiation of hMSC to osteoblasts.

Targeting Androgen/Estrogen Receptors Crosstalk in Cancer

The actions of estrogens are mediated by estrogen receptors, ERα and ERβ. Recent genomic landscaping of ERα- and ERβ-binding sites has revealed important distinctions regarding their transcriptional activity. ERβ and its isoforms have been correlated with endocrine treatment responsiveness in breast tumors, while post-translational modifications, receptor dimerization patterns, and subcellular localization are increasingly recognized as crucial modulators in prostate carcinogenesis. Androgen receptor (AR) is essential for the development and progression of prostate cancer as well as of certain breast cancer types. The balance between the activity of these two hormone receptors and their molecular interactions in different clinical settings is influenced by several coregulators. This comprises a dynamic regulatory network enhancing or limiting the activity of AR-directed treatments in breast and prostate tumorigenesis. In this review, we discuss the molecular background regarding the therapeutic targeting of androgen/estrogen receptor crosstalk in breast and prostate cancer.

Calcium sensing receptor activation by calcimimetic R-568 in human amniotic fluid mesenchymal stem cells: correlation with osteogenic differentiation

Human amniotic fluid mesenchymal stem cells (hAFMSCs) are promising for therapeutic applications in bone damage. Calcium sensing receptor (CaSR), a G protein-coupled receptor, plays a physiological role in the regulation of bone metabolism. Thus, the bone CaSR could be targeted by calcimimetic agonists, which may be potentially helpful in treating bone diseases. The aim of our study was to characterize CaSR expression in hAFMSCs and to assess the activity of calcimimetic R-568 during in vitro osteogenesis. Using western blotting, immunofluorescence, and flow cytometry, we consistently observed constitutive CaSR in osteo-differentiating hAFMSCs. Notably, both R-568 and calcium significantly enhanced hAFMSC osteogenic differentiation after exposure to osteogenic medium. To provide further evidence of the involvement of CaSR in osteogenesis, we correlated its expression with that of established osteogenic markers, that is, alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), and osteopontin (OPN), and novel, not yet completely defined regulators of osteogenesis. Among these are β-catenin and Slug, which are mediators of Wnt signaling, and nuclear factor of activated T cells c1 (NFATc1), which plays a critical role in calcium/calcineurin signaling. Taken together, our results demonstrate that CaSR is expressed in hAFMSCs, positively correlates with osteogenic markers, and is activated by R-568. Notably, downregulation of CaSR by RNA interference supports the conclusion that CaSR activation plays a central role in hAFMSC osteogenesis. Thus, this study provides significant information on the mechanisms of hAFMSC osteogenesis, which could provide additional molecular basis for the use of calcimimetics in bone regenerative medicine.

Downregulation of miR-221/222 enhances sensitivity of breast cancer cells to tamoxifen through upregulation of TIMP3

Aberrantly expressed microRNAs (miRNAs) are involved in breast tumorigenesis. It is still unclear if and how miRNAs-221/222 are implicated in breast cancer and the resistance to estrogen receptor modulator tamoxifen. We investigated the roles and mechanisms of miR-221/222 in breast cancer cells, particularly in modulating response to tamoxifen therapy. MCF-7 and MDA-MB-231 breast cancer cells were transfected with antisense oligonucleotides AS-miR-221 and AS-miR-222 and their expression of miR-221 and miR-222 was assessed. The correlation of miR-221/222 with tissue inhibitor of metalloproteinase-3 (TIMP3) expression was investigated by fluorescence quantitative PCR and western blotting analysis. The therapeutic sensitivity of these cells, transfected and untransfected, to tamoxifen was determined. Transfection of AS-miR-221 and AS-miR-222 dramatically inhibited expression of miR-221 and miR-222, respectively, in both MCF-7 and MDA-MB-231 cells (P<0.05-0.01). Downregulation of miR-221/222 significantly increased the expression of TIMP3 compared with controls (P<0.05-0.01). The viability of estrogen receptor (ER)-positive MCF-7 cells transfected with AS-miR-221 or/and AS-miR-222 was significantly reduced by tamoxifen (P<0.05-0.01). We have demonstrated for the first time that suppression of miRNA-221/222 increases the sensitivity of ER-positive MCF-7 breast cancer cells to tamoxifen. This effect is mediated through upregulation of TIMP3. These findings suggest that upregulation of TIMP3 via inhibition of miRNA-221/222 could be a promising therapeutic approach for breast cancer.

Chondrogenic potential of Slug-depleted human mesenchymal stem cells

The use of short interfering RNA (siRNA) in combination with stem cells and biocompatible scaffolds is a promising strategy in regenerative medicine. Our experimental strategy was to explore the possibility of forcing or guiding the chondrogenic differentiation of human mesenchymal stem cells (hMSCs) by knocking down a negative regulator of chondrogenesis, Slug transcription factor (TF), thus altering cell behavior. We found that TGFβ-driven chondrogenic differentiation of hMSCs cultured onto a hyaluronan-based scaffold, HYAFF(®)-11, was strengthened after cell exposure to siRNA against Slug. Slug silencing was effective in promoting the expression of chondrogenic markers, including Col2A1, aggrecan, Sox9, LEF1, and TRPS1. In addition, we confirmed that HYAFF-11 is a good scaffold candidate for hMSC use in tissue engineering applications, and showed that it is effective in sustaining TGFβ3 treatment associated with a specific gene silencing. Interestingly, preliminary results from the experimental model described here suggested that, even in the absence of differentiation supplements, Slug silencing showed a pro-chondrogenic effect, highlighting both its potential use as an alternative to TGFβ treatment, and the critical role of the Slug TF in determining the fate of hMSCs.

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.

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.

Correlation between Slug transcription factor and miR-221 in MDA-MB-231 breast cancer cells

BACKGROUND

Breast cancer and its metastatic progression is mainly directed by epithelial to mesenchymal transition (EMT), a phenomenon supported by specific transcription factors and miRNAs.

METHODS

In order to investigate a possible correlation between Slug transcription factor and miR-221, we performed Slug gene silencing in MDA-MB-231 breast cancer cells and evaluated the expression of genes involved in supporting the breast cancer phenotype, using qRT-PCR and Western blot analysis. Chromatin immunoprecipitation and wound healing assays were employed to determine a functional link between these two molecules.

RESULTS

We showed that Slug silencing significantly decreased the level of miR-221 and vimentin, reactivated Estrogen Receptor α and increased E-cadherin and TRPS1 expression. We demonstrated that miR-221 is a Slug target gene, and identified a specific region of miR-221 promoter that is transcriptionally active and binds the transcription factor Slug "in vivo". In addition, we showed that in Slug-silenced cells, wich retained residual miR-221 (about 38%), cell migration was strongly inhibited. Cell migration was inhibited, but to a less degree, following complete knockdown of miR-221 expression by transfection with antagomiR-221.

CONCLUSIONS

We report for the first time evidence of a correlation between Slug transcription factor and miR-221 in breast cancer cells. These studies suggest that miR-221 expression is, in part, dependent on Slug in breast cancer cells, and that Slug plays a more important role than miR-221 in cell migration and invasion.

Estrogen receptors β1 and β2 have opposing roles in regulating proliferation and bone metastasis genes in the prostate cancer cell line PC3

The estrogen receptor (ER)β1 is successively lost during cancer progression, whereas its splice variant, ERβ2, is expressed in advanced prostate cancer. The latter form of cancer often metastasizes to bone, and we wanted to investigate whether the loss of ERβ1 and/or the expression of ERβ2 affect such signaling pathways in prostate cancer. Using PC3 and 22Rv1 prostate cancer cell lines that stably express ERβ1 or ERβ2, we found that the ERβ variants differentially regulate genes known to affect tumor behavior. We found that ERβ1 repressed the expression of the bone metastasis regulator Runx2 in PC3 cells. By contrast, RUNX2 expression was up-regulated at the mRNA level by ERβ2 in PC3 cells, whereas Slug was up-regulated by ERβ2 in both PC3 and 22Rv1 cells. In addition, the expression of Twist1, a factor whose expression strongly correlates with high Gleason grade prostate carcinoma, was increased by ERβ2. In agreement with the increased Twist1 expression, we found increased expression of Dickkopf homolog 1; Dickkopf homolog 1 is a factor that has been shown to increase the RANK ligand/osteoprotegerin ratio and enhance osteoclastogenesis, indicating that the expression of ERβ2 can cause osteolytic cancer. Furthermore, we found that only ERβ1 inhibited proliferation, whereas ERβ2 increased proliferation. The expression of the proliferation markers Cyclin E, c-Myc, and p45(Skp2) was differentially affected by ERβ1 and ERβ2 expression. In addition, nuclear β-catenin protein and its mRNA levels were reduced by ERβ1 expression. In conclusion, we found that ERβ1 inhibited proliferation and factors known to be involved in bone metastasis, whereas ERβ2 increased proliferation and up-regulated factors involved in bone metastasis. Thus, in prostate cancer cells, ERβ2 has oncogenic abilities that are in strong contrast to the tumor-suppressing effects of ERβ1.

MiR-1 and miR-200 inhibit EMT via Slug-dependent and tumorigenesis via Slug-independent mechanisms

Epithelial-mesenchymal transition (EMT) is a developmental program of signaling pathways that determine commitment to epithelial and mesenchymal phenotypes. In the prostate, EMT processes have been implicated in benign prostatic hyperplasia and prostate cancer progression. In a model of Pten- and TP53-null prostate adenocarcinoma that progresses via transforming growth factor β-induced EMT, mesenchymal transformation is characterized by plasticity, leading to various mesenchymal lineages and the production of bone. Here we show that SLUG is a major regulator of mesenchymal differentiation. As microRNAs (miRs) are pleiotropic regulators of differentiation and tumorigenesis, we evaluated miR expression associated with tumorigenesis and EMT. Mir-1 and miR-200 were reduced with progression of prostate adenocarcinoma, and we identify Slug as one of the phylogenetically conserved targets of these miRs. We demonstrate that SLUG is a direct repressor of miR-1 and miR-200 transcription. Thus, SLUG and miR-1/miR-200 act in a self-reinforcing regulatory loop, leading to amplification of EMT. Depletion of Slug inhibited EMT during tumorigenesis, whereas forced expression of miR-1 or miR-200 inhibited both EMT and tumorigenesis in human and mouse model systems. Various miR targets were analyzed, and our findings suggest that miR-1 has roles in regulating EMT and mesenchymal differentiation through Slug and functions in tumor-suppressive programs by regulating additional targets.

Human mesenchymal stem cells seeded on extracellular matrix-scaffold: viability and osteogenic potential

The development and the optimization of novel culture systems of mesenchymal osteoprogenitors are some of the most important challenges in the field of bone tissue engineering (TE). A new combination between cells and extracellular matrix (ECM)-scaffold, containing ECM has here been analyzed. As source for osteoprogenitors, mesenchymal stem cells obtained from human umbilical cord Wharton's Jelly (hWJMSCs), were used. As ECM-scaffold, a powder form of isolated and purified porcine urinary bladder matrix (pUBM), was employed. The goals of the current work were: (1) the characterization of the in vitro hWJMSCs behavior, in terms of viability, proliferation, and adhesion to ECM-scaffold; (2) the effectiveness of ECM-scaffold to induce/modulate the osteoblastic differentiation; and (3) the proposal for a possible application of cells/ECM-scaffold construct to the field of cell/TE. In this respect, the properties of the pUBM-scaffold in promoting and guiding the in vitro adhesion, proliferation, and three-dimensional colonization of hWJMSCs, without altering viability and morphological characteristics of the cells, are here described. Finally, we have also demonstrated that pUBM-scaffolds positively affect the expression of typical osteoblastic markers in hWJMSCs.

Orthopaedic research in italy: state of the art

The most significant results in experimental and clinical orthopaedic research in Italy within the last three years have been primarily in major congenital diseases, bone tumors, regenerative medicine, joint replacements, spine, tendons and ligaments. The data presented in the following discussion is comparable with leading international results, highlighting Italian orthopaedic research excellemce as well as its shortcomings.

Nuclear proteome analysis reveals a role of Vav1 in modulating RNA processing during maturation of tumoral promyelocytes

Vav1 is a key molecule in the ATRA-induced acquisition of a mature phenotype by tumoral myeloid precursors. Since ATRA acts throughout events that require extensive changes of nuclear architecture and activity and considering that Vav1 accumulates inside the nuclear compartment of differentiating APL-derived cells, the possible role of this protein in modulating the nuclear proteome was investigated. Membrane-depleted nuclei purified from NB4 cells induced to differentiate with ATRA in the presence of forcedly down-modulated Vav1 were subjected to 2D-DIGE followed by mass spectra analysis. The obtained data demonstrated that, in NB4 cells treated with ATRA, Vav1 is involved in determining the nuclear amount of proteins involved in molecular complexes with DNA and may participate to RNA processing by carrying in the nucleus molecules involved in modulating mRNA production and stability, like hnRNPs and SR proteins. Our results provide the first evidence that, at least in maturation of tumoral myeloid precursors, Vav1 is part of interconnected networks of functionally related proteins ended to regulate different aspects of gene expression. Since defects in mRNA processing are common in tumor development, our data suggest that Vav1 is a potential target molecule for developing new anti-cancer strategies.

Expression of Snail2 in long bone osteosarcomas correlates with tumour malignancy

Snail2 is a marker of malignancy in epithelial tumours; however, in sarcomas, it is not known if this protein is present. Here we examine the expression of Snail2 in one type of sarcoma, osteosarcoma, and explore its relationship to tumour grade, subtype and anatomical location in cases of long bone and cranial bone osteosarcoma. Long bone osteosarcomas typically have a much greater metastatic capability and a poorer prognosis. We find that Snail2 is expressed in the three main subtypes of long bone osteosarcoma—osteoblastic, chondroblastic and fibroblastic. Regression analysis showed that Snail 2 expression was statistically correlated with tumour grade (p = 0.014) in all of these subtypes. Snail2 was only expressed in high-grade cranial bone osteosarcomas, suggesting a link between Snail2 expression and metastasis. This is the first time Snail2 has been associated with any sarcoma, and this study shows that Snail2 may be a useful prognostic marker for this disease.

Slug contributes to the regulation of CXCL12 expression in human osteoblasts

CXCL12/CXCR4 chemokine/receptor axis signaling has recently been found to play an important role in the remodeling of bone tissue, but little is known about the molecular mechanisms that are involved. The present study shows that CXCL12 is present at high levels both in human mesenchymal stem cells (hMSCs) and primary osteoblasts (hOBs). When osteogenesis was induced, CXCL12 expression was strictly confined to mineralized nodules. To investigate what mechanisms contribute to the maintenance of a correct expression of CXCL12 in bone cellular context, we analyzed the relationship between CXCL12 and Slug, a transcription factor recently associated with osteoblast maturation. By gene silencing and chromatin immunoprecipitation assay, we showed that both proteins are required for the mineralization process and CXCL12 is transcriptionally and functionally regulated by Slug, which is recruited at specific sites to its gene promoter in vivo. These findings showed for the first time a positive correlation between CXCL12 signaling and Slug activity, thus corroborating the role of these two proteins in bone cellular context and suggesting a new potential target for bone tissue repair and regeneration.

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

Background

Lymphoid Enhancer Factor-1 (Lef-1) is a member of a transcription factor family that acts as downstream mediator of the Wnt/β-catenin signalling pathway which plays a critical role in osteoblast proliferation and differentiation. In a search for Lef-1 responsive genes in human osteoblasts, we focused on the transcriptional regulation of the SLUG, a zinc finger transcription factor belonging to the Snail family of developmental proteins. Although the role of SLUG in epithelial-mesenchymal transition and cell motility during embryogenesis is well documented, the functions of this factor in most normal adult human tissues are largely unknown. In this study we investigated SLUG expression in normal human osteoblasts and their mesenchymal precursors, and its possible correlation with Lef-1 and Wnt/β-catenin signalling.

Results

The experiments were performed on normal human primary osteoblasts obtained from bone fragments, cultured in osteogenic conditions in presence of Lef-1 expression vector or GSK-3β inhibitor, SB216763. We demonstrated that the transcription factor SLUG is present in osteoblasts as well as in their mesenchymal precursors obtained from Wharton's Jelly of human umbilical cord and induced to osteoblastic differentiation. We found that SLUG is positively correlated with RUNX2 expression and deposition of mineralized matrix, and is regulated by Lef-1 and β-catenin. Consistently, Chromatin Immunoprecipitation (ChIP) assay, used to detect the direct Lef/Tcf factors that are responsible for the promoter activity of SLUG gene, demonstrated that Lef-1, TCF-1 and TCF4 are recruited to the SLUG gene promoter "in vivo".

Conclusion

These studies provide, for the first time, the evidence that SLUG expression is correlated with osteogenic commitment, and is positively regulated by Lef-1 signal in normal human osteoblasts. These findings will help to further understand the regulation of the human SLUG gene and reveal the biological functions of SLUG in the context of bone tissue.