The endogenous ratio of Smad2 and Smad3 influences the cytostatic function of Smad3

Glial cell line-derived neurotrophic factor and its role in attenuating renal fibrosis: a review

Chronic kidney disease is estimated to affect approximately 10 to 15% of the Chinese population. Renal fibrosis is characterized by progressive extracellular matrix deposition in the kidney parenchyma with eventual tissue scarring and inevitable deterioration of renal function. Vascular rarefaction, glomerulosclerosis, interstitial inflammation, and fibrogenesis are associated with or contribute to renal fibrosis. Recent studies have revealed that glial cell-derived neurotrophic factor (GDNF) is involved in kidney morphogenesis and amelioration of renal injury. Ideal therapies targeting the pathogenesis of renal fibrosis should have the potential to inhibit glomerular and tubulointerstitial fibrosis by targeting multiple pathological events. GDNF plays a unique role in both renal development and improvement of renal fibrosis, and GDNF kidney receptors and signaling pathways can ameliorate renal apoptosis and inflammation. Our work contributes to the establishment of GDNF as an emerging therapy that can increase the effectiveness of currently used interventions to improve renal fibrosis. This literature review focuses on the important role of GDNF in renal development and its relationship with renal fibrosis.

Modulation of TGF-β signaling new approaches toward kidney disease and fibrosis therapy

The prevalence of chronic kidney disease (CKD) is increasing worldwide, posing a significant healthcare challenge. Despite the immense burden of CKD, optimal therapies remain limited in impact. Kidney fibrosis is a common mediator of all CKD progression, characterized by excessive extracellular matrix deposition and scarring of kidney parenchyma. Transforming growth factor-β (TGF-β) is a potent pro-fibrotic cytokine that signals through canonical and non-canonical pathways to promote kidney cell damage and fibrosis progression, thus garnering much interest as an optimal therapeutic target for CKD. However, the clinical translation of TGF-β inhibition in CKD and other disease settings has faced substantial challenges, particularly due to the highly pleiotropic effects of TGF-β in organ homeostasis and disease. Here, we review the kidney cell-specific biological effects of TGF-β signaling, discuss the current challenges in therapeutic targeting TGF-β in CKD, and provide the rationale for alternative targeting strategies of TGF-β signaling as potential approaches in CKD therapy. Selective inhibition of TGF-β signaling modulators to fine-tune TGF-β inhibition without a broad blockade may lead to new and safer treatments for CKD.

Analysis of the DNA-binding properties of TGF-β-activated Smad complexes unveils a possible molecular basis for cellular context-dependent signaling

Transforming growth factor-β (TGF-β) is a pleiotropic cytokine that modulates a wide variety of cellular responses by regulating target gene expression. It principally transmits signals via receptor-activated transcription factors Smad2 and Smad3, which form trimeric complexes with Smad4 upon activation and regulate gene expression by binding to genomic DNA. Here, we examined the mechanisms by which TGF-β regulates the transcription of target genes in a cell context-dependent manner by screening a double-stranded DNA oligonucleotide library for DNA sequences bound to endogenous activated Smad complexes. Screening was performed by cyclic amplification of selected targets (CASTing) using an anti-Smad2/3 antibody and nuclear extracts isolated from three cell lines (A549, HepG2, and HaCaT) stimulated with TGF-β. The preference of the activated Smad complexes for conventional Smad-binding motifs such as Smad-binding element (SBE) and CAGA motifs was different in HepG2 than in the other two cell lines, which may indicate the distinct composition of the activated Smad complexes. Several transcription factor-binding motifs other than SBE or CAGA, including the Fos/Jun-binding motifs, were detected in the enriched sequences. Reporter assays using sequences containing these transcription factor-binding motifs together with Smad-binding motifs indicated that some of the motifs may be involved in cell type-dependent transcriptional activation by TGF-β. The results suggest that the CASTing method is useful for elucidating the molecular basis of context-dependent Smad signaling.

Receptor-activated transcription factors and beyond: multiple modes of Smad2/3-dependent transmission of TGF-β signaling

Transforming growth factor β (TGF-β) is a pleiotropic cytokine that is widely distributed throughout the body. Its receptor proteins, TGF-β type I and type II receptors, are also ubiquitously expressed. Therefore, the regulation of various signaling outputs in a context-dependent manner is a critical issue in this field. Smad proteins were originally identified as signal-activated transcription factors similar to signal transducer and activator of transcription proteins. Smads are activated by serine phosphorylation mediated by intrinsic receptor dual specificity kinases of the TGF-β family, indicating that Smads are receptor-restricted effector molecules downstream of ligands of the TGF-β family. Smad proteins have other functions in addition to transcriptional regulation, including post-transcriptional regulation of micro-RNA processing, pre-mRNA splicing, and m6A methylation. Recent technical advances have identified a novel landscape of Smad-dependent signal transduction, including regulation of mitochondrial function without involving regulation of gene expression. Therefore, Smad proteins are receptor-activated transcription factors and also act as intracellular signaling modulators with multiple modes of function. In this review, we discuss the role of Smad proteins as receptor-activated transcription factors and beyond. We also describe the functional differences between Smad2 and Smad3, two receptor-activated Smad proteins downstream of TGF-β, activin, myostatin, growth and differentiation factor (GDF) 11, and Nodal.

Effect of aging on the formation and growth of colonic epithelial organoids by changes in cell cycle arrest through TGF-β-Smad3 signaling

BACKGROUND

This study aimed to investigate how aging alters the homeostasis of the colonic intestinal epithelium and regeneration after tissue injury using organoid models and to identify its underlying molecular mechanism.

METHODS

To investigate aging-related changes in the colonic intestinal epithelium, we conducted organoid cultures from old (older than 80 weeks) and young (6-10 weeks) mice and compared the number and size of organoids at day 5 of passage 0 and the growth rate of organoids between the two groups.

RESULTS

The number and size of organoids from old mice was significantly lower than that from young mice (p < 0.0001) at day 5 of passage 0. The growth rate of old-mouse organoids from day 4 to 5 of passage 0 was significantly slower than that of young-mouse organoids (2.21 times vs. 1.16 times, p < 0.001). RNA sequencing showed that TGF-β- and cell cycle-associated genes were associated with the aging effect. With regard to mRNA and protein levels, Smad3 and p-Smad3 in the old-mouse organoids were markedly increased compared with those in the young-mouse organoids. Decreased expression of ID1, increased expression of p16^INK4a, and increased cell cycle arrest were observed in the old mouse-organoids. Treatment with SB431542, a type I TGF-β receptor inhibitor, significantly increased the formation and growth of old-mouse organoids, and TGF-β1 treatment markedly suppressed the formation of young-mouse organoids. In the acute dextran sulfate sodium-colitis model and its organoid experiments, the colonic epithelial regeneration after tissue injury in old mice was significantly decreased compared with young mice.

CONCLUSIONS

Aging reduced the formation ability and growth rate of colonic epithelial organoids by increasing cell cycle arrest through TGF-β-Smad3-p16^INK4a signaling.

3D collagen migration patterns reveal a SMAD3-dependent and TGF-β1-independent mechanism of recruitment for tumour-associated fibroblasts in lung adenocarcinoma

BACKGROUND

The TGF-β1 transcription factor SMAD3 is epigenetically repressed in tumour-associated fibroblasts (TAFs) from lung squamous cell carcinoma (SCC) but not adenocarcinoma (ADC) patients, which elicits a compensatory increase in SMAD2 that renders SCC-TAFs less fibrotic. Here we examined the effects of altered SMAD2/3 in fibroblast migration and its impact on the desmoplastic stroma formation in lung cancer.

METHODS

We used a microfluidic device to examine descriptors of early protrusions and subsequent migration in 3D collagen gels upon knocking down SMAD2 or SMAD3 by shRNA in control fibroblasts and TAFs.

RESULTS

High SMAD3 conditions as in shSMAD2 fibroblasts and ADC-TAFs exhibited a migratory advantage in terms of protrusions (fewer and longer) and migration (faster and more directional) selectively without TGF-β1 along with Erk1/2 hyperactivation. This enhanced migration was abrogated by TGF-β1 as well as low glucose medium and the MEK inhibitor Trametinib. In contrast, high SMAD2 fibroblasts were poorly responsive to TGF-β1, high glucose and Trametinib, exhibiting impaired migration in all conditions.

CONCLUSIONS

The basal migration advantage of high SMAD3 fibroblasts provides a straightforward mechanism underlying the larger accumulation of TAFs previously reported in ADC compared to SCC. Moreover, our results encourage using MEK inhibitors in ADC-TAFs but not SCC-TAFs.

Smad2Δexon3 and Smad3 have distinct properties in signal transmission leading to TGF-β-induced cell motility

In mammalian cells, Smad2 and Smad3, two receptor-regulated Smad proteins, play crucial roles in the signal transmission of transforming growth factor-β (TGF-β) and are involved in various cell regulatory processes, including epithelial-mesenchymal transition-associated cell responses, that is, cell morphological changes, E-cadherin downregulation, stress fiber formation, and cell motility enhancement. Smad2 contains an additional exon encoding 30 amino acid residues compared with Smad3, leading to distinct Smad2 and Smad3 functional properties. Intriguingly, Smad2 also has an alternatively spliced isoform termed Smad2Δexon3 (also known as Smad2β) lacking the additional exon and behaving similarly to Smad3. However, Smad2Δexon3 and Smad3 signaling properties have not yet been compared in detail. In this study, we reveal that Smad2Δexon3 rescues multiple TGF-β-induced in vitro cellular responses that would become defective upon SMAD3 KO but does not rescue cell motility enhancement. Using Smad2Δexon3/Smad3 chimeric proteins, we identified that residues Arg-104 and Asn-210 in Smad3, which are not conserved in Smad2Δexon3, are key for TGF-β-enhanced cell motility. Moreover, we discovered that Smad2Δexon3 fails to rescue the enhanced cell motility as it does not mediate TGF-β signals to downregulate transcription of ARHGAP24, a GTPase-activating protein that targets Rac1. This study reports for the first time distinct signaling properties of Smad2Δexon3 and Smad3.

SIS3 Alleviates Cisplatin-Induced Acute Kidney Injury by Regulating the LncRNA Arid2-IR-Transferrin Receptor Pathway

INTRODUCTION

TGF-β/Smad3 may be involved in the pathogenesis of acute kidney injury (AKI), but its functional role and mechanism of action in cisplatin-induced AKI are unclear. Here, we established a cisplatin-induced AKI mouse model to demonstrate that Smad3 may have roles in cisplatin nephropathy because of its potential effects on tubular epithelial cell (TEC) death and regeneration.

METHODS

Using a cisplatin-induced AKI model, the expression levels of lncRNA Arid2-IR were measured by qRT-PCR and the location detected by FISH. Transfected with overexpression of lncRNA Arid2-IR by lentiviral vector in TECs, and the expression of cleaved caspase 3, Bax, Bcl-2, PCNA, p21, p27, transferrin receptor (TFRC), FTH, and FTL were measured by Western blot. Protein molecules bound to lncRNA Arid2-IR were identified by RIP, RNA pull-down assay, mass spectrometry.

RESULTS

LncRNA Arid2-IR was significantly downregulated in vivo and in vitro. SIS3 decreased cell apoptosis and promoted cell regeneration by upregulating lncRNA Arid2-IR expression. LncRNA Arid2-IR regulated the cell cycle by decreasing expression of the cyclin-dependent kinase inhibitors p21 and p27. Finally, lncRNA Arid2-IR interacted with the TFRC, and overexpression of lncRNA Arid2-IR increased TFRC expression and decreased FTH and FTL.

CONCLUSION

Smad3 regulated lncRNA Arid2-IR via TFRC, thereby regulating the cell cycle, protecting against cell apoptosis, and promoting cell regeneration.

Deep learning for de-convolution of Smad2 versus Smad3 binding sites

Background

The transforming growth factor beta-1 (TGF β-1) cytokine exerts both pro-tumor and anti-tumor effects in carcinogenesis. An increasing body of literature suggests that TGF β-1 signaling outcome is partially dependent on the regulatory targets of downstream receptor-regulated Smad (R-Smad) proteins Smad2 and Smad3. However, the lack of Smad-specific antibodies for ChIP-seq hinders convenient identification of Smad-specific binding sites.

Results

In this study, we use localization and affinity purification (LAP) tags to identify Smad-specific binding sites in a cancer cell line. Using ChIP-seq data obtained from LAP-tagged Smad proteins, we develop a convolutional neural network with long-short term memory (CNN-LSTM) as a deep learning approach to classify a pool of Smad-bound sites as being Smad2- or Smad3-bound. Our data showed that this approach is able to accurately classify Smad2- versus Smad3-bound sites. We use our model to dissect the role of each R-Smad in the progression of breast cancer using a previously published dataset.

Conclusions

Our results suggests that deep learning approaches can be used to dissect binding site specificity of closely related transcription factors.

Supplementary Information

The online version contains supplementary material available at (10.1186/s12864-022-08565-x).

Mechanical Strain Induces Transcriptomic Reprogramming of Saphenous Vein Progenitors

Intimal hyperplasia is the leading cause of graft failure in aortocoronary bypass grafts performed using human saphenous vein (SV). The long-term consequences of the altered pulsatile stress on the cells that populate the vein wall remains elusive, particularly the effects on saphenous vein progenitors (SVPs), cells resident in the vein adventitia with a relatively wide differentiation capacity. In the present study, we performed global transcriptomic profiling of SVPs undergoing uniaxial cyclic strain in vitro. This type of mechanical stimulation is indeed involved in the pathology of the SV. Results showed a consistent stretch-dependent gene regulation in cyclically strained SVPs vs. controls, especially at 72 h. We also observed a robust mechanically related overexpression of Adhesion Molecule with Ig Like Domain 2 (AMIGO2), a cell surface type I transmembrane protein involved in cell adhesion. The overexpression of AMIGO2 in stretched SVPs was associated with the activation of the transforming growth factor β pathway and modulation of intercellular signaling, cell-cell, and cell-matrix interactions. Moreover, the increased number of cells expressing AMIGO2 detected in porcine SV adventitia using an in vivo arterialization model confirms the upregulation of AMIGO2 protein by the arterial-like environment. These results show that mechanical stress promotes SVPs' molecular phenotypic switching and increases their responsiveness to extracellular environment alterations, thus prompting the targeting of new molecular effectors to improve the outcome of bypass graft procedure.

miR-218-5p Induces Interleukin-1β and Endovascular Trophoblast Differentiation by Targeting the Transforming Growth Factor β-SMAD2 Pathway

The acquisition of an endovascular trophoblast (enEVT) phenotype is essential for normal placental development and healthy pregnancy. MicroRNAs (miRNAs) are small noncoding RNAs that play critical roles in regulating gene expression. We have recently reported that miR-218-5p promotes enEVT differentiation and spiral artery remodeling in part by targeting transforming growth factor β2 (TGFβ2). We also identified IL1B, which encodes interleukin 1β (IL1β), as one of the most highly upregulated genes by miR-218-5p. In this study, we investigated how miR-218-5p regulates IL1B expression and IL1β secretion and the potential role of IL1β in enEVT differentiation. Using two cell lines derived from extravillous trophoblasts (EVTs), HTR-8/SVneo and Swan 71, we found that stable overexpression of miR-218-5p precursor, mir-218-1, or transient transfection of miR-218-5p mimic, significantly increased IL1B mRNA and IL1β protein levels in cells and conditioned media. We also showed that miR-218-5p directly interacted with SMAD2 3'UTR and reduced SMAD2 at mRNA and protein levels. Knockdown of SMAD2 induced IL1B expression and attenuated the inhibitory effect of TGFβ2 on IL1B expression. On the other hand, overexpression of SMAD2 reduced IL1β levels and blocked the stimulatory effects of miR-218-5p on IL1B expression, trophoblast migration and endothelial-like network formation. In addition, treatment of trophoblasts with IL1β induced the formation of endothelial-like networks and the expression of enEVT markers in a dose-dependent manner. These results suggest that miR-218-5p inhibits the TGFβ/SMAD2 pathway to induce IL1β and enEVT differentiation. Finally, low doses of IL1β also inhibited the expression of miR-218-5p, suggesting the existence of a negative feedback regulatory loop. Taken together, our findings suggest a novel interactive miR-218-5p/TGFβ/SMAD2/IL1β signaling nexus that regulates enEVT differentiation.

p38β - MAPK11 and its role in female cancers

Background

The p38MAPK family of Mitogen Activated Protein Kinases are a group of signalling molecules involved in cell growth, survival, proliferation and differentiation. The widely studied p38α isoform is ubiquitously expressed and is implicated in a number of cancer pathologies, as are p38γ and p38δ. However, the mechanistic role of the isoform, p38β, remains fairly elusive. Recent studies suggest a possible role of p38β in both breast and endometrial cancer with research suggesting involvement in bone metastasis and cancer cell survival. Female tissue specific cancers such as breast, endometrial, uterine and ovary account for over 3,000,000 cancer related incidents annually; advancements in therapeutics and treatment however require a deeper understanding of the molecular aetiology associated with these diseases. This study provides an overview of the MAPK signalling molecule p38β (MAPK11) in female cancers using an in-silico approach.

Methods

A detailed gene expression and methylation analysis was performed using datasets from cBioportal, CanSar and MEXPRESS. Breast, Uterine Endometrial, Cervical, Ovarian and Uterine Carcinosarcoma TCGA cancer datasets were used and analysed.

Results

Data using cBioportal and CanSAR suggest that expression of p38β is lower in cancers: BRCA, UCEC, UCS, CESC and OV compared to normal tissue. Methylation data from SMART and MEXPRESS indicate significant probe level variation of CpG island methylation status of the gene MAPK11. Analysis of the genes’ two CpG islands shows that the gene was hypermethylated in the CpG1 with increased methylation seen in BRCA, CESC and UCEC cancer data sets with a slight increase of expression recorded in cancer samples. CpG2 exhibited hypomethylation with no significant difference between samples and high levels of expression. Further analysis from MEXPRESS revealed no significance between probe methylation and altered levels of expression. In addition, no difference in the expression of BRCA oestrogen/progesterone/HER2 status was seen.

Conclusion

This data provides an overview of the expression of p38β in female tissue specific cancers, showing a decrease in expression of the gene in BRCA, UCEC, CESC, UCS and OV, increasing the understanding of p38β MAPK expression and offering insight for future in-vitro investigation and therapeutic application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13048-021-00834-9.

Elucidating evolutionarily conserved mechanisms of diapause regulation using an in silico approach

Embryonic diapause is an enigmatic phenomenon that appears in diverse species. Although regulatory mechanisms have been established, there is much to be discovered. Herein, we have made the first comprehensive attempt to elucidate diapause regulatory mechanisms using a computational approach. We found transcription factors unique to promoters of genes in diapause species. From pathway analysis and STRING PPI networks, the signaling pathways regulated by these unique transcription factors were identified. The pathways were then consolidated into a model to combine various known mechanisms of diapause regulation. This work also highlighted certain transcription factors that may act as 'master transcription factors' to regulate the phenomenon. Promoter analysis further suggested evidence for independent evolution for some of regulatory elements involved in diapause.

TGFβ1 orchestrates renal fibrosis following Escherichia coli pyelonephritis

Renal scarring after pyelonephritis is linked to long-term health risks for hypertension and chronic kidney disease. Androgen exposure increases susceptibility to, and severity of, uropathogenic Escherichia coli (UPEC) pyelonephritis and resultant scarring in both male and female mice, while anti-androgen therapy is protective against severe urinary tract infection (UTI) in these models. This work employed androgenized female C57BL/6 mice to elucidate the molecular mechanisms of post-infectious renal fibrosis and to determine how these pathways are altered by the presence of androgens. We found that elevated circulating testosterone levels primed the kidney for fibrosis by increasing local production of TGFβ1 before the initiation of UTI, altering the ratio of transcription factors Smad2 and Smad3 and increasing the presence of mesenchymal stem cell (MSC)-like cells and Gli1 + activated myofibroblasts, the cells primarily responsible for deposition of scar components. Increased production of TGFβ1 and aberrations in Smad2:Smad3 were maintained throughout the course of infection in the presence of androgen, correlating with renal scarring that was not observed in non-androgenized female mice. Pharmacologic inhibition of TGFβ1 signaling blunted myofibroblast activation. We conclude that renal fibrosis after pyelonephritis is exacerbated by the presence of androgens and involves activation of the TGFβ1 signaling cascade, leading to increases in cortical populations of MSC-like cells and the Gli1 + activated myofibroblasts that are responsible for scarring.

Human Skin Keratinocytes on Sustained TGF-β Stimulation Reveal Partial EMT Features and Weaken Growth Arrest Responses

Defects in wound closure can be related to the failure of keratinocytes to re-epithelize. Potential mechanisms driving this impairment comprise unbalanced cytokine signaling, including Transforming Growth Factor-β (TFG-β). Although the etiologies of chronic wound development are known, the relevant molecular events are poorly understood. This lack of insight is a consequence of ethical issues, which limit the available evidence to humans. In this work, we have used an in vitro model validated for the study of epidermal physiology and function, the HaCaT cells to provide a description of the impact of sustained exposure to TGF-β. Long term TGF-β1 treatment led to evident changes, HaCaT cells became spindle-shaped and increased in size. This phenotype change involved conformational re-arrangements for actin filaments and E-Cadherin cell-adhesion structures. Surprisingly, the signs of consolidated epithelial-to-mesenchymal transition were absent. At the molecular level, modified gene expression and altered protein contents were found. Non-canonical TGF-β pathway elements did not show relevant changes. However, R-Smads experienced alterations best characterized by decreased Smad3 levels. Functionally, HaCaT cells exposed to TGF-β1 for long periods showed cell-cycle arrest. Yet, the strength of this restraint weakens the longer the treatment, as revealed when challenged by pro-mitogenic factors. The proposed setting might offer a useful framework for future research on the mechanisms driving wound chronification.

Smad2 and Smad3 play antagonistic roles in high glucose-induced renal tubular fibrosis via the regulation of SnoN

Diabetic nephropathy (DN) is a serious microvascular complication of diabetes mellitus.The main pathological features of DN include glomerular sclerosis and renal tubular interstitial fibrosis, which results in epithelial mesenchymal transition (EMT) and excessive extracellular matrix (ECM) deposition.Transforming growth factor-β1(TGF-β1) is a critical factor that regulates the manifestation of renal fibrosis.Smad2 and Smad3 are the main downstream of the TGF-β1 pathway. Ski-related novel protein N(SnoN) is a negative regulator of TGF-β1, and inhibits the activation of the TGF-β1/Smad2/3 signalling pathway. In this study, the expression of Smad2 and Smad3 proteins, SnoN mRNA, SnoN proteins, and the ubiquitination levels of SnoN were determined in DN rats and renal tubular epithelial cells(NRK52E cells). Knockdown and overexpression of Smad2 or Smad3 in NRK52E cells were used to investigate the specific roles of Smad2 and Smad3 in the development of high glucose-induced renal tubular fibrosis, with a specific focus on their effect on the regulation of SnoN expression. Our study demonstrated that Smad3 could inhibit SnoN expression and increase ECM deposition in NRK52E cells, to promote high glucose-induced renal tubular fibrosis. In contrast, Smad2 could induce SnoN expression and reduce ECM deposition, to inhibit high glucose-induced fibrosis. The underlying mechanism involves regulation of SnoN expression. These findings provide a novel mechanism to understanding the significant role of the TGF-β1/ Smad2/3 pathway in DN.

Loss of LRP1 promotes acquisition of contractile-myofibroblast phenotype and release of active TGF-β1 from ECM stores

In healing tissue, fibroblasts differentiate to α-smooth muscle actin (SMA)-expressing contractile-myofibroblasts, which pull the wound edges together ensuring proper tissue repair. Uncontrolled expansion of the myofibroblast population may, however, lead to excessive tissue scarring and finally to organ dysfunction. Here, we demonstrate that the loss of low-density lipoprotein receptor-related protein (LRP) 1 overactivates the JNK1/2-c-Jun-Fra-2 signaling pathway leading to the induction of α-SMA and periostin expression in human lung fibroblasts (hLF). These changes are accompanied by increased contractility of the cells and the integrin- and protease-dependent release of active transforming growth factor (TGF)-β1 from the extracellular matrix (ECM) stores. Liberation of active TGF-β1 from the ECM further enhances α-SMA and periostin expression thus accelerating the phenotypic switch of hLF. Global gene expression profiling of LRP1-depleted hLF revealed that the loss of LRP1 affects cytoskeleton reorganization, cell-ECM contacts, and ECM production. In line with these findings, fibrotic changes in the skin and lung of Fra-2 transgenic mice were associated with LRP1 depletion and c-Jun overexpression. Altogether, our results suggest that dysregulation of LRP1 expression in fibroblasts in healing tissue may lead to the unrestrained expansion of contractile myofibroblasts and thereby to fibrosis development. Further studies identifying molecules, which regulate LRP1 expression, may provide new therapeutic options for largely untreatable human fibrotic diseases.

HIC-5 in cancer-associated fibroblasts contributes to esophageal squamous cell carcinoma progression

Esophageal squamous cell carcinoma (ESCC) remains one of the most common malignancies in China and has a high metastasis rate and poor prognosis. Cancer-associated fibroblasts (CAFs), a prominent component of the tumor microenvironment, can affect tumor progression and metastasis, but the underlying mechanism remains unclear. There are no studies that explore the role of hydrogen peroxide-inducible clone 5 (HIC-5) in ESCC or compare the role of HIC-5 in CAFs and adjacent noncancerous normal fibroblasts (NFs). In this study, we isolated primary CAFs and NFs from ESCC patients. HIC-5 was highly expressed in CAFs from the tumor stroma of human ESCC patients. HIC-5 knockdown in CAFs inhibited the migration and invasion of ESCC cells in vitro. Supernatant CCL2 levels of CAFs were significantly higher after TGF-β stimulation and lower after knocking down HIC-5 expression, independent of TGF-β treatment. HIC-5 knockdown in CAFs led xenograft tumors derived from ESCC cells mixed with CAFs to present more regular morphology, express higher CDH1, and lower CCL2. Further RNA-seq data showed that HIC-5 has distinct biological functions in CAFs vs. NFs, especially in cell movement and the Rho GTPase signaling kinase pathway, which was verified by wound-healing assays and western blotting. An ESCC tissue microarray revealed that increased HIC-5 expression in the tumor stroma was associated with positive lymph node metastasis and a higher TNM stage. In summary, we identified that stromal HIC-5 was a predictive risk factor for lymph node metastasis in human ESCC and that CAF-derived HIC-5 regulated ESCC cell migration and invasion by regulating cytokines and modifying the ECM.

Smad3 influences Smad2 expression via the transcription factor C/EBPα and C/EBPβ during bovine myoblast differentiation

Transforming growth factor β (TGFβ) has participated in a variety of cellular biological processes. Smad2 and Smad3 are equally important TGFβ downstream effectors in mediating TGFβ signals. However, genes involved in controlling the balance between these two signaling pathways are unknown. In this study, we showed that although Smad2 and Smad3 are structurally similar, with 89% amino acid sequence similarity in bovine, Smad3 significantly decreased Smad2 mRNA and protein expression during bovine myoblast differentiation, but not by binding on its promoter. Luciferase assays and electrophoretic mobility shift assays (EMSA) demonstrated that the transcription factors C/EBPα and C/EBPβ activate Smad2 promoter activity and expression under high serum medium (GM), whereas the opposite was observed under low serum medium (DM). Moreover, over-expression and interference assays revealed that Smad3 has a different effect on C/EBPα and C/EBPβ expression under GM versus DM conditions. After mutation of the C/EBPα and C/EBPβ binding sites, Smad3 had a reduced effect on Smad2 promoter activity. Therefore, these results demonstrated that Smad3 inhibits Smad2 expression via its transcription factors C/EBPα and C/EBPβ during bovine myoblast differentiation. This novel mechanism of the Smad2/3 genes may offer clues for further investigation of TGFβ signal function.

CDKL5 deficiency predisposes neurons to cell death through the deregulation of SMAD3 signaling

CDKL5 deficiency disorder (CDD) is a rare encephalopathy characterized by early onset epilepsy and severe intellectual disability. CDD is caused by mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene, a member of a highly conserved family of serine-threonine kinases. Only a few physiological substrates of CDKL5 are currently known, which hampers the discovery of therapeutic strategies for CDD. Here, we show that SMAD3, a primary mediator of TGF-β action, is a direct phosphorylation target of CDKL5 and that CDKL5-dependent phosphorylation promotes SMAD3 protein stability. Importantly, we found that restoration of the SMAD3 signaling through TGF-β1 treatment normalized defective neuronal survival and maturation in Cdkl5 knockout (KO) neurons. Moreover, we demonstrate that Cdkl5 KO neurons are more vulnerable to neurotoxic/excitotoxic stimuli. In vivo treatment with TGF-β1 prevents increased NMDA-induced cell death in hippocampal neurons from Cdkl5 KO mice, suggesting an involvement of the SMAD3 signaling deregulation in the neuronal susceptibility to excitotoxic injury of Cdkl5 KO mice. Our finding reveals a new function for CDKL5 in maintaining neuronal survival that could have important implications for susceptibility to neurodegeneration in patients with CDD.

NIT1 suppresses tumour proliferation by activating the TGFβ1-Smad2/3 signalling pathway in colorectal cancer

NIT1 protein has been reported to be a potential tumour suppressor in tumour progression. However, little is known about the specific role of NIT1 in tumour development and progression. In this study, we confirmed the specific effects of NIT1 in the regulation of colorectal carcinoma cell proliferation. Here, we showed that NIT1 was significantly downregulated in colorectal cancer tissues compared with that in adjacent normal tissues. The decreased expression of NIT1 was significantly correlated with poor differentiation and more serosal invasion. Functional experiments showed that NIT1 inhibited CRC cell growth both in vitro and in vivo. NIT1 induced cell cycle arrest and apoptosis. Furthermore, NIT1 recruited Smad2/3 to the TGFβ receptor and activated the TGFβ–Smad2/3 pathway by interacting with SARA and SMAD2/3 in CRC. Further study has shown that SMAD3 directly binds to the promoter regions of NIT1 and enhances the transcription of NIT1. Together, our findings indicate that NIT1 suppresses CRC proliferation through a positive feedback loop between NIT1 and activation of the TGFβ–Smad signalling pathway. This study might provide a new promising strategy for CRC.

Genetic deletion of osteopontin in TRAMP mice skews prostate carcinogenesis from adenocarcinoma to aggressive human-like neuroendocrine cancers

Osteopontin (OPN) is a secreted glycoprotein, that belongs to the non-structural extracellular matrix (ECM), and its over expression in human prostate cancer has been associated with disease progression, androgen independence and metastatic ability. Nevertheless, the pathophysiology of OPN in prostate tumorigenesis has never been studied. We crossed TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mice with OPN deficient (OPN-/-) mice and followed tumor onset and progression in these double mutants. Ultrasound examination detected the early onset of a rapidly growing, homogeneous and spherical tumor in about 60% of OPN-/- TRAMP mice. Such neoplasms seldom occurred in parental TRAMP mice otherwise prone to adenocarcinomas and were characterized for being androgen receptor negative, highly proliferative and endowed with neuroendocrine (NE) features. Gene expression profiling showed up-regulation of genes involved in tumor progression, cell cycle and neuronal differentiation in OPN-deficient versus wild type TRAMP tumors. Down-regulated genes included key genes of TGFa pathway, including SMAD3 and Filamin, which were confirmed at the protein level. Furthermore, NE genes and particularly those characterizing early prostatic lesions of OPN-deficient mice were found to correlate with those of human prostate NE tumours. These data underscore a novel role of OPN in the early stages of prostate cancer growth, protecting against the development of aggressive NE tumors.

STAT3 selectively interacts with Smad3 to antagonize TGF-β signalling

Smad and STAT proteins are critical signal transducers and transcription factors in controlling cell growth and tumorigenesis. Here we report that the STAT3 signaling pathway attenuates transforming growth factor-β (TGF-β)-induced responses through a direct Smad3-STAT3 interplay. Activated STAT3 blunts TGF-β-mediated signaling. Depletion of STAT3 promotes TGF-β-mediated transcriptional and physiological responses, including cell cycle arrest, apoptosis and epithelial-to-mesenchymal transition. STAT3 directly interacts with Smad3 in vivo and in vitro, resulting in attenuation of the Smad3-Smad4 complex formation and suppression of DNA-binding ability of Smad3. The N-terminal region of DNA-binding domain of STAT3 is responsible for the STAT3-Smad3 interaction and also indispensable for STAT3-mediated inhibition of TGF-β signaling. Thus, our finding illustrates a direct crosstalk between the STAT3 and Smad3 signaling pathways that may contribute to tumor development and inflammation.

Smad2 overexpression enhances adhesion of gingival epithelial cells

OBJECTIVE

Gingival epithelial cells play an important role in preventing the initiation of periodontitis, by their hemidesmosomal adhesion to the tooth root surface. Adhesion requires integrin-extracellular matrix (ECM) interactions that are intricately regulated by transforming growth factor-β (TGF-β) signaling. However, the mechanisms underlying the interplay between adhesion molecules and TGF-β, especially the respective roles of Smad2 and Smad3, remain elusive. In this study, we examined the effects of Smad overexpression on gingival epithelial cell adhesion and expression profiles of integrin and ECM-related genes.

METHODS

Human gingival epithelial cells immortalized by the SV40 T-antigen were transfected with Smad2- and Smad3-overexpression vectors. A cell adhesion assay involving fluorescence detection of attached cells was performed using the ArrayScan imaging system. Real-time PCR was performed to examine the kinetics of integrin and ECM gene expression. In vitro and in vivo localization of adhesion molecules was examined by immunofluorescence analysis.

RESULTS

By using SB431542, a specific inhibitor of the TGF-β type I receptor, Smad2/3 signaling was confirmed to be dominant in TGF-β1-induced cell adhesion. The Smad2-transfectant demonstrated higher potency for cell adhesion and integrin expression (α2, α5, β4, and β6) than the Smad3-transfectant, whereas little or no change in ECM expression was observed in either transfectant. Moreover, the gingival epithelium of transgenic mice that overexpressed Smad2 driven by the keratin 14 promoter showed increased integrin α2 expression.

CONCLUSION

These findings indicate the crucial role of Smad2 in increased adhesion of gingival epithelial cells via upregulation of integrin α2.

Smad2 and Smad3 have differential sensitivity in relaying TGFβ signaling and inversely regulate early lineage specification

The transforming growth factor beta (TGFβ) related signaling is one of the most important signaling pathways regulating early developmental events. Smad2 and Smad3 are structurally similar and it is mostly considered that they are equally important in mediating TGFβ signals. Here, we show that Smad3 is an insensitive TGFβ transducer as compared with Smad2. Smad3 preferentially localizes within the nucleus and is thus sequestered from membrane signaling. The ability of Smad3 in oligomerization with Smad4 upon agonist stimulation is also impaired given its unique linker region. Smad2 mediated TGFβ signaling plays a crucial role in epiblast development and patterning of three germ layers. However, signaling unrelated nuclear localized Smad3 is dispensable for TGFβ signaling-mediated epiblast specification, but important for early neural development, an event blocked by TGFβ/Smad2 signaling. Both Smad2 and Smad3 bind to the conserved Smads binding element (SBE), but they show nonoverlapped target gene binding specificity and differential transcriptional activity. We conclude that Smad2 and Smad3 possess differential sensitivities in relaying TGFβ signaling and have distinct roles in regulating early developmental events.

TGF-β/Smad signaling in renal fibrosis

TGF-β (transforming growth factor-β) is well identified as a central mediator in renal fibrosis. TGF-β initiates canonical and non-canonical pathways to exert multiple biological effects. Among them, Smad signaling is recognized as a major pathway of TGF-β signaling in progressive renal fibrosis. During fibrogenesis, Smad3 is highly activated, which is associated with the down-regulation of an inhibitory Smad7 via an ubiquitin E3-ligases-dependent degradation mechanism. The equilibrium shift between Smad3 and Smad7 leads to accumulation and activation of myofibroblasts, overproduction of ECM (extracellular matrix), and reduction in ECM degradation in the diseased kidney. Therefore, overexpression of Smad7 has been shown to be a therapeutic agent for renal fibrosis in various models of kidney diseases. In contrast, another downstream effecter of TGF-β/Smad signaling pathway, Smad2, exerts its renal protective role by counter-regulating the Smad3. Furthermore, recent studies demonstrated that Smad3 mediates renal fibrosis by down-regulating miR-29 and miR-200 but up-regulating miR-21 and miR-192. Thus, overexpression of miR-29 and miR-200 or down-regulation of miR-21 and miR-192 is capable of attenuating Smad3-mediated renal fibrosis in various mouse models of chronic kidney diseases (CKD). Taken together, TGF-β/Smad signaling plays an important role in renal fibrosis. Targeting TGF-β/Smad3 signaling may represent a specific and effective therapy for CKD associated with renal fibrosis.

FOXL2 suppresses proliferation, invasion and promotes apoptosis of cervical cancer cells

FOXL2 is a transcription factor that is essential for ovarian function and maintenance, the germline mutations of which give rise to the blepharophimosis ptosis epicanthus inversus syndrome (BPES), often associated with premature ovarian failure. Recently, its mutations have been found in ovarian granulosa cell tumors (OGCTs). In this study, we measured the expression of FOXL2 in cervical cancer by immunohistochemistry and its mRNA level in cervical cancer cell lines Hela and Siha by RT-PCR. Then we overexpressed FOXL2 in Hela cells and silenced it in Siha cells by plasmid transfection and verified using western blotting. When FOXL2 was overexpressed or silenced, cells proliferation and apoptosis were determined by Brdu assay and Annexin V/PI detection kit, respectively. In addition, we investigated the effects of FOXL2 on the adhesion and invasion of Hela and Siha cells. Finally, we analyzed the influences of FOXL2 on Ki67, PCNA and FasL by flow cytometry. The results showed that FOXL2 was highly expressed in cervical squamous cancer. Overexpressing FOXL2 suppressed Hela proliferation and facilitated its apoptosis. Silencing FOXL2 enhanced Siha proliferation and inhibited its apoptosis. Meanwhile, silencing FOXL2 promoted Siha invasion, but it had no effect on cells adhesion. In addition, overexpressing FOXL2 decreased the expression of Ki67 in Hela and Siha cells. Therefore, our results suggested that FOXL2 restrained cells proliferation and enhanced cells apoptosis mainly through decreasing Ki67 expression.

Functional roles of TGF-β1 in intestinal epithelial cells through Smad-dependent and non-Smad pathways

BACKGROUND AND AIMS

Transforming growth factor-β1 (TGF-β1) is one of the growth factors expressed in the gut, and has been shown to play an important role in intestinal mucosal healing. We investigated the effects of TGF-β1 on the cellular functions of intestinal epithelial cells, and also evaluated its signaling pathways in these cells.

METHODS

We used the rat IEC-6 intestinal epithelial cell line for these studies. The expression of TGF-β1/Smad signaling molecules was examined. We evaluated the effect of TGF-β1 on the proliferation and differentiation by the BrdU incorporation assay and real-time PCR. We manipulated the expression levels of Smad2 and Smad3 using an adenovirus system and small interfering RNA to examine the signaling pathways. The expression of Smad2 and Smad3 along the crypt-villus axis was also examined in the murine intestine.

RESULTS

IEC-6 cells produced TGF-β1 and expressed functional TGF-β/Smad signaling molecules. The addition of TGF-β1 in the culture medium suppressed the proliferation and increased the expression of a differentiation marker of enterocytes, in a dose-dependent manner. The adenovirus-mediated and small interfering RNA-mediated studies clearly showed that the growth inhibitory effect and the promotion of differentiation were exerted through a Smad3-dependent and a Smad2-dependent pathway, respectively. IEC-6 cells exhibited upregulated expression of an inhibitory Smad (Smad7) as a form of negative feedback via a non-Smad pathway. Smad2 was predominantly expressed in villi, and Smad3 in crypts.

CONCLUSIONS

TGF-β1 regulates the cellular functions of intestinal epithelial cells through both Smad-dependent and non-Smad pathways.

Comparative study of expression of smad3 in oral lichen planus and normal oral mucosa

Oral lichen planus (OLP) is a chronic inflammatory disease of the oral mucosa which is considered by the World Health Organization (WHO) as a premalignant condition. One step in malignant development is so called epithelial mesenchymal transition (EMT), a process whereby epithelial cells acquire mesenchymal characteristics. A factor known to induce EMT is the transforming growth factor-β (TGF-β), which uses the Smad proteins as mediators for its signaling. The aim of this study was to compare the expression of Smad 3 in Oral Lichen Planus and normal oral mucosa. This descriptive analytic study was performed on 30 patients with OLP (21 women and 9 men with mean age of 45.23± 2.44 years) and 20 normal oral mucosa (14 women and 6 men with mean age of 46.95± 2.21 years). The samples were studied by immunohistochemical staining. Data were analyzed with paired T-test and Wilcoxon test by SPSS software. Expression of Smad3 in OLP samples and normal oral mucosa was different. This difference was statistically significant (P<0.001). The apparently higher expression of Smad 3 in oral lichen planus compared to normal oral mucosa might help to discuss its higher potential for malignant transition.

Smad3 linker phosphorylation attenuates Smad3 transcriptional activity and TGF-β1/Smad3-induced epithelial-mesenchymal transition in renal epithelial cells

Transforming growth factor-β1 (TGF-β1) has a distinct role in renal fibrosis associated with epithelial-mesenchymal transition (EMT) of the renal tubules and synthesis of extracellular matrix. Smad3 plays an essential role in fibrosis initiated by EMT. Phosphorylation of Smad3 in the C-terminal SSXS motif by type I TGF-β receptor kinase is essential for mediating TGF-β response. Smad3 activity is also regulated by phosphorylation in the linker region. However, the functional role of Smad3 linker phosphorylation is not well characterized. We now show that Smad3 EPSM mutant, which mutated the four phosphorylation sites in the linker region, markedly enhanced TGF-β1-induced EMT of Smad3-deficient primary renal tubular epithelial cells, whereas Smad3 3S-A mutant, which mutated the C-terminal phosphorylation sites, was unable to induce EMT in response to TGF-β1. Furthermore, immunoblotting and RT-PCR analysis showed a marked induction of fibrogenic gene expression with a significant reduction in E-cadherin in HK2 human renal epithelial cells expressing Smad3 EPSM. TGF-β1 could not induce the expression of α-SMA, vimentin, fibronectin and PAI-1 or reduce the expression of E-cadherin in HK2 cells expressing Smad3 3S-A in response to TGF-β1. Our results suggest that Smad3 linker phosphorylation has a negative regulatory role on Smad3 transcriptional activity and TGF-β1/Smad3-induced renal EMT. Elucidation of mechanism regulating the Smad3 linker phosphorylation can provide a new strategy to control renal fibrosis.

Dynamics of TGF-β/Smad signaling

The physiological responses to TGF-β stimulation are diverse and vary amongst different cell types and environmental conditions. Even though the principal molecular components of the canonical and the non-canonical TGF-β signaling pathways have been largely identified, the mechanism that underlies the well-established context dependent physiological responses remains a mystery. Understanding how the components of TGF-β signaling function as a system and how this system functions in the context of the global cellular regulatory network requires a more quantitative and systematic approach. Here, we review the recent progress in understanding TGF-β biology using integration of mathematical modeling and quantitative experimental analysis. These studies reveal many interesting dynamics of TGF-β signaling and how cells quantitatively decode variable doses of TGF-β stimulation.

Dynamics and feedback loops in the transforming growth factor β signaling pathway

Transforming growth factor β (TGF-β) ligands activate a signaling cascade with multiple cell context dependent outcomes. Disruption or disturbance leads to variant clinical disorders. To develop strategies for disease intervention, delineation of the pathway in further detail is required. Current theoretical models of this pathway describe production and degradation of signal mediating proteins and signal transduction from the cell surface into the nucleus, whereas feedback loops have not exhaustively been included. In this study we present a mathematical model to determine the relevance of feedback regulators (Arkadia, Smad7, Smurf1, Smurf2, SnoN and Ski) on TGF-β target gene expression and the potential to initiate stable oscillations within a realistic parameter space. We employed massive sampling of the parameters space to pinpoint crucial players for potential oscillations as well as transcriptional product levels. We identified Smad7 and Smurf2 with the highest impact on the dynamics. Based on these findings, we conducted preliminary time course experiments.

Crosstalk between Smad and Mitogen-Activated Protein Kinases for the Regulation of Apoptosis in Cyclosporine A- Induced Renal Tubular Injury

Background/Aims

It remains elusive whether there is a crosstalk between Smad and mitogen-activated protein kinases (MAPKs) and whether it regulates cyclosporine A (CyA)-induced apoptosis in renal proximal tubular cells (RPTCs).

Methods

The effect of CyA on nuclear translocation of Smad2/3 and MAPKs (measured by Western blotting or immunofluorescence) and apoptosis (determined by Hoechst 33258 staining) was examined in HK-2 cells.

Results

CyA induced apoptosis at 24 h and nuclear translocation of phosphorylated (p)-Smad2/3 at 3 h, which was continued till 24 h. CyA enhanced the expression of p-ERK at 1 h, which was continued till 24 h, and of p-p38MAPK at 1–6 h, which returned to control level at 12 h. CyA did not affect JNK. An inhibitor of ERK, PD98059, prevented CyA-induced nuclear translocation of Smad2/3 and apoptosis. An inhibitor of p38MAPK, SB202190, deteriorated CyA-induced nuclear translocation of p-Smad2/3. Epidermal growth factor (EGF) activated ERK and p38MAPK but not JNK. EGF-induced activation of MAPKs ameliorated CyA-induced nuclear translocation of p-Smad2/3 and apoptosis. Inhibition of p38MAPK but not of ERK abolished the protective effect of EGF on CyA-induced nuclear translocation of p-Smad2/3 and apoptosis.

Conclusion

Crosstalk between R-Smad and p38MAPK/ERK, but not JNK differentially regulates apoptosis in CyA-induced RPTC injury.

Differential roles of Smad2 and Smad3 in the regulation of TGF-β1-mediated growth inhibition and cell migration in pancreatic ductal adenocarcinoma cells: control by Rac1

BACKGROUND

Progression of pancreatic ductal adenocarcinoma (PDAC) is largely the result of genetic and/or epigenetic alterations in the transforming growth factor-beta (TGF-β)/Smad signalling pathway, eventually resulting in loss of TGF-β-mediated growth arrest and an increase in cellular migration, invasion, and metastasis. These cellular responses to TGF-β are mediated solely or partially through the canonical Smad signalling pathway which commences with activation of receptor-regulated Smads (R-Smads) Smad2 and Smad3 by the TGF-β type I receptor. However, little is known on the relative contribution of each R-Smad, the possible existence of functional antagonism, or the crosstalk with other signalling pathways in the control of TGF-β1-induced growth inhibition and cell migration. Using genetic and pharmacologic approaches we have inhibited in PDAC cells endogenous Smad2 and Smad3, as well as a potential regulator, the small GTPase Rac1, and have analysed the consequences for TGF-β1-mediated growth inhibition and cell migration (chemokinesis).

RESULTS

SiRNA-mediated silencing of Smad3 in the TGF-β responsive PDAC cell line PANC-1 reduced TGF-β1-induced growth inhibition but increased the migratory response, while silencing of Smad2 enhanced growth inhibition but decreased chemokinesis. Interestingly, siRNA-mediated silencing of the small GTPase Rac1, or ectopic expression of a dominant-negative Rac1 mutant largely mimicked the effect of Smad2 silencing on both TGF-β1-induced growth inhibition, via upregulation of the cdk inhibitor p21WAF1, and cell migration. Inhibition of Rac1 activation reduced both TGF-β1-induction of a Smad2-specific transcriptional reporter and Smad2 C-terminal phosphorylation in PDAC cells while Smad3-specific transcriptional activity and Smad3 C-terminal phosphorylation appeared increased. Disruption of autocrine TGF-β signalling in PANC-1 cells rendered cells less susceptible to the growth-suppressive effect of Rac1 inhibition, suggesting that the decrease in "basal" proliferation upon Rac1 inhibition was caused by potentiation of autocrine TGF-β growth inhibition.

CONCLUSIONS

In malignant cells with a functional TGF-β signalling pathway Rac1 antagonizes the TGF-β1 growth inhibitory response and enhances cell migration by antagonistically regulating Smad2 and Smad3 activation. This study reveals that Rac1 is prooncogenic in that it can alter TGF-β signalling at the R-Smad level from a tumour-suppressive towards a tumour-promoting outcome. Hence, Rac1 might represent a viable target for therapeutic intervention to inhibit PDAC progression.

Smad3 dosage determines androgen responsiveness and sets the pace of postnatal testis development

The establishment and maturation of the testicular Sertoli cell population underpins adult male fertility. These events are influenced by hormones and endocrine factors, including FSH, testosterone and activin. Activin A has developmentally regulated effects on Sertoli cells, enhancing proliferation of immature cells and later promoting postmitotic maturation. These differential responses correlate with altered mothers against decapentaplegic (SMAD)-2/3 signaling: immature cells signal via SMAD3, whereas postmitotic cells use both SMAD2 and SMAD3. This study examined the contribution of SMAD3 to postnatal mouse testis development. We show that SMAD3 production and subcellular localization are highly regulated and, through histological and molecular analyses, identify effects of altered Smad3 dosage on Sertoli and germ cell development. Smad3(+/-) and Smad3(-/-) mice had smaller testes at 7 d postpartum, but this was not sustained into adulthood. Juvenile and adult serum FSH levels were unaffected by genotype. Smad3-null mice displayed delayed Sertoli cell maturation and had reduced expression of androgen receptor (AR), androgen-regulated transcripts, and Smad2, whereas germ cell and Leydig cell development were essentially normal. This contrasted remarkably with advanced Sertoli and germ cell maturation and increased expression of AR and androgen-regulated transcripts in Smad3(+/-) mice. In addition, SMAD3 was down-regulated during testis development and testosterone up-regulated Smad2, but not Smad3, in the TM4 Sertoli cell line. Collectively these data reveal that appropriate SMAD3-mediated signaling drives normal Sertoli cell proliferation, androgen responsiveness, and maturation and influences the pace of the first wave of spermatogenesis, providing new clues to causes of altered pubertal development in boys.

A novel mouse model of cutaneous radiation injury

BACKGROUND

Radiation therapy is a cornerstone of oncologic treatment. Skin tolerance is often the limiting factor in radiotherapy. To study these issues and create modalities for intervention, the authors developed a novel murine model of cutaneous radiation injury.

METHODS

The dorsal skin was isolated using a low-pressure clamp and irradiated. Mice were followed for 8 weeks with serial photography and laser Doppler analysis. Sequential skin biopsy specimens were taken and examined histologically. Tensiometry was performed and Young's modulus calculated.

RESULTS

High-dose radiation isolated to dorsal skin causes progressive changes in skin perfusion, resulting in dermal thickening, fibrosis, persistent alopecia, and sometimes ulceration. There is increased dermal Smad3 expression, and decreased elasticity and bursting strength.

CONCLUSIONS

This model of cutaneous radiation injury delivers reproducible localized effects, mimicking the injury pattern seen in human subjects. This technique can be used to study radiation-induced injury to evaluate preventative and therapeutic strategies for these clinical issues.

Comparative effects of TGF-β2/Smad2 and TGF-β2/Smad3 signaling pathways on proliferation, migration, and extracellular matrix production in a human lens cell line

The signaling pathway of transforming growth factor β2 (TGF-β2)/Smad plays an important role in the pathological process in posterior capsule opacification (PCO) after cataract surgery. Smad2 and Smad3 are both receptor-regulated Smads (R-Smads) of the TGF-β2 signaling pathway. We aim to find which among Smad2, Smad3, and Smad2&3 plays a key role in PCO pathology. The signal characteristics of TGF-β2 and Smad proteins in the human lens cell line HLE-B3 were investigated. Smad2, Smad3, or Smad2&3 were silenced using small interfering RNA. We then tested cell proliferation by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and cell growth curve assays, migration by transwell and wound-healing assays, and extracellular matrix production including α-smooth muscle actin (αSMA), fibronectin, and type I collagen by real-time PCR assay, with and without TGF-β2 exposure. Silencing Smad3 blocked the effect of TGF-β2 on cell proliferation and production of fibronectin and type I collagen. Silencing Smad2 blocked the effect of TGF-β2 on cell migration and production of αSMA. Smad2 depletion enhanced Smad3 activity in cell proliferation and ECM production, whereas Smad3 depletion enhanced Smad2 activity in migration and αSMA expression. Silencing Smad2 and Smad3 efficiently blocked the effect of TGF-β2on cell proliferation, migration, and extracellular matrix production. Smad2 and Smad3 are both key in the TGF-β2 signaling pathway. We can prevent the development of PCO following cataract surgery by blocking the TGF-β2/Smad2&3 signaling pathway.

A novel approach for the generation of genetically modified mammary epithelial cell cultures yields new insights into TGFβ signaling in the mammary gland

INTRODUCTION

Molecular dissection of the signaling pathways that underlie complex biological responses in the mammary epithelium is limited by the difficulty of propagating large numbers of mouse mammary epithelial cells, and by the inability of ribonucleic acid interference (RNAi)-based knockdown approaches to fully ablate gene function. Here we describe a method for the generation of conditionally immortalized mammary epithelial cells with defined genetic defects, and we show how such cells can be used to investigate complex signal transduction processes using the transforming growth factor beta (TGFβ/Smad pathway as an example.

METHODS

We intercrossed the previously described H-2Kb-tsA58 transgenic mouse (Immortomouse) which expresses a temperature-sensitive mutant of the simian virus-40 large T-antigen (tsTAg), with mice of differing Smad genotypes. A panel of conditionally immortalized mammary epithelial cell (IMEC) cultures were derived from the virgin mammary glands of offspring of these crosses and used to assess the Smad dependency of different biological responses to TGFβ.

RESULTS

IMECs could be propagated indefinitely at permissive temperatures and had a stable epithelial phenotype, resembling primary mammary epithelial cells with respect to several criteria, including responsiveness to TGFβ. Using this panel of cells, we demonstrated that Smad3, but not Smad2, is necessary for TGFβ-induced apoptotic, growth inhibitory and EMT responses, whereas either Smad can support TGFβ-induced invasion as long as a threshold level of total Smad is exceeded.

CONCLUSIONS

This work demonstrates the practicality and utility of generating conditionally immortalized mammary epithelial cell lines from genetically modified Immortomice for detailed investigation of complex signaling pathways in the mammary epithelium.

Increased expression of Smad proteins, and in particular Smad3, in oral lichen planus compared to normal oral mucosa

BACKGROUND

Oral lichen planus (OLP) is a chronic inflammatory disease of the oral mucosa which the World Health Organisation (WHO) considers a premalignant condition. One step in malignant development is so called epithelial mesenchymal transition (EMT), a process whereby epithelial cells acquire mesenchymal characteristics. EMT occurs during embryogenesis and wound healing but also in some human diseases such as cancer and fibrosis. A factor known to induce EMT is transforming growth factor-β (TGF-β), which uses the Smad proteins as mediators for its signalling. TGF-β is also often over-expressed in squamous cell carcinoma of the head and neck (SCCHN).

METHODS

In the present study we mapped expression of Smad proteins in OLP lesions by immunohistochemistry, and compared to expression in normal and sensitive oral mucosa. The latter group of patients had developed SCCHN after shorter or longer periods of diffuse oral symptoms. The aim was to see if there were any signs of EMT related changes in the OLP lesions, as judged by changes in the TGF-β pathway.

CONCLUSION

Changes in the TGF-β pathway related to EMT are seen in the very earliest stages of oral malignancy and become more severe as lesions progress.

MiR-21 regulates adipogenic differentiation through the modulation of TGF-beta signaling in mesenchymal stem cells derived from human adipose tissue

A better understanding of the molecular mechanisms that govern human adipose tissue-derived mesenchymal stem cells (hASCs) differentiation could improve hASCs-based cell therapy and provide new insights into a number of diseases, including obesity. In this study, we examined the roles of microRNA-21 (miR-21) in adipogenic differentiation of hASCs. We found that miR-21 expression was transiently increased after induction of adipogenic differentiation, peaked at 3 days, and returned to the baseline level 8 days. Lentiviral overexpression of miR-21 enhanced adipogenic differentiation. Overexpression of miR-21 decreased both protein and mRNA levels of TGFBR2. The expression of TGFBR2 was decreased during adipogenic differentiation of hASCs in concordance with an increase in the level of miR-21. In contrast, inhibiting miR-21 with 2'-O-methyl-antisense microRNA increased TGFBR2 protein levels in hASCs, accompanied by decreased adipogenic differentiation. The activity of a luciferase construct containing the miR-21 target site from the TGFBR2 3'UTR was lower in LV-miR21-infected hASCs than in LV-miLacZ infected cells. TGF-beta-induced inhibition of adipogenic differentiation was significantly decreased in miR-21 overexpressing cells compared with control lentivirus-transduced cells. RNA interference-mediated downregulation of SMAD3, but not of SMAD2, increased adipogenic differentiation. Overexpression and inhibition of miR-21 altered SMAD3 phosphorylation without affecting total levels of SMAD3 protein. Our data are the first to demonstrate that the role of miR-21 in the adipogenic differentiation of hASCs is mediated through the modulation of TGF-beta signaling. This study improves our knowledge of the molecular mechanisms governing hASCs differentiation, which may underlie the development of obesity or other metabolic diseases.

Smad3 deficiency reduces neurogenesis in adult mice

Transforming growth factor-beta signaling through Smad3 inhibits cell proliferation in many cell types. As cell proliferation in the brain is an integral part of neurogenesis, we sought to determine the role of Smad3 in adult neurogenesis through examining processes and structures important to neurogenesis in adult Smad3 null mice. We find that there are fewer proliferating cells in neurogenic regions of adult Smad3 null mouse brains and reduced migration of neuronal precursor cells from the subventricular zone to the olfactory bulb. Alterations in astrocyte number and distribution within the rostral migratory stream of Smad3 null mice give rise to a smaller and more disorganized structure that may impact on neuronal precursor cell migration. However, the proportion of proliferating cells that become neurons is similar in wild type and Smad3 null mice. Our results suggest that signaling through Smad3 is needed to maintain the rate of cell division of neuronal precursors in the adult brain and hence the amount of neurogenesis, without altering neuronal cell fate.

Functional exploration of the adult ovarian granulosa cell tumor-associated somatic FOXL2 mutation p.Cys134Trp (c.402C>G)

Background

The somatic mutation in the FOXL2 gene c.402C>G (p.Cys134Trp) has recently been identified in the vast majority of adult ovarian granulosa cell tumors (OGCTs) studied. In addition, this mutation seems to be specific to adult OGCTs and is likely to be a driver of malignant transformation. However, its pathogenic mechanisms remain elusive.

Methodology/Principal Findings

We have sequenced the FOXL2 open reading frame in a panel of tumor cell lines (NCI-60, colorectal carcinoma cell lines, JEG-3, and KGN cells). We found the FOXL2 c.402C>G mutation in the adult OGCT-derived KGN cell line. All other cell lines analyzed were negative for the mutation. In order to gain insights into the pathogenic mechanism of the p.Cys134Trp mutation, the subcellular localization and mobility of the mutant protein were studied and found to be no different from those of the wild type (WT). Furthermore, its transactivation ability was in most cases similar to that of the WT protein, including in conditions of oxidative stress. A notable exception was an artificial promoter known to be coregulated by FOXL2 and Smad3, suggesting a potential modification of their interaction. We generated a 3D structural model of the p.Cys134Trp variant and our analysis suggests that homodimer formation might also be disturbed by the mutation.

Conclusions/Significance

Here, we confirm the specificity of the FOXL2 c.402C>G mutation in adult OGCTs and begin the exploration of its molecular significance. This is the first study demonstrating that the p.Cys134Trp mutant does not have a strong impact on FOXL2 localization, solubility, and transactivation abilities on a panel of proven target promoters, behaving neither as a dominant-negative nor as a loss-of-function mutation. Further studies are required to understand the specific molecular effects of this outstanding FOXL2 mutation.

Developmentally regulated SMAD2 and SMAD3 utilization directs activin signaling outcomes

Activin is required for testis development. Activin signals via phosphorylation and nuclear accumulation of SMAD2 and SMAD3. We present novel findings of developmentally regulated activin signaling leading to specific transcriptional outcomes in testicular Sertoli cells. In immature, proliferating, Sertoli cells, activin A induces nuclear accumulation of SMAD3, but not SMAD2, although both proteins become phosphorylated. In postmitotic differentiating cells, both SMAD proteins accumulate in the nucleus. Furthermore, immature Sertoli cells are sensitive to activin dosage; higher concentrations induce maximal SMAD3 nuclear accumulation and a small increase in nuclear SMAD2. Microarray analysis identified distinct transcriptional outcomes correlating with differential SMAD utilization and new activin target genes, including Gja1 and Serpina5, which are essential for Sertoli cell development and male fertility. In transgenic mice with altered activin bioactivity that display fertility phenotypes, Gja1 and Serpina5 are significantly altered. Thus, differential SMAD utilization in response to activin features during Sertoli cell maturation.

Smad3 is a key nonredundant mediator of transforming growth factor beta signaling in Nme mouse mammary epithelial cells

Smad2 and Smad3 are intracellular mediators of transforming growth factor beta (TGFbeta) signaling that share various biochemical properties, but data emerging from functional analyses in several cell types indicate that these two Smad proteins may convey distinct cellular responses. Therefore, we have investigated the individual roles of Smad2 and Smad3 in mediating the cytostatic and proapoptotic effects of TGFbeta as well as their function in epithelial-to-mesenchymal transition. For this purpose, we transiently depleted mouse mammary epithelial cells (Nme) of Smad2 and/or Smad3 mainly by a strategy relying on RNaseH-induced degradation of mRNA. The effect of such depletion on hallmark events of TGFbeta-driven epithelial-to-mesenchymal transition was analyzed, including dissolution of epithelial junctions, formation of stress fibers and focal adhesions, activation of metalloproteinases, and transcriptional regulation of acknowledged target genes. Furthermore, we investigated the effect of Smad2 and Smad3 knockdown on the TGFbeta-regulated transcriptome by microarray analysis. Our results identify Smad3 as a key factor to trigger TGFbeta-regulated events and ascribe tumor suppressor as well as oncogenic activities to this protein.

Critical role of Smad2 in tumor suppression and transforming growth factor-beta-induced apoptosis of prostate epithelial cells

Transforming growth factor-beta (TGF-beta) functions as a tumor suppressor of the prostate through mechanisms that remain unresolved. Although TGF-beta receptors directly activate both Smads 2 and 3, to date, Smad3 has been shown to be the essential mediator of most Smad-dependent TGF-beta responses, including control of gene expression, cell growth, apoptosis, and tumor suppression. Using a robust lentiviral short hairpin RNA system to silence Smads 2 and/or 3 in the NRP-152 nontumorigenic rat prostate basal epithelial cell line, we provide the first evidence for Smad2 as a critical mediator of TGF-beta-induced apoptosis and gene expression. Parallel analyses revealed that Smad3 is the major mediator of TGF-beta-induced transcriptional and apoptotic responses in the NRP-154 rat prostate carcinoma cell line. Remarkably, silencing Smad2 alone caused malignant transformation of NRP-152 cells, as assayed by s.c. tumor growth in athymic mice, whereas silencing Smad3 alone did not induce tumors. Nevertheless, tumors induced by silencing both Smads 2 and 3 were larger than those from silencing Smad2 alone. Given previous reports that NRP-152 cells have a stem cell phenotype, we speculate a critical role for Smad2 as a tumor suppressor in the basal epithelial or stem cell compartment of the prostate.

Using RNA interference to identify the different roles of SMAD2 and SMAD3 in NIH/3T3 fibroblast cells

Smad proteins are principal intracellular signaling mediators of transforming growth factor beta (TGF-beta) that regulate a wide range of biological processes. However, the identities of Smad partners mediating TGF-beta signaling are not fully understood. We firstly examined the expression of Smad2 and Smad3 induced by TGF-beta 1 in normal NIH/3T3 cells. The expression of Smad2 and Smad3 was assessed by RT-PCR and Western blotting. The results showed that the expression of Smad2 was increased after treatment with TGF-betaI, but Smad3 was more sensitive to TGF-betaI than Smad2. RNA interference (RNAi) provides a new approach for elucidation of gene function. Use of hairpin siRNA expression vectors for RNAi has provided a rapid and versatile method for assessing gene function in mammalian cells. Here, we have constructed Smad2 and Smad3 hairpin siRNA expression plasmids, and then transfected them into mouse NIH/3T3 cells. Endogenous Smad2 and Smad3 proteins decreased significantly at 48 h after transfection. We found the expression of Smad3 in Smad2-depleted cells was increased, however, the expression of Smad2 in Smad3-depleted cells was not changed. Consistently, the expression of Smad4 mRNA was also attenuated in Smad3-depleted cells. From these data, we suggest that Smad3, but not Smad2, may play a key role in TGF-beta signaling.