Cell biology of Smad2/3 linker region phosphorylation in vascular smooth muscle

Smad transcription factors as mediators of 7 transmembrane G protein-coupled receptor signalling

The Smad transcription factors are well known for their role at the core of transforming growth factor-β (TGF-β) signalling. However, recent evidence shows that the Smad transcription factors play a vital role downstream of other classes of receptors including G protein-coupled receptors (GPCR). The versatility of Smad transcription factors originated from the two regions that can be differently activated by the TGF-β receptor superfamily or through the recruitment of intracellular kinases stimulated by other receptors classes such as GPCRs. The classic GPCR signalling cascade is further expanded to conditional adoption of the Smad transcription factor under the stimulation of Akt, demonstrating the unique involvement of the Smad transcription factor in GPCR signalling pathways in disease environments. In this review, we provide a summary of the signalling pathways of the Smad transcription factors as an important downstream mediator of GPCRs, presenting exciting opportunities for discovering new therapeutic targets for diseases.

Response to retention hypothesis as a source of targets for arterial wall-directed therapies to prevent atherosclerosis: A critical review

The subendothelial retention of circulating lipoproteins on extracellular matrix proteins and proteoglycans is one of the earliest events in the development of atherosclerosis. Multiple factors, including the size, type, composition, surrounding pH, and chemical modifications to lipoproteins, influence the electrostatic interactions between relevant moieties of the apolipoproteins on lipoproteins and the glycosaminoglycans of proteoglycans. The length and chemical composition of glycosaminoglycan chains attached to proteoglycan core proteins determine the extent of initial lipoprotein binding and retention in the artery wall. The phenomena of hyperelongation of glycosaminoglycan chains is associated with initial lipid retention and later atherosclerotic plaque formation. This review includes a summary of the current literature surrounding cellular mechanisms leading to GAG chain modification and lipid retention and discusses potential therapeutic strategies to target lipoprotein:proteoglycan interactions to prevent the development and progression of atherosclerosis.

Gliovascular transcriptional perturbations in Alzheimer's disease reveal molecular mechanisms of blood brain barrier dysfunction

To uncover molecular changes underlying blood-brain-barrier dysfunction in Alzheimer's disease, we performed single nucleus RNA sequencing in 24 Alzheimer's disease and control brains and focused on vascular and astrocyte clusters as main cell types of blood-brain-barrier gliovascular-unit. The majority of the vascular transcriptional changes were in pericytes. Of the vascular molecular targets predicted to interact with astrocytic ligands, SMAD3, upregulated in Alzheimer's disease pericytes, has the highest number of ligands including VEGFA, downregulated in Alzheimer's disease astrocytes. We validated these findings with external datasets comprising 4,730 pericyte and 150,664 astrocyte nuclei. Blood SMAD3 levels are associated with Alzheimer's disease-related neuroimaging outcomes. We determined inverse relationships between pericytic SMAD3 and astrocytic VEGFA in human iPSC and zebrafish models. Here, we detect vast transcriptome changes in Alzheimer's disease at the gliovascular-unit, prioritize perturbed pericytic SMAD3-astrocytic VEGFA interactions, and validate these in cross-species models to provide a molecular mechanism of blood-brain-barrier disintegrity in Alzheimer's disease.

Differential Smad2/3 linker phosphorylation is a crosstalk mechanism of Rho/ROCK and canonical TGF-β3 signaling in tenogenic differentiation

The transforming growth factor (TGF)-β3 is a well-known inducer for tenogenic differentiation, signaling via the Smad2/3 pathway. Furthermore, other factors like extracellular matrix or mechanical force can induce tenogenic differentiation and possibly alter the response to TGF-β3 by signaling via the Rho/ROCK pathway. The aim of this study was to investigate the interplay of Rho/ROCK and TGF-β3/Smad signaling in tenogenic differentiation, with the Smad2/3 molecule hypothesized as a possible interface. Cultured as monolayers or on collagen I matrices, mesenchymal stromal cells (MSC) were treated with the ROCK inhibitor Y-27632 (10 µM), TGF-β3 (10 ng/ml) or both combined. Control cells were cultured accordingly, without Y-27632 and/or without TGF-β3. At different time points, MSC were analyzed by real-time RT-PCR, immunofluorescence, and Western blot. Cultivation of MSC on collagen matrices and ROCK inhibition supported tenogenic differentiation and fostered the effect of TGF-β3. The phosphorylation of the linker region of Smad2 was reduced by cultivation on collagen matrices, but not by ROCK inhibition. The latter, however, led to increased phosphorylation of the linker region of Smad3. In conclusion, collagen matrices and the Rho/ROCK signaling pathway influence the TGF-β3/Smad2/3 pathway by regulating different phosphorylation sites of the Smad linker region.

The 12-bp indel in the SMAD family member 2 gene is associated with goat growth traits

SMAD family member 2 (SMAD2) is a member of the TGFβ signaling pathway and functions as an essential regulator in the processes of development, cell proliferation, and bone formation. A previous observation reported that a 12-bp deletion of this gene affected the litter size in goats. However, according to our knowledge, no study has reported an association between this polymorphism and goat body measurement traits. The purpose of this study was to investigate the association of the insertion/deletion (indel) within the SMAD2 gene with the growth traits of goats. The indel polymorphism was found to be significantly associated with chest width and bust (p < 0.05), while cannon circumference was significantly the strongest compared to other traits (p < 0.01) and individuals with the DD genotypes were more dominant genotypes than other genotypes. In summary, we found evidence that the 12-bp indel within the SMAD2 gene could improve goat body measurement traits, paving the way for marker-assisted selection in the field of goat genetics and breeding.

Leucine-Rich Alpha-2 Glycoprotein 1 Accumulates in Complicated Atherosclerosis and Promotes Calcification

Atherosclerosis is the primary cause of cardiovascular disease. The development of plaque complications, such as calcification and neo-angiogenesis, strongly impacts plaque stability and is a good predictor of mortality in patients with atherosclerosis. Despite well-known risk factors of plaque complications, such as diabetes mellitus and chronic kidney disease, the mechanisms involved are not fully understood. We and others have identified that the concentration of circulating leucine-rich α-2 glycoprotein 1 (LRG1) was increased in diabetic and chronic kidney disease patients. Using apolipoprotein E knockout mice (ApoE-/-) (fed with Western diet) that developed advanced atherosclerosis and using human carotid endarterectomy, we showed that LRG1 accumulated into an atherosclerotic plaque, preferentially in calcified areas. We then investigated the possible origin of LRG1 and its functions on vascular cells and found that LRG1 expression was specifically enhanced in endothelial cells via inflammatory mediators and not in vascular smooth muscle cells (VSMC). Moreover, we identified that LRG1 was able to induce calcification and SMAD1/5-signaling pathways in VSMC. In conclusion, our results identified for the first time that LRG1 is a direct contributor to vascular calcification and suggest a role of this molecule in the development of plaque complications in patients with atherosclerosis.

Docetaxel suppressed cell proliferation through Smad3/HIF-1α-mediated glycolysis in prostate cancer cells

BACKGROUND

Tumor glycolysis is a critical event for tumor progression. Docetaxel is widely used as a first-line drug for chemotherapy and shown to have a survival advantage. However, the role of docetaxel in tumor glycolysis remained poorly understood.

METHODS

The effect of Docetaxel in tumor glycolysis and proliferation were performed by CCK-8, Western blotting, real-time PCR, glucose, and lactate detection and IHC. ChIP and luciferase assay were used to analyze the mechanism of Docetaxel on Smad3-mediated HIF-1α transactivity.

RESULTS

In this study, we showed that docetaxel treatment led to a significant inhibition of cell proliferation in prostate cancer cells through PFKP-mediated glycolysis. Addition of lactate, a production of glycolysis, could reverse the inhibitory effect of docetaxel on cell proliferation. Further analysis has demonstrated that phosphorylation of Smad3 (Ser213) was drastically decreased in response to docetaxel stimulation, leading to reduce Smad3 nuclear translocation. Luciferase and Chromatin immunoprecipitation (ChIP) analysis revealed that docetaxel treatment inhibited the binding of Smad3 to the promoter of the HIF-1α gene, suppressing transcriptional activation of HIF-1α. Moreover, ectopic expression of Smad3 in prostate cancer cells could overcome the decreased HIF-1α expression and its target gene PFKP caused by docetaxel treatment. Most importantly, endogenous Smad3 regulated and interacted with HIF-1α, and this interaction was destroyed in response to docetaxel treatment. What's more, both HIF-1α and PFKP expression were significantly reduced in prostate cancer received docetaxel treatment in vivo.

CONCLUSION

These findings extended the essential role of docetaxel and revealed that docetaxel inhibited cell proliferation by targeting Smad3/HIF-1α signaling-mediated tumor Warburg in prostate cancer cells. Video Abstract.

Lipopolysaccharide acting via toll-like receptor 4 transactivates the TGF-β receptor in vascular smooth muscle cells

Toll-like receptors (TLRs) recognise pathogen‑associated molecular patterns, which allow the detection of microbial infection by host cells. Bacterial-derived toxin lipopolysaccharide activates TLR4 and leads to the activation of the Smad2 transcription factor. The phosphorylation of the Smad2 transcription factor is the result of the activation of the transforming growth factor-β receptor 1 (TGFBR1). Therefore, we sought to investigate LPS via TLR4-mediated Smad2 carboxy terminal phosphorylation dependent on the transactivation of the TGFBR1. The in vitro model used human aortic vascular smooth muscle cells to assess the implications of TLR4 transactivation of the TGFBR1 in vascular pathophysiology. We show that LPS-mediated Smad2 carboxy terminal phosphorylation is inhibited in the presence of TGFBR1 inhibitor, SB431542. Treatment with MyD88 and TRIF pathway antagonists does not affect LPS-mediated phosphorylation of Smad2 carboxy terminal; however, LPS-mediated Smad2 phosphorylation was inhibited in the presence of MMP inhibitor, GM6001, and unaffected in the presence of ROCK inhibitor Y27632 or ROS/NOX inhibitor DPI. LPS via transactivation of the TGFBR1 stimulates PAI-1 mRNA expression. TLRs are first in line to respond to exogenous invading substances and endogenous molecules; our findings characterise a novel signalling pathway in the context of cell biology. Identifying TLR transactivation of the TGFBR1 may provide future insight into the detrimental implications of pathogens in pathophysiology.

Dihydroartemisinin Promoted Bone Marrow Mesenchymal Stem Cell Homing and Suppressed Inflammation and Oxidative Stress against Prostate Injury in Chronic Bacterial Prostatitis Mice Model

Although bone marrow mesenchymal stem cells (BMMSCs) are effective in treating chronic bacterial prostatitis (CBP), the homing of BMMSCs seems to require ultrasound induction. Dihydroartemisinin (DHA) is an important derivative of artemisinin (ART) and has been previously reported to alleviate inflammation and autoimmune diseases. But the effect of DHA on chronic prostatitis (CP) is still unclear. This study aims to clarify the efficacy and mechanism of DHA in the treatment of CBP and its effect on the accumulation of BMMSCs. The experimental CBP was produced in C57BL/6 male mice via intraurethrally administered E. coli solution. Results showed that DHA treatment concentration-dependently promoted the accumulation of BMMSCs in prostate tissue of CBP mice. In addition, DHA and BMMSCs cotreatment significantly alleviated inflammation and improved prostate damage by decreasing the expression of proinflammatory factors such as TNF-α, IL-1β, and chemokines CXCL2, CXCL9, CXCL10, and CXCL11 in prostate tissue of CBP mice. Moreover, DHA and BMMSCs cotreatment displayed antioxidation property by increasing the production of glutathione peroxidase (GSH-Px), SOD, and decreasing malondialdehyde (MDA) expression. Mechanically, DHA and BMMSCs cotreatment significantly inhibited the expression of TGFβ-RI, TGFβ-RII, phosphor (p)-Smad2/3, and Smad4 in a dose-dependent manner while stimulated Smad7 expression in the same manner. In conclusion, our findings provided evidence that DHA effectively eliminated inflammatory and oxidative stress against prostate injury, and this effect involved the TGF-β/Smad signaling pathway in CBP.

The BMP Pathway in Blood Vessel and Lymphatic Vessel Biology

Bone morphogenetic proteins (BMPs) were originally identified as the active components in bone extracts that can induce ectopic bone formation. In recent decades, their key role has broadly expanded beyond bone physiology and pathology. Nowadays, the BMP pathway is considered an important player in vascular signaling. Indeed, mutations in genes encoding different components of the BMP pathway cause various severe vascular diseases. Their signaling contributes to the morphological, functional and molecular heterogeneity among endothelial cells in different vessel types such as arteries, veins, lymphatic vessels and capillaries within different organs. The BMP pathway is a remarkably fine-tuned pathway. As a result, its signaling output in the vessel wall critically depends on the cellular context, which includes flow hemodynamics, interplay with other vascular signaling cascades and the interaction of endothelial cells with peri-endothelial cells and the surrounding matrix. In this review, the emerging role of BMP signaling in lymphatic vessel biology will be highlighted within the framework of BMP signaling in the circulatory vasculature.

TGF-β1 increases permeability of ciliated airway epithelia via redistribution of claudin 3 from tight junction into cell nuclei

TGF-β1 is a major mediator of airway tissue remodelling during atopic asthma and affects tight junctions (TJs) of airway epithelia. However, its impact on TJs of ciliated epithelia is sparsely investigated. Herein we elaborated effects of TGF-β1 on TJs of primary human bronchial epithelial cells. We demonstrate that TGF-β1 activates TGF-β1 receptors TGFBR1 and TGFBR2 resulting in ALK5-mediated phosphorylation of SMAD2. We observed that TGFBR1 and -R2 localize specifically on motile cilia. TGF-β1 activated accumulation of phosphorylated SMAD2 (pSMAD2-C) at centrioles of motile cilia and at cell nuclei. This triggered an increase in paracellular permeability via cellular redistribution of claudin 3 (CLDN3) from TJs into cell nuclei followed by disruption of epithelial integrity and formation of epithelial lesions. Only ciliated cells express TGF-β1 receptors; however, nuclear accumulations of pSMAD2-C and CLDN3 redistribution were observed with similar time course in ciliated and non-ciliated cells. In summary, we demonstrate a role of motile cilia in TGF-β1 sensing and showed that TGF-β1 disturbs TJ permeability of conductive airway epithelia by redistributing CLDN3 from TJs into cell nuclei. We conclude that the observed effects contribute to loss of epithelial integrity during atopic asthma.

The Molecular Genetics of Marfan Syndrome

Marfan syndrome (MFS) is a complex connective tissue disease that is primarily characterized by cardiovascular, ocular and skeletal systems disorders. Despite its rarity, MFS severely impacts the quality of life of the patients. It has been shown that molecular genetic factors serve critical roles in the pathogenesis of MFS. FBN1 is associated with MFS and the other genes such as FBN2, transforming growth factor beta (TGF-β) receptors (TGFBR1 and TGFBR2), latent TGF-β-binding protein 2 (LTBP2) and SKI, amongst others also have their associated syndromes, however high overlap may exist between these syndromes and MFS. Abnormalities in the TGF-β signaling pathway also contribute to the development of aneurysms in patients with MFS, although the detailed molecular mechanism remains unclear. Mutant FBN1 protein may cause unstableness in elastic structures, thereby perturbing the TGF-β signaling pathway, which regulates several processes in cells. Additionally, DNA methylation of FBN1 and histone acetylation in an MFS mouse model demonstrated that epigenetic factors play a regulatory role in MFS. The purpose of the present review is to provide an up-to-date understanding of MFS-related genes and relevant assessment technologies, with the aim of laying a foundation for the early diagnosis, consultation and treatment of MFS.

Cdon mutation and fetal alcohol converge on Nodal signaling in a mouse model of holoprosencephaly

Holoprosencephaly (HPE), a defect in midline patterning of the forebrain and midface, arises ~1 in 250 conceptions. It is associated with predisposing mutations in the Nodal and Hedgehog (HH) pathways, with penetrance and expressivity graded by genetic and environmental modifiers, via poorly understood mechanisms. CDON is a multifunctional co-receptor, including for the HH pathway. In mice, Cdon mutation synergizes with fetal alcohol exposure, producing HPE phenotypes closely resembling those seen in humans. We report here that, unexpectedly, Nodal signaling is a major point of synergistic interaction between Cdon mutation and fetal alcohol. Window-of-sensitivity, genetic, and in vitro findings are consistent with a model whereby brief exposure of Cdon mutant embryos to ethanol during gastrulation transiently and partially inhibits Nodal pathway activity, with consequent effects on midline patterning. These results illuminate mechanisms of gene-environment interaction in a multifactorial model of a common birth defect.

Toll-like Receptor 4 Stimulates Gene Expression via Smad2 Linker Region Phosphorylation in Vascular Smooth Muscle Cells

Atherosclerosis begins in the vessel wall with the retention of low density lipoproteins to modified proteoglycans with hyperelongated glycosaminoglycan (GAG) chains. Bacterial infections produce endotoxins such as lipopolysaccharide that exacerbate the outcome of atherosclerosis by generating a heightened state of inflammation. Lipopolysaccharide (LPS) via its toll-like receptor (TLR) is well-known for its role in mediating an inflammatory response in the body. Emerging evidence demonstrates that TLRs are involved in regulating vascular functions. In this study we sought to investigate the role of LPS in proteoglycan modification and GAG chain elongation, and we hypothesize that LPS will signal via Smad2 dependent pathways to regulate GAG chain elongation. The in vitro model used human aortic vascular smooth muscle cells. GAG gene expression was assessed by quantitative real-time polymerase chain reaction. Western blotting was performed using whole-cell protein lysates to assess the signaling pathway. LPS via TLR4 stimulates the expression of GAG synthesizing enzymes to an equal extent to traditional cardiovascular agonists. LPS phosphorylates the Smad2 linker region via TAK-1/MAPK dependent pathways which correlated with genes associated with GAG chain initiation and elongation. The well-characterized role of LPS in inflammation and our data on GAG gene expression demonstrates that GAG chain elongation is the earliest marker of the inflammatory cascade in atherosclerosis development.

Smad linker region phosphorylation is a signalling pathway in its own right and not only a modulator of canonical TGF-β signalling

Transforming growth factor (TGF)-β signalling pathways are intensively investigated because of their diverse association with physiological and pathophysiological states. Smad transcription factors are the key mediators of TGF-β signalling. Smads can be directly phosphorylated in the carboxy terminal by the TGF-β receptor or in the linker region via multiple intermediate serine/threonine kinases. Growth factors in addition to hormones and TGF-β can activate many of the same kinases which can phosphorylate the Smad linker region. Historically, Smad linker region phosphorylation was shown to prevent nuclear translocation of Smads and inhibit TGF-β signalling pathways; however, it was subsequently shown that Smad linker region phosphorylation can be a driver of gene expression. This review will cover the signalling pathways of Smad linker region phosphorylation that drive the expression of genes involved in pathology and pathophysiology. The role of Smad signalling in cell biology is expanding rapidly beyond its role in TGF-β signalling and many signalling paradigms need to be re-evaluated in terms of Smad involvement.

GPCR transactivation signalling in vascular smooth muscle cells: role of NADPH oxidases and reactive oxygen species

The discovery and extension of G-protein-coupled receptor (GPCR) transactivation-dependent signalling has enormously broadened the GPCR signalling paradigm. GPCRs can transactivate protein tyrosine kinase receptors (PTKRs) and serine/threonine kinase receptors (S/TKRs), notably the epidermal growth factor receptor (EGFR) and transforming growth factor-β type 1 receptor (TGFBR1), respectively. Initial comprehensive mechanistic studies suggest that these two transactivation pathways are distinct. Currently, there is a focus on GPCR inhibitors as drug targets, and they have proven to be efficacious in vascular diseases. With the broadening of GPCR transactivation signalling, it is therefore important from a therapeutic perspective to find a common transactivation pathway of EGFR and TGFBR1 that can be targeted to inhibit complex pathologies activated by the combined action of these receptors. Reactive oxygen species (ROS) are highly reactive molecules and they act as second messengers, thus modulating cellular signal transduction pathways. ROS are involved in different mechanisms of GPCR transactivation of EGFR. However, the role of ROS in GPCR transactivation of TGFBR1 has not yet been studied. In this review, we will discuss the involvement of ROS in GPCR transactivation-dependent signalling.

Endothelin-1 increases CHSY-1 expression in aortic endothelial cells via transactivation of transforming growth factor β type I receptor induced by type B receptor endothelin-1

Objectives

TGF-β through hyperelongation of glycosaminoglycan (GAG) chains leads to binding of low-density lipoproteins to the proteoglycans. The vasoactive peptide, endothelin-1 (ET-1), plays a key role in the development of atherosclerosis. This study addressed the question whether ET-1 by activating the Rho kinase and cytoskeletal rearrangement can transactivate the TGF-β receptor leading to phosphorylation of the transcription factor Smad2 and increased expression of the GAG chain synthesizing enzyme such as chondroitin synthase-1 (CHSY-1) in bovine aortic endothelial cells (BAECs).

Methods

In this study, intermediates in ET-1-induced Smad2C phosphorylation and the protein level of CHSY-1 were identified and quantified by Western blotting.

Key findings

Endothelin-1 caused time-dependent phosphorylation of Smad2C which was inhibited in the presence of the endothelin B receptor antagonist, BQ788. The response to ET-1 was inhibited by the Rho/ROCK kinase antagonist, Y27632 and by cytochalasin D, an inhibitor of actin polymerization but the ET-1-mediated pSmad2C was not inhibited by the matrix metalloproteinase (MMP) inhibitor, GM6001. ET-1 increased CHSY-1 protein level, which was inhibited in the presence of BQ788, cytochalasin D and Y27632.

Conclusions

Endothelin-1 signalling via the ETB receptor utilizes cytoskeletal rearrangement and Rho kinase but not MMPs leading to TβRI transactivation signalling and phosphorylation of Smad2C and through this pathway increased the level of CHSY-1.

Transforming growth factor-β1 mediated CHST11 and CHSY1 mRNA expression is ROS dependent in vascular smooth muscle cells

Transforming growth factor (TGF)-β1 mediates glycosaminoglycan (GAG) chain hyperelongation on secreted proteoglycans and these modifications are associated with increased lipid binding in the vessel wall and the development of atherosclerosis. In vascular smooth muscle cells (VSMCs), TGF-β1 regulated GAG elongation via extracellular signal-regulated kinase (ERK) and p38 as well as Smad2 linker region phosphorylation. In this study, our aim was to identify the TGF-β1 mediated signalling pathway involving reactive oxygen species (ROS) and Smad2 linker region phosphorylation that regulate the mRNA expression of GAG synthesizing enzymes, chondroitin 4-O-sulfotransferase 1 (CHST11) and chondroitin sulfate synthase 1 (CHSY1) which are the rate limiting enzymes involved in GAG chain elongation. Signalling molecules were assessed by western blotting, quantitative real-time PCR was used for analysis of gene expression and intracellular ROS level was measured by a fluorescence based assay. TGF-β1 induced ROS production in VSMCs. Nicotinamide adenine dinucleotide phosphate oxidase (Nox) inhibitors, diphenyleneiodonium (DPI) and apocynin blocked TGF-β1 mediated Smad2 linker region phosphorylation. TGF-β1 treatment increased the mRNA levels of CHST11 and CHSY1. Pharmacological inhibition of Nox blocked TGF-β1 mediated mitogen activated protein kinases (MAPKs) phosphorylation and TGF-β1 stimulated CHST11 and CHSY1 mRNA expression. These findings demonstrated that TGF-β1 mediated expression of CHST11 and CHSY1 can occur via Nox-dependent pathways and Smad2 linker region phosphorylation.

Individual Smad2 linker region phosphorylation sites determine the expression of proteoglycan and glycosaminoglycan synthesizing genes

Growth factors such as thrombin and transforming growth factor (TGF)-β facilitate glycosaminoglycan (GAG) chain hyperelongation on proteoglycans, a phenomenon that increases lipoprotein binding in the vessel wall and the development of atherosclerosis. TGF-β signals via canonical carboxy terminal phosphorylation of R-Smads and also non-canonical linker region phosphorylation of R-Smads. The G protein coupled receptor agonist, thrombin, can transactivate the TGF-β receptor leading to both canonical and non-canonical Smad signalling. Linker region phosphorylation drives the expression of genes for the synthesis of the proteoglycan, biglycan. Proteoglycan synthesis involves core protein synthesis, the initiation of GAG chains and the subsequent elongation of GAG chains. We have explored the relationship between the thrombin stimulated phosphorylation of individual serine and threonine sites in the linker region of Smad2 and the expression of GAG initiation xylosyltransferase-1 (XT-1) and GAG elongation chondroitin 4-sulfotransferase-1 (C4ST-1) and chondroitin synthase-1 (CHSY-1) genes. Thrombin stimulated the phosphorylation of all four target residues (Thr220, Ser245, Ser250 and Ser255 residues) with a similar temporal pattern - phosphorylation was maximal at 15 min (the earliest time point studied) and the level of the phospho-proteins declined thereafter over the following 4 h. Jnk, p38 and PI3K, selectively mediated the phosphorylation of the Thr220 residue whereas the serine residues were variously phosphorylated by multiple kinases. Thrombin stimulated the expression of all three genes - XT-1, C4ST-1 and CHSY-1. The three pathways mediating Thr220 phosphorylation were also involved in the expression of XT-1. The target pathways (excluding Jnk) were involved in the expression of the GAG elongation genes (C4ST-1 and CHSY-1). These findings support the contention that individual Smad linker region phosphorylation sites are linked to the expression of genes for the initiation and elongation of GAG chains on proteoglycans. The context of this work is that a specific inhibitor of GAG elongation represents a potential therapeutic agent for preventing GAG elongation and lipid binding and the results indicate that the specificity of the pathways is such that it might be therapeutically feasible to specifically target GAG elongation without interfering with other physiological processes with which proteoglycans are involved.

Reactive Oxygen Species and p38MAPK Have a Role in the Smad2 Linker Region Phosphorylation Induced by TGF-β

BACKGROUND

Transforming growth factor-β (TGF-β) in addition to the C-terminal region can phosphorylate receptor-regulated Smads (R-Smads) in their linker region. The aim of the present study was to evaluate the role of signaling mediators such as NAD(P)H oxidases (reactive oxygen species [ROS] generators), ROS, and ROS-sensitive p38 mitogen-activated protein kinase (p38MAPK) in this signaling pathway in cultured human vascular smooth muscle cells (VSMCs).

METHODS

The present in vitro study was performed on human VSMCs. Proteins were detected by western blotting utilizing an anti-phospho-Smad2 (Ser245/250/255) rabbit polyclonal antibody and a horseradish peroxidase-labeled secondary antibody. Glyceraldehyde-3-phosphate dehydrogenase was used as a loading control. The phospho-Smad2 linker region (pSmad2L) was detected in all the experimental groups: a control group (untreated group), a group treated with TGF-β (2 ng/mL), and a group treated with TGF-β plus different inhibitors. The data were normalized and presented as mean±SEM. The statistical analyses were performed using SPSS, version 16.0, and the nonparametric Kruskal-Wallis test. A P value smaller than 0.05 was considered statistically significant.

RESULTS

The VSMCs treated with TGF-β (2 ng/mL) showed a time-dependent increase in the pSmad2L level. The highest level was observed at 15 minutes (P=0.03). The inhibitors of NAD(P)H oxidases (diphenyleneiodonium and apocynin) (P=0.04), ROS scavenger (N-acetylcysteine) (P=0.04), and p38MAPK inhibitor (SB-202190) (P=0.04) were able to reduce the increased level of the pSmad2L by TGF-β.

CONCLUSION

Our results suggested that NAD(P)H oxidases played an important role in the Smad2L phosphorylation in the human VSMCs. Furthermore, our results confirmed that ROS and p38MAPK were involved in this signaling pathway. Thus, TGF-β via a ROS-dependent mechanism can transmit its signals to the pSmad2L.

Thrombospondin immune regulation and the kidney

Most therapeutic attempts to prevent the progression of kidney diseases have been based on interventions to inhibit the production of transforming growth factor-β (TGF-β). Thrombospondins (TSPs) play an important role in activating TGF-β. In the healthy kidney, two TSPs are expressed, TSP1 and TSP2, which exert contrasting effects. While TSP1 is a major activator of TGF-β in renal cells and exerts pro-inflammatory effects both in vitro and in vivo, TSP2 lacks the ability for TGF-β activation but regulates matrix remodeling and inflammation in experimental kidney disease. The effects of TSPs in the kidney have been mostly investigated by using the murine model of unilateral ureteral obstruction. In this model, TSP1 expression is increased along with the development of interstitial fibrosis and TGF-β. Relief of the obstruction gradually improves renal function and decreases the expression in TSP1 and TGF-β1. Several inhibitors of TSP1 prevented progressive interstitial fibrosis in murine models of ureteral obstruction, suggesting that control of latent TGF-β activation by inhibiting TSP1 might represent a novel potential target for preventing renal interstitial fibrosis. However, further studies are needed to assess whether TSP1-mediated TGF-β activation can be safely used in humans. In fact, TSPs normally act to suppress tumors in vivo. Moreover, TGF-β can exert a pivotal function in the immune system, as it may induce the production of regulatory T cells and suppress B cell responses. Knowledge of the molecular mechanisms involved in TGF-β regulation may help in finding effective treatments of tissue fibrosis, cancer and autoimmune disease.

MiR-1 suppresses tumor cell proliferation in colorectal cancer by inhibition of Smad3-mediated tumor glycolysis

Aberrant expression of microRNA (miR)-1 has been observed in many human malignancies. However, the function and underlying mechanism of miR-1 remains elusive. To address the specific role of miR-1 in tumor glycolysis using the gain- or loss-of-function studies. Metabolic studies combined with gene expression analysis were performed in vitro and in vivo. We demonstrated aberrant expression of miR-1 in aerobic glycolysis, the Warburg effect, in cancer cells. MiR-1 suppressed aerobic glycolysis and tumor cell proliferation via inactivation of Smad3 and targeting HIF-1α, leading to reduce HK2 and MCT4 expression, which illustrated a novel pathway to mediate aerobic glycolysis in cancer cells. Overexpression of miR-1 mimics significantly decreased tumor glycolysis, including lactate production and glucose uptake, and cell proliferation, and these effects were reversed by ectopic expression of Smad3. Importantly, endogenous Smad3 regulated and interacted with HIF-1α, resulting in increasing activity of Smad3, and this interaction was dramatically abolished by addition of miR-1. We further demonstrated that Smad3 was central to the effects of miR-1 in colorectal cancer cells, establishing a previously unappreciated mechanism by which the miR-1/Smad3/HIF-1α axis facilitates the Warburg effect to promote cancer progression in vitro and in vivo. The results indicate that miR-1 may have an essential role as a tumor suppressor, suggesting its potential role in molecular therapy of patients with advanced colorectal cancer.

Multiple Growth Factors, But Not VEGF, Stimulate Glycosaminoglycan Hyperelongation in Retinal Choroidal Endothelial Cells

A major feature of early age-related macular degeneration (AMD) is the thickening of Bruch's membrane in the retina and an alteration in its composition with increased lipid deposition. In certain pathological conditions proteoglycans are responsible for lipid retention in tissues. Growth factors are known to increase the length of glycosaminoglycan chains and this can lead to a large increase in the interaction between proteoglycans and lipids. Using choroidal endothelial cells, we investigated the effects of a number of AMD relevant growth factors TGFβ, thrombin, PDGF, IGF and VEGF on proteoglycan synthesis. Cells were characterized as of endothelial origin using the specific cell markers endothelial nitric oxide synthesis and von Willebrand factor and imaged using confocal microscopy. Cells were treated with growth factors in the presence and absence of the appropriate inhibitors and were radiolabeled with [35S]-SO4. Proteoglycans were isolated by ion exchange chromatography and sized using SDS-PAGE. Radiosulfate incorporation was determined by the cetylpyridinium chloride (CPC) precipitation technique. To measure cellular glycosaminoglycan synthesizing capacity we added xyloside and assessed the xyloside-GAGs by SDS-PAGE. TGFβ, thrombin, PDGF & IGF dose-dependently stimulated radiosulfate incorporation and GAG elongation as well as xyloside-GAG synthesis, however VEGF treatment did not stimulate any changes in proteoglycan synthesis. VEGF did not increase pAKT but caused a large increase in pERK relative to the response to PDGF. Thus, AMD relevant agonists cause glycosaminoglycan hyperelongation of proteoglycans synthesised and secreted by retinal choroidal endothelial cells. The absence of a response to VEGF is intriguing and identifies proteoglycans as a novel potential target in AMD. Future studies will examine the relevance of these changes to enhanced lipid binding and the development of AMD.

Evaluation of the potential synergism of imatinib-related poly kinase inhibitors using growth factor stimulated proteoglycan synthesis as a model response

INTRODUCTION

Tyrosine kinase inhibitors were the first class of smart drugs being specifically designed to inhibit a disease causing target. There is a very important but unresolved question as whether or not the overall therapeutic role of an individual tinib results from an action at its primary target, a single most likely, tyrosine kinase, or from the combined or aggregate action at the multiple targets which each tinib addresses.

METHODS

We selected a series of ten tinibs (gefitinib, sunitinib, lapatinib, erlotinib, imatinib, sorafenib, axitinib, vanitinib, bosutinib, dasatinib) with various known targets and investigated their activities in the inhibition of proteoglycan synthesis and GAG hyperelongation stimulated by a tyrosine kinase receptor agonist, platelet derived growth factor (PDGF) and for contrast, a serine/threonine kinase receptor agonist, TGF β and some downstream signalling pathways.

RESULTS

The inhibitory activity varied from little to total inhibition. The actions of the tinibs were directed more towards inhibition of the tyrosine kinase, PDGF receptor signalling pathway compared to the TGF β.

CONCLUSION

There was no suggestion of any synergistic effect arising from inhibition of multiple kinases as the most potent compound, dasatinib, is known to inhibit the broadest spectrum of kinases.

Smad3 deficiency protects mice from obesity-induced podocyte injury that precedes insulin resistance

Signaling by TGF-β/Smad3 plays a key role in renal fibrosis. As obesity is one of the major risk factors of chronic and end-stage renal disease, we studied the role of Smad3 signaling in the pathogenesis of obesity-related renal disease. After switching to a high fat diet, the onset of Smad3 C-terminal phosphorylation, increase in albuminuria, and the early stages of peripheral and renal insulin resistance occurred at 1 day, and 4 and 8 weeks, respectively, in C57BL/6 mice. The loss of synaptopodin, a functional marker of podocytes, and phosphorylation of the Smad3 linker region (T179 and S213) appeared after 4 weeks of the high fat diet. This suggests a temporal pattern of Smad3 signaling activation leading to kidney injury and subsequent insulin resistance in the development of obesity-related renal disease. In vivo, Smad3 knockout attenuated the high fat diet-induced proteinuria, renal fibrosis, overall podocyte injury, and mitochondrial dysfunction in podocytes. In vitro palmitate caused a rapid activation of Smad3 in 30 min, loss of synaptopodin in 2 days, and impaired insulin signaling in 3 days in isolated mouse podocytes. Blockade of either Smad3 phosphorylation by SIS3 (a Smad3 inhibitor) or T179 phosphorylation by flavopiridol (a CDK9 inhibitor) prevented the palmitate-induced loss of synaptopodin and mitochondrial function in podocytes. Thus, Smad3 signaling plays essential roles in obesity-related renal disease and may be a novel therapeutic target.

Transforming growth factor β-mediated site-specific Smad linker region phosphorylation in vascular endothelial cells

Objectives

Transforming growth factor (TGF)-β regulates the function of vascular endothelial cells and may be involved in endothelial dysfunction. The canonical TGF-β pathway involves TGF-β receptor-mediated carboxy-terminal phosphorylation of Smad2; however, TGF-β signalling also activates numerous serine/threonine kinases that phosphorylate Smad2 in its linker region. The expression of phosphorylated Smad linker proteins were determined following TGF-β stimulation in the absence and presence of different serine/threonine kinase inhibitors in vascular endothelial cells.

Methods

Proteins were quantified by Western blotting using specific antibodies to individual phosphorylated Smad2 linker region residues.

Key findings

TGF-β mediated the phosphorylation of all four Smad2 linker region residues of interest. Erk and Jnk specifically phosphorylate Ser245 while all mitogen-activated protein kinases phosphorylate Ser250 and Ser255. Thr220 and Ser245 are phosphorylated by phosphoinositide 3 kinase (PI3K), while Ser255 was phosphorylated by the PI3K/Akt pathway. CDK and GSK-3 were shown to phosphorylate Thr220 and Ser245. TGF-β also mediated plasminogen activator inhibitor-1 gene expression that was attenuated by p38 and CDK inhibitors.

Conclusions

TGF-β-mediated phosphorylation of individual serine/threonine sites in the linker region of Smad2 occurs in a highly specific manner by kinases. These phosphorylations provide an opportunity to further understand a therapeutically targeted and very specific signalling pathway in vascular endothelial cells.

Identification and characterization of functional Smad8 and Smad4 homologues from Echinococcus granulosus

Smad family proteins are essential cellular mediators of the transforming growth factor-β superfamily. In the present study, we identified two members of the Smad proteins, Smad8 and Smad4 homologues (termed as EgSmadE and EgSmadD, respectively), from Echinococcus granulosus, the causative agent of cystic echinococcosis (CE). Phylogenetic analysis placed EgSmadE in the Smad1, 5, and 8 subgroup of the R-Smad sub-family and EgSmadD in the Co-Smad family. Furthermore, EgSmadE and EgSmadD attained a high homology to EmSmadE and EmSmadD of E. multilocularis, respectively. Both EgSmadE and EgSmadD were co-expressed in the larval stages and exhibited the highest transcript levels in activated protoscoleces, and their encoded proteins were co-localized in the sub-tegumental and tegumental layer of the parasite. As shown by yeast two-hybrid and pull-down analysis, EgSmadE displayed a positive binding interaction with EgSmadD. In addition, EgSmadE localized in the nuclei of Mv1Lu cells (mink lung epithelial cells) upon treatment with human TGF-β1 or human BMP2, indicating that EgSmadE is capable of being translocated into nucleus, in vitro. Our study suggests that EgSmadE and EgSmadD may take part in critical biological processes, including echinococcal growth, development, and parasite-host interaction.

Endothelial dysfunction exacerbates renal interstitial fibrosis through enhancing fibroblast Smad3 linker phosphorylation in the mouse obstructed kidney

Endothelial dysfunction and enhanced transforming growth factor-β (TGF-β)/Smad3 signalling are common features of progressive renal fibrosis. This study investigated a potential link between these mechanisms. In unilateral ureteric obstruction (UUO) we observed an acute (6 hr) down-regulation of nitric oxide synthase 3 (NOS3/eNOS) levels and increased phosphorylation of the linker region of Smad3 at T179 and S208 in Smad3/JNK complexes. These events preceded Smad3 C-terminal domain phosphorylation and the induction of myofibroblast proliferation at 48 hrs. Mice deficient in NOS3 showed enhanced myofibroblast proliferation and collagen accumulation compared to wild type mice in a 7 day UUO model. This was associated with enhanced phosphorylation of Smad3 T179 and S208 by 92% and 88%, respectively, whereas Smad3-C-terminal phosphorylation was not affected. Resolvin D1 (RvD1) can suppress renal fibrosis in the UUO model, and further analysis herein showed that RvD1 protected against endothelial dysfunction and suppressed Smad3/JNK complex formation with a consequent reduction in phosphorylation of Smad3 T179 and S208 by 78% and 65%, respectively, while Smad3 C-terminal phosphorylation was unaltered. In vitro, conditioned media from mouse microvascular endothelial cells (MMEC) treated with a general inhibitor of nitric oxide synthase (L-NAME) augmented the proliferation and collagen production of renal fibroblasts (NRK49F cells) compared to control MMEC media and this was associated with increased phosphorylation of JNK and Smad3 T179 and S208, whereas Smad3-C-terminal domain phosphorylation was unaffected. The addition of RvD1 to L-NAME treated MMEC abrogated these effects of the conditioned media on renal fibroblasts. Finally, Smad3 T179/V and S208/A mutations significantly inhibit TGF-β1 induced up-regulation collagen I promoter. In conclusion, these data suggest that endothelial dysfunction can exacerbate renal interstitial fibrosis through increased fibroblast proliferation and collagen production via enhanced Smad3 linker phosphorylation.

Signal transduction in cerebral arteries after subarachnoid hemorrhage-a phosphoproteomic approach

After subarachnoid hemorrhage (SAH), pathologic changes in cerebral arteries contribute to delayed cerebral ischemia and poor outcome. We hypothesize such changes are triggered by early intracellular signals, targeting of which may prevent SAH-induced vasculopathy. We performed an unbiased quantitative analysis of early SAH-induced phosphorylations in cerebral arteries and evaluated identified signaling components as targets for prevention of delayed vasculopathy and ischemia. Labeled phosphopeptides from rat cerebral arteries were quantified by high-resolution tandem mass spectrometry. Selected SAH-induced phosphorylations were validated by immunoblotting and monitored over a 24-hour time course post SAH. Moreover, inhibition of key phosphoproteins was performed. Major SAH-induced phosphorylations were observed on focal adhesion complexes, extracellular regulated kinase 1/2 (ERK1/2), calcium calmodulin-dependent kinase II, signal transducer and activator of transcription (STAT3) and c-Jun, the latter two downstream of ERK1/2. Inhibition of ERK1/2 6-hour post SAH prevented increases in cerebrovascular constrictor receptors, matrix metalloprotease-9, wall thickness, and improved neurologic outcome. STAT3 inhibition partially mimicked these effects. The study shows that quantitative mass spectrometry is a strong approach to study in vivo vascular signaling. Moreover, it shows that targeting of ERK1/2 prevents delayed pathologic changes in cerebral arteries and improves outcome, and identifies SAH-induced signaling components downstream and upstream of ERK1/2.

Transforming growth factor-β signalling: role and consequences of Smad linker region phosphorylation

Transforming growth factor-β (TGF-β) is a secreted homodimeric protein that plays an important role in regulating various cellular responses including cell proliferation and differentiation, extracellular matrix production, embryonic development and apoptosis. Disruption of the TGF-β signalling pathway is associated with diverse disease states including cancer, renal and cardiac fibrosis and atherosclerosis. At the cell surface TGF-β complex consists of two type I and two type II transmembrane receptors (TβRI and TβRII respectively) which have serine/threonine kinase activity. Upon TGF-β engagement TβRII phosphorylates TβRI which in turn phosphorylates Smad2/3 on two serine residues at their C-terminus which enables binding to Smad4 to form heteromeric Smad complexes that enter the nucleus to initiate gene transcription including for extracellular matrix proteins. TGF-β signalling is also known to activate other serine/threonine kinase signalling that results in the phosphorylation of the linker region of Smad2. The Smad linker region is defined as the domain which lies between the MH1 and MH2 domains of a Smad protein. Serine/threonine kinases that are known to phosphorylate the Smad linker region include mitogen-activated protein kinases, extracellular-signal regulated kinase, Jun N-terminal kinase and p38 kinase, the tyrosine kinase Src, phosphatidylinositol 3'-kinase, cyclin-dependent kinases, rho-associated protein kinase, calcium calmodulin-dependent kinase and glycogen synthase kinase-3. This review will cover the role of Smad linker region phosphorylation downstream of TGF-β signalling in vascular cells. Key factors including the identification of the kinases that phosphorylate individual Smad residues, the upstream agents that activate these kinases, the cellular location of the phosphorylation event and the importance of the linker region in regulation and expression of genes induced by TGF-β are covered.