Linking Smads and transcriptional activation

Transcriptional responses to direct and indirect TGFB1 stimulation in cancerous and noncancerous mammary epithelial cells

BACKGROUND

Transforming growth factor beta (TGFβ) is important for the morphogenesis and secretory function of the mammary gland. It is one of the main activators of the epithelial-mesenchymal transition (EMT), a process important for tissue remodeling and regeneration. It also provides cells with the plasticity to form metastases during tumor progression. Noncancerous and cancer cells respond differently to TGFβ. However, knowledge of the cellular signaling cascades triggered by TGFβ in various cell types is still limited.

METHODS

MCF10A (noncancerous, originating from fibrotic breast tissue) and MCF7 (cancer, estrogen receptor-positive) breast epithelial cells were treated with TGFB1 directly or through conditioned media from stimulated cells. Transcriptional changes (via RNA-seq) were assessed in untreated cells and after 1-6 days of treatment. Differentially expressed genes were detected with DESeq2 and the hallmark collection was selected for gene set enrichment analysis.

RESULTS

TGFB1 induces EMT in both the MCF10A and MCF7 cell lines but via slightly different mechanisms (signaling through SMAD3 is more active in MCF7 cells). Many EMT-related genes are expressed in MCF10A cells at baseline. Both cell lines respond to TGFB1 by decreasing the expression of genes involved in cell proliferation: through the repression of MYC (and the protein targets) in MCF10A cells and the activation of p63-dependent signaling in MCF7 cells (CDKN1A and CDKN2B, which are responsible for the inhibition of cyclin-dependent kinases, are upregulated). In addition, estrogen receptor signaling is inhibited and caspase-dependent cell death is induced only in MCF7 cells. Direct incubation with TGFB1 and treatment of cells with conditioned media similarly affected transcriptional profiles. However, TGFB1-induced protein secretion is more pronounced in MCF10A cells; therefore, the signaling is propagated through conditioned media (bystander effect) more effectively in MCF10A cells than in MCF7 cells.

CONCLUSIONS

Estrogen receptor-positive breast cancer patients may benefit from high levels of TGFB1 expression due to the repression of estrogen receptor signaling, inhibition of proliferation, and induction of apoptosis in cancer cells. However, some TGFB1-stimulated cells may undergo EMT, which increases the risk of metastasis.

Transforming growth factor- β mediated regulation of epigenome is required for epithelial to mesenchymal transition associated features in liver cancer cells

Hepatocellular carcinoma (HCC) frequently unfolds under an inflammatory condition, which is a hub for a plethora of cytokines. A better understanding of the cytokine functions and their contributions to disease development is key to design of future therapeutic strategies and reduction of global HCC burden. In this context, one of the major cytokines present in the HCC tumour milieu is the transforming growth factor-β (TGF-β). One of its classical functions involve facilitation of epithelial to mesenchymal transition (EMT), in tumour cells, promoting an invasive phenotype. In spite of its clinical relevance, the cellular events associated with TGF-β-induced EMT and its molecular regulation is poorly elucidated. Therefore, as part of this study, we treated HCC cells with TGF-β and characterized the cellular processes associated with EMT. Interestingly, EMT triggered by TGF-β was found to be associated with cytostasis and altered cellular metabolism. TGF-β resulted in down-regulation of cell cycle-associated transcripts, like Cyclin A2 (CCNA2), and metabolic genes, like Glutamic-oxaloacetic transaminase 1 (GOT1) through epigenetic silencing. An overall increase in total histone repressive mark (H3K27me3) associated with a specific enrichment of H3K27me3 at the upstream promoter region of CCNA2 and GOT1 was observed after TGF-β exposure, leading to their down-regulation. Importantly, TGF-β-downstream signalling mediator- SMAD and chromatin repressive complex member-enhancer of zeste homolog 2 (EZH2) were found to co-immunoprecipitate and were required for the above effects. Overall, our findings reflect that HCC cells undergoing EMT, attain cytostasis and modulate metabolic demands to efficiently facilitate the EMT differentiation switch, and these events are regulated at the epigenomic level through TGF-β-mediated signalling. Our results provide better understanding of cellular invasive features which can lead to development of novel therapeutic strategies.

The role of TGF-beta3 in cartilage development and osteoarthritis

Articular cartilage serves as a low-friction, load-bearing tissue without the support with blood vessels, lymphatics and nerves, making its repair a big challenge. Transforming growth factor-beta 3 (TGF-β3), a vital member of the highly conserved TGF-β superfamily, plays a versatile role in cartilage physiology and pathology. TGF-β3 influences the whole life cycle of chondrocytes and mediates a series of cellular responses, including cell survival, proliferation, migration, and differentiation. Since TGF-β3 is involved in maintaining the balance between chondrogenic differentiation and chondrocyte hypertrophy, its regulatory role is especially important to cartilage development. Increased TGF-β3 plays a dual role: in healthy tissues, it can facilitate chondrocyte viability, but in osteoarthritic chondrocytes, it can accelerate the progression of disease. Recently, TGF-β3 has been recognized as a potential therapeutic target for osteoarthritis (OA) owing to its protective effect, which it confers by enhancing the recruitment of autologous mesenchymal stem cells (MSCs) to damaged cartilage. However, the biological mechanism of TGF-β3 action in cartilage development and OA is not well understood. In this review, we systematically summarize recent progress in the research on TGF-β3 in cartilage physiology and pathology, providing up-to-date strategies for cartilage repair and preventive treatment.

Downregulation of CR6-interacting factor 1 suppresses keloid fibroblast growth via the TGF-β/Smad signaling pathway

Keloids are a type of aberrant skin scarring characterized by excessive accumulation of collagen and extracellular matrix (ECM), arising from uncontrolled wound healing responses. While typically non-pathogenic, keloids are occasionally regarded as a form of benign tumor. CR6-interacting factor 1 (CRIF1) is a well-known CR6/GADD45-interacting protein, that has both nuclear and mitochondrial functions, and also exerts regulatory effects on cell growth and apoptosis. In this study, cell proliferation, cell migration, collagen production and TGF-β signaling was compared between normal fibroblasts (NFs) and keloid fibroblasts (KFs). Subsequently, the effects of CRIF1 deficiency were investigated in both NFs and KFs. Cell proliferation, cell migration, collagen production and protein expressions of TGF-β, phosphorylation of Smad2 and Smad3 were all found to be higher in KFs compared to NFs. CRIF1 deficiency in NFs and KFs inhibited cell proliferation, migration, and collagen production. In addition, phosphorylation of Smad2 and Smad3, which are transcription factors of collagen, was decreased. In contrast, mRNA expression levels of Smad7 and SMURF2, two important inhibitory proteins of Smad2/3, were increased, suggesting that CRIF1 may regulate collagen production. CRIF1 deficiency decreases the proliferation and migration of KFs, thereby inhibiting their overgrowth via the transforming growth factor-β (TGF-β)/Smad pathway. CRIF1 may therefore represent a potential therapeutic target in keloid pathogenesis.

The role of Müller cell glucocorticoid signaling in diabetic retinopathy

Diabetic retinopathy (DR) is a sight-threatening complication associated with the highly prevalent diabetes disorder. Both the microvascular damage and neurodegeneration detected in the retina caused by chronic hyperglycemia have brought special attention to Müller cells, the major macroglia of the retina that are responsible for retinal homeostasis. Given the role of glucocorticoid signaling in anti-inflammatory responses and the almost exclusive expression of glucocorticoid receptors (GRs) in retinal Müller cells, administration of corticosteroid agonists as a potential treatment option has been widely studied. Although these approaches have been moderately efficacious in treating or de-escalating DR pathomechanisms, there are various side effects and gaps of knowledge with regard to introducing exogenous glucocorticoids to the diseased retina. In this paper, we provide a review of the literature concerning the available evidence for the role of Müller cell glucocorticoid signaling in DR and we discuss previously investigated approaches in modulating this system as possible treatment options. Furthermore, we propose a novel alternative to the available choices of treatment by using gene therapy as a tool to regulate the expression of GR in retinal Müller cells. Upregulating GR expression allows for induced glucocorticoid signaling with more enduring effects compared to injection of agonists. Hence, repetitive injections would no longer be required. Lastly, side effects of glucocorticoid therapy such as glucocorticoid resistance of GR following chronic exposure to excess ligands or agonists can be avoided.

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.

Cellular and molecular mechanisms of cleft palate development

Cleft lip and palate are common craniofacial deformities. The etiology underlying these deformities is complex and multifactorial and they can occur as part of one of many chromosomal syndromes, Mendelian single gene disorders, teratogenic effects, and as yet uncharacterized syndromes. Our paper will provide an overview of the multiple genes and molecular pathways that have been implicated in palatal fusion. We believe that understanding the molecular mechanisms of cleft formation can help clinicians anticipate which patients may have difficulties healing and in the future allow them to make surgical and medical treatment decisions based on genetic information.

Sirt1 interaction with active Smad2 modulates transforming growth factor-β regulated transcription

Background

The simplicity of Transforming Growth Factor ß (TGFβ) signaling pathway, linear and non-amplified, hardly sustains its variety of responses. This is often justified by the complex regulation showed by Smad proteins, TGFβ signaling intracellular transducers, object of post-translational modifications that modulate TGFβ-dependent transcription. Protein acetylation is emerging as a compelling mechanism affecting the activities of significant transcription factors, including p53, FOXO or NF-kB. Smad proteins might be controlled by this mechanism, implying that accessory factors capable of altering Smads-transcriptional complexes acetylation status and hence regulate TGFβ responses remain to be identified. Understanding this interaction may help in the assessment of TGFβ signaling outcomes, extending from healthy physiology to pathological conditions and cancer.

Methods

A two-hybrid chimera interacting system allowed to identify Sirt1, a NAD+ dependent type III histone deacetylase, as a novel Smad2 interactor. Several well stablished cellular models were applied to characterize this interaction by means of co-immunoprecipitation of tagged proteins and immuno-fluorescence staining. The occurrence of the interaction at Smad2 driven transcriptomic complexes was studied by means of DNA-pull-down and chromatin immunoprecipitation (ChIP), while its effects were assessed by protein over-expression and siRNA applied into a TGFβ-dependent reporter gene assay.

Results

The interaction was confirmed and observed to be enhanced upon Smad2 acetylation, a known feature of active and nuclear Smad2. However, Sirt1 did not play a major role in Smad2 deacetylation. Anti-Sirt1 ChIP showed increased recovery of promoter regions corresponding to Smad2-driven genes after TGFβ-stimulation, while its occurrence at Smad2-dependent transcriptomic complexes on DNA was found to effectively modulate gene expression.

Conclusions

Sirt1 presence on Smad2-driven TGFβ-dependent regulatory elements was detected and found to increase after TGFβ treatment. Moreover, Sirt1 overexpression resulted in a decrease of the activity of a Smad2-driven TGFβ-dependent reporter gene, while Sirt1 interference increased its activity. This would confirm the relevance of the discovered Sirt1-Smad2 interaction for the regulation of TGFβ-dependent gene transcription.

Electronic supplementary material

The online version of this article (10.1186/s12964-017-0205-y) contains supplementary material, which is available to authorized users.

Shikonin reduces TGF-β1-induced collagen production and contraction in hypertrophic scar-derived human skin fibroblasts

Hypertrophic scarring/hypertrophic scars (HS) is a highly prevalent condition following burns and trauma wounds. Numerous studies have demonstrated that transforming growth factor-β1 (TGF-β1) plays an essential role in the wound healing process by regulating cell differentiation, collagen production and extracellular matrix degradation. The increased expression of TGF-β1 is believed to result in the formation of HS. Shikonin (SHI), an active component extracted from the Chinese herb, Radix Arnebiae, has previously been found to downregulate the expression of TGF-β1 in keratinocyte/fibroblast co-culture conditioned medium. In view of this, in this study, we aimed to further investigate the effects of SHI on TGF-β1-stimulated hypertrophic scar-derived human skin fibroblasts (HSFs) and examined the underlying mechanisms. Cell viability and proliferation were measured using alamarBlue and CyQUANT assays. The total amount of collagen and cell contraction were examined using Sirius red staining and the cell contraction assay kit. Gene expression and signalling pathway activation were detected using reverse transcription-quantitative polymerase chain reaction and western blot analysis. Our results revealed that SHI reduced TGF-β1-induced collagen production through the ERK/Smad signalling pathway and attenuated TGF-β1-induced cell contraction by downregulating α-smooth muscle actin (αSMA) expression in the HSFs. The data from this study provide evidence supporting the potential use of SHI as a novel treatment for HS.

An integrated approach of predicted miR-34a targets identifies a signature for gastric cancer

microRNA-34a (miRNA/miR-34a) functions as a tumor suppressor gene in gastric cancer and may be involved in system-wide regulatory networks. To clarify the expression of all predicted target genes of this miRNA, a comprehensive and systematic analysis of miR-34a-target genes in gastric cancer was conducted in the present study. In the initial analysis, the potential functions, pathways and networks of gastric cancer-associated molecules and miR-34a targets were identified. In the final integrative analysis of gastric cancer-associated miR-34a targets, 30 hub genes were identified using overlap calculations, indicating that miR-34a may be significant in the development and progression of gastric cancer through the Smad signaling pathway, the cell cycle, the mitogen-activated protein kinase signaling pathway, apoptosis, the Notch signaling pathway and other pathways. The present study provides a bioinformatic analysis of miR-34a-targets in gastric cancer, describes numerous target genes and novel coregulatory networks, and may provide an opportunity to identify a critical regulatory network for predicting the molecular mechanisms of miR-34a in the development and progression of gastric cancer.

Transforming growth factor Beta family: insight into the role of growth factors in regulation of fracture healing biology and potential clinical applications

The transforming growth factor beta (TGF-β) family forms a group of three isoforms, TGF-β1, TGF-β2, and TGF-β3, with their structure formed by interrelated dimeric polypeptide chains. Pleiotropic and redundant functions of the TGF-β family concern control of numerous aspects and effects of cell functions, including proliferation, differentiation, and migration, in all tissues of the human body. Amongst many cytokines and growth factors, the TGF-β family is considered a group playing one of numerous key roles in control of physiological phenomena concerning maintenance of metabolic homeostasis in the bone tissue. By breaking the continuity of bone tissue, a spread-over-time and complex bone healing process is initiated, considered a recapitulation of embryonic intracartilaginous ossification. This process is a cascade of local and systemic phenomena spread over time, involving whole cell lineages and various cytokines and growth factors. Numerous in vivo and in vitro studies in various models analysing cytokines and growth factors' involvement have shown that TGF-β has a leading role in the fracture healing process. This paper sums up current knowledge on the basis of available literature concerning the role of the TGF-β family in the fracture healing process.

Regulation of chondroitin-4-sulfotransferase (CHST11) expression by opposing effects of arylsulfatase B on BMP4 and Wnt9A

In this report, the gene regulatory mechanism by which decline in arylsulfatase B (ARSB; N-acetylgalactosamine-4-sulfatase) reduces CHST11 (chondroitin-4-sulfotransferase; C4ST) mRNA expression in human colonic epithelial cells and in colonic epithelium of ARSB-deficient mice is presented. ARSB controls the degradation of chondroitin 4-sulfate (C4S) by removing the 4-sulfate group at the non-reducing end of the C4S chain, but has not previously been shown to affect C4S biosynthesis. The decline in CHST11 expression following ARSB reduction is attributable to effects of ARSB on bone morphogenetic protein (BMP)4, since BMP4 expression and secretion declined when ARSB was silenced. Inhibition of BMP4 by neutralizing antibody also reduced CHST11 expression. When C4S was more sulfated due to decline in ARSB, more BMP4 was sequestered by C4S in the cell membrane, and CHST11 expression declined. Exogenous recombinant BMP4, acting through a phospho-Smad3 binding site in the CHST11 promoter, increased the mRNA expression of CHST11. In contrast to the decline in BMP4 that followed decline in ARSB, Wnt9A mRNA expression was previously shown to increase when ARSB was silenced and C4S was more highly sulfated. Galectin-3 bound less to the more highly sulfated C4S, leading to increased nuclear translocation and enhanced galectin-3 interaction with Sp1 in the Wnt9A promoter. Silencing Wnt9A increased the expression of CHST11 in the colonic epithelial cells, and chromatin immunoprecipitation assay demonstrated enhancing effects of Wnt9A siRNA and exogenous BMP4 on the CHST11 promoter through the pSmad3 binding site. These findings suggest that cellular processes mediated by differential effects of Wnt9A and BMP4 can result from opposing effects on CHST11 expression.

Mast cell chymase in keloid induces profibrotic response via transforming growth factor-β1/Smad activation in keloid fibroblasts

This study was to examine whether mast cell chymase exists in human keloids and exerts its profibrotic effect via transforming growth factor-β1/Smad signaling pathway. The number of mast cells and the expression levels of chymase in keloids and normal skin were examined by immunohistochemistry assays. The mRNA expression and activity changes of chymase in keloids and normal skin were determined by real-time quantitative PCR and radioimmunoassay. After keloid fibroblasts were treated with different concentrations of chymase (0, 15, 30, 60, and 120 ng/mL) for various time periods, the proliferation of keloid fibroblasts, collagen synthesis, mRNA and protein expression of TGF-β1, and the protein expression of phosphorylated Smad2/3, Smad2/3 and Smad7 were investigated using MTT assay, ELISA and Western blotting. Mast cells and chymase exist in keloid. Gene expression and activity of mast cell chymase in keloid are significantly higher than those in normal skin. Chymase promotes keloid fibroblast proliferation and collagen synthesis by activating TGF-β1. The activation of Smad protein signaling pathway by chymase is related to the elevated P-Smad protein expression in keloid fibroblasts. Our data demonstrated that mast cell chymase plays an important role in keloid formation through TGF-β1/Smad signaling pathway.

Aortopathy in Marfan syndrome: an update

Marfan syndrome (MFS) is an inherited autosomal dominant multisystem disease caused by mutations in the FBN1 gene encoding fibrillin-1, an extracellular matrix glycoprotein widely distributed in mesenchymal-derived tissues that provide a scaffold for elastin deposition. MFS is characterized by variable clinical manifestations, including skeletal, ocular, and cardiovascular abnormalities; ascending aortic aneurysm with ensuing dissection and rupture is the main life-threatening cardiovascular manifestation of MFS. Histological aspects of MFS aortopathy include a medial degeneration from disarray and fragmentation of elastic fibers and accumulation of basophilic ground substance areas depleted of smooth muscle cells (SMCs). Transmission electron microscopy well evidences the high number of interruptions and the thick appearance of the elastic lamellae and the accumulation of abundant extracellular glycosaminoglycan-rich material, sometimes SMCs showing a prevalent synthetic phenotype. The aberrant signaling of transforming growth factor-β (TGF-β) as the consequence of the altered structure of fibrillin-1 induces activation and the overexpression of Smad-dependent profibrotic signaling pathway and ERK1/2-mediated increased synthesis of matrix metalloproteinases. In addition, MFS is accompanied by an impaired aortic contractile function and aortic endothelial-dependent relaxation, which is caused by an enhancement of the oxidative stress and increased reactive oxygen species during the progression of the disease. Many studies are currently evaluating the contribution of TGF-β-mediated biomolecular pathways to the progression of MFS aortopathy and aneurysm development, in order to discover new targets for pharmacological strategies aimed to counteract aortic dilation.

Tgf-beta induced Erk phosphorylation of smad linker region regulates smad signaling

The Transforming Growth Factor-Beta (TGF-β) family is involved in regulating a variety of cellular processes such as apoptosis, differentiation, and proliferation. TGF-β binding to a Serine/Threonine kinase receptor complex causes the recruitment and subsequent activation of transcription factors known as smad2 and smad3. These proteins subsequently translocate into the nucleus to negatively or positively regulate gene expression. In this study, we define a second signaling pathway leading to TGF-β receptor activation of Extracellular Signal Regulated Kinase (Erk) in a cell-type dependent manner. TGF-β induced Erk activation was found in phenotypically normal mesenchymal cells, but not normal epithelial cells. By activating phosphotidylinositol 3-kinase (PI3K), TGF-β stimulates p21-activated kinase2 (Pak2) to phosphorylate c-Raf, ultimately resulting in Erk activation. Activation of Erk was necessary for TGF-β induced fibroblast replication. In addition, Erk phosphorylated the linker region of nuclear localized smads, resulting in increased half-life of C-terminal phospho-smad 2 and 3 and increased duration of smad target gene transcription. Together, these data show that in mesenchymal cell types the TGF-β/PI3K/Pak2/Raf/MEK/Erk pathway regulates smad signaling, is critical for TGF-β-induced growth and is part of an integrated signaling web containing multiple interacting pathways rather than discrete smad/non-smad pathways.

Aberrant expression in multiple components of the transforming growth factor-β1-induced Smad signaling pathway during 7,12-dimethylbenz[a]anthracene-induced hamster buccal-pouch squamous-cell carcinogenesis

Transforming growth factor (TGF)-β1 signaling controls a plethora of cellular processes including tumorigenesis. The TGF-β1 ligand initiates signaling by binding to TGF-βreceptor II (TβRII) and allowing heterodimerization with TGF-βreceptor I (TβRI); thus, TβRI is phosphorylated by TβRII. After phosphorylation, Smad2 and Smad3 heterodimerize with Smad4, and this complex migrates to the nucleus to regulate the expression of specific target genes. However, Smad7 interrupts above signal transduction by preventing phosphorylation of Smad2 or Smad3. The objective of this study was to examine the TGF-β1-induced Smad signaling pathway during 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch squamous-cell carcinogenesis. Fifty 6-week-old male Syrian golden hamsters were divided into three experimental and two control groups (10 animals in each). Both pouches of each animal in the experimental groups were painted with 0.5% DMBA solution, and both pouches of each animal of one of the control groups were similarly treated with mineral oil; the other control group remained untreated throughout the experiment. Animals from three experimental groups were sacrificed at the end of 3rd, 9th, and 14th-weeks after DMBA treatment, respectively, and animals from two control groups were all sacrificed at 14th-weeks after the treatment. Immunohistochemical staining for TGF-β1, TβRI, TβRII, Smad2-4 and Smad7 were performed.

RESULTS

A significant increase in the expression of Smad7 and significant decreases in the expression of TβRII, Smad 2, Smad3 and Smad4 were noted during hamster buccal-pouch carcinogenesis induced by DMBA. Our findings indicate that a disruption in TGF-β1-induced Smad signaling occurs as a result of aberrant expression of multiple components in the TGF-β1 signaling pathway during DMBA-induced hamster buccal-pouch carcinogenesis, leading to loss of TGF-β1 growth-suppressive effects on transformed pouch keratinocytes.

Smad linker region phosphorylation in the regulation of extracellular matrix synthesis

The canonical TGF-β signalling pathway involves Smad transcription factors through direct serine phosphorylation of the carboxy termini, nuclear translocation and regulation of transcription by receptor-regulated (R)-Smad complexes. Smads can also be phosphorylated in the linker region most prominently by the action of mitogen-activated protein (MAP) kinases, which in turn have been activated by TGF-β or a multitude of other growth factors and hormones. Linker region phosphorylation can prevent nuclear translocation of Smads and inhibit TGF-β signalling, potentially leading to oncogenesis. However, some evidence has revealed that linker region phosphorylated Smads can be translocated to the nucleus where they regulate transcription particularly of the synthesis of extracellular matrix molecules. Matrix molecules such as collagen and proteoglycans are involved in diseases such a fibrosis and atherosclerosis, respectively, and the involvement of linker region phosphorylation may represent a new therapeutic target.

Crystal optimization and preliminary diffraction data analysis of the Smad1 MH1 domain bound to a palindromic SBE DNA element

The bone morphogenetic protein (BMP) signalling pathway regulates diverse processes such as cell differentiation, anterior/posterior axis specification, cell growth and the formation of extra-embryonic tissues. The transcription factor Smad1 relays the BMP signal from the cytoplasm to the nucleus, where it binds short DNA-sequence motifs and regulates gene expression. However, how Smad1 selectively targets particular genomic regions is poorly understood. In order to understand the physical basis of the specific interaction of Smad1 with DNA and to contrast it with the highly homologous but functionally distinct Smad3 protein, the DNA-binding Mad-homology 1 (MH1) domain of Smad1 was cocrystallized with a 17-mer palindromic Smad-binding element (SBE). The extensive optimizations of the length, binding-site spacing and terminal sequences of the DNA element in combination with the other crystallization parameters necessary for obtaining diffraction-quality crystals are described here. A 2.7 angstrom resolution native data set was collected at the National Synchrotron Radiation Research Centre, Taiwan, from crystals grown in a solution containing 0.2 M ammonium tartrate dibasic, 20% PEG 3350, 3% 2-propanol and 10% glycerol. The data set was indexed and merged in space group P222, with unit-cell parameters a = 73.94, b = 77.49, c = 83.78 angstrom, alpha = beta = gamma = 90 degrees. The solvent content in the unit cell is consistent with the presence of two Smad1 MH1 molecules bound to the duplex DNA in the asymmetric unit.

TGF-beta signal transduction in chronic kidney disease

Transforming growth factor (TGF)-beta is a central stimulus of the events leading to chronic progressive kidney disease, having been implicated in the regulation of cell proliferation, hypertrophy, apoptosis and fibrogenesis. The fact that it mediates these varied events suggests that multiple mechanisms play a role in determining the outcome of TGF-beta signaling. Regulation begins with the availability and activation of TGF-beta and continues through receptor expression and localization, control of the TGF-beta family-specific Smad signaling proteins, and interaction of the Smads with multiple signaling pathways extending into the nucleus. Studies of these mechanisms in kidney cells and in whole-animal experimental models, reviewed here, are beginning to provide insight into the role of TGF-beta in the pathogenesis of renal dysfunction and its potential treatment.

Fussel-15, a novel Ski/Sno homolog protein, antagonizes BMP signaling

The Ski family of nuclear oncoproteins represses transforming growth factor-beta (TGF-beta) signaling through inhibition of transcriptional activity of Smad proteins. In this study, we identified a novel gene, fussel-15 (functional smad suppressing element on chromosome 15) with high homology to the recently discovered Fussel-18 protein. Both, Fussel-15 and Fussel-18, share important structural features, significant homology and similar genomic organization with the homolog Ski family members, Ski and SnoN. Unlike Ski and SnoN, which are ubiquitously expressed in human tissues, Fussel-15 expression, like Fussel-18, is much more restricted in its expression and is principally found in the nervous system of mouse and humans. Interestingly, Fussel-15 expression is even more restricted in adulthood to Purkinje cells of human cerebellum. In contrast to Fussel-18 that interacts with Smad 2, Smad3 and Smad4 and has an inhibitory activity on TGF-beta signaling, Fussel-15 interacts with Smad1, Smad2 and Smad3 molecules and suppresses mainly BMP signaling pathway but has only minor effects on TGF-beta signaling. This new protein expands the family of Ski/Sno proto-oncoproteins and represents a novel molecular regulator of BMP signaling.

Smad4 protein expression correlates with grade, stage, and DNA ploidy in prostatic adenocarcinomas

The tumor suppressor gene Smad4 (DPC4) has been localized to chromosome 18q21.1 and is a member of the Smad family that mediates the transforming growth factor beta signaling pathway suppressing epithelial cell growth. However, variable expression of this protein has been reported, with a loss in some cancers and increased expression in others. Given both the variability and lack of consensus reported regarding Smad4 expression in prostate cancer, we assessed Smad4 immunoreactivity in prostatic adenocarcinomas (PACs). Formalin-fixed, paraffin-embedded tissue sections from 133 PACs were immunostained by a manual method using indirect biotin streptavidin horseradish peroxidase and diaminobenzidine detection using a monoclonal mouse antihuman Smad4 antibody (sc-7966; Santa Cruz Biotechnology Inc, Santa Cruz, Calif). Nuclear immunoreactivity and cytoplasmic immunoreactivity were each semiquantitatively scored based on intensity and percentage of positive cells. Deoxyribonucelic acid ploidy was determined on Feulgen-stained tissue sections by static image analysis. Results were correlated with morphological and prognostic variables. Variable nuclear and cytoplasmic Smad4 positivity was noted in the adjacent benign glands in all cases. Of 133 PACs, 64 (48%) featured increased nuclear and 68 (51%) featured increased cytoplasmic protein expression. Nuclear Smad4 overexpression correlated with tumor grade (P = .02), stage (P = .04), and DNA ploidy (P = .04). Cytoplasmic overexpression correlated with tumor grade (P = .04) and DNA ploidy (P = .04) while showing a trend for correlation with tumor stage (P = .08). Neither nuclear nor cytoplasmic Smad4 overexpression correlated with postsurgical biochemical disease recurrence. Smad4 protein expression persists in PACs compared with benign glands, with both nuclear and cytoplasmic overexpression correlating with prognostic variables indicative of aggressive tumor behavior. Given the significant reported variability of Smad4 in several different cancers, further studies in prostate and other tumors are warranted to elucidate its role in tumorigenesis.