Activation Of Smad Signaling Research Articles

Borrmann’s Macroscopic Criteria and p-Smad2 Expression Are Useful Predictive Prognostic Markers for Cytology-Positive Gastric Cancer Patients Without Overt Peritoneal Metastasis

All patients with peritoneal-free cancer cells (CY1) do not always develop a peritoneal recurrence (P1). The goal of this study was to identify characteristic features of peritoneal-free cancer cells that could develop into peritoneal recurrence. Of 1,474 patients, 91 were identified with CY1P0, and the remaining 1,383 with CY0P0. Immunohistochemical staining with anti-phosphorylated Smad 2 (p-Smad2) was performed on paraffin-embedded specimens from the 91 CY1P0 patients. CY1 was significantly correlated with Borrmann's type-4 cancer, clinical T stage, and lymph node metastasis. CY1P0 patients with Borrmann's type-4 cancer more frequently develop peritoneal recurrence than do those with other types of tumors. The 5-year survival rate of patients with Borrmann's type-4 tumors was significantly (p = 0.023) low (6.3%) compared with that of patients with other types of tumors (27.7%). The prognosis for p-Smad2-positive patients was significantly poorer than that of p-Smad2-negative patients. In CY1 and/or P1 patients with Borrmann's type-4 tumors, no significant difference in prognosis was identified between those who had surgery and those who did not. Activated Smad signaling might be associated with a high potential for peritoneal recurrence in CY1P0 patients. Borrmann's macroscopic criteria and p-Smad2 expression are useful markers for surgeons selecting advanced gastric cancer patients with CY1P0 for gastrectomy.

Inductive specification and axonal orientation of spinal neurons mediated by divergent bone morphogenetic protein signaling pathways

BackgroundBone morphogenetic protein (BMP)7 evokes both inductive and axon orienting responses in dorsal interneurons (dI neurons) in the developing spinal cord. These events occur sequentially during the development of spinal neurons but in these and other cell types such inductive and acute chemotactic responses occur concurrently, highlighting the requirement for divergent intracellular signaling. Both type I and type II BMP receptor subtypes have been implicated selectively in orienting responses but it remains unclear how, in a given cell, divergence occurs. We have examined the mechanisms by which disparate BMP7 activities are generated in dorsal spinal neurons.ResultsWe show that widely different threshold concentrations of BMP7 are required to elicit the divergent inductive and axon orienting responses. Type I BMP receptor kinase activity is required for activation of pSmad signaling and induction of dI character by BMP7, a high threshold response. In contrast, neither type I BMP receptor kinase activity nor Smad1/5/8 phosphorylation is involved in the low threshold orienting responses of dI axons to BMP7. Instead, BMP7-evoked axonal repulsion and growth cone collapse are dependent on phosphoinositide-3-kinase (PI3K) activation, plausibly through type II receptor signaling. BMP7 stimulates PI3K-dependent signaling in dI neurons. BMP6, which evokes neural induction but does not have orienting activity, activates Smad signaling but does not stimulate PI3K.ConclusionsDivergent signaling through pSmad-dependent and PI3K-dependent (Smad-independent) mechanisms mediates the inductive and orienting responses of dI neurons to BMP7. A model is proposed whereby selective engagement of BMP receptor subunits underlies choice of signaling pathway.

Quantitative analysis of TGFBR2 mutations in Marfan-syndrome-related disorders suggests a correlation between phenotypic severity and Smad signaling activity

Mutations in the gene encoding transforming growth factor-beta receptor type II (TGFBR2) have been described in patients with Loeys-Dietz syndrome (LDS), Marfan syndrome type 2 (MFS2) and familial thoracic aortic aneurysms and dissections (TAAD). Here, we present a comprehensive and quantitative analysis of TGFBR2 expression, turnover and TGF-β-induced Smad and ERK signaling activity for nine mutations identified in patients with LDS, MFS2 and TAAD. The mutations had different effects on protein stability, internalization and signaling. A dominant-negative effect was demonstrated for mutations associated with LDS and MFS2. No mutation showed evidence of an immediate cell-autonomous paradoxical activation of TGF-β signaling. There were no cell biological differences between mutations described in patients with LDS and MFS2. By contrast, R460C, which has been found in familial TAAD but not in MFS2 or LDS, showed a less-severe dominant-negative effect and retained residual Smad phosphorylation and transcriptional activity. TAAD is characterized primarily by thoracic aortic aneurysms or dissections. By contrast, MFS2 is characterized by numerous skeletal abnormalities, and patients with LDS additionally can display craniofacial and other abnormalities. Therefore, our findings suggest that the balance between defects in Smad and ERK signaling might be an important determinant of phenotypic severity in disorders related to mutations in TGFBR2.

Rap1-GTP Augments Activation of Smad and p38 Mediated Signaling Downstream of TGF-β Receptor In T Lymphocytes

AbstractAbstract 956Rap1A, a member of the Ras superfamily, was discovered as a gene product that reverted K-Ras-induced transformation. Although it was initially thought that Rap1A (thereafter referred to as Rap1) opposes Ras-induced transformation by competing for common downstream effector(s), it has now become apparent that Ras and Rap1 proteins operate in different signaling networks and mediate distinct functions. In lymphocytes Rap1 is activated by BCR and TCR mediated signals and is involved in inside-out activation of integrins. To understand the role of Rap1 in T cell responses we generated transgenic (Tg) mice that express the active Rap1 mutant Rap1E63 in T cells. Rap1E63-Tg and littermate control mice had no statistically significant difference in absolute thymocyte numbers and differentiation profiles of double positive and single positive thymocytes. In contrast to thymocyte numbers, Rap1E63-Tg mice had reduced T cell numbers in peripheral lymphoid organs. In peripheral lymph nodes and spleen, the total T cell numbers were decreased to approximately one third to one forth of those in littermate controls. Strikingly, Rap1E63-Tg mice had a 4-fold increase in the CD4+CD103+ T cell fraction in spleens and lymph nodes compared to their littermate controls. CD103 defines a subset of peripherally generated Treg with potent suppressive function. CD4+CD103+ Treg cells in RapE63-Tg mice expressed CD45RBlow, CD44high, CD54high, CD62Llow and LFA-1high, findings consistent with an effector memory phenotype. TGF-β is the strongest stimulus for induction of CD103 expression. To examine whether Rap1 affected TGF-β-mediated signaling in T cells, we used stable Jurkat T cell lines expressing Rap1E63, Jurkat T cell lines, in which endogenous Rap1 was depleted by shRNA (Rap1-KD), and primary T cells from Rap1E63-Tg mice and Rap1-KO mice. TGF-β signaling involves the interaction of two membrane-bound receptors, TGF-βRI and II. TGF-β binds the exracellular domain of TGF-βRII, which then recruits TGF-βRI resulting in transphosphorylation. TGF-βRI activation propagates downstream signaling via the Smad family proteins Smad2 and Smad3 and also via p38 MAPK, in a Smad-independent manner. Incubation of Rap1E63 Jurkat T cells with TGF-β resulted in enhanced and sustained phosphorylation of Smad2 and Smad3, which was observed with very low concentrations of TGF-β that were incapable of inducing detectable phosphorylation of Smad2 or Smad3 in control cells. In contrast, diminished level and duration of Smad2 and Smad3 phosphorylation was observed in Rap1-KD Jurkat cells. Activation of p38 downstream of TGF-βRI displayed a dramatically augmented and sustained induction, whereas the opposite effect was observed in Rap1-KD cells. Similar patterns of responses to those observed in Rap1E63 Jurkat T cells and in Rap1-KD cells were observed in primary mouse T cells isolated from Rap1E63-Tg mice and Rap1 deficient mice, respectively. Assessment of TGF-β binding on TGF-β surface receptors by using biotinylated TGF-β revealed that Rap1E63 expressing cells displayed significantly enhanced TGF-β binding compared to their relevant controls, whereas reduced TGF-β binding was observed in Rap1 deficient cells. These results indicate that active Rap1 modulates TGF-β receptor binding and enhances TGF-β mediated signaling, gene transcription, and functional outcome. Our data reveal a novel and unexpected mechanism by which Rap1 regulates T cell responses that may have important implications on TGF-β-mediated T cell homeostasis and maintenance of immune quiescence. Disclosures:No relevant conflicts of interest to declare.

P66 Histone deacetylase inhibitor CBHA attenuates the expression of plasminogen activator inhibitor-1 in human pleural mesothelial cells

BackgroundPlasminogen activator inhibitor-1 (PAI-1), primarily up-regulated by transforming growth factor (TGF)-β, is essential for development of fibrosis. Histone deacetylases (HDACs) have been shown to modulate gene expression and fibrogenesis in...

The Protective Effects of Long‐Term Oral Administration of Marine Collagen Hydrolysate from Chum Salmon on Collagen Matrix Homeostasis in the Chronological Aged Skin of Sprague‐Dawley Male Rats

To investigate the long-term effects of marine collagen hydrolysate (MCH) from Chum Salmon skin on the aberrant collagen matrix homeostasis in chronological aged skin, Sprague-Dawley male rats of 4-wk-old were orally administrated with MCH at the diet concentrations of 2.25% and 4.5% for 24 mo. Histological and biochemical analysis revealed that MCH had the potential to inhibit the collagen loss and collagen fragmentation in chronological aged skin. Based on immunohistochemistry and western blot analysis, collagen type I and III protein expression levels in MCH-treated groups significantly increased as compared with the aged control group. Furthermore, quantitative real-time polymerase chain reaction and western blot analysis showed MCH was able to increase the expressions of procollagen type I and III mRNA (COL1A2 and COL3A1) through activating Smad signaling pathway with up-regulated TGF-βRII (TβRII) expression level. Meanwhile, MCH was shown to inhibit the age-related increased collagen degradation through attenuating MMP-1 expression and increasing tissue inhibitor of metalloproteinases-1 expression in a dose-dependent manner. Moreover, MCH could alleviate the oxidative stress in chronological aged skin, which was revealed from the data of superoxide dismutase activity and the thiobarbituric acid reactive substances level in skin homogenates. Therefore, MCH was demonstrated to have the protective effects on chronological skin aging due to the influence on collagen matrix homeostasis. And the antioxidative property of MCH might play an important role in the process.

α-Lipoic acid induces collagen biosynthesis involving prolyl hydroxylase expression via activation of TGF-β-Smad signaling in human dermal fibroblasts

The collapse of collagenous networks with aging results in comprehensive changes in the functional properties of skin. α-Lipoic acid (LA) is known to possess beneficial effects against skin aging, effects often presumed to be its antioxidant potential. However, the effects of LA on fibrillogenesis in dermal fibroblasts have not been adequately assessed. In this study, we demonstrated for the first time that LA enhances the biosynthesis of new collagen in normal human dermal fibroblasts (NHDFs). By using a quantitative dye-binding method and immunochemical approaches, we showed that LA effectively increased the expression and subsequently the deposition of type I collagen in NHDFs. LA also facilitated the expression of a collagen-processing enzyme, prolyl-4-hydroxylase, pointing to the existence of a posttranslational mechanism among the LA-mediated effects on collagen synthesis. In addition, we determined that both Smad 2/3 were rapidly phosphorylated by treatment with LA within 30 min, indicating that LA enhances type I collagen synthesis through the activation of Smad signaling. Pretreatment of SB431542, a specific transforming growth factor-β (TGF-β) receptor type I (TβRI) kinase inhibitor, blocked LA-mediated Smad 2/3 phosphorylations and both type I collagen and prolyl-4-hydroxylase expression, suggesting that LA-mediated cell responses are regulated by TβRI kinase-dependent pathway. Levels of TGF-β secretion after 4 hr of treatment with LA were not remarkably elevated, indicating that LA may be able to mimic TGF-β-mediated cell response. The study results produced new insights into the molecular pharmacology of LA in NHDFs, with potential applications in the treatment of aging skin.

Role of chymase in cigarette smoke-induced pulmonary artery remodeling and pulmonary hypertension in hamsters

BackgroundCigarette smoking is an important risk factor for pulmonary arterial hypertension (PAH) in chronic obstructive pulmonary disease (COPD). Chymase has been shown to function in the enzymatic production of angiotensin II (AngII) and the activation of transforming growth factor (TGF)-β1 in the cardiovascular system. The aim of this study was to determine the potential role of chymase in cigarette smoke-induced pulmonary artery remodeling and PAH.MethodsHamsters were exposed to cigarette smoke; after 4 months, lung morphology and tissue biochemical changes were examined using immunohistochemistry, Western blotting, radioimmunoassay and reverse-transcription polymerase chain reaction.ResultsOur results show that chronic cigarette smoke exposure significantly induced elevation of right ventricular systolic pressures (RVSP) and medial hypertrophy of pulmonary arterioles in hamsters, concurrent with an increase of chymase activity and synthesis in the lung. Elevated Ang II levels and enhanced TGF-β1/Smad signaling activation were also observed in smoke-exposed lungs. Chymase inhibition with chymostatin reduced the cigarette smoke-induced increase in chymase activity and Ang II concentration in the lung, and attenuated the RVSP elevation and the remodeling of pulmonary arterioles. Chymostatin did not affect angiotensin converting enzyme (ACE) activity in hamster lungs.ConclusionsThese results suggest that chronic cigarette smoke exposure can increase chymase activity and expression in hamster lungs. The capability of activated chymase to induce Ang II formation and TGF-β1 signaling may be part of the mechanism for smoking-induced pulmonary vascular remodeling. Thus, our study implies that blockade of chymase might provide benefits to PAH smokers.

Role of TGF-β1, its receptor TGFβRII, and Smad proteins in the progression of colorectal cancer

In the current study, we investigated the expression of TGF-beta1, its receptor TGFbetaRII, and the signaling proteins Smad4 and Smad7 in colorectal cancer tissue in relation to infiltration with antigen-presenting cells and some clinical and pathologic parameters of disease progression in patients with colorectal cancer (CRC). The immunohistochemical expression of TGF-beta1, TGFbetaRII, Smad4, Smad7, HLA-DR antigen, CD1a, CD83, and CD68 was evaluated in 142 patients (50 females and 92 males) with CRC, followed-up for 6-8 years period. In our study, 127 (89.4%) out of 142 colorectal cancers displayed cytoplasmic TGF-beta1 immunoreactivity. Common-mediator Smad4 was detected in the tumor cytoplasm in 124 cancers (79.5%) and inhibitory Smad7 immunostaining was observed in 110 (77.4%) tumor specimens. TGFbetaRII was expressed on tumor cell membranes in 119 (76.3%) of the cancers. The increased TGF-beta1 expression in tumor cytoplasm was related to low CD68(+)- and CD83(+)-cell infiltration in tumor tissues. Patients with TGF-beta1 overexpression had worse prognosis after surgical therapy compared to those with low expression of TGF-beta1. The observed association was more pronounced for the patients in T1-T2 stage (p = 0.0015). The expression of TGF-beta1, its receptor TGFbetaRII, and signaling proteins Smad4 and Smad7 was observed in the majority of colorectal cancer specimens. Our results suggest that TGF-beta1 production by tumor cells may affect the tumor environment via suppression of tumor-infiltrating immune cells and probably contributes to tumor cells aggressiveness through autocrine activation of Smad signaling.

FoxO Proteins Mediate Hypoxic Induction of Connective Tissue Growth Factor in Endothelial Cells

Hypoxia, a driving force in neovascularization, promotes alterations in gene expression mediated by hypoxia-inducible factor (HIF)-1alpha. Connective tissue growth factor (CTGF, CCN2) is a modulator of endothelial cell growth and migration, but its regulation by hypoxia is poorly understood. Therefore, we analyzed signaling pathways involved in the regulation of CTGF by hypoxia in endothelial cells. Exposure to low oxygen tension or treatment with the hypoxia-mimetic dimethyloxalyl glycine (DMOG) stabilized HIF-1alpha and up-regulated CTGF in human umbilical vein endothelial cells and in a murine microvascular endothelial cell line. Induction of CTGF correlated with a HIF-dependent increase in protein and mRNA levels, and nuclear accumulation of the transcription factor FoxO3a. By contrast, gene expression and cellular localization of FoxO1 were not significantly altered by hypoxia. Expression of CTGF was strongly reduced by siRNA silencing of FoxO1 or FoxO3a. Furthermore, nuclear exclusion of FoxO1/3a transcription factors by inhibition of serine/threonine protein phosphatases by okadaic acid inhibited CTGF expression, providing evidence for both FoxO proteins as regulators of CTGF expression. The DMOG-stimulated induction of CTGF was further increased when endothelial cells were co-incubated with transforming growth factor-beta, an activator of Smad signaling. Activation of RhoA-Rho kinase signaling by the microtubule-disrupting drug combretastatin A4 also enhanced the DMOG-induced CTGF expression, thus placing CTGF induction by hypoxia in a network of interacting signaling pathways. Our findings provide evidence that FoxO1, hypoxia-stimulated expression of FoxO3a and its nuclear accumulation are required for the induction of CTGF by hypoxia in endothelial cells.

Mechanism of chronic aristolochic acid nephropathy: role of Smad3

Aristolochic acid nephropathy (AAN) has become a worldwide disease and is the most severe complication related to the use of traditional Chinese medicine. However, the pathogenic mechanisms of AAN remain unclear and therapies are limited. The present study tested the hypothesis that transforming growth factor (TGF)-beta/Smad3 may be a key pathway leading to chronic AAN. This was examined in vivo in Smad3 wild-type/knockout (WT/KO) mice and in vitro in tubular epithelial cells with knockdown of Smad2 or Smad3. Results revealed that chronic administration of aristolochic acid (AA) resulted in a severe AAN characterized by progressive renal dysfunction and tubulointerstitial fibrosis including epithelial-mesenchymal transition (EMT) in Smad3 WT mice, but not in Smad3 KO mice, suggesting a critical role for Smad3 in the development of AAN. This was further tested in vitro. We found that AA was able to activate Smad signaling to mediate EMT and renal fibrosis via both TGF-beta-dependent and JNK/MAP kinase-dependent mechanisms because blockade of JNK and specific knockdown of Smad3, but not Smad2, were able to attenuate AA-stimulated collagen matrix expression and EMT. In conclusion, TGF-beta/Smad3 may be an essential mediator for chronic AAN. Results from this study indicate that specific blockade of the TGF-beta/Smad3 signaling pathway may have therapeutic potential for chronic AAN.

Advanced Glycation End-Products Induce Tubular CTGF via TGF-β–Independent Smad3 Signaling

Advanced glycation end-products (AGEs) can induce expression of connective tissue growth factor (CTGF), which seems to promote the development of diabetic nephropathy, but the exact signaling mechanisms that mediate this induction are unknown. Here, AGEs induced CTGF expression in tubular epithelial cells (TECs) that either lacked the TGF-beta1 gene or expressed dominant TGF-beta receptor II, demonstrating independence of TGF-beta. Furthermore, conditional knockout of the gene encoding TGF-beta receptor II from the kidney did not prevent AGE-induced renal expression of CTGF and collagen I. More specific, AGEs induced CTGF expression via the receptor for AGEs-extracellular signal-regulated kinase (RAGE-ERK)/p38 mitogen-activated protein kinase-Smad cross-talk pathway because inhibition of this pathway by several methods (anti-RAGE antibody, specific inhibitors, or dominant negative adenovirus to ERK1/2 and p38) blocked this induction. Overexpressing Smad7 abolished AGE-induced Smad3 phosphorylation and CTGF expression, demonstrating the necessity for activation of Smad signaling in this process. More important, knockdown of either Smad3 or Smad2 demonstrated that Smad3 but not Smad2 is essential for CTGF induction in response to AGEs. In conclusion, AGEs induce tubular CTGF expression via the TGF-beta-independent RAGE-ERK/p38-Smad3 cross-talk pathway. These data suggest that overexpression of Smad7 or targeting Smad3 may have therapeutic potential for diabetic nephropathy.

BRCA1 Interacts with Smad3 and Regulates Smad3-Mediated TGF-β Signaling during Oxidative Stress Responses

BackgroundBRCA1 is a key regulatory protein participating in cell cycle checkpoint and DNA damage repair networks. BRCA1 plays important roles in protecting numerous cellular processes in response to cell damaging signals. Transforming growth factor-beta (TGF-β) is a potent regulator of growth, apoptosis and invasiveness of tumor cells. TFG-β activates Smad signaling via its two cell surface receptors, the TbetaRII and ALK5/TbetaRI, leading to Smad-mediated transcriptional regulation.Methodology/Principal FindingsHere, we report an important role of BRCA1 in modulating TGF-β signaling during oxidative stress responses. Wild-type (WT) BRCA1, but not mutated BRCA1 failed to activate TGF-β mediated transactivation of the TGF-β responsive reporter, p3TP-Lux. Further, WT-BRCA1, but not mutated BRCA1 increased the expression of Smad3 protein in a dose-dependent manner, while silencing of WT-BRCA1 by siRNA decreased Smad3 and Smad4 interaction induced by TGF-β in MCF-7 breast cancer cells. BRCA1 interacted with Smad3 upon TGF-β1 stimulation in MCF-7 cells and this interaction was mediated via the domain of 298–436aa of BRCA1 and Smad3 domain of 207–426aa. In addition, H2O2 increased the colocalization and the interaction of Smad3 with WT-BRCA1. Interestingly, TGF-β1 induced Smad3 and Smad4 interaction was increased in the presence of H2O2 in cells expressing WT-BRCA1, while the TGF-β1 induced interaction between Smad3 and Smad4 was decreased upon H2O2 treatment in a dose-dependent manner in HCC1937 breast cancer cells, deficient for endogenous BRCA1. This interaction between Smad3 and Smad4 was increased in reconstituted HCC1937 cells expressing WT-BRCA1 (HCC1937/BRCA1). Further, loss of BRCA1 resulted in H2O2 induced nuclear export of phosphor-Smad3 protein to the cytoplasm, resulting decreased of Smad3 and Smad4 interaction induced by TGF-β and in significant decrease in Smad3 and Smad4 transcriptional activities.Conclusions/SignificanceThese results strongly suggest that loss or reduction of BRCA1 alters TGF-β growth inhibiting activity via Smad3 during oxidative stress responses.

Role of ERK/mTOR signaling in TGFβ-modulated focal adhesion kinase mRNA stability and protein synthesis in cultured rat IEC-6 intestinal epithelial cells

Increasing evidence is available showing the importance of the FAK (focal adhesion kinase) protein level in the migration and homeostasis of intestinal cells. TGFbeta (transforming growth factor beta) modulates FAK protein expression in a complex fashion not only by inducing the activation of p38 and Smad signaling resulting in increased fak promoter activity and increased FAK protein levels, but also by activating ERK (extracellular signal regulated kinases), p38, and the Smad pathway. We show that the blockade of ERK signaling by a specific MEK (MAPK kinase) inhibitor attenuates TGFbeta-induced FAK mRNA stability and reduces FAK protein levels in rat IEC-6 intestinal epithelial cells. The mTOR (mammalian target of rapamycin)-specific inhibitor rapamycin and small interfering RNAs for mTOR and p70(S6) kinase also block TGFbeta-induced FAK protein synthesis. Furthermore, we have found that a TGFbeta-induced increase in wound closures in monolayers of these cells is abolished in the presence ERK or mTOR inhibition. Thus, TGFbeta also modulates FAK protein levels in cultured rat IEC-6 intestinal epithelial cells via ERK activation, acting at the transcriptional level to complement Smad signaling and at on the translational level via the mTOR pathway downstream of ERK, which in turn promotes intestinal epithelial cell migration.

BMP6 attenuates oxidant injury in HK-2 cells via Smad-dependent HO-1 induction

Oxidative stress is involved in a variety of kidney diseases, and heme oxygenase 1 (HO-1) induction is a protective response to oxidative stress. Downregulation of bone morphogenetic protein 6 (BMP6) is associated with renal damage in intrauterine growth-restricted newborns. However, it is unknown whether BMP6 has a renoprotective effect or HO-1 induction property. In this study, we demonstrate that BMP6 effectively protects renal proximal tubule cells (HK-2) against hydrogen peroxide (H 2O 2)-induced cell injury. BMP6 also increased HO-1 gene expression and activity of HO. Inhibition of de novo gene expression, the HO inhibitor ZnPPIX, HO-1 knockdown, or the carbon monoxide (CO) scavenger hemoglobin attenuated the cytoprotective effect of BMP6, whereas HO-1 constitutive expression, the HO-1 inducer hemin, or the hemin metabolites bilirubin and CO ameliorated H 2O 2-induced cell injury. Stimulation of HK-2 cells with BMP6 activated Smad signaling but not mitogen-activated protein kinases. In addition, BMP6-mediated induction of HO-1 expression and increase in HO activity were inhibited by Smad5 knockdown. Furthermore, deletion or mutation of the Smad-binding element in the HO-1 promoter also inhibited BMP6-induced luciferase activity. In summary, these findings suggest that induction of HO-1 through a Smad-dependent mechanism is responsible for the cytoprotective effect of BMP6 in H 2O 2-mediated renal cell injury.

Mechanisms responsible for pulmonary hypertension

Mechanisms responsible for pulmonary hypertension

Mechanisms of Arterial Remodeling in Hypertension

Diverse data collected over the past 4 decades suggest the existence of a mechanical homeostasis across multiple length and time scales in the vasculature. For example,1 stress fibers within endothelial and vascular smooth muscle cells appear to disassemble and then reassemble in a mechanically preferred manner when perturbed from a normal value of mechanical stress or strain; focal adhesions in smooth muscle cells and fibroblasts tend to increase in area in response to local increases in mechanical loading so as to maintain the stress constant at a preferred value; fibroblasts tend to increase the tractions that they exert on the extracellular matrix when external loads are decreased from a preferred value, thus suggesting an attempt to enforce a “tensional homeostasis”; vascular smooth muscle cells tend to relengthen to their normal, preferred values when an arteriole is forced into a vasoconstricted state for an extended period; and arteries tend to decrease in caliber in response to sustained decreases in flow-induced wall shear stress, to increase in thickness in response to sustained increases in pressure-induced circumferential stress, and to lengthen in response to extension-induced increases in axial stress. Although changes in the cytoskeleton and integrins occur within minutes, changes at the cell-cell and cell-matrix levels occur over hours, and those at the vessel level occur over days to weeks or months. Hence, despite marked differences in length scales (dimensions from nanometers to centimeters) and time scales (durations from minutes to months), mechanobiological control mechanisms in the vasculature tend to restore values of stress or strain toward preferred (homeostatic) values in response to diverse perturbations from normal.2–5 Biomechanics and mechanobiology thus play key roles in vascular development, tissue maintenance in maturity, normal adaptations, aging, disease progression, and responses to injury or clinical interventions. A current challenge in hypertension research is to …

Heparan Sulfate Regulates Self-renewal and Pluripotency of Embryonic Stem Cells

Embryonic stem (ES) cell self-renewal and pluripotency are maintained by several signaling cascades and by expression of intrinsic factors, such as Oct3/4 and Nanog. The signaling cascades are activated by extrinsic factors, such as leukemia inhibitory factor, bone morphogenic protein, and Wnt. However, the mechanism that regulates extrinsic signaling in ES cells is unknown. Heparan sulfate (HS) chains are ubiquitously present as the cell surface proteoglycans and are known to play crucial roles in regulating several signaling pathways. Here we investigated whether HS chains on ES cells are involved in regulating signaling pathways that are important for the maintenance of ES cells. RNA interference-mediated knockdown of HS chain elongation inhibited mouse ES cell self-renewal and induced spontaneous differentiation of the cells into extraembryonic endoderm. Furthermore, autocrine/paracrine Wnt/beta-catenin signaling through HS chains was found to be required for the regulation of Nanog expression. We propose that HS chains are important for the extrinsic signaling required for mouse ES cell self-renewal and pluripotency.

A possible link between resveratrol and TGF-β: Resveratrol induction of TGF-β expression and signaling

Resveratrol, a polyphenolic compound found in the skin of red fruits, exhibits anti-inflammatory, anti-oxidative, and anti-proliferative characteristics. Transforming growth factor-β (TGF-β) is a pleiotropic cytokine that also displays such properties. We therefore hypothesized that there might be a functional link between resveratrol and TGF-β. This study reports that resveratrol increased transcription of the TGF-β2 gene, enhanced the production of TGF-β2 protein, and activated Smad signaling in an autocrine manner in A549 human lung epithelial cell line. Thus, some of the beneficial effects of resveratrol on human health might be mediated, in part, through its effects on TGF-β expression and signaling.

Activation of Bone Morphogenetic Protein Signaling by a Gemini Vitamin D3 Analogue Is Mediated by Ras/Protein Kinase Cα

Bone morphogenetic proteins (BMP) are members of the transforming growth factor-beta superfamily, and they play an important role for embryonic development, for bone and cartilage formation, and during carcinogenesis. We have previously shown that the novel Gemini vitamin D(3) analogue, Ro-438-3582 [Ro3582; 1 alpha,25-dihydroxy-20S,21(3-hydroxy-3-methylbutyl)-23-yne-26,27-hexafluorocholecalciferol], inhibited cell proliferation and activated the BMP/Smad signaling pathway in MCF10AT1 breast epithelial cells. In this report, we investigated the upstream signaling pathways responsible for the activation of BMP/Smad signaling by Ro3582. Among seven different serine/threonine kinase inhibitors that we tested, protein kinase C (PKC) inhibitors blocked the effects of Ro3582 on the phosphorylation of Smad1/5, mRNA synthesis for BMP-2 and BMP-6, and cell growth in MCF10AT1 cells. Overexpression of PKC alpha, but not PKC epsilon, PKC delta or PKC zeta isoforms, increased Ro3582-induced phosphorylation of Smad1/5, suggesting that PKC alpha mediates the activation of Smad signaling and inhibition of cell proliferation. Interestingly, the activation of Smad signaling by Ro3582 was shown in Ha-ras-transfected MCF10AT1 cells, but not in the parent cell line (MCF10A without Ras). Inhibiting Ras activity blocked the translocation of PKC alpha to the plasma membrane and the phosphorylation of Smad1/5 induced by Ro3582, indicating that Ras is necessary for the activation of PKC alpha and Smad signaling. In conclusion, Ro3582 inhibits cell proliferation and activates BMP/Smad signaling via a Ras and PKC alpha pathway in breast epithelial cells.