Smad Transcriptional Corepressors in TGFβ Family Signaling

Mechanism of Cordyceps sinensis and its Extracts in the Treatment of Diabetic Kidney Disease: A Review

Diabetic kidney disease (DKD) is the major reason of chronic kidney disease (CKD)-caused end-stage renal failure (ESRF), and leads to high mortality worldwide. At present, the treatment of DKD is mainly focused on controlling the hyperglycemia, proteinuria, and hypertension, but is insufficient on the effective delay of DKD progression. Cordyceps sinensis is a kind of wild-used precious Chinese herb. Its extracts have effects of nephroprotection, hepatoprotection, neuroprotection, and protection against ischemia/reperfusion-induced injury, as well as anti-inflammatory and anti-oxidant activities. According to the theory of traditional Chinese medicine, Cordyceps sinensis can tonify the lung and the kidney. Several Chinese patent medicines produced from Cordyceps sinensis are often used to treat DKD and achieved considerable efficacy. This review summarized the clinical usage of Cordyceps sinensis, as well as its mainly biological activities including anti-hyperglycemic, anti-inflammatory, immunomodulatory, anti-oxidant, anti-fibrotic activities and regulation of apoptosis.

TGIF1 functions as a tumor suppressor in pancreatic ductal adenocarcinoma

A prominent function of TGIF1 is suppression of transforming growth factor beta (TGF-β) signaling, whose inactivation is deemed instrumental to the progression of pancreatic ductal adenocarcinoma (PDAC), as exemplified by the frequent loss of the tumor suppressor gene SMAD4 in this malignancy. Surprisingly, we found that genetic inactivation of Tgif1 in the context of oncogenic Kras, KrasG12D , culminated in the development of highly aggressive and metastatic PDAC despite de-repressing TGF-β signaling. Mechanistic experiments show that TGIF1 associates with Twist1 and inhibits Twist1 expression and activity, and this function is suppressed in the vast majority of human PDACs by KrasG12D /MAPK-mediated TGIF1 phosphorylation. Ablating Twist1 in KrasG12D ;Tgif1KO mice completely blunted PDAC formation, providing the proof-of-principle that TGIF1 restrains KrasG12D -driven PDAC through its ability to antagonize Twist1. Collectively, these findings pinpoint TGIF1 as a potential tumor suppressor in PDAC and further suggest that sustained activation of TGF-β signaling might act to accelerate PDAC progression rather than to suppress its initiation.

TEL (ETV6)-AML1 (RUNX1) initiates self-renewing fetal pro-B cells in association with a transcriptional program shared with embryonic stem cells in mice

The initial steps involved in the pathogenesis of acute leukemia are poorly understood. The TEL-AML1 fusion gene usually arises before birth, producing a persistent and covert preleukemic clone that may convert to precursor B cell leukemia following the accumulation of secondary genetic "hits." Here, we show that TEL-AML1 can induce persistent self-renewing pro-B cells in mice. TEL-AML1+ cells nevertheless differentiate terminally in the long term, providing a "window" period that may allow secondary genetic hits to accumulate and lead to leukemia. TEL-AML1-mediated self-renewal is associated with a transcriptional program shared with embryonic stem cells (ESCs), within which Mybl2, Tgif2, Pim2, and Hmgb3 are critical and sufficient components to establish self-renewing pro-B cells. We further show that TEL-AML1 increases the number of leukemia-initiating cells that are generated in collaboration with additional genetic hits, thus providing an overall basis for the development of novel therapeutic and preventive measures targeting the TEL-AML1-associated transcriptional program.

Preventive effects and mechanisms of rhein on renal interstitial fibrosis in obstructive nephropathy

Renal interstitial fibrosis is a common outcome of a variety of chronic renal diseases. Here we evaluated the therapeutic efficacy of rhein on renal interstitial fibrosis induced by unilateral ureteral obstruction (UUO) and investigated the potential mechanisms. Mice underwent UUO, followed by orally administrated rhein (150 mg/kg/d) or control vehicle. Renal interstitial injury and the degree of fibrosis were evaluated by pathological staining and Western blot. The possible mechanisms were studied by Western blot, indirect immune-fluorescence and enzyme-linked immunosorbent assay. Our results showed that rhein therapy markedly ameliorated renal interstitial fibrotic lesions, reduced α-smooth muscle actin (α-SMA) expression, attenuated deposition of fibronectin (FN). Rhein also suppressed transforming growth factor-β1 (TGF-β1) and its type I receptor expression in obstructed kidneys. In vitro, rhein abolished the α-SMA and fibronectin expression of rat kidney interstitial fibroblasts cells (NRK-49F) induced by TGF-β1. These observations strongly suggest that rhein is a potent inhibitor of renal interstitial fibrosis, and its therapeutic mechanism is, at least in part, blocking interstitial fibroblasts cells activation.

Cordycepin inhibits renal interstitial myofibroblast activation probably by inducing hepatocyte growth factor expression

Renal interstitial fibrosis is the common end point of progressive renal diseases leading to the deterioration and eventual loss of renal function. This study investigated the effect and potential mechanism of cordycepin on activation of renal interstitial fibroblast cells. The time and dose-responses of cordycepin in rat renal interstitial fibroblast (NRK-49F) cells were analyzed. The proliferation of NRK-49F and the expression of α-smooth muscle actin (α-SMA) and fibronectin (FN) were examined. The expression and translocation of Smad proteins also were measured by western blot and indirect immunofluorescence staining. The mRNA level of hepatocyte growth factor (HGF) and the expression of HGF receptor c-Met and its phosphorylation (p-Met) were also detected. Cordycepin suppressed the proliferation of NRK-49F and the expression of α-SMA and FN induced by transforming growth factor-β1 (TGF-β1). The pretreatment of cordycepin markedly attenuated the nuclear translocation and accumulation of activated Smad2/3 in NRK-49F cells. Furthermore, cordycepin not only increased HGF expression, but also induced HGF secretion, as well as HGF receptor phosphorylation in NRK-49F cells. Cordycepin possesses renoprotective activity through suppression myofibroblast activation. This action is mediated, at least in part, by blocking nuclear translocation and accumulation of activated Smad2/3 protein and up-regulating anti-fibrotic HGF expression and secretion and HGF receptor activation.

Regulation of collagen synthesis by inhibitory Smad7 in cardiac myofibroblasts

Transforming growth factor-beta(1) (TGF-beta(1)) signal and downstream Smads play an important role in tissue fibrosis and matrix remodeling in various etiologies of heart failure. Inhibitory Smad7 (I-Smad7) is an inducible regulatory Smad protein that antagonizes TGF-beta(1) signal mediated via direct abrogation of R-Smad phosphorylation. The effect of ectopic I-Smad7 on net collagen production was investigated using hydroxyproline assay. Adenovirus-mediated I-Smad7 gene (at 100 multiplicity of infection) transfer was associated with significant decrease of collagen synthesis in the presence and absence of TGF-beta(1) in primary rat cardiac myofibroblasts. In I-Smad7-infected cells, we also observed the ablation of TGF-beta(1)-induced R-Smad2 phosphorylation vs. LacZ controls. Overdriven I-Smad7 was associated with significantly increased expression of immunoreactive 65-kDa matrix metalloproteinase-2 (MMP-2) protein in culture medium of myofibroblast compared with LacZ-infected cells. Expression of the 72-kDa MMP-2 variant, e.g., the inactive form, was not altered by exogenous I-Smad7 transfection/overexpression. Furthermore, I-Smad7 overexpression was associated with a significant increase and decrease in expression of p27 and phospho-Rb protein, respectively, as well as reduced [(3)H]thymidine incorporation vs. Ad-LacZ-infected controls. We suggest that negative modulation of R-Smad phosphorylation by ectopic I-Smad7 may contribute to the downregulation of collagen in cardiac myofibroblasts and may suppress the proliferation of these cells. Thus treatments targeting the collagen deposition by overexpression of I-Smad7 may provide a new therapeutic strategy for cardiac fibrosis.

Smad4 regulates claudin-1 expression in a transforming growth factor-beta-independent manner in colon cancer cells

We have recently reported that the expression of a tight junction protein, claudin-1, is increased during colon carcinogenesis and particularly metastatic colorectal cancer. Manipulation of claudin-1 levels in colon cancer cells showed a positive correlation between claudin-1 expression and tumor growth and metastasis. However, the mechanisms underlying the increased claudin-1 expression in colorectal cancer remains unknown. The tumor suppressor Smad4 is a central intracellular signal transduction component of the transforming growth factor-beta (TGF-beta) family of cytokines. Loss of Smad4 protein expression is correlated with poor prognosis and is frequently observed in invasive and metastatic colorectal carcinoma. In the present study, we report an inverse relationship between Smad4 and claudin-1 expression in human colorectal carcinoma tumor samples and in human colon cancer cell lines. We found that the expression of Smad4 in Smad4-deficient but claudin-1-positive SW480 or HT29 colon cancer cell lines down-regulates claudin-1 expression through transcriptional repression by modulating beta-catenin/T-cell factor/lymphocyte enhancer factor activity. Furthermore, this Smad4-dependent inhibition of claudin-1 expression is independent of TGF-beta signaling because Smad4 expression alone is insufficient to restore TGF-beta signaling in the SW480 cells, and the selective TGF-beta receptor kinase inhibitor LY364947 did not prevent the Smad4 suppression of claudin-1 protein expression in either SW480 or HT29 cells. Taken together, these findings suggest a novel mechanism underlying Smad4 tumor-suppressive function through regulation of a potential metastatic modulator, claudin-1, in a TGF-beta-independent manner.

Expression profiling of transforming growth factor beta superfamily genes in developing orofacial tissue

BACKGROUND

Numerous signaling molecules have been shown to participate in the dynamic process of orofacial development. Among these signal mediators, members of the transforming growth factor beta (TGFbeta) superfamily have been shown to play critical roles. Developing orofacial tissue expresses TGFbeta and bone morphogenetic protein (BMP) mRNAs, their protein isoforms and TGFbeta- and BMP-specific receptors. All these molecules display unique temporospatial patterns of expression in embryonic orofacial tissue, suggesting functional roles in orofacial development. For example, the TGFbetas and BMPs regulate maxillary mesenchymal cell proliferation and extracellular matrix synthesis. This is particularly noteworthy in that perturbation of either process results in orofacial clefting. Although the cellular and phenotypic effects of the TGFbeta superfamily of growth factors on embryonic orofacial tissue have been extensively studied, the specific genes that function as effectors of these cytokines in orofacial development have not been well defined.

METHODS

In the present study, oligonucleotide-based microarray technology was utilized to provide a comprehensive analysis of the expression of the panoply of genes related to the TGFbeta superfamily, as well as those encoding diverse groups of proteins functionally associated with this superfamily, during orofacial ontogenesis.

RESULTS

Of the 7000 genes whose expression was detected in the developing orofacial region, 249 have been identified that encode proteins related to the TGFbeta superfamily. Expression of some (27) of these genes was temporally regulated. In addition, several candidate genes, whose precise role in orofacial development is still unknown, were also identified. Examples of genes constituting this cluster include: TGFbeta1-induced antiapoptotic factor-1 and -2, TGFbeta-induced factor 2, TGFbeta1 induced transcript-1 and -4, TGFbeta-inducible early growth response 1, follistatin-like 1, follistatin-like 3, transmembrane protein with EGF-like and two follistatin-like domains (Tmeff)-1 and -2, nodal modulator 1, various isoforms of signal transducers and activators of transcription (Stat), notch, and growth and differentiation factors.

CONCLUSIONS

Elucidation of the precise physiological roles of these proteins in orofacial ontogenesis should provide unique insights into the intricacies of the TGFbeta superfamily signal transduction pathways utilized during orofacial development.

Both Sp1 and Smad participate in mediating TGF-β1-induced HGF receptor expression in renal epithelial cells

Hepatocyte growth factor (HGF) receptor is a transmembrane receptor tyrosine kinase encoded by the c-met protooncogene. In this study, we demonstrated that c-met expression was upregulated in the kidney after obstructive injury in mice. Because the pattern of c-met induction was closely correlated with transforming growth factor-β1 (TGF-β1) expression in vivo, we further investigated the regulation of c-met expression in renal tubular epithelial (HKC) cells by TGF-β1 in vitro. Real-time RT-PCR and Northern and Western blot analyses revealed that TGF-β1 significantly induced c-met expression in HKC cells, which primarily took place at the gene transcriptional level. Overexpression of inhibitory Smad7 completely abolished c-met induction, indicating its dependence on Smad signaling. Interestingly, TGF-β1-induced c-met expression was also contingent on a functional Sp1, as ablation of Sp1 binding with mithramycin A abrogated c-met induction in HKC cells. Transfection and sequence analysis identified a cis-acting TGF-β1-responsive region in the c-met promoter, in which resided a putative Smad-binding element (SBE) and an adjacent Sp1 site. TGF-β1 not only induced Smad binding to the SBE/Sp1 sites in the c-met promoter, but also enhanced the binding of Sp proteins. Furthermore, Sp1 could form a complex with Smads in a TGF-β1-dependent fashion. These results suggest a novel regulatory mechanism controlling c-met expression by TGF-β1 in renal epithelial cells, in which both Smad and Sp proteins participate and cooperate in activating c-met gene transcription.

Prostacyclin derivatives prevent the fibrotic response to TGF-beta by inhibiting the Ras/MEK/ERK pathway

The SMAD-mediated induction of connective tissue growth factor (CTGF), a fibroproliferative cytokine, by transforming growth factor (TGF)beta is required for the development of sustained fibrosis in humans. Here, we show that in fibroblasts, activation of the Ras/MEK/ERK pathway is required for the SMAD-mediated induction of CTGF by TGFbeta2. We then show that activation of protein kinase A (PKA) in fibroblasts is able to block Ras/MEK/ERK signaling and abolish the fibrotic response. Previously, we found that prostacyclin agonists were able to prevent the induction of CTGF in fibroblasts, and in patients with the fibrotic disease scleroderma. Here, we confirm the in vitro and in vivo antifibrotic effects of prostacyclin derivatives and show that these effects are due to PKA-dependent inhibition of the Ras/MEK/ERK pathway. Ras/MEK/ERK does not directly affect SMAD signaling. The coordinate and varied biological responses to TGFbeta are in part due to the interactions of signaling pathways within target cells. Specific inhibition of fibroblast Ras/MEK/ERK signaling might prevent fibrosis while leaving other physiological effects of TGFbeta unaltered.

TGF-beta-mediated control of allergen-specific T-cell responses

Control of allergen-specific response by suppressive cytokines involves several layers of regulation, including secretion of the cytokine, deviation of cytokine expression by altered T-cell differentiation, immediate (de-) phosphorylation events upon binding of suppressive cytokines, and laterations in susceptibility of suppression.

Expression profiling of palmitate- and oleate-regulated genes provides novel insights into the effects of chronic lipid exposure on pancreatic beta-cell function

Chronic lipid exposure is implicated in beta-cell dysfunction in type 2 diabetes. We therefore used oligonucleotide arrays to define global alterations in gene expression in MIN6 cells after 48-h pretreatment with oleate or palmitate. Altogether, 126 genes were altered > or =1.9-fold by palmitate, 62 by oleate, and 46 by both lipids. Importantly, nine of the palmitate-regulated genes are known to be correspondingly changed in models of type 2 diabetes. A tendency toward beta-cell de-differentiation was also apparent with palmitate: pyruvate carboxylase and mitochondrial glycerol 3-phosphate dehydrogenase were downregulated, whereas lactate dehydrogenase and fructose 1,6-bisphosphatases were induced. Increases in the latter (also seen with oleate), along with glucosamine-phosphate N-acetyl transferase, imply upregulation of the hexosamine biosynthesis pathway in palmitate-treated cells. However, palmitate also increased expression of calcyclin and 25-kDa synaptosomal-associated protein (SNAP25), which control distal secretory processes. Consistent with these findings, secretory responses to noncarbohydrate stimuli, especially palmitate itself, were upregulated in palmitate-treated cells (much less so with oleate). Indeed, glucose-stimulated secretion was slightly sensitized by chronic palmitate exposure but inhibited by oleate treatment, whereas both lipids enhanced basal secretion. Oleate and palmitate also induced expression of chemokines (MCP-1 and GRO1 oncogene) and genes of the acute phase response (serum amyloid A3). Increases in transcriptional modulators such as ATF3, CCAAT/enhancer binding protein-beta (C/EBPbeta), C/EBPdelta, and c-fos were also seen. The results highlight links between regulated gene expression and phenotypic alterations in palmitate versus oleate-pretreated beta-cells.