Intracellular signal transduction pathways induced by leptin in C2C12 cells

As experimental evidence suggests that leptin may have direct effects on peripheral tissues, we investigated some of the transductional molecules induced by leptin in C2C12 cells. In immunoprecipitation experiments using anti-p85 antibodies (a regulatory subunit of phosphatidylinositol-3-kinase; PI3K), we observed a significant increase in PI3K activity. Immunoblot analyses showed that Akt, GSK3, ERK1, ERK2, and p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation significantly increased after leptin treatment. Protein kinase C (PKC)-zeta was also activated by leptin, as documented by an immunocomplex kinase assay and immunoblotting experiments. The treatment of C2C12 cells with Wortmannin before leptin administration inhibited induction of the phosphorylation of ERKs (extracellular signal-regulated kinases) but not that of p38 MAPK, whereas pre-treatment with a PKC-zeta inhibitor partially decreased ERK phosphorylation. Taken together, our in vitro results further support the hypothesis that leptin acts acutely on skeletal muscle tissue through some of the components of insulin signalling, including PKC-zeta.     

Prion protein induced signaling cascades in monocytes

Prion proteins play a central role in transmission and pathogenesis of transmissible spongiform encephalopathies. The cellular prion protein (PrP(C)), whose physiological function remains elusive, is anchored to the surface of a variety of cell types including neurons and cells of the lymphoreticular system. In this study, we investigated the response of a mouse monocyte/macrophage cell line to exposure with PrP(C) fusion proteins synthesized with a human Fc-tag. PrP(C) fusion proteins showed an attachment to the surface of monocyte/macrophages in nanomolar concentrations. This was accompanied by an increase of cellular tyrosine phosphorylation as a result of activated signaling pathways. Detailed investigations exhibited activation of downstream pathways through a stimulation with PrP fusion proteins, which include phosphorylation of ERK(1,2) and Akt kinase. Macrophages opsonize and present antigenic structures, contact lymphocytes, and deliver cytokines. The findings reported here may become the basis of understanding the molecular function of PrP(C) in monocytes and macrophages.     

RGS与G蛋白信号转导的调节

ＲＧＳｓ（ｒｅｇｕｌａｔｏｒｓ ｏｆ Ｇ－ｐｒｏｔｅｉｎ ｓｉｇｎａｌｉｎｇ）是最近发现的Ｇ－蛋白信号转导的负调节子,大部分ＲＧＳｓ通过ＧＡＰｓ（ＧＴＰａｓｅ ａｃｔｉｖａｔｉｎｇ ｐｒｏｔｅｉｎｓ）方式发挥作用,ＲＧＳ的作用具有高度特异性,在体内受到严密的调节。对ＲＧＳ的深入研究有利于对信号转导调节的了解。     

P311 binds to the latency associated protein and downregulates the expression of TGF-beta1 and TGF-beta2

P311 is an 8-kDa protein originally found in neurons and muscle. We recently showed that expression of P311 in NIH 3T3 cells induced a myofibroblast phenotype with low TGF-beta1 expression. Here we demonstrate that P311 downregulates not only TGF-beta1, but also TGF-beta2, expression, with no effect on TGF-beta3. In addition, P311 interacts with TGF-beta2 in a yeast two-hybrid system through a sequence encompassing part of the TGF-beta latent associated protein (LAP) and part of mature TGF-beta2. Coimmunoprecipitations demonstrated interaction between P311 and TGF-beta1 and 2, but not TGF-beta3. Additional coimmunoprecipitations after introducing LAP or mature TGF-beta1 into cells demonstrated P311 binding to LAP, but not to mature TGF-beta. P311 has a conserved PEST domain, which generally serves as a rapid degradation signal. Deletion of the PEST domain reversed the effect of P311 on TGF-beta isoforms. Finally, Smad3 activity was decreased in P311-expressing cells, but was corrected by exogenous TGF-beta1 treatment, which also elevated TGF-beta1 mRNA level. This suggested that P311 downregulates TGF-beta1 and 2 in part by blocking TGF-beta autoinduction.     

Towards an understating of signal transduction protein interaction networks

Protein network analysis has witnessed a number of advancements in the past for understanding molecular characteristics for important network topologies in biological systems. The signaling pathway regulates cell cycle progression and anti-apoptotic molecules. This pathway is also involved in maintaining cell survival by modulating the activity of apoptosis through RAS, P13K, AKT and BAD activities. The importance of protein-protein interactions to improve usability of the interactome by scoring and ranking interaction data for proteins in signal transduction networks is illustrated using available data and resources.     

Thymosin beta 4 stimulates laminin-5 production independent of TGF-beta

Thymosin beta 4 (Tbeta(4)) stimulates epithelial cell migration and promotes laminin-5 (LM-5) expression. Using gene expression analysis with human corneal epithelial cells treated with Tbeta(4), we find that both LM-5 gamma2 chain and transforming growth factor beta 1 (TGFbeta-1) are increased by more than 2-fold over untreated cells. These findings were confirmed by RT-PCR and at the protein level. Although TGFbeta-1 increases LM-5 synthesis in a dose-dependent manner, it does not appear to be the mechanism by which Tbeta(4) acts on LM-5 gamma2 chain synthesis based on three independent experiments. In a time-course analysis, Tbeta(4) increases LM-5 gamma2 chain expression at 2 h and peaks at 6 h, while TGFbeta-1 increases LM-5 gamma2 chain expression only at 4 h and peaks at 8 h. When Tbeta(4)-induced LM-5 gamma2 chain expression is blocked with neutralizing antibodies to TGFbeta-1, LM-5 gamma2 chain expression is increased. Finally, in TGFbeta-1 knock-out mice, Tbeta(4) increases LM-5 gamma2 chain expression to levels higher than that observed in wild-type mice treated with Tbeta(4). These findings demonstrate that Tbeta(4) induces both TGFbeta-1 and LM-5 gamma2 chain expression in corneal epithelial cells. Tbeta(4) and TGFbeta-1 increase LM-5 gamma2 chain expression by independent pathways. Suppression of TGFbeta-1 further increases LM-5 gamma2 chain expression.     

葡萄糖转运子4 转位信号转导通路的研究进展

葡萄糖是大部分细胞主要能量来源,它进入细胞的过程在生命的维持中无疑成为一个重要的步骤。而葡萄糖进入细胞是依赖于这些细胞上的葡萄糖转运子和相应的对其进行调节的因子。葡萄糖转运子4（GLUT4）在糖进入细胞维持血糖平衡中起了重要的作用。近年有关GLUT4的研究文献很多,但却总给人不系统的感觉。本文对GLUT4转位的胰岛素依赖和非胰岛素依赖的信号途径以及其远端过程及机制作一综述,同时分析了GLUT4转位的信号途径的研究中存在的问题和将来研究的方向。     

TGF-beta induces formation of F-actin cores and matrix degradation in human breast cancer cells via distinct signaling pathways

Transforming growth factor beta regulates many biological processes including cell motility and invasion. Podosomes are specialized F-actin rich structures found in normal cells, such as osteoclasts and macrophages. Tumor cells often form related structures called invadopodia that are thought to promote invasion and metastasis. Here we show that human breast cancer cells organize F-actin rich structures in response to transforming growth factor beta that colocalize with areas of extracellular matrix degradation. We further show that organizing the complex of proteins needed to form these structures requires signaling through phosphatidylinositide 3-kinase and Src kinase, while activating the proteases involved in degradation of extracellular matrix requires extracellular signal-regulated kinase signaling, and that each of these pathways is activated by transforming growth factor beta in CA1D human breast cancer cells.     

TGF-β/Smads通路转导蛋白在心力衰竭发病中的研究进展

转化生长因子-β（transforming growth factor-β,TGF-β）作用复杂,广泛参与哺乳动物的各种病理生理过程如影响细胞的增殖分化、参与心力衰竭发展。TGF-β信号通路关键的信号传导分子为胞浆蛋白Smads。TGF-β诱导分化心肌成纤维细胞,刺激胶原蛋白等细胞间质成分的合成,促进细胞间质的沉积和抑制弹性蛋白酶等的分泌,刺激蛋白酶抑制剂的表达,从而抑制Ⅰ型胶原成分的降解,促进心肌纤维化发展,进一步了解TGF-β/Smads通路转导蛋白的作用及机制,通过抑制TGF-β/Smads通路转导蛋白作为治疗新靶点为最终防止心力衰竭提供了新的思路。     

The ubiquitin–proteasome system and signal transduction pathways regulating Epithelial Mesenchymal transition of cancer

Epithelial to Mesenchymal transition (EMT) in cancer, a process permitting cancer cells to become mobile and metastatic, has a signaling hardwire forged from development. Multiple signaling pathways that regulate carcinogenesis enabling characteristics in neoplastic cells such as proliferation, resistance to apoptosis and angiogenesis are also the main players in EMT. These pathways, as almost all cellular processes, are in their turn regulated by ubiquitination and the Ubiquitin-Proteasome System (UPS). Ubiquitination is the covalent link of target proteins with the small protein ubiquitin and serves as a signal to target protein degradation by the proteasome or to other outcomes such as endocytosis, degradation by the lysosome or specification of cellular localization. This paper reviews signal transduction pathways regulating EMT and being regulated by ubiquitination.     

Ghalpha/tissue transglutaminase 2: an emerging G protein in signal transduction

Gh protein is an heterodimer made up of two subunits alpha and beta. Different from the traditional monomeric and heterotrimeric G proteins, Ghalpha subunit exhibits both GTPase and transglutaminase activities whereas Ghbeta was identified as calreticulin. Activation of Gh by G protein-coupled receptors (GPCR) turns off transglutaminase activity and shifts Ghalpha to signal transducer. Thereafter, Ghalpha regulates downstream effectors. All these aspects are discussed in the present review, in order to shed new light on this atypical G protein.     

Peptides as probes for G protein signal transduction

Triggered by agonist binding to cell surface receptors, the heterotrimeric G proteins dissociate into and βγ subunits, each activating distinct second messenger pathways. Peptides from the primary sequences of receptors, G proteins, and effectors have been used to study the molecular interactions between these proteins. Receptor-derived peptides from the second, third and fourth intracellular loops and certain naturally occurring peptides antagonize G protein interactions and can directly activate G protein. These peptides bind to G protein sites that include the N and C terminal regions of the subunit and a yet to be identified region of the β subunit. Peptides have also been useful in characterizing G protein-effector interactions. The identification of the contact sites between proteins involved in G protein signal transduction should aid in the development of non-peptide mimetic therapeutics which could specifically modify G protein-mediated cellular responses.     

中性粒细胞CXCR1、CXCR2活化及其信号传导

中性粒细胞属非特异性免疫细胞,其表面可表达CXCR1和CXCR2.IL-8是其共同配体,它们彼此结合激活后续级联信号传导,产生一系列生物学效应,在介导炎症反应、促进血管新生、维持中性粒细胞稳态等起重要作用.Reparixin是非竞争变构的CXCR1和CXCR2阻滞剂,可抑制中性粒细胞过度趋化、迁移介导的炎症反应.     

STAT1 is involved in signal transduction in the EPO induced HEL cells

Erythropoietin(EPO) is the major regulator of mamalian erythropoisis,which stimulates the growth and differentiation of hematopoietic cells through interaction with its receptor(EPO-R),Here we use HEL cells (a human erythro-leukemia cell line) as a model to elucidate the pathway of signal transduction in the EPO-induced HEL cells.Our data show that the EPOR (EPO receptor) on the surface of HEL cells interacts with the Janus tyrosine protein kinase(Jak2) to transduce intracellular signals through phosphorylation of cytoplasmic proteins in EPO-treated HEL cells.Both STAT1 and STAT5 in this cell line are tyrosine-phosphorylated and translocated to nucleus following the dinding of EPO to HEL cells.Furthermore,the dinding of both STAT1 and STAT5 proteins to specific DNA elements(SIE and PIE elements) is revealed in an EPO-dependent manner,Our data demonstrate that the pathway of signal transduction following the binding of EPO to HEL cells is similar to immature eryhroid cell from the spleen of mice infected with anemia strain of Friend virus.     

C-reactive protein-induced upregulation of extracellular matrix metalloproteinase inducer in macrophages: inhibitory effect of fluvastatin

OBJECTIVE: Extracellular matrix metalloproteinase inducer (EMMPRIN) and matrix metalloproteinase (MMP)-9 were reported to be expressed at the macrophage-rich area in human coronary atherosclerotic plaque. We examined whether C-reactive protein (CRP) activates macrophages to express EMMPRIN and MMP-9 in vitro and whether statins inhibit it. METHODS AND RESULTS: Rat peritoneal macrophages were collected by peritoneal lavage, and were incubated in the presence or absence of CRP. CRP at 5 microg/ml increased the gene expression of EMMPRIN relative to GAPDH, measured by RT-PCR, by 1.67+/-0.07 fold at 24 h and by 1.85+/-0.49 fold at 48 h (both p<0.05). The gene expression of MMP-9 in the presence of CRP at 5 microg/ml was followed by 1.36+/-0.11 fold increase at 24 h and by 3.95+/-0.81 fold at 48 h (both p<0.05). CRP at 5 microg/ml for 48 h increased by 6 fold MMP-9 activity, measured by zymography, without affecting tissue inhibitor of metalloproteinases-1. Boiled CRP at 5 mug/ml for 48 h unaffected MMP-9 activity. Fluvastatin blocked the CRP-induced increases in EMMPRIN and MMP-9 expression and activity. Diphenylene iodonium, an inhibitor of NADPH oxidase, had a similar effect on MMP-9 activity. Fluvastatin suppressed the CRP-induced increases in 8-epi-prostaglandin F(2alpha) levels in the condition media. CONCLUSIONS: CRP is an activator for macrophages to enhance EMMPRIN and MMP-9 expression. Fluvastatin inhibits them presumably through its antioxidant effect.     

Understanding signal integration through targeted mutations of an adapter protein

Immunoreceptor engagement leads to the activation of multiple second messenger cascades, and integration of these pathways requires proper function of a number of adapter proteins. Although adapters possess no intrinsic enzymatic function, they nucleate the formation of multi-molecular protein complexes to support downstream signaling. Since adapters contain functionally distinct domains, intense investigation has been devoted to understanding how these regions act to integrate signals. This review describes the evolution of studies investigating one of these adapters, the SH2 domain-containing leukocyte protein of 76 kDa. Through utilizing biochemical, genetic and imaging techniques, a model has emerged describing how this adapter regulates signals resulting in complex immune responses.     

Regulation of interleukin-21 receptor expression and its signal transduction by WSB-2

Interleukin-21 (IL-21) is a pleiotropic cytokine that regulates T-cell, B-cell, NK-cell, and myeloid-cell functions. IL-21 binds with its cognate receptor complex, which consists of the IL-21 receptor (IL-21R) and the common gamma chain (γc) receptor subunit. We identified novel IL-21R-binding molecule, WD-40 repeats containing SOCS-box-2, WSB-2. WSB-2 associated with the membrane-proximal intracytoplasmic region of IL-21R, including box1 and box2. Overexpression study of WSB-2 showed the reduction of IL-21R expression and IL-21-induced signal transduction. On the other hand, small interfering RNA for WSB-2 enhanced the expression level of IL-21R and IL-21-induced STAT3 activation, indicating that WSB-2 negatively controls the receptor expression. This report provides the first evidence that WSB-2 is a regulator of IL-21R expression and IL-21-induced signal transduction.