Overexpression of GEFT,a Rho family guanine nucleotide exchange factor,predicts poor prognosis in patients with rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is one of the most common soft-tissue sarcomas in children and adolescents with poor prognosis. Yet, there is lack of effective prognostic biomarkers for RMS. The present study, therefore, aimed to explore potential biomarkers for RMS based on our previous findings using array comparative genomic hybridization. We investigated guanine nucleotide exchange factor, GEFT, at expression level in 45 RMS patients and 36 normal striated muscle controls using immunohistochemistry using tissue microarrays. The expression rate of GEFT in RMS samples (42/45, 93.33%) was significantly higher (P<0.05) than that in normal controls (5/36, 13.89%). Moreover, the overexpression rate of GEFT in RMS (31/45, 68.89%) was also significantly higher (P<0.05) than that in normal controls (0/36, 0.00%). Increased expression of GEFT correlated significantly with advanced disease stages (stages III/IV) (P=0.001), lymph node metastasis (P=0.019), and distant metastasis (P=0.004), respectively, in RMS patients. In addition, RMS patients having overexpressed GEFT experienced worse overall survival (OS) than those having low levels of GEFT (P=0.001). GEFT overexpression was determined to be an independent prognostic factor for poor OS in RMS patients (hazard ratio: 3.491, 95% confidence interval: 1.121-10.871, P=0.004). In conclusion, these observations provide the first evidence of GEFT overexpression in RMS and its correlations with disease aggressiveness and metastasis. These findings suggest that GEFT may serve as a promising biomarker predicting poor prognosis in RMS patients, thus implying its potential as a therapeutic target.     

梗死灶周围心肌C3G蛋白表达增加参与了异丙肾上腺素诱导的梗死后心脏重塑恶化的发病机制

 目的 通过观察梗死灶周围心肌C3G蛋白的表达及异丙肾上腺素(ISO)对其的影响,探讨梗死灶周围心肌C3G蛋白是否参与了异丙肾上腺素诱导的梗死后心脏重塑恶化的发病机制。方法 按Litwin方法建立心肌梗死(心梗)及假手术模型。 术后7天仍存活的雄性SD大鼠分为心梗组,假手术组,心梗ISO组,假手术ISO组。其中,心梗组及假手术组给予生理盐水5ml/kg每三天一次, 腹腔注射,至干预后12周;心梗ISO组及假手术ISO组给予ISO 5mg/kg每三天一次, 腹腔注射,余方法同上。免疫印迹检测梗死灶周围心肌C3G 蛋白的表达。结果 干预后12周, 梗死灶周围心肌C3G蛋白表达积分光密度标化值分别为：心梗组（1.14±0.29, n=8）, 假手术组（0.90±0.10,n=6）, 心梗ISO组（1.51±0.18,n=10 ）, 假手术ISO组（0.97±0.26, n=8）。心梗组较假手术组、 心梗ISO组较假手术ISO组、及心梗ISO组较心梗组梗死灶周围心肌C3G蛋白的表达均显著增高（P＜0.05）。 结论 梗死灶周围心肌C3G蛋白表达显著增加, 而ISO可使C3G蛋白表达更显著增加; C3G蛋白表达增加参与了梗死后心室重塑,缺血性心肌病及心力衰竭的发病机制,且C3G蛋白表达进一步增加参与了ISO诱导的梗死后心室重塑,缺血性心肌病及心力衰竭恶化的发病机制。     

Guanine nucleotide exchange factors for the Rho GTPases: a role in human disease?

 The Rho family of low molecular weight GTP-binding proteins control important aspects of cell shape, adhesion, movement and growth. The DBL-homology (DH) protein family of upstream regulators of Rho GTPases has recently been identified, and deregulated expression of these proteins can have dramatic cellular consequences. This review examines the possible role of DH proteins and Rho GTPases in oncogenesis, metastasis and development. Received: 29 March 1996 / Accepted: 3 June 1996     

Organization of proximal signal initiation at the TCR:CD3 complex

Summary:  The series of events leading to T-cell activation following antigen recognition has been extensively investigated. Although the exact mechanisms of ligand binding and transmission of this extracellular interaction into a productive intracellular signaling sequence remains incomplete, it has been known for many years that the immunoreceptor tyrosine activation motifs (ITAMs) of the T-cell receptor (TCR):CD3 complex are required for initiation of this signaling cascade because of the recruitment and activation of multiple protein tyrosine kinases, signaling intermediates, and adapter molecules. It however remains unclear why the TCR:CD3 complex requires 10 ITAMs, while many other ITAM-containing immune receptors, such as Fc receptors (FcRs) and the B cell receptor (BCR), contain far fewer ITAMs. We have recently demonstrated that various parameters of T cell development and activation are influenced by the number, as well as location and type, of ITAMs within the TCR:CD3 complex and hence propose that the TCR is capable of 'scalable signaling' that facilitates the initiation and orchestration of diverse T-cell functions. While many of the underlying mechanisms remain hypothetical, this review intends to amalgamate what we have learned from conventional biochemical analyses regarding initiation and diversification of T-cell signaling, with more recent evidence from molecular and fluorescent microscopic analyses, to propose a broader purpose for the TCR:CD3 ITAMs. Rather than simply signal initiation, individual ITAMs may also be responsible for the differential recruitment of signaling and regulatory molecules which ultimately affects T-cell development, activation and differentiation.     

Rho guanine nucleotide exchange factor is an NFL mRNA destabilizing factor that forms cytoplasmic inclusions in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset progressive disorder of unknown etiology characterized by the selective degeneration of motor neurons. Recent evidence supports the hypothesis that alterations in RNA metabolism in motor neurons can explain the development of protein inclusions, including neurofilamentous aggregates, observed in this pathology. In mice, p190RhoGEF, a guanine nucleotide exchange factor, is involved in neurofilament protein aggregation in an RNA-triggered transgenic model of motor neuron disease. Here, we observed that rho guanine nucleotide exchange factor (RGNEF), the human homologue of p190RhoGEF, binds low molecular weight neurofilament mRNA and affects its stability via 3′ untranslated region destabilization. We observed that the overexpression of RGNEF in a stable cell line significantly decreased the level of low molecular weight neurofilament protein. Furthermore, we observed RGNEF cytoplasmic inclusions in ALS spinal motor neurons that colocalized with ubiquitin, p62/sequestosome-1, and TAR (trans-active regulatory) DNA-binding protein 43 (TDP-43). Our results provide further evidence that RNA metabolism pathways are integral to ALS pathology. This is also the first described link between ALS and an RNA binding protein with aggregate formation that is also a central cell signaling pathway molecule.     

Netrin signal transduction and the guanine nucleotide exchange factor DOCK180 in attractive signaling

Netrins are prototypical axon guidance cues whose attractive signaling requires the small GTPase Rac1. It remains unclear how Rac1 is regulated in the netrin pathway. DOCK180 is a member of a new family of guanine nucleotide exchange factors for Rho GTPases. Here we provide evidence implicating DOCK180 in netrin signal transduction. Netrin promoted the formation of a protein-protein interaction complex that included DOCK180 and the netrin receptor deleted in colorectal carcinoma (DCC). Inhibition of DOCK180 reduced activation of Rac1 by netrin. Both axon outgrowth and axon attraction induced by netrin were inhibited after DOCK180 knockdown in vertebrate neurons. The in vivo functional role of DOCK180 was demonstrated by its requirement for projection of commissural axons in the neural tube. These findings indicate that netrin stimulation recruits DOCK180 through DCC, which then activates small GTPases, suggesting an essential role for DOCK180 in mediating attractive responses by neurons to netrin-1.     

Insights into the biological functions of Dock family guanine nucleotide exchange factors

Rho GTPases play key regulatory roles in many aspects of embryonic development, regulating processes such as differentiation, proliferation, morphogenesis, and migration. Two families of guanine nucleotide exchange factors (GEFs) found in metazoans, Dbl and Dock, are responsible for the spatiotemporal activation of Rac and Cdc42 proteins and their downstream signaling pathways. This review focuses on the emerging roles of the mammalian DOCK family in development and disease. We also discuss, when possible, how recent discoveries concerning the biological functions of these GEFs might be exploited for the development of novel therapeutic strategies.     

膀胱癌中整合素连接激酶及相关信号转导通路分子的表达及意义

目的 探讨整合素连接激酶(integrin linked kinase,ILK)及相关信号转导通路分子在膀胱癌中的表达及其临床意义.方法 采用免疫组化SP法检测47例膀胱癌及25例癌旁组织中ILK、AKT及β-catenin的表达.结果 ILK、AKT和β-eatenin在膀胱癌和癌旁组织中的阳性率分别为53.19％和12.00％、44.68％和20.00％、48.94％和12.00％,且差异均有显著性(x2=11.651,x2=4.309,x2=9.650,P＜0.05).同时,ILK、AKT及β-catenin在高分化膀胱癌组中的表达明显低于低分化癌组,差异有统计学意义(P＜0.05).AKT、β-catenin和ILK在膀胱癌中的表达均呈正相关.结论 ILK、AKT及β-catenin的异常表达在膀胱癌的恶性进展中起重要作用,三者联合检测可能为揭示膀胱癌发生、发展的有关机制提供理论依据.ILK、AKT及β-catenin的异常表达与膀胱癌的临床病理分级密切相关,可能参与膀胱癌的发生、发展,联合检测有助于判断膀胱癌的恶性程度.     

T细胞抗原受体复合体信号转导及其与疾病关系的研究进展

 T 细胞抗原受体（TCR）是由 TCRαβ 或 TCRγδ 组成的异源二聚体，它与 CD3 分子组成跨膜蛋白复合体结构。抗原在诱导幼稚 T 细胞或记忆性T细胞进行增殖进而分化成效应细胞时，需要有两个信号刺激，第一信号来自TCR与抗原的特异性结合，第二信号来自抗原提呈细胞（antigen presenting cell，APC）表面的协同刺激因子与 T细胞表面相应受体的相互作用。TCR 通过胞外部分可变区（V 区）的互补决定区（CDR）特异性识别结合抗原；胞内部分在CD3、CD4/CD8 和 CD28 等分子的辅助下，将胞外刺激信号经磷脂酶 C（PLC）-γ活化途径和促分裂原活化蛋白激酶（mitogen activated protein kinaes，MAPK）活化途径传递至胞内，使转录因子活化，这一过程称为 T 细胞活化的信号转导。而这一过程可使 T细胞活化而发挥其生物学作用。TCR/CD3 复合体介导的信号转导是T细胞活化并发生抗原特异性免疫反应的重要途径，很多疾病的发生都与其信号转导异常有关，因此更深入地了解 T 细胞信号转导的分子机制显得尤为重要。本文对 TCR 介导的信号转导途径作了较为系统地阐述，并简要介绍了其异常与几种重要疾病的关系。......     

Molecular properties and physiological roles of ion channels in the immune system

The discovery of a diverse and unique set of ion channels in T lymphocytes has led to a rapidly growing body of knowledge about their functional roles in the immune system. Here we review the biophysical and molecular characterization of K⁺, Ca²⁺, and Cl^– channels in T lymphocytes. Potent and specific blockers, especially of K⁺ channels, have provided molecular tools to elucidate the involvement of voltage- and calcium-activated potassium channels in T-cell activation and cell-volume regulation. Their unique and differential expression makes lymphocyte K⁺ channels excellent pharmaceutical targets for modulating immune system function. This review surveys recent progress at the biophysical, molecular, and functional roles of the ion channels found in T lymphocytes.     

Separate membrane targeting and anchoring domains function in the localization of the<Emphasis Type="Italic"> S. cerevisiae</Emphasis> Cdc24p guanine nucleotide exchange factor

The Saccharomyces cerevisiae Cdc24p guanine nucleotide exchange factor (GEF) activates the Cdc42p GTPase to a GTP-bound state. Cdc42p and Cdc24p co-localize at polarized growth sites during the cell cycle; and analysis of Cdc24p carboxyl-terminal truncation and site-specific mutations identified a 56-amino-acid domain as being necessary and sufficient for localization to these sites. This domain, however, was unable to anchor Cdc24p at these sites. Anchoring was restored by fusing the targeting domain to either the Cdc24p carboxyl-terminal PC domain that interacts with the Bem1p scaffold protein or the Cdc42p KKSKKCTIL membrane-anchoring domain. Mutant analysis and protein solubilization data indicated that anchoring required Bem1p, the Rsr1p/Bud1p GTPase, and the potential transmembrane protein YGR221Cp/Tos2p. These data are consistent with Cdc24p localization being a function of both membrane-specific targeting and subsequent anchoring within a multi-protein complex. Given the highly conserved roles of GEFs in Cdc42p signaling pathways, it is likely that similar targeting and anchoring mechanisms exist for Rho GEFs in other eukaryotes.Communicated by S. Hohmann     

Differential expression pattern of the four mitochondrial adenine nucleotide transporter ant genes and their roles during the development of Caenorhabditis elegans.

The adenine nucleotide transporter (ANT) mediates exchange of cytosolic ADP and mitochondrial ATP. Although most species contain more than one ANT family member, it is not known whether their roles in developmental processes are redundant or specific. Here, we show that the Caenorhabditis elegans genome encodes four candidate ant genes (ant-1.1, ant-1.2, ant-1.3, and ant-1.4). We have investigated their spatiotemporal expression patterns and discovered that, whereas ANT-1.1 is a ubiquitously expressed mitochondrial protein, the other three ANT proteins show a restricted range of cell type expression. Moreover, only the disruption of ant-1.1 function, through RNA interference (RNAi), gives a mutant phenotype. Most of the ant-1.1(RNAi) mutant embryos arrest before the morphogenesis stage. Furthermore, ant-1.1 is also required postembryonically because RNAi mutants exhibit small size and life-span extension. Our results suggest that ant-1.1 is the only ant gene strictly required for embryonic and postembryonic development in C. elegans.     

The role of tyrosine phosphorylation and PTP-1C in CTLA-4 signal transduction

Recently, there has been increasing interest in the inhibitory regulators of lymphocyte activation, and in particular, the role of CD28 homologue CTLA-4 in the regulation of T cell responses. Interaction of CTLA-4 with B7 ligands inhibits T cell responses, including T cell proliferation and interleukin-2 (IL-2) secretion. The mechanism(s) responsible for CTLA-4 signal transduction are unknown, but it has been suggested that tyrosine phosphorylation is involved. Here we demonstrate that phorbol ester phorbol 12-myrislate 13-acetate (PMA), which increases tyrosine phosphorylation by stimulating protein kinase C and p21ras, can overcome the CTLA-4-mediated inhibition of T cell proliferation. This provides the first functional evidence that tyrosine phosphorylation is involved in CTLA-4 signal transduction. Most interestingly, CTLA-4-mediated inhibition of IL-2 secretion was not influenced by the presence of PMA. Further, we demonstrate that CTLA-4 cross-linking inhibits proliferation and IL-2 secretion of T cells from motheaten mice. These mice lack PTP-1C, a tyrosine phosphatase which mediates in a number of lymphocyte inhibitory responses, indicating that PTP-1C is not essential for CTLA-4 signaling. Collectively, these results demonstrate that regulation of tyrosine phosphorylation plays a pivotal role in CTLA-4 function, and that the inhibition of the transition from G0/G1 to the S phase of the cell cycle and the inhibition of IL-2 secretion require distinct signaling pathways. These experiments provide a useful model system which can be used to elucidate the signaling pathways involved in CTLA-4 function and to understand how CTLA-4, CD28 and T cell receptor-mediated signals are integrated in T cell responses to antigen.     

IL-6 cytokine family and signal transduction: a model of the cytokine system

The interleukin 6 (IL-6) cytokine family, which includes IL-6, leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), IL-11 and cardiotrophin-1 (CT-1), exhibits pleiotropy and redundancy in biological activities. The IL-6 family cytokines exhibit a helical structure. Their receptors belong to the type 1 cytokine receptor family. The receptors of the IL-6 family cytokines share a receptor subunit, which explains one of the mechanisms of functional redundancy. In this review, we describe the general features of the IL-6 cytokine family and its signal transduction mechanisms. Many functional properties of the IL-6 family of cytokines and their receptors are general features of the cytokine system.     

Internalization of extraintestinal Escherichia coli O18 strains by epithelial cells is modulated by EGF, insulin, and effectors of transmembrane signal transduction

Adhesion to and internalization into host cells is an essential step in the pathogenesis of various bacterial infections. Here we investigated the effects of growth factors on the internalization of Escherichia coli O18 strains isolated from patients with urinary tract infection (UTI) by human epithelial cells. A dramatic increase in the uptake of Escherichia coli was observed after treatment of epithelial cells with epidermal growth factor (EGF) and to a lower extent with insulin. EGF-dependent internalization can be suppressed by tyrosine kinase inhibitors suggesting an involvement of the receptor tyrosine kinases in the regulation of the endocytotic process. Inhibitors of phospholipase A2, lipoxygenase, and cyclooxygenase significantly decreased internalization of bacteria induced by EGF. Finally, the specific inhibitor of PI 3-kinases Wortmannin was shown to suppress completely the EGF-independent internalization. The data of this analysis indicate the involvement of several signaling paths in bacterial internalization of uropathogenic Escherichia coli O18 strains and contribute to the comprehension of the pathogenesis of recurrent UTI.