凝溶胶蛋白的结构与功能

凝溶胶蛋白（gelsolin）是凝溶胶蛋白超家族的成员之一,是一种重要的肌动蛋白结合蛋白,其通过切断、封端肌动蛋白丝,或使肌动蛋白聚集成核等方式来控制肌动蛋白的结构.凝溶胶蛋白除了在重组肌动蛋白丝中发挥作用以外,还在细胞运动、控制细胞程序性死亡等细胞活动中发挥重要的作用.此外,肿瘤细胞中凝溶胶蛋白的表达量也发生变化.凝溶胶蛋白的变异还是某些遗传疾病的基础.最近的研究发现,凝溶胶蛋白可以作为转录辅激活蛋白,促进雄激素受体的转录活性.本文对凝溶胶蛋白的结构特点、参与调节细胞的功能和机制及其研究现状进行概述.     

凝溶胶蛋白与相关疾病的关系

凝溶胶蛋白（gelsolin,GSN）是一种在机体内普遍存在的,对细胞结构和代谢功能具有多种调节作用的蛋白。GSN作为凝溶胶蛋白超家族的成员之一,是一种重要的肌动蛋白（actin）结合蛋白,可通过切断、封闭肌动蛋白丝,或使actin聚集成核等方式来调控actin的结构与代谢功能.GSN不仅能在重组的肌动蛋白细丝（F-actin）中发挥作用,而且在细胞运动、细胞凋亡等细胞活动中也发挥着重要的作用。GSN有血浆型（plasma gelsolin,pGSN）和细胞质型（cytoplasmic gelsolin,cGSN）两种亚型,它们在淀粉样变性、炎症、癌症、心血管疾病、阿茨海默病（AD）及肾脏疾病中都起着重要的作用,GSN可能成为多种疾病的一个新的生物标记物或者治疗靶点。本文将就GSN与相关疾病的关系的研究进展做一综述。     

肌切蛋白的结构与功能多样性

肌切蛋白（scinderin）是一种重要的肌动蛋白结合蛋白,在哺乳动物和脊椎动物中广泛表达.肌切蛋白作为凝溶胶蛋白超家族的成员之一,通过肌动蛋白丝切割、肌动蛋白聚集等方式来控制肌动蛋白的结构.肌切蛋白生物活性具有多样性,除影响肌动蛋白丝重组外,肌切蛋白还参与细胞胞吐作用、调节细胞运动、细胞分化等细胞活动.此外,肌切蛋白在慢性炎症、凝血过程、免疫性疾病和肿瘤发生发展中也发挥了重要作用.本文对肌切蛋白的结构特点、参与调节细胞的功能和机制进行概述.     

凝溶胶蛋白对植物微丝的调节作用及在花粉中的定位

以植物花粉为实验材料, 研究了来源于动物的凝溶胶蛋白对植物肌动蛋白丝的作用及凝溶胶蛋白在植物细胞中的定位. 利用离心沉淀丝状肌动蛋白及电子显微镜负染的实验结果显示, 花粉纯化肌动蛋白丝及粗提液中肌动蛋白丝可被凝溶胶蛋白剪切, 而且这种剪切作用依赖于Ca²⁺. 另外, 利用免疫沉淀测定凝溶胶蛋白与花粉肌动蛋白单体结合的实验表明, 当溶液中有Ca²⁺. 存在时, 花粉肌动蛋白与凝溶胶蛋白的摩尔比值约为2.0 ± 0.21; 用EGTA去除Ca²⁺. 后, 该比值有所降低, 减至1.2 ± 0.23; 而加入PIP2后, 这种结合比值又降至0.8 ± 0.10, 表明植物肌动蛋白与凝溶胶蛋白的结合有类似于动物肌动蛋白的特性, 受到Ca²⁺. 和PIP2的调节. 花粉中凝溶胶蛋白的免疫鉴定及免疫荧光定位实验结果表明, 花粉中存在凝溶胶蛋白, 在未萌发的花粉粒中凝溶胶蛋白主要集中在萌发沟处, 而在萌发2 h的花粉管中, 花粉管胞质内均可看到荧光分布, 但花粉管顶端荧光较强, 推测凝溶胶蛋白可能参与花粉的萌发和花粉管的生长.     

Bcl-2家族蛋白及其在细胞凋亡中的作用

Bcl-2家族蛋白是目前已知的细胞凋亡中最重要的调控因子,在细胞凋亡通路中起着重要的调节作用．对其作用机制的研究将有助于对肿瘤,自身免疫性和神经变性等疾病的治疗。该文介绍Bcl-2家族中主要的几种蛋白在凋亡中的作用,以及对线粒体膜通透性的调控作用。     

植物肌动蛋白解聚因子ADF的研究进展

肌动蛋白解聚因子/丝切蛋白(actin depolymerizing factor,ADF/cofilin)是一种重要的肌动蛋白结合蛋白。在植物细胞中,ADF/cofilin通过与肌动蛋白相结合,在植物生长发育以及响应外界刺激方面起着重要的作用,以此对各种动态生命活动进行调控。该文对国内外近年来有关ADF/cofilin家族的序列结构特征及定位,与肌动蛋白的互作机制、促进细胞生长、抗生物和非生物逆境胁迫能力等的生物学功能,以及磷酸化作用、环境pH、PIP2对其功能影响的调控模式和作用机制进行了综述,为ADF/cofilin新的抗逆功能机制解析提供参考。     

Bcl-2家族蛋白的生理功能及结构基础

细胞凋亡是一个重要的生物学过程,对细胞命运及稳态的调控起着关键作用。B细胞淋巴瘤-2(Bcl-2)家族蛋白是凋亡途径的重要组分,其功能异常与多种疾病相关,包括癌症、神经退行性疾病和自身免疫疾病等。近十年涌现了大量关于Bcl-2家族蛋白生理功能及结构的报道,加深了我们对Bcl-2家族蛋白的作用机制及其病理意义的认识,且在过去几年中,许多针对不同Bcl-2成员的药物已经被开发并进入临床阶段。但Bcl-2家族蛋白功能和结构的复杂性及多样性导致该研究领域仍有大量问题尚待解决。该文总结了目前关于Bcl-2蛋白家族结构和功能的知识,还讨论了Bcl-2蛋白作为有效分子治疗靶点的药理学意义。     

Bcl—2家族蛋白与细胞凋亡

Bcl 2家族蛋白是在细胞凋亡过程中起关键性作用的一类蛋白质。在线粒体上 ,Bcl 2家族蛋白通过与其他凋亡蛋白的协同作用 ,调控线粒体结构与功能的稳定性 ,发挥着细胞凋亡“主开关”的作用。Bcl 2家族包括两类蛋白质 :一类是抗凋亡蛋白 ,另一类是促凋亡蛋白。在细胞凋亡时 ,Bcl 2家族中的促凋亡蛋白成员发生蛋白质的加工修饰 ,易位到线粒体的外膜上 ,引起细胞色素c、凋亡诱导因子等其他促凋亡因子的释放 ,导致细胞凋亡 ;而平时被隔离在线粒体等细胞器内的该家族的抗凋亡蛋白成员则抑制细胞色素c和凋亡诱导因子等促凋亡因子的释放 ,具有抑制细胞凋亡的功能。但一旦这类抗凋亡蛋白成员与激活的促凋亡蛋白发生相互作用后 ,便丧失了对细胞凋亡的抑制作用 ,造成线粒体等细胞器的功能丧失和细胞器内促凋亡因子的释放 ,导致细胞凋亡。现以Bcl 2家族调控细胞凋亡的最新研究进展为基础 ,对Bcl 2家族成员及其蛋白质结构、分布和调控细胞凋亡的分子机制进行综述。     

小热应激蛋白与动物繁殖机能的关系研究进展

热应激是指机体受到超过本身体温调节能力的高温刺激而产生的非特异性防御反应,热应激蛋白是机体热应激反应发生后细胞新合成或合成数量增加的一类蛋白质,小分子热应激蛋白是热应激蛋白家族中重要的一类成员,作为分子伴侣在细胞的正常代谢和生理条件下表达和发挥作用。目前已证实小热应激蛋白还参与调控细胞增殖和凋亡、生物膜膜脂的流动性、核质穿梭作用、免疫应答和疾病治疗等。本综述分别就小热应激蛋白在雄性动物生精细胞发育过程中参与的增殖、分化及凋亡调控作用以及在雌性动物卵母细胞发育、成熟、妊娠维持和生育调节功能的研究进展做一概述,旨在为小热应激蛋白生物学功能深入研究提供参考。     

ROCK蛋白与肿瘤

ROCK蛋白作为Rho亚家族下游最重要的效应分子之一,主要通过调节肌动蛋白在调控细胞的形态、极性、细胞骨架重构和细胞迁移等多个方面发挥生理功能。研究发现ROCK蛋白在肿瘤的发生发展中起着重要作用,主要参与调控肿瘤细胞的生存与凋亡,以及恶性肿瘤的侵袭与转移。文章论述了ROCK蛋白与肿瘤关系的研究进展,为寻找新的抗癌药物治疗靶点提供依据。     

Gelsolin inhibits apoptosis by blocking mitochondrial membrane potential loss and cytochrome c release

Apoptotic cell death, characterized by chromatin condensation, nuclear fragmentation, cell membrane blebbing, and apoptotic body formation, is also accompanied by typical mitochondrial changes. The latter includes enhanced membrane permeability, fall in mitochondrial membrane potential (Deltapsi(m)) and release of cytochrome c into the cytosol. Gelsolin, an actin regulatory protein, has been shown to inhibit apoptosis, but when cleaved by caspase-3, a fragment that is implicated as an effector of apoptosis is generated. The mechanism by which the full-length form of gelsolin inhibits apoptosis is unclear. Here we show that the overexpression of gelsolin inhibits the loss of Deltapsi(m) and cytochrome c release from mitochondria resulting in the lack of activation of caspase-3, -8, and -9 in Jurkat cells treated with staurosporine, thapsigargin, and protoporphyrin IX. These effects were corroborated in vitro using recombinant gelsolin protein on isolated rat mitochondria stimulated with Ca(2+), atractyloside, or Bax. This protective function of gelsolin, which was not due to simple Ca(2+) sequestration, was inhibited by polyphosphoinositide binding. In addition we confirmed that gelsolin, besides its localization in the cytosol, is also present in the mitochondrial fraction of cells. Gelsolin thus acts on an early step in the apoptotic signaling at the level of mitochondria.     

Inhibition of apoptosis by the actin-regulatory protein gelsolin.

Gelsolin is an actin-regulatory protein that modulates actin assembly and disassembly, and is believed to regulate cell motility in vivo through modulation of the actin network. In addition to its actin-regulatory function, gelsolin has also been proposed to affect cell growth. Our present experiments have tested the possible involvement of gelsolin in the regulation of apoptosis, which is significantly affected by growth. When overexpressed in Jurkat cells, gelsolin strongly inhibited apoptosis induced by anti-Fas antibody, C2-ceramide or dexamethasone, without changing the F-actin morphology or the levels of Fas or Bcl-2 family proteins. Upon the induction of apoptosis, an increase in CPP32(-like) protease activity was observed in the control vector transfectants, while it was strongly suppressed in the gelsolin transfectants. Pro-CPP32 protein, an inactive form of CPP32 protease, remained uncleaved by anti-Fas treatment in the gelsolin transfectants, indicating that gelsolin blocks upstream of this protease. The tetrapeptide inhibitor of CPP32(-like) proteases strongly inhibited Fas-mediated apoptosis, but only partially suppressed both C2-ceramide- and dexamethasone-induced apoptosis. These data suggest that the critical target responsible for the execution of apoptosis may exist upstream of CPP32(-like) proteases in Jurkat cells and that gelsolin acts on this target to inhibit the apoptotic cell death program.     

Aging-associated increase of gelsolin for apoptosis resistance

Gelsolin, a Ca(2+)-dependent actin regulatory protein, was recently suggested to participate in apoptosis regulation. In this study, we found that the level of gelsolin is elevated in senescent human diploid fibroblasts (HDFs) and also in the tissues of old rats, i.e., in the liver, kidney, heart, spleen, stomach, and brain, etc. The ubiquitous increase of gelsolin in the aged organs and cells led us to assume that it might be related with one of the cardinal senescent phenotypes, aging-associated apoptosis resistency. Thus, we tested the sensitivity of senescent cells to apoptosis by menadione, an apoptosis-inducing agent, before and after the down-regulation of gelsolin. The down-regulation of gelsolin in senescent HDFs, independently of Bcl-2 family expression, resulted in an increased sensitivity to menadione-induced apoptotic cell death. The observed ubiquitous increase of gelsolin in the senescent states of cells and tissues, and the increased sensitivity to apoptosis-induction by gelsolin down-regulation, suggests that gelsolin would be partly responsible for age-related apoptosis resistance.     

N-terminal region of gelsolin induces apoptosis of activated hepatic stellate cells by a caspase-dependent mechanism

Activated hepatic stellate cells (HSCs) are the major source for alteration of extracellular matrix in fibrosis and cirrhosis. Conditioned medium (CM) collected from immortalized human hepatocytes (IHH) have earlier been shown to be responsible for apoptosis of HSCs. In this study, we have shown that antibodies raised against a peptide derived from a linear B-cell epitope in the N-terminal region of gelsolin identified a gelsolin fragment in IHH CM. Analysis of activated stellate cell death by CM collected from Huh7 cells transfected with plasmids encoding gelsolin deletion mutants suggested that the N-terminal half of gelsolin contained sequences which were responsible for stellate cell death. Further analysis determined that this activity was restricted to a region encompassing amino acids 1-70 in the gelsolin sequence; antibody directed to an epitope within this region was able to neutralize stellate cell death. Gelsolin modulation of cell death using this fragment involved upregulation of TRAIL-R1 and TRAIL-R2, and involved caspase 3 activation by extrinsic pathway. The apoptotic activity of N-terminal gelsolin fragments was restricted to activated but not quiescent stellate cells indicating its potential application in therapeutic use as an anti-fibrotic agent. Gelsolin fragments encompassing N-terminal regions in polypeptides of different molecular sizes were detected by N-terminal peptide specific antiserum in IHH CM immunoprecipitated with chronically HCV infected patient sera, suggesting the presence of autoantibodies generated against N-terminal gelsolin fragments in patients with chronic liver disease.     

Decreased levels of the gelsolin plasma isoform in patients with rheumatoid arthritis

Introduction  

Gelsolin is an intracellular actin-binding protein involved in cell shape changes, cell motility, and apoptosis. An extracellular gelsolin isoform, plasma gelsolin circulates in the blood of healthy individuals at a concentration of 200 ± 50 mg/L and has been suggested to be a key component of an extracellular actin-scavenging system during tissue damage. Levels of plasma gelsolin decrease during acute injury and inflammation, and administration of recombinant plasma gelsolin to animals improves outcomes following sepsis or burn injuries. In the present study, we investigated plasma gelsolin in patients with rheumatoid arthritis.     

Gelsolin-induced epithelial cell invasion is dependent on Ras-Rac signaling

Gelsolin is a widely distributed actin binding protein involved in controlling cell morphology, motility, signaling and apoptosis. The role of gelsolin in tumor progression, however, remains poorly understood. Here we show that expression of green fluorescent protein (GFP)-tagged gelsolin in MDCK-AZ, MDCKtsSrc or HEK293T cells promotes invasion into collagen type I. In organ culture assays, MDCK cells expressing gelsolin-GFP invaded pre-cultured chick heart fragments. Gelsolin expression inhibited E-cadherin-mediated cell aggregation but did not disrupt the E-cadherin-catenin complex. Co-expression of dominant-negative Rac1N17, but not RhoAN19 or Cdc42N17, counteracted gelsolin-induced invasion, suggesting a requirement for Rac1 activity. Increased ARF6, PLD or PIP5K 1alpha activity canceled out gelsolin-induced invasion. Furthermore, we found that invasion induced by gelsolin is dependent on Ras activity, acting through the PI3K-Rac pathway via the Ras guanine nucleotide exchange factor Sos-1. These findings establish a connection between gelsolin and the Ras oncogenic signaling pathway.     

Regulation of neural differentiation by normal and mutant (G654A, amyloidogenic) gelsolin.

Gelsolin belongs to a family of proteins that modulate the structural dynamics of cytoskeletal actin. Gelsolin activity is required for the redistribution of actin occurring during membrane ruffling, cell crawling, and platelet activation. A point mutation (G654A) in the gelsolin gene causes a dominantly inherited systemic amyloidosis called familial amyloidosis of the Finnish type (FAF). This disease is characterized by a cranial neuropathy that cannot be explained solely by amyloid deposits. To address the question of whether gelsolin has a specific role in neural cell development, we transfected cDNA for wild type and G654A point-mutated gelsolin into a neural cell line, Paju, which can be induced to differentiate by treatment with phorbol 12-myristate 13-acetate. Overexpressed wild type gelsolin inhibited neural differentiation whereas mutated gelsolin did not, indicating that appropriate gelsolin activity is essential for neural sprouting. The G654A mutant gelsolin induced stabilization of F-actin and reduced the plasticity of neural development. This provides a novel etiopathogenetic mechanism for the neuronal dysfunction in FAF.     

凝溶胶蛋白治疗阿尔茨海默症的研究进展

阿尔茨海默症(Alzheimer’s disease,AD)的病理学特征之一是患者脑内存在以β-淀粉样肽(Aβ)为主要成分的老年斑。大量的实验证据表明,以Aβ为靶目标,清除老年斑有助于提高患者的认知能力,是防治AD的一个重要研究方向。凝溶胶蛋白在细胞骨架结构重排和细胞运动等过程中都发挥重要作用。目前多个小组的研究成果显示,凝溶胶蛋白与AD的发生、发展密切相关。凝溶胶蛋白能够抑制Aβ积聚形成纤维,也能够引发已形成的Aβ纤维发生解聚。更重要的是,凝溶胶蛋白能够清除转基因AD模型小鼠脑内的老年斑和降低Aβ的水平。未来凝溶胶蛋白有可能被应用于AD的预防和治疗。