液泡ATP酶在肿瘤中的作用及机制

液泡ATP酶（vacuolar ATPases,V-ATPases）是真核细胞中高度保守的一类大型多亚基复合物,广泛分布于质膜及溶酶体、内体、囊泡等细胞内膜系统,能够借助水解ATP产生的能量控制H+的跨膜转运。V-ATPases通过对细胞内外多种结构的酸化作用调控着一系列重要的细胞活动,如膜运输、蛋白质加工和降解等。近年来,V-ATPases在肿瘤形成中的功能正逐渐成为研究热点。本文重点综述了V-ATPases通过调控细胞内外环境pH,从而在肿瘤发生过程中所行使的多种功能,例如V-ATPases抑制肿瘤细胞凋亡,参与肿瘤细胞自噬,促进肿瘤的侵袭、迁移与增殖,以及参与肿瘤耐药性的产生等。阐明V-ATPases在肿瘤中的作用机制有望为肿瘤治疗策略的探索、新型药物的开发以及相关科学研究的开展提供参考。     

靶向肿瘤酸性微环境的抗肿瘤新策略

越来越多的体内体外实验及临床检测都证明了肿瘤酸性微环境对肿瘤的发生、发展和迁移起着重要作用。在肿瘤酸性微环境的重要调节因子中,V型ATP酶（V-ATPases）的作用至关重要。这些蛋白能将离子泵出膜外,在正常细胞和肿瘤细胞中都有着多种功能。本文回顾和总结了该领域的最新研究成果：在异种移植人肿瘤细胞的动物模型中,体内实验显示,采用小分子干扰RNA（siRNA）可抑制V．ATPaseS的功能,加入药物性质子泵抑制剂可显著地抑制人肿瘤细胞的生长。这些结果提示V-ATPases可作为癌症治疗中一个重要的新选择靶标。     

线粒体ATP合酶抑制因子(ATPIF1)在能量代谢中的作用

线粒体是真核细胞中动态双层膜结构的细胞器,由外至内可以划分为四个功能区,分别是线粒体外膜(OMM),线粒体膜间隙,线粒体内膜(IMM)和线粒体基质。在线粒体内膜上的复合体V(complex V)即为ATP合酶,其主要功能是合成ATP。实际上,ATP合酶既合成也水解ATP,对细胞ATP水平有双向调节作用。ATP合酶的活性受抑制因子(ATPIF1)的调节。ATPIF1与ATP合酶结合后,对其ATP合成和水解功能进行抑制,从而影响线粒体和细胞内ATP水平。ATPIF1活性受到组氨酸质子化状态和丝氨酸磷酸化修饰的调节。在缺氧,交感神经兴奋和肿瘤等条件下,ATPIF1发挥重要代谢调节作用,但其在代谢紊乱疾病中的作用尚不明确。本文在综述ATPIF1文献的基础上,对其在糖脂代谢紊乱疾病中的作用进行分析及展望。     

溶血卵磷脂对大豆下胚轴质膜H^＋—ATPase ATP和对—硝基苯磷酸水解活性的影响

研究了溶血卵磷脂 (lysophosphatidylcholine,lyso PC)对大豆 (Glycinemax (L .)Merr.)下胚轴质膜H _ATPaseATP和对_硝基苯磷酸 (ρ_nitrophenylphosphate ,PNPP)水解的影响。结果显示 ,lyso_PC可以刺激ATP水解活力 ,当lyso_PC浓度在 0～ 0 .0 3%范围时 ,ATP水解活力明显提高 ,lyso_PC浓度高于 0 .0 3%后增加缓慢 ;当lyso_PC浓度为0 .0 3%时 ,ATP水解活力提高 80 .5 %。动力学分析表明 ,lyso_PC处理可以使ATP水解的Vmax从 0 .46 μmolPi·mg-1protein·min-1升高到 0 .87μmolPi·mg-1protein·min-1;使Km 从 0 .88mmol/L升高到 1.15mmol/L。最适pH也从 6 .5变为 7.0。实验还发现lyso_PC可以促进羟胺对ATP水解的抑制作用 ,lyso_PC处理后ATP水解被羟胺 (2 0 0mmol/L)抑制 84.4% ,而未经lyso_PC处理的对照组则仅被抑制 74.4%。然而 ,lyso_PC处理不影响PNPP水解活力和钒酸钠抑制效应。以上结果表明 ,质膜H _ATPase的激酶结构域可能是其C末端自抑制结构域的作用位点或调节区域     

豌豆根胞质V1-ATPase的鉴定

利用免疫印迹、免疫电镜和ATP水解活性的测定对豌豆(Pisum sativum L.)根细胞胞质中V1-ATPase复合物的存在进行鉴定.用兔抗绿豆V-type H+-ATPase 的A、B亚基的抗体进行的immuno-blotting和胶体金电镜结果都表明,胞质中存在有A、B亚基.活性测定结果进一步表明胞质具有ATP水解活性.这些结果说明豌豆根胞质具有有活性的V1-ATPase复合物.这是首次直接证明植物中有胞质V1-ATPase的存在.     

P-糖蛋白结构及作用机制

ABC (ATP-binding cassette) 转运蛋白广泛存在于各种生物体细胞中,例如细菌的内层细胞浆膜和真核生物的细胞膜和细胞器膜.其利用与ATP的结合和水解供能进行底物的跨膜转运,其中一部分ABC转运蛋白能转运多种疏水性分子.P-糖蛋白隶属于ABC转运蛋白超家族,是研究最为透彻的一员,主要功能是防止机体对外来有害物质的摄入.P-糖蛋白(P-glycoprotein)由4 个基本结构域组成,2 个跨膜区和2 个位于细胞浆内的核苷酸结合区.核苷酸结合区参与ATP的结合和水解,而各由6 个α 跨膜螺旋组成的2个跨膜区联合构成了底物跨膜转运的通道.P 糖蛋白能转运多种不同结构的底物,包括脂类、胆汁酸、多肽和外源性化学物质,这对机体的生存至关重要,但同时也存在不利的一面,包括干扰了药物的运输,从而导致了多药耐药现象的产生.本文就P-糖蛋白的分子结构和作用机制的最新研究进展进行综述.     

V型H＋－ATP酶的分子结构及其药理学意义

V型ATP酶广泛存在于细胞内膜系统,如溶酶体,内膜体,高尔基体,分泌颗粒等,V-ATP酶水解ATP,建立跨膜质子电化学梯度(△μH^＋),酸化细胞内外环境.研究证明△μH^＋和酸化作用为细胞的内吞、外泌、膜流和物质转运等生理生化反应提供了必需的条件.V-ATP酶在生命活动中的重要性和它的实际意义,日益引起人们的兴趣与关注,是当前H^＋-ATP酶家族中一个异常活跃的研究分支.     

V-ATPase:结构、功能及其在肿瘤细胞中的作用

真核细胞膜及管泡细胞器膜上广泛分布一种与H^ 主动转运有关的蛋白——V-ATPase。V-ATPase的结构由跨膜的V0和细胞质内的V1两个亚单位组成,前者为H^ 提供通道,后者能分解ATP,为逆浓度梯度转运H^ 提供能量。V0和V1只有在聚合时,V-ATPase全酶才有功能。肿瘤细胞中V-ATPase的过度表达或过度活跃,遏制了由酵解增强乳酸聚集导致的细胞内酸化趋势,使细胞避免了凋亡的命运。而H^ 排至细胞外,改变蛋白水解酶的活性,使细胞外基质分解增强,细胞更有侵袭力。肿瘤细胞的V-ATPase可望成为抑制细胞增生、扩散的有效靶点。     

CHD4在染色体重塑中的作用

染色质作为真核细胞遗传信息,体内外各种因素的作用致使不断的产生损伤,但是细胞仍能保持正常的生长、分裂和繁殖,这与基因组稳定性和完整性保持,并且通过自身的损伤修复有着密切的联系。ATP依赖的染色质重塑是染色质重塑的最重要的方式之一,主要是利用ATP水解释放的能量,将凝聚的异染色质打开,协调损伤修复蛋白与DNA损伤位点的作用,通过对组蛋白的共价键修饰或ATP依赖的染色质重塑复合物开启了DNA的损伤修复的大门。CHD4/Mi-2β的类SWI2/SNF2 ATP酶/解螺旋酶域结构域保守性最强,这一结构域存在与多种依赖于ATP的核小体重构复合物。Mi-2蛋白复合物称为核小体重塑及去乙酰化酶NuRd(nucleoside remodeling and deacetylase,NuRD),是个多亚基蛋白复合物,Mi2β/CHD4是该复合物的核心成员。近来的研究发现,CHD4具有染色质重塑功能,并且参与DNA损伤修复的调控。CHD4羧基端的PHD通过乙酰化或甲基化识别组蛋白H3氨基端Lys9(H3K9ac和H3K9me),并且通过Lys4甲基化(H3K4me)或Ala1乙酰化(H3A Lac)抑制与H3、H4的结合,为染色质重塑提供了保障。Mi-2β/CHD4参与DNA损伤反应,定位于DNA损伤γ-H2AX的foci。沉默Mi-2β/CHD4基因,细胞自发性DNA损伤增多和辐射敏感性增强。表明CHD4在染色质重塑中具有重要的作用。     

胰蛋白酶处理对质膜H~ -ATPase钒酸钠抑制效应的影响

采用经蔗糖密度梯度法纯化的大豆 (GlycinemaxL .)下胚轴质膜微囊为材料 ,分析了胰蛋白酶处理对质膜H ATPase钒酸钠抑制效应的影响。实验结果显示 ,温和胰蛋白酶处理显著提高H ATPase的ATP水解活力。并且发现酶切处理降低了钒酸钠对ATPase的抑制效应 ,当钒酸钠浓度为 2mmol/L时 ,ATPase活力仅被抑制 5 3.49% ,而未经酶切的对照组则被抑制 6 4.13%。ATP水解动力学分析表明 ,胰蛋白酶酶切处理既不影响ATP水解的Km 值也不影响钒酸钠的抑制类型 ,酶切前后的Km 值都等于 0 .34mmol/L ,并且都属于反竞争抑制。以上结果显示胰蛋白酶酶切处理可能改变了磷酸酶结构域的结构而影响了钒酸钠的抑制效应 ,暗示C_末端调节着磷酸酶结构域的结构和功能     

Proton translocation driven by ATP hydrolysis in V-ATPases

The vacuolar H(+)-ATPases (or V-ATPases) are a family of ATP-dependent proton pumps responsible for acidification of intracellular compartments and, in certain cases, proton transport across the plasma membrane of eukaryotic cells. They are multisubunit complexes composed of a peripheral domain (V(1)) responsible for ATP hydrolysis and an integral domain (V(0)) responsible for proton translocation. Based upon their structural similarity to the F(1)F(0) ATP synthases, the V-ATPases are thought to operate by a rotary mechanism in which ATP hydrolysis in V(1) drives rotation of a ring of proteolipid subunits in V(0). This review is focused on the current structural knowledge of the V-ATPases as it relates to the mechanism of ATP-driven proton translocation.     

Structure and regulation of the vacuolar ATPases

The vacuolar (H(+))-ATPases (V-ATPases) are ATP-dependent proton pumps responsible for both acidification of intracellular compartments and, for certain cell types, proton transport across the plasma membrane. Intracellular V-ATPases function in both endocytic and intracellular membrane traffic, processing and degradation of macromolecules in secretory and digestive compartments, coupled transport of small molecules such as neurotransmitters and ATP and in the entry of pathogenic agents, including envelope viruses and bacterial toxins. V-ATPases are present in the plasma membrane of renal cells, osteoclasts, macrophages, epididymal cells and certain tumor cells where they are important for urinary acidification, bone resorption, pH homeostasis, sperm maturation and tumor cell invasion, respectively. The V-ATPases are composed of a peripheral domain (V(1)) that carries out ATP hydrolysis and an integral domain (V(0)) responsible for proton transport. V(1) contains eight subunits (A-H) while V(0) contains six subunits (a, c, c', c', d and e). V-ATPases operate by a rotary mechanism in which ATP hydrolysis within V(1) drives rotation of a central rotary domain, that includes a ring of proteolipid subunits (c, c' and c'), relative to the remainder of the complex. Rotation of the proteolipid ring relative to subunit a within V(0) drives active transport of protons across the membrane. Two important mechanisms of regulating V-ATPase activity in vivo are reversible dissociation of the V(1) and V(0) domains and changes in coupling efficiency of proton transport and ATP hydrolysis. This review focuses on recent advances in our lab in understanding the structure and regulation of the V-ATPases.     

Function, structure and regulation of the vacuolar (H+)-ATPases

The vacuolar ATPases (or V-ATPases) are ATP-driven proton pumps that function to both acidify intracellular compartments and to transport protons across the plasma membrane. Intracellular V-ATPases function in such normal cellular processes as receptor-mediated endocytosis, intracellular membrane traffic, prohormone processing, protein degradation and neurotransmitter uptake, as well as in disease processes, including infection by influenza and other viruses and killing of cells by anthrax and diphtheria toxin. Plasma membrane V-ATPases are important in such physiological processes as urinary acidification, bone resorption and sperm maturation as well as in human diseases, including osteopetrosis, renal tubular acidosis and tumor metastasis. V-ATPases are large multi-subunit complexes composed of a peripheral domain (V₁) responsible for hydrolysis of ATP and an integral domain (V₀) that carries out proton transport. Proton transport is coupled to ATP hydrolysis by a rotary mechanism. V-ATPase activity is regulated in vivo using a number of mechanisms, including reversible dissociation of the V₁ and V₀ domains, changes in coupling efficiency of proton transport and ATP hydrolysis and changes in pump density through reversible fusion of V-ATPase containing vesicles. V-ATPases are emerging as potential drug targets in treating a number of human diseases including osteoporosis and cancer.     

Structure and Regulation of the V-ATPases

The V-ATPases are ATP-dependent proton pumps present in both intracellular compartments and the plasma membrane. They function in such processes as membrane traffic, protein degradation, renal acidification, bone resorption and tumor metastasis. The V-ATPases are composed of a peripheral V₁ domain responsible for ATP hydrolysis and an integral V₀ domain that carries out proton transport. Our recent work has focused on structural analysis of the V-ATPase complex using both cysteine-mediated cross-linking and electron microscopy. For cross-linking studies, unique cysteine residues were introduced into structurally defined sites within the B and C subunits and used as points of attachment for the photoactivated cross-linking reagent MBP. Disulfide mediated cross-linking has also been used to define helical contact surfaces between subunits within the integral V₀ domain. With respect to regulation of V-ATPase activity, we have investigated the role that intracellular environment, luminal pH and a unique domain of the catalytic A subunit play in controlling reversible dissociation in vivo.     

Introduction: A Close Look at the Vacuolar ATPase

The vacuolar ATPases (V-type ATPases) are a family of ATP-dependent ion pumps and found in two principal locations, in endomembranes and in plasma membranes. This family of ATPases is responsible for acidification of intracellulare compartments and, in certain cases, ion transport across the plasma membrane of eucaryotic cells. V-ATPases are composed of two distinct domains: a catalytic V₁ sector, in which ATP hydrolysis takes place, and the membrane-embedded sector, V₀, which functions in ion conduction. In the past decade impressive progress has been made in elucidating the properties structure, function and moleculare biology. These knowledge sheds light also on the evolution of V-ATPases and their related families of A-(A₁A₀-ATPase) and F-type (F₁F₀-ATPases)ATPases.     

Structure,subunit function and regulation of the coated vesicle and yeast vacuolar (H(+))-ATPases

The vacuolar (H(+))-ATPases (or V-ATPases) are ATP-dependent proton pumps that function to acidify intracellular compartments in eukaryotic cells. This acidification is essential for such processes as receptor-mediated endocytosis, intracellular targeting of lysosomal enzymes, protein processing and degradation and the coupled transport of small molecules. V-ATPases in the plasma membrane of specialized cells also function in such processes as renal acidification, bone resorption and pH homeostasis. Work from our laboratory has focused on the V-ATPases from clathrin-coated vesicles and yeast vacuoles.Structurally, the V-ATPases are composed of two domains: a peripheral complex (V(1)) composed of eight different subunits (A-H) that is responsible for ATP hydrolysis and an integral complex (V(0)) composed of five different subunits (a, d, c, c' and c") that is responsible for proton translocation. Electron microscopy has revealed the presence of multiple stalks connecting the V(1) and V(0) domains, and crosslinking has been used to address the arrangement of subunits in the complex. Site-directed mutagenesis has been employed to identify residues involved in ATP hydrolysis and proton translocation and to study the topology of the 100 kDa a subunit. This subunit has been shown to control intracellular targeting of the V-ATPase and to influence reversible dissociation and coupling of proton transport and ATP hydrolysis.     

Subunit H of the vacuolar (H+) ATPase inhibits ATP hydrolysis by the free V1 domain by interaction with the rotary subunit F

The vacuolar (H+) ATPases (V-ATPases) are large, multimeric proton pumps that, like the related family of F1F0 ATP synthases, employ a rotary mechanism. ATP hydrolysis by the peripheral V1 domain drives rotation of a rotary complex (the rotor) relative to the stationary part of the enzyme (the stator), leading to proton translocation through the integral V0 domain. One mechanism of regulating V-ATPase activity in vivo involves reversible dissociation of the V1 and V0 domains. Unlike the corresponding domains in F1F0, the dissociated V1 domain does not hydrolyze ATP, and the free V0 domain does not passively conduct protons. These properties are important to avoid generation of an uncoupled ATPase activity or an unregulated proton conductance upon dissociation of the complex in vivo. Previous results (Parra, K. J., Keenan, K. L., and Kane, P. M. (2000) J. Biol. Chem. 275, 21761-21767) showed that subunit H (part of the stator) inhibits ATP hydrolysis by free V1. To test the hypothesis that subunit H accomplishes this by bridging rotor and stator in free V1, cysteine-mediated cross-linking studies were performed. Unique cysteine residues were introduced over the surface of subunit H from yeast by site-directed mutagenesis and used as the site of attachment of the photo-activated cross-linking reagent maleimido benzophenone. After UV-activated cross-linking, cross-linked products were identified by Western blot using subunit-specific antibodies. The results indicate that the subunit H mutant S381C shows cross-linking between subunit H and subunit F (a rotor subunit) in the free V1 domain but not in the intact V1V0 complex. These results indicate that subunits H and F are proximal in free V1, supporting the hypothesis that subunit H inhibits free V1 by bridging the rotary and stator domains.     

The vacuolar (H+)-ATPase: subunit arrangement and in vivo regulation

The V-ATPases are responsible for acidification of intracellular compartments and proton transport across the plasma membrane. They play an important role in both normal processes, such as membrane traffic, protein degradation, urinary acidification, and bone resorption, as well as various disease processes, such as viral infection, toxin killing, osteoporosis, and tumor metastasis. V-ATPases contain a peripheral domain (V₁) that carries out ATP hydrolysis and an integral domain (V₀) responsible for proton transport. V-ATPases operate by a rotary mechanism involving both a central rotary stalk and a peripheral stalk that serves as a stator. Cysteine-mediated cross-linking has been used to localize subunits within the V-ATPase complex and to investigate the helical interactions between subunits within the integral V₀ domain. An essential property of the V-ATPases is the ability to regulate their activity in vivo. An important mechanism of regulating V-ATPase activity is reversible dissociation of the complex into its component V₁ and V₀ domains. The dependence of reversible dissociation on subunit isoforms and cellular environment has been investigated. Qi and Wang contributed equally to this work.     

Characterization of the functional coupling of bovine brain vacuolar-type H(+)-translocating ATPase. Effect of divalent cations,phospholipids, and subunit H (SFD)

Vacuolar-type H+-translocating ATPases (V-ATPases or V-pumps) are complex proteins containing multiple subunits and are organized into two functional domains: a peripheral catalytic sector V1 and a membranous proton channel V0. The functional coupling of ATP hydrolysis activity to proton transport in V-pumps requires a regulatory component known as subunit H (SFD) as has been shown both in vivo and in vitro (Ho, M. N., Hirata, R., Umemoto, N., Ohya, Y., Takatsuki, A., Stevens, T. H., and Anraku, Y. (1993) J. Biol. Chem. 268, 18286-18292; Xie, X. S., Crider, B. P., Ma, Y. M., and Stone, D. K. (1994) J. Biol. Chem. 269, 25809-25815). Ca2+ is thought to uncouple V-pumps because it is found to support ATP hydrolysis but not proton transport, while Mg2+ supports both activities. The direct effect of phospholipids on the coupling of V-ATPases has not been reported, likely due to the fact that phospholipids are constituents of biological membranes. We now report that Ca2+-induced uncoupling of the bovine brain V-ATPase can be reversed by imposition of a favorable membrane potential. Furthermore we report a simple "membrane-free" assay system using the V0 proton channel-specific inhibitor bafilomycin as a probe to detect the coupling of V-ATPase under certain conditions. With this system, we have characterized the functional effect of subunit H, divalent cations, and phospholipids on bovine brain V-ATPase and have found that each of these three factors plays a critical role in the functional coupling of the V-pump.