Activation of the neutrophil respiratory burst by chemoattractants: Regulation of the N-formyl peptide receptor in the plasma membrane

The N-formyl peptide receptor mediates a number of host defensive responses of human neutrophils that result in chemotaxis, secretion of hydrolytic enzymes, and superoxide generation. Inappropriate activation or defective regulation of these responses can result in pathogenic states responsible for inflammatory disease. The receptor is a 50 to 70-kD, integral plasma membrane glycoprotein with intracellular and surface localization. Its abundance in the membrane is regulated by membrane flow and recycling processes. Cytoskeletal interactions are believed to control its organization in the plane of the membrane and interaction with other proteins. The receptor's most important interaction is with guanyl nucleotide binding proteins that serve as signal transduction partners ultimately leading to activation of effector responses. Because the interaction of the receptor with G proteins is necessary for transduction, control of this interaction may be at the root of understanding the molecular control of responses in these cells. This review briefly summarizes some of the molecular properties, dynamics, and interactions of this receptor system in human neutrophils and discusses how these characteristics may pertain to the activation and control of superoxide generation.     

Multiple signaling pathways are involved in endothelin-1-induced brain endothelial cell migration

We have observed that the vasoactive peptide endothelin-1 is a potent inducer of migration of primary human brain-derived microvascular endothelial cells. By blocking signal transduction pathways with specific inhibitors, and using dominant negative mutant infections, we have demonstrated that multiple pathways are involved in endothelin-1-induced migration. Absolutely required for migration are protein tyrosine kinase Src, Ras, protein kinase C (PKC), phosphatidylinositol 3-kinase, ERK, and JNK; partial requirements were exhibited by cAMP-activated protein kinase and p38 kinase. Partial elucidation of the signal transduction sequences showed that the MAPKs ERK, JNK, and p38 are positioned downstream of both PKC and cAMP-activated protein kinase in the signal transduction scheme. The results show that human brain endothelial cell migration has distinct characteristics, different from cells derived from other vascular beds, or from other species, often used as model systems. Furthermore, the results indicate that endothelin-1, secreted by many tumors, is an important contributor to tumor-produced proangiogenic microenvironment. This growth factor has been associated with increased microvessel density in tumors and is responsible for endothelial cell proliferation, migration, invasion, and tubule formation. Because many signal transduction pathways investigated in this study are potential or current targets for anti-angiogenesis therapy, these results are of critical importance for designing physiological antiangiogenic protocols. signal transduction; angiogenesis; microvessels; vasoactive peptides     

Membrane ruffling and signal transduction

One of the earliest structural changes observed in cells in response to many extracellular factors is membrane ruffling: the formation of motile cell surface protrusions containing a meshwork of newly polymerized actin filaments. It is becoming clear that actin reorganization is an integral part of early signal transduction pathways, and that many signalling molecules interact with the actin cytoskeleton. The small GTP-binding protein Rac is a key regulator of membrane ruffling, and proteins that can regulate Rac activity, such as Bcr, are likely to act on this signalling pathway. In addition, several previously characterized signal transducing molecules are implicated in the membrane-ruffling response, including Ras, the adaptor protein Grb2, phosphatidyl inositol 3-kinase, phospholipase A₂ and phorbol ester-responsive proteins. Changes in polyphosphoinositide metabolism and intracellular Ca²⁺ levels may also play a role. A number of actin-binding and organizing proteins localize to membrane ruffles and are potential targets for these signal transducing molecules.     

Helicobacter pylori induces formation of stress fibers and membrane ruffles in AGS cells by rac activation

Helicobacter pylori induces signaling cascades leading to changes in cytoskeleton and an inflammatory response. Information on the morphological changes and cytoskeletal rearrangements induced by attachment of the bacterium is contradictory and signal transduction pathways are not well known. Since rho family of small GTPases is known to mediate cytoskeletal response to various extracellular stimuli, and is also involved in several other important signal transduction pathways, we have investigated the role of rac and cdc42 in H. pylori-induced cytoskeletal changes in cultured carcinoma AGS cells. AGS cells grown with serum expressed actin filaments in the form of short stress fibers and thin network at the edges, which were depolymerized by removal of serum. In serum-starved cells both type I and type II strains of H. pylori induced formation of actin filaments and lamellipodia-like structures. Microinjection of active rac induced similar changes, but injection of inactive rac prevented the effects of H. pylori, while active or inactive cdc42 did not have any significant effect. Cytoskeletal effects of H. pylori were inhibited by actinomycin D, but not completely by cycloheximide. These results indicate that rac activation is involved in signal transduction cascade leading to cytoskeletal reorganization induced by H. pylori and that gene activation and synthesis of new proteins is necessary in this process.     

How actin filaments and microtubules steer growth cones to their targets

Guidance molecules steer growth cones to their targets by attracting or repelling them. Turning in a new direction requires remodeling of the growth cone and bending of the axon. This depends upon reorganization of actin filaments and microtubules, which are the primary cytoskeletal components of growth cones. This article discusses how these cytoskeletal components induce turning. The importance of each component as well as how interactions between them result in axon guidance is discussed. Current evidence shows that microtubules are influenced by both the organization and dynamics of actin filaments in the peripheral domain of growth cones. Cytoskeletal models for repulsive and attractive turning are presented. Molecular candidates that may link actin filaments with microtubules are suggested and potential signal transduction pathways that allow these cytoskeletal components to affect each other are discussed.     

Bioengineering plant resistance to abiotic stresses by the global calcium signal system

Considerable progresses have taken place both in the methodology available to study changes in intracellular cytosolic calcium and in our understanding of calcium signaling cascades. It is generally accepted that the global calcium signal system functions importantly in coping with plant abiotic stresses, especially drought stress, which has been proved further by the recent transgenic and molecular breeding reports under soil water deficits. In plant cells, calcium plays roles as a universal transducer coupling a wide range of extracellular stimuli with intracellular responses. Different extracellular stimuli trigger specific calcium signatures: dynamics, amplitude and duration of calcium transients specify the nature, implication and intensity of stimuli. Calcium-binding proteins (sensors) play a critical role in decoding calcium signatures and transducing signals by activating specific targets and corresponding metabolic pathways. Calmodulin (CAM) is a calcium sensor known to regulate the activity of many mammalian proteins, whose targets in plants are now being identified. Higher plants possess a rapidly growing list of CAM targets with a variety of cellular functions. Nevertheless, many targets appear to be unique to higher plant cells and remain characterized, calling for a concerted effort from plant and animal scientists to elucidate their functions. To date, three major classes of plant calcium signals encoding elements in the calcium signal system, including calcium-permeable ion channels,Ca(2)+/ H(+) antiporters and Ca(2)+-ATPases, are responsible for drought stress signal transduction directly or indirectly. This review summarizes the current knowledge of calcium signals involved in plant abiotic stresses and presents suggestions for future focus areas of study.     

Kinases as targets in the treatment of solid tumors

The protein kinase family, one of the largest gene families in eukaryotes, plays an important role in regulating various cellular processes such as cell proliferation, cell death, cell cycle progression, differentiation and cell survival. Therefore, it is not surprising that the deregulation of many kinases is usually directly linked to cancer development. In all solid tumors, changes in protein kinase expression levels and activities, as well as alterations in the degree of posttranslational modifications can contribute to cancer development. Consequently, the identification of molecular targets and signaling pathways specific to cancer cells is becoming more and more important for cancer drug development and cancer therapies. Inhibition of various protein kinases has already been investigated in many pre-clinical and clinical trials targeting all stages of signal transduction, demonstrating promising results in cancer therapy. Conventional chemotherapeutics are often ineffective as well as harmful; hence a combination of both chemotherapeutics and protein kinase inhibitors may result in new and more successful therapeutic approaches. In this review we focus on protein kinases involved in different signaling pathways and their alterations in solid tumors.     

细胞骨架与胰岛素相关信号转导通路

细胞骨架是蛋白质纤维交织形成的立体网架体系,它是一个动态结构,可随着生理条件的改变不断进行组装和去组装,并受到细胞内外因素的调节.胰岛素是参与机体内诸多生理过程如葡萄糖转运、基因表达和DNA合成等的重要激素, 而胰岛素的正常分泌是其功能发挥的重要前提.越来越多的研究表明,细胞骨架在胰岛素行使功能和胰岛素的分泌过程中起重要作用,其具体机制与胰岛素相关的信号转导通路密切相关.当细胞骨架成分发生改变,继而影响到胰岛素相关的信号转导过程时,就会影响胰岛素的分泌,同时会导致胰岛素抵抗的发生.     

Cellular signal transduction and the reversal of malignancy

Animal cells contain only a few defined molecular systems that transduce hormonal and growth signals from the external environment to the intracellular milieu to regulate cellular growth and differentiation. Among the most ubiquitous of these "second messenger" pathways are those utilizing cyclic AMP and phosphatidylinositide turnover. The former activates protein kinase A, while the latter leads to the activation of protein kinase C and mobilization of intracellular calcium. Lesions induced by oncogenes in signal transduction systems may be responsible for the cancerous transformation of cells. In many tumor cell lines, including some transformed by the ras and sis oncogenes, activation of protein kinase A by elevation of cyclic AMP or activation of protein kinase C by addition of phorbol esters can restore many normal aspects of growth and morphology. Such "reverse transformation" is accompanied by the phosphorylation of unique cellular proteins and alterations in the phosphoinositide cycle. Molecular mechanisms by which activation of signal transduction systems can attenuate the malignant phenotype are considered in the context of cellular growth and differentiation.     

Microtubules and signal transduction

Although molecular components of signal transduction pathways are rapidly being identified, how elements of these pathways are positioned spatially and how signals traverse the intracellular environment from the cell surface to the nucleus or to other cytoplasmic targets are not well understood. The discovery of signaling molecules that interact with microtubules (MTs), as well as the multiple effects on signaling pathways of drugs that destabilize or hyperstabilize MTs, indicate that MTs are likely to be critical to the spatial organization of signal transduction. MTs themselves are also affected by signaling pathways and this may contribute to the transmission of signals to downstream targets.     

Physical modulation of intracellular signaling processes by locational regulation.

Recent observations in the field of signal transduction suggest that where a protein is located within a cell can be as important as its activity measured in solution for activation of its downstream pathway. The physical organization of the cell can provide an additional layer of control upon the chemical reaction networks that govern ultimately perceived signals. Using the cytosol and plasma membrane as relevant compartmental distinctions, we analyze the effect of relocation on the rate of association with a membrane-associated target. We quantify this effect as an enhancement factor E in terms of measurable parameters such as the number of available targets, molecular diffusivities, and intrinsic reaction rate constants. We then employ two simple yet relevant example models to illustrate how relocation can affect the dynamics of signal transduction pathways. The temporal profiles and phase behavior of these models are investigated. We also relate experimentally observable aspects of signal transduction such as peak activation and the relative time scales of stimulus and response to quantitative aspects of the relocation mechanisms in our models. In our example schemes, nearly complete relocation of the cytosolic species in the signaling pair is required to generate meaningful activation of the model pathways when the association rate enhancement factor E is as low as 10; when E is 100 or greater, only a small fraction of the protein must be relocated.     

钙—钙调素信号系统与环境刺激

植物抗逆研究已有很大进展,但传递各种外界刺激的信号通路仍未可知,目前已有一些研究发现很多环境刺激与钙－钙调素系统有关,Ca^2 信号系统是很重要的一种信号途径,CaM是目前已知的胞内Ca^2 信号受体中最重要的一种,参与了多种生理活动的调节,在热激领域中,研究者已提出Ca^2 -CaM系统可能参与了热激反应,在基因调节水平,转录水平,蛋白水平均有Ca^2 和CaM参与热激的证据,其它环境刺激也能引起植物体内Ca^2 和CaM的一系列变化,这为研究各种环境刺激可能的信号通路提供了基础和依据。     

Effects of sequestration on signal transduction cascades

The building blocks of most signal transduction pathways are pairs of enzymes, such as kinases and phosphatases, that control the activity of protein targets by covalent modification. It has previously been shown [Goldbeter A & Koshland DE (1981) Proc Natl Acad Sci USA 78, 6840-6844] that these systems can be highly sensitive to changes in stimuli if their catalysing enzymes are saturated with their target protein substrates. This mechanism, termed zero-order ultrasensitivity, may set thresholds that filter out subthreshold stimuli. Experimental data on protein abundance suggest that the enzymes and their target proteins are present in comparable concentrations. Under these conditions a large fraction of the target protein may be sequestrated by the enzymes. This causes a reduction in ultrasensitivity so that the proposed mechanism is unlikely to account for ultrasensitivity under the conditions present in most in vivo signalling cascades. Furthermore, we show that sequestration changes the dynamics of a covalent modification cycle and may account for signal termination and a sign-sensitive delay. Finally, we analyse the effect of sequestration on the dynamics of a complex signal transduction cascade: the mitogen-activated protein kinase (MAPK) cascade with negative feedback. We show that sequestration limits ultrasensitivity in this cascade and may thereby abolish the potential for oscillations induced by negative feedback.     

钙_钙调素信号系统与环境刺激

植物抗逆研究已有很大进展,但传递各种外界刺激的信号通路仍未可知,目前已有一些研究发现很多环境刺激与钙_钙调素系统有关。Ca2+信号系统是很重要的一种信号途径,CaM是目前已知的胞内Ca2+信号受体中最重要的一种,参与了多种生理活动的调节。在热激领域中,研究者已提出Ca2+ CaM系统可能参与了热激反应,在基因调节水平、转录水平、蛋白水平均有Ca2+和CaM参与热激的证据。其它环境刺激也能引起植物体内Ca2+和CaM的一系列变化。这为研究各种环境刺激可能的信号通路提供了基础和依据。     

高等植物对环境胁迫的适应与其胁迫信号的转导

高等植物适应环境胁迫有多种水平与尺度的生理与生化方式,但其本质却是分子水平的基因时空表达与调控,它又受到胁迫信号转导途径的多重调控与影响。环境胁迫的主要形式是冷害、干旱、盐碱胁迫与UV-B辐射等,而它们又是影响高等植物生长、发育、繁殖等重要过程的生态因子,同时也是作物高效生产必需重视的因素,对其与植物相互作用的分子机理的认识有重要理论意义与实践意义。从细胞与组织和器官水平获得的分子生物学规律,只有应用到个体,群体,及生态系统中才会更有生命力。如何将这些数据资料成为宝贵的永续资源是21世纪植物系统生物学面临的主要挑战之一。主要从农业生态环境角度阐述环境胁迫信号转导的分子生物学作用方式,新进展资料的整合并建立起它们的可能联系及本领域中存在的相关问题和可能的解决途径,为高效的农业生态可持续发展提供分子生物学方面的理论基础。