植物蛋白质SUMO化修饰体外高效检测系统

蛋白质SUMO化修饰是一种调控蛋白命运的关键修饰方式, 广泛参与植物生长发育及逆境胁迫响应。SUMO化修饰过程主要由激活酶(E1)-结合酶(E2)-连接酶(E3)组成的级联酶促反应催化, 其关键酶组分将SUMO分子缀合至底物蛋白的赖氨酸残基, 形成共价异肽键以完成SUMO化修饰过程。该文报道了1种植物蛋白质SUMO化修饰体外高效检测系统, 通过在大肠杆菌(Escherichia coli)中构建拟南芥(Arabidopsis thaliana) SUMO化修饰的关键通路实现对底物蛋白的SUMO化修饰, 结果可通过免疫印迹进行检测。该系统可以简化植物蛋白质SUMO化修饰的检测流程, 为植物细胞SUMO化修饰的功能研究提供了有力工具。     

TRPV3 and TRPV4 mediate warmth-evoked currents in primary mouse keratinocytes

Recently, a family of temperature-activated ion channels has been identified in mammalian and nonmammalian species that appear to contribute to thermosensation. Two of these proteins, TRPV3 and TRPV4, are ion channels activated by modest increases in ambient temperature. Localization studies have indicated that both proteins, in addition to being expressed in sensory neurons, are also expressed in skin keratinocytes. These and other findings have suggested that keratinocytes might act in concert with sensory neurons to perceive our thermal environment. In this study, we demonstrate that primary keratinocytes isolated from mouse skin exhibit two distinct heat-evoked current responses to mild increases in ambient temperature. The more common of these response types bears considerable similarity to responses mediated by recombinant TRPV4, is absent in mice lacking this ion channel, and is restored upon TRPV4 reintroduction. The second, rarer response strongly resembles those mediated by recombinant TRPV3. Together, these findings demonstrate that keratinocytes can indeed act as thermosensory cells and that they do so via at least two distinct transduction mechanisms.     

Opa proteins and CEACAMs: pathways of immune engagement for pathogenic Neisseria

Neisseria meningitidis and Neisseria gonorrhoeae are globally important pathogens, which in part owe their success to their ability to successfully evade human immune responses over long periods. The phase-variable opacity-associated (Opa) adhesin proteins are a major surface component of these organisms, and are responsible for bacterial adherence and entry into host cells and interactions with the immune system. Most immune interactions are mediated via binding to members of the carcinoembryonic antigen cell adhesion molecule (CEACAM) family. These Opa variants are able to bind to different receptors of the CEACAM family on epithelial cells, neutrophils, and T and B lymphocytes, influencing the innate and adaptive immune responses. Increased epithelial cell adhesion creates the potential for prolonged infection, invasion and dissemination. Furthermore, Opa proteins may inhibit T-lymphocyte activation and proliferation, B-cell antibody production, and innate inflammatory responses by infected epithelia, in addition to conferring increased resistance to antibody-dependent, complement-mediated killing. While vaccines containing Opa proteins could induce adhesion-blocking and bactericidal antibodies, the consequence of CEACAM binding by a candidate Opa-containing vaccine requires further investigation. This review summarizes current knowledge of the immunological consequences of the interaction between meningococcal and gonococcal Opa proteins and human CEACAMs, considering the implications for pathogenesis and vaccine development.     

Strategies for manipulating apoptosis for cancer therapy with tumor necrosis factor and lymphotoxin

Tumor necrosis factor (TNF) and lymphotoxin (LT), initially described as tumoricidal proteins, may be useful as adjuncts in cancer therapy. Treatment with TNF or LT was found to protect cells and animals against damage mediated by radiation or cytotoxic anticancer drugs. By contrast, tumor cells treated with TNF or LT were sensitized to these insults. We present a model in which TNF or LT induces both the synthesis of “protective” proteins such as manganous superoxide dismutase (MnSOD) and the activation of “killing” proteins, such as proteases, depending on the level of the inducing signal. Although the p55-TNF/LT receptor is structurally related to the Fas receptor, they can each signal apoptosis by distinct pathways. Furthermore, activation of both receptors acts synergistically in stimulating apoptosis. © 1996 Wiley-Liss, Inc.     

Bruton's tyrosine kinase together with PI 3-kinase are part of Toll-like receptor 2 multiprotein complex and mediate LTA induced Toll-like receptor 2 responses in macrophages

Lipoteichoic acid (LTA) of Gram-positive bacteria initiates innate immune responses via Toll-like receptor-2 (TLR2), resulting in the activation of intracellular signaling and production of inflammatory cytokines in macrophages. Although Bruton's tyrosine kinase (Btk) is biologically important molecule implicated in immune regulation and recently in TLR signaling its importance for LTA-TLR2 mediated responses has not been evaluated. In this study, we detected Btk in the LTA signaling complex with TLR2 and PI 3-kinase (PI3K). The constitutive interaction of these proteins was mediated via PI3K Src homology (SH3) -domain. Both Btk and PI3K were activated by LTA stimulation and the LTA induced cytokine expression was differentially modulated by these kinases. LTA induced the activation of nuclear factor kappaB (NFkappaB), however, only Btk inhibition affected the LTA induced Ser536 phosphorylation and DNA-binding of NFkappaB. In conclusion, our results demonstrate that Btk and PI3K occupy important roles in TLR2-induced activation of macrophages, resulting in selective regulation of cytokines.     

Coupling of ETB Endothelin Receptor to Mitogen-Activated Protein Kinase Stimulation and DNA Synthesis in Primary Cultures of Rat Astrocytes

Abstract: Astrocytes have been shown to express endothelin (ET) receptors functionally coupled, via different heterotrimeric G proteins, to several intracellular pathways. To assess the relative contribution of each subtype in the astrocytic responses to ET-1, effects of BQ123, an antagonist selective for the ET receptor subtype A (ET_A-R), and IRL1620, an agonist selective for the ET receptor subtype B (ET_B-R), were investigated in primary cultures of rat astrocytes. Binding experiments indicated that the ET_B-R is the predominant subtype in these cells. Inhibition of forskolin-stimulated cyclic AMP production was observed under ET_B-R stimulation. Bordetella pertussis toxin (PTX) pretreatment completely abolished this effect, indicating that this pathway is coupled to the ET_B-R via G_i protein. Increases of tyrosine phosphorylation of cellular proteins, stimulation of mitogen-activated protein kinase (MAPK), and DNA synthesis were also found to be mediated by the ET_B-R, but through PTX-insensitive G protein. IRL1620-induced MAPK activation involved the adapter proteins Shc and Grb2 and the serine/threonine kinase Raf-1. This study reveals that the various effects of ET-1 in astrocytes are mediated by the ET_B-R, which couples to multiple signaling pathways including the MAPK cascade.     

Coagulation cascade proteases and tissue fibrosis

Fibrotic disorders of the liver, kidney and lung are associated with excessive deposition of extracellular matrix proteins and ongoing coagulation-cascade activity. In addition to their critical roles in blood coagulation, thrombin and the immediate upstream coagulation proteases, Factors Xa and VIIa, influence numerous cellular responses that may play critical roles in subsequent inflammatory and tissue repair processes in vascular and extravascular compartments. The cellular effects of these proteases are mediated via proteolytic activation of a novel family of cell-surface receptors, the protease-activated receptors (PAR-1, -2, -3 and -4). Although thrombin is capable of activating PAR-1, -3 and -4, there is accumulating in vitro evidence that the profibrotic effects of thrombin are predominantly mediated via PAR-1. Factor Xa is capable of activating PAR-1 and PAR-2, but its mitogenic effects for fibroblasts are similarly mediated via PAR-1. These proteases do not exert their profibrotic effects directly, but act via the induction of potent fibrogenic mediators, such as platelet-derived growth factor and connective tissue growth factor. In vivo studies using proteolytic inhibitors, PAR-1 antagonists and PAR-1-deficient mice have provided evidence that coagulation proteases play a key role in tissue inflammation and in a number of vascular pathologies associated with hyperproliferation of smooth muscle cells. More recently, coagulation proteases have also been shown to play a role in the pathogenesis of fibrosis but the relative contribution of their cellular versus their procoagulant effects awaits urgent evaluation in vivo. These studies will be informative in determining the potential application of PAR-1 antagonists as antifibrotic agents.     

Differential role of ionotropic glutamatergic mechanisms in responses to NTS P(2x) and A(2a) receptor stimulation

Activation of ATP P(2x) receptors in the subpostremal nucleus tractus solitarii (NTS) via microinjection of alpha,beta-methylene ATP (alpha,beta-MeATP) elicits fast initial depressor and sympathoinhibitory responses that are followed by slow, long-lasting inhibitory effects. Activation of NTS adenosine A(2a) receptors via microinjection of CGS-21680 elicits slow, long-lasting decreases in arterial pressure and renal sympathetic nerve activity (RSNA) and an increase in preganglionic adrenal sympathetic nerve activity (pre-ASNA). Both P(2x) and A(2a) receptors may operate via modulation of glutamate release from central neurons. We investigated whether intact glutamatergic transmission is necessary to mediate the responses to NTS P(2x) and A(2a) receptor stimulation. The hemodynamic and neural (RSNA and pre-ASNA) responses to microinjections of alpha,beta-MeATP (25 pmol/50 nl) and CGS-21680 (20 pmol/50 nl) were compared before and after pretreatment with kynurenate sodium (KYN; 4.4 nmol/100 nl) in chloralose-urethan-anesthetized male Sprague-Dawley rats. KYN virtually abolished the fast responses to alpha,beta-MeATP and tended to enhance the slow component of the neural responses. The depressor responses to CGS-21680 were mostly preserved after pretreatment with KYN, although the increase in pre-ASNA was reduced by one-half following the glutamatergic blockade. We conclude that the fast responses to stimulation of NTS P(2x) receptors are mediated via glutamatergic ionotropic mechanisms, whereas the slow responses to stimulation of NTS P(2x) and A(2a) receptors are mediated mostly via other neuromodulatory mechanisms.     

Two novel WD40 domain-containing proteins, Ere1 and Ere2, function in the retromer-mediated endosomal recycling pathway

Regulated secretion, nutrient uptake, and responses to extracellular signals depend on cell-surface proteins that are internalized and recycled back to the plasma membrane. However, the underlying mechanisms that govern membrane protein recycling to the cell surface are not fully known. Using a chemical-genetic screen in yeast, we show that the arginine transporter Can1 is recycled back to the cell surface via two independent pathways mediated by the sorting nexins Snx4/41/42 and the retromer complex, respectively. In addition, we identify two novel WD40-domain endosomal recycling proteins, Ere1 and Ere2, that function in the retromer pathway. Ere1 is required for Can1 recycling via the retromer-mediated pathway, but it is not required for the transport of other retromer cargoes, such as Vps10 and Ftr1. Biochemical studies reveal that Ere1 physically interacts with internalized Can1. Ere2 is present in a complex containing Ere1 on endosomes and functions as a regulator of Ere1. Taken together, our results suggest that Snx4/41/42 and the retromer comprise two independent pathways for the recycling of internalized cell-surface proteins. Moreover, a complex containing the two novel proteins Ere1 and Ere2 mediates cargo-specific recognition by the retromer pathway.     

Transportin-SR is required for proper splicing of resistance genes and plant immunity

Transportin-SR (TRN-SR) is a member of the importin-β super-family that functions as the nuclear import receptor for serine-arginine rich (SR) proteins, which play diverse roles in RNA metabolism. Here we report the identification and cloning of mos14 (modifier of snc1-1, 14), a mutation that suppresses the immune responses conditioned by the auto-activated Resistance (R) protein snc1 (suppressor of npr1-1, constitutive 1). MOS14 encodes a nuclear protein with high similarity to previously characterized TRN-SR proteins in animals. Yeast two-hybrid assays showed that MOS14 interacts with AtRAN1 via its N-terminus and SR proteins via its C-terminus. In mos14-1, localization of several SR proteins to the nucleus was impaired, confirming that MOS14 functions as a TRN-SR. The mos14-1 mutation results in altered splicing patterns of SNC1 and another R gene RPS4 and compromised resistance mediated by snc1 and RPS4, suggesting that nuclear import of SR proteins by MOS14 is required for proper splicing of these two R genes and is important for their functions in plant immunity.     

气孔运动中的活性氧信号

大量研究证明活性氧(ROS)在气孔运动中起信号分子的作用。保卫细胞中ROS的产生依赖于特定的酶,其中NADPH氧化酶组分RBOH已得到深入研究,并已证实其参与生物与非生物胁迫反应。植物激素包括脱落酸(ABA)、水杨酸(SA)、乙烯、生长素及细胞分裂素等,它们均通过ROS的介导来调控气孔运动。生物胁迫(如毒性细菌和真菌)也会调控气孔运动。ROS参与这些调控过程。保卫细胞中存在多层次对ROS产生及其作用的调节,抗氧化活性物质和ROS敏感蛋白(如蛋白激酶和磷酸酶)均可传递ROS信号并调节气孔运动。ROS对离子通道调节的证据也越来越多。保卫细胞由于可通过ROS整合复杂的信号途径,已成为研究植物ROS信号转导过程的良好模式系统。     

Bacterial type two secretion system secreted proteins: double-edged swords for plant pathogens

The type two secretion system (T2S) is important for virulence of a number of gram-negative bacterial plant pathogens. Most of the T2S-secreted proteins that have been characterized to date are involved in degrading different components of plant cell walls. Functional redundancy appears to exist among T2S-secreted proteins because significant effects on virulence are observed only in strains in which multiple secreted proteins are mutated. Several T2S-secreted proteins have been shown to induce plant defense responses, including hypersensitive response-like reactions. Bacterial pathogens can suppress these defense responses, and recent results indicate that suppression is mediated through the type three secretion system.     

气孔运动中的活性氧信号

大量研究证明活性氧(ROS)在气孔运动中起信号分子的作用。保卫细胞中ROS的产生依赖于特定的酶, 其中NADPH氧化酶组分RBOH已得到深入研究, 并已证实其参与生物与非生物胁迫反应。植物激素包括脱落酸(ABA)、水杨酸(SA)、乙烯、生长素及细胞分裂素等, 它们均通过ROS的介导来调控气孔运动。生物胁迫(如毒性细菌和真菌)也会调控气孔运动。ROS参与这些调控过程。保卫细胞中存在多层次对ROS产生及其作用的调节, 抗氧化活性物质和ROS敏感蛋白(如蛋白激酶和磷酸酶)均可传递ROS信号并调节气孔运动。ROS对离子通道调节的证据也越来越多。保卫细胞由于可通过ROS整合复杂的信号途径, 已成为研究植物ROS信号转导过程的良好模式系统。