Rapid Remodeling of Invadosomes by Gi-coupled Receptors: DISSECTING THE ROLE OF Rho GTPases*

Invadosomes are actin-rich membrane protrusions that degrade the extracellular matrix to drive tumor cell invasion. Key players in invadosome formation are c-Src and Rho family GTPases. Invadosomes can reassemble into circular rosette-like superstructures, but the underlying signaling mechanisms remain obscure. Here we show that Src-induced invadosomes in human melanoma cells (A375M and MDA-MB-435) undergo rapid remodeling into dynamic extracellular matrix-degrading rosettes by distinct G protein-coupled receptor agonists, notably lysophosphatidic acid (LPA; acting through the LPA₁ receptor) and endothelin. Agonist-induced rosette formation is blocked by pertussis toxin, dependent on PI3K activity and accompanied by localized production of phosphatidylinositol 3,4,5-trisphosphate, whereas MAPK and Ca²⁺ signaling are dispensable. Using FRET-based biosensors, we show that LPA and endothelin transiently activate Cdc42 through G_i, concurrent with a biphasic decrease in Rac activity and differential effects on RhoA. Cdc42 activity is essential for rosette formation, whereas G_12/13-mediated RhoA-ROCK signaling suppresses the remodeling process. Our results reveal a G_i-mediated Cdc42 signaling axis by which G protein-coupled receptors trigger invadosome remodeling, the degree of which is dictated by the Cdc42-RhoA activity balance.     

Signaling,Regulation, and Specificity of the Type II p21-activated Kinases

The p21-activated kinases (PAKs) are a family of six serine/threonine kinases that act as key effectors of RHO family GTPases in mammalian cells. PAKs are subdivided into two groups: type I PAKs (PAK1, PAK2, and PAK3) and type II PAKs (PAK4, PAK5, and PAK6). Although these groups are involved in common signaling pathways, recent work indicates that the two groups have distinct modes of regulation and have both unique and common substrates. Here, we review recent insights into the molecular level details that govern regulation of type II PAK signaling. We also consider mechanisms by which signal transduction is regulated at the level of substrate specificity. Finally, we discuss the implications of these studies for clinical targeting of these kinases.     

A-kinase Anchoring Protein 79/150 Recruits Protein Kinase C to Phosphorylate Roundabout Receptors

Anchoring proteins direct protein kinases and phosphoprotein phosphatases toward selected substrates to control the efficacy, context, and duration of neuronal phosphorylation events. The A-kinase anchoring protein AKAP79/150 interacts with protein kinase A (PKA), protein kinase C (PKC), and protein phosphatase 2B (calcineurin) to modulate second messenger signaling events. In a mass spectrometry-based screen for additional AKAP79/150 binding partners, we have identified the Roundabout axonal guidance receptor Robo2 and its ligands Slit2 and Slit3. Biochemical and cellular approaches confirm that a linear sequence located in the cytoplasmic tail of Robo2 (residues 991–1070) interfaces directly with sites on the anchoring protein. Parallel studies show that AKAP79/150 interacts with the Robo3 receptor in a similar manner. Immunofluorescent staining detects overlapping expression patterns for murine AKAP150, Robo2, and Robo3 in a variety of brain regions, including hippocampal region CA1 and the islands of Calleja. In vitro kinase assays, peptide spot array mapping, and proximity ligation assay staining approaches establish that human AKAP79-anchored PKC selectively phosphorylates the Robo3.1 receptor subtype on serine 1330. These findings imply that anchored PKC locally modulates the phosphorylation status of Robo3.1 in brain regions governing learning and memory and reward.     

Sumoylation of the GTPase Ran by the RanBP2 SUMO E3 Ligase Complex

The SUMO E3 ligase complex RanBP2/RanGAP1*SUMO1/Ubc9 localizes at cytoplasmic nuclear pore complex (NPC) filaments and is a docking site in nucleocytoplasmic transport. RanBP2 has four Ran binding domains (RBDs), two of which flank RanBP2''s E3 ligase region. We thus wondered whether the small GTPase Ran is a target for RanBP2-dependent sumoylation. Indeed, Ran is sumoylated both by a reconstituted and the endogenous RanBP2 complex in semi-permeabilized cells. Generic inhibition of SUMO isopeptidases or depletion of the SUMO isopeptidase SENP1 enhances sumoylation of Ran in semi-permeabilized cells. As Ran is typically associated with transport receptors, we tested the influence of Crm1, Imp β, Transportin, and NTF2 on Ran sumoylation. Surprisingly, all inhibited Ran sumoylation. Mapping Ran sumoylation sites revealed that transport receptors may simply block access of the E2-conjugating enzyme Ubc9, however the acceptor lysines are perfectly accessible in Ran/NTF2 complexes. Isothermal titration calorimetry revealed that NTF2 prevents sumoylation by reducing RanGDP''s affinity to RanBP2''s RBDs to undetectable levels. Taken together, our findings indicate that RanGDP and not RanGTP is the physiological target for the RanBP2 SUMO E3 ligase complex. Recognition requires interaction of Ran with RanBP2''s RBDs, which is prevented by the transport factor NTF2.     

Structural Studies of Potassium Transport Protein KtrA Regulator of Conductance of K+ (RCK) C Domain in Complex with Cyclic Diadenosine Monophosphate (c-di-AMP)

Although it was only recently identified as a second messenger, c-di-AMP was found to have fundamental importance in numerous bacterial functions such as ion transport. The potassium transporter protein, KtrA, was identified as a c-di-AMP receptor. However, the co-crystallization of c-di-AMP with the protein has not been studied. Here, we determined the crystal structure of the KtrA RCK_C domain in complex with c-di-AMP. The c-di-AMP nucleotide, which adopts a U-shaped conformation, is bound at the dimer interface of RCK_C close to helices α3 and α4. c-di-AMP interacts with KtrA RCK_C mainly by forming hydrogen bonds and hydrophobic interactions. c-di-AMP binding induces the contraction of the dimer, bringing the two monomers of KtrA RCK_C into close proximity. The KtrA RCK_C was able to interact with only c-di-AMP, but not with c-di-GMP, 3′,3-cGAMP, ATP, and ADP. The structure of the KtrA RCK_C domain and c-di-AMP complex would expand our understanding about the mechanism of inactivation in Ktr transporters governed by c-di-AMP.     

Modulation of the basal activity of N-acetylglucosaminyltransferase V by phosphatidylinositol-3-kinase/protein kinase B signaling pathway in human hepatocarcinoma cells

The modulation of GnT-V activity by signaling molecules in PI-3-K/PKB pathway in human hepatocarcinoma cell line 7721 was studied. GnT-V activity was determined after the transfection of sense or antisense cDNA of PKB into the cells, as well as the addition of activators, specific inhibitors, and the antibodies to the enzyme assay system or culture medium. It was found that the basal activity of GnT-V was up regulated by the sense and down regulated by the antisense cDNA of PKB transfected into 7721 cells. GnT-V was activated by PIP₂, PIP₃ or GTP[S] added to the assay system, and the activation of PIP₂ or GTP[S] was abolished by LY2940002, a specific inhibitor of PI-3-K, but the activation of PIP₃ was not attenuated by LY2940002. In addition, GnT-V activity in cultured parental or H-ras transfected cells was inhibited by the antibody against PKB or PI-3-K. These findings demonstrated the involvement of PI-3-K/PKB signaling pathway in the regulation of GnT-V. Moreover, ET18-OCH₃, an inhibitor of Raf translocation and PI-PLC enzyme, which produces the activator of PKC, as well as the antibodies against Raf-1 or MEK also inhibited GnT-V activity in the parental and H-ras transfected cells. The inhibitory rates, however, were less in the transfected cells than those in the parental cells. These results reveal that in parental and H-ras transfected 7721 cells, the basal activity of GnT-V is also regulated by the Ras/Raf-1/MEK/MAPK cascade in addition to PI-3-K/PKB signaling pathway. The significance of these two pathways in the regulation of GnT-V and their relations to the activation of PKC previously reported by our laboratory (Ju TZ et al., 1995 Glyconjugate J 12, 767–772) was discussed.     

具有蛋白酶及解旋酶活性的HCV-NS3重组蛋白的纯化及活性分析

为深入探讨HCV-NS3蛋白的酶动力学性质,制备了具有蛋白酶及解旋酶活性的HCVNS3重组蛋白。利用PCR扩增HCV非结构基因NS3,插入pPIC9,测序分析。携带NS3基因的重组质粒(pPIC9-NS3)转化毕氏酵母菌菌株GS115,甲醇诱导表达NS3蛋白。重组蛋白首先采用Hitrap chelating柱进行亲和分离,之后使用Mono S HR柱进一步纯化。对纯化后的NS3重组蛋白的酶活性进行分析,结果表明,获得的重组蛋白分别具有蛋白酶及解旋酶活性。本研究为深入探讨NS3编码酶的功能和开发抗病毒药物创造条件。     

Prolonged Alzheimer-like tau hyperphosphorylation induced by simultaneous inhibition of phosphoinositol-3 kinase and protein kinase C in N2a cells

Co-injection of wortmannin (inhibitor of phosphatidylinositol-3 kinase, PI3K) and GF109203X(inhibitor of protein kinase C, PKC) into the rat brain was found to induce spatial memory deficiency and enhance tau hyperphosphorylation in the hippocampus of rat brain. To establish a cell model with durative Alzheimer-like tau hyperphosphorylation in this study, we treated N2a neuroblastoma cells with wortmannin and GF109203X separately and simultaneously, and measured the glycogen synthase kinase 3 (GSK-3)activity by y-32p-labeling and the level of tau phosphorylation by Western blotting. It was found that the application of wortmannin alone only transitorily increased the activity of GSK-3 (about 1 h) and the level of tau hyperphosphorylation at Ser^396/Ser^404 and Ser^199/Ser^202 sites (no longer than 3 h); however, a prolonged and intense activation of GSK-3 (over 12 h) and enhanced tau hyperphosphorylation (about 24 h) were observed when these two selective kinase inhibitors were applied together. We conclude that the simultaneous inhibition of PI3K and PKC can induce GSK-3 overactivation, and further strengthen and prolong the Alzheimerlike tau hyperphosphorylation in N2a cells, suggesting the establishment of a cell model with early pathological events of Alzheimer‘s disease.     

具有蛋白酶及解旋酶活性的HCV-NS3重组蛋白的纯化及活性分析

为深入探讨HCV-NS3蛋白的酶动力学性质,制备了具有蛋白酶及解旋酶活性的HCV NS3重组蛋白.利用PCR扩增HCV非结构基因NS3,插入pPIC9,测序分析.携带NS3基因的重组质粒(pPIC9-NS3)转化毕氏酵母菌菌株GS115,甲醇诱导表达NS3蛋白.重组蛋白首先采用Hitrap chelating柱进行亲和分离,之后使用Mono S HR柱进一步纯化.对纯化后的NS3重组蛋白的酶活性进行分析,结果表明,获得的重组蛋白分别具有蛋白酶及解旋酶活性.本研究为深入探讨NS3编码酶的功能和开发抗病毒药物创造条件.     

TAR DNA-Binding Protein 43 is Cleaved by the Protease 3C of Enterovirus A71

Enterovirus A71(EV-A71) is one of the etiological pathogens leading to hand, foot, and mouth disease(HFMD), which can cause severe neurological complications. The neuropathogenesis of EV-A71 infection is not well understood. The mislocalization and aggregation of TAR DNA-binding protein 43(TDP-43) is the pathological hallmark of amyotrophic lateral sclerosis(ALS). However, whether TDP-43 was impacted by EV-A71 infection is unknown. This study demonstrated that TDP-43 was cleaved during EV-A71 infection. The cleavage of TDP-43 requires EV-A71 replication rather than the activated caspases due to viral infection. TDP-43 is cleaved by viral protease 3 C between the residues 331 Q and332 S, while mutated TDP-43(Q331 A) was not cleaved. In addition, mutated 3 C which lacks the protease activity failed to induce TDP-43 cleavage. We also found that TDP-43 was translocated from the nucleus to the cytoplasm, and the mislocalization of TDP-43 was induced by viral protease 2 A rather than 3 C. Taken together, we demonstrated that TDP-43 was cleaved by viral protease and translocated to the cytoplasm during EV-A71 infection, implicating the possible involvement of TDP-43 in the pathogenesis of EV-A71 infection.     

The Structure of a Type 3 Secretion System (T3SS) Ruler Protein Suggests a Molecular Mechanism for Needle Length Sensing

The type 3 secretion system (T3SS) and the bacterial flagellum are related pathogenicity-associated appendages found at the surface of many disease-causing bacteria. These appendages consist of long tubular structures that protrude away from the bacterial surface to interact with the host cell and/or promote motility. A proposed “ruler” protein tightly regulates the length of both the T3SS and the flagellum, but the molecular basis for this length control has remained poorly characterized and controversial. Using the Pseudomonas aeruginosa T3SS as a model system, we report the first structure of a T3SS ruler protein, revealing a “ball-and-chain” architecture, with a globular C-terminal domain (the ball) preceded by a long intrinsically disordered N-terminal polypeptide chain. The dimensions and stability of the globular domain do not support its potential passage through the inner lumen of the T3SS needle. We further demonstrate that a conserved motif at the N terminus of the ruler protein interacts with the T3SS autoprotease in the cytosolic side. Collectively, these data suggest a potential mechanism for needle length sensing by ruler proteins, whereby upon T3SS needle assembly, the ruler protein''s N-terminal end is anchored on the cytosolic side, with the globular domain located on the extracellular end of the growing needle. Sequence analysis of T3SS and flagellar ruler proteins shows that this mechanism is probably conserved across systems.     

Secretory galectin-3 induced by glucocorticoid stress triggers stemness exhaustion of hepatic progenitor cells

Adult progenitor cell populations typically exist in a quiescent state within a controlled niche environment. However, various stresses or forms of damage can disrupt this state, which often leads to dysfunction and aging. We built a glucocorticoid (GC)-induced liver damage model of mice, found that GC stress induced liver damage, leading to consequences for progenitor cells expansion. However, the mechanisms by which niche factors cause progenitor cells proliferation are largely unknown. We demonstrate that, within the liver progenitor cells niche, Galectin-3 (Gal-3) is responsible for driving a subset of progenitor cells to break quiescence. We show that GC stress causes aging of the niche, which induces the up-regulation of Gal-3. The increased Gal-3 population increasingly interacts with the progenitor cell marker CD133, which triggers focal adhesion kinase (FAK)/AMP-activated kinase (AMPK) signaling. This results in the loss of quiescence and leads to the eventual stemness exhaustion of progenitor cells. Conversely, blocking Gal-3 with the inhibitor TD139 prevents the loss of stemness and improves liver function. These experiments identify a stress-dependent change in progenitor cell niche that directly influence liver progenitor cell quiescence and function.     

Efficiency Enhancement of Polymer Solar Cells Based on Poly(3‐hexylthiophene)/Indene‐C70 Bisadduct via Methylthiophene Additive

Photovoltaic performance of polymer solar cells based on poly(3‐hexylthiophene) (P3HT) as the donor and indene‐C₇₀ bisadduct (IC₇₀BA) as the acceptor is improved by adding 3 vol% 3‐methylthiophene (MT) or 3‐hexylthiophene (HT) as processing additives. The results of UV‐vis absorption spectroscopy, X‐ray diffraction analysis and atomic force microscopy indicate that with the MT or HT processing additive, the active layer of the blend of P3HT/IC₇₀BA showed strengthened absorbance, enhanced crystallinity and improved film morphology. The power conversion efficiency (PCE) of the PSCs was improved from 5.80% for the device without the additive to 6.35% for the device with HT additive and to 6.69% with MT additive. The PCE of 6.69% is the top value reported so far for the PSCs based on P3HT.     

敲低低密度脂蛋白受体相关蛋白1抑制C3H10T1/2多潜能干细胞定向成脂

C3H10T1/2多潜能干细胞成脂过程分为定向和分化两个阶段,骨形成蛋白4(BMP4)可以诱导其定向成前脂肪细胞．已有的研究表明,脂肪组织特异性敲除低密度脂蛋白受体相关蛋白1(Lrp1)的小鼠体重减轻,脂肪组织含量减少,揭示此基因对成脂具有重要作用．然而,目前尚不清楚Lrp1是否在成脂定向过程中发挥作用．采用小干扰RNA技术(RNAi),在体外水平研究低密度脂蛋白Lrp1对C3H10T1/2多潜能干细胞成脂定向的作用．分别在C3H10T1/2成脂的定向期和脂滴成熟期敲低Lrp1,通过显微镜下观察、油红O染色、Western blotting等实验证实,定向期而非脂滴成熟期敲低Lrp1显著抑制C3H10T1/2多潜能干细胞成脂．BMP4通过激活下游Smad1/5/8信号通路发挥作用,而敲低Lrp1显著抑制BMP4诱导的Smad1/5/8磷酸化．这些结果说明：敲低Lrp1通过下调Smad信号通路,抑制BMP4诱导的C3H10T1/2多潜能干细胞成脂定向．     

Ⅲ型纤连蛋白组件包含蛋白5通过抑制ERK1/2磷酸化抑制C3H10T1/2细胞成脂分化

旨在探究Ⅲ型纤连蛋白组件包含蛋白5(type Ⅲ domain-containing protein5,FNDC5)对C3H10T1/2细胞成脂分化的调控作用.利用qRT-PCR和Western印迹检测FNDC5在C3H10T1/2细胞成脂分化过程中的时序性表达规律;构建慢病毒包被的过表达/干扰FNDC5载体,转染C3...