Elongation factor-1 alpha is a novel substrate of rho-associated kinase

Effect of the Rho-Kinase/ROCK Signaling Pathway on Cytoskeleton Components

The mechanical properties of cells are important in tissue homeostasis and enable cell growth, division, migration and the epithelial-mesenchymal transition. Mechanical properties are determined to a large extent by the cytoskeleton. The cytoskeleton is a complex and dynamic network composed of microfilaments, intermediate filaments and microtubules. These cellular structures confer both cell shape and mechanical properties. The architecture of the networks formed by the cytoskeleton is regulated by several pathways, a key one being the Rho-kinase/ROCK signaling pathway. This review describes the role of ROCK (Rho-associated coiled-coil forming kinase) and how it mediates effects on the key components of the cytoskeleton that are critical for cell behaviour.

High eEF1A1 Protein Levels Mark Aggressive Prostate Cancers and the In Vitro Targeting of eEF1A1 Reveals the eEF1A1-actin Complex as a New Potential Target for Therapy

Although the eukaryotic elongation factor eEF1A1 plays a role in various tumours, there is little information on its prognosis/therapeutic value in prostate carcinoma. In high-grade and castration-resistant prostate carcinoma (CRPC), the identification of novel therapeutic markers/targets remains a priority. The expression of eEF1A1 protein was determined in formalin-fixed, paraffin-embedded prostate cancer and hyperplasia tissue by IHC. The role of eEF1A1 was investigated in a cellular model using a DNA aptamer (GT75) we previously developed. We used the aggressive CRPC cancer PC-3 and non-tumourigenic PZHPV-7 lines. Cytotoxicity was measured by the MTS assay and eEF1A1 protein levels by in-cell Western assays. The mRNA levels of eEF1A1 were measured by qPCR and ddPCR. Higher expression of eEF1A1 was found in Gleason 7-8 compared with 4-6 tissues (Gleason ≥ 7, 87% versus Gleason ≤ 6, 54%; p = 0.033). Patients with a high expression of eEF1A1 had a worse clinical outcome. In PC-3, but not in PZHPV-7, GT75 decreased cell viability and increased autophagy and cell detachment. In PC-3 cells, but not in PZHPV-7, GT75 mainly co-localised with the fraction of eEF1A1 bound to actin. Overexpression of the eEF1A1 protein can identify aggressive forms of prostate cancer. The targeting of eEF1A1 by GT75 impaired cell viability in PC-3 cancer cells but not in PZHPV-7 non-tumourigenic cells, indicating a specific role for the protein in cancer survival. The eEF1A1-actin complexes appear to be critical for the viability of PC-3 cancer cells, suggesting that eEF1A1 may be an attractive target for therapeutic strategies in advanced forms of prostate cancer.

Vascular Stiffening Mediated by Rho-Associated Coiled-Coil Containing Kinase Isoforms

Background

The pathogenesis of vascular stiffening and hypertension is marked by non‐compliance of vessel wall because of deposition of collagen fibers, loss of elastin fibers, and increased vascular thickening. Rho/Rho‐associated coiled‐coil containing kinases 1 and 2 (ROCK1 and ROCK2) have been shown to regulate cellular contraction and vascular remodeling. However, the role of ROCK isoforms in mediating pathogenesis of vascular stiffening and hypertension is not known.

Methods and Results

Hemizygous Rock mice (Rock1^+/− and Rock2^+/−) were used to determine the role of ROCK1 and ROCK2 in age‐related vascular dysfunction. Both ROCK activity and aortic stiffness increased to a greater extent with age in wild‐type mice compared with that of Rock1^+/− and Rock2^+/− mice. As a model for age‐related vascular stiffening, we administered angiotensin II (500 ng/kg per minute) combined with nitric oxide synthase inhibitor, L‐N^ω‐nitroarginine methyl ester (0.5 g/L) for 4 weeks to 12‐week‐old male Rock1^+/− and Rock2^+/− mice. Similar to advancing age, angiotensin II/L‐N^ω‐nitroarginine methyl ester caused increased blood pressure, aortic stiffening, and vascular remodeling, which were attenuated in Rock2^+/−, and to a lesser extent, Rock1^+/− mice. The reduction of aortic stiffening in Rock2^+/− mice was accompanied by decreased collagen deposition, relatively preserved elastin content, and less aortic wall hypertrophy. Indeed, the upregulation of collagen I by transforming growth factor‐β1 or angiotensin II was greatly attenuated in Rock2^−/− mouse embryonic fibroblasts.

Conclusions

These findings indicate that ROCK1 and ROCK2 mediate both age‐related and pharmacologically induced aortic stiffening, and suggest that inhibition of ROCK2, and to a lesser extent ROCK1, may have therapeutic benefits in preventing age‐related vascular stiffening.

Mutational analysis reveals potential phosphorylation sites in eukaryotic elongation factor 1A that are important for its activity

Previous studies have suggested that phosphorylation of translation elongation factor 1A (eEF1A) can alter its function, and large‐scale phospho‐proteomic analyses in Saccharomyces cerevisiae have identified 14 eEF1A residues phosphorylated under various conditions. Here, a series of eEF1A mutations at these proposed sites were created and the effects on eEF1A activity were analyzed. The eEF1A‐S53D and eEF1A‐T430D phosphomimetic mutant strains were inviable, while corresponding alanine mutants survived but displayed defects in growth and protein synthesis. The activity of an eEF1A‐S289D mutant was significantly reduced in the absence of the guanine nucleotide exchange factor eEF1Bα and could be restored by an exchange‐deficient form of the protein, suggesting that eEF1Bα promotes eEF1A activity by a mechanism other than nucleotide exchange. Our data show that several of the phosphorylation sites identified by high‐throughput analysis are critical for eEF1A function.

Molecular Targets of Epigallocatechin-Gallate (EGCG): A Special Focus on Signal Transduction and Cancer

Green tea is a beverage that is widely consumed worldwide and is believed to exert effects on different diseases, including cancer. The major components of green tea are catechins, a family of polyphenols. Among them, epigallocatechin-gallate (EGCG) is the most abundant and biologically active. EGCG is widely studied for its anti-cancer properties. However, the cellular and molecular mechanisms explaining its action have not been completely understood, yet. EGCG is effective in vivo at micromolar concentrations, suggesting that its action is mediated by interaction with specific targets that are involved in the regulation of crucial steps of cell proliferation, survival, and metastatic spread. Recently, several proteins have been identified as EGCG direct interactors. Among them, the trans-membrane receptor 67LR has been identified as a high affinity EGCG receptor. 67LR is a master regulator of many pathways affecting cell proliferation or apoptosis, also regulating cancer stem cells (CSCs) activity. EGCG was also found to be interacting directly with Pin1, TGFR-II, and metalloproteinases (MMPs) (mainly MMP2 and MMP9), which respectively regulate EGCG-dependent inhibition of NF-kB, epithelial-mesenchimal transaction (EMT) and cellular invasion. EGCG interacts with DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), which modulates epigenetic changes. The bulk of this novel knowledge provides information about the mechanisms of action of EGCG and may explain its onco-suppressive function. The identification of crucial signalling pathways that are related to cancer onset and progression whose master regulators interacts with EGCG may disclose intriguing pharmacological targets, and eventually lead to novel combined treatments in which EGCG acts synergistically with known drugs.

Myosin phosphatase: Unexpected functions of a long-known enzyme

Myosin phosphatase (MP) holoenzyme is a Ser/Thr specific enzyme, which is the member of protein phosphatase type 1 (PP1) family and composed of a PP1 catalytic subunit (PP1c/PPP1CB) and a myosin phosphatase targeting subunit (MYPT1/PPP1R12A). PP1c is required for the catalytic activity of the holoenzyme, while MYPT1 regulates MP through targeting the holoenzyme to its substrates. Above the well-characterized function of MP, as the major regulator of smooth muscle contractility mediating the dephosphorylation of 20 kDa myosin light chain, accumulating data support its role in other, non-contractile functions. In this review, we summarize the scaffold function of MP holoenzyme and its roles in processes such as cell cycle, development, gene expression regulation and neurotransmitter release. In particular, we highlight novel interacting proteins of MYPT1 and pathophysiological functions of MP relevant to tumorigenesis, insulin resistance and neurodegenerative disorders. This article is part of a Special Issue entitled: Protein Phosphatases as Critical Regulators for Cellular Homeostasis edited by Prof. Peter Ruvolo and Dr. Veerle Janssens.

Neuroprotection Mediated by Upregulation of Endothelial Nitric Oxide Synthase in Rho-Associated, Coiled-Coil-Containing Kinase 2 Deficient Mice

BACKGROUND

Rho-associated kinases (ROCK1 and ROCK2) are important regulators of the actin cytoskeleton and endothelial nitric oxide synthase (eNOS). Because the phosphorylation of eukaryotic elongation factor-1A1 (eEF1A1) by ROCK2 is critical for eNOS expression, we hypothesized that this molecular pathway may play a critical role in neuroprotection following focal cerebral ischemia.

METHODS AND RESULTS

Adult male wild-type (WT) and mutant ROCK2 and eNOS-/-mice were subjected to middle cerebral artery occlusion (MCAO), and cerebral infarct size, neurological deficit and absolute cerebral blood flow were measured. In addition, aortic endothelium-dependent response to acetylcholine, NG-nitro-L-arginine methyl ester (L-NAME) and sodium nitroprusside were assessed ex vivo. Endothelial cells from mouse brain or heart were used to measure eNOS and eEF1A activity, as well as NO production and eNOS mRNA half-life. In global hemizygous ROCK2+/-and endothelial-specific EC-ROCK2-/-mice, eNOS mRNA stability and eNOS expression were increased, which correlated with enhanced endothelium-dependent relaxation and neuroprotection following focal cerebral ischemia. Indeed, when ROCK2+/-mice were place on an eNOS-/-background, the neuroprotective effects observed in ROCK2+/-mice were abolished.

CONCLUSIONS

These findings indicate that the phosphorylation of eEF1A1 by ROCK2 is physiologically important for eNOS expression and NO-mediated neuroprotection, and suggest that targeting endothelial ROCK2 and eEF1A may have therapeutic benefits in ischemic stroke and cardiovascular disease.

Holophytochrome-Interacting Proteins in Physcomitrella: Putative Actors in Phytochrome Cytoplasmic Signaling

Phytochromes are the principle photoreceptors in light-regulated plant development, primarily acting via translocation of the light-activated photoreceptor into the nucleus and subsequent gene regulation. However, several independent lines of evidence indicate unambiguously that an additional cytoplasmic signaling mechanism must exist. Directional responses in filament tip cells of the moss Physcomitrella patens are steered by phy4 which has been shown to interact physically with the blue light receptor phototropin at the plasma membrane. This complex might perceive and transduce vectorial information leading to cytoskeleton reorganization and finally a directional growth response. We developed yeast two-hybrid procedures using photochemically functional, full-length phy4 as bait in Physcomitrella cDNA library screens and growth assays under different light conditions, revealing Pfr-dependent interactions possibly associated with phytochrome cytoplasmic signaling. Candidate proteins were then expressed in planta with fluorescent protein tags to determine their intracellular localization in darkness and red light. Of 14 candidates, 12 were confirmed to interact with phy4 in planta using bimolecular fluorescence complementation. We also used database information to study their expression patterns relative to those of phy4. We discuss the likely functional characteristics of these holophytochrome-interacting proteins (HIP's) and their possible roles in signaling.

Transcriptome profiling of differentially expressed genes in floral buds and flowers of male sterile and fertile lines in watermelon

Background

Male sterility is an important mechanism for the production of hybrid seeds in watermelon. Although fruit development has been studied extensively in watermelon, there are no reports on gene expression in floral organs. In this study, RNA-sequencing (RNA-seq) was performed in two near-isogenic watermelon lines (genic male sterile [GMS] line, DAH3615-MS and male fertile line, DAH3615) to identify the differentially expressed genes (DEGs) related to male sterility.

Results

DEG analysis showed that 1259 genes were significantly associated with male sterility at a FDR P-value of < 0.01. Most of these genes were only expressed in the male fertile line. In addition, 11 functional clusters were identified using DAVID functional classification analysis. Of detected genes in RNA-seq analysis, 19 were successfully validated by qRT-PCR.

Conclusions

In this study, we carried out a comprehensive floral transcriptome sequence comparison of a male fertile line and its near-isogenic male sterile line in watermelon. This analysis revealed essential genes responsible for stamen development, including pollen development and pollen tube elongation, and allowed their functional classification. These results provided new information on global mechanisms related to male sterility in watermelon.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2186-9) contains supplementary material, which is available to authorized users.

Elongation factor-1A1 is a novel substrate of the protein phosphatase 1-TIMAP complex

TIMAP (TGF-β inhibited membrane associated protein) is a protein phosphatase 1 (PP1) regulatory subunit highly abundant in endothelial cells and it is involved in the maintenance of pulmonary endothelial barrier function. It localizes mainly in the plasma membrane, but it is also present in the nuclei and cytoplasm. Direct interaction of TIMAP with the eukaryotic elongation factor 1 A1 (eEF1A1) is shown by pull-down, LC-MS/MS, Far-Western and immunoprecipitations. In connection with the so called moonlighting functions of the elongation factor, eEF1A is thought to establish protein-protein interactions through a transcription-dependent nuclear export motif, TD-NEM, and to aid nuclear export of TD-NEM containing proteins. We found that a TD-NEM-like motif of TIMAP has a critical role in its specific binding to eEF1A1. However, eEF1A1 is not or not exclusively responsible for the nuclear export of TIMAP. On the contrary, TIMAP seems to regulate membrane localization of eEF1A1 as the elongation factor co-localized with TIMAP in the plasma membrane fraction of control endothelial cells, but it has disappeared from the membrane in TIMAP depleted cells. It is demonstrated that membrane localization of eEF1A1 depends on the phosphorylation state of its Thr residue(s); and ROCK phosphorylated eEF1A1 is a novel substrate for TIMAP-PP1 underlining the complex regulatory role of TIMAP in the endothelium. The elongation factor seems to be involved in the regulation of endothelial cell attachment and spreading as silencing of eEF1A1 positively affected these processes which were monitored by transendothelial resistance measurements.

Translational connection of TGFβ signaling: Phosphorylation of eEF1A1 by TβR-I inhibits protein synthesis

Transforming growth factor-β (TGFβ) signaling pathways regulate a wide array of cellular activities that are crucial for cell proliferation, apoptosis, migration and differentiation. TGFβ signaling pathways are initiated by ligand-activated TGFβ receptors, with type I TGFβ receptors (TβR-I) kinase being essential for phosphorylation of downstream targets. Until now, a prevalent view was that the TGFβ intracellular signaling targets would regulate transcription. Recently, we uncovered a novel TGFβ signaling pathway that exerts a direct regulatory effect on mRNA translation and protein synthesis. Eukaryotic elongation factor eEF1A1 is a GTP-binding protein that plays a central role in protein synthesis. By using a screening method for kinase substrate that was developed in our laboratory, we identified eEF1A1 as a novel substrate of TβR-I. This shed a new light on the convergence of TGFβ signaling and protein synthesis. We also showed phosphorylation of eEF1A1 at Ser300 by TβR-I prevents aa-tRNA binding to eEF1A1. As a consequence, TGFβ-dependent phosphorylation of eEF1A1 has an inhibitory effect on protein synthesis and cell proliferation. Therefore, we unveiled a novel regulatory mechanism of cellular proliferation by TGFβ at the translational level. Here we discuss this finding in the context of its potential role in the multiplicity of TGFβ signaling, and in the regulation of fundamental cellular functions, such as proliferation.

Characterization of a modified ROCK2 protein that allows use of N6-ATP analogs for the identification of novel substrates

Background

The Rho-associated coiled-coil kinase-2 (ROCK2) is an important signaling transducer in the transmission of extracellular signals effecting organization of the actin cytoskeleton. ROCK2 has been implicated in numerous pathologies and the current focus is on understanding the molecular events that couple ROCK2 activity to biological function. To aid in the search for new ROCK2 substrates, we have developed an analog-sensitive (AS) ROCK2 protein that allows the use of selective ATP analogs that are not efficiently utilized by other protein kinases.

Results

The analog sensitive protein, M160A ROCK2, was highly active and could phosphorylate proteins from a cellular homogenate with γ³²P-N₆ (benzyl)ATP. We show the utility of this approach by identifying a putative ROCK2 substrate, elongation initiation factor-1-α1. We further show that the major site of ROCK2 phosphorylation of EIF1α1 is Thr⁴³².

Conclusions

Our work demonstrates that AS-ROCK2 could be useful in a systematic proteomic approach for identifying novel ROCK2 substrates.

Rho-associated coiled-coil kinase (ROCK) signaling and disease

The small Rho GTPase family of proteins, encompassing the three major G-protein classes Rho, Rac and cell division control protein 42, are key mitogenic signaling molecules that regulate multiple cancer-associated cellular phenotypes including cell proliferation and motility. These proteins are known for their role in the regulation of actin cytoskeletal dynamics, which is achieved through modulating the activity of their downstream effector molecules. The Rho-associated coiled-coil kinase 1 and 2 (ROCK1 and ROCK2) proteins were the first discovered Rho effectors that were primarily established as players in RhoA-mediated stress fiber formation and focal adhesion assembly. It has since been discovered that the ROCK kinases actively phosphorylate a large cohort of actin-binding proteins and intermediate filament proteins to modulate their functions. It is well established that global cellular morphology, as modulated by the three cytoskeletal networks: actin filaments, intermediate filaments and microtubules, is regulated by a variety of accessory proteins whose activities are dependent on their phosphorylation by the Rho-kinases. As a consequence, they regulate many key cellular functions associated with malignancy, including cell proliferation, motility and viability. In this current review, we focus on the role of the ROCK-signaling pathways in disease including cancer.

Cardioprotective Effects of Quercetin in Cardiomyocyte under Ischemia/Reperfusion Injury

Quercetin, a polyphenolic compound existing in many vegetables, fruits, has antiinflammatory, antiproliferation, and antioxidant effect on mammalian cells. Quercetin was evaluated for protecting cardiomyocytes from ischemia/reperfusion injury, but its protective mechanism remains unclear in the current study. The cardioprotective effects of quercetin are achieved by reducing the activity of Src kinase, signal transducer and activator of transcription 3 (STAT3), caspase 9, Bax, intracellular reactive oxygen species production, and inflammatory factor and inducible MnSOD expression. Fluorescence two-dimensional differential gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) can reveal the differentially expressed proteins of H9C2 cells treated with H₂O₂ or quercetin. Although 17 identified proteins were altered in H₂O₂-induced cells, these proteins such as alpha-soluble NSF attachment protein (α-SNAP), Ena/VASP-like protein (Evl), and isopentenyl-diphosphate delta-isomerase 1 (Idi-1) were reverted by pretreatment with quercetin, which correlates with kinase activation, DNA repair, lipid, and protein metabolism. Quercetin dephosphorylates Src kinase in H₂O₂-induced H9C2 cells and likely blocks the H₂O₂-induced inflammatory response through STAT3 kinase modulation. This probably contributes to prevent ischemia/reperfusion injury in cardiomyocytes.

Hepatitis B virus X protein blocks filamentous actin bundles by interaction with eukaryotic translation elongat ion factor 1 alpha 1

Hepatitis B virus (HBV)-encoded X protein (HBx protein) is a multi-functional regulatory protein. It functions by protein-protein interaction and plays a pivotal role in the pathogenesis of HBV-related diseases. However, the partners in hepatocytes interacting with HBx protein are far from understood fully. In this study, immunoprecipitation was employed to screen for binding partners for the HBx protein from huh-7 hepatoma cells infected with recombinant adenovirus expressing HBx protein, and five cellular proteins including eukaryotic translation elongation factor 1 alpha 1 (eEF1A1), were identified. The interaction between HBx protein and eEF1A1 was confirmed further using a GST pull-down assay and co-immunoprecipitation, respectively. In Huh-7 hepatoma cells, the HBx protein inhibits dimer formation of eEF1A1, hence blocks filamentous actin bundling. These findings provide new insights into the molecular mechanisms involved in the functions of the HBx protein.

Novel mechanism for negatively regulating Rho-kinase (ROCK) signaling through Coronin1B protein in neuregulin 1 (NRG-1)-induced tumor cell motility

Although many mechanisms that activate ROCK are known, corresponding negative regulatory mechanisms required for cytoskeletal plasticity are poorly understood. We have discovered that Coronin1B is a novel attenuator of ROCK signaling. We initially identified Coronin1A in a proteomics screen for ROCK2-binding proteins, and here we demonstrate that Coronin1A/B bind directly to ROCK2 through its PH (Pleckstrin Homology) domain. The consequence of the ROCK2-Coronin1B interaction was tested and revealed that increased expression of Coronin1B inhibited, whereas knockdown of Coronin1B stimulated, phosphorylation of the ROCK substrate myosin light chain phosphatase and subsequently, myosin light chain. Thus, Coronin1B is a previously unrecognized inhibitor of ROCK signaling to myosin. Furthermore, we found that the phosphatase Slingshot IL (SSH1L) was required for Coronin1B to inhibit ROCK signaling. To test the significance of this novel mechanism in tumor cell motility, we investigated its role in neuregulin 1 (NRG-1)-induced cell scattering. Importantly, we found that attenuation of the ROCK signaling by Coronin1B was required for NRG-1 stimulated scattering. Our data support a model in which Coronin1B fine-tunes ROCK signaling to modulate myosin activity, which is important for tumor cell motility.

ROCKing Regeneration: Rho Kinase Inhibition as Molecular Target for Neurorestoration

Regenerative failure in the CNS largely depends on pronounced growth inhibitory signaling and reduced cellular survival after a lesion stimulus. One key mediator of growth inhibitory signaling is Rho-associated kinase (ROCK), which has been shown to modulate growth cone stability by regulation of actin dynamics. Recently, there is accumulating evidence the ROCK also plays a deleterious role for cellular survival. In this manuscript we illustrate that ROCK is involved in a variety of intracellular signaling pathways that comprise far more than those involved in neurite growth inhibition alone. Although ROCK function is currently studied in many different disease contexts, our review focuses on neurorestorative approaches in the CNS, especially in models of neurotrauma. Promising strategies to target ROCK by pharmacological small molecule inhibitors and RNAi approaches are evaluated for their outcome on regenerative growth and cellular protection both in preclinical and in clinical studies.

Glucosamine increases vascular contraction through activation of RhoA/Rho kinase pathway in isolated rat aorta

Diabetes is a well-known independent risk factor for vascular disease. However, its underlying mechanism remains unclear. It has been reported that increased influx of the hexosamine biosynthesis pathway (HBP) induces O-GlcNAcylation of proteins, leading to insulin resistance. In this study, we determined whether or not O-GlcNAc modification of proteins could increase vessel contraction. Using an endothelium-denuded aortic ring, we observed that glucosamine induced OGlcNAcylation of proteins and augmented vessel contraction stimulated by U46619, a thromboxane A(2) agonist, via augmentation of the phosphorylation of MLC(20), MYPT1(Thr855), and CPI17, but not phenylephrine. Pretreatment with OGT inhibitor significantly ameliorated glucosamine-induced vessel constriction. Glucosamine treatment also increased RhoA activity, which was also attenuated by OGT inhibitor. In conclusion, glucosamine, a product of glucose influx via the HBP in a diabetic state, increases vascular contraction, at least in part, through activation of the RhoA/Rho kinase pathway, which may be due to O-GlcNAcylation.

Protein Expression of STRO-1 Cells in Response to Different Topographic Features

Human skeletal stem cells (STRO-1 positive) display distinct responses to different topographical features. On a flat surface, skeletal cells spread, and in vitro, they typically display a polarized, fibroblast-like morphology. However, on microgrooved surfaces, these cells prefer to stretch along the grooves forming a similar morphology to in vivo, bipolarized fibroblasts. In contrast, on nanopits, these cells display a polygonal and osteoblastic phenotype. We have examined mechanotransduction events of STRO-1 positive in response to fibroblastic, microgrooved and osteogenic, controlled disorder nanopit, topographies using proteomics after 3 days in culture. Protein expression profiles were analyzed by difference gel electrophoresis to identify proteins that showed modulation of expression in response to different topographic features to assess early decision events in these cells on these discrete topographies. After only 72 hours in culture, STRO-1 positive displayed differential regulations of families of proteins involved in cell migration and proliferation. The current study indicated that osteogenic decision specific events had already occurred. Runx2 was localized in nuclei of the skeletal stem cells on the osteogenic nanopits; however, few signaling pathway changes were observed. This study demonstrated that micro- and nanotopographies activated skeletal stem cells at different times and with distinct mechanotransduction profiles.

Green tea polyphenol sensing

Green tea polyphenols have emerged over the past two decades as an important dietary factor for health promotion. There is considerable evidence that tea polyphenols, in particular (-)-epigallocatechin-3-gallate (EGCG) inhibit carcinogenesis. However, the mechanisms for the cancer-preventive activity of EGCG are not completely characterized and many features remain to be elucidated. Recently we have identified a cell-surface EGCG receptor and the relating molecules that confer EGCG responsiveness to many cancer cells at physiological concentrations. Here, we review some of the reported mechanisms for the cancer chemopreventive action of EGCG and provide an overview of several molecules that sense and manage the physiological functions of EGCG.

Rho-kinase/ROCK: A key regulator of the cytoskeleton and cell polarity

Rho-associated kinase (Rho-kinase/ROCK/ROK) is an effector of the small GTPase Rho and belongs to the AGC family of kinases. Rho-kinase has pleiotropic functions including the regulation of cellular contraction, motility, morphology, polarity, cell division, and gene expression. Pharmacological analyses have revealed that Rho-kinase is involved in a wide range of diseases such as vasospasm, pulmonary hypertension, nerve injury, and glaucoma, and is therefore considered to be a potential therapeutic target. This review focuses on the structure, function, and modes of activation and action of Rho-kinase.

Identification of regulators of chaperone-mediated autophagy

Chaperone-mediated autophagy (CMA) is a selective mechanism for the degradation of cytosolic proteins in lysosomes that contributes to cellular quality control and becomes an additional source of amino acids when nutrients are scarce. A chaperone complex delivers CMA substrates to a receptor protein at the lysosomal membrane that assembles into multimeric translocation complexes. However, the mechanisms regulating this process remain, for the most part, unknown. In this work, we have identified two regulatory proteins, GFAP and EF1alpha, that mediate a previously unknown inhibitory effect of GTP on CMA. GFAP stabilizes the multimeric translocation complex against chaperone-mediated disassembly, whereas GTP-mediated release of EF1alpha from the lysosomal membrane promotes self-association of GFAP, disassembly of the CMA translocation complex, and the consequent decrease in CMA. The dynamic interactions of these two proteins at the lysosomal membrane unveil now a role for GTP as a negative regulator of CMA.

The SAM domain of the RhoGAP DLC1 binds EF1A1 to regulate cell migration

Deleted in liver cancer 1 (DLC1) is a multi-modular Rho-GTPase-activating protein (RhoGAP) and a tumor suppressor. Besides its RhoGAP domain, functions of other domains in DLC1 remain largely unknown. By protein precipitation and mass spectrometry, we identified eukaryotic elongation factor 1A1 (EF1A1) as a novel partner for the sterile alpha motif (SAM) domain of DLC1 but not the SAM domain of DLC2. The solution structure of DLC1 SAM revealed a new monomeric fold with four parallel helices, similar to that of DLC2 SAM but distinct from other SAM domains. Mutating F38, L39 and F40 within a hydrophobic patch retained its overall structure but abolished its interaction with EF1A1 with F38 and L39 forming an indispensable interacting motif. DLC1 SAM did not localize to and was not required for DLC1 to suppress the turnover of focal adhesions. Instead, DLC1 SAM facilitated EF1A1 distribution to the membrane periphery and ruffles upon growth factor stimulation. Compared with wild-type DLC1, the non-interactive DLC1 mutant is less potent in suppressing cell migration, whereas overexpression of the DLC1 SAM domain alone, but not the non-interactive mutant SAM or DLC2 SAM, greatly enhanced cell migration. This finding reveals a novel contribution of the SAM-EF1A1 interaction as a potentially important GAP-independent modulation of cell migration by DLC1.

The application of expression analysis in elucidating the eukaryotic elongation factor one alpha gene family in Arabidopsis thaliana

Eukaryotic elongation factor one alpha (eEF1A) encoding genes are part of the large GTP binding protein family. The eEF1A family is important for protein synthesis and actin filament and bundle formation. In this study, the expression of four eEF1A genes in Arabidopsis thaliana is reported. Microarray analyses of the gene family showed high expression levels in germinating seeds, embryos, and shoot and root meristems. Quantitative real time RT-PCR was used to determine individual eEF1A gene expression. Unlike animals, in Arabidopsis tissues all four eEF1A genes were expressed in all tissues sampled. However, the abundance of each transcript varied spatially. Knocking out expression of one eEF1A gene produced seedlings with stunted roots and a subsequent change in expression of the other three eEF1A genes. The varying abundance of each gene in different tissues may indicate different concentration requirements for each message product. These results will be very useful for elucidating the role of each gene in growth, development, and stress responses of the plant.

A monoclonal antibody that inhibits translation in Sf21 cell lysates is specific for glyceraldehyde-3-phosphate dehydrogenase

Monoclonal antibody (Mab) 8B7 was shown in a previous study to inhibit protein translation in lysates of Sf21 cells. The antibody was thought to be specific for a 60-kDa form of elongation factor-1 alpha (EF-1alpha), primarily because the antigen immunoprecipitated by Mab 8B7 cross-reacted with Mab CBP-KK1, an antibody generated to EF-1alpha from Trypanosoma brucei. The purpose of the current study was to investigate further the antigenic specificity of Mab 8B7. The concentration of the 60-kDa antigen relative to total cellular protein proved insufficient for its definitive identification. However, subcellular fractionation of Sf21 cells yielded an additional protein of 37 kDa in the cytosolic and microsomal fractions that was reactive with Mab 8B7. The 37-kDa protein could be easily visualized by colloidal Coomassie Blue G-250 staining as a series of pI 6.9-8.4 spots on two-dimensional gels. Excision of an abundant immunoreactive spot enabled identification of the protein as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) and protein database searching. Subsequent immunoblotting of purified rabbit skeletal muscle GAPDH with Mab 8B7 confirmed the antibody's specificity for GAPDH. Besides the pivotal role GAPDH plays in glycolysis, the enzyme has a number of noncanonical functions, including binding to mRNA and tRNA. The ability of Mab 8B7 to disrupt these lesser-known functions of GAPDH may account for the antibody's inhibitory effect on in vitro translation.

Tumor necrosis factor-alpha downregulates endothelial nitric oxide synthase mRNA stability via translation elongation factor 1-alpha 1

Endothelium-derived nitric oxide (NO) is an important regulator of vascular function. NO is produced by endothelial NO synthase (eNOS), whose expression is downregulated by tumor necrosis factor (TNF)-alpha at the posttranscriptional level. To elucidate the molecular basis of TNF-alpha-mediated eNOS mRNA instability, eNOS 3' untranslated region (3'-UTR) binding proteins were purified by RNA affinity chromatography from cytosolic fractions of TNF-alpha-stimulated human umbilical vein endothelial cells (HUVECs). The formation of 3'-UTR ribonucleoprotein complexes, with molecular weight of 52 and 57 kDa, was increased by TNF-alpha. Matrix-assisted laser desorption ionization time-of-flight mass spectrometric analysis of the 52-kDa protein identified 3 peptides that comprise the peptide sequence of translation elongation factor 1-alpha 1 (eEF1A1). In HUVECs, TNF-alpha rapidly increased eEF1A1 expression, which is maximal after 1 hour and persists for up to 48 hours. RNA gel mobility-shift and UV cross-linking assays indicated that recombinant glutathione S-transferase-eEF1A1 fusion protein specifically binds to a UC-rich sequence in the 3'-UTR of eNOS mRNA. In addition, the domain III of eEF1A1 mediates the binding of eNOS 3'-UTR in eEF1A1. Overexpression of eEF1A1 markedly attenuated the expression of eNOS and luciferase gene fused with eNOS 3'-UTR in both COS-7 cells and bovine aortic endothelial cells (BAECs). Furthermore, adenovirus-mediated overexpression of eEF1A1 increased eNOS mRNA instability, whereas knockdown of eEF1A1 substantially attenuated TNF-alpha-induced destabilization of eNOS mRNA and downregulation of eNOS expression in HUVECs. These results indicate that eEF1A1 is a novel eNOS 3'-UTR binding protein that plays a critical role in mediating TNF-alpha-induced decrease in eNOS mRNA stability.

Superoxide from NADPH oxidase upregulates type 5 phosphodiesterase in human vascular smooth muscle cells: inhibition with iloprost and NONOate

BACKGROUND AND PURPOSE

To determine whether there is an association between vascular NADPH oxidase (NOX), superoxide, the small GTPase Rac(1) and PDE type 5 (PDE5) in human vascular smooth muscle cell (hVSMCs).

EXPERIMENTAL APPROACH

hVSMCs were incubated with xanthine-xanthine oxidase (X-XO; a superoxide generating system) or the thromboxane A(2) analogue, U46619 (+/-superoxide dismutase (SOD) or apocynin) for 16 h. The expression of PDE5 and NOX-1 was assessed using Western blotting and superoxide measured. The role of Rac(1) in superoxide generation was assessed by overexpressing either the dominant-negative or constitutively active Rac isoforms. The effects of iloprost, DETA-NONOate and the Rho-kinase inhibitor, Y27632, on PDE5 and NOX-1 expression were also studied.

KEY RESULTS

Following 16 h incubation, U46619 and X-XO promoted the expression of PDE5 and NOX-1, an effect blocked by SOD or apocynin when co-incubated over the same time course. X-XO and U46619 both promoted the formation of superoxide. Overexpression of dominant-negative Rac(1) or addition of iloprost, DETA-NONOate or Y27632 completely blocked both superoxide release and PDE5 protein expression and activity.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate that superoxide derived from NOX upregulates the expression of PDE5 in human VSMCs. As PDE5 hydrolyses cyclic GMP, this effect may blunt the vasculoprotective actions of NO.

Involvement of 67-kDa laminin receptor-mediated myosin phosphatase activation in antiproliferative effect of epigallocatechin-3-O-gallate at a physiological concentration on Caco-2 colon cancer cells

Previously we reported that 67-kDa laminin receptor (67LR) mediates epigallocatechin-3-O-gallate (EGCG)-induced cell growth inhibition and reduction of myosin regulatory light chain (MRLC) phosphorylation at Thr-18/Ser-19, which is important for cytokinesis. Here, we found that human colon adenocarcinoma Caco-2 cells exhibited higher expression level of 67LR and EGCG at a physiologically achievable concentration (1 microM) significantly accumulated the cells in G(2)/M phase without affecting expression of Wnt-signaling components. We also found that myosin phosphatase targeting subunit 1 (MYPT1) phosphorylation at Thr-696, which inhibits myosin phosphatase and promotes MRLC phosphorylation, was reduced in response to 1 microM EGCG. 67LR knockdown by RNA interference abolished the inhibitory effects of 1 microM EGCG on cell cycle progression and the phosphorylation of MRLC and MYPT1. These results suggest that through 67LR, EGCG at a physiological concentration can activate myosin phosphatase by reducing MYPT1 phosphorylation and that may be involved in EGCG-induced cell growth inhibition.

Eukaryotic elongation factor 1A interacts with sphingosine kinase and directly enhances its catalytic activity

Sphingosine 1-phosphate (S1P) has many important roles in mammalian cells, including contributing to the control of cell survival and proliferation. S1P is generated by sphingosine kinases (SKs), of which two mammalian isoforms have been identified (SK1 and SK2). To gain a better understanding of SK regulation, we have used a yeast two-hybrid screen to identify SK1-interacting proteins and established elongation factor 1A (eEF1A) as one such protein that associates with both SK1 and SK2. We show the direct interaction of eEF1A with the SKs in vitro, whereas the physiological relevance of this association was demonstrated by co-immunoprecipitation of the endogenous proteins from cell lysates. Although the canonical role of eEF1A resides in protein synthesis, it has also been implicated in other roles, including regulating the activity of some signaling enzymes. Thus, we examined the potential role of eEF1A in regulation of the SKs and show that eEF1A is able to directly increase the activity of SK1 and SK2 approximately 3-fold in vitro. Substrate kinetics demonstrated that eEF1A increased the catalytic rate of both SKs, while having no observable effect on substrate affinities of these enzymes for either ATP or sphingosine. Overexpression of eEF1A in quiescent Chinese hamster ovary cells increased cellular SK activity, whereas a small interfering RNA-mediated decrease in eEF1A levels in MCF7 cells substantially reduced cellular SK activity and S1P levels, supporting the in vivo physiological relevance of this interaction. Thus, this study has established a novel mechanism of regulation of both SK1 and SK2 that is mediated by their interaction with eEF1A.

Green tea polyphenol epigallocatechin-3-gallate signaling pathway through 67-kDa laminin receptor

(-)-Epigallocatechin-3-gallate (EGCG), the principal polyphenol in green tea, has been shown to be a potent chemopreventive agent. Recently, 67-kDa laminin receptor (67LR) has been identified as a cell surface receptor for EGCG that mediates the anticancer activity of EGCG. Indeed, expression of 67LR confers EGCG responsiveness to tumor cells; however, the molecular basis for the anticancer activity of EGCG in vivo is not entirely understood. Here we show that (i) using a direct genetic screen, eukaryotic translation elongation factor 1A (eEF1A) is identified as a component responsible for the anticancer activity of EGCG; (ii) through both eEF1A and 67LR, EGCG induces the dephosphorylation of myosin phosphatase targeting subunit 1 (MYPT1) at Thr-696 and activates myosin phosphatase; and (iii) silencing of 67LR, eEF1A, or MYPT1 in tumor cells results in abrogation of EGCG-induced tumor growth inhibition in vivo. Additionally, we found that eEF1A is up-regulated by EGCG through 67LR. Overall, these findings implicate both eEF1A and MYPT1 in EGCG signaling for cancer prevention through 67LR.

ROCK and Rho: biochemistry and neuronal functions of Rho-associated protein kinases

Rho-associated protein kinases (ROCKs) play key roles in mediating the control of the actin cytoskeleton by Rho family GTPases in response to extracellular signals. Such signaling pathways contribute to diverse neuronal functions from cell migration to axonal guidance to dendritic spine morphology to axonal regeneration to cell survival. In this review, the authors summarize biochemical knowledge of ROCK function and categorize neuronal ROCK-dependent signaling pathways. Further study of ROCK signal transduction mechanisms and specificities will enhance our understanding of brain development, plasticity, and repair. The ROCK pathway also provides a potential site for therapeutic intervention to promote neuronal regeneration and to limit degeneration.

Molecular architecture of leishmania EF-1α reveals a novel site that may modulate protein translation: A possible target for drug development

Elongation factor-1alpha plays an essential role in eukaryotic protein biosynthesis. Recently, we have shown by protein structure modeling the presence of a hairpin-loop of 12 amino acids in mammalian EF-1alpha that is absent in the leishmania homologue [D. Nandan, A. Cherkasov, R. Sabouti, T. Yi, N.E. Reiner, Molecular cloning, biochemical and structural analysis of elongation factor-1 alpha from Leishmania donovani: comparison with the mammalian homologue, Biochem. Biophys. Res. Commun. 302 (2003) 646-652]. As a consequence of this deletion, an exposed region is available on the main body of leishmania EF-1alpha. Here we report the generation of an anti-EF-1alpha antibody (DN-3) which bound selectively to the exposed region of leishmania EF-1alpha, with no reactivity with human EF-1alpha. In a leishmania cell-free protein translation system, DN-3 substantially inhibited protein translation. A similar inhibitory effect was observed when a specific peptide based on the exposed region was used in the cell-free protein translation assay. The application of structure-based in silico methods to identify potential ligands to target the exposed region identified a small molecule that selectively attenuated in vitro translation using leishmania extracts. Moreover, this small molecule showed selective suppressive effect on multiplication of leishmania in culture. Taken together, these findings identify a novel, exposed region in leishmania EF-1alpha that may be involved in protein synthesis and a potential site for drug targeting.

Caveolin-1 and Lipid Rafts in Confluent BeWo Trophoblasts: Evidence for Rock-1 Association with Caveolin-1

Lipid rafts are detergent-insoluble, low-density membrane domains that are rich in cholesterol and sphingolipids; caveolae are a subdomain of the biochemically defined glycolipid raft whose expression is associated with the protein caveolin-1. This protein associates with numerous signalling molecules, regulating their activity by holding them inactive. Human villous cytotrophoblasts contain caveolin-1, but levels reduce greatly during their differentiation into syncytiotrophoblast. Since caveolin-1 is a known regulator of apoptosis and trophoblast syncytialisation involves the apoptotic cascade, we hypothesised that cytotrophoblast caveolin-1 may also play a role in regulating fusion events involved in syncytium formation. The BeWo choriocarcinoma cell line has previously proved valuable for studying trophoblast syncytialisation, hence the present work was carried out to determine whether BeWo cells could be used as a model for the exploration of caveolin-1's role in regulating the syncytialisation process. Undifferentiated BeWo cells were found to express caveolin-1 in similar amounts to villous cytotrophoblasts isolated from term placenta. Lipid raft fractions prepared from these BeWo cells at confluence contained the raft-associated proteins caveolin-1 and -2, flotillin-1 and -2, stomatin and the heterotrimeric G protein, Galphaq. Confocal immunofluorescence studies revealed that caveolin-1 is internalized to the mitochondria, but not to the Golgi or endoplasmic reticulum, in subconfluent BeWo and that the protein relocates to the plasma membrane upon confluence, an observation confirmed by caveolin-1 and cytochrome c Western blotting of lipid raft fractions and mitochondria purified from confluent and subconfluent cells. Western blotting and immunofluorescence experiments comparing undifferentiated cells and those induced to differentiate using the cAMP analogue, dibutyryl cAMP, showed that BeWo syncytialisation was accompanied by a reduction in caveolin-1 levels, similar to the situation in primary villous cytotrophoblasts. Confluent, undifferentiated BeWo cultures were then used to investigate the cellular localisation of Rock-1, a protein which promotes cytoskeletal re-organisation important for syncytialisation and apoptosis. Its association with caveolin-1 was evidenced by the demonstration that the 160kDa proenzyme form of Rock-1 co-immunoprecipitates with caveolin-1 and vice versa, as well as by the co-localisation of the two proteins at the plasma membrane, as shown in immunofluorescence studies. A proportion of the total cell Rock-1 content was found in BeWo lipid raft fractions, confirming its membrane presence in confluent cells. This close association of plasmalemmal caveolin-1 with Rock-1 protein raises the possibility that caveolin-1 may regulate Rock-1 in these trophoblasts. We conclude that cell-cell contact is required for BeWo trophoblast to exhibit plasmalemmal caveolin-1; BeWo cells at confluence offer a useful model for the study of trophoblast raft behaviour during syncytialisation and for the exploration of the potential Rock-1-regulating role of caveolin-1 in this process.

Airway smooth muscle as a target of asthma therapy: history and new directions

Ultimately, asthma is a disease characterized by constriction of airway smooth muscle (ASM). The earliest approach to the treatment of asthma comprised the use of xanthines and anti-cholinergics with the later introduction of anti-histamines and anti-leukotrienes. Agents directed at ion channels on the smooth muscle membrane (Ca2+ channel blockers, K+ channel openers) have been tried and found to be ineffective. Functional antagonists, which modulate intracellular signalling pathways within the smooth muscle (beta-agonists and phosphodiesterase inhibitors), have been used for decades with success, but are not universally effective and patients continue to suffer with exacerbations of asthma using these drugs. During the past several decades, research energies have been directed into developing therapies to treat airway inflammation, but there have been no substantial advances in asthma therapies targeting the ASM. In this manuscript, excitation-contraction coupling in ASM is addressed, highlighting the current treatment of asthma while proposing several new directions that may prove helpful in the management of this disease.

Distribution of elongation factor-1alpha in larval tissues of the fall armyworm, Spodoptera frugiperda

Elongation factor-1alpha (EF-1alpha) promotes the delivery of aminoacyl-tRNA to the acceptor site of the ribosome during protein synthesis. The enzyme has a number of additional functions, including regulation of apoptosis and interaction with the cytoskeleton. We determined the distribution of EF-1alpha in larval tissues of the fall armyworm, Spodoptera frugiperda , with a monoclonal antibody generated to EF-1alpha from Sf21 cells, a cell line developed from ovarian tissue of S. frugiperda. Enzyme-linked immunosorbent assay showed that EF-1alpha comprised 1.9-9.9% of the total protein within the tissues that were examined, which included fat body, Malpighian tubules, midgut, muscle, salivary glands, trachea, and ventral nerve cord. To a certain extent, EF-1alpha concentrations reflected the expected metabolic activity level of each of the represented tissues. Closer examination by immunofluorescence microscopy revealed that EF-1alpha concentrations varied among different cell types within a given tissue, i.e. midgut columnar epithelial cells yielded strong signals, while goblet cells failed to react with the EF-1alpha-specific antibody.

Tumor cell pseudopodial protrusions. Localized signaling domains coordinating cytoskeleton remodeling, cell adhesion, glycolysis, RNA translocation, and protein translation

The pseudopodial protrusions of Moloney sarcoma virus (MSV)-Madin-Darby canine kidney (MDCK)-invasive (INV) variant cells were purified on 1-microm pore polycarbonate filters that selectively allow passage of the pseudopodial domains but not the cell body. The purified pseudopodial fraction contains phosphotyrosinated proteins, including Met and FAK, and various signaling proteins, including Raf1, MEK1, ERK2, PKBalpha (Akt1), GSK3alpha, GSK3beta, Rb, and Stat3. Pseudopodial proteins identified by liquid chromatography tandem mass spectrometry included actin and actin-regulatory proteins (ERM, calpain, filamin, myosin, Sra-1, and IQGAP1), tubulin, vimentin, adhesion proteins (vinculin, talin, and beta1 integrin), glycolytic enzymes, proteins associated with protein translation, RNA translocation, and ubiquitin-mediated protein degradation, as well as protein chaperones (HSP90 and HSC70) and signaling proteins (RhoGDI and ROCK). Inhibitors of MEK1 (U0126) and HSP90 (geldanamycin) significantly reduced MSV-MDCK-INV cell motility and pseudopod expression, and geldanamycin treatment inhibited Met phosphorylation and induced the expression of actin stress fibers. ROCK inhibition did not inhibit cell motility but transformed the pseudopodial protrusions of MSV-MDCK-INV cells into extended lamellipodia. Dominant negative Rho disrupted pseudopod expression and, in serum-starved cells, L-alpha-lysophosphatidic acid (oleoyl) activation of Rho induced pseudopodial protrusions or, in the presence of the ROCK inhibitor, extended lamellipodia. RNA was localized to the actin-rich pseudopodial domains of MSV-MDCK-INV cells, but the extent of colocalization with dense actin ruffles was reduced in the extended lamellipodia formed upon ROCK inhibition. Rho/ROCK activation in epithelial tumor cells therefore regulates RNA translocation to a pseudopodial domain that contains proteins involved in signaling, cytoskeleton remodeling, cell adhesion, glycolysis, and protein translation and degradation.

Leishmania donovani engages in regulatory interference by targeting macrophage protein tyrosine phosphatase SHP-1

Protozoan parasites of the genus leishmania are obligate intracellular parasites of monocytes and macrophages. These pathogens have evolved to invade the mammalian immune system and typically survive for long periods of time. Leishmania have developed a variety of remarkable strategies to prevent their elimination by both innate and acquired immune effector mechanisms. One particular strategy of interest involves manipulation of host cell regulatory pathways so as to prevent macrophage activation required for efficient microbicidal activity. These interference mechanisms are the main focus of this review. Several lines of evidence have been developed to show that the Src homology-2 domain containing tyrosine phosphatase-1 (SHP-1) becomes activated in leishmania-infected cells and that this contributes to disease pathogenesis. Recent studies aimed at understanding the mechanism responsible for the change in activation state of SHP-1 led to the identification of leishmania EF-1alpha as an SHP-1 binding protein and SHP-1 activator. This was a surprising finding given that this ubiquitous and highly conserved protein plays an essential role in protein translation in both prokaryotic and eukaryotic cells. The role of leishmania EF-1alpha as an SHP-1 activator and its contribution to pathogenesis are reviewed with particular attention to the properties that distinguish it from host EF-1alpha.

Functional diversity of protein phosphatase-1, a cellular economizer and reset button

The protein serine/threonine phosphatase protein phosphatase-1 (PP1) is a ubiquitous eukaryotic enzyme that regulates a variety of cellular processes through the dephosphorylation of dozens of substrates. This multifunctionality of PP1 relies on its association with a host of function-specific targetting and substrate-specifying proteins. In this review we discuss how PP1 affects the biochemistry and physiology of eukaryotic cells. The picture of PP1 that emerges from this analysis is that of a "green" enzyme that promotes the rational use of energy, the recycling of protein factors, and a reversal of the cell to a basal and/or energy-conserving state. Thus PP1 promotes a shift to the more energy-efficient fuels when nutrients are abundant and stimulates the storage of energy in the form of glycogen. PP1 also enables the relaxation of actomyosin fibers, the return to basal patterns of protein synthesis, and the recycling of transcription and splicing factors. In addition, PP1 plays a key role in the recovery from stress but promotes apoptosis when cells are damaged beyond repair. Furthermore, PP1 downregulates ion pumps and transporters in various tissues and ion channels that are involved in the excitation of neurons. Finally, PP1 promotes the exit from mitosis and maintains cells in the G1 or G2 phases of the cell cycle.

eEF1A isoforms change in abundance and actin-binding activity during maize endosperm development

Eukaryotic elongation factor 1A (eEF1A) appears to be a multifunctional protein because several biochemical activities have been described for this protein, in addition to its role in protein synthesis. In maize (Zea mays) endosperm, the synthesis of eEF1A is increased in o2 (opaque2) mutants, and its concentration is highly correlated with the protein-bound lysine content. To understand the basis of this relationship, we purified eEF1A isoforms from developing endosperm and investigated their accumulation and their functional and structural properties. Formation of three isoforms appears to be developmentally regulated and independent of the o2 mutation, although one isoform predominated in one high lysine o2 inbred. The purified proteins differ in their ability to bind F-actin in vitro, suggesting that they are functionally distinct. However, they share similar aminoacyl-tRNA-binding activities. Tandem mass spectrometry revealed that each isoform is composed of the four same gene products, which are modified posttranslationally by methylation and phosphorylation. The chemical differences that account for their different actin-binding activities could not be determined.

Proteomics identification of acyl-acceptor and acyl-donor substrates for transglutaminase in a human intestinal epithelial cell line. Implications for celiac disease

Transglutaminase (TG)-catalyzed cross-linking of both intracellular and extracellular proteins is an important biochemical event. However, increased concentrations of cross-linked proteins have been observed in many disorders. Moreover, TG-catalyzed modification of proteins might generate new self-antigens responsible for the autoimmune response, as in celiac disease. The identification of available substrates may offer an understanding of how the TG-catalyzed post-translational modification has an impact on physiology and disease. We used a proteomic approach to identify TG-modified protein targets in human intestinal epithelial cells to determine the extent to which transglutaminase specifically contributes to celiac disease. Two probes were used for endogenous TG activity: 5-(biotinamido)pentylamine, which represents the acyl-acceptor, and a biotinylated glutamine-containing peptide, which represents the acyl-donor. This approach identified >25 proteins, which range from 30,000 to 300,000 Daltons and can serve as acyl-acceptor and/or acyl-donor for transglutaminase. Some of them were known transglutaminase substrates, whereas others had not been previously identified. These targets include proteins involved in cytoskeletal network organization, folding of proteins, transport processes, and miscellaneous metabolic functions.

The formins: active scaffolds that remodel the cytoskeleton

Evolutionarily conserved in eukaryotes, formin homology (FH) proteins, or formins, exert their effects on the actin and microtubule (MT) networks during meiosis, mitosis, the maintenance of cell polarity, vesicular trafficking, signaling to the nucleus and embryonic development. Once thought to be only molecular scaffolds that indirectly affected cellular functions through the binding of other proteins, recent in vitro studies have illustrated that they can function as actin nucleators in the formation of new filaments. The connection between formins and MTs is less well understood. In yeast, the MT effects appear to be dependent on the ability of formins to generate polarized actin cables whereas, in mammalian cells, formin signals that cause MT stabilization and polarization might be more direct. A subclass of formins, the Diaphanous-related formins (Drfs), can act as effectors for Rho small GTPases, yet it is not clear what GTPase binding contributes to formin function.

Rocks: multifunctional kinases in cell behaviour

ROCKs, or Rho kinases, are serine/threonine kinases that are involved in many aspects of cell motility, from smooth-muscle contraction to cell migration and neurite outgrowth. Recent experiments have defined new functions of ROCKs in cells, including centrosome positioning and cell-size regulation, which might contribute to various physiological and pathological states.

Monoclonal antibodies to elongation factor-1alpha inhibit in vitro translation in lysates of Sf21 cells

Elongation factor-1alpha (EF-1alpha) is an enzyme that is essential for protein synthesis. Although EF-1alpha offers an excellent target for the disruption of insect metabolism, agents known to interfere with EF-1alpha activity are toxic to humans. In this article, we describe the development of monoclonal antibodies (MAbs) that can disrupt the activity of insect EF-1alpha without cross-reacting with the human enzyme. MAbs were generated to EF-1alpha from Sf21 cells derived from the fall armyworm, Spodoptera frugiperda, by immunizing mice with EF-1alpha eluted from SDS-PAGE gels. The MAbs reacted with EF-1alpha in eggs and first through fifth instars of the fall armyworm in immunoblots of SDS-PAGE gels, but did not recognize EF-1alpha in human carcinoma cells and normal tissues. MAbs with the ability to recognize EF-1alpha in its native conformation, identified through immunoprecipitation experiments, were added to Sf21 cell lysates to determine whether the antibodies could inhibit incorporation of [(35)S]methionine into newly synthesized in vitro translation products. Of the four EF-1alpha-specific MAbs tested, three significantly inhibited protein synthesis when compared to the negative control antibody (P < 0.001, one-way ANOVA; followed by Dunnett's test, P < 0.05).

Leishmania EF-1alpha activates the Src homology 2 domain containing tyrosine phosphatase SHP-1 leading to macrophage deactivation

The human leishmaniasis are persistent infections of macrophages caused by protozoa of the genus Leishmania. The chronic nature of these infections is in part related to induction of macrophage deactivation, linked to activation of the Src homology 2 domain containing tyrosine phosphatase-1 (SHP-1) in infected cells. To investigate the mechanism of SHP-1 activation, lysates of Leishmania donovani promastigotes were subjected to SHP-1 affinity chromatography and proteins bound to the matrix were sequenced by mass spectrometry. This resulted in the identification of Leishmania elongation factor-1alpha (EF-1alpha) as a SHP-1-binding protein. Purified Leishmania EF-1alpha, but not host cell EF-1alpha, bound directly to SHP-1 in vitro leading to its activation. Three independent lines of evidence indicated that Leishmania EF-1alpha may be exported from the phagosome thereby enabling targeting of host SHP-1. First, cytosolic fractions prepared from macrophages infected with [(35)S]methionine-labeled organisms contained Leishmania EF-1alpha. Second, confocal, fluorescence microscopy using Leishmania-specific antisera detected Leishmania EF-1alpha in the cytosol of infected cells. Third, co-immunoprecipitation showed that Leishmania EF-1alpha was associated with SHP-1 in vivo in infected cells. Finally, introduction of purified Leishmania EF-1alpha, but not the corresponding host protein into macrophages activated SHP-1 and blocked the induction of inducible nitric-oxide synthase expression in response to interferon-gamma. Thus, Leishmania EF-1alpha is identified as a novel SHP-1-binding and activating protein that recapitulates the deactivated phenotype of infected macrophages.

Gene expression patterns in the lungs of patients with primary pulmonary hypertension: a gene microarray analysis

Primary pulmonary hypertension (PPH) is a disease of unknown etiology characterized by lumen-obliterating endothelial cell proliferation and vascular smooth muscle hypertrophy of the small precapillary pulmonary arteries. Because the vascular lesions are homogeneously distributed throughout the entire lung, we propose that a tissue fragment of the lung is representative of the whole lung. RNA extracted from the fragments is likely to provide meaningful information regarding the changes in gene expression pattern in PPH when compared with structurally normal lung tissue. We hypothesize that the lung tissue gene expression pattern of patients with PPH has a characteristic profile when compared with the gene expression pattern of structurally normal lungs and that this characteristic gene expression profile provides new insights into the pathobiology of PPH. Using oligonucleotide microarray technology, we characterized the expression pattern in the lung tissue obtained from 6 patients with primary pulmonary hypertension (PPH)-including 2 patients with the familial form of PPH (FPPH)-and from 6 patients with histologically normal lungs. For the data analysis, gene clusters were generated and the gene expression pattern differences between PPH and normal lung tissue and between PPH and FPPH lung tissue were compared. All PPH lung tissue samples showed a decreased expression of genes encoding several kinases and phosphatases, whereas several oncogenes and genes coding for ion channel proteins were upregulated in their expression. Importantly, we could distinguish by pattern comparison between sporadic PPH and FPPH, because alterations in the expression of transforming growth factor-beta receptor III, bone morphogenic protein 2, mitogen-activated protein kinase kinase 5, RACK 1, apolipoprotein C-III, and the gene encoding the laminin receptor 1 were only found in the samples from patients with sporadic PPH, but not in FPPH samples. We conclude that the microarray gene expression technique is a new and useful molecular tool that provides novel information pertinent to a better characterization and understanding of the pathobiology of the distinct clinical phenotypes of pulmonary hypertension.