The RNA binding proteins LARP4A and LARP4B promote sarcoma and carcinoma growth and metastasis

RNA-binding proteins (RBPs) are emerging as important regulators of cancer pathogenesis. We reveal that the RBPs LARP4A and LARP4B are differentially overexpressed in osteosarcoma and osteosarcoma lung metastases, as well as in prostate cancer. Depletion of LARP4A and LARP4B reduced tumor growth and metastatic spread in xenografts, as well as inhibiting cell proliferation, motility, and migration. Transcriptomic profiling and high-content multiparametric analyses unveiled a central role for LARP4B, but not LARP4A, in regulating cell cycle progression in osteosarcoma and prostate cancer cells, potentially through modulating key cell cycle proteins such as Cyclins B1 and E2, Aurora B, and E2F1. This first systematic comparison between LARP4A and LARP4B assigns new pro-tumorigenic functions to LARP4A and LARP4B in bone and prostate cancer, highlighting their similarities while also indicating distinct functional differences. Uncovering clear biological roles for these paralogous proteins provides new avenues for identifying tissue-specific targets and potential druggable intervention.

The metabolic effects of intermittent versus continuous feeding in critically ill patients

Intermittent (or bolus) feeding regimens in critically ill patients have been of increasing interest to clinicians and scientists. Changes in amino acid, fat and carbohydrate metabolites over time might yet deliver other benefits (e.g. modulation of the circadian rhythm and sleep, and impacts on ghrelin secretion, insulin resistance and autophagy). We set out to characterise these changes in metabolite concentration. The Intermittent versus Continuous Feeding in Critically Ill paitents study (NCT02358512) was an eight-centre single-blinded randomised controlled trial. Patients were randomised to received a continuous (control arm) or intermittent (6x/day, intervention arm) enteral feeding regimen. Blood samples were taken on trial days 1, 7 and 10 immediately before and 30 min after intermittent feeds, and at equivalent timepoints in the control arm. A pre-planned targeted metabolomic analysis was performend using Nuclear Resonance Spectroscopy. Five hundred and ninety four samples were analysed from 75 patients. A total of 24 amino acid-, 19 lipid based-, and 44 small molecule metabolite features. Across the main two axes of variation (40-60% and 6-8% of variance), no broad patterns distinguished between intermittent or continuous feeding arms, across intra-day sampling times or over the 10 days from initial ICU admission. Logfold decreases in abundance were seen in metabolites related to amino acids (Glutamine - 0.682; Alanine - 0.594), ketone body metabolism (Acetone - 0.64; 3-Hydroxybutyric Acid - 0.632; Acetonacetic Acid - 0.586), fatty acid (carnitine - 0.509) and carbohydrate metabolism ( Maltose - 0.510; Citric Acid - 0.485). 2-3 Butanediol, a by-product of sugar-fermenting microbial metabolism also decreased (- 0.489). No correlation was seen with change in quadriceps muscle mass for any of the 20 metabolites varying with time (all p > 0.05). Increasing severity of organ failure was related to increasing ketone body metabolism (3 Hydroxybutyric Acid-1 and - 3; p = 0.056 and p = 0.014), carnitine deficiency (p = 0.002) and alanine abundancy (p - 0.005). A 6-times a day intermittent feeding regimen did not alter metabolite patterns across time compared to continuous feeding in critically ill patients, either within a 24 h period or across 10 days of intervention. Future research on intermittent feeding regimens should focus on clinical process benefits, or extended gut rest and fasting.

LARP4A and LARP4B in cancer: The new kids on the block

Recent developments have mounted a stunning body of evidence underlying the importance of RNA binding proteins (RBPs) in cancer research. In this minireview we focus on LARP4A and LARP4B, two paralogs belonging to the superfamily of La-related proteins, and provide a critical overview of current research, including their roles in cancer pathogenesis and cell proliferation, migration, cell cycle and apoptosis. We highlight current controversies surrounding LARP4A and LARP4B and conclude that their complex roles in tumorigenesis are cell-, tissue- and context-dependent, warning that caution must be exercised before categorising either protein as an oncoprotein or tumour-suppressor. We also reveal that LARP4A and LARP4B have often been confused with one another, adding uncertainty in delineating their functions. We suggest that further functional and mechanistic studies of LARP4 proteins present significant challenges for future investigations to recognise the vital contributions of these RBPs in cancer research.

AMPK is a mechano-metabolic sensor linking cell adhesion and mitochondrial dynamics to Myosin-dependent cell migration

Cell migration is crucial for cancer dissemination. We find that AMP-activated protein kinase (AMPK) controls cell migration by acting as an adhesion sensing molecular hub. In 3-dimensional matrices, fast-migrating amoeboid cancer cells exert low adhesion/low traction linked to low ATP/AMP, leading to AMPK activation. In turn, AMPK plays a dual role controlling mitochondrial dynamics and cytoskeletal remodelling. High AMPK activity in low adhering migratory cells, induces mitochondrial fission, resulting in lower oxidative phosphorylation and lower mitochondrial ATP. Concurrently, AMPK inactivates Myosin Phosphatase, increasing Myosin II-dependent amoeboid migration. Reducing adhesion or mitochondrial fusion or activating AMPK induces efficient rounded-amoeboid migration. AMPK inhibition suppresses metastatic potential of amoeboid cancer cells in vivo, while a mitochondrial/AMPK-driven switch is observed in regions of human tumours where amoeboid cells are disseminating. We unveil how mitochondrial dynamics control cell migration and suggest that AMPK is a mechano-metabolic sensor linking energetics and the cytoskeleton.

Metabolic rewiring in MYC-driven medulloblastoma by BET-bromodomain inhibition

Medulloblastoma (MB) is the most common malignant brain tumour in children. High-risk MB patients harbouring MYC amplification or overexpression exhibit a very poor prognosis. Aberrant activation of MYC markedly reprograms cell metabolism to sustain tumorigenesis, yet how metabolism is dysregulated in MYC-driven MB is not well understood. Growing evidence unveiled the potential of BET-bromodomain inhibitors (BETis) as next generation agents for treating MYC-driven MB, but whether and how BETis may affect tumour cell metabolism to exert their anticancer activities remains unknown. In this study, we explore the metabolic features characterising MYC-driven MB and examine how these are altered by BET-bromodomain inhibition. To this end, we employed an NMR-based metabolomics approach applied to the MYC-driven MB D283 and D458 cell lines before and after the treatment with the BETi OTX-015. We found that OTX-015 triggers a metabolic shift in both cell lines resulting in increased levels of myo-inositol, glycerophosphocholine, UDP-N-acetylglucosamine, glycine, serine, pantothenate and phosphocholine. Moreover, we show that OTX-015 alters ascorbate and aldarate metabolism, inositol phosphate metabolism, phosphatidylinositol signalling system, glycerophospholipid metabolism, ether lipid metabolism, aminoacyl-tRNA biosynthesis, and glycine, serine and threonine metabolism pathways in both cell lines. These insights provide a metabolic characterisation of MYC-driven childhood MB cell lines, which could pave the way for the discovery of novel druggable pathways. Importantly, these findings will also contribute to understand the downstream effects of BETis on MYC-driven MB, potentially aiding the development of new therapeutic strategies to combat medulloblastoma.

Allosteric regulation of the soluble epoxide hydrolase by nitro fatty acids using a combined experimental and computational approach

The human soluble epoxide hydrolase (hsEH) is a key regulator of epoxy fatty acid (EpFA) metabolism. Inhibition of sEH can maintain endogenous levels of beneficial EpFAs and reduce the levels of their corresponding diol products, thus ameliorating a variety of pathological conditions including cardiovascular, central nervous system and metabolic diseases. The quest for orthosteric drugs that bind directly to the catalytic crevice of hsEH has been prolonged and sustained over the past decades, but the disappointing outcome of clinical trials to date warrants alternative pharmacological approaches. Previously, we have shown that hsEH can be allosterically inhibited by the endogenous electrophilic lipid 15-deoxy-Δ^12,14-Prostaglandin-J₂, via covalent adduction to two cysteines, C423 and C522. In this study, we explore the properties and behaviour of three electrophilic lipids belonging to the class of the nitro fatty acids, namely 9- and 10-nitrooleate and 10-nitrolinoleate. Biochemical and biophysical investigations revealed that, in addition to C423 and C522, nitro fatty acids can covalently bind to additional nucleophilic residues in hsEH C-terminal domain (CTD), two of which predicted in this study to be latent allosteric sites. Systematic mapping of the protein mutational space and evaluation of possible propagation pathways delineated selected residues, both in the allosteric patches and in other regions of the enzyme, envisaged to play a role on allosteric signalling. The responses elicited by the ligands on the covalent adduction sites supports future fragment-based design studies of new allosteric effectors for hsEH with increased efficacy and selectivity.

Structural basis of dimerization and nucleic acid binding of human DBHS proteins NONO and PSPC1

The Drosophila behaviour/human splicing (DBHS) proteins are a family of RNA/DNA binding cofactors liable for a range of cellular processes. DBHS proteins include the non-POU domain-containing octamer-binding protein (NONO) and paraspeckle protein component 1 (PSPC1), proteins capable of forming combinatorial dimers. Here, we describe the crystal structures of the human NONO and PSPC1 homodimers, representing uncharacterized DBHS dimerization states. The structures reveal a set of conserved contacts and structural plasticity within the dimerization interface that provide a rationale for dimer selectivity between DBHS paralogues. In addition, solution X-ray scattering and accompanying biochemical experiments describe a mechanism of cooperative RNA recognition by the NONO homodimer. Nucleic acid binding is reliant on RRM1, and appears to be affected by the orientation of RRM1, influenced by a newly identified 'β-clasp' structure. Our structures shed light on the molecular determinants for DBHS homo- and heterodimerization and provide a basis for understanding how DBHS proteins cooperatively recognize a broad spectrum of RNA targets.

A thiol redox sensor in soluble epoxide hydrolase enables oxidative activation by intra-protein disulfide bond formation

Soluble epoxide hydrolase (sEH), an enzyme that broadly regulates the cardiovascular system, hydrolyses epoxyeicosatrienoic acids (EETs) to their corresponding dihydroxyeicosatrienoic acids (DHETs). We previously showed that endogenous lipid electrophiles adduct within the catalytic domain, inhibiting sEH to lower blood pressure in angiotensin II-induced hypertensive mice. As angiotensin II increases vascular H2O2, we explored sEH redox regulation by this oxidant and how this integrates with inhibition by lipid electrophiles to regulate vasotone. Kinetics analyses revealed that H2O2 not only increased the specific activity of sEH but increased its affinity for substrate and increased its catalytic efficiency. This oxidative activation was mediated by formation of an intra-disulfide bond between C262 and C264, as determined by mass spectrometry and substantiated by biotin-phenylarsinate and thioredoxin-trapping mutant assays. C262S/264S sEH mutants were resistant to peroxide-induced activation, corroborating the disulfide-activation mechanism. The physiological impact of sEH redox state was determined in isolated arteries and the effect of the pro-oxidant vasopressor angiotensin II on arterial sEH redox state and vasodilatory EETs indexed in mice. Angiotensin II induced the activating intra-disulfide in sEH, causing a decrease in plasma EET/DHET ratios that is consistent with the pressor response to this hormone. Although sEH C262-C264 disulfide formation enhances hydrolysis of vasodilatory EETs, this modification also sensitized sEH to inhibition by lipid electrophiles. This explains why angiotensin II decreases EETs and increases blood pressure, but when lipid electrophiles are also present, that EETs are increased and blood pressure lowered.

LARP6C orchestrates posttranscriptional reprogramming of gene expression during hydration to promote pollen tube guidance

Increasing evidence suggests that posttranscriptional regulation is a key player in the transition between mature pollen and the progamic phase (from pollination to fertilization). Nonetheless, the actors in this messenger RNA (mRNA)-based gene expression reprogramming are poorly understood. We demonstrate that the evolutionarily conserved RNA-binding protein LARP6C is necessary for the transition from dry pollen to pollen tubes and the guided growth of pollen tubes towards the ovule in Arabidopsis thaliana. In dry pollen, LARP6C binds to transcripts encoding proteins that function in lipid synthesis and homeostasis, vesicular trafficking, and polarized cell growth. LARP6C also forms cytoplasmic granules that contain the poly(A) binding protein and possibly represent storage sites for translationally silent mRNAs. In pollen tubes, the loss of LARP6C negatively affects the quantities and distribution of storage lipids, as well as vesicular trafficking. In Nicotiana benthamiana leaf cells and in planta, analysis of reporter mRNAs designed from the LARP6C target MGD2 provided evidence that LARP6C can shift from a repressor to an activator of translation when the pollen grain enters the progamic phase. We propose that LARP6C orchestrates the timely posttranscriptional regulation of a subset of mRNAs in pollen during the transition from the quiescent to active state and along the progamic phase to promote male fertilization in plants.

LARP6C orchestrates posttranscriptional reprogramming of gene expression during hydration to promote pollen tube guidance

Increasing evidence suggests that posttranscriptional regulation is a key player in the transition between mature pollen and the progamic phase (from pollination to fertilization). Nonetheless, the actors in this messenger RNA (mRNA)-based gene expression reprogramming are poorly understood. We demonstrate that the evolutionarily conserved RNA-binding protein LARP6C is necessary for the transition from dry pollen to pollen tubes and the guided growth of pollen tubes towards the ovule in Arabidopsis thaliana. In dry pollen, LARP6C binds to transcripts encoding proteins that function in lipid synthesis and homeostasis, vesicular trafficking, and polarized cell growth. LARP6C also forms cytoplasmic granules that contain the poly(A) binding protein and possibly represent storage sites for translationally silent mRNAs. In pollen tubes, the loss of LARP6C negatively affects the quantities and distribution of storage lipids, as well as vesicular trafficking. In Nicotiana benthamiana leaf cells and in planta, analysis of reporter mRNAs designed from the LARP6C target MGD2 provided evidence that LARP6C can shift from a repressor to an activator of translation when the pollen grain enters the progamic phase. We propose that LARP6C orchestrates the timely posttranscriptional regulation of a subset of mRNAs in pollen during the transition from the quiescent to active state and along the progamic phase to promote male fertilization in plants.

Mining the PDB for Tractable Cases Where X-ray Crystallography Combined with Fragment Screens Can Be Used to Systematically Design Protein-Protein Inhibitors: Two Test Cases Illustrated by IL1β-IL1R and p38α-TAB1 Complexes

Nowadays, it is possible to combine X-ray crystallography and fragment screening in a medium throughput fashion to chemically probe the surfaces used by proteins to interact and use the outcome of the screens to systematically design protein-protein inhibitors. To prove it, we first performed a bioinformatics analysis of the Protein Data Bank protein complexes, which revealed over 400 cases where the crystal lattice of the target in the free form is such that large portions of the interacting surfaces are free from lattice contacts and therefore accessible to fragments during soaks. Among the tractable complexes identified, we then performed single fragment crystal screens on two particular interesting cases: the Il1β-ILR and p38α-TAB1 complexes. The result of the screens showed that fragments tend to bind in clusters, highlighting the small-molecule hotspots on the surface of the target protein. In most of the cases, the hotspots overlapped with the binding sites of the interacting proteins.

Structural dynamics in the La-module of La-related proteins

The La-related proteins (LaRPs) are a superfamily of eukaryotic RNA-binding proteins with important and varied roles. To understand LaRP functions it is essential to unravel the divergent features responsible for their RNA target selectivity, which underlie their distinct identities and cellular roles. LaRPs are built on a common structural module called the ‘La-module’ that acts as a main locus for RNA recognition. The La-module is comprised of two tethered domains whose relative structural and dynamic interplay has been proposed to regulate RNA-target selection, albeit the mechanistic underpinning of this recognition remains to be elucidated. A main unsolved conundrum is how conserved La-modules across LaRPs are able to bind to extremely diverse RNA ligands.

In this work, we employed Small Angle X-ray Scattering (SAXS) to investigate several human LaRP La-modules in the absence and, where applicable, in the presence of their RNA target, with the aim to explore the structural dynamics of their RNA recognition and provide information on the architectural landscape accessible to these proteins. Integration of these SAXS experiments with prior X-ray crystallography and NMR data suggests that RNA binding is generally accompanied by a compaction and loss of flexibility of the La-module. Nonetheless, the La-modules appear to experience a considerably different degree of inherent flexibility in their apo state. Furthermore, although they all exist in discrete subsets of accessible populations in equilibrium, these vary from LaRP to LaRP and can be either extended or compact. We propose that these divergent features may be critical for RNA substrate discrimination.

Maternal Larp6 controls oocyte development, chorion formation and elevation

La-related protein 6 (Larp6) is a conserved RNA-binding protein found across eukaryotes that has been suggested to regulate collagen biogenesis, muscle development, ciliogenesis, and various aspects of cell proliferation and migration. Zebrafish have two Larp6 family genes: larp6a and larp6b Viable and fertile single and double homozygous larp6a and larp6b zygotic mutants revealed no defects in muscle structure, and were indistinguishable from heterozygous or wild-type siblings. However, larp6a mutant females produced eggs with chorions that failed to elevate fully and were fragile. Eggs from larp6b single mutant females showed minor chorion defects, but chorions from eggs laid by larp6a;larp6b double mutant females were more defective than those from larp6a single mutants. Electron microscopy revealed defective chorionogenesis during oocyte development. Despite this, maternal zygotic single and double mutants were viable and fertile. Mass spectrometry analysis provided a description of chorion protein composition and revealed significant reductions in a subset of zona pellucida and lectin-type proteins between wild-type and mutant chorions that paralleled the severity of the phenotype. We conclude that Larp6 proteins are required for normal oocyte development, chorion formation and egg activation.

The La-related proteins: structures and interactions of a versatile superfamily of RNA-binding proteins

The La-related proteins (LaRPs) are an ancient superfamily of RNA-binding proteins orchestrating the major fates of RNA, from processing and maturation to regulation of mRNA translation. LaRPs are instrumental in modulating complex assemblies where the RNA is bound, folded, processed, escorted and presented to the functional effectors often through recruitment of protein partners. This intricate web of protein-RNA and protein-protein interactions is enabled by the modular nature of the LaRPs, comprising several structured domains connected by flexible linkers, and other sequences lacking recognizable folded motifs. Recent structures, together with biochemical and biophysical studies, have provided insights into how each LaRP family has evolved unique mechanisms of RNA recognition, not only through the conserved RNA-binding unit, the La-module, but also mediated by other family-specific motifs. Furthermore, in a series of unexpected twists and turns, they have revealed that the dynamic and conformational interplay of multi-structured domains and disordered regions operate in unison to achieve RNA substrate discrimination. This review proposes a perspective of our current knowledge of the structure-function relationship of the LaRP superfamily.

Isothermal Titration Calorimetry Enables Rapid Characterization of Enzyme Kinetics and Inhibition for the Human Soluble Epoxide Hydrolase

Isothermal titration calorimetry (ITC) is conventionally used to acquire thermodynamic data for biological interactions. In recent years, ITC has emerged as a powerful tool to characterize enzyme kinetics. In this study, we have adapted a single-injection method (SIM) to study the kinetics of human soluble epoxide hydrolase (hsEH), an enzyme involved in cardiovascular homeostasis, hypertension, nociception, and insulin sensitivity through the metabolism of epoxy-fatty acids (EpFAs). In the SIM method, the rate of reaction is determined by monitoring the thermal power, while the substrate is being depleted, overcoming the need for synthetic substrates and reducing postreaction processing. Our results show that ITC enables the detailed, rapid, and reproducible characterization of the hsEH-mediated hydrolysis of several natural EpFA substrates. Furthermore, we have applied a variant of the single-injection ITC method for the detailed description of enzyme inhibition, proving the power of this approach in the rapid screening and discovery of new hsEH inhibitors using the enzyme’s physiological substrates. The methods described herein will enable further studies on EpFAs’ metabolism and biology, as well as drug discovery investigations to identify and characterize hsEH inhibitors. This also promises to provide a general approach for the characterization of lipid catalysis, given the challenges that lipid metabolism studies pose to traditional spectroscopic techniques.

PDXK mutations cause polyneuropathy responsive to pyridoxal 5'-phosphate supplementation

OBJECTIVE

To identify disease-causing variants in autosomal recessive axonal polyneuropathy with optic atrophy and provide targeted replacement therapy.

METHODS

We performed genome-wide sequencing, homozygosity mapping, and segregation analysis for novel disease-causing gene discovery. We used circular dichroism to show secondary structure changes and isothermal titration calorimetry to investigate the impact of variants on adenosine triphosphate (ATP) binding. Pathogenicity was further supported by enzymatic assays and mass spectroscopy on recombinant protein, patient-derived fibroblasts, plasma, and erythrocytes. Response to supplementation was measured with clinical validated rating scales, electrophysiology, and biochemical quantification.

RESULTS

We identified biallelic mutations in PDXK in 5 individuals from 2 unrelated families with primary axonal polyneuropathy and optic atrophy. The natural history of this disorder suggests that untreated, affected individuals become wheelchair-bound and blind. We identified conformational rearrangement in the mutant enzyme around the ATP-binding pocket. Low PDXK ATP binding resulted in decreased erythrocyte PDXK activity and low pyridoxal 5'-phosphate (PLP) concentrations. We rescued the clinical and biochemical profile with PLP supplementation in 1 family, improvement in power, pain, and fatigue contributing to patients regaining their ability to walk independently during the first year of PLP normalization.

INTERPRETATION

We show that mutations in PDXK cause autosomal recessive axonal peripheral polyneuropathy leading to disease via reduced PDXK enzymatic activity and low PLP. We show that the biochemical profile can be rescued with PLP supplementation associated with clinical improvement. As B6 is a cofactor in diverse essential biological pathways, our findings may have direct implications for neuropathies of unknown etiology characterized by reduced PLP levels. ANN NEUROL 2019;86:225-240.

15-deoxy-Δ12,14-Prostaglandin J2 inhibits human soluble epoxide hydrolase by a dual orthosteric and allosteric mechanism

Human soluble epoxide hydrolase (hsEH) is an enzyme responsible for the inactivation of bioactive epoxy fatty acids, and its inhibition is emerging as a promising therapeutical strategy to target hypertension, cardiovascular disease, pain and insulin sensitivity. Here, we uncover the molecular bases of hsEH inhibition mediated by the endogenous 15-deoxy-Δ12,14-Prostaglandin J2 (15d-PGJ2). Our data reveal a dual inhibitory mechanism, whereby hsEH can be inhibited by reversible docking of 15d-PGJ2 in the catalytic pocket, as well as by covalent locking of the same compound onto cysteine residues C423 and C522, remote to the active site. Biophysical characterisations allied with in silico investigations indicate that the covalent modification of the reactive cysteines may be part of a hitherto undiscovered allosteric regulatory mechanism of the enzyme. This study provides insights into the molecular modes of inhibition of hsEH epoxy-hydrolytic activity and paves the way for the development of new allosteric inhibitors.

LARP4A recognizes polyA RNA via a novel binding mechanism mediated by disordered regions and involving the PAM2w motif, revealing interplay between PABP, LARP4A and mRNA

LARP4A belongs to the ancient RNA-binding protein superfamily of La-related proteins (LARPs). In humans, it acts mainly by stabilizing mRNAs, enhancing translation and controlling polyA lengths of heterologous mRNAs. These activities are known to implicate its association with mRNA, protein partners and translating ribosomes, albeit molecular details are missing. Here, we characterize the direct interaction between LARP4A, oligoA RNA and the MLLE domain of the PolyA-binding protein (PABP). Our study shows that LARP4A-oligoA association entails novel RNA recognition features involving the N-terminal region of the protein that exists in a semi-disordered state and lacks any recognizable RNA-binding motif. Against expectations, we show that the La module, the conserved RNA-binding unit across LARPs, is not the principal determinant for oligoA interaction, only contributing to binding to a limited degree. Furthermore, the variant PABP-interacting motif 2 (PAM2w) featured in the N-terminal region of LARP4A was found to be important for both RNA and PABP recognition, revealing a new role for this protein-protein binding motif. Our analysis demonstrates the mutual exclusive nature of the PAM2w-mediated interactions, thereby unveiling a tantalizing interplay between LARP4A, polyA and PABP.

Resonance assignment of human LARP4A La module

Human LARP4A belongs to a superfamily of RNA binding proteins called La-related proteins (LARPs). Whilst being a positive regulator of protein synthesis and a promoter of mRNA stability, LARP4A also controls cell morphology and motility in human breast and prostate cancer cells. All LARPs share a characteristic RNA binding unit named the La-module, which despite a high level of primary structure conservation exhibits a great versatility in RNA target selection. Human LARP4A La-module is the most divergent compared with other LARPs and its RNA recognition properties have only recently started to be revealed. Given the key role of LARP4A protein in cancer cell biology, we have initiated a complete NMR characterisation of its La-module and here we report the assignment of 1H, 15N and 13C resonances resulting from our studies.

Expression, purification, and characterisation of human soluble Epoxide Hydrolase (hsEH) and of its functional C-terminal domain

The human soluble Epoxide Hydrolase (hsEH) is an enzyme involved in the hydrolysis of endogenous anti-inflammatory and cardio-protective signalling mediators known as epoxyeicosatrienoic acids (EETs). EETs’ conversion into the corresponding diols by hsEH generates non-bioactive molecules, thereby the enzyme inhibition would be expected to enhance the EETs bioavailability, and their beneficial properties. Numerous inhibitors have been developed to target the enzyme, some of which are showing promising antihypertensive and anti-inflammatory properties in vivo. Thus far, the preparation of the recombinant enzyme for enzymatic and structural in vitro studies has been performed mainly using a baculovirus expression system. More recently, it was reported that the enzyme could be exogenously expressed and isolated from E. coli, although limited amounts of active protein were obtained. We herein describe two novel methods to yield pure recombinant enzyme. The first describes the expression and purification of the full-length enzyme from eukaryotic cells HEK293-F, whilst the second concerns the C-terminal domain of hsEH obtained from the cost-effective and rapid E. coli prokaryotic system. The two methods successfully generated satisfactory amounts of functional enzyme, with virtually identical enzymatic activity. Overall, the protocols described in this paper can be employed for the recombinant expression and purification of active hsEH, to be used in future biomedical investigations and for high-throughput screening of inhibitors for potential use in the treatment of cardiovascular disease.

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hsEH is a key regulator of cardiovascular homeostasis.

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A HEK293-F mammalian expression system for hsEH full-length (FL) was developed.

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An E. coli expression system for the hsEH C-terminal Domain (CTD) was established.

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Both proteins exhibited the same enzymatic specific activity in vitro.

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The CTD preparation provides benefits of easy operation, and high yield and purity.

The La and related RNA-binding proteins (LARPs): structures, functions, and evolving perspectives

La was first identified as a polypeptide component of ribonucleic protein complexes targeted by antibodies in autoimmune patients and is now known to be a eukaryote cell-ubiquitous protein. Structure and function studies have shown that La binds to a common terminal motif, UUU-3'-OH, of nascent RNA polymerase III (RNAP III) transcripts and protects them from exonucleolytic decay. For precursor-tRNAs, the most diverse and abundant of these transcripts, La also functions as an RNA chaperone that helps to prevent their misfolding. Related to this, we review evidence that suggests that La and its link to RNAP III were significant in the great expansions of the tRNAomes that occurred in eukaryotes. Four families of La-related proteins (LARPs) emerged during eukaryotic evolution with specialized functions. We provide an overview of the high-resolution structural biology of La and LARPs. LARP7 family members most closely resemble La but function with a single RNAP III nuclear transcript, 7SK, or telomerase RNA. A cytoplasmic isoform of La protein as well as LARPs 6, 4, and 1 function in mRNA metabolism and translation in distinct but similar ways, sometimes with the poly(A)-binding protein, and in some cases by direct binding to poly(A)-RNA. New structures of LARP domains, some complexed with RNA, provide novel insights into the functional versatility of these proteins. We also consider LARPs in relation to ancestral La protein and potential retention of links to specific RNA-related pathways. One such link may be tRNA surveillance and codon usage by LARP-associated mRNAs. WIREs RNA 2017, 8:e1430. doi: 10.1002/wrna.1430 For further resources related to this article, please visit the WIREs website.

Analysis of the interaction of Plexin-B1 and Plexin-B2 with Rnd family proteins

The Rnd family of proteins, Rnd1, Rnd2 and Rnd3, are atypical Rho family GTPases, which bind to but do not hydrolyse GTP. They interact with plexins, which are receptors for semaphorins, and are hypothesised to regulate plexin signalling. We recently showed that each Rnd protein has a distinct profile of interaction with three plexins, Plexin-B1, Plexin-B2 and Plexin-B3, in mammalian cells, although it is unclear which region(s) of these plexins contribute to this specificity. Here we characterise the binary interactions of the Rnd proteins with the Rho-binding domain (RBD) of Plexin-B1 and Plexin-B2 using biophysical approaches. Isothermal titration calorimetry (ITC) experiments for each of the Rnd proteins with Plexin-B1-RBD and Plexin-B2-RBD showed similar association constants for all six interactions, although Rnd1 displayed a small preference for Plexin-B1-RBD and Rnd3 for Plexin-B2-RBD. Furthermore, mutagenic analysis of Rnd3 suggested similarities in its interaction with both Plexin-B1-RBD and Plexin-B2-RBD. These results suggest that Rnd proteins do not have a clear-cut specificity for different Plexin-B-RBDs, possibly implying the contribution of additional regions of Plexin-B proteins in conferring functional substrate selection.

The RNA-binding protein LARP4 regulates cancer cell migration and invasion

LARP4 is a La-related RNA-binding protein implicated in regulating mRNA translation, which interacts with poly(A)-binding protein (PABP). We previously identified LARP4 in an RNAi screen as one of several genes that regulate the shape of PC3 prostate cancer cells. Here we show that LARP4 depletion induces cell elongation in PC3 cells and MDA-MB-231 breast cancer cells. LARP4 depletion increases cell migration and invasion, as well as inducing invasive cell protrusions in 3D Matrigel. Conversely, LARP4 over-expression reduces cell elongation and increases cell circularity. LARP4 mutations are found in a variety of cancers. Introduction of some of these cancer-associated mutations, including a truncation mutant, into LARP4 enhances its effects on cell morphology. The truncation mutant shows enhanced interaction with PABP. We propose that LARP4 inhibits migration and invasion of cancer cells, and that some cancer-associated mutations stimulate these effects of LARP4. © 2016 The Authors. Cytoskeleton Published by Wiley Periodicals, Inc.

A crystallographic study of human NONO (p54(nrb)): overcoming pathological problems with purification, data collection and noncrystallographic symmetry

Non-POU domain-containing octamer-binding protein (NONO, a.k.a. p54(nrb)) is a central player in nuclear gene regulation with rapidly emerging medical significance. NONO is a member of the highly conserved Drosophila behaviour/human splicing (DBHS) protein family, a dynamic family of obligatory dimeric nuclear regulatory mediators. However, work with the NONO homodimer has been limited by rapid irreversible sample aggregation. Here, it is reported that L-proline stabilizes purified NONO homodimers, enabling good-quality solution small-angle X-ray structure determination and crystallization. NONO crystallized in the apparent space group P21 with a unique axis (b) of 408.9 Å and with evidence of twinning, as indicated by the cumulative intensity distribution L statistic, suggesting the possibility of space group P1. Structure solution by molecular replacement shows a superhelical arrangement of six NONO homodimers (or 12 in P1) oriented parallel to the long axis, resulting in extensive noncrystallographic symmetry. Further analysis revealed that the crystal was not twinned, but the collected data suffered from highly overlapping reflections that obscured the L-test. Optimized data collection on a new crystal using higher energy X-rays, a smaller beam width and an increased sample-to-detector distance produced non-overlapping reflections to 2.6 Å resolution. The steps taken to analyse and overcome this series of practical difficulties and to produce a biologically informative structure are discussed.

(1)H, (15)N and (13)C chemical shift assignments of the La motif and RRM1 from human LARP6

We report here the nearly complete (1)H, (15)N and (13)C resonance assignment of the La motif and RNA recognition motif 1 of human LARP6, an RNA binding protein involved in regulating collagen synthesis.

Rest perfusion abnormalities in hypertrophic cardiomyopathy: correlation with myocardial fibrosis and risk factors for sudden cardiac death

Aim

To measure the prevalence of abnormal rest perfusion in a population of consecutive patients with known hypertrophic cardiomyopathy (HCM) referred for cardiovascular MRI (CMR), and to assess any associations between abnormal rest perfusion and the presence, pattern, and severity of myocardial scar and the presence of risk factors for sudden death.

Materials and methods

Eighty consecutive patients with known HCM referred for CMR underwent functional imaging, rest first-pass perfusion, and late gadolinium enhancement (LGE).

Results

Thirty percent of the patients had abnormal rest perfusion, all of them corresponding to areas of mid-myocardial LGE and to a higher degree of segmental hypertrophy. Rest perfusion abnormalities correlated with more extensive and confluent LGE. The subgroup of patients with myocardial fibrosis and rest perfusion abnormalities (fibrosis+/perfusion+) had more than twice the incidence of episodes of non-sustained ventricular tachycardia on Holter monitoring in comparison to patients with myocardial fibrosis and normal rest perfusion (fibrosis+/perfusion–) and patients with no fibrosis and normal rest perfusion (fibrosis–/perfusion–).

Conclusions

First-pass perfusion CMR identifies abnormal rest perfusion in a significant proportion of patients with HCM. These abnormalities are associated with the presence and distribution of myocardial scar and the degree of hypertrophy. Rest perfusion abnormalities identify patients with increased incidence of episodes of non-sustained ventricular tachycardia on Holter monitoring, independently from the presence of myocardial fibrosis.

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30% of patients with HCM have perfusion abnormalities related to scar.

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No rest perfusion abnormalities were observed in areas of viable myocardium.

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Scar-related perfusion abnormalities were associated with the incidence of NSVT.

Synergic interplay of the La motif, RRM1 and the interdomain linker of LARP6 in the recognition of collagen mRNA expands the RNA binding repertoire of the La module

The La-related proteins (LARPs) form a diverse group of RNA-binding proteins characterized by the possession of a composite RNA binding unit, the La module. The La module comprises two domains, the La motif (LaM) and the RRM1, which together recognize and bind to a wide array of RNA substrates. Structural information regarding the La module is at present restricted to the prototypic La protein, which acts as an RNA chaperone binding to 3' UUUOH sequences of nascent RNA polymerase III transcripts. In contrast, LARP6 is implicated in the regulation of collagen synthesis and interacts with a specific stem-loop within the 5' UTR of the collagen mRNA. Here, we present the structure of the LaM and RRM1 of human LARP6 uncovering in both cases considerable structural variation in comparison to the equivalent domains in La and revealing an unprecedented fold for the RRM1. A mutagenic study guided by the structures revealed that RNA recognition requires synergy between the LaM and RRM1 as well as the participation of the interdomain linker, probably in realizing tandem domain configurations and dynamics required for substrate selectivity. Our study highlights a considerable complexity and plasticity in the architecture of the La module within LARPs.

Mechanism and consequence of the autoactivation of p38α mitogen-activated protein kinase promoted by TAB1

p38α Mitogen-activated Protein Kinase (p38α) is activated by a variety of mechanisms, including autophosphorylation initiated by TGFβ-activated kinase 1 binding protein 1 (TAB1) during myocardial ischemia and other stresses. Chemical genetic approaches and co-expression in mammalian, bacterial and cell-free systems revealed that mouse p38α autophosphorylation occurs in cis by direct interaction with TAB1(371-416). In isolated rat cardiac myocytes and perfused mouse hearts TAT-TAB1(371-416) rapidly activates p38 and profoundly perturbs function. Crystal structures and characterization in solution revealed a bipartite docking site for TAB1 in the p38α C-terminal kinase lobe. TAB1 binding stabilizes active p38α and induces rearrangements within the activation segment by helical extension of the Thr-Gly-Tyr motif that allows auto-phosphorylation in cis. Interference with p38α recognition by TAB1 abolishes its cardiac toxicity. Potentially, such intervention could circumvent the drawbacks seen when pharmacological inhibitors of p38 catalytic activity are used clinically.

The association of a La module with the PABP-interacting motif PAM2 is a recurrent evolutionary process that led to the neofunctionalization of La-related proteins

La-related proteins (LARPs) are largely uncharacterized factors, well conserved throughout evolution. Recent reports on the function of human LARP4 and LARP6 suggest that these proteins fulfill key functions in mRNA metabolism and/or translation. We report here a detailed evolutionary history of the LARP4 and 6 families in eukaryotes. Genes coding for LARP4 and 6 were duplicated in the common ancestor of the vertebrate lineage, but one LARP6 gene was subsequently lost in the common ancestor of the eutherian lineage. The LARP6 gene was also independently duplicated several times in the vascular plant lineage. We observed that vertebrate LARP4 and plant LARP6 duplication events were correlated with the acquisition of a PABP-interacting motif 2 (PAM2) and with a significant reorganization of their RNA-binding modules. Using isothermal titration calorimetry (ITC) and immunoprecipitation methods, we show that the two plant PAM2-containing LARP6s (LARP6b and c) can, indeed, interact with the major plant poly(A)-binding protein (PAB2), while the third plant LARP6 (LARP6a) is unable to do so. We also analyzed the RNA-binding properties and the subcellular localizations of the two types of plant LARP6 proteins and found that they display nonredundant characteristics. As a whole, our results support a model in which the acquisition by LARP4 and LARP6 of a PAM2 allowed their targeting to mRNA 3' UTRs and led to their neofunctionalization.

RNA chaperone activity of human La protein is mediated by variant RNA recognition motif

La proteins are conserved factors in eukaryotes that bind and protect the 3' trailers of pre-tRNAs from exonuclease digestion via sequence-specific recognition of UUU-3'OH. La has also been hypothesized to assist pre-tRNAs in attaining their native fold through RNA chaperone activity. In addition to binding polymerase III transcripts, human La has also been shown to enhance the translation of several internal ribosome entry sites and upstream ORF-containing mRNA targets, also potentially through RNA chaperone activity. Using in vitro FRET-based assays, we show that human and Schizosaccharomyces pombe La proteins harbor RNA chaperone activity by enhancing RNA strand annealing and strand dissociation. We use various RNA substrates and La mutants to show that UUU-3'OH-dependent La-RNA binding is not required for this function, and we map RNA chaperone activity to its RRM1 motif including a noncanonical α3-helix. We validate the importance of this α3-helix by appending it to the RRM of the unrelated U1A protein and show that this fusion protein acquires significant strand annealing activity. Finally, we show that residues required for La-mediated RNA chaperone activity in vitro are required for La-dependent rescue of tRNA-mediated suppression via a mutated suppressor tRNA in vivo. This work delineates the structural elements required for La-mediated RNA chaperone activity and provides a basis for understanding how La can enhance the folding of its various RNA targets.

Analysis of the interaction with the hepatitis C virus mRNA reveals an alternative mode of RNA recognition by the human La protein

Human La protein is an essential factor in the biology of both coding and non-coding RNAs. In the nucleus, La binds primarily to 3' oligoU containing RNAs, while in the cytoplasm La interacts with an array of different mRNAs lacking a 3' UUU(OH) trailer. An example of the latter is the binding of La to the IRES domain IV of the hepatitis C virus (HCV) RNA, which is associated with viral translation stimulation. By systematic biophysical investigations, we have found that La binds to domain IV using an RNA recognition that is quite distinct from its mode of binding to RNAs with a 3' UUU(OH) trailer: although the La motif and first RNA recognition motif (RRM1) are sufficient for high-affinity binding to 3' oligoU, recognition of HCV domain IV requires the La motif and RRM1 to work in concert with the atypical RRM2 which has not previously been shown to have a significant role in RNA binding. This new mode of binding does not appear sequence specific, but recognizes structural features of the RNA, in particular a double-stranded stem flanked by single-stranded extensions. These findings pave the way for a better understanding of the role of La in viral translation initiation.

Resonance assignment of nsp7α from arterivirus

The (1)H, (15)N and (13)C resonance assignment of nsp7α, a non-structural protein of unknown function from the equine arteritis virus, is reported.

La-related protein 4 binds poly(A), interacts with the poly(A)-binding protein MLLE domain via a variant PAM2w motif, and can promote mRNA stability

The conserved RNA binding protein La recognizes UUU-3'OH on its small nuclear RNA ligands and stabilizes them against 3'-end-mediated decay. We report that newly described La-related protein 4 (LARP4) is a factor that can bind poly(A) RNA and interact with poly(A) binding protein (PABP). Yeast two-hybrid analysis and reciprocal immunoprecipitations (IPs) from HeLa cells revealed that LARP4 interacts with RACK1, a 40S ribosome- and mRNA-associated protein. LARP4 cosediments with 40S ribosome subunits and polyribosomes, and its knockdown decreases translation. Mutagenesis of the RNA binding or PABP interaction motifs decrease LARP4 association with polysomes. Several translation and mRNA metabolism-related proteins use a PAM2 sequence containing a critical invariant phenylalanine to make direct contact with the MLLE domain of PABP, and their competition for the MLLE is thought to regulate mRNA homeostasis. Unlike all ∼150 previously analyzed PAM2 sequences, LARP4 contains a variant PAM2 (PAM2w) with tryptophan in place of the phenylalanine. Binding and nuclear magnetic resonance (NMR) studies have shown that a peptide representing LARP4 PAM2w interacts with the MLLE of PABP within the affinity range measured for other PAM2 motif peptides. A cocrystal of PABC bound to LARP4 PAM2w shows tryptophan in the pocket in PABC-MLLE otherwise occupied by phenylalanine. We present evidence that LARP4 expression stimulates luciferase reporter activity by promoting mRNA stability, as shown by mRNA decay analysis of luciferase and cellular mRNAs. We propose that LARP4 activity is integrated with other PAM2 protein activities by PABP as part of mRNA homeostasis.

Epidemiology and patterns of care of patients admitted to Italian Intensive Cardiac Care units: the BLITZ-3 registry

BACKGROUND

Intensive cardiac care units (ICCUs) have shifted from the observation of patients with myocardial infarction to the care of different acute cardiac diseases. However, few data on such an evolution are available.

METHODS AND RESULTS

From 7 to 20 April 2008, 6986 consecutive patients admitted to 81% of Italian ICCUs were prospectively enrolled. Patients observed were mainly elderly men (median age 72 years) with several co-morbidities. Most of them were triaged to ICCU from the emergency room, but 15% of admissions were transfer-in from other hospitals. Several diagnostic and therapeutic procedures were applied (78% had echocardiography and 35% coronary angiography) during the ICCU stay [median length 4 days, interquartile range (IQR) 2-5]. The discharge diagnosis was ST-elevation acute coronary syndrome (ACS) in 21%, non-ST-elevation ACS in 31%, acute heart failure (AHF) in 14% and other acute non-ACS, non-AHF cardiac diseases in 34%. Of those with ST-elevation ACS, 60% received reperfusion (15% fibrinolysis and 45% primary percutaneous coronary intervention). The overall in-ICCU crude mortality was 3.3%.

CONCLUSION

The BLITZ-3 survey provides a unique snapshot of current epidemiology and patterns of care of patients admitted to ICCUs. Although ACS still remains the most frequent admission diagnosis, the number of non-ACS patients is substantial. However, the correct standard of care for these non-ACS patients has to be defined.

Heterodimerization of the human RNase P/MRP subunits Rpp20 and Rpp25 is a prerequisite for interaction with the P3 arm of RNase MRP RNA

Rpp20 and Rpp25 are two key subunits of the human endoribonucleases RNase P and MRP. Formation of an Rpp20–Rpp25 complex is critical for enzyme function and sub-cellular localization. We present the first detailed in vitro analysis of their conformational properties, and a biochemical and biophysical characterization of their mutual interaction and RNA recognition. This study specifically examines the role of the Rpp20/Rpp25 association in the formation of the ribonucleoprotein complex. The interaction of the individual subunits with the P3 arm of the RNase MRP RNA is revealed to be negligible whereas the 1:1 Rpp20:Rpp25 complex binds to the same target with an affinity of the order of nM. These results unambiguously demonstrate that Rpp20 and Rpp25 interact with the P3 RNA as a heterodimer, which is formed prior to RNA binding. This creates a platform for the design of future experiments aimed at a better understanding of the function and organization of RNase P and MRP. Finally, analyses of interactions with deletion mutant proteins constructed with successively shorter N- and C-terminal sequences indicate that the Alba-type core domain of both Rpp20 and Rpp25 contains most of the determinants for mutual association and P3 RNA recognition.

Letter to the Editor: resonance assignment of SlyD from E. coli

SlyD from Escherichia coli is a peptidyl-prolyl cis-trans isomerase involved in [Ni-Fe] hydrogenase metallocentre assembly in bacteria. We present here the backbone and side chain assignments for E. coli SlyD.

Getting to the end of RNA: structural analysis of protein recognition of 5' and 3' termini

The specific recognition by proteins of the 5' and 3' ends of RNA molecules is an important facet of many cellular processes, including RNA maturation, regulation of translation initiation and control of gene expression by degradation and RNA interference. The aim of this review is to survey recent structural analyses of protein binding domains that specifically bind to the extreme 5' or 3' termini of RNA. For reasons of space and because their interactions are also governed by catalytic considerations, we have excluded enzymes that modify the 5' and 3' extremities of RNA. It is clear that there is enormous structural diversity among the proteins that have evolved to bind to the ends of RNA molecules. Moreover, they commonly exhibit conformational flexibility that appears to be important for binding and regulation of the interaction. This flexibility has sometimes complicated the interpretation of structural results and presents significant challenges for future investigations.

The interaction of the Escherichia coli protein SlyD with nickel ions illuminates the mechanism of regulation of its peptidyl-prolyl isomerase activity

The sensitive to lysis D (SlyD) protein from Escherichia coli is related to the FK506-binding protein family, and it harbours both peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone-like activity, preventing aggregation and promoting the correct folding of other proteins. Whereas a functional role of SlyD as a protein-folding catalyst in vivo remains unclear, SlyD has been shown to be an essential component for [Ni-Fe]-hydrogenase metallocentre assembly in bacteria. Interestingly, the isomerase activity of SlyD is uniquely modulated by nickel ions, which possibly regulate its functions in response to external stimuli. In this work, we investigated the solution structure of SlyD and its interaction with nickel ions, enabling us to gain insights into the molecular mechanism of this regulation. We have revealed that the PPIase module of SlyD contains an additional C-terminal alpha-helix packed against the catalytic site of the domain; unexpectedly, our results show that the interaction of SlyD with nickel ions entails participation of the novel structural features of the PPIase domain, eliciting structural alterations of the catalytic pocket. We suggest that such conformational rearrangements upon metal binding underlie the ability of nickel ions to regulate the isomerase activity of SlyD.

NMR assignment of the N-terminal region of human La free and in complex with RNA

(1)H, (15)N and (13)C chemical shift assignments are presented for the N-terminal region of human La protein, in the apo and 5'-UUUU RNA-bound state. Secondary structure analysis shows conformational changes in the interdomain linker upon complex formation.

Structural analysis reveals conformational plasticity in the recognition of RNA 3' ends by the human La protein

The eukaryotic La protein recognizes the 3' poly(U) sequences of nascent RNA polymerase III transcripts to assist folding and maturation. The 3' ends of such RNAs are bound by the N-terminal domain of La (LaNTD). We have solved the crystal structures of four LaNTD:RNA complexes, each containing a different single-stranded RNA oligomer, and compared them to the structure of a previously published LaNTD:RNA complex containing partially duplex RNA. The presence of purely single-stranded RNA in the binding pocket at the interface between the La motif and RRM domains allows significantly closer contact with the 3' end of the RNA. Comparison of the different LaNTD:RNA complexes identifies a conserved set of interactions with the last two nucleotides at the 3' end of the RNA ligand that are key to binding. Strikingly, we also observe two alternative conformations of bound ssRNA, indicative of an unexpected degree of plasticity in the modes of RNA binding.

Primary angioplasty and routine utilization of thrombus aspiration devices: feasibility and results in a consecutive series of 486 patients

BACKGROUND

Primary percutaneous transluminal coronary angioplasty (PTCA) is the treatment of choice for acute ST-segment elevation myocardial infarction (STEMI) in high-volume centres with experienced operators, but is often limited by a suboptimal microvascular perfusion due to distal embolization and impaired myocardial perfusion. The present study investigates whether routine use of thrombus aspiration (TA) devices is feasible in daily practice, along with its safety and effectiveness.

METHODS

This study is based on a series of 486 consecutive STEMI patients treated at our single institution by the same three operators (from 2001 to 2005). They underwent primary PTCA with or without TA according to these angiographic features: infarct related artery (IRA) diameter>or=3 mm; thrombotic occlusion or angiographic evidence of thrombus; absence of severe proximal tortuosity or calcification. We evaluate the efficacy of TA in terms of procedural success, coronary thrombolysis in myocardial infarction (TIMI) flow, myocardial blush grade (MBG), resolution>or=50% of ST segment elevation, and clinical events during hospital stay and at 6-month follow-up.

RESULTS

A total of 486 primary PTCAs were performed, 217 (44.6%) with TA as a first device using RESCUE (n=65), EXPORT (n=140) and DIVER-CE (n=12) catheters. In 141 (65%) cases, macroscopic material was aspirated. The patients submitted to TA were more often males (84.7% versus 71.7%, P<0.05) and younger (age: 61.02+/-11.91 versus 64.47+/-10.59 years, P<0.01) than patients treated with traditional PTCA and the IRA was more frequently occluded at angiography (basal TIMI 0: 70.5% versus 47.9%). Application of the TA did not increase the complexity of the procedure (door-to-balloon times, minutes of fluoroscopy and amount of dye). TA alone was effective to restore TIMI 3 flow in 187 cases (86.2%) as a first device and in three other cases (1.4%) after predilatation with balloon. Direct stenting without predilatation was possible in 144 cases (66.4%) after TA. TA was not effective in 27 cases (12.4%) and this subgroup had both angiographic and clinical unfavourable results in comparison with the effective TA group (final TIMI 1 in 11.1% versus 0.5%, P<0.015; final MBG 1 in 55.5% versus 9.5%, P<0.001; lack of ST segment resolution>or=50% in 44.4% versus 7.9%, P<0.001; in-hospital mortality 14.8% versus 2.6%, P<0.05 and mortality at 6 months 18.5% versus 3.1%, P<0.05). In the whole TA population, final TIMI 3 flow was achieved in 203 cases (93.5%), final MBG 3 in 145 cases (66.8%) and ST segment resolution>or=50% in 185 cases (85.2%), in-hospital mortality was 4.1% and cumulative mortality at 6-month follow-up was 5.5%.

CONCLUSIONS

In our case series, 486 consecutive unselected patients with STEMI were treated in a primary PTCA high-volume centre using TA devices. Our study demonstrates that, in STEMI patients treated with primary PTCA, a routine strategy with TA before angioplasty guided by angiographic selection criteria is feasible in almost 50% of cases, is safe and effective, does not increase procedural time and offers good results in terms of tissue perfusion, both epicardial (TIMI flow) and myocardial (MBG, ST regression). When successfully performed, TA identifies a population with favourable in-hospital and 6-month outcome.

A terminal affair: 3'-end recognition by the human La protein

The La protein, an autoantigen in rheumatic disease, orchestrates several aspects of the metabolism of noncoding RNA molecules. More than 20 years ago it was shown that La primarily binds the 3' UUU-OH tails of nascent transcripts of RNA polymerase III. A recent study now reveals how the structure of the amino-terminal domain of the human La protein achieves specific 3'-end recognition.

Structure of the eukaryotic initiation factor (eIF) 5 reveals a fold common to several translation factors

Eukaryotic initiation factor 5 (eIF5) plays multiple roles in translation initiation. Its N-terminal domain functions as a GTPase-activator protein (GAP) for GTP bound to eIF2, while its C-terminal region nucleates the interactions between multiple translation factors, including eIF1, which acts to inhibit GTP hydrolysis or P(i) release, and the beta subunit of eIF2. These proteins and the events in which they participate are critical for the accurate recognition of the correct start codon during translation initiation. Here, we report the three-dimensional solution structure of the N-terminal domain of human eIF5, comprising two subdomains, both reminiscent of nucleic-acid-binding modules. The N-terminal subdomain contains the "arginine finger" motif that is essential for GAP function but which, unusually, resides in a partially disordered region of the molecule. This implies that a conformational reordering of this portion of eIF5 is likely to occur upon formation of a competent complex for GTP hydrolysis, following the appropriate activation signal. Interestingly, the N-terminal subdomain of eIF5 reveals an alpha/beta fold structurally similar to both the archaeal orthologue of the beta subunit of eIF2 and, unexpectedly, to eIF1. These results reveal a novel protein fold common to several factors involved in related steps of translation initiation. The implications of these observations are discussed in terms of the mechanism of translation initiation.