Structural basis for cytoplasmic dynein-1 regulation by Lis1.

The lissencephaly 1 gene, LIS1, is mutated in patients with the neurodevelopmental disease lissencephaly. The Lis1 protein is conserved from fungi to mammals and is a key regulator of cytoplasmic dynein-1, the major minus-end-directed microtubule motor in many eukaryotes. Lis1 is the only dynein regulator known to bind directly to dynein's motor domain, and by doing so alters dynein's mechanochemistry. Lis1 is required for the formation of fully active dynein complexes, which also contain essential cofactors: dynactin and an activating adaptor. Here, we report the first high-resolution structure of the yeast dynein-Lis1 complex. Our 3.1 Å structure reveals, in molecular detail, the major contacts between dynein and Lis1 and between Lis1's ß-propellers. Structure-guided mutations in Lis1 and dynein show that these contacts are required for Lis1's ability to form fully active human dynein complexes and to regulate yeast dynein's mechanochemistry and in vivo function.

Lp-PLA2 activity and mass and CRP are associated with incident symptomatic peripheral arterial disease.

Long follow up is needed in prospective cohort study evaluation of plasma biomarkers for incident peripheral arterial disease (PAD) Middle-aged PAD-free individuals from the cardiovascular cohort of the Malmö Diet and Cancer study (n = 5550; 1991-94) were followed prospectively for a median time of 23.4 years. The plasma biomarkers lipoprotein-associated phospholipase A2 (Lp-PLA2) activity and mass, proneurotensin, and CRP, were studied in relation to incidence of PAD until December 31st, 2016. The diagnosis of PAD could be validated and confirmed in 98%. Cox regression was used to calculate hazard ratios (HR) per 1 standard deviation increment of each respective log transformed plasma biomarker. Cumulative incidence of PAD was 4.4% (men 5.9%, women 3.3%). Adjusting for age, gender, smoking, body mass index, hypertension, diabetes mellitus, Lp-PLA2 activity (HR 1.33; 95% CI 1.17-1.52), Lp-PLA2 mass (HR 1.20; 95% CI 1.05-1.37) and CRP (HR 1.55; 95% CI 1.36-1.76) remained independently associated with incident PAD. The plasma biomarkers Lp-PLA2 activity and mass, and CRP were markers of PAD risk, implying that they might be useful biomarkers for subclinical atherosclerosis and atherosclerotic disease.

Lis1 Has Two Opposing Modes of Regulating Cytoplasmic Dynein.

Regulation is central to the functional versatility of cytoplasmic dynein, a motor involved in intracellular transport, cell division, and neurodevelopment. Previous work established that Lis1, a conserved regulator of dynein, binds to its motor domain and induces a tight microtubule-binding state in dynein. The work we present here-a combination of biochemistry, single-molecule assays, and cryoelectron microscopy-led to the surprising discovery that Lis1 has two opposing modes of regulating dynein, being capable of inducing both low and high affinity for the microtubule. We show that these opposing modes depend on the stoichiometry of Lis1 binding to dynein and that this stoichiometry is regulated by the nucleotide state of dynein's AAA3 domain. The low-affinity state requires Lis1 to also bind to dynein at a novel conserved site, mutation of which disrupts Lis1's function in vivo. We propose a new model for the regulation of dynein by Lis1.

Identification of a multifunctional docking site on the catalytic unit of phosphodiesterase-4 (PDE4) that is utilised by multiple interaction partners.

Cyclic AMP (cAMP)-specific phosphodiesterase-4 (PDE4) enzymes underpin compartmentalised cAMP signalling by localising to distinct signalling complexes. PDE4 long isoforms can be phosphorylated by mitogen-activated protein kinase-activated protein kinase 2 (MK2), which attenuates activation of such enzymes through their phosphorylation by protein kinase A. Here we show that MK2 interacts directly with PDE4 long isoforms and define the sites of interaction. One is a unique site that locates within the regulatory upstream conserved region 1 (UCR1) domain and contains a core Phe141, Leu142 and Tyr143 (FLY) cluster (PDE4A5 numbering). Located with the second site is a critical core Phe693, Glu694, Phe695 (FQF) motif that is also employed in the sequestering of PDE4 long forms by an array of other signalling proteins, including the signalling scaffold ß-arrestin, the tyrosyl kinase Lyn, the SUMOylation E2 ligase UBC9, the dynein regulator Lis1 (PAFAH1B1) and the protein kinase Erk. We propose that the FQF motif lies at the heart of a multifunctional docking (MFD) site located within the PDE4 catalytic unit. It is clear from our data that, as well as aiding fidelity of interaction, the MFD site confers exclusivity of binding between PDE4 and a single specific partner protein from the cohort of signalling proteins whose interaction with PDE4 involves the FQF motif.

Two microtubule-plus-end binding proteins LIS1-1 and LIS1-2, homologues of human LIS1 in Neurospora crassa.

LIS1 is a microtubule (Mt) plus-end binding protein that interacts with the dynein/dynactin complex. In humans, LIS1 is required for proper nuclear and organelle migration during cell growth. Although gene duplication is absent from Neurospora crassa, we found two paralogues of human LIS1. We named them LIS1-1 and LIS1-2 and studied their dynamics and function by fluorescent tagging. At the protein level, LIS1-1 and LIS1-2 were very similar. Although, the characteristic coiled-coil motif was not present in LIS1-2. LIS1-1-GFP and LIS1-2-GFP showed the same cellular distribution and dynamics, but LIS1-2-GFP was less abundant. Both LIS1 proteins were found in the subapical region as single fluorescent particles traveling toward the cell apex, they accumulated in the apical dome forming prominent short filament-like structures, some of which traversed the Spitzenkörper (Spk). The fluorescent structures moved exclusively in anterograde fashion along straight paths suggesting they traveled on Mts. There was no effect in the filament behavior of LIS1-1-GFP in the Δlis1-2 mutant but the dynamics of LIS1-2-GFP was affected in the Δlis1-1 mutant. Microtubular integrity and the dynein-dynactin complex were necessary for the formation of filament-like structures of LIS1-1-GFP in the subapical and apical regions; however, conventional kinesin (KIN-1) was not. Deletion mutants showed that the lack of lis1-1 decreased cell growth by ∼75%; however, the lack of lis1-2 had no effect on growth. A Δlis1-1;Δlis1-2 double mutant showed slower growth than either single mutant. Conidia production was reduced but branching rate increased in Δlis1-1 and the Δlis1-1;Δlis1-2 double mutants. The absence of LIS1-1 had a strong effect on Mt organization and dynamics and indirectly affected nuclear and mitochondrial distribution. The absence of LIS1-1 filaments in dynein mutants (ropy mutants) or in benomyl treated hyphae indicates the strong association between this protein and the regulation of the dynein-dynactin complex and Mt organization. LIS1-1 and LIS1-2 had a high amino acid homology, nevertheless, the absence of the coiled-coil motif in LIS1-2 suggests that its function or regulation may be distinct from that of LIS1-1.

Lis1 acts as a "clutch" between the ATPase and microtubule-binding domains of the dynein motor.

The lissencephaly protein Lis1 has been reported to regulate the mechanical behavior of cytoplasmic dynein, the primary minus-end-directed microtubule motor. However, the regulatory mechanism remains poorly understood. Here, we address this issue using purified proteins from Saccharomyces cerevisiae and a combination of techniques, including single-molecule imaging and single-particle electron microscopy. We show that rather than binding to the main ATPase site within dynein's AAA+ ring or its microtubule-binding stalk directly, Lis1 engages the interface between these elements. Lis1 causes individual dynein motors to remain attached to microtubules for extended periods, even during cycles of ATP hydrolysis that would canonically induce detachment. Thus, Lis1 operates like a "clutch" that prevents dynein's ATPase domain from transmitting a detachment signal to its track-binding domain. We discuss how these findings provide a conserved mechanism for dynein functions in living cells that require prolonged microtubule attachments.

The study of ghrelin deacylation enzymes.

Like other posttranslational modifications, fatty acid modification of amino acid residues in peptide chains is a critical determinant of their functional properties. A unique feature of ghrelin is the attachment of an acyl moiety at the third serine residue. Ghrelin is a hormone present in the circulation with roles in the release of growth hormone, control of behaviors related to appetite, and diverse cellular functions. Although lipid modification of ghrelin is essential for its binding to the ghrelin receptor, several lines of evidence suggest that deacylated ghrelin has physiological activity or activities similar to and distinct from the activities of the acylated form. Therefore, the understanding of deacylating process of ghrelin in vivo is key to accepting the physiological importance of ghrelin. In this review, we summarize results and methodology relevant to our recent efforts to determine the molecular mechanisms involved in ghrelin processing, including (1) immunological and mass spectrometry-based detection of ghrelin, (2) quantification of ghrelin deacylase activity, and (3) characterization of ghrelin deacylation enzymes isolated from biological fluids and using heterologous expression systems.

Naturally occurring human plasminogen, like genetically related apolipoprotein(a), contains oxidized phosphatidylcholine adducts.

Human apolipoprotein(a) (apo(a)), synthesized in the liver, contains oxidized phosphatidylcholine (oxPtdPC) adducts probably generated at the hepatic site. Since plasminogen (Plg), also synthesized in the liver, is genetically related and structurally homologous to apo(a), we wanted to determine whether it contains oxPtdPCs and their location. We used Plg isolated from fresh or frozen normal human plasma and several commercial preparations. Some were freed of non-covalently bound lipids by organic solvent extraction. By immunoblot analyses, all products reacted against T15, a natural IgM monoclonal antibody specific for phosphorylcholine -containing oxidized phospholipids (ox-PLs). This immunoreactivity was retained in urokinase type plasminogen activator -generated plasmin and was abrogated in Plg previously digested with lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), a reaction that generated predominantly C16:0 lysophosphatidylcholine species as determined by mass spectrometry. Lyso derivatives were also generated upon the cleavage by Lp-PLA2 of a model ox-PL chemically linked to a lysine-containing pentapeptide. From inorganic phosphorous analyses, we found 2 mol of oxPtdPC/mole of Plg distributed between the kringles 1-4 and mini-Plg domain. OxPtdPCs were also present in the Plg isolated from the serum-free medium of cultured human HepG2 cells. In conclusion, our results provide strong evidence that naturally occurring Plg contains oxPtdPC probably linked by a Schiff base and also suggest that the linkage occurs at the hepatic site. Given the emerging evidence for the cardiovascular pathogenicity of oxPtdPCs, we speculate that they may impart athero-thrombogenic properties to Plg under inflammatory conditions.

Novel mechanism for regulation of plasma platelet-activating factor acetylhydrolase expression in mammalian cells.

The plasma form of PAF-AH [PAF (platelet-activating factor) acetylhydrolase; also known as LpPLA(2) (lipopoprotein-associated phospholipase A(2)), PLA(2)G7] catalyses the release of sn-2 fatty acyl residues from PAF, oxidatively fragmented phospholipids, and esterified isoprostanes. The plasma levels of this enzyme vary widely among mammalian species, including mice and humans, but the mechanisms that account for these differences are largely unknown. We investigated the basis for these variations using molecular and biochemical approaches. We identified an N-terminal domain that played key roles in the determination of steady-state expression levels. The mouse N-terminal domain robustly enhanced protein expression levels, possibly owing to its ability to adopt a globular conformation that is absent in the human protein. We investigated the mechanism(s) whereby the N-terminal stretch modulated PAF-AH levels and found that differential expression was not due to variations in the efficiency of transcription, translation, or mRNA stability. Studies designed to evaluate the ability of precursor forms of PAF-AH to mature to fully active proteins indicated that the N-terminal end of human and mouse PAF-AH played important and opposite roles in this process. These domains also modulated the levels of expression of an unrelated polypeptide by affecting the stability of precursor forms of the protein. These studies provide insights that contribute to our understanding of the molecular features and mechanisms that contribute to differential expression of plasma PAF-AH in mammals.

Ndel1 palmitoylation: a new mean to regulate cytoplasmic dynein activity.

Regulated activity of the retrograde molecular motor, cytoplasmic dynein, is crucial for multiple biological activities, and failure to regulate this activity can result in neuronal migration retardation or neuronal degeneration. The activity of dynein is controlled by the LIS1-Ndel1-Nde1 protein complex that participates in intracellular transport, mitosis, and neuronal migration. These biological processes are subject to tight multilevel modes of regulation. Palmitoylation is a reversible posttranslational lipid modification, which can dynamically regulate protein trafficking. We found that both Ndel1 and Nde1 undergo palmitoylation in vivo and in transfected cells by specific palmitoylation enzymes. Unpalmitoylated Ndel1 interacts better with dynein, whereas the interaction between Nde1 and cytoplasmic dynein is unaffected by palmitoylation. Furthermore, palmitoylated Ndel1 reduced cytoplasmic dynein activity as judged by Golgi distribution, VSVG and short microtubule trafficking, transport of endogenous Ndel1 and LIS1 from neurite tips to the cell body, retrograde trafficking of dynein puncta, and neuronal migration. Our findings indicate, to the best of our knowledge, for the first time that Ndel1 palmitoylation is a new mean for fine-tuning the activity of the retrograde motor cytoplasmic dynein.

The proangiogenic phenotype of tumor-derived endothelial cells is reverted by the overexpression of platelet-activating factor acetylhydrolase.

PURPOSE: We previously reported that human tumor-derived endothelial cells (TEC) have an angiogenic phenotype related to the autocrine production of several angiogenic factors. The purpose of the present study was to evaluate whether an enhanced synthesis of platelet-activating factor (PAF) might contribute to the proangiogenic characteristics of TEC and whether its inactivation might inhibit angiogenesis. EXPERIMENTAL DESIGN: To address the potential role of PAF in the proangiogenic characteristics of TEC, we engineered TEC to stably overexpress human plasma PAF-acetylhydrolase (PAF-AH), the major PAF-inactivating enzyme, and we evaluated in vitro and in vivo angiogenesis. RESULTS: TECs were able to synthesize a significantly enhanced amount of PAF compared with normal human microvascular endothelial cells when stimulated with thrombin, vascular endothelial growth factor, or soluble CD154. Transfection of TEC with PAF-AH (TEC-PAF-AH) significantly inhibited apoptosis resistance and spontaneous motility of TEC. In addition, PAF and vascular endothelial growth factor stimulation enhanced the motility and adhesion of TEC but not of TEC-PAF-AH. In vitro, TEC-PAF-AH lost the characteristic ability of TEC to form vessel-like structures when plated on Matrigel. Finally, when cells were injected s.c. within Matrigel in severe combined immunodeficiency mice or coimplanted with a renal carcinoma cell line, the overexpression of PAF-AH induced a significant reduction of functional vessel formation. CONCLUSIONS: These results suggest that inactivation of PAF, produced by TEC, by the overexpression of plasma PAF-AH affects survival, migration, and the angiogenic response of TEC both in vitro and in vivo.

Purification and characterization of 45 kDa PAF acetylhydrolase from bovine colostrum.

Platelet activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine; PAF) acetylhydrolase (PAF-AH) activity has been identified in bovine colostrum and high levels of this activity are found in early colostrum (within 24 h after parturition). In this study, PAF-AH in early colostrum was purified by ammonium sulfate precipitation, and sequential use of butyl-Toyopearl 650M, DEAE-Sepharose, heparin-Sepharose, hydroxyapatite, chelating-Sepharose and Mono Q HPLC column chromatography. This enzyme is a monomeric polypeptide with a molecular weight of approximately 45 kDa on 12.5% SDS-PAGE. The V(max) and K(m) for PAF-AH were 87.6 microM and 7.96 nmol/min/mg respectively. This enzyme was inhibited by phenylmethylsulfonyl fluoride, iodoacetamide and p-bromophenacylbromide, suggesting that both serine and histidine residues are required for enzyme activity. It was not inactivated by NaF or dithiothreitol. The purified enzyme did not degrade phospholipids with a long chain fatty acyl group at the sn-2 position. Accordingly, this enzyme is distinct from phospholipase A(2). In addition, PAF-AH selectively hydrolyzed oxidatively modified phosphatidylcholine. Furthermore, this enzyme was shown by Western blot analysis using antibody to human plasma PAF-AH to be plasma type PAF-AH. These results clearly demonstrate that 45 kDa plasma type PAF-AH activity exists in bovine colostrum.

cDNA cloning and expression of biologically active platelet activating factor-acetylhydrolase (PAF-AH) from bovine mammary gland.

Platelet activating factor (PAF)-acetylhydrolase (PAF-AH) is an enzyme that hydrolyzes the acetyl ester at the sn-2 position of PAF, and converts it to the inactive metabolite, lyso PAF. This enzyme is distributed widely in the intracellular as well as the extracellular matrix and is believed to be a defense mechanism that protects the host against the toxic effects of PAF and other biologically active oxidized phospholipids. Purification and expression of cDNA cloning of the intracellular and extracellular types of PAF-AH from several sources from different species have been reported. In this study, the cDNA for PAF-AH was cloned by reverse transcription (RT)-PCR from total RNA of bovine mammary gland. The complete amino acid sequences from the cDNA contains 444 amino acids and was identical to that of the PAF-AH isolated from the bovine spleen cDNA library except for two mismatches of amino acid residues (Thr-247 to Met and Ile-431 to Thr). Recombinant PAF-AH was expressed in HEK 293 cells, which exhibited enzyme activity in the in vitro assay system. Furthermore, recombinant bovine PAF-AH was identified by western blot using human plasma PAF-AH antibody as a monomeric polypeptide with a molecular weight of approximately 43 kDa. This protein can be applied to in vivo models to test its protective role against the deleterious PAF actions.

Coupling PAF signaling to dynein regulation: structure of LIS1 in complex with PAF-acetylhydrolase.

Mutations in the LIS1 gene cause lissencephaly, a human neuronal migration disorder. LIS1 binds dynein and the dynein-associated proteins Nde1 (formerly known as NudE), Ndel1 (formerly known as NUDEL), and CLIP-170, as well as the catalytic alpha dimers of brain cytosolic platelet activating factor acetylhydrolase (PAF-AH). The mechanism coupling the two diverse regulatory pathways remains unknown. We report the structure of LIS1 in complex with the alpha2/alpha2 PAF-AH homodimer. One LIS1 homodimer binds symmetrically to one alpha2/alpha2 homodimer via the highly conserved top faces of the LIS1 beta propellers. The same surface of LIS1 contains sites of mutations causing lissencephaly and overlaps with a putative dynein binding surface. Ndel1 competes with the alpha2/alpha2 homodimer for LIS1, but the interaction is complex and requires both the N- and C-terminal domains of LIS1. Our data suggest that the LIS1 molecule undergoes major conformational rearrangement when switching from a complex with the acetylhydrolase to the one with Ndel1.

Anti-apoptotic actions of the platelet-activating factor acetylhydrolase I alpha2 catalytic subunit.

Platelet-activating factor (PAF) is an important mediator of cell loss following diverse pathophysiological challenges, but the manner in which PAF transduces death is not clear. Both PAF receptor-dependent and -independent pathways are implicated. In this study, we show that extracellular PAF can be internalized through PAF receptor-independent mechanisms and can initiate caspase-3-dependent apoptosis when cytosolic concentrations are elevated by approximately 15 pM/cell for 60 min. Reducing cytosolic PAF to less than 10 pM/cell terminates apoptotic signaling. By pharmacological inhibition of PAF acetylhydrolase I and II (PAF-AH) activity and down-regulation of PAF-AH I catalytic subunits by RNA interference, we show that the PAF receptor-independent death pathway is regulated by PAF-AH I and, to a lesser extent, by PAF-AH II. Moreover, the anti-apoptotic actions of PAF-AH I are subunit-specific. PAF-AH I alpha1 regulates intracellular PAF concentrations under normal physiological conditions, but expression is not sufficient to reduce an acute rise in intracellular PAF levels. PAF-AH I alpha2 expression is induced when cells are deprived of serum or exposed to apoptogenic PAF concentrations limiting the duration of pathological cytosolic PAF accumulation. To block PAF receptor-independent death pathway, we screened a panel of PAF antagonists (CV-3988, CV-6209, BN 52021, and FR 49175). BN 52021 and FR 49175 accelerated PAF hydrolysis and inhibited PAF-mediated caspase 3 activation. Both antagonists act indirectly to promote PAF-AH I alpha2 homodimer activity by reducing PAF-AH I alpha1 expression. These findings identify PAF-AH I alpha2 as a potent anti-apoptotic protein and describe a new means of pharmacologically targeting PAF-AH I to inhibit PAF-mediated cell death.