Structure-function analysis with tissue-type plasminogen activator. Effect of deletion of NH2-terminal domains on its biochemical and biological properties

Tissue-type plasminogen activator (t-PA) is a mosaic protein containing several distinct structural domains attached to the serine protease catalytic unit present at its COOH terminus. To investigate structure-function relationships in t-PA, we deleted the NH2-terminal domains, finger and epidermal growth factor, by genetic engineering. The genes for the parent and mutant t-PA were expressed in a bovine papilloma virus-dependent mammalian cell system. The secreted proteins were purified to homogeneity. The mutant protein was processed to the expected size of about 60 kDa compared to approximately 68 kDa for the parent t-PA, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fibrin autography. While the mutant t-PA had amidolytic activity comparable to native t-PA, it did not bind appreciably to fibrin. Consequently, fibrin-dependent enzymic activity, i.e. plasminogen activation in the presence of soluble fibrin and fibrinolysis were lower than with native recombinant t-PA. The effect of deletion of NH2-terminal domains on the plasma half-life (t1/2) was investigated by injecting native and mutant t-PA into mice. While the majority of the t-PA disappeared initially with a t1/2 of about 2 min, mutant t-PA cleared at a much slower rate with t1/2 of about 50 min. These findings suggest that the NH2-terminal domains of t-PA not only determine its specificity for binding to fibrin but also mediate its clearance from plasma in vivo. Furthermore, the catalytic unit in t-PA seems to function autonomously.     

Interactions between cadherin-11 and platelet-derived growth factor receptor-alpha signaling link cell adhesion and proliferation

Cadherins are homophilic cell-to-cell adhesion molecules that help cells respond to environmental changes. Newly formed cadherin junctions are associated with increased cell phosphorylation, but the pathways driving this signaling response are largely unknown. Since cadherins have no intrinsic signaling activity, this phosphorylation must occur through interactions with other signaling molecules. We previously reported that cadherin-11 engagement activates joint synovial fibroblasts, promoting inflammatory and degradative pathways important in rheumatoid arthritis (RA) pathogenesis. Our objective in this study was to discover interacting partners that mediate cadherin-11 signaling. Protein array screening showed that cadherin-11 extracellular binding domains linked to an Fc domain (cad11Fc) induced platelet-derived growth factor (PDGFR)-α phosphorylation in synovial fibroblasts and glioblastoma cells. PDGFRs are growth factor receptor tyrosine kinases that promote cell proliferation, survival, and migration in mesodermally derived cells. Increased PDGFR activity is implicated in RA pathology and associates with poor prognosis in several cancers, including sarcoma and glioblastoma. PDGFRα activation by cadherin-11 signaling promoted fibroblast proliferation, a signaling pathway independent from cadherin-11-stimulated IL-6 or matrix metalloproteinase (MMP)-3 release. PDGFRα phosphorylation mediated most of the cad11Fc-induced phosphatidyl-3-kinase (PI3K)/Akt activation, but only part of the mitogen-activated protein kinase (MAPK) response. PDGFRα-dependent signaling did not require cell cadherin-11 expression. Rather, cad11Fc immunoprecipitated PDGFRα, indicating a direct interaction between cadherin-11 and PDGFRα extracellular domains. This study is the first to report an interaction between cadherin-11 and PDGFRα and adds to our growing understanding that cadherin-growth factor receptor interactions help balance the interplay between tissue growth and adhesion.     

A proteomics approach to identifying novel protein targets involved in erinacine A–mediated inhibition of colorectal cancer cells’ aggressiveness

Erinacine A, a major active component of a diterpenoid derivative isolated from Hericium erinaceus mycelium, has been demonstrated to exert anticancer effects. Herein, we present an investigation of the molecular mechanism of erinacine A induction associated with cancer cells’ aggressive status and death. A proteomic approach was used to purify and identify the differentially expressed proteins following erinacine A treatment and the mechanism of its action in apoptotic and the targets of erinacine A. Our results demonstrate that erinacine A treatment of HCT‐116 and DLD‐1 cells increased cell cytotoxicity and reactive oxygen species (ROS) production as well as decreased cell proliferation and invasiveness. Ten differentially displayed proteins were determined and validated in vitro and in vivo between the erinacine A‐treated and untreated groups. In addition, erinacine A time‐dependent induction of cell death and inhibitory invasiveness was associated with sustained phosphorylation of the PI3K/mTOR/p70S6K and ROCK1/LIMK2/Cofilin pathways. Furthermore, we demonstrated that erinacine A–induced HCT‐116 and DLD‐1 cells viability and anti‐invasion properties by up‐regulating the activation of PI3K/mTOR/p70S6K and production of ROS. Experiments involving specific inhibitors demonstrated that the differential expression of cofilin‐1 (COFL1) and profilin‐1 (PROF1) during erinacine A treatment could be involved in the mechanisms of HCT‐116 and DLD‐1 cells death and decreased aggressiveness, which occurred via ROCK1/LIMK2/Cofilin expression, with activation of the PI3K/mTOR/p70S6K signalling pathway. These findings elucidate the mechanism of erinacine A inhibiting the aggressive status of cells by activating PI3K/mTOR/p70S6K downstream signalling and the novel protein targets COF1 and PROF1; this could be a good molecular strategy to limit the aggressiveness of CRC cells.     

Protective effects of several amino acid-nutrients on gastric hemorrhagic erosions in acid-irrigated stomachs of septic rats

Our previous report demonstrates that severe gastric mucosal damage is produced in lipopolysaccharide (LPS)-intoxicated rats. In the present study, we examined protective effects of several amino acids including taurine, phenylalanine and L-Arginine on gastric hemorrhagic erosions in acid-irrigated stomachs of LPS rats. The animals were deprived of food for 24 hr. Intravenous LPS (3 mg/kg) was challenged 12 hr after withdrawal of food. Gastric vagotomy was performed, followed by irrigation the stomachs for 3 hr with a physiological acid solution containing 100 mM HCl and 54 mM NaCl. The ulcerogenic parameters including increased gastric acid back-diffusion, mucosal histamine concentrations, lipid peroxide productions, luminal hemoglobin contents, stomach erosions and the lowered glutathione levels were markedly enhanced in LPS rat stomachs irrigated with acid solution. Both phenylalanine and taurine caused dose-dependent attenuations of these ulcerogenic parameters in LPS rats. L-arginine also was effective in inhibition. The inhibitory effect was restored by pretreatment of nitric oxide synthase inhibitors, such as N(G)-nitro-L-arginine-methyl ester or L-N(G)-(1-iminoethyl)-lysine. Furthermore, marked amelioration of hemorrhagic erosions in LPS rats was observed when a combination of these amino acid nutrients was used. The results provide evidence that these amino acid nutrients may ameliorate gastric hemorrhagic erosion via GSH synthesis stimulation, histamine cell membrane stabilization and antioxidant actions in LPS rat stomachs.     

Ammonium accumulation is associated with senescence of rice leaves

The relationship between ammonium accumulation and senescence of detached rice leaves was investigated. Ammonium accumulation in detached rice leaves coincided closely with dark-induced senescence. Exogenous NH4Cl and methionine sulfoximine, which caused an accumulation of ammonium in detached rice leaves, promoted senescence. Treatments such as light and benzyladenine, which retarded senescence, decreased ammonium level in detached rice leaves. Abscisic acid, which promoted senescence, increased ammonium level in detached rice leaves. The current results suggest that ammonium accumulation may be involved in regulating senescence. Evidence was presented to show that ammonium accumulated in detached rice leaves increases tissue sensitivity to ethylene. The accumulation of ammonium in detached rice leaves during dark-induced senescence is attributed to a decrease in glutamine synthetase activity and an increase in reduction of nitrate.     

Use of the SAMe-TT2R2 Score to Predict Good Anticoagulation Control with Warfarin in Chinese Patients with Atrial Fibrillation: Relationship to Ischemic Stroke Incidence

Background

The efficacy and safety of warfarin therapy for stroke prevention in atrial fibrillation (AF) depends on the time in therapeutic range (TTR). We aimed to assess the predictive ability of SAMe-TT₂R₂ score in Chinese AF patients on warfarin, whose TTR is notoriously poor.

Methods and Results

This is a single-centre retrospective study. Patients with non-valvular AF on warfarin diagnosed between 1997 and 2011 were stratified according to SAMe-TT₂R₂ score, and TTR was calculated using Rosendaal method. The predictive power of SAMe-TT₂R₂ scores for good TTR i.e. >70% was assessed. We included 1,428 Chinese patients (mean age 76.2±8.7 years, 47.5% male) with non-valvular AF on warfarin. The mean and median TTR were 38.2±24.4% and 38.8% (interquartile range: 17.9% and 56.2%) respectively. TTR decreased progressively with increasing SAMe-TT₂R₂ score (p = 0.016). When the cut-off value of SAMe-TT₂R₂ score was set to 2, the sensitivity and specificity to predict TTR<70% were 85.7% and 17.8%, respectively. The corresponding positive and negative predictive values were 10.1% and 92.0%. After a mean follow-up of 4.7±3.6 years, 338 patients developed an ischemic stroke (4.96%/year). Patients with TTR≥70% had a lower annual risk of ischemic stroke of 3.67%/year compared with than those with TTR<70% (5.13%/year)(p = 0.08). Patients with SAMe-TT₂R₂ score ≤2 had the lowest risk of annual risk of ischemic stroke (3.49%/year) compared with those with SAMe-TT₂R₂ score = 3 (4.56%/year), and those with SAMe-TT₂R₂ score ≥4 (6.41%/year)(p<0.001). There was also a non-significant trend towards more intracranial hemorrhage with increasing SAMe-TT₂R₂ score.

Conclusions

The SAMe-TT₂R₂ score correlates well with TTR in Chinese AF patients, with a score >2 having high sensitivity and negative predictive values for poor TTR. Ischemic stroke risk increased progressively with increasing SAMe-TT₂R₂ score, consistent with poorer TTRs at high SAMe-TT₂R₂ scores.     

Ethanol production from selected lignocellulosic hydrolysates by genome shuffled strains of Scheffersomyces stipitis

Two genome-shuffled Scheffersomyces stipitis strains, GS301 and GS302, exhibiting improved tolerance to hardwood spent sulphite liquor, were tested for growth and fermentation performance on three wood hydrolysates: (a) steam-pretreated enzymatically hydrolyzed poplar hydrolysate from Mascoma Canada, (b) steam pretreated poplar hydrolysate from University of British Columbia Forest Products Biotechnology Laboratory, and (c) mixed hardwoods pre-hydrolysate from FPInnovations (FPI). In the FPI hydrolysate, the wild type (WT) died off within 25 h, while GS301 and GS302 survived beyond 100 h. In fermentation tests, GS301 and GS302 completely utilized glucose and xylose in each hydrolysate and produced 0.39–1.4% (w/v) ethanol. In contrast, the WT did not utilize or poorly utilized glucose and xylose and produced non-detectable to trace amounts of ethanol. The results demonstrated cross tolerance of the mutants to inhibitors in three different wood hydrolysates and reinforced the utility of mating-based genome shuffling approach in industrial yeast strain improvement.     

Antizyme, a natural ornithine decarboxylase inhibitor, induces apoptosis of haematopoietic cells through mitochondrial membrane depolarization and caspases’ cascade

Antizymes delicately regulate ornithine decarboxylase (ODC) enzyme activity and polyamine transportation. One member of the family, antizyme-1, plays vital roles in molecular and cellular functions, including developmental regulation, cell cycle, proliferation, cell death, differentiation and tumorigenesis. However, the question of how does it participate in the cell apoptotic mechanism is still unsolved. To elucidate the contribution of human antizyme-1 in haematopoietic cell death, we examine whether inducible overexpression of antizyme enhances apoptotic cell death. Antizyme reduced the viability in a dose- and time-dependent manner of human leukemia HL-60 cells, acute T leukemia Jurkat cells and mouse macrophage RAW 264.7 cells. The apoptosis-inducing activities were determined by nuclear condensation, DNA fragmentation, sub-G₁ appearance, loss of mitochondrial membrane potential (Δψ _m ), release of mitochondrial cytochrome c into cytoplasm and proteolytic activation of caspase 9 and 3. Following conditional antizyme overexpression, all protein levels of cyclin-dependent kinases (Cdks) and cyclins are not significantly reduced, except cyclin D, before their entrance into apoptotic cell death. However, introduced cyclin D1 into Jurkat T tetracycline (Tet)-On cell system still couldn’t rescue cells from apoptosis. Antizyme doesn’t influence the expression of tumor suppressor p53 and its downstream p21, but it interferes in the expressions of Bcl-2 family. Inducible antizyme largely enters mitochondria resulting in cytochrome c release from mitochondria to cytosol following Bcl-xL decrease and Bax increase. According to these data, we suggest that antizyme induces apoptosis mainly through mitochondria-mediated and cell cycle-independent pathway. Furthermore, antizyme induces apoptosis not only by Bax accumulation reducing the function of the Bcl-2 family, destroying the Δψ _m , and releasing cytochrome c to cytoplasm but also by the activation of apoptosomal caspase cascade.     

Investigation of the Role of a Conserved Glycine Motif in the Saccharomyces cerevisiae Xylose Reductase

All yeast xylose reductases, with the exception of that from Schizosaccharomyces pombe, possess the catalytic and coenzyme-binding elements from both the aldo–keto reductase and short-chain dehydrogenase–reductase (SDR) enzyme families in their primary sequences. In the Saccharomyces cerevisiae xylose reductase (XR), the SDR-like coenzyme-binding GXXXGXG motif (Gly motif) is located between residues 128 and 134, with the third Gly residue being replaced by an Asp. We used site-directed mutagenesis to study the role of this SDR-like Gly motif in the S. cerevisiae xylose reductase. Site-directed mutagenesis of the individual conserved Gly residue positions (G128A, G132A, D134G, and D134A) did not significantly affect the specific activity, kinetic constants (K_m, K_cat, and K_cat/K_m), or dissociation constants (K_d) in any of the variants compared with the wild type. Deletion of the entire Gly motif produced an unstable protein that could not be purified. These results indicate that the SDR-like Gly motif likely provides support to the overall structure of the enzyme, but it does not contribute directly to coenzyme binding in this XR.     

Membrane lysis by the antibacterial peptides cecropins B1 and B3: A spin-label electron spin resonance study on phospholipid bilayers

Custom antibacterial peptides, cecropins B1 (CB1) and B3 (CB3), were synthesized. These peptides have particular sequence characteristics, with CB1 having two amphipathic alpha-helical segments and CB3 having two hydrophobic alpha-helical segments. These differences were exploited for a study of their efficacy in breaking up liposomes, which had different combinations of phosphatidic acid (PA) and phosphatidylcholine (PC), and a study of their lipid binding ability. Binding and nonbinding lysis actions of CB1 and CB3 on liposomes were examined further by electron spin resonance (ESR). The spin-labeled lipids 5'SL-PC, 7'SL-PC, 10'SL-PC, 12'SL-PC, and 16'SL-PC were used as probes. The ESR spectra revealed larger outer hyperfine splittings (2A(max)) for CB1 when the interactions of CB1 and CB3 with liposomes were compared. These observations indicate a larger restriction of the motion of the spin-labeled chains in the presence of CB1. Plots of the effective order parameter at the various probe positions (chain flexibility gradient) versus the peptide-lipid ratio further suggested that the lysis action of CB1 is related to its capacity to bind to the lipid bilayers. In contrast, there is no evidence of binding for CB3. To augment these findings, four spin-labeled peptides, C8SL-CB1, C32SL-CB1, C5SL-CB3, and C30SL-CB3, were also examined for their binding to and their state of aggregation within the lipid bilayers. Association isotherms of the peptides were measured for liposomes containing two molar fractions of PA (0.25 and 0.75). The membrane binding of the CB1 peptides exhibited a cooperative behavior, whereas the association isotherm of CB3 revealed binding to the lipid only for beta = 0.75 liposomes. To further identify the location of CB1 in the lipid bilayers, measurements of the collision rate with chromium oxalate in solution were conducted. Results from ESR power saturation measurements suggested that the NH(2)-terminal alpha-helix of CB1 is located on the surface of the lipid bilayers, whereas the COOH-terminal alpha-helix of CB1 is embedded below the surface of the lipid bilayers. These conclusions were further supported by the observed relationship between the partition distribution of peptides bound to liposomes at different PA/PC ratios and the amounts of free peptides. Based on the above observations, possible mechanisms of the bilayer lysis induced by CB1 and CB3 on liposomes of different composition are discussed.