Aminoglycosides suppress the protein folding activity of the molecular chaperone HSC70: implication of a structure-activity relationship.

BACKGROUND: The mechanism of aminoglycoside (AG)-induced nephrotoxicity has not been fully elucidated. We previously reported that gentamicin suppresses the functions of HSC70, a heat shock cognate protein, which is a cytosolic molecular chaperone in mammalian cells. However, the relationship between HSC70 dysfunction and nephrotoxicity has not been clarified yet. METHODS: The effects of 11 AGs, including gentamicin, on the function, protein refolding and substrate binding of HSC70 were examined in vitro. The protein refolding activity of HSC70 was examined by enzymatic activity restoration of the denatured firefly luciferase. Substrate binding activity of HSC70 was examined by the binding of fluorescent-dye-labeled reduced carboxymethlylated α-lactalbumin determined by HSC70/substrate complex formation by native polyacrylamide gel electrophoresis. RESULTS: Strong inhibitory activity of AGs on the protein refolding activity of HSC70 was observed for arbekacin, gentamicin, neomycin and sisomicin, but not spectinomycin, streptomycin, ribostamycin and paromomycin, and inhibition was weak for tobramycin, amikacin and kanamycin. Neomycin strongly suppressed the formation of the HSC70/substrate complex and had the lowest concentration that resulted in 50% inhibition (IC50; in the order of 10(-4) M). Arbekacin, gentamicin, sisomicin and tobramycin had IC50 values in the order of 10(-3) M. Amikacin, ribostamycin and paromomycin had no effective potencies. CONCLUSIONS: The inhibition efficacies of AGs for protein refolding of HSC70 were as follows: neomycin >> gentamicin, arbekacin, and sisomicin > tobramycin, amikacin and kanamycin > spectinomycin, streptomycin, ribostamycin and paromomycin. Amino groups and/or hydroxyl groups located at 2', 3', 4', and 6' of amino sugar residue II, as well as the number of amino sugar rings were closely associated with the inhibition efficacies of AGs. Inhibition efficacies of AGs towards the function of HSC70 correlated well with the nephrotoxicity of AGs deduced from the in vivo studies previously reported. Amino groups/hydroxyl groups and the number of amino sugar rings of AGs were shown to be important for inhibition efficacies. The results strongly suggest that the AG-induced dysfunction of HSC70 is involved in the nephrotoxicity.

HSC70 from Haemaphysalis flava (Acari: Ixodidae) exerts anticoagulation activity in vitro.

Ticks and tick-borne diseases are major global health threats. During blood feeding, ticks insert their hypostomes into hosts and inject an array of anticoagulant molecules to maintain fluidity of the blood-meal. These anticoagulant molecules may provide insights into understanding the feeding biology of ticks and to develop vaccines against infestations. In Haemaphysalis flava, the heat shock cognate 70 (HSC70), a member of the heat shock protein (HSP) family, is differentially expressed in salivary glands at different levels of engorgement during blood feeding. However, its function in ticks is largely not known. The present study was designed to explore the possible effects of HSC70 on the plasma. The open reading frame (ORF) of HSC70 was expressed in a prokaryotic system, and recombinant HSC70 (rHSC70) was purified and characterized. The anticoagulation activity of rHSC70 was estimated by measuring prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT) and fibrinogen (FIB) with/without its inhibitor, VER155008. The results demonstrated that rHSC70 from H. flava extended TT (P < 0.001) and FIB clotting times (>300 s), but showed little effect on PT and APTT. Adding an inhibitor reversed anticlotting effects of rHSC70 on TT and FIB. These data indicate that rHSC70 is an anticoagulant agent, and the anticlotting activity likely attributes to the inhibition of thrombin and the transformation of fibrinogen into fibrin.

Reconstitution of Clathrin Coat Disassembly for Fluorescence Microscopy and Single-Molecule Analysis.

The disassembly of the clathrin lattice surrounding coated vesicles is the obligatory last step in their life cycle. It is mediated by the coordinated recruitment of auxilin and Hsc70, an ATP-driven molecular clamp. Here, we describe the preparation of reagents and the single-particle fluorescence microscopy imaging assay in which we visualize directly the Hsc70-driven uncoating of synthetic clathrin coats or clathrin-coated vesicles.

Does Japanese encephalitis virus share the same cellular receptor with other mosquito-borne flaviviruses on the C6/36 mosquito cells?

Japanese encephalitis virus (JEV) is a member of mosquito-borne Flaviviridae. To date, the mechanisms of the early events of JEV infection remain poorly understood, and the cellular receptors are unidentified. There are evidences that the structure of the virus attachment proteins (VAP), envelope glycoprotein of mosquito-borne flaviviruses is very similar, and the vector-virus interaction of mosquito-borne flaviviruses is also very similar. Based on the studies previously demonstrated that the similar molecules present on the mosquito cells involved in the uptake process of JEV, West Nile virus (WNV) and Dengue virus (DV), it is proposed that the same receptor molecules for mosquito-borne flaviviruses (JEV, WNV and DV) may present on the surface of C6/36 mosquito cells. By co-immunoprecipitation assay, we investigated a 74-KDa protein on the C6/36 cells binds JEV, and the mass spectrometry results indicated it may be heat shock cognate protein 70(HSC70) from Aedes aegypti. Based upon some other viruses use of heat shock protein 70 (HSP70) family proteins as cell receptors, its possible HSC70's involvement in the fusion of the JEV E protein with the C6/36 cells membrane, and known form of cation channels in the interaction of HSC70 with the lipid bilayer, it will further be proposed that HSC70 as a penetration receptor mediates JEV entry into C6/36 cells.

Heat shock proteins purified from autologous tumors using antibody-based affinity chromatography.

Heat shock proteins (HSP) isolated from autologous tumors have become a promising tool for active-specific anticancer immunotherapy due to their properties as carriers of antigenic peptides on one hand and as immunostimulatory adjuvants on the other. Rapid and efficient isolation of HSP-peptide complexes from a patient's tumor is fundamental for their clinical application. Herein, we describe the purification of the HSP Gp96 and Hsc70/Hsp70 from human autologous tumor sources by one-step antibody-based affinity chromatography. Recombinant anti-Gp96 and anti-Hsp70 single-chain Fv antibodies are covalently coupled to a chromatographic bead resin to obtain highly specific affinity matrices. Chromatographic columns are assembled and then used to simultaneously isolate various HSP from the supernatant of lysates of human tumor samples of different origin in a single chromatographic step.

Identification of a novel human LAP1 isoform that is regulated by protein phosphorylation.

Lamina associated polypeptide 1 (LAP1) is an integral protein of the inner nuclear membrane that is ubiquitously expressed. LAP1 binds to lamins and chromatin, probably contributing to the maintenance of the nuclear envelope architecture. Moreover, LAP1 also interacts with torsinA and emerin, proteins involved in DYT1 dystonia and X-linked Emery-Dreifuss muscular dystrophy disorder, respectively. Given its relevance to human pathological conditions, it is important to better understand the functional diversity of LAP1 proteins. In rat, the LAP1 gene (TOR1AIP1) undergoes alternative splicing to originate three LAP1 isoforms (LAP1A, B and C). However, it remains unclear if the same occurs with the human TOR1AIP1 gene, since only the LAP1B isoform had thus far been identified in human cells. In silico analysis suggested that, across different species, potential new LAP1 isoforms could be generated by alternative splicing. Using shRNA to induce LAP1 knockdown and HPLC-mass spectrometry analysis the presence of two isoforms in human cells was described and validated: LAP1B and LAP1C; the latter is putatively N-terminal truncated. LAP1B and LAP1C expression profiles appear to be dependent on the specific tissues analyzed and in cultured cells LAP1C was the major isoform detected. Moreover, LAP1B and LAP1C expression increased during neuronal maturation, suggesting that LAP1 is relevant in this process. Both isoforms were found to be post-translationally modified by phosphorylation and methionine oxidation and two LAP1B/LAP1C residues were shown to be dephosphorylated by PP1. This study permitted the identification of the novel human LAP1C isoform and partially unraveled the molecular basis of LAP1 regulation.

Target molecules of molecular chaperone (HSP70 family) in injured gastric mucosa in vivo.

AIMS: Several recent studies, including ours, have indicated the importance of heat shock proteins (HSPs) in cytoprotection against cytotoxic agents and environmental stresses mediated by the chaperone function of HSPs (molecular chaperones). However, the target molecule that is recognized by HSPs in damaged cells currently remains unknown. As HSPs rapidly recognize and bind to degenerated protein in cells, target molecules of HSPs might be key molecules for the initiation and pathogenesis of cellular damage. In the present study, gastric mucosal proteins that specifically bind to the HSP70 family (HSC70) were analyzed using HSC70-affinity chromatography. MAIN METHODS: The gastric mucosa was removed from Sprague-Dawley rats after exposure to water immersion-stress for 0, 1, 3 or 5 h. Soluble fractions of each gastric mucosa were applied to the HSC70-affinity column separately. After washing off non-specific binding proteins, specific binding proteins were eluted by ATP-containing buffer. Binding proteins were analyzed by SDS-polyacrylamide gel electrophoresis. In addition, the amino acid sequence of purified proteins was also analyzed. KEY FINDINGS: Specific HSC70-binding proteins with a molecular weight of 200-kDa and 45-kDa were eluted from an affinity column when gastric mucosal homogenate of 1-h stress exposure was applied. The amino acid sequencing showed that these binding proteins were cytoskeletal myosin (heavy chain) and actin, respectively. SIGNIFICANCE: During the pathogenesis of stress-induced gastric mucosal damage, structurally degenerated cytoskeletal myosin (heavy chain) and actin may be key or initiation molecules which structural changes were firstly recognized by molecular chaperone.