Plerixafor and resatorvid inhibit hepatitis B virus in vitro by upregulating elongation factor Tu GTP-binding domain containing 2.

Background: An increase in the demand for a functional cure has accelerated research on new methods of therapy for chronic hepatitis B, which is mainly focused on restoring antiviral immunity for controlling viral infections. Previously, we had described elongation factor Tu GTP-binding domain containing 2 (EFTUD2) as an innate immune regulator and suggested that it might be an antiviral target. Methods: In this study, we generated the Epro-LUC-HepG2 cell model for screening compounds that target EFTUD2. Plerixafor and resatorvid were screened from 261 immunity and inflammation-related compounds due to their ability to highly upregulate EFTUD2. The effects of plerixafor and resatorvid on hepatitis B virus (HBV) were examined in HepAD38 cells and HBV-infected HepG2-NTCP cells. Results: The dual-luciferase reporter assays showed that the EFTUD2 promoter hEFTUD2pro-0.5 kb had the strongest activity. In Epro-LUC-HepG2 cells, plerixafor and resatorvid significantly upregulated the activity of the EFTUD2 promoter and the expression of the gene and protein. In HepAD38 cells and HBV-infected HepG2-NTCP cells, treatment with plerixafor and resatorvid strongly inhibited HBsAg, HBV DNA, HBV RNAs, and cccDNA in a dose-dependent manner. Furthermore, the anti-HBV effect was enhanced when entecavir was administered along with either of the previous two compounds, and the effect could be blocked by knocking down EFTUD2. Conclusion: We established a convenient model for screening compounds that target EFTUD2 and further identified plerixafor and resatorvid as novel HBV inhibitors in vitro. Our findings provided information on the development of a new class of anti-HBV agents that act on host factors rather than viral enzymes.

Cell surface-associated protein elongation factor Tu interacts with fibronectin mediating the adhesion of Lactobacillus plantarum HC-2 to Penaeus vannamei intestinal epithelium and inhibiting the apoptosis induced by LPS and pathogen in Caco-2 cells.

The adherent colonization of lactic acid bacteria in the animal intestine is the basis for their probiotic effect, and their bacteria surface proteins play an important role in this process. Previous work has demonstrated that Lactobacillus plantarum HC-2 can adhere and colonize the intestine of Penaeus vannamei, modulate the intestinal immune response and microbial diversity, protect the intestinal tissues from pathogenic damage, and improve the protection rate of shrimp. The aim of this work was to identify adhesion molecules on the surface of HC-2 and its adhesion receptors in the intestinal epithelium of shrimp. The elongation factor Tu (EF-Tu) on the surface of HC-2 was found to interact with Fibronectin (Fib) in the shrimp intestine by immunoblotting and yeast two-hybrid assays, and this interaction relationship was verified by immunoprecipitation (Co-IP). The adhesion of HC-2 to Caco-2 cells could be blocked via EF-Tu antibody confinement, and the adhesion of Fib to HC-2 could be blocked by Fib antibody confinement. Expression of Fib on the surface of HEK293T cells revealed a significant increase in the adhesion rate of HC-2 to HEK293T cells. Using immunofluorescence, a significant reduction in HC-2 adhesion to the intestine of shrimp was observed after blocking the Fib site in the shrimp intestine, particularly in Vibrio parahaemolyticus E1-infected intestines. In addition, the recombinant protein rEF-Tu was found to promote the growth of Caco-2 cells in a certain concentration range and significantly inhibit the apoptosis induced by LPS, Staphylococcus aureus and V. parahaemolyticus E1. Our results indicate that EF-Tu might participate in gut immunity and homeostasis, through its binding to the shrimp intestinal cells and inhibiting apoptosis.

Synergistic combination of YS-1 and adriamycin inhibits human renal cancer through ERK1/2 signaling pathway in vitro and in vivo.

Adriamycin (ADM) is a principal drug for the treatment of renal cell cancer (RCC). Due to its limited response and high renal and cardiac toxicity, synergistic effects of ADM in combination with other drugs have been widely researched. In this study, we found the combination between YS-1 and ADM, performed higher anticancer activity on 786-O human RCC cells in vitro and in vivo, than that reported on its anti-angiogenesis effect compared with monotherapy of ADM. Our data showed that when combined with ADM, YS-1 promoted the sensitivity of 786-O cells to ADM. The combination of YS-1 and ADM also inhibited cell proliferation, but without affecting cell apoptosis. We found that ADM monotherapy treatment notably upregulated the activity of extracellular signal-regulated kinase ERK1 and ERK2 (ERK1/2), but when combined with YS-1, the p-ERK1/2 level was reduced; then inhibited the Ras/Raf/MEK pathway. Additionally, the synergistic effects on cell cycle arrest inhibition were eliminated when ERK1/2 was silenced using siRNA. Our combination therapy of YS-1 with ADM showed the strongest antitumor effects in vivo (inhibition ratio: 5 mg/kg YS-1 combined with 1 mg/kg ADM, 68.19%) in comparison with individual effects (inhibition ratio: 5 mg/kg YS-1, 30.07%; 1 mg/kg ADM, 50.42%). Collectively, these findings indicated that YS-1 did not only enhance the ability of ADM to inhibit tumor proliferation, but also reduce the renal toxicity to protect the normal renal tissues.

Two distinct EF-Tu epitopes induce immune responses in rice and Arabidopsis.

Plants sense potential pathogens by recognizing conserved pathogen-associated molecular patterns (PAMPs) that cause PAMP-triggered immunity (PTI). We previously reported that rice recognizes flagellin from the rice-incompatible N1141 strain of Acidovorax avenae and subsequently induces immune responses. Cell extracts isolated from flagellin-deficient N1141 (Δfla1141) still induced PTI responses, suggesting that Δfla1141 possesses an additional PAMP distinct from flagellin. Here, we show that elongation factor Tu (EF-Tu), one of the most abundant bacterial proteins, acts as a PAMP in rice and causes several PTI responses. In Brassicaceae species, EF-Tu and an N-acetylated peptide comprising the first 18 amino acids of the N-terminus, termed elf18, are fully active as inducers of PTI responses. By contrast, elf18 did not cause any immune responses in rice, whereas an EF-Tu middle region comprising Lys176 to Gly225, termed EFa50, is fully active as a PAMP in rice. In the leaves of rice plants, EF-Tu induced H2O2 generation and callose deposition, and also triggered resistance to coinfection with pathogenic bacteria. Taken together, these data demonstrate that rice recognizes EFa50, which is distinct from elf18, and that this epitope induces PTI responses.

The influence of YS-1 on the Dll4-Notch1 signaling pathway.

In this study, we investigated the role and molecular mechanism of p43 and YS-1 (recombinant human p43 protein) in Dll4-Notch1 signaling pathway. Active, small interfering RNA and recombinant plasmid targeting of p43 protein were used to infect human umbilical vein endothelial cells (HUVECs). Three-dimensional sprouting model, endothelial cell migration assay, and sprouting and tube formation assay were used to deduce the function of p43 and YS-1 in angiogenesis. Semi-quantitative reverse transcription-polymerase chain reaction and western blot analysis were performed to detect the efficiency of p43 in Dll4-Notch1 signaling in HUVECs. It was found that silencing and overexpression of p43 could upregulate Dll4-Notch and stimulate angiogenesis. p43 plays a complex role in angiogenesis. When the concentration is under 100 nM, it promotes angiogenesis; instead, when the concentration is over 100 nM, it inhibits angiogenesis. In this study, we found that the expression level of p43 was under 60 nM. However, recombinant human p43 protein, YS-1, inhibited endothelial cell sprouting, and 500 µg/ml of YS-1 attenuated the activation of Dll4-Notch1 signaling. These results suggested that YS-1 could directly inhibit angiogenesis through Dll4-Notch1 signal transduction pathway, while p43 plays a modulating role in this signaling pathway.

Pattern-triggered immunity suppresses programmed cell death triggered by fumonisin b1.

Programmed cell death (PCD) is a crucial process for plant innate immunity and development. In plant innate immunity, PCD is believed to prevent the spread of pathogens from the infection site. Although proper control of PCD is important for plant fitness, we have limited understanding of the molecular mechanisms regulating plant PCD. Plant innate immunity triggered by recognition of effectors (effector-triggered immunity, ETI) is often associated with PCD. However pattern-triggered immunity (PTI), which is triggered by recognition of elicitors called microbe-associated molecular patterns (MAMPs), is not. Therefore we hypothesized that PTI might suppress PCD. Here we report that PCD triggered by the mycotoxin fumonisin B1 (FB1) can be suppressed by PTI in Arabidopsis. FB1-triggered cell death was suppressed by treatment with the MAMPs flg22 (a part of bacterial flagellin) or elf18 (a part of the bacterial elongation factor EF-Tu) but not chitin (a component of fungal cell walls). Although plant hormone signaling is associated with PCD and PTI, both FB1-triggered cell death and suppression of cell death by flg22 treatment were still observed in mutants deficient in jasmonic acid (JA), ethylene (ET) and salicylic acid (SA) signaling. The MAP kinases MPK3 and MPK6 are transiently activated and inactivated within one hour during PTI. We found that FB1 activated MPK3 and MPK6 about 36-48 hours after treatment. Interestingly, this late activation was attenuated by flg22 treatment. These results suggest that PTI suppression of FB1-triggered cell death may involve suppression of MPK3/MPK6 signaling but does not require JA/ET/SA signaling.

MPK11-a fourth elicitor-responsive mitogen-activated protein kinase in Arabidopsis thaliana.

Recognition of pathogen attack or elicitation with pathogen-associated molecular patterns (PAMPs) leads to defense signaling that includes activation of the three mitogen-activated protein kinases (MPKs), MPK3, MPK4 and MPK6 in Arabidopsis. Recently, we demonstrated the activation of a fourth MPK, MPK11, after treatment with flg22, a 22 amino acid PAMP derived from bacterial flagellin. Here, we extended the study by examining elicitation with two other PAMPs, elf18 (derived from bacterial elongation factor EF-Tu) and ch8 (N-acetylchitooctaose derived from fungal chitin). Both PAMPs led to rapid MPK11 transcript accumulation and increased MPK11 kinase activity, suggesting that multiple PAMPs (or stresses) can activate MPK11. However, probably due to functional redundancies, bacteria-induced phytoalexin accumulation does not absolutely require MPK11.

Cautionary notes on the use of C-terminal BAK1 fusion proteins for functional studies.

Detailed phenotypic characterization reveals that several BAK1 fusion proteins with C-terminal tags strongly impair complementation of bak1 null mutants with respect to responsiveness to the bacterial pathogen-associated molecular patterns flagellin and EF-Tu. This raises concerns about the widespread use of such protein variants of this important regulatory Leu-rich repeat receptor-like kinase (RLK) for functional analyses of RLK-based signaling.

TLR4-dependent activation of inflammatory cytokine response in macrophages by Francisella elongation factor Tu.

The bacterial determinants of pulmonary Francisella induced inflammatory responses and their interaction with host components are not clearly defined. In this study, proteomic and immunoblot analyses showed presence of a cytoplasmic protein elongation factor Tu (EF-Tu) in the membrane fractions of virulent Francisella novicida, LVS and SchuS4, but not in an attenuated F. novicida mutant. EF-Tu was immunodominant in mice vaccinated and protected from virulent F. novicida. Moreover, recombinant EF-Tu induced macrophages to produce inflammatory cytokines in a TLR4 dependent manner. This study shows immune stimulatory properties of a cytoplasmic protein EF-Tu expressed on the membrane of virulent Francisella strains.

Cytokine-like activities of some aminoacyl-tRNA synthetases and auxiliary p43 cofactor of aminoacylation reaction and their role in oncogenesis.

Multifunctionality of proteins is among mechanisms accounting for the complexity of interactome networks in higher eukaryotes. During oncogenesis and other pathologic conditions many proteins perform additional functions without changes in three dimensional structures. One family of these moonlighting proteins is represented by enzymes and cofactors of aminoacylation reactions, by means of which tRNAs are attached to their cognate amino acids. Tyrosyl-tRNA synthetase (TyrRS), tryptophanyl-tRNA synthetases (TrpRS) and auxiliary factor of mammalian multi-aminoacyl-tRNA synthetases, p43 (precusor of endothelial monocyte activating polypeptide II - EMAP II) upon their release in intracellular environment become proinflammatory cytokines with multiple activities during apoptosis, angiogenesis and inflammation. In addition, these proteins play important role in cancer progression, modulating tumor angiogenesis and its escape from surveillance by immune system.

Studies on ATPase(GTPase) intrinsic to E. coli ribosomes.

(1) Escherichia coli 70S ribosomes showed intrinsic ATPase and GTPase activities, although they were much lower than those of rat liver ribosomes. The latter activity was higher than the former one. (2) The ATPase activity was inhibited by GTP and GMP-P(NH)P, and the GTPase activity was inhibited by ATP and AMP-P(NH)P, indicating a close relationship between the two enzymes. (3) Elongation components alone or in combination enhanced the ATPase activity, indicating the possible correlation of ribosomal ATPase with elongational components. (4) Vanadate at the concentrations that did not inhibit the GTPase activities of EF-Tu and EF-G, depressed the poly(U)-dependent polyphe synthesis, suggesting that ribosomal ATPase (GTPase) participates in peptide elongation by inducing positive conformational changes of ribosomes required for the attachment of elongational components.

Cross-linking of selected residues in the N- and C-terminal domains of Escherichia coli protein L7/L12 to other ribosomal proteins and the effect of elongation factor Tu.

Five different variants of protein L7/L12, each with a single cysteine substitution at a selected site, were produced, modified with 125I-N-[4-(p-azidosalicylamido)-butyl]-3-(2'-pyridyldithio)propion amide, a radiolabeled, sulfhydryl-specific, heterobifunctional, cleavable photocross-linking reagent that transfers radiolabel to the target molecule upon reduction of the disulfide bond. The proteins were reconstituted with core particles depleted of wild type L7/L12 to yield 70 S ribosomes. Cross-linked molecules were identified and quantified by the radiolabel. No cross-linking of RNA was detected. Two sites in the dimeric N-terminal domain, Cys-12 and Cys-33, cross-linked strongly to L10 and in lower yield to L11 but to no other proteins. The three sites in the globular C-terminal domain all cross-linked strongly to L11 and, in lower yield, to L10. Weaker cross-linking to 50 S proteins L2 and L5 occurred from all three C-terminal domain locations. The 30 S ribosomal proteins S2, S3, S7, S14, S18 were also cross-linked from all three of these sites. Binding of the ternary complex [14C]Phe-tRNA-elongation factor Tu.guanyl-5'-yl imidodiphosphate) but not [14C]Phe-tRNA.elongation factor Tu.GDP.kirromycin increased labeling of L2, L5, and all of the 30 S proteins. These results imply the flexibility of L7/L12 and the transient proximity of three surfaces of the C-terminal domain with the base of the stalk, the peptidyl transferase domain, and the head of the 30 S subunit.

Targeted screening for elongation factor Tu binding antibiotics.

The development of a screen targeted to antibiotics which bind elongation factor Tu (EF-Tu) is described. The method was based on selection of antimicrobial activities which were antagonized by exogenous EF-Tu. Kirromycin, a known inhibitor of EF-Tu, was positive in this screen. Among 47,000 microorganisms screened, several producers of kirromycin-type antibiotics were detected and the novel antibiotics GE2270 and GE37468 were discovered. These thiopeptide molecules constitute, along with amithiamycin, a novel class of antibiotics acting on EF-Tu.

Rabbit translation elongation factor 1 alpha stimulates the activity of homologous aminoacyl-tRNA synthetase.

Functional and structural sequestration of aminoacyl-tRNA has been recently found in eukaryotic cells and the aminoacyl-tRNA channeling has been suggested [B.S. Negrutskii et al., Proc. Natl. Acad. Sci. 91 (1994) 964-968], but molecular details and mechanism of the process remained unclear. In this paper we have verified a possible interaction between rabbit aminoacyl-tRNA synthetase and homologous translation elongation factor 1 alpha (EF-1 alpha), the proteins which may play a role of sequential components involved in the transfer of the aminoacyl-tRNA along the protein synthetic metabolic chain. The stimulation of the phenylalanyl-tRNA synthetase activity by EF-1 alpha is found. The effect is shown to be specific towards the origin of tRNA and elongation factor molecules. The data obtained favor the direct transfer mechanism of the aminoacyl-tRNA channeling process during eukaryotic protein synthesis.

Immunosuppression by breast cancer associated p43-effect of immunomodulators.

It has been previously shown that p43- a breast cancer associated antigen-has immunosuppressive properties. The present study was carried out in order to elucidate the pathomechanisms of immunosuppression in breast cancer patients influenced by the expression of p43. Lymphocytes were cultured from blood of 29 women with benign lesions in the breast as well as from 41 female patients with breast cancer. Lymphocyte stimulation was performed by addition of Concanavalin (Con A) in cultures with lymphocytes alone (CONLYM) or in lymphocytes incubated with p43 (CONAg). In other series immunomodulation was tried by addition of indomethacin (INDLYM, INDAg), levamisole (LEVLYM, LEVAg), or interleukin-2 (ILLYM, ILAG). In breast cancer patients, addition of p43 significantly inhibited the activation of lymphocyte proliferation by Con A compared to women with benign tumors. The addition of indomethacin or levamisole did not influence this inhibitory effect of p43 in breast cancer patients. Contrary to these observations, addition of IL-2 resulted in increased proliferation of lymphocytes from patients with benign as well as malignant tumors, which was inhibited after addition of p43. Analysis of the correlation of the immunosuppressive properties of p43 in correlation with prognostic factors for breast cancer showed evidence for a stronger activity of p43 in early stage tumors (i.e. smaller than 2 cm, lymph node negative, histologic grading GI), confirming previous observations of a higher expression of p43 in early stages of breast cancer.

How does ppGpp affect translational accuracy in the stringent response?

With an in vitro poly(Phe) synthesis system we have tested recent models concerning translational accuracy in the stringent response during aminoacid starvation. We have found that cognate, deacylated tRNA of very high concentrations is unable to block the A-site. No influence of EF-Tu.ppGpp on ribosomal proofreading has been found. Alternative mechanisms to keep translational errors low by the stringent response are discussed.

Action of erythromycin and virginiamycin S on polypeptide synthesis in cell-free systems.

Erythromycin (a 14-membered macrolide) and virginiamycin S (a type B synergimycin) block protein biosynthesis in bacteria, but are virtually inactive on poly(U)-directed poly(Phe) synthesis. We have recently shown, however, that these antibiotics inhibit the in vitro polypeptide synthesis directed by synthetic copolymers: this effect is analyzed further in the present work. We were unable to find any consistent alteration produced by these antibiotics on coupled and uncoupled EF-G- and EF-Tu-dependent GTPases, on the EF-Tu-directed binding of aminoacyl-tRNA to ribosomes, and on the EF-G- and GTP-mediated translocation of peptidyl-tRNA bound to poly(U,C).ribosome complexes. With these complexes, the peptidyl transfer reaction, as measured by peptidylpuromycin synthesis, was 10-30% inhibited by virginiamycin S and erythromycin. A direct relationship between the virginiamycin S- and erythromycin-promoted inhibition of poly(A,C)-directed polypeptide synthesis, on the one hand, and the EF-G concentration and the rate of the polymerization reaction, on the other hand, was observed, in agreement with a postulated reversible inhibitor action of these antibiotics. The increased inhibitory activity, which was observed during the first 4-6 rounds of elongation, in the presence of virginiamycin S or erythromycin, was suggestive of a specific action of these antibiotics on the correct positioning of peptidyl-tRNA at the P site. The marked stimulation of premature release of peptidyl-tRNA from poly(A,C).ribosome complexes can be referred to an altered interaction of the C-terminal aminoacyl residue of the growing peptidyl chain with the ribosome. We conclude that the action of virginiamycin S and erythromycin entails a template-dependent alteration of the interaction of peptidyl-tRNA with the donor site of peptidyltransferase, which may lead to a transient functional block of the ribosome and in some instances to a premature release of peptidyl-tRNA and termination of the elongation process.

Allosteric interactions between the ribosomal transfer RNA-binding sites A and E.

We have previously proposed a three-site model for the elongation cycle. The model is characterized by the presence of two tRNAs on the ribosome before and after translocation. We have already shown a first consequence of the model, namely that the translocation reaction is not coupled with a release of deacylated tRNA. Here we demonstrate the following conclusions. Occupation of the A site triggers the tRNA release from the E site, i.e. the A site occupation induces a drastic decrease in the affinity of the E site for deacylated tRNA. In the concentration range of deacylated tRNA in which a ribosome binds a second tRNA in addition to that one already present at the P site the deacylated tRNA does not compete for one and the same binding site with an A site ligand (AcPhe-tRNA) at 37 degrees C. It follows that the second deacylated tRNA binds to a site, the E site, which is physically distinct from the A site. When the ribosome binds a deacylated tRNA at the E site (in addition to a tRNA at the P site), the A site cannot be occupied by AcPhe-tRNA at 0 degree C and only poorly by the ternary complex elongation factor Tu . Phe-tRNA . guanyl-5'-yl imidodiphosphate. At 37 degrees C a significant A site binding is observed, with a corresponding tRNA release from the E site. In contrast, if the E site is free and only the P site occupied, the A site can bind significant amounts of charged tRNA already at 0 degree C. It follows that an occupied E site induces a low-affinity state of the A site. Thus, the ribosome always contains two high-affinity binding sites, which are A and P sites before and P and E sites after translocation. A and E sites are allosterically linked in a bidirectional manner.