[Show abstract][Hide abstract] ABSTRACT: Novel anti-HIV lectin family which shows a strict binding specificity for high mannose glycans has been found in lower organisms. The bacterial orthologue has been identified in the genome of Pseudomonas fluorescens Pf0-1 and the gene coding a putative lectin was cloned, expressed in Escherichia coli and purified by one step gel filtration. Glycan array screening of the recombinant lectin, termed PFL, has revealed that PFL preferentially recognizes high mannose glycans with α1-3 Man that was highly exposed at the D2 position. In contrast, masking of this α1-3 Man with α1-2 Man dramatically impaired lectin-carbohydrate interactions. Reducing terminal disaccharide, GlcNAc-GlcNAc of high mannose glycans was also essential for PFL-binding. PFL showed a potent anti-influenza virus activity by inhibiting the virus entry into cells at doses of low nanomolar concentration. At micromolar concentration or higher, PFL showed a cytotoxicity accompanying loss of the cell adhesion against human gastric cancer MKN28 cells. The cell surface molecule to which PFL bound was co-precipitated with biotin-labeled PFL and identified as integrin α2 by peptide mass fingerprinting using MALDI-TOF mass spectrometry. Intriguingly, upon treatment with exogenous PFL, integrin α2 on the cell surface underwent rapid internalization to the cytoplasm and accumulated to perinuclear region, together with the bound PFL. The resulting loss of cell adherence would trigger a signaling pathway that induced anoikis-like cell death. These events were effectively inhibited by pretreatment of PFL with mannnan, indicating the involvement of high mannose glycans on PFL-induced cell death that was triggered by PFL-integrin α2 interactions.
PLoS ONE 01/2012; 7(9):e45922. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The transcription mode of rabies virus high egg passage-Flury (HEP) strain was examined and compared with that of Evelyn Rokitniki Abelseth (ERA) strain by northern blot analysis using rabies virus gene-specific probes. The ERA strain was shown to exclusively produce monocistronic mRNAs in transcription. All combinations of multicistronic transcripts, including five monocistronic mRNAs, were detected in the viral RNA transcripts of HEP strain. It was concluded that the unique transcription mode is not due to the nucleotide structure of the genome RNA template, but rather to the viral RNA polymerase of HEP strain. The viral polymerase of HEP strain read through the gene junction at a high frequency. The HEP strain has been passaged many times in chick embryo and cultured cells, and has adapted to propagate well in the baby hamster kidney-21 (BHK-21) cells. Through these passages in various hosts, the HEP strain has acquired a unique transcription mode that might have an advantage in amplification of the virus.
Microbiology and Immunology 06/2011; 55(8):558-64. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The complete amino acid sequence of a lectin from the green alga Boodlea coacta (BCA), which was determined by a combination of Edman degradation of its peptide fragments and cDNA cloning, revealed the following: 1) B. coacta used a noncanonical genetic code (where TAA and TAG codons encode glutamine rather than a translation termination), and 2) BCA consisted of three internal tandem-repeated domains, each of which contains the sequence motif similar to the carbohydrate-binding site of Galanthus nivalis agglutinin-related lectins. Carbohydrate binding specificity of BCA was examined by a centrifugal ultrafiltration-HPLC assay using 42 pyridylaminated oligosaccharides. BCA bound to high mannose-type N-glycans but not to the complex-type, hybrid-type core structure of N-glycans or oligosaccharides from glycolipids. This lectin had exclusive specificity for α1-2-linked mannose at the nonreducing terminus. The binding activity was enhanced as the number of terminal α1-2-linked mannose substitutions increased. Mannobiose, mannotriose, and mannopentaose were incapable of binding to BCA. Thus, BCA preferentially recognized the nonreducing terminal α1-2-mannose cluster as a primary target. As predicted from carbohydrate-binding propensity, this lectin inhibited the HIV-1 entry into the host cells at a half-maximal effective concentration of 8.2 nm. A high association constant (3.71 × 10(8) M(-1)) of BCA with the HIV envelope glycoprotein gp120 was demonstrated by surface plasmon resonance analysis. Moreover, BCA showed the potent anti-influenza activity by directly binding to viral envelope hemagglutinin against various strains, including a clinical isolate of pandemic H1N1-2009 virus, revealing its potential as an antiviral reagent.
Journal of Biological Chemistry 04/2011; 286(22):19446-58. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The carbohydrate binding profile of the red algal lectin KAA-2 from Kappaphycus alvarezii was evaluated by a centrifugal ultrafiltration-HPLC method using pyridylaminated oligosaccharides. KAA-2 bound exclusively to high mannose type N-glycans, but not to other glycans such as complex type, hybrid type, or the pentasaccharide core of N-glycans. This lectin exhibited a preference for an exposed α1-3 Man on a D2 arm in a similar manner to Eucheuma serra agglutinin (ESA-2), which shows various biological activities, such as anti-HIV and anti-carcinogenic activity. We tested the anti-influenza virus activity of KAA-2 against various strains including the recent pandemic H1N1-2009 influenza virus. KAA-2 inhibited infection of various influenza strains with EC50s of low nanomolar levels. Immunofluorescence microscopy using an anti-influenza antibody demonstrated that the antiviral activity of KAA-2 was exerted by interference with virus entry into host cells. This mechanism was further confirmed by the evidence of direct binding of KAA-2 to a viral envelope protein, hemagglutinin (HA), using an ELISA assay. These results indicate that this lectin would be useful as a novel antiviral reagent for the prevention of infection.
Biochemical and Biophysical Research Communications 02/2011; 405(2):291-6. · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The structural changes of the nominal phosphoprotein (P) of rabies virus using a monoclonal antibody, mAb #402-13, was investigated. This mAb recognized a linear epitope that was mapped roughly to a C-terminal region of the P protein, ranging from aa 256 to 297. The P gene products were detected by the mAb in immunoblot assays, the products of which were produced either in BHK-21 cells or in Escherichia coli cells. The mAb, however, detected very low levels of P gene products in immunoprecipitation assays. The mAb recognized the nucleocapsid (NC)-associated P proteins but recognized free P protein and free N-P complex produced in the infected cells much less efficiently. When the P proteins were released from the NC, however, they were no longer recognized by the mAb. Similar results were obtained from BHK-21 cells co-transfected with P and N cDNAs. Furthermore, studies with C-terminally truncated P protein mutants revealed that the NC-binding ability of the P protein was dependent on the presence of the C-terminal epitope region. From these results, it is thought that the 402-13 epitope region is concealed when the P protein is present in a free form or free N-P complex but is exposed when it is associated with the NC. The C-terminal epitope region seemed to be essential for the P protein to be associated with the NC but not for the formation of free N-P complexes with newly synthesized N protein.
Journal of General Virology 01/2003; 83(Pt 12):3035-43. · 3.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated a virus-neutralizing conformational epitope of the rabies virus glycoprotein (G) that is recognized by an anti-G monoclonal antibody (mAb; #1-46-12) and shared by most of the laboratory strains of the virus. To investigate the epitope structure, we isolated escape mutants from the HEP-Flury virus (wild-type; wt) after repeated passages in culture in the presence of the mAb. Immunofluorescence studies indicated that the mutants could be classified into two groups; the Group I lacked the epitope, while Group II preserved the epitope. The latter was dominant under the passage conditions, since Group I disappeared during the continuous passages. G proteins showed different electrophoretic mobilities; G protein of Group I migrated at the same rate as wt G protein, while that of Group II migrated at a slower rate, which was shown to be due to acquisition of an additional oligosaccharide side chain. Nucleotide sequencing of the G gene strongly suggested that amino acid substitutions at Thr-36 by Pro and Ser-39 by Thr of the G protein are responsible for the escape mutations of Groups I and II, respectively. The latter is a unique mutation of the rabies virus that allows the G protein to be glycosylated additionally at Asn-37, a potential glycosylation site that is not glycosylated in the parent virus, in preserving the epitope-positive conformation. These results suggest that to keep the 1-46-12 epitope structure is of greater survival advantage for the virus to escape the neutralization than to destroy it, which could be achieved by acquiring an additional oligosaccharide chain at Asn-37.
Microbiology and Immunology 02/2002; 46(7):449-61. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the antigenic maturation of rabies virus N protein, for which we used some conformational epitope-specific monoclonal antibodies (MAbs) and an MAb (5-2-26) against a phosphorylation-dependent linear epitope. Infected cells were lysed with a deoxycholate-free lysis buffer and separated by ultracentrifugation into the soluble top and the nucleocapsid fractions. None of the study MAbs recognized N proteins in the top fraction, whereas nucleocapsid-associated N proteins were recognized by all of the MAbs. Immunoprecipitation with polyclonal anti-N antibodies coprecipitated the P proteins from the top fraction, indicating that soluble N proteins are mostly associated with the P protein. The N proteins dissociated from both the N–P complex and nucleocapsids were recognized by none of the study MAbs, whereas the MAb 5-2-6 recognized the SDS-denatured N proteins of the nucleocapsid but not of the top fraction. In addition, the phosphorylation-deficient mutant N proteins were shown to be similarly accumulated as the wild-type N proteins into the viral inclusion bodies, defined as the virus-specific structures composed of viral nucleocapsids, that are produced in the cytoplasm of the infected cells. Based on these results, we believe that newly synthesized N proteins are not immediately phosphorylated at serine-389 (a common phosphorylation site) but are first associated with the P protein. After being used for encapsidation of the viral RNA, the N proteins undergo conformational changes, whereby epitopes for the conformation-specific MAbs are formed and become phosphorylated at serine-389.
[Show abstract][Hide abstract] ABSTRACT: We investigated the relationship between the two forms of rabies virus P protein, a non-catalytic subunit of rabies virus RNA polymerase. The two displayed different electrophoretic mobilities as 37- and 40-kDa polypeptides, hence termed as p37 and p40, respectively. Double labeling experiments with [3H]leucine and [32P]orthophosphate demonstrated that p40 was much more phosphorylated than p37. Treatment of the virion proteins with alkaline phosphatase eliminated only p40, and not 37-kDa polypeptide. The p37 was a major product of the P gene, and was accumulated in the infected cell and incorporated into the virion. On the other hand, p40 was apparently detected only in the virion, and little detected in the cells. Treatment of infected cells with okadaic acid, however, resulted in significant accumulation of p40 in the cell, suggesting that p40 was continuously produced in the cell but dephosphorylated quickly. We detected both 37- and 40-kDa products in P cDNA-transfected animal cells, while only a 37-kDa product was produced in Escherichia coli. Incubation of 37-kDa products from E. coli with the lysates of animal cells in vitro resulted in the production of a 40-kDa product, which was also shown to be suppressed by the heparin. From these results, it is suggested that p40 is produced by the hyperphosphorylation of a 37-kDa polypeptide, which depends on certain heparin-sensitive cellular enzyme(s) and occurs even in the absence of the other viral gene products, and that p40 is reverted quickly to p37 in the infected cells, probably being dependent on some virus-induced factor(s).
Microbiology and Immunology 02/1998; 42(11):761-71. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To investigate the RNA polymerase of rabies virus, we cloned a cDNA of the catalytic subunit (called L protein because of its large molecular size) of the HEP-Flury strain, an avirulent strain obtained by high frequencies of serial embryonated hen egg passages. Nucleotide sequencing showed that the cDNA encodes a long polypeptide of 2,127 amino acids (Mr. 242,938). A comparison of the deduced amino acid sequence with that of other strains (PV and SAD B19) indicated that the sequence was highly conserved, except for several amino acid substitutions which were accumulated in some limited regions. A fragment of the cDNA was used for expression in Escherichia coli (E. coli) to prepare the L antigen for raising the antibodies in rabbits. Immunoprecipitation studies with the rabbit antiserum showed that the polypeptides produced in the L cDNA-transfected COS-7 cells displayed almost the same electrophoretic mobility as that of authentic L protein. Immunofluorescence studies indicated that both L and P (another subunit of RNA polymerase) proteins displayed colocalized distribution with the nucleocapsid antigen (N) in the cytoplasmic inclusion bodies, where envelope proteins (G and M) were absent. On the other hand, expression of the L protein alone did not cause inclusion body-like granular distribution, suggesting that the inclusion body-like accumulation depends on certain interaction(s) with other viral gene products, probably with the ribonucleoproteins comprising the inclusion bodies.
Microbiology and Immunology 02/1998; 42(7):485-96. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Regional and cellular distribution of mRNAs for prostaglandin E (PGE) receptor subtypes was investigated in the mouse gastrointestinal tract by in situ hybridization. Strong signals for EP1 transcripts were detected in cells of the muscularis mucosae layer, especially in the body of the stomach. Intense signals for EP3 transcripts were detected in neurons of the myenteric ganglia throughout the tract. Moderate EP3 mRNA expression was also observed in fundic gland epithelial cells, except for surface mucous cells in the stomach. Expression of EP4 mRNA was moderate in surface epithelial cells of the corpus and in glands from the surface to the base of the antrum. Strong EP4 signals were observed in the epithelium in the duodenum, jejunum, and ileum. In the ileum, signals were only observed in the upper part of the villi. However, no or weak signals for EP2 transcripts were detected. These findings suggest that PGE2 modulates various gastric or intestinal functions via at least three different PGE receptors.
The American journal of physiology 04/1997; 272(3 Pt 1):G681-7. · 3.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have investigated a phosphatase-sensitive sequential epitope of the nucleoprotein (N), one of the phosphoproteins of rabies virus, which is recognized by the monoclonal antibody (MAb) #5-2-26. The epitope was shared in common by all of the rabies virus strains we tested, including the HEP, ERA, CVS and Japanese strains (Nishigahara and Komatsukawa). Thin layer chromatography of the acid hydrolyzates of 32P-labeled N protein showed that the protein contained phosphoserine and phosphothreonine at a molar ratio of about 4 to 1, while no phosphotyrosine was detected. Immunoprecipitation studies with several deletion mutants of the N protein showed that the epitope is located in a region spanning from amino acid 344 to 415. If the phosphatase-sensitive epitope is located at or near the phosphoamino acid, the location of the latter could be narrowed further to a region from amino acid 354 to 389 by comparing the amino-acid sequences among the viral strains. To examine this assumption, point mutation was introduced by amino-acid substitution with alanine at either of five potential phosphorylation sites (i.e., positions 354, 375, 377, 386 and 389) in the 354-389 region. Among those, only one substitution, at position 389, greatly affected the antigenicity. Substitution of serine-389 by threonine also reduced the antigenicity. These results strongly suggest that serine-389 is a phosphorylation site and essential for constructing or stabilizing the antigenic structure for MAb 5-2-26.
Microbiology and Immunology 02/1997; 41(3):229-40. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We prepared monoclonal antibodies (MAbs) against the rabies virus N protein, among which one antibody (MAb 5-2-26) was shown to lack reactivity with the phosphatase-treated N protein. The MAb was able to recognize the sodium dodecyl sulfate (SDS)-denatured N protein. The MAb did not recognize the N-protein analogues produced in Escherichia coli (E. coli), indicating that the N-gene products were not normally processed in E. coli after translation. On the other hand, the MAb reacted normally with N-gene products produced in COS-7 cells, but not with those produced in the presence of K-252a (a protein kinase inhibitor of a broad spectrum). The MAb displayed weak cross-reactivity with the Triton-insoluble network structures composed of several components, while another phosphoprotein (M1) of the virus was not recognized at all. These results suggest that MAb 5-2-26 preferentially recognizes a phosphatase-sensitive linear epitope of N protein, which may enable further investigations to be conducted on the mechanism of N-protein phosphorylation and its role(s) in virus replication.
Microbiology and Immunology 02/1997; 41(1):33-42. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The relationship between the expression of mRNA encoding the prostaglandin F2 alpha (PGF2 alpha) receptor and luteal cell apoptosis as determined by oligonucleosome formation was determined in mouse corpora lutea on days 2 (early phase), 6 (mid-phase), and 11 and 13 (late phase) of pseudopregnancy. No signals for mRNA encoding the PGF2 alpha receptor were detected in the ovary as shown by RNA blot analysis of pregnant mares' serum gonadotrophin (PMSG)-treated mice. The expression of the mRNA that could be detected in the corpora lutea on day 2 after hCG treatment was low, but it was increased on day 6 and reached a plateau on days 11 and 13. On days 11 and 13, in situ hybridization signals for mRNA encoding the PGF2 alpha receptor were localized to large luteal cells of the corpora lutea, especially the cells in the superficial layer. However, ethidium bromide staining revealed marked oligonucleosome formation in the corpora lutea on days 11 and 13. Similarly, positive signals of in situ nick-DNA-end labelling were also detected in the corpora lutea on days 11 and 13. Analysis of the adjacent sections of the corpora lutea on day 13 showed that both signals for DNA strand breaks and mRNA encoding the PGF2 alpha receptor were co-expressed in the corpus luteum. These results suggest that apoptosis during structural luteolysis closely associates with the increased expression of mRNA encoding the PGF2 alpha receptor in luteal cells of pseudopregnant mice.
[Show abstract][Hide abstract] ABSTRACT: As an initial step to clarify the mechanisms of various uterine actions of PGE2, expression patterns of the messenger RNAs (mRNAs) for four subtypes of PGE receptors, EP1, EP2, EP3, and EP4, were investigated in the mouse uterus during pseudopregnancy. Relative expression levels were investigated by Northern blot analysis of mRNA levels in uteri obtained on days 0, 1, 3, 5, 7, and 9 of pseudopregnancy (day 0 = 48 h after PMSG injection), and cellular localization was determined by in situ hybridization in uteri obtained on days 0 and 5. EP2 mRNA was specifically expressed on day 5, and its expression was confined to the luminal epithelium. On the other hand, the level of the EP3 mRNA expression progressively increased until day 5. Cell populations expressing the EP3 mRNA were confined to the longitudinal smooth muscle on day 0, but they changed to the circular smooth muscle on day 5. The expression level of EP4 mRNA was low on days 0 and 1, but it became high on days 3 and 5. On day 0, EP4 mRNA was localized to the luminal epithelium. On day 5, diffuse, but significant, EP4 expression was observed over the endometrial stroma and epithelium. No EP1 mRNA signals were observed. Transient expression of EP2 on day 5 of pseudopregnancy in the luminal epithelium suggests its involvement in blastocyst implantation signaling. EP4 in the endometrial stroma is suggested to be involved in decidual transformation of the stromal cells, whereas EP3 in the myometrium is believed to be involved in regulation of myometrial activity.
[Show abstract][Hide abstract] ABSTRACT: We investigated unusual structures produced in BHK-21 cells infected with rabies virus (HEP-Flury strain). Sellers' staining of the cells revealed, in addition to Negri body-like structures (inclusion bodies), production of a fuchsin-stained cytoplasmic structure (FCPS) which encircled the nucleus. The frequency of the FCPS-forming cells increased as replication progressed. The FCPS was different from the inclusion body because the former contained the viral glycoprotein (G) and matrix protein (M2) antigens, while the latter contained nucleocapsid antigens. In the early phase of infection, we observed accumulation of viral envelope antigens in a cytoplasmic structure that was considered to be expanded rough endoplasmic reticulum (rER) because of its concomitant increase in BiP content. Time-course studies suggested that the envelope antigen-containing structure, which was not stained with basic fuchsin, translocated to the perinuclear region to form the FCPS. FCPS formation was dependent on incubation temperature and was decreased at 30 degrees C, while the development of virus-induced cytopathic effect (CPE) was delayed. When the incubation temperature was shifted up to 37 degrees C, FCPS formation was induced again and progression of CPE was accelerated in approximate proportion to the increasing number of FCPS-positive cells. From these studies, we conclude that viral G proteins gradually accumulate in the rER with M2 protein and the expanded rER converts eventually into the FCPS, which may be closely related to accelerated host cell death.
Journal of General Virology 10/1996; 77 ( Pt 9):2137-47. · 3.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A functional cDNA clone for the mouse prostaglandin (PG) E receptor EP2 subtype was isolated from a mouse cDNA library. The mouse EP2 receptor consists of 362 amino acid residues with seven putative transmembrane domains. [3H]PGE2 bound specifically to the membrane of Chinese hamster ovary cells stably expressing the cloned receptor. This binding was displaced by unlabeled prostanoids in the order of PGE2 = PGE1 > iloprost, a stable PGI2 agonist > PGF2 alpha > PGD2. Binding was also inhibited by butaprost (an EP2 agonist) and to a lesser extent by M&B 28767 (an EP3 agonist), but not by sulprostone (an EP1 and EP3 agonist) or SC-19220 (an EP1 antagonist). PGE2 and butaprost increased the cAMP level in the Chinese hamster ovary cells in a concentration-dependent manner. Northern blot analysis revealed that EP2 mRNA is expressed most abundantly in the uterus, followed by the spleen, lung, thymus, ileum, liver, and stomach.
[Show abstract][Hide abstract] ABSTRACT: We have established a murine hybridoma cell line RG719 which produces a rabies virus-neutralizing IgM-type monoclonal antibody (referred to as MAb RG719). Immunoblot analysis indicated that the antibody recognized a sequential epitope of G protein. Among four rabies virus strains tested, the antigenicity to MAb RG719 was absent from the Nishigahara strain, while the other three strains (HEP, ERA and CVS) reacted to the MAb. Studies with deletion mutants of the G protein indicated that the epitope was located in a middle region of the primary structure of G protein, ranging from position 242 to 300. By comparing the estimated amino acid sequence of the four strains, we found in this region two amino acids (at positions 263 and 291) which are common to three of those strains but are not shared by the Nishigahara strain. The site-directed point mutagenesis revealed that replacement of phenylalanine-263 by leucine destroyed the epitope of the HEP G protein, while the epitope was generated on the Nishigahara G protein whose leucine-263 was replaced by phenylalanine. These observations suggest that phenylalanine-263 is essential for constructing the epitope for MAb RG719. The synthetic 20-mer peptide produced by mimicking the amino acid sequence (ranging from amino acid positions 249 to 268) of the presumed epitope region was shown to bind specifically to MAb RG719 and also to raise the virus-neutralizing antibodies in rabbits. Vaccination with the HEP vaccine produced in Japan induced in humans and rabbits production of significant amounts of the antibodies which reacted with the 20-mer peptide.
Microbiology and Immunology 02/1995; 39(9):693-702. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated a possible mechanism of G protein shedding occurring in the rabies virus-infected BHK-21 cell cultures. Quantitative analysis showed that about 10% of the newly synthesized G proteins were shed from the cells as Gs protein, a soluble form of G protein which lacked the C-terminal anchoring region of the protein, into the culture medium. Pulse-chase experiments revealed that the release of tritium-labeled Gs proteins began soon after the synthesis, but ceased after a short time (within about 2 hr). On the other hand, the release of the virion-associated G protein began 30 to 60 min behind the start of Gs protein shedding and continued for more than 10 hr. Gs protein could not be detected in the cells by biochemical and immunological methods at the time when large amounts of Gs protein were actively being shed. With an antiserum against the C-terminal of G protein we could detect in the cell a polypeptide having a size that is seemingly the same as that which was lost from Gs protein. These results suggest that Gs proteins are generated by a proteolytic cleavage of newly synthesized G proteins, and the cleavage seems to be stopped at a certain stage of the G protein maturation.