[Enzyme activity of neuraminidase 1 correlated with the biological behavior of prostate cancer PC3 and DU145 cell lines]

OBJECTIVE

To investigate the effects of the enzyme activity of neuraminidase 1 (Neu1) on the biological behavior of prostate cancer PC3 and DU145 cell lines.

METHODS

We detected the expression of Neul in the prostate cancer PC3 and DU145 cell lines by Western blot. Using sialidase inhibitors and antibody blocking, we suppressed the enzyme activity of Neu1 and then measured the proliferation and invasiveness of the two cell lines by CCK-8 and Transwell assay, respectively.

RESULTS

No statistically significant difference was found in the Neu1 expression between the PC3 and DU145 cell lines. The proliferation and invasiveness of the two types of cells were both increased after inhibition of the Neu1 enzyme activity.

CONCLUSIONS

The enzyme activity of Neu1 is correlated with the biological behavior of prostate cancer PC3 and DU145 cells and capable of inhibiting the proliferation and invasiveness of the two types of cells.

Aberrant sialylation in ovarian cancers

Sialylation (the covalent addition of sialic acid to the terminal end of glycoproteins or glycans), tightly regulated cell- and microenvironment-specific process and orchestrated by sialyltransferases and sialidases (neuraminidases) family, is one of the posttranslational modifications, which plays an important biological role in the maintenance of normal physiology and involves many pathological dysfunctions. Glycans have roles in all the cancer hallmarks, referring to capabilities acquired during all steps of cancer development to initiate malignant transformation (a driver of a malignant genotype), enable cancer cells to survive, proliferate, and metastasize (a consequence of a malignant phenotype), which includes sustaining proliferative signaling, evading growth suppressor, resisting cell apoptosis, enabling replicative immortality, inducing angiogenesis, reprogramming of energy metabolism, evading tumor destruction, accumulating inflammatory microenvironment, and activating invasion and accelerating metastases. Regarding the important role of altered sialylation of cancers, further knowledge about the initiation and the consequences of altered sialylation pattern in tumor cells is needed, because all may offer a better chance for developing novel therapeutic strategy. In this review, we would like to update alteration of sialylation in ovarian cancers.

Non-small cell lung cancer (NSCLC), EGFR downstream pathway activation and TKI targeted therapies sensitivity: Effect of the plasma membrane-associated NEU3

Adenocarcinoma of Non-Small Cell Lung Cancer (NSCLC) is a severe disease. Patients carrying EGFR mutations may benefit from EGFR targeted therapies (e.g.: gefitinib). Recently, it has been shown that sialidase NEU3 directly interacts and regulates EGFR. In this work, we investigate the effect of sialidase NEU3 overexpression on EGFR pathways activation and EGFR targeted therapies sensitivity, in a series of lung cancer cell lines. NEU3 overexpression, forced after transfection, does not affect NSCLC cell viability. We demonstrate that NEU3 overexpression stimulates the ERK pathway but this activation is completely abolished by gefitinib treatment. The Akt pathway is also hyper-activated upon NEU3 overexpression, but gefitinib is able only to decrease, and not to abolish, such activation. These findings indicate that NEU3 can act directly on the ERK pathway through EGFR and both directly and indirectly with respect to EGFR on the Akt pathway. Furthermore, we provide evidence that a healthy mucosa cell line (with EGFR wild-type gene sequence) is slightly sensitive to gefitinib, especially in the presence of NEU3 overexpression, thus hypothesizing that NEU3 overexpressing patients may benefit from EGFR targeted therapies also in absence of EGFR point mutations. Overall, the expression of NEU3 may be a novel diagnostic marker in NSCLC because, by its ability to stimulate EGFR downstream pathways with direct and indirect mechanisms, it may help in the identification of patients who can profit from EGFR targeted therapies in absence of EGFR activating mutations or from new combinations of EGFR and Akt inhibitors.

Differences in survival, virulence and biofilm formation between sialidase-deficient and W83 wild-type Porphyromonas gingivalis strains under stressful environmental conditions

BACKGROUND

Porphyromonas gingivalis is a major causative pathogen of chronic periodontitis. Within the inflammatory microenvironment, there exists extreme pH values, elevated temperatures and oxidative stress. Pathogens adapt to these stressful environmental conditions by regulating the transcription of virulence genes, modifying themselves with macromolecules and by aggregating and entering into a biofilm growth phase. Our previous study showed that the P. gingivalis sialidase can help cells obtain sialic acid from the environment, which is used to modify macromolecules on the surface of P. gingivalis cells. In this study, we compared the survival, virulence factors and biofilm formation of a sialidase-deficient strain (ΔPG0352) and the wild-type P. gingivalis W83 strain under various pH values, temperatures and oxidative stress conditions to identify the roles of sialidase in the adaptation of P. gingivalis to stressful conditions.

RESULTS

Compared to the growth of the P. gingivalis W83 strain, the growth of the △PG0352 was more inhibited by oxidative stress (0.25 and 0.5 mM H2O2) and exhibited greater cell structure damage when treated with H2O2 as assessed by transmission electron microscopy. Both Lys-gingipain (Kgp) and Arg-gingipain (Rgp) activities were lower in the ΔPG0352 than those in the P. gingivalis W83 strain under all the assayed culture conditions. The lipopolysaccharide (LPS) activity of the W83 strain was higher than that of the ΔPG0352 under acidic conditions (pH 5.0), but no differences between the strains were observed under other conditions. Compared to the biofilms formed by P. gingivalis W83, those formed by the ΔPG0352 were decreased and discontinuous under acidic, alkaline and oxidative stress conditions.

CONCLUSION

Compared to the P. gingivalis W83 strain, the survival, virulence and biofilm formation of the ΔPG0352 were decreased under stressful environmental conditions.

A 20-amino-acid deletion in the neuraminidase stalk and a five-amino-acid deletion in the NS1 protein both contribute to the pathogenicity of H5N1 avian influenza viruses in mallard ducks

Since 2003, H5N1-subtype avian influenza viruses (AIVs) with both a deletion of 20 amino acids in the stalk of the neuraminidase (NA) glycoprotein (A−) and a deletion of five amino acids at positions 80 to 84 in the non-structural protein NS1 (S−) have become predominant. To understand the influence of these double deletions in the NA and NS1 proteins on the pathogenicity of H5N1-subtype AIVs, we selected A/mallard/Huadong/S/2005 as a parental strain to generate rescued wild-type A−S− and three variants (A−S+ with a five-amino-acid insertion in the NS1 protein, A+S− with a 20-amino-acid insertion in the NA stalk, and A+S+ with insertions in both NA and NS1 proteins) and evaluated their biological characteristics and virulence. The titers of the AIVs with A− and/or S− replicated in DEF cells were higher than that of A+S+, and the A−S− virus exhibited a replication predominance when co-infected with the other variants in DEF cells. In addition, A−S− induced a more significant increase in the expression of immune-related genes in peripheral blood mononuclear cells of mallard ducks in vitro compared with the other variants. Furthermore, an insertion in the NA and/or NS1 proteins of AIVs resulted in a notable decrease in virulence in ducks, as determined by intravenous pathogenicity index, and the two insertions exerted a synergistic effect on the attenuation of pathogenicity in ducks. In addition, compared with A+S+ and A+S−, the A−S+ and A−S− viruses that were introduced via the intranasal inoculation route exhibited a faster replication ability in the lungs of ducks. These data indicate that both the deletions in the NA stalk and the NS1 protein contribute to the high pathogenicity of H5N1 AIVs in ducks.

Influenza neuraminidase as a vaccine antigen

Neuraminidase (NA) is the second most abundant influenza surface glycoprotein and contributes to virus replication in several ways, most notably by removing sialic acids from the host and viral glycoproteins, releasing newly formed virus particles from infected cells. Antibodies that block this enzyme activity restrict virus replication in vitro. This chapter describes foundational epidemiologic and human influenza challenge studies that provide evidence of an association between NA inhibiting antibodies and resistance to disease. Mouse challenge studies show that while NA immunity is infection-permissive, NA-specific antibodies attenuate infection and prevent severe disease. NA immunity is most effective against homologous viruses but there is substantial protection against viruses with a heterologous NA (different lineage within a NA subtype). Monoclonal antibodies specific for conserved antigenic domains of subtype N1 protect against seasonal and pandemic H1N1 as well as H5N1 virus challenge. Clinical studies demonstrate that licensed seasonal vaccines contain immunogenic amounts of NA, but the contribution of this immunity to vaccine efficacy is currently not known. New types of influenza vaccines could be designed to elicit NA immunity. Because NA induces heterologous immunity, it could be an important constituent of universal influenza vaccines that aim to protect against unexpected emerging viruses.

The low-pH stability discovered in neuraminidase of 1918 pandemic influenza A virus enhances virus replication

The “Spanish” pandemic influenza A virus, which killed more than 20 million worldwide in 1918-19, is one of the serious pathogens in recorded history. Characterization of the 1918 pandemic virus reconstructed by reverse genetics showed that PB1, hemagglutinin (HA), and neuraminidase (NA) genes contributed to the viral replication and virulence of the 1918 pandemic influenza virus. However, the function of the NA gene has remained unknown. Here we show that the avian-like low-pH stability of sialidase activity discovered in the 1918 pandemic virus NA contributes to the viral replication efficiency. We found that deletion of Thr at position 435 or deletion of Gly at position 455 in the 1918 pandemic virus NA was related to the low-pH stability of the sialidase activity in the 1918 pandemic virus NA by comparison with the sequences of other human N1 NAs and sialidase activity of chimeric constructs. Both amino acids were located in or near the amino acid resides that were important for stabilization of the native tetramer structure in a low-pH condition like the N2 NAs of pandemic viruses that emerged in 1957 and 1968. Two reverse-genetic viruses were generated from a genetic background of A/WSN/33 (H1N1) that included low-pH-unstable N1 NA from A/USSR/92/77 (H1N1) and its counterpart N1 NA in which sialidase activity was converted to a low-pH-stable property by a deletion and substitutions of two amino acid residues at position 435 and 455 related to the low-pH stability of the sialidase activity in 1918 NA. The mutant virus that included “Spanish Flu”-like low-pH-stable NA showed remarkable replication in comparison with the mutant virus that included low-pH-unstable N1 NA. Our results suggest that the avian-like low-pH stability of sialidase activity in the 1918 pandemic virus NA contributes to the viral replication efficiency.

Transforming growth factor-β: activation by neuraminidase and role in highly pathogenic H5N1 influenza pathogenesis

Transforming growth factor-beta (TGF-β), a multifunctional cytokine regulating several immunologic processes, is expressed by virtually all cells as a biologically inactive molecule termed latent TGF-β (LTGF-β). We have previously shown that TGF-β activity increases during influenza virus infection in mice and suggested that the neuraminidase (NA) protein mediates this activation. In the current study, we determined the mechanism of activation of LTGF-β by NA from the influenza virus A/Gray Teal/Australia/2/1979 by mobility shift and enzyme inhibition assays. We also investigated whether exogenous TGF-β administered via a replication-deficient adenovirus vector provides protection from H5N1 influenza pathogenesis and whether depletion of TGF-β during virus infection increases morbidity in mice. We found that both the influenza and bacterial NA activate LTGF-β by removing sialic acid motifs from LTGF-β, each NA being specific for the sialic acid linkages cleaved. Further, NA likely activates LTGF-β primarily via its enzymatic activity, but proteases might also play a role in this process. Several influenza A virus subtypes (H1N1, H1N2, H3N2, H5N9, H6N1, and H7N3) except the highly pathogenic H5N1 strains activated LTGF-β in vitro and in vivo. Addition of exogenous TGF-β to H5N1 influenza virus-infected mice delayed mortality and reduced viral titers whereas neutralization of TGF-β during H5N1 and pandemic 2009 H1N1 infection increased morbidity. Together, these data show that microbe-associated NAs can directly activate LTGF-β and that TGF-β plays a pivotal role protecting the host from influenza pathogenesis.

Competitive fitness of oseltamivir-sensitive and -resistant highly pathogenic H5N1 influenza viruses in a ferret model

The fitness of oseltamivir-resistant highly pathogenic H5N1 influenza viruses has important clinical implications. We generated recombinant human A/Vietnam/1203/04 (VN; clade 1) and A/Turkey/15/06 (TK; clade 2.2) influenza viruses containing the H274Y neuraminidase (NA) mutation, which confers resistance to NA inhibitors, and compared the fitness levels of the wild-type (WT) and resistant virus pairs in ferrets. The VN-H274Y and VN-WT viruses replicated to similar titers in the upper respiratory tract (URT) and caused comparable disease signs, and none of the animals survived. On days 1 to 3 postinoculation, disease signs caused by oseltamivir-resistant TK-H274Y virus were milder than those caused by TK-WT virus, and all animals survived. We then studied fitness by using a novel approach. We coinoculated ferrets with different ratios of oseltamivir-resistant and -sensitive H5N1 viruses and measured the proportion of clones in day-6 nasal washes that contained the H274Y NA mutation. Although the proportion of VN-H274Y clones increased consistently, that of TK-H274Y virus decreased. Mutations within NA catalytic (R292K) and framework (E119A/K, I222L, H274L, and N294S) sites or near the NA enzyme active site (V116I, I117T/V, Q136H, K150N, and A250T) emerged spontaneously (without drug pressure) in both pairs of viruses. The NA substitutions I254V and E276A could exert a compensatory effect on the fitness of VN-H274Y and TK-H274Y viruses. NA enzymatic function was reduced in both drug-resistant H5N1 viruses. These results show that the H274Y NA mutation affects the fitness of two H5N1 influenza viruses differently. Our novel method of assessing viral fitness accounts for both virus-host interactions and virus-virus interactions within the host.

The special neuraminidase stalk-motif responsible for increased virulence and pathogenesis of H5N1 influenza A virus

The variation of highly pathogenic avian influenza H5N1 virus results in gradually increased virulence in poultry, and human cases continue to accumulate. The neuraminidase (NA) stalk region of influenza virus varies considerably and may associate with its virulence. The NA stalk region of all N1 subtype influenza A viruses can be divided into six different stalk-motifs, H5N1/2004-like (NA-wt), WSN-like, H5N1/97-like, PR/8-like, H7N1/99-like and H5N1/96-like. The NA-wt is a special NA stalk-motif which was first observed in H5N1 influenza virus in 2000, with a 20-amino acid deletion in the 49^th to 68^th positions of the stalk region. Here we show that there is a gradual increase of the special NA stalk-motif in H5N1 isolates from 2000 to 2007, and notably, the special stalk-motif is observed in all 173 H5N1 human isolates from 2004 to 2007. The recombinant H5N1 virus with the special stalk-motif possesses the highest virulence and pathogenicity in chicken and mice, while the recombinant viruses with the other stalk-motifs display attenuated phenotype. This indicates that the special stalk-motif has contributed to the high virulence and pathogenicity of H5N1 isolates since 2000. The gradually increasing emergence of the special NA stalk-motif in H5N1 isolates, especially in human isolates, deserves attention by all.

Neuraminidase inhibitor drug susceptibility differs between influenza N1 and N2 neuraminidase following mutagenesis of two conserved residues

Neuraminidase (NA) inhibitors are a class of antivirals designed to target the conserved residues of the influenza NA active site. While there are many conserved residues in the NA active site that are involved in NA inhibitor binding, only a few have been demonstrated to confer resistance. As such, little is known regarding the potential of the other conserved residues in the NA active site to cause NA inhibitor resistance. Two conserved residues (E227 and E276) of an N1 NA that have not previously been associated with resistance to NA inhibitors were investigated. Site-directed mutagenesis was used to generate three alternative amino acids at each residue. Reverse genetics was used to generate recombinant mutant viruses which were characterized for growth, NA activity and NA inhibitor sensitivity. Of the six recombinant viruses expressing NA with mutations at either E227 or E276, only the E227D and E276D viruses were able to grow without supplementary NA activity, and all mutant viruses had a significant reduction in NA activity. The E227D virus demonstrated significantly reduced sensitivity to zanamivir while the E276D virus did not demonstrate any significant changes in NA inhibitor sensitivity. Interestingly, the resistance profiles of E227D and E276D in N1 NA were significantly different from these sites that have been reported for N2 NA. This study confirmed the essential role of NA active site residues in viral fitness, and identified clear differences in the role of residues E227 and E276 in NA inhibitor resistance with N1 and N2 neuraminidases.

Variation in the divalent cation requirements of influenza A virus N1 neuraminidases

Enzymatic kinetic parameters of influenza A virus N1 neuraminidases (NA) chromatographically purified from several vaccine candidate strains were tested. With ionic strength held constant, Ca2+ or Mg2+ increased the initial rate of enzymatic activity. The 1934 and 1943 strains had statistically significant highest initial velocities, V(max)/K(m) and V(max). There were no significant differences among the influenza virus strains from 1947 to 1991. Measured K(m) for the 1943 strain (6.2 x 10(-5) M) was significantly higher than other strains (3.1-4.7 x 10(-5) M). V(max)/K(m) varied from 0.78 M(-1) s(-1) to 0.91 M(-1) s(-1) and V(max) varied from 3.0 s(-1) to 5.5 s(-1) before the addition of a divalent cation and increased approximately 2-fold for each of these kinetic parameters for each strain after the addition of exogenous Ca2+ or Mg2+. Dialysis reduced the initial velocity and immunogenicity of each strain with significant differences found among strains. Enzymatic activity and immunogenicity were partially restored by the addition of exogenous Ca2+. Nucleic acid sequence analysis could not predict these differences. Selection of vaccine strains must include analysis of antigenic changes, but also enzymatic studies and determination of the requirement of divalent cations to maintain immunogenicity and activity during production.

A crucial role of plasma membrane-associated sialidase in the survival of human cancer cells

Human plasma membrane-associated sialidase (NEU3), a key enzyme for ganglioside degradation, is markedly upregulated in human cancers, leading to apoptosis suppression. To define molecular mechanisms and the possible target for NEU3, its encoding gene was silenced by small interference RNA (siRNA) or overexpressed in human cells. NEU3 siRNA-induced apoptosis with no special stimuli in HeLa cells, accompanied with decreased Bcl-xL and increased mda7 and GM3 synthase mRNA levels, whereas overexpression resulted in the opposite. Carcinoma HT-29 and MCF-7 cells appeared to be similarly affected, but normal cell lines demonstrated no significant changes. NEU3 siRNA was found to inhibit and NEU3 overexpression to stimulate Ras activation with consequent influence on extracellular signal-regulated kinases and Akt. Ras activation by NEU3 was abrogated by PP2 (src inhibitor) or AG1478 (epidermal growth factor receptor (EGFR) inhibitor), and NEU3 actually enhanced EGF-stimulated tyrosine-phosphorylation of EGFR, suggesting that the upstream targets might be tyrosine kinases including src and EGFR, and the subsequent stimulation of Ras cascade leads to the inhibition of cell apoptosis. Glycolipid changes observed seemed to be one of the causes of the cell effects. NEU3 may thus be an essential gene for cancer cell survival and siRNAs targeting this protein could have utility for gene-based therapy of human cancers.

Increased hepatic expression of ganglioside-specific sialidase, NEU3, improves insulin sensitivity and glucose tolerance in mice

Membrane microdomains rich in gangliosides are recognized as being critical for proper compartmentalization of insulin signaling. Plasma membrane-associated sialidase, NEU3, is a key enzyme for ganglioside hydrolysis. We previously reported that mice overexpressing NEU3 mainly in muscles developed severe insulin-resistant diabetes. To examine the possible contributions of NEU3 to in vivo insulin sensitivity and glucose tolerance, NEU3 was expressed by using adenoviral vectors in the livers of C57BL/6 mice on standard and high-fat diets, and insulin-resistant KKAy mice on standard diets. Hepatic NEU3 overexpression paradoxically improved glucose tolerance and insulin sensitivity in the C57BL/6 mice fed standard diets, and glucose tolerance in the C57BL/6 mice fed high-fat diets and in KKAy mice. Hepatic NEU3 overexpression increased hepatic glycogen deposition and triglyceride accumulation, and enhanced the hepatic peroxisome proliferator-activated receptor gamma and fetuin expression in the C57BL/6 mice on standard and high-fat diets, and in KKAy mice. Thin-layer chromatographic analysis demonstrated increased levels of GM1 and markedly reduced GM3 in the livers of mice with hepatic NEU3 overexpression (NEU3 mice). Basal and insulin-stimulated tyrosine phosphorylations of insulin receptor substrate 1 were significantly increased, but tyrosine phosphorylations of the insulin receptor and insulin receptor substrate 2 in the NEU3 liver were unchanged. Insulin-stimulated tyrosine phosphorylations of the insulin receptor were increased in adipose tissues of NEU3 mice. These results suggest that hepatic NEU3 overexpression improves insulin sensitivity and glucose tolerance through modification of ganglioside composition and peroxisome proliferator-activated receptor gamma signaling. Our findings also provide further evidence that NEU3 is an important regulator of insulin sensitivity and glucose tolerance.

A conserved domain of the gp85/trans-sialidase family activates host cell extracellular signal-regulated kinase and facilitates Trypanosoma cruzi infection

Chagas' disease is a chronic, debilitating and incapacitating illness, caused by the protozoan parasite Trypanosoma cruzi when infective trypomastigotes invade host cells. Although the mechanism of trypomastigotes interaction with mammalian cells has been intensively studied, a final and integrated picture of the signal transduction mechanisms involved still remains to be elucidated. Our group has previously shown that the conserved FLY domain (VTVXNVFLYNR), present in all members of the gp85/trans-sialidase glycoprotein family coating the surface of trypomastigotes, binds to cytokeratin 18 (CK18) on the surface of LLC-MK(2) epithelial cells, and significantly increases parasite entry into mammalian cells. Now it is reported that FLY, present on the surface of trypomastigotes or on latex beads binds to CK18, promotes dephosphorylation and reorganization of CK18 and activation of the ERK1/2 signaling cascade culminating in an increase of approximately 9-fold in the number of parasites/cell. Inhibition of ERK1/2 phosphorylation completely blocks the adhesion of FLY to cells and blocks by 57% the host cell infection by T. cruzi. Taken together our results indicate that the conserved FLY domain is an important tool that trypomastigotes have evolved to specific exploit the host cell machinery and guarantee a successful infection.

Role of sialidase in Mycoplasma alligatoris-induced pulmonary fibroblast apoptosis

Mycoplasma alligatoris causes acute lethal cardiopulmonary disease of susceptible hosts. A survey of its genome implicated sialidase and hyaluronidase, synergistic regulators of hyaluronan receptor CD44-mediated signal transduction leading to apoptotic cell death, as virulence factors of M. alligatoris. In this study, after the existence of a CD44 homolog in alligators was established by immunolabeling primary pulmonary fibroblasts with monoclonal antibody IM7 against murine CD44, the sialidase inhibitor 2,3-didehydro-2-deoxy-N-acetylneuraminic acid (DANA) was used to examine the effects of sialidase on fibroblast apoptosis following in vitro infection with M. alligatoris. While their CD44 expression remained constant, infected cells exhibited morphologic changes characteristic of apoptosis including decreased size, rounding, disordered alpha-tubulin, and nuclear disintegration compared to untreated controls. DANA was a potent, non-toxic inhibitor of the sialidase activity, equivalent to about 1mU of Clostridium perfringens Type VI sialidase, expressed by M. alligatoris in the inoculum. Although DANA did not measurably reduce the proportion of infected fibroblasts labeled by a specific ligand of activated caspases, co-incubation with DANA protected (P<0.01) fibroblasts in a concentration-dependent fashion from the M. alligatoris-induced trends toward increased apoptosis receptor CD95 expression, and increased 5-bromo-2'-deoxyuridine incorporation measured in a terminal dUTP nick end-labeling apoptosis assay. In contrast, incubation with 200-fold excess purified C. perfringens sialidase alone did not affect CD95 expression or chromatin integrity, or induce fibroblast apoptosis. From those observations we conclude that interaction of its sialidase with hyaluronidase or another virulence factor(s) is necessary to elicit the pro-apoptotic effects of M. alligatoris infection.

Pneumococcal neuraminidases A and B both have essential roles during infection of the respiratory tract and sepsis

We examined the role of the neuraminidases NanA and NanB in colonization and infection in the upper and lower respiratory tract by Streptococcus pneumoniae, as well as the role of these neuraminidases in the onset and development of septicemia following both intranasal and intravenous infection. We demonstrated for the first time using outbred MF1 mouse models of infection that both NanA and NanB were essential for the successful colonization and infection of the upper and lower respiratory tract, respectively, as well as pneumococcal survival in nonmucosal sites, such as the blood. Our studies have shown that in vivo a neuraminidase A mutant is cleared from the nasopharynx, trachea, and lungs within 12 h postinfection, while a neuraminidase B mutant persists but does not increase in either the nasopharynx, trachea, or lungs. We also demonstrated both neuraminidase mutants were unable to cause sepsis following intranasal infections. When administered intravenously, however, both mutants survived initially but were unable to persist in the blood beyond 48 h postinfection and were progressively cleared. The work presented here demonstrates the importance of pneumococcal neuraminidase A and for the first time neuraminidase B in the development of upper and lower respiratory tract infection and sepsis.

[Biological significance of amino acids deletion in NA stalk of H5N1 avian influenza virus]

It has been reported that NA gene of some H1N1 Influenza A virus strains isolated since 1933 is characterized by a deletion of 11 to 16 amino acids in the stalk. The spontaneous mutant in NA stalk of H1N1 virus lacks enzyme activity with large substrate (fetuin) but not with small substrate (sialyllactose). Recently, H5N1 virus also has been found that NA has the same unique mutation in the stalk, a deletion of 15 to 20 amino acids. However, biological significance of this mutation has not yet been reported. In order to investigate biological significance of the amino acids deletion in NA stalk of H5N1, five reassorted H5N1/PR8 viruses were generated via eight-plasmid based reverse genetics system. These five viruses were named 506, m506-, 646, m646+ and 196, respectively. The six internal genes of recombinants were all from A/PR8/34(H1N1), and HA gene was from A/G/JS/03(H5N1), however, they had different NA genes. 506 and m506- held NA fragments derived from A/G/HD/00(H5N1), and the former was distinguished with a longer NA which had no 20 amino acids deletion in the stalk. 646 and m646+ held NA fragments from A/G/JS/03(H5N1), and the NA stalk of m646+ was 20 amino acids longer than that of 646. The NA of 196 was derived from A/PR8/34 which had 15 amino acids deletion in its stalk. Biological characteristics of these viruses showed that recombinants with different NA length could grow well in embryonated SPF eggs, and their EID50, MDT, and viral titers were similar. However, the length of NA was related to the capacity of eluting viruses from erythrocytes for 506 and 646+ which holding longer NA stalks eluted from erythrocytes more quickly than m506-, 646 and 196 did. Moreover, 15 or 20 amino acids deletion in NA stalk had a pronounced effect on virus growth ability in MDCK cells. Viral titers in supernatant of MDCK infected with m506- or 646 were 10 to 100 folds higher than those infected by 506 or m646+. And the plaque size of m506- and 646 were larger than that of 506 and m646+. The results reveals that H5N1 AIV with amino acids deletion in NA stalk would expand its host range. The unique amino acids deletion in NA molecule of H5N1 may be associated with the adaptation of virus to terrestrial poultry or the increasing ability of interspecies transmission.

Expression of trypomastigote trans-sialidase in metacyclic forms of Trypanosoma cruzi increases parasite escape from its parasitophorous vacuole

Trypanosoma cruzi actively invades mammalian cells by forming parasitophorous vacuoles (PVs). After entry, the parasite has to escape from these vacuoles in order to replicate inside the host cell cytosol. Trans-sialidase (TS), a parasite enzyme that is used to obtain sialic acid from host glycoconjugates, has been implicated in cell invasion and PV exit, but how the enzyme acts in these processes is still unknown. Here we show that trypomastigotes derived from infected mammalian cells express and release 20 times more TS activity than axenic metacyclic trypomastigotes, which correspond to the infective forms derived from the insect vector. Both forms have the same capacity to invade mammalian cells, but cell derived trypomastigotes exit earlier from the vacuole. To test whether high TS expression is responsible for this increased exit from the PV, trypomastigote TS was expressed on the surface of metacyclic forms. Transfected and non-transfected metacyclics attached to and invaded HeLa or CHO cells equally. In contrast, metacyclics expressing TS on the surface escaped earlier from the vacuole than non-transfected metacyclics, or metacyclics expressing TS in their cytoplasm. Sialic acid may act as a barrier, which is removed by surface and/or secreted TS, because all types of parasites escaped earlier from the vacuoles of sialic acid-deficient Lec 2 cells than wild-type CHO cells. In addition, trypomastigotes and metacyclic forms expressing TS differentiated earlier into amastigotes. These results indicate that the increased expression of TS in cell-derived trypomastigotes is responsible for the earlier exit from the PV to the cytoplasm and their subsequent differentiation into amastigotes.

A mutant fusion (F) protein of simian virus 5 induces hemagglutinin-neuraminidase-independent syncytium formation despite the internalization of the F protein

The fusion (F) protein of simian virus 5 strain W3A induces syncytium formation independently of coexpression of the hemagglutinin-neuraminidase protein. This property can be transferred to the F protein of strain WR by replacing the leucine at position 22 with the W3A F counterpart, proline. The resulting mutant L22P has a conformation that is distinct from that of the WR F protein. Se-L22P is a cleavage site mutant of L22P that is cleavable only by addition of exogenous trypsin. We showed here that the cell surface-localized L22P was internalized with a t1/2 of 25 min and degraded in the cell, while the WR F protein was not. The cell surface-localized Se-L22P underwent a significant conformational change upon cleavage. Intriguingly, it disappeared from the cell surface due to its internalization, while inducing extensive syncytium formation. These results indicate that L22P may display an internalization signal during the course of fusion induction.

An adult with acute poststreptococcal glomerulonephritis complicated by hemolytic uremic syndrome and nephrotic syndrome

We report the case of a 47-year-old man with the simultaneous occurrence of clinical and laboratory features consistent with acute poststreptococcal glomerulonephritis (APSGN), hemolytic uremic syndrome (HUS), and nephrotic syndrome. Acute nephritic syndrome occurred 3 weeks after having pharyngeal pain and diarrhea. He presented with edema and hypertension on admission. Laboratory evaluation showed hemolytic anemia with fragmentation, thrombocytopenia, elevated lactic dehydrogenase level, low haptoglobin level, low complement C3 level, and elevated antistreptolysin-O titer. Serum creatinine level was 1.22 mg/dL (108 micromol/L), and urinalysis showed marked proteinuria, with protein of 8.7 g/d, and hematuria. The renal biopsy specimen was characteristic of APSGN, but not HUS. Moderate expansion of the mesangial matrix, moderate proliferation of epithelial and endothelial cells, and marked infiltration of neutrophils was seen by means of light microscopy, and many subepithelial humps were seen by means of electron microscopy. Neither fibrin deposition nor evidence of thrombotic microangiopathy was found. Complement C3 deposition along the capillary wall and tubules was seen in an immunofluorescence study. The patient was administered plasma infusion at 320 mL/d and antihypertensive drugs. Serum complement C3 and haptoglobin levels returned to normal within 3 weeks. This is a rare case of the simultaneous occurrence of APSGN, HUS, and nephrotic syndrome.

The trans-sialidase from Trypanosoma cruzi induces thrombocytopenia during acute Chagas' disease by reducing the platelet sialic acid contents

Strong thrombocytopenia is observed during acute infection with Trypanosoma cruzi, the parasitic protozoan agent of American trypanosomiasis or Chagas' disease. The parasite sheds trans-sialidase, an enzyme able to mobilize the sialyl residues on cell surfaces, which is distributed in blood and is a virulence factor. Since the sialic acid content on the platelet surface is crucial for determining the half-life of platelets in blood, we examined the possible involvement of the parasite-derived enzyme in thrombocytopenia induction. We found that a single intravenous injection of trans-sialidase into naive mice reduced the platelet count by 50%, a transient effect that lasted as long as the enzyme remained in the blood. CD43(-/-) mice were affected to a similar extent. When green fluorescent protein-expressing platelets were treated in vitro with trans-sialidase, their sialic acid content was reduced together with their life span, as determined after transfusion into naive animals. No apparent deleterious effect on the bone marrow was observed. A central role for Kupffer cells in the clearance of trans-sialidase-altered platelets was revealed after phagocyte depletion by administration of clodronate-containing liposomes and splenectomy. Consistent with this, parasite strains known to exhibit more trans-sialidase activity induced heavier thrombocytopenia. Finally, the passive transfer of a trans-sialidase-neutralizing monoclonal antibody to infected animals prevented the clearance of transfused platelets. Results reported here strongly support the hypothesis that the trans-sialidase is the virulence factor that, after depleting the sialic acid content of platelets, induces the accelerated clearance of the platelets that leads to the thrombocytopenia observed during acute Chagas' disease.

[Lipid raft and influenza virus--viral glycoproteins on a raft]

Lipid molecules of the plasma membrane are not distributed homogeneously, but form a lateral organization resulting from preferential packaging of sphingolipid and cholesterol into lipid microdomain rafts, in which specific membrane proteins become incorporated. Evidence has accumulated that a variety of viruses including influenza virus use the raft during some steps of their replication cycles. Influenza virus glycoproteins, hemagglutinin (HA) and neuraminidase, associate intrinsically with the rafts. The HA protein is distributed in clusters at the plasma membrane and concentrated in the small area by interacting with the raft. A mutant influenza virus, whose HA protein lacks the ability to associate with the raft, contains reduced amounts of the HA proteins and exhibits a decreased virus to cell fusion activity, resulting in greatly reduced infectivity. Thus, the raft may play an important role in virus production by acting as a concentrating devise or an efficient carrier to transport the HA protein to the site of virus budding.

Neuraminidase is important for the initiation of influenza virus infection in human airway epithelium

Influenza virus neuraminidase (NA) plays an essential role in release and spread of progeny virions, following the intracellular viral replication cycle. To test whether NA could also facilitate virus entry into cell, we infected cultures of human airway epithelium with human and avian influenza viruses in the presence of the NA inhibitor oseltamivir carboxylate. Twenty- to 500-fold less cells became infected in drug-treated versus nontreated cultures (P < 0.0001) 7 h after virus application, indicating that the drug suppressed the initiation of infection. These data demonstrate that viral NA plays a role early in infection, and they provide further rationale for the prophylactic use of NA inhibitors.

Induction of lysosomal and plasma membrane-bound sialidases in human T-cells via T-cell receptor

Among the three isoenzymes of neuraminidase (Neu) or sialidase, Neu-1 has been suggested to be induced by cell activation and to be involved in IL (interleukin)-4 biosynthesis in murine T-cells. In the present study, we found that antigen-induced airway eosinophilia, a typical response dependent on Th2 (T-helper cell type 2) cytokines, as well as mRNA expression of Th2 cytokines, including IL-4, are suppressed in Neu-1-deficient mice, thereby demonstrating the in vivo role of murine Neu-1 in regulation of Th2 cytokines. To elucidate the roles of various sialidases in human T-cell activation, we investigated their tissue distribution, gene induction and function. Neu-1 is the predominant isoenzyme at the mRNA level in most tissues and cells in both mice and humans, including T-cells. T-cells also have significant levels of Neu-3 mRNAs, albeit much lower than those of Neu-1, whereas the levels of Neu-2 mRNAs are minimal. In human T-cells, both Neu-1 and Neu-3 mRNAs are significantly induced by T-cell-receptor stimulation, as is sialidase activity against 4-methylumbelliferyl- N -acetylneuramic acid (a substrate for both Neu-1 and Neu-3) and the ganglioside G(D1a) [NeuAcalpha2-3Galbeta1-3GalNAcbeta1-4(NeuAcalpha2-3)Galbeta1-4Glcbeta1-cer] (a substrate for Neu-3, but not for Neu-1). The expression of the two sialidase genes may be under differential regulation. Western blot analysis and enzymic comparison with recombinant sialidases have revealed that Neu-3 is induced as a major isoform in activated cells. The induction of Neu-1 and Neu-3 in T-cells is unique. In human monocytes and neutrophils stimulated with various agents, the only observation of sialidase induction has been by IL-1 in neutrophils. Functionally, a major difference has been observed in Jurkat T-cell lines over-expressing Neu-1- and Neu-3. Upon T-cell receptor stimulation, IL-2, interferon-gamma, IL-4 and IL-13 are induced in the Neu-1 line, whereas in the Neu-3 line the same cytokines are induced, with the exception of IL-4. Taken together, these results suggest an important immunoregulatory role for both Neu-1 and Neu-3 in humans.

Neu4, a Novel Human Lysosomal Lumen Sialidase, Confers Normal Phenotype to Sialidosis and Galactosialidosis Cells

Three different mammalian sialidases have been described as follows: lysosomal (Neu1, gene NEU1), cytoplasmic (Neu2, gene NEU2), and plasma membrane (Neu3, gene NEU3). Because of mutations in the NEU1 gene, the inherited deficiency of Neu1 in humans causes the severe multisystemic neurodegenerative disorder sialidosis. Galactosialidosis, a clinically similar disorder, is caused by the secondary Neu1 deficiency because of genetic defects in cathepsin A that form a complex with Neu1 and activate it. In this study we describe a novel lysosomal lumen sialidase encoded by the NEU4 gene on human chromosome 2. We demonstrate that Neu4 is ubiquitously expressed in human tissues and has broad substrate specificity by being active against sialylated oligosaccharides, glycoproteins, and gangliosides. In contrast to Neu1, Neu4 is targeted to lysosomes by the mannose 6-phosphate receptor and does not require association with other proteins for enzymatic activity. Expression of Neu4 in the cells of sialidosis and galactosialidosis patients results in clearance of storage materials from lysosomes suggesting that Neu4 may be useful for developing new therapies for these conditions.

Role of transmembrane domain and cytoplasmic tail amino acid sequences of influenza a virus neuraminidase in raft association and virus budding

Influenza virus neuraminidase (NA), a type II transmembrane glycoprotein, possesses receptor-destroying activity and thereby facilitates virus release from the cell surface. Among the influenza A viruses, both the cytoplasmic tail (CT) and transmembrane domain (TMD) amino acid sequences of NA are highly conserved, yet their function(s) in virus biology remains unknown. To investigate the role of amino acid sequences of the CT and TMD on the virus life cycle, we systematically mutagenized the entire CT and TMD of NA by converting two to five contiguous amino acids to alanine. In addition, we also made two chimeric NA by replacing the CT proximal one-third amino acids of the NA TMD [NA(1T2N)NA] and the entire NA TMD (NATRNA) with that of human transferrin receptor (TR) (a type II transmembrane glycoprotein). We rescued transfectant mutant viruses by reverse genetics and examined their phenotypes. Our results show that all mutated and chimeric NAs could be rescued into transfectant viruses. Different mutants showed pleiotropic effects on virus growth and replication. Some mutants (NA2A5, NA3A7, and NA4A10) had little effect on virus growth while others (NA3A2, NA5A27, and NA5A31) produced about 50- to 100-fold-less infectious virus and still some others (NA5A14, NA4A19, and NA4A23) exhibited an intermediate phenotype. In general, mutations towards the ectodomain-proximal sequences of TMD progressively caused reduction in NA enzyme activity, affected lipid raft association, and attenuated virus growth. Electron microscopic analysis showed that these mutant viruses remained aggregated and bound to infected cell surfaces and could be released from the infected cells by bacterial NA treatment. Moreover, viruses containing mutations in the extreme N terminus of the CT (NA3A2) as well as chimeric NA containing the TMD replaced partially [NA(1T2N)NA] or fully (NATRNA) with TR TMD caused reduction in virus growth and exhibited the morphological phenotype of elongated particles. These results show that although the sequences of NA CT and TMD per se are not absolutely essential for the virus life cycle, specific amino acid sequences play a critical role in providing structural stability, enzyme activity, and lipid raft association of NA. In addition, aberrant morphogenesis including elongated particle formation of some mutant viruses indicates the involvement of NA in virus morphogenesis and budding.

The Plasma Membrane-associated Sialidase MmNEU3 Modifies the Ganglioside Pattern of Adjacent Cells Supporting Its Involvement in Cell-to-Cell Interactions

We describe herein the enzyme behavior of MmNEU3, the plasma membrane-associated sialidase from mouse (Mus musculus). MmNEU3 is localized at the plasma membrane as demonstrated directly by confocal microscopy analysis. In addition, administration of the radiolabeled ganglioside GD1a to MmNEU3-transfected cells, under conditions that prevent lysosomal activity, led to its hydrolysis into ganglioside GM1, further indicating the plasma membrane topology of MmNEU3. Metabolic labeling with [1-(3)H]sphingosine allowed the characterization of the ganglioside patterns of COS-7 cells. MmNEU3 expression in COS-7 cells led to an extensive modification of the cell ganglioside pattern, i.e. GM3 and GD1a content was decreased to about one-third compared with mock-transfected cells. At the same time, a 35% increase in ganglioside GM1 content was observed. Mixed culture of MmNEU3-transfected cells with [1-(3)H]sphingosine-labeled cells demonstrates that the enzyme present at the cell surface is able to recognize gangliosides exposed on the membrane of nearby cells. Under these experimental conditions, the extent of ganglioside pattern changes was a function of MmNEU3 transient expression. Overall, the variations in GM3, GD1a, and GM1 content were very similar to those observed in the case of [1-(3)H]sphingosine-labeled MmNEU3-transfected cells, indicating that the enzyme mainly exerted its activity toward ganglioside substrates present at the surface of neighboring cells. These results indicate that the plasma membrane-associated sialidase MmNEU3 is able to hydrolyze ganglioside substrates in intact living cells at a neutral pH, mainly through cell-to-cell interactions.

[Influenza virus infection and apoptosis]

Many viruses including influenza virus induce apoptosis of host cells. Influenza virus-induced apoptosis shares common features of apoptosis, i.e. activation of caspases and inhibition by bcl-2. Fas and its ligand and double stranded-RNA activated-protein kinase (PKR) are partly involved in the apoptosis. Virus proteins as nonstructural protein I, neuraminidase as well as a novel protein, PB1-F2, play some roles in promoting the virus-induced apoptosis. Apoptotic cells are effectively engulfed by macrophages, which recognize phosphatidylserine on the outer leaflet of the membrane of apoptotic cell. Neuraminidase activity is required for the effective phagocytosis. All these evidence suggest that the virus-induced apoptosis is one of the mechanisms of host defense system.

Tumor necrosis factor-alpha induces functionally active hyaluronan-adhesive CD44 by activating sialidase through p38 mitogen-activated protein kinase in lipopolysaccharide-stimulated human monocytic cells

Interaction of CD44, an adhesion molecule, with its ligand, hyaluronan (HA), in monocytic cells plays a critical role in cell migration, inflammation, and immune responses. Most cell types express CD44 but do not bind HA. The biological functions of CD44 have been attributed to the generation of the functionally active, HA-adhesive form of this molecule. Although lipopolysaccharide (LPS) and cytokines induce HA-adhesive CD44, the molecular mechanism underlying this process remains unknown. In this study, we show that LPS-induced CD44-mediated HA (CD44-HA) binding in monocytes is regulated by endogenously produced tumor necrosis factor (TNF)-alpha and IL-10. Furthermore, p38 mitogen-activated protein kinase (MAPK) activation was required for LPS- and TNF-alpha-induced, but not IL-10-induced, CD44-HA-binding in normal monocytes. To dissect the signaling pathways regulating CD44-HA binding independently of cross-regulatory IL-10-mediated effects, IL-10-refractory promonocytic THP-1 cells were employed. LPS-induced CD44-HA binding in THP-1 cells was regulated by endogenously produced TNF-alpha. Our results also suggest that lysosomal sialidase activation may be required for the acquisition of the HA-binding form of CD44 in LPS- and TNF-alpha-stimulated monocytic cells. Studies conducted to understand the role of MAPKs in the induction of sialidase activity revealed that LPS-induced sialidase activity was dependent on p42/44 MAPK-mediated TNF-alpha production. Blocking TNF-alpha production by PD98059, a p42/44 inhibitor, significantly reduced the LPS-induced sialidase activity and CD44-HA binding. Subsequently, TNF-alpha-mediated p38 MAPK activation induced sialidase activity and CD44-HA binding. Taken together, our results suggest that TNF-alpha-induced p38 MAPK activation may regulate the induction of functionally active HA-binding form of CD44 by activating sialidase in LPS-stimulated human monocytic cells.

Role of neuraminidase in lethal synergism between influenza virus and Streptococcus pneumoniae

A lethal synergism exists between influenza virus and Streptococcus pneumoniae, accounting for excess mortality during influenza epidemics. Using a model of viral-bacterial synergism, we assessed the role that the influenza virus neuraminidase (NA) has in priming mice for pneumococcal infection. Administration of the selective NA inhibitor oseltamivir improved survival, independent of viral replication and morbidity from influenza. Both pathologic examination of the lungs and live imaging of pneumonic lesions, using a bioluminescent pneumococcus, suggested that the effect of NA inhibition was to limit the extent of pneumococcal pneumonia during early infection. Adherence assays and immunohistochemical staining for sialic acids in lungs from infected mice demonstrated that the influenza virus NA potentiates development of pneumonia by stripping sialic acid from the lung, thus exposing receptors for pneumococcal adherence. Selective NA inhibitors may be useful clinically to interrupt this novel mechanism of synergism and to prevent excess mortality from secondary bacterial pneumonia.

Decreased virulence of a pneumolysin-deficient strain of Streptococcus pneumoniae in murine meningitis

Pneumolysin, neuraminidases A and B, and hyaluronidase are virulence factors of Streptococcus pneumoniae that appear to be involved in the pathogenesis of meningitis. In a murine model of meningitis after intracerebral infection using mutants of S. pneumoniae D39, only mice infected with a pneumolysin-deficient strain were healthier at 32 and 36 h, had lower bacterial titers in blood at 36 h, and survived longer than the D39 parent strain. Cerebellar and spleen bacterial titers, meningeal inflammation, and neuronal damage scores remained uninfluenced by the lack of any of the virulence factors.

Pandemic influenza: its origin and control

A "new" influenza virus will appear at some time in the future. This virus will arise by natural processes, which we do not fully understand, or it might be created by some bioterrorist. The world's population will have no immunity to the new virus, which will spread like wild-fire, causing much misery, economic disruption and many deaths. Vaccines will take time to develop and the only means of control, at least in the early stages of the epidemic, are anti-viral drugs, of which the neuraminidase inhibitors currently seem the most effective.

Characterization of a novel Vibrio pathogenicity island (VPI-2) encoding neuraminidase (nanH) among toxigenic Vibrio cholerae isolates

Acquisition of virulence genes encoded on mobile genetic elements has played an important role in the emergence of pathogenic isolates of Vibrio cholerae, the causative agent of the diarrhoeal disease cholera. The genes encoding cholera toxin (ctxAB), the main cause of profuse secretory diarrhoea in cholera, are encoded on a filamentous bacteriophage CTXphi. The toxin coregulated pilus (TCP), an essential intestinal colonization factor, was originally designated as part of a pathogenicity island named the Vibrio pathogenicity island (VPI), but this island has more recently been proposed to be the genome of a filamentous phage, VPIphi. In this study, it is shown that nanH, which encodes neuraminidase, maps within a novel pathogenicity island designated VPI-2. The 57.3 kb VPI-2 has all of the characteristic features of a pathogenicity island, including the presence of a bacteriophage-like integrase (int), insertion in a tRNA gene (serine) and the presence of direct repeats at the chromosomal integration sites. Additionally, the G+C content of VPI-2 (42 mol%) is considerably lower than that of the entire genome (47 mol%). VPI-2 encodes several gene clusters, such as a restriction modification system (hsdR and hsdM) and genes required for the utilization of amino sugars (nan-nag region) as well as neuraminidase. To determine the distribution of VPI-2 among V. cholerae, 78 natural isolates were examined using PCR and Southern hybridization analysis for the presence of this region. All toxigenic V. cholerae O1 serogroup isolates examined contained VPI-2, whereas non-toxigenic isolates lacked the island. Of 14 V. cholerae O139 serogroup isolates examined, only one strain, MO2, contained the entire 57.3 kb island, whereas 13 O139 isolates contained only a 20.0 kb region with most of the 5' region of VPI-2 which included nanH deleted in these strains.

Recent development in mammalian sialidase molecular biology

This review summarizes the recent research development on mammalian sialidase molecular cloning. Sialic acid-containing compounds are involved in several physiological processes, and sialidases, as glycohydrolytic enzymes that remove sialic acid residues, play a pivotal role as well. Sialidases hydrolyze the nonreducing, terminal sialic acid linkage in various natural substrates, such as glycoproteins, glycolipids, gangliosides, and polysaccharides. Mammalian sialidases are present in several tissues/organs and cells with a typical subcellular distribution: they are the lysosomal, the cytosolic, and the plasma membrane-associated sialidases. Starting in 1993, 12 different mammalian sialidases have been cloned and sequenced. A comparison of their amino acid sequences revealed the presence of highly conserved regions. These conserved regions are shared with viral and microbial sialidases that have been characterized at three-dimensional structural level, allowing us to perform the molecular modeling of the mammalian proteins and suggesting a monophyletic origin of the sialidase enzymes. Overall, the availability of the cDNA species encoding mammalian sialidases is an important step leading toward a comprehensive picture of the relationships between the structure and biological function of these enzymes.

Costimulation of host T lymphocytes by a trypanosomal trans-sialidase: involvement of CD43 signaling

Trans-sialidase is a membrane-bound and shed sialidase from Trypanosoma cruzi, the protozoan parasite responsible for Chagas disease. We investigated the role of soluble trans-sialidase on host CD4+ T cell activation. Trans-sialidase activated naive CD4+ T cells in vivo. Both enzymatically active and inactive recombinant trans-sialidases costimulated CD4+ T cell activation in vitro. Costimulation resulted in increased mitogen-activated protein kinase activation, proliferation, and cytokine synthesis. Furthermore, active and inactive trans-sialidases blocked activation-induced cell death in CD4+ T cells from T. cruzi-infected mice. By flow cytometry, inactive trans-sialidase bound the highly sialylated surface Ag CD43 on host CD4+ T cells. Both costimulatory and antiapoptotic effects of trans-sialidases required CD43 signaling. These results suggest that trans-sialidase family proteins are involved in exacerbated host T lymphocyte responses observed in T. cruzi infection.

Correlation between levels of apoptosis, levels of infection and haemagglutinin receptor binding interaction of various subtypes of influenza virus: does the viral neuraminidase have a role in these associations

Previously, we have shown that an H3N2 influenza virus (clone 7a) induced more apoptosis in MDCK cells than an H1N1 (A/Fiji) influenza virus and that the virion neuraminidase (NA) played a role in the induction of apoptosis. In this study we have examined a further 6 N2 (H3/H2) and 3 N1 (Hsw/H1) viruses and confirmed that the N2 viruses induce more apoptosis in MDCK cells than the N1 viruses. Furthermore, the level of apoptosis, the level of cell infection and the NA activity of the virus preparations paralleled each other for all the viruses. The levels of infection depended upon the degree of interaction of the viral haemagglutinin (HA) with its receptors: while all the viruses utilised NeuAc alpha-2,6 Gal containing receptors, the H3/H2 viruses showed a greater interaction than the Hsw/H1 viruses. Removal of sialic acid from virions by treatment with bacterial NA enhanced infection and apoptosis but the effect was much greater for the A/Fiji virus than for the clone 7a virus. Thus, while the relative interaction of the HAs for their receptors is the major factor influencing infectivity and apoptosis, the viral NA possibly plays an indirect role by removing sialic acid from the HA, thereby increasing its receptor binding.

Expression, mutagenesis and kinetic analysis of recombinant K1E endosialidase to define the site of proteolytic processing and requirements for catalysis

Catalytically active, recombinant fusion proteins of bacteriophage E endosialidase were expressed and purified from Escherichia coli. Constructs with different fusion partners added to the amino terminus of the endosialidase were enzymatically active. A post-translational proteolytic cleavage was shown to occur between serine 706 and aspartate 707 to generate the 76 kDa mature enzyme from the 90 kDa translation product. Endosialidase truncated at the C-terminus from aspartate 707 was observed to have the same 76 kDa molecular weight as wild-type enzyme using denaturing SDS-PAGE but, under native PAGE conditions, was not observed to form the approximately 250 kDa trimeric wild-type enzyme, implying that the C-terminus of the enzyme may be required for correct assembly of active trimer, rather than as part of the active site as has been previously suggested. Mutagenesis of aspartate 138 to alanine greatly reduced enzyme activity whereas conversion of other selected aspartate residues to alanine had less effect, consistent with similarities between the structure and cata-lytic mechanism of bacteriophage E endosialidase and those of exosialidases.

Exploitation of the Herpes simplex virus translocating protein VP22 to carry influenza virus proteins into cells for studies of apoptosis: direct confirmation that neuraminidase induces apoptosis and indications that other proteins may have a role

Previously, we have shown that apoptosis induced by influenza virus was inhibited by an anti-neuraminidase compound [4-guanidino-2, 3-dehydro-N-acetylneuraminic acid (GG167; Relenza; Zanamivir)], which does not enter cells, and acts at the attachment/entry phase of virus replication. Furthermore, a virulent virus, clone 7a, induced greater levels of apoptosis than the attenuated A/Fiji and had greater neuraminidase (NA) activity. To confirm more directly that NA induces apoptosis, the NA of clone 7a and A/Fiji was expressed fused to the Herpes simplex virus tegument coat protein VP22, transfected into HeLa cells and the level of apoptosis determined. VP22 translocates between cells via the medium thus allowing expressed proteins to transfer to a larger number of cells than those originally transfected. Clone 7a NA fused to VP22 induced a significant level of apoptosis whereas A/Fiji NA/VP22 did not, confirming that NA activity is an important determinant of apoptosis acting during fusion protein translocation between cells. Furthermore, the induction of apoptosis was abrogated by antibody to transforming growth factor-beta, which is activated by NA. This approach also showed that VP22/NS1 proteins of both clone 7a and A/Fiji induced apoptosis when expressed alone but inhibited double stranded RNA-induced apoptosis suggesting that this protein may have a dual mode of action. Also, the M1 and M2 proteins of both viruses induced apoptosis but their NP proteins did not.

Mucinases and sialidases: their role in the pathogenesis of sexually transmitted infections in the female genital tract

BACKGROUND

Mucinases and sialidases contribute to the process of invasion and colonisation in many conditions and infections of the female reproductive tract by degrading the protective cervical mucus. The role of hydrolytic enzymes in the pathogenesis of sexually transmitted diseases and their effect on cervical mucus are discussed in this review.

METHODS

Articles were searched for using the keywords "sialidase," "mucinase," "protease," and "sexually transmitted infections." As well as review and other articles held by our group, searches were conducted using PubMed, Grateful Med, and the University of Bath search engine, BIDS.

RESULTS

Numerous publications were found describing the production of hydrolytic enzymes in sexually transmitted diseases. Because the number of publications exceeded the restrictions imposed on the size of the review, the authors selected and discussed those which they considered of the most relevance to sexually transmitted infections.

Lysosomal multienzyme complex: biochemistry, genetics, and molecular pathophysiology

Lysosomal enzymes sialidase (alpha-neuraminidase), beta-galactosidase, and N-acetylaminogalacto-6-sulfate sulfatase are involved in the catabolism of glycolipids, glycoproteins, and oligosaccharides. Their functional activity in the cell depends on their association in a multienzyme complex with lysosomal carboxypeptidase, cathepsin A. We review the data suggesting that the integrity of the complex plays a crucial role at different stages of biogenesis of lysosomal enzymes, including intracellular sorting and proteolytic processing of their precursors. The complex plays a protective role for all components, extending their half-life in the lysosome from several hours to several days; and for sialidase, the association with cathepsin A is also necessary for the expression of enzymatic activity. The disintegration of the complex due to genetic mutations in its components results in their functional deficiency and causes severe metabolic disorders: sialidosis (mutations in sialidase), GM1-gangliosidosis and Morquio disease type B (mutations in beta-galactosidase), galactosialidosis (mutations in cathepsin A), and Morquio disease type A (mutations in N-acetylaminogalacto-6-sulfate sulfatase). The genetic, biochemical, and direct structural studies described here clarify the molecular pathogenic mechanisms of these disorders and suggest new diagnostic tools.

Plasminogen-binding activity of neuraminidase determines the pathogenicity of influenza A virus

When expressed in vitro, the neuraminidase (NA) of A/WSN/33 (WSN) virus binds and sequesters plasminogen on the cell surface, leading to enhanced cleavage of the viral hemagglutinin. To obtain direct evidence that the plasminogen-binding activity of the NA enhances the pathogenicity of WSN virus, we generated mutant viruses whose NAs lacked plasminogen-binding activity because of a mutation at the C terminus, from Lys to Arg or Leu. In the presence of trypsin, these mutant viruses replicated similarly to wild-type virus in cell culture. By contrast, in the presence of plasminogen, the mutant viruses failed to undergo multiple cycles of replication while the wild-type virus grew normally. The mutant viruses showed attenuated growth in mice and failed to grow at all in the brain. Furthermore, another mutant WSN virus, possessing an NA with a glycosylation site at position 130 (146 in N2 numbering), leading to the loss of neurovirulence, failed to grow in cell culture in the presence of plasminogen. We conclude that the plasminogen-binding activity of the WSN NA determines its pathogenicity in mice.