Analysis of Acanthamoeba polyphaga surface carbohydrate exposure by FITC-lectin binding and fluorescence evaluation

Stimulation of Acanthamoeba castellanii excystment by enzyme treatment and consequences on trophozoite growth

Acanthamoeba castellanii is a widespread Free-Living Amoeba (FLA) that can cause severe ocular or cerebral infections in immunocompetent and immunocompromised patients, respectively, besides its capacity to transport diverse pathogens. During their life cycle, FLA can alternate between a vegetative form, called a trophozoite, and a latent and resistant form, called a cyst. This resistant form is characterized by the presence of a cell wall containing two layers, namely the ectocyst and the endocyst, mainly composed of cellulose and proteins. In the present work, we aimed to stimulate Acanthamoeba castellanii excystment by treating their cysts with a cellulolytic enzyme, i.e., cellulase, or two proteolytic enzymes, i.e., collagenase and pepsin. While 11 days were necessary to obtain total excystment in the control at 27°C, only 48 h were sufficient at the same temperature to obtain 100% trophozoites in the presence of 25 U/mL cellulase, 50 U/mL collagenase or 100 U/mL pepsin. Additionally, more than 96% amoebae have excysted after only 24 h with 7.5 U/mL cellulase at 30°C. Nevertheless, no effect of the three enzymes was observed on the excystment of Balamuthia mandrillaris and Vermamoeba vermiformis. Surprisingly, A. castellanii trophozoites excysted in the presence of cellulase displayed a markedly shorter doubling time at 7 h, in comparison to the control at 23 h. Likewise, trophozoites doubled their population in 9 h when both cellulose and cellulase were added to the medium, indicating that Acanthamoeba cyst wall degradation products promote their trophozoite proliferation. The analysis of cysts in epifluorescent microscopy using FITC-lectins and in electron microscopy revealed a disorganized endocyst and a reduction of the intercystic space area after cellulase treatment, implying that these cellular events are preliminary to trophozoite release during excystment. Further studies would be necessary to determine the signaling pathways involved during this amoebal differentiation process to identify new therapeutic targets for the development of anti-acanthamoebal drugs.

Mimivirus Fibrils Are Important for Viral Attachment to the Microbial World by a Diverse Glycoside Interaction Repertoire

Acanthamoeba polyphaga mimivirus (APMV) is a giant virus from the Mimiviridae family. It has many unusual features, such as a pseudoicosahedral capsid that presents a starfish shape in one of its vertices, through which the ∼ 1.2-Mb double-stranded DNA is released. It also has a dense glycoprotein fibril layer covering the capsid that has not yet been functionally characterized. Here, we verified that although these structures are not essential for viral replication, they are truly necessary for viral adhesion to amoebae, its natural host. In the absence of fibrils, APMV had a significantly lower level of attachment to the Acanthamoeba castellanii surface. This adhesion is mediated by glycans, specifically, mannose and N-acetylglucosamine (a monomer of chitin and peptidoglycan), both of which are largely distributed in nature as structural components of several organisms. Indeed, APMV was able to attach to different organisms, such as Gram-positive bacteria, fungi, and arthropods, but not to Gram-negative bacteria. This prompted us to predict that (i) arthropods, mainly insects, might act as mimivirus dispersers and (ii) by attaching to other microorganisms, APMV could be ingested by amoebae, leading to the successful production of viral progeny. To date, this mechanism has never been described in the virosphere.

IMPORTANCE

APMV is a giant virus that is both genetically and structurally complex. Its size is similar to that of small bacteria, and it replicates inside amoebae. The viral capsid is covered by a dense glycoprotein fibril layer, but its function has remained unknown, until now. We found that the fibrils are not essential for mimivirus replication but that they are truly necessary for viral adhesion to the cell surface. This interaction is mediated by glycans, mainly N-acetylglucosamine. We also verified that APMV is able to attach to bacteria, fungi, and arthropods. This indicates that insects might act as mimivirus dispersers and that adhesion to other microorganisms could facilitate viral ingestion by amoebae, a mechanism never before described in the virosphere.

Transparent exopolymer particle production and aggregation by a marine planktonic diatom (Thalassiosira weissflogii) at different growth rates

Transparent exopolymer particles (TEP) play an important role in the ocean carbon cycle as they are sticky and affect particle aggregation and the biological carbon pump. We investigated the effect of growth rate on TEP production in nitrogen limited semi-continuous cultures of the diatom Thalassiosira weissflogii (Grunow) G. Fryxell & Hasle. Steady-state diatom concentrations and other indicators of biomass (chl a, and total carbohydrate) were inversely related to growth rate, while individual cell volume increased with growth rate. There was no change in total TEP area with growth rate; however, individual TEP were larger at high growth rates and the number of individual TEP particles was lower. TEP concentration per cell was higher at higher growth rates. SYTOX Green staining showed that <5% of the diatom population had permeable cell membranes, with the proportion increasing at low growth rates. However, TEP production rates were greater at high growth rates, refuting our hypothesis that TEP formation is dependent on dying cells with compromised cell membranes in a diatom population. Measurements of particle size distribution in the cultures using laser scattering showed that they were most aggregated at high growth rates. These results indicate a coupling between TEP production and growth rate in diatoms under N limitation, with fast growing T. weissflogii producing more TEP and aggregates.

Knockdown of β3GnT8 reverses 5-fluorouracil resistance in human colorectal cancer cells via inhibition the biosynthesis of polylactosamine-type N-glycans

Aberrant glycosylation is known to be associated with cancer chemoresistance. β-1,3-N-acetyl-glucosaminyltransferase (β3GnT)8, which synthesizes polylactosamine on β1-6 branched N-glycans, is dramatically upregulated in colorectal cancer (CRC). 5-Fluorouracil (5-FU) resistance remains a major obstacle to the chemotherapy of CRC. However, little is known with regard to the correlation between 5‑FU resistance and the expression of β3GnT8 in CRC. In this study, a 5-FU‑resistant cell line (SW620/5-FU) was generated, and 50% inhibition concentration (IC50) of 5-FU was determined by MTT assay. Flow cytometry and lectin blot analysis were performed to detect the alteration of polylactosamine structures. Quantitative RT-‑PCR and western blot analysis were used to identify and evaluate candidate genes involved in the synthesis of polylactosamine in SW620/5-FU cells. We found polylactosamine chains were significantly increased in SW620/5-FU cells. Inhibition of the biosynthesis of polylactosamine by 3'-azidothymidine (AZT) was able to reduce 5-FU tolerance. Further studies showed that β3GnT8 expression was also upregulated in 5-FU‑resistant cancer cells, and knockdown of β3GnT8 by RNA interference reversed 5-FU resistance through, at least partly, by suppressing the formation of polylactosamine. In conclusion, the alteration of β3GnT8 in CRC cells correlates with tumor sensitivity to the chemotherapeutic drug and has significant implication for the development of new treatment strategies.

Functional roles of glycogene and N-glycan in multidrug resistance of human breast cancer cells

Drug resistance is a major problem in cancer chemotherapy. Aberrant glycosylation has been known to be associated with cancer chemoresistance. Aim of this work is to investigate the alterations of glycogene and N-glycan involved in multidrug resistance (MDR) in human breast cancer cell lines. Using real-time polymerase chain reaction (PCR) for quantification of glycogenes, fluorescein isothiocyanate (FITC)-lectin binding for glycan profiling, and mass spectrometry for N-glycan composition, the expression of glycogenes, glycan profiling, and N-glycan composition differed between drug-resistant MCF/ADR cells and the parental MCF-7 line. Further analysis of the N-glycan regulation by tunicamycin (TM) application or PNGase F treatment in MCF/ADR cells showed partial inhibition of the N-glycan biosynthesis and increased sensitivity to chemotherapeutic drugs dramatically both in vitro and in vivo. Using an RNA interference strategy, we showed that the downregulation of MGAT5 in MCF/ADR cells could enhance the chemosensitivity to antitumor drugs both in vitro and in vivo. Conversely, a stable high expression of MGAT5 in MCF-7 cells could increase resistance to chemotherapeutic drugs both in vitro and in vivo. In conclusion, the alterations of glycogene and N-glycan in human breast cancer cells correlate with tumor sensitivity to chemotherapeutic drug and have significant implications for the development of new treatment strategies. © 2013 IUBMB Life, 65(5):409-422, 2013.

Killing the dead: chemotherapeutic strategies against free-living cyst-forming protists (Acanthamoeba sp. and Balamuthia mandrillaris)

The opportunist free-living protists such as Acanthamoeba spp. and Balamuthia mandrillaris have become a serious threat to human life. As most available drugs target functional aspects of pathogens, the ability of free-living protists to transform into metabolically inactive cyst forms presents a challenge in treatment. It is hoped, that the development of broad spectrum antiprotist agents acting against multiple cyst-forming protists to provide target-directed inhibition will offer a viable drug strategy in the treatment of these rare infections. Here, we present a comprehensive report on upcoming drug targets, with emphasis on cyst wall biosynthesis along with the related biochemistry of encystment pathways, as we strive to bring ourselves a step closer to being able to combat these deadly diseases.

Exploring the unique N-glycome of the opportunistic human pathogen Acanthamoeba

Glycans play key roles in host-pathogen interactions; thus, knowing the N-glycomic repertoire of a pathogen can be helpful in deciphering its methods of establishing and sustaining a disease. Therefore, we sought to elucidate the glycomic potential of the facultative amoebal parasite Acanthamoeba. This is the first study of its asparagine-linked glycans, for which we applied biochemical tools and various approaches of mass spectrometry. An initial glycomic screen of eight strains from five genotypes of this human pathogen suggested, in addition to the common eukaryotic oligomannose structures, the presence of pentose and deoxyhexose residues on their N-glycans. A more detailed analysis was performed on the N-glycans of a genotype T11 strain (4RE); fractionation by HPLC and tandem mass spectrometric analyses indicated the presence of a novel mannosylfucosyl modification of the reducing terminal core as well as phosphorylation of mannose residues, methylation of hexose and various forms of pentosylation. The largest N-glycan in the 4RE strain contained two N-acetylhexosamine, thirteen hexose, one fucose, one methyl, and two pentose residues; however, in this and most other strains analyzed, glycans with compositions of Hex(8-9)HexNAc(2)Pnt(0-1) tended to dominate in terms of abundance. Although no correlation between pathogenicity and N-glycan structure can be proposed, highly unusual structures in this facultative parasite can be found which are potential virulence factors or therapeutic targets.

Glycogenes mediate the invasive properties and chemosensitivity of human hepatocarcinoma cells

Aberrant cell-surface glycosylation patterns are present on tumors and have been linked to tumor progression. This study aimed to identify the alterations of glycogene and N-glycan involved in tumor invasion, tumorigenicity and drug resistance in MHCC97-H and MHCC97-L human hepatocarcinoma cell lines, which have high, low metastatic potential, respectively. Using real-time PCR for quantification of glycogene and FITC-lectin binding for glycan profiling, we found that the expression of glycogenes and glycan profiling were different in MHCC97-H cells, as compared to those in MHCC97-L cells. We silenced the expression levels of glycogenes MGAT3 and MGAT5, which were over-expressed in MHCC97-L and MHCC97-H cells. Knockdown of MGAT3 expression promoted MHCC97-L cells invasion and increased resistance to 5-fluorouracil in vitro. The silencing of MGAT5 in MHCC97-H cells inhibited invasion and increased sensitivity to 5-fluorouracil in vitro. Further analysis of the N-glycan regulation by tunicamycin application or PNGase F treatment in MHCC97-H and MHCC97-L cells showed partial inhibition of N-glycan glycosylation, decreased invasion, tumorigenicity and increased sensitivity to 5-fluorouracil both in vitro and in vivo. These findings suggest that alterations of glycogene and N-glycan in human hepatocarcinoma cells correlate with tumor invasion, tumorigenicity and sensitivity to chemotherapeutic drug, and have significant implications for the development of treatment strategies.

Biotinylation and characterization of Cryptococcus neoformans cell surface proteins

AIMS

To develop a novel procedure for isolating and characterizing cryptococcal cell-surface proteins using biotinylation, fluorescein isothiocyanate (FITC)-streptavidin, flow cytometry and associated ligand-receptor analysis, confocal microscopy and electrophoretic separation.

METHODS AND RESULTS

Cell proteins of both acapsulate and encapsulated Cryptococcus neoformans cells were labelled using sulfo-NHS-biotin which, in turn, was complexed with FITC-streptavidin. Resulting cell population fluorescence supported visualization of cell-surface protein distribution by confocal microscopy, as well as evaluation of protein exposure by flow cytometry and the calculation of the ligand-binding determinants EC(50), F(max) and H(n). Biotinylation of cell-surface proteins also supported their isolation by affinity chromatography and characterization by SDS/PAGE. Ligand-binding determinants, such as EC(50) values, indicated that acapsulate and stationary phase cells have greatest affinity for biotin. F(max) values demonstrated greatest protein exposure among stationary phase cells; in turn, encapsulated cells expose more protein than acapsulate counterparts. H(n) values of below unity potentially confirm the complex multi-receptor nature of biotin binding to cryptococcal cell surfaces under investigation. Fluorescence visualization showed marked but localized fluorescence indicative of protein exposure around sites of cell division. In turn, biotinylation of cell-surface proteins and their release under reducing conditions demonstrated at least two noncovalently linked proteinaceous entities, of 43 and 57 kDa, exposed on acapsulate cryptococcal cell walls.

CONCLUSIONS

A novel method for identifying, in situ, cell-surface proteins exposed by C. neoformans was established. This novel technique was successfully implemented using both acapsulate and encapsulated C. neoformans cells, both were found to have dynamic and markedly localized protein distribution around sites of cell division and associated cell wall trauma.

SIGNIFICANCE AND IMPACT OF THE STUDY

A novel procedure, employing a versatile combination of flow cytometry, ligand-receptor analysis, confocal microscopy and biotinylation, supported the characterization and isolation of cryptococcal cell-surface proteins.

Cell surface lectin-binding glycoconjugates on marine planktonic protists

Carbohydrate-protein interactions appear to play an important role in the phagocytosis of microbial prey by free-living protozoa. The present study utilizes FITC-labelled plant lectins to investigate the presence and localization of cell surface glycoconjugates on live and fixed planktonic protists (Dunaliella primolecta, Oxyrrhis marina, Goniomonas amphinema, Paraphysomonas vestita and Euplotes vannus). With live flagellate preparations, lectins primarily bound to external cell surfaces, with minimal internal staining observed. In contrast, cell fixation permeabilized cell membranes, allowing lectins to bind to internal structures, such as nuclear membranes and food vacuoles, interfering with the characterization of cell surface glycoconjugates. The method developed to label cell surface sugar moieties of live planktonic protists successfully overcomes the problems associated with fixation, and thus provides a useful protocol for future studies on protistan cell surface carbohydrate characterization.

Lectin/glycan interactions play a role in recognition in a coral/dinoflagellate symbiosis

Recognition is an important stage in the establishment of highly specific mutualistic associations. Yet, for the majority of symbioses, very few of the mechanisms involved in recognition and specificity are known. In this study, we provide evidence for a recognition mechanism at the onset of symbiosis between larvae of the coral Fungia scutaria and their endosymbiotic dinoflagellate algae. This recognition step occurs during initial cellular contact between the symbiotic partners through a lectin/glycan interaction. We determined that an intact algal cell surface was required for successful infection of F. scutaria larvae. Modification of the algal cell surface by enzymatic digestion with trypsin or N-glycosidase significantly reduced infection success, and implicated algal cell surface glycans in recognition. Using flow cytometry, alpha-mannose/alpha-glucose and alpha-galactose residues were identified as potential recognition ligands on the algal cell surface. Finally, inhibition of these cell surface glycans significantly reduced infection of F. scutaria larvae by the algae. These data provide evidence that the algal cell surface contains glycan ligands, such as alpha-mannose/alpha-glucose and alpha-galactose, which play a role in recognition during initial contact at the onset of symbiosis with F. scutaria larvae.

Characterization of Acanthamoeba–microsphere association by multiparameter flow cytometry and confocal microscopy

BACKGROUND

Acanthamoebae, in common with other protozoa, readily endocytose particulate material, which in turn may lead to the spread of infectious disease.

METHODS

Evaluation and quantification of plain and carboxylate FITC-microsphere association with acanthamoebal trophzoites was undertaken using a combination of flow cytometry and confocal microscopy. Trophozoites from strains and species of Acanthamoeba were exposed to plain and carboxylate FITC-microspheres. Microsphere size and aspects such as trophozoite starvation, maturity, and exposure to metabolic inhibitors were assessed.

RESULTS

All species and strains of Acanthamoeba readily endocytosed plain and carboxylate microspheres. Starving trophozoites significantly increased binding and potential ingestion of microspheres, whereas trophozoites of increasing maturity lost such abilities. Trophozoites showed a significant preference for 2.0- and 3.0-microm-diameter microspheres when compared with other sizes, which in turn could occupy much of the cytoplasm. The physiological inhibitors sodium azide, 2,4-dinitrophenol, and cytochalasin B reduced microsphere association with trophozoites; however, some microspheres still bound and associated with trophozoites after inhibitor exposure, a manifestation of both active and inactive agent involvement in microsphere endocytosis.

CONCLUSIONS

Even though the origins of microsphere binding by acanthamoebal trophozoite remains shrouded, the combination of flow cytometry and confocal microscopy supported synergistic quantification and qualification of trophozoite-microsphere endocytosis.