Integrin-mediated cell migration is blocked by inhibitors of human neuraminidase

Programmed immobilization of living cells using independent click pairs

Therapeutic devices incorporating living cells or tissues have been intensively investigated for applications in tissue engineering and regenerative medicine. Because many biological processes are governed by spatially dependent signals, programmable immobilization of materials is crucial for manipulating multiple types of cells. In this study, click chemistry substrates were introduced onto the surfaces of cells and cover glass, and the cells were fixed on the cover glass via covalent bonds for selective cell deposition. Azide group (Az)-labeled living cells were prepared by metabolic labeling with azido sugars. Following the introduction of Az, TCO (trans-cyclooctene) was metabolically labeled into the living cells by reacting with TCO-DBCO (dibenzocyclooctyne). Az and TCO in the cells were detected using DBCO-FAM (fluorescein)and tetrazine-Cy3, respectively. The mixture of Az-labeled green fluorescent protein HeLa cells and TCO-labeled red fluorescent protein HeLa cells was reacted in a culture dish in which three different cover glasses, DBCO-, tetrazine-, or methyl-coated, were added. Az- or TCO-labeled cells could be immobilized in a functional group-dependent manner. Next, tetrazine-labeled cells were incubated on TCO- or Az-labeled cell layers instead of cover glass. Functional group-dependent immobilization was also achieved in the cell layer. Introducing substrates for the click reaction could achieve cell-selective immobilization on different patterned glass surfaces, as well as cell-cell immobilization.

Hepatic Sinusoid Capillarizate via IGTAV/FAK Pathway Under High Glucose

The incidence of diabetic patients with non-alcoholic fatty liver disease (NAFLD) is continuously increasing worldwide. However, the specific mechanisms of NAFLD patients with diabetes are still not clear. Recent studies have indicated that integrins play an important role in NAFLD. In this study, we considered the relationship between integrin αv (IGTAV)/FAK pathway and sinusoidal capillarization. We investigated the difference between the expression of IGTAV, laminin (LN), focal adhesion kinase (FAK), and phosphor-FAK protein in human liver sinusoidal endothelial cells (HLSECs) to explore the specific mechanisms of the diseases of NAFLD with diabetes under high glucose. We cultured and identified the HLSECs and constructed the recombinant lentivirus vector with IGTAV shRNA by quantitative real-time PCR (qRT-PCR) to silence the IGTAV gene. Cells were divided into groups of 25 mmol/L glucose and 25 mmol/L mannitol. We measured the protein levels of IGTAV, LN, FAK, and phosphor-FAK by western blot at 2 h, 6 h, and 12 h before and after IGTAV gene silencing. The lentivirus vector was successfully constructed with IGTAV shRNA. The HLSECs under high glucose were observed by scanning electron microscope. SPSS19.0 was used for statistical analysis. High glucose significantly increased the expression of IGTAV, LN, and phosphor-FAK protein in HLSECs; the shRNA IGTAV could effectively inhibit the expression of phosphor-FAK and LN at 2 h and 6 h. Inhibition of the phosphor-FAK could effectively decrease the expression of LN in HLSECs at 2 h and 6 h under high glucose. Inhibition of IGTAV gene of HLSECs under high glucose could improve hepatic sinus capillarization. Inhibition of IGTAV and phosphor-FAK decreased the expression of LN. High glucose led to hepatic sinus capillarization via IGTAV/ FAK pathway.

Neuraminidase 4 (NEU4): new biological and physiological player

Sialidases are found in viruses, bacteria, fungi, avians, and mammals. Mammalian sialidases differ in their specificity, optimum pH, subcellular localization, and tissue expression. To date, four genes encoding mammalian sialidases (NEU1-4) have been cloned. This review examines the functional impact of NEU4 sialidase on complex physiological and cellular processes. The intracellular localization and trafficking of NEU4 and its potential target molecules are discussed along with its impact on cancer, lysosomal storage disease, and cellular differentiation. Modulation of NEU4 expression may be essential not only for the breakdown of sialylated glycoconjugates, but also in the activation or inactivation of functionally important cellular events.

The extracellular sialidase NEU3 primes neutrophils

Some extracellular glycoconjugates have sialic acid as the terminal sugar, and sialidases are enzymes that remove this sugar. Mammals have 4 sialidases and can be elevated in inflammation and fibrosis. In this report, we show that incubation of human neutrophils with the extracellular human sialidase NEU3, but not NEU1, NEU2 or NEU4, induces human male and female neutrophils to change from a round to a more amoeboid morphology, causes the primed human neutrophil markers CD11b, CD18, and CD66a to localize to the cell cortex, and decreases the localization of the unprimed human neutrophil markers CD43 and CD62-L at the cell cortex. NEU3, but not the other 3 sialidases, also causes human male and female neutrophils to increase their F-actin content. Human neutrophils treated with NEU3 show a decrease in cortical levels of Sambucus nigra lectin staining and an increase in cortical levels of peanut agglutinin staining, indicating a NEU3-induced desialylation. The inhibition of NEU3 by the NEU3 inhibitor 2-acetylpyridine attenuated the NEU3 effect on neutrophil morphology, indicating that the effect of NEU3 is dependent on its enzymatic activity. Together, these results indicate that NEU3 can prime human male and female neutrophils, and that NEU3 is a potential regulator of inflammation.

The Janus-like role of neuraminidase isoenzymes in inflammation

The processes of activation, extravasation, and migration of immune cells to a site are early and essential steps in the induction of an acute inflammatory response. These events are an essential part of the inflammatory cascade, which involves multiple regulatory steps. Using a murine air pouch model of inflammation with LPS as an inflammation inducer, we demonstrate that isoenzymes of the neuraminidase family (NEU1, 3, and 4) play essential roles in these processes by acting as positive or negative regulators of leukocyte infiltration. In genetically knocked‐out (KO) mice for different NEU genes (Neu1 KO, Neu3 KO, Neu4 KO, and Neu3/4 double KO mice) with LPS‐induced air pouch inflammation, leukocytes at the site of inflammation were counted, and the inflamed tissue was analyzed using immunohistochemistry. Our data show that leukocyte recruitment was decreased in NEU1‐ and NEU3‐deficient mice, while it was increased in NEU4‐deficient animals. Consistent with these results, systemic as well as pouch exudate levels of pro‐inflammatory cytokines were reduced in Neu1 and increased in Neu4 KO mice. Pharmacological inhibitors specific for NEU1, NEU3, and NEU4 isoforms also affected leukocyte recruitment. Together our data demonstrate that NEU isoenzymes have distinct—and even opposing—effects on leukocyte recruitment, and therefore warrant further investigation to determine their mechanisms and importance as regulators of the inflammatory cascade.

Inhibitors of Human Neuraminidase Enzymes Block Transmigration in vitro

Cell migration to a site of inflammation is an important step of the immune response. This process is coordinated by cytokines, receptors, and the signal processing machinery of the cell. Many cellular receptors are glycosylated, and their activity can be modulated through changes in glycan structure. Furthermore, glycosylation can be critical to the folding and trafficking of receptors. In this work, we investigated the role of native human neuraminidase enzymes (NEU) in transmigration. We used a cultured T cell line (Jurkat) and a transwell assay with fibronectin (FN) coated wells and cytokines (IL-4 and TNF-α) as chemoattractants in the bottom chamber. We observed that NEU1, NEU3, and NEU4 were positive regulators of transmigration using an siRNA knockdown. Furthermore, we found that pharmacological inhibition of these enzymes inhibited transmigration. We conclude that human NEU isoenzymes NEU1, NEU3, and NEU4 can act as positive regulators of transmigration and should be investigated as targets for anti-inflammatory strategies.

Isoenzyme-Selective Inhibitors of Human Neuraminidases Reveal Distinct Effects on Cell Migration

The human neuraminidase enzymes (NEU1, NEU2, NEU3, and NEU4) are a class of enzymes implicated in pathologies including cancer and diabetes. Several reports have linked neuraminidase activity to the regulation of cell migration in cancer cells. Using an in vitro cell migration assay on fibronectin (FN) coated surfaces, we have investigated the role of these enzymes in integrin-mediated cell migration. We observed that neuraminidase inhibition caused significant retardation of cell migration in breast cancer (MDA-MB-231) and prostate cancer (PC-3) cell lines when using inhibitors of NEU3 and NEU4. In contrast, inhibition of NEU1 caused a significant increase in cell migration for the same cell lines. We concluded that the blockade of human neuraminidase enzymes with isoenzyme-selective inhibitors can lead to disparate results and has significant potential in the development of anticancer or wound healing therapeutics.

Neuraminidase-3 Is a Negative Regulator of LFA-1 Adhesion

Within the plasma membrane environment, glycoconjugate-receptor interactions play an important role in the regulation of cell-cell interactions. We have investigated the mechanism and activity of the human neuraminidase (NEU) isoenzyme, NEU3, on T cell adhesion receptors. The enzyme is known to prefer glycolipid substrates, and we confirmed that exogenous enzyme altered the glycolipid composition of cells. NEU3 was able to modify the sialic acid content of purified LFA-1 in vitro. Enzymatic activity of NEU3 resulted in re-organization of LFA-1 into large clusters on the membrane. This change was facilitated by an increase in the lateral mobility of LFA-1 upon NEU3 treatment. Changes to the lateral mobility of LFA-1 were specific for NEU3 activity, and we observed no significant change in diffusion when cells were treated with a bacterial NEU (NanI). Furthermore, we found that NEU3 treatment of cells increased surface expression levels of LFA-1. We observed that NEU3-treated cells had suppressed LFA-1 adhesion to an ICAM-1 coated surface using an in vitro static adhesion assay. These results establish that NEU3 can modulate glycoconjugate composition and contribute to the regulation of integrin activity. We propose that NEU3 should be investigated to determine its role on LFA-1 within the inflammatory cascade.

GRASP depletion-mediated Golgi destruction decreases cell adhesion and migration via the reduction of α5β1 integrin

The Golgi apparatus is a membrane-bound organelle that serves as the center for trafficking and processing of proteins and lipids. To perform these functions, the Golgi forms a multilayer stacked structure held by GRASP55 and GRASP65 trans-oligomers and perhaps their binding partners. Depletion of GRASP proteins disrupts Golgi stack formation and impairs critical functions of the Golgi, such as accurate protein glycosylation and sorting. However, how Golgi destruction affects other cellular activities is so far unknown. Here, we report that depletion of GRASP proteins reduces cell attachment and migration. Interestingly, GRASP depletion reduces the protein level of α5β1 integrin, the major cell adhesion molecule at the surface of HeLa and MDA-MB-231 cells, due to decreased integrin protein synthesis. GRASP depletion also increases cell growth and total protein synthesis. These new findings enrich our understanding on the role of the Golgi in cell physiology and provide a potential target for treating protein-trafficking disorders.

Sialic acid as a target for the development of novel antiangiogenic strategies

Sialic acid is associated with glycoproteins and gangliosides of eukaryotic cells. It regulates various molecular interactions, being implicated in inflammation and cancer, where its expression is regulated by sialyltransferases and sialidases. Angiogenesis, the formation of new capillaries, takes place during inflammation and cancer, and represents the outcome of several interactions occurring at the endothelial surface among angiogenic growth factors, inhibitors, receptors, gangliosides and cell-adhesion molecules. Here, we elaborate on the evidences that many structures involved in angiogenesis are sialylated and that their interactions depend on sialic acid with implications in angiogenesis itself, inflammation and cancer. We also discuss the possibility to exploit sialic acid as a target for the development of novel antiangiogenic drugs.

Host membrane glycosphingolipids and lipid microdomains facilitate Histoplasma capsulatum internalisation by macrophages

Recognition and internalisation of intracellular pathogens by host cells is a multifactorial process, involving both stable and transient interactions. The plasticity of the host cell plasma membrane is fundamental in this infectious process. Here, the participation of macrophage lipid microdomains during adhesion and internalisation of the fungal pathogen Histoplasma capsulatum (Hc) was investigated. An increase in membrane lateral organisation, which is a characteristic of lipid microdomains, was observed during the first steps of Hc-macrophage interaction. Cholesterol enrichment in macrophage membranes around Hc contact regions and reduced levels of Hc-macrophage association after cholesterol removal also suggested the participation of lipid microdomains during Hc-macrophage interaction. Using optical tweezers to study cell-to-cell interactions, we showed that cholesterol depletion increased the time required for Hc adhesion. Additionally, fungal internalisation was significantly reduced under these conditions. Moreover, macrophages treated with the ceramide-glucosyltransferase inhibitor (P4r) and macrophages with altered ganglioside synthesis (from B4galnt1^-/- mice) showed a deficient ability to interact with Hc. Coincubation of oligo-GM1 and treatment with Cholera toxin Subunit B, which recognises the ganglioside GM1, also reduced Hc association. Although purified GM1 did not alter Hc binding, treatment with P4 significantly increased the time required for Hc binding to macrophages. The content of CD18 was displaced from lipid microdomains in B4galnt1^-/- macrophages. In addition, macrophages with reduced CD18 expression (CD18^low ) were associated with Hc at levels similar to wild-type cells. Finally, CD11b and CD18 colocalised with GM1 during Hc-macrophage interaction. Our results indicate that lipid rafts and particularly complex gangliosides that reside in lipid rafts stabilise Hc-macrophage adhesion and mediate efficient internalisation during histoplasmosis.

Galectin-3 alters the lateral mobility and clustering of β1-integrin receptors

Glycoprotein receptors are influenced by myriad intermolecular interactions at the cell surface. Specific glycan structures may interact with endogenous lectins that enforce or disrupt receptor-receptor interactions. Glycoproteins bound by multivalent lectins may form extended oligomers or lattices, altering the lateral mobility of the receptor and influencing its function through endocytosis or changes in activation. In this study, we have examined the interaction of Galectin-3 (Gal-3), a human lectin, with adhesion receptors. We measured the effect of recombinant Gal-3 added exogenously on the lateral mobility of the α5β1 integrin on HeLa cells. Using single-particle tracking (SPT) we detected increased lateral mobility of the integrin in the presence of Gal-3, while its truncated C-terminal domain (Gal-3C) showed only minor reductions in lateral mobility. Treatment of cells with Gal-3 increased β1-integrin mediated migration with no apparent changes in viability. In contrast, Gal-3C decreased both cell migration and viability. Fluorescence microscopy allowed us to confirm that exogenous Gal-3 resulted in reorganization of the integrin into larger clusters. We used a proteomics analysis to confirm that cells expressed endogenous Gal-3, and found that addition of competitive oligosaccharide ligands for the lectin altered the lateral mobility of the integrin. Together, our results are consistent with a Gal-3-integrin lattice model of binding and confirm that the lateral mobility of integrins is natively regulated, in part, by galectins.

Human Sialidase Neu3 is S-Acylated and Behaves Like an Integral Membrane Protein

Membrane-bound sialidase Neu3 is involved in the catabolism of glycoconjugates, and plays crucial roles in numerous biological processes. Since the mechanism of its association with membranes is still not completely understood, the aim of this work was to provide further information regarding this aspect. Human Neu3 was found to be associated with the plasma membrane and endomembranes, and it was not released from the lipid bilayer under conditions that typically release peripheral membrane proteins. By different experimental approaches, we demonstrated that its C-terminus is exposed to the cytosol while another portion of the protein is exposed to the extracellular space, suggesting that Neu3 possesses the features of a transmembrane protein. However, in silico analysis and homology modeling predicted that the sialidase does not contain any α-helical transmembrane segment and shares the same β-propeller fold typical of viral and bacterial sialidases. Additionally, we found that Neu3 is S-acylated. Since this post-translational modification is restricted to the cytosolic side of membranes, this finding strongly supports the idea that Neu3 may contain a cytosolic-exposed domain. Although it remains to be determined exactly how this sialidase crosses the lipid bilayer, this study provides new insights about membrane association and topology of Neu3.