Interactions of lectins with CHO cell surface membranes. II. Differential effects of local anesthetics on endocytosis of Con A and WGA binding sites

Biogenesis of Exosomes Laden with Metallic Silver-Copper Nanoparticles Liaised by Wheat Germ Agglutinin for Targeted Delivery of Therapeutics to Breast Cancer

The anticancer property of silver-copper metallic nanoparticles (AgCu-NPs) is of greater interest in cancer therapeutics; however, its off-target toxicity limits its therapeutic application. Exosomes emerge as one of the leading idiosyncratic nanocarrier choices for cancer therapeutics due to their size, stability, and phenotypic diversity; however, to encapsulate NPs in extracellular vesicles (EVs) without disrupting their inherited functions is far from the expectations. Here, the loading strategy of AgCu-NP conjugated with wheat germ agglutinin (AgCu-NP-WGA) in exosomes during biogenesis for the targeted delivery of anticancer therapeutics to breast cancer is reported. Based on the intrinsic mechanism of endocytosis of WGA, results show that internalization of WGA or AgCu-NP-WGA bypasses the lysosomal pathway and recycles in EVs. On the contrary, the transport of naked AgCu-NPs to lysosomes; mechanistically, an acidic environment causes oxidation of AgCu-NP. Next, the analysis of EVs harvested by differential centrifugation shows that only AgCu-NPs-WGA (Exo-NP) retain their metallic state. Furthermore, Exo-NP cytotoxicity results manifest that MCF10A-derived Exo-NPs are toxic to its homologous breast cancer cells (MCF-7 and MDA-MB 231) and nontoxic to heterologous cancers NC1-1975 and MCF 10A. In conclusion, this study shows the self-assembly of AgCu-NP in exosomes to target and deliver therapeutics for breast cancer.

Fungal lectin, XCL, is internalized via clathrin-dependent endocytosis and facilitates uptake of other molecules

The lectin isolated from Xerocomus chrysenteron (XCL) displays a toxic activity towards insects. In order to assess its possible mode of action and to gather useful data for its potential use in insect-resistant transgenic plants, we investigated the effects of XCL at the cellular level. Immunofluorescence microscopy studies revealed that XCL is rapidly internalized into small endocytic vesicles that further coalesce in the perinuclear region. We show that XCL is endocytosed by the clathrin-dependent pathway, and is delivered to late endosome/lysosome compartments. The internalization of XCL seems to be general since it occurs in different cell types such as insect (SF9) or mammalian (NIH-3T3 and Hela) cell lines. In the presence of XCL, the uptake of GFP and BSA is greatly enhanced, demonstrating that XCL facilitates endocytosis. Thus, XCL could serve as a delivery agent to facilitate the endocytosis of proteins that do not enter the cell alone.

Endocytosis of wheat germ agglutinin binding sites from the cell surface into a tubular endosomal network

By using fluorescence and electron microscopy, the endocytic pathway encountered by cell surface components after they had bound wheat germ agglutinin (WGA) was visualized. The majority of these components are thought to consist of sialylated glycoproteins (HMWAG) that represent a subpopulation of the total cell surface proteins but most of the externally disposed plasma membrane proteins of the cell. Examination of semi-thin sections by medium- and high-voltage electron microscopy revealed the three-dimensional organization of vesicular and tubular endosomes. Binding of either fluorescein isothiocyanate-, horseradish peroxidase-, or ferritin-conjugated WGA to cells at 4 degrees C showed that the HMWAG were distributed uniformly over the cell surface. Warming of surface-labeled cells to 37 degrees C resulted in the endocytosis of WGA into peripheral endosomes via invagination of regions of both coated and uncoated membrane. The peripheral endosome appeared as isolated complexes comprising a vesicular element (300-400 nm diam.) surrounded by and continuous with tubular cisternae (45-60 nm diam.), which did not interconnect the endosomes. After 30 min or more label also became localized in a network of anastomosing tubules (45-60 nm diam.) that were located in the centrosomal region of the cell. Endocytosed WGA-HMWAG complexes did not become associated with cisternae of the Golgi apparatus, although tubular and vesicular endosomes were noted in the vicinity of the trans-Golgi region. The accumulation of WGA-HMWAG in the endosomes within the centrosomal region was inhibited when cells were incubated at 18 degrees C. None of these compartments contained acid phosphatase activity, a result that is consistent with other data that the HMWAG do not pass through lysosomes initially. The kinetics of labeling were consistent with the interpretation that recycling of most of the WGA binding surface glycoproteins occurred rapidly from early peripheral endosomes followed by the late trans-Golgi compartment. In conclusion, a portion of cell surface glycoproteins are routed to a complex arrangement of tubular and vesicular compartments following endocytosis that includes a putative post-endosomal, tubular reticulum that appears to be separate from the trans-most Golgi saccule.

Airway permeability in rats exposed to ozone or treated with cytoskeleton-destabilizing drugs

Ozone (O3) exposure of rats increases airway epithelial permeability. We hypothesized that this increased permeability may be mediated by the epithelial cell cytoskeleton. To test this hypothesis, we studied the effect of cytoskeletal disruption on the transmucosal transport of tracers from airway lumen to blood and compared the results with the effects of O3 exposure. No increase in transport occurred following disruption of microtubules by vinblastine, but disruption of microfilaments with cytochalasin D resulted in increased transport of radiolabeled tracers [99mTc- and 111In-labeled diethylenetriamine-pentacetate (DTPA) and 125I-labeled bovine serum albumin (BSA)]. In control rats, both horseradish peroxidase (HRP) and BSA, localized by cytochemistry and autoradiography, respectively, were detected on the epithelial cell surfaces and in endocytic vesicles. In rats treated with cytochalasin D or exposed to O3, the tracer molecules also penetrated the intercellular spaces, though the apical tight junctions remained devoid of the tracers. Increased numbers of endocytic vesicles containing HRP and aggregation of 125I-labeled BSA autoradiographic grains in the subepithelial region were also seen after either treatment. We conclude that destabilization of cytoskeletal elements following O3 exposure is a possible mechanism of increased transmucosal transport, which may be a combined effect of accelerated transport through both endocytic and paracellular pathways.

The application of lectins to the characterization and isolation of mammalian cell populations

Mammalian cells invariably contain a vast array of glycosylated moieties, both inside the cell and on the cell surface. There is an increasing awareness of the utility of these carbohydrates in delineating the phenotype or function of many populations of cells. To this end lectins are extremely useful reagents. Lectins are carbohydrate-binding proteins and glycoproteins of non-immune origin derived from numerous plants and animals. A wide variety of lectins with many distinct carbohydrate specificities have been isolated. Historically the most common laboratory techniques utilizing lectins have been agglutination, mitogen stimulation, and fluorescence techniques. Recent advances in the development and conjugation procedure for labels and matrices have led to the creation of numerous novel lectin-based assays. Lectins are currently used not only to identify cells with specified carbohydrate groups, but also to quantitate the carbohydrate groups or to isolate the carbohydrate-bearing cells or structures.