Cell Biology

Cell-based carrier exhibits inherent advantages as the next generation of drug delivery system, namely high biocompatibility and physiological function. Current cell-based carriers are constructed via direct payload internalization or conjugation between cell and payload. However, the cells involved in these strategies must be firstly extracted from the body and the cell-based carrier must be prepared in vitro. Herein, we synthesize bacteria-mimetic gold nanoparticles (GNPs) for the construction of cell-based carrier in mice. Both β-cyclodextrin (β-CD)-modified GNPs and adamantane (ADA)-modified GNPs are coated by E. coli outer membrane vesicles (OMVs). The E. coli OMVs induce the phagocytosis of GNPs by circulating immune cells, leading to intracellular degradation of OMVs and subsequent supramolecular self-assembly of GNPs driven by β-CD-ADA host–guest interactions. In vivo construction of cell-based carrier based on bacteria-mimetic GNPs avoids the immunogenicity induced by allogeneic cells and restriction by the number of separated cells. Due to the inflammatory tropism, endogenous immune cells carry the intracellular GNP aggregates to the tumor tissues in vivo.

Graphical overview

Collect the outer membrane vesicles (OMVs) of E. coli by gradient centrifugation (a) and coat on gold nanoparticles (GNP) surface (b) to prepare OMV-coated cyclodextrin (CD)-GNPs and OMV-coated adamantane (ADA)-GNPs (c) via ultrasonic method

Stopped-Flow Light Scattering (SFLS) is a method devised to analyze the kinetics of fast chemical reactions that result in a significant change of the average molecular weight and/or in the shape of the reaction substrates. Several modifications of the original stopped-flow system have been made leading to a significant extension of its technical applications. One of these modifications allows the biophysical characterization of the water and solute permeability of biological and artificial membranes.

Here, we describe a protocol of SFLS to measure the glycerol permeability of isolated human red blood cells (RBCs) and evaluate the pharmacokinetics properties (selectivity and potency) of isoform-specific inhibitors of AQP3, AQP7 and AQP9, three mammalian aquaglyceroporins allowing transport of glycerol across membranes. Suspensions of RBCs (1% hematocrit) are exposed to an inwardly directed gradient of 100 mM glycerol in a SFLS apparatus at 20 °C and the resulting changes in scattered light intensity are recorded at a monochromatic wavelength of 530 nm for 120 s. The SFLS apparatus is set up to have a dead time of 1.6-ms and 99% mixing efficiency in less than 1 ms. Data are fitted to a single exponential function and the related time constant (, seconds) of the cell-swelling phase of light scattering corresponding to the osmotic movement of water that accompanies the entry of glycerol into erythrocytes is measured. The coefficient of glycerol permeability (P_gly, cm/s) of RBCs is calculated with the following equation:



where (s) is the fitted exponential time constant and S/V is the surface-to-volume ratio (cm^-1) of the analyzed RBC specimen. Pharmacokinetics of the isoform-specific inhibitors of AQP3, AQP7 and AQP9 are assessed by evaluating the extent of RBC P_gly values resulting after the exposure to serial concentrations of the blockers.

Pollen germination is an excellent process to study cell polarity establishment. During this process, the tip-growing pollen tube will start elongating. The plasma membrane as the selectively permeable barrier that separates the inner and outer cell environment plays crucial roles in this process. This protocol described an efficient aqueous polymer two-phase system followed by alkaline solution washing to prepare Lilium davidii or Oryza sativa plasma membrane with high purity.

This protocol describes the isolation of tonoplast vesicles from tomato fruit. The vesicles isolated using this procedure are of sufficiently high purity for downstream proteomic analysis whilst remaining transport competent for functional assays. The methodology was used to study the transport of amino acids during tomato fruit ripening (Snowden et al., 2015) and based on the procedure used by Betty and Smith (Bettey and Smith, 1993). Such vesicles may be useful in further studies into the dynamic transfer of metabolites across the tonoplast for storage and metabolism during tomato fruit development.

This protocol details the isolation of enriched Golgi membranes from rat liver, using discontinuous density gradient centrifugation. This high-yield extraction method is useful for several applications, including immunoprecipitation of solubilised Golgi membrane proteins (preparation included) and electron microscopy. Protocol adapted from Leelavathi et al. (1970).

Eukaryotic cilia/flagella are ideal organelles for the analysis of membrane trafficking, membrane assembly, and the functions of a variety of signal transduction molecules. Cilia are peninsular organelles and the membrane lipids, membrane proteins, and microtubular-associated components are selectively transported into cilia through the region formed by the basal body/transition region and tightly associated ciliary membrane. Cilia can be isolated from many organisms without disrupting cells and many will rapidly regenerate cilia (with the ciliary membrane lipids and proteins) to replace those that are released. Despite their ease of isolation, we have relatively little understanding of the mechanisms that regulate lipid and protein transport into ciliary membranes (Pazour and Bloodgood, 2008; Bloodgood, 2009; Bloodgood, 2012).

Chlamydomonas flagella shed membrane vesicles, also called ectosomes (Wood et al., 2013) from flagellar tips and these vesicles can be purified from the culture medium without damaging or deflagellating cells (McLean et al., 1974; Bergman et al., 1975; Snell, 1976; Kalshoven et al., 1990). Based on a comparison of biotinylated proteins on the shed vesicles with biotinylated proteins isolated from purified flagella and cell bodies, the ectosomes contain most, but not all, flagellar surface proteins and none of the major cell body proteins (Dentler, 2013). Although ectosomes have only been purified from Chlamydomonas cells, preliminary evidence indicates that similar vesicles are released from Tetrahymena cilia (Dentler, unpublished).

Flagellar (and ciliary) membranes or membrane proteins also can be released from purified flagella/cilia. Most membrane proteins can be solubilized by extracting purified cilia with nonionic detergent [Triton X-100 or X-114 or Nonidet P-40 (NP-40)] and pelleting the microtubules (axonemes). However, not all membranes are released by detergent (Dentler, 1980) and the supernatant also contains all of the flagellar proteins that are not attached to the microtubules.

Intact membrane vesicles can be released from flagella by agitation of flagella, often with low concentrations of nonionic detergents or freeze-thawing (Witman et al., 1972; Snell, 1976; Dentler, 1980; Dentler, 1995; Bloodgood and May, 1982; Pasquale and Goodenough, 1987; Iomini et al., 2006; Huang et al., 2007). Once released, they can be purified from axonemes by differential centrifugation.

Each of these methods may enrich for different populations of axonemal and membrane proteins and lipids. The different solubility of membranes may reveal local differences in lipid or protein composition (Bloodgood, 2009). The ectosomes contain most but not all surface proteins found on purified Chlamydomonas flagella (Dentler, 2013). The ectosomes vesicles may be enriched in different soluble flagellar proteins than those trapped as vesicles are released from purified flagella. The detergent-solubilized “membrane+matrix” will contain all soluble membrane proteins as well as all of the soluble proteins in the flagellar compartment.

In this paper, a method to purify ectosomes vesicles released from the tips of living Chlamydomonas cells is presented as are two methods to release flagellar membrane vesicles and proteins from purified flagella.

As for all positive strand RNA viruses, hepatitis C virus (HCV) RNA replication is tightly associated with rearranged host cell membranes, termed viral replication factories. However, up to now little is known about both viral and cellular constituents of viral replication factories. Here, we describe a protocol to specifically isolate HCV-remodeled host cell membranes and endoplasmic reticulum (ER) membranes of naïve cells, by using a functional NS4B HA-tagged subgenomic replicon and a C-terminally HA-tagged calnexin-overexpressing cell line, respectively. Post-nuclear whole cell membrane fractions are first enriched by density gradient centrifugation, followed by HA-specific affinity tag purification. Upon elution under native conditions, purified samples can be subject to a variety of biochemical and functional assays.

A common feature of every eukaryotic and prokaryotic cell is that they exhibit a plasma membrane. In Bacillus subtilis (B. subtilis) roughly 25% of all proteins are putative trans- or membrane associated proteins. Here we describe a relatively simple method to separate and prepare membrane and cytosolic proteins by ultra-centrifugation.

Membrane preparation has been widely used for characterization the membrane proteins. Membrane fractions can be separated by a combination of differential and density-gradient centrifugation techniques (Hodges et al., 1972; Leonard and Vanderwoude, 1976). Here we firstly describe a method to isolate total microsomal fractions including plasma membrane, intracellular vesicles, Golgi membranes, endoplasma reticulum, and tonoplast (vacuolar membrane) from 5-7 days old seedlings, which is often analyzed for auxin transporters in Arabidopsis (Leonard and Vanderwoude, 1976; Titapiwatanakun, et al., 2009; Yang et al., 2013; Blakeslee et al., 2007). After homogenization, plant debris including cell walls, chloroplasts and nucleus were removed by low speed centrifugation (8,000 x g), then total microsomal membranes were pelleted by high speed centrifugation (10,000 x g) and separated from soluble fractions. We secondly describe a method to separate microsomal fractions according to size or density in a sucrose density-gradient system by centrifugation. The linear sucrose gradient from 20%-55% (1.09-1.26 g cm^-3) were used to separate membranes with different densities: tonoplast, 1.10-1.12 cm^-3, Golgi membranes, 1.12-1.15 cm^-3, rough endoplasmic reticulum 1.15-1.17 cm^-3, thylakoids, 1.16-1.18 cm^-3, plasma membrane, 1.14-1.17 g cm^-3, and mitochondrial membranes, 1.18-1.20 cm^-3 (Leonard and Vanderwoude, 1976; Larsson et al., 1987; Briskin and Leonard, 1980). However, the plasma membrane can also be isolated according to its outer surface properties which are very different from intracellular membrane surfaces. Thus, the right-side-out plasma membrane vesicles can be separated in an aqueous Dextran-polyethylene glycol two-phase system. The plasma membranes can be purified to > 90% in the upper phase (Larsson et al., 1987; Alexandersson et al., 2008). Two-phase systems for Arabidopsis seedlings were described in the section 3. Sucrose density gradient membrane fractionation followed by western blot is often used to analyze the distribution of certain membrane protein, while Two-phase separation is used when high purity of plasma membrane or intracellular membrane is required.

Immunoprecipitation (IP) is a widely used method to isolate a specific protein from a mixed protein sample using an antibody that exclusively binds to that particular protein. This technique allows studying protein-protein and protein-nucleic acid interactions or to identify post-translational protein modifications. Many proteins, in particular cell surface receptors, localize to different compartments within cells where they elicit distinct functions by interacting with specific proteins. Integrins represent a major family of cell surface receptors consisting of non-covalently associated α and β subunits that mediate the interaction of cells with their environment. However, integrins do not only localize to the cell surface but are also present in other compartments including the endoplasmic reticulum and endosomes where they engage with a distinct set of interacting partners or show distinct post-translational modifications. Standard immunoprecipitation of β1 integrins from a cell lysate without prior fractionation isolates β1 integrins from all compartments. In contrast, selective immunoprecipitation of cell surface β1 integrin allows enriching for the pool of β1 integrin on the cell surface thereby minimizing contaminations with β1 integrins from other subcellular compartments. To achieve this, living cells are incubated with a β1 integrin-specific antibody on ice to label cell surface β1 integrins prior to cell lysis and precipitation.