Secreted Form Of Alkaline Phosphatase Research Articles

A cell-based biosensor for nanomaterials cytotoxicity assessment in three dimensional cell culture.

Nanoparticles (NPs) are widely used in consumer and medicinal products. The high prevalence of nanoparticles in the environment raises concerns regarding their effects on human health, but there is limited knowledge about how NPs interact with cells or tissues. Because the European Union has called for a substantial reduction of animal experiments for scientific purposes (Directive 2010/63), increased efforts are required to develop in vitro models to evaluate potentially hazardous agents. Here, we describe a new cell-based biosensor for the evaluation of NPs cytotoxicity. The new biosensor is based on transgenic human hepatoblastoma cells (HepG2) that express a secreted form of alkaline phosphatase (SEAP) as a reporter protein whose expression is induced upon activation of a stress response pathway controlled by the transcription regulator nuclear factor-κB (NF-κB). The NF-κB_HepG2 sensor cells were cultured in a Matrigel-based three dimensional environment to simulate the in vivo situation. The new biosensor cells offer the advantage of generating fast and reproducible readout at lower concentrations and shorter incubation time than conventional viability assays, avoid possible interaction between nanomaterials and assay compounds, therefore, minimize generation of false positive or negative results and indicate mechanism of toxicity through NF-κB signaling.

Quaternized Poly(4-vinylpyridine)s as Model Gene Delivery Polycations: Structure−Function Study by Modification of Side Chain Hydrophobicity and Degree of Alkylation

To optimize polycation-based gene delivery agents, the influence of molecular characteristics of the polycations on physicochemical properties of polycation/DNA complexes and their relationships to cellular gene transfer need to be understood. With this aim, we have synthesized a series of model polymers based on quaternized poly(4-vinylpyridine)s (CnPVP-beta) with the same DP of 1600 but differing by the number n of methylene groups in N-alkyl ester substituents from 1 to 6 and/or by degree of alkylation beta from 25% to 95%. For polycations CnPVP-95, the efficiency of transfection of a plasmid vector expressing a secreted form of alkaline phosphatase started to be detectable at n = 4, noticeable at n = 5, and again undetectable at n = 6. A decrease in beta of active C5PVP-95 from 95% to 65% resulted in a further noticeable increase of activity with a 9-fold increase for C5PVP-65. This finding was attributed to the proton sponge mechanism due to protonation of non-alkylated pyridine moieties of CnPVP-beta/DNA complexes in slightly acidic media that was supported by the fluorescence quenching assay. The data demonstrate the advantages of partial alkylation of tertiary polyamines with medium-length alkyl agents for preparation of efficient nonviral gene delivery vectors.

Cationized pullulan 3D matrices as new materials for gene transfer

This study deals with the development of a novel biocompatible cationized pullulan three-dimensional matrix for gene delivery. A water-soluble cationic polysaccharide, diethylaminoethyl-pullulan (DEAE-pullulan), was first synthesized and characterized. Fluorescence quenching and gel retardation assays evidenced the complexation in solution of DNA with DEAE-pullulan, but not with neutral pullulan. On cultured smooth muscle cells (SMCs) incubated with DEAE-pullulan and a plasmid vector expressing a secreted form of alkaline phosphatase (pSEAP), SEAP activity was 150-fold higher than with pSEAP alone or pSEAP with neutral pullulan. DEAE-pullulan was then chemically crosslinked using phosphorus oxychloride. The resulting matrices were obtained in less than a minute and molded as discs of 12 mm diameter and 2 mm thickness. Such DEAE-pullulan 3D matrices were loaded with up to 50 microg of plasmid DNA, with a homogeneous plasmid loading observed with YOYO-1 fluorescence staining. Moreover, the DEAE-pullulan matrix was shown to protect pSEAP from DNase I degradation. Incubation of cultured SMCs with pSEAP-loaded DEAE-pullulan matrices resulted in significant gene transfer without cell toxicity. This study suggests that these cationized pullulan 3D matrices could be useful biomaterials for local gene transfer.

1111. Removal of Empty Particles from Type 1 Adeno-Associated Virus Vector Stocks by Ion Exchange Chromatography Potentiates Transgene Expression

Production of recombinant adeno-associated virus (rAAV) results in substantial quantities of empty capsids or virus-like particles (VLPs), a virus protein shell without the vector genome. The contaminating VLPs would interfere with transduction by competing for cell surface receptors and when administered in vivo, contribute to antigen load, which may elicit a stronger immune response. Density-gradient ultracentrifugation provides a means to separate VLPs from rAAV particles, but is not feasible for large scale preparations of vectors. Since the compositions of the VLP and vector differ by the single-stranded DNA genome, we hypothesized that the isoelectric points of the vector may differ from that of the VLP. In an attempt to separate type 1 rAAV particles from VLPs by ion exchange chromatography, we tested a number of buffer systems and found that trimethylammonium sulfate, or [(CH3)4N] 2SO4, effectively separated rAAV1 particles from VLPs, which was confirmed by electron microscopic observation of samples from pooled fractions. The rAAV1-GFP or -SEAP (secreted form of alkaline phosphatase) chromatographically separated from VLPs induced stronger transgene expression in HEK293 cells than rAAV1 contaminated with VLPs. The transduction of mouse muscles with VLP-free rAAV1-SEAP also showed higher serum SEAP levels than rAAV1-SEAP contaminated with VLPs. These results suggested that chromatographic separation of rAAV1 from empty capsids was possible and increased the efficacy of rAAV1. It will be useful for the purification of large quantities of rAAV1 for large-animal or human applications. Production of recombinant adeno-associated virus (rAAV) results in substantial quantities of empty capsids or virus-like particles (VLPs), a virus protein shell without the vector genome. The contaminating VLPs would interfere with transduction by competing for cell surface receptors and when administered in vivo, contribute to antigen load, which may elicit a stronger immune response. Density-gradient ultracentrifugation provides a means to separate VLPs from rAAV particles, but is not feasible for large scale preparations of vectors. Since the compositions of the VLP and vector differ by the single-stranded DNA genome, we hypothesized that the isoelectric points of the vector may differ from that of the VLP. In an attempt to separate type 1 rAAV particles from VLPs by ion exchange chromatography, we tested a number of buffer systems and found that trimethylammonium sulfate, or [(CH3)4N] 2SO4, effectively separated rAAV1 particles from VLPs, which was confirmed by electron microscopic observation of samples from pooled fractions. The rAAV1-GFP or -SEAP (secreted form of alkaline phosphatase) chromatographically separated from VLPs induced stronger transgene expression in HEK293 cells than rAAV1 contaminated with VLPs. The transduction of mouse muscles with VLP-free rAAV1-SEAP also showed higher serum SEAP levels than rAAV1-SEAP contaminated with VLPs. These results suggested that chromatographic separation of rAAV1 from empty capsids was possible and increased the efficacy of rAAV1. It will be useful for the purification of large quantities of rAAV1 for large-animal or human applications.

Identification of p115 as a PLCγ1-binding protein and the role of Src homology domains of PLCγ1 in the vesicular transport

In order to gain further insight into the function(s) of PLCγ1, we tried to identify the binding partners that can interact with the SH223 domains of PLCγ1. Immunoscreening was performed with the purified antisera that are specific to SH223-binding proteins. Several immunoreactive clones were identified as the putative binding proteins and one of them was identified as p115. p115 was reported to be required for transcytotic fusion and subsequent binding of the vesicles to the target membrane. The interaction between PLCγ1 and p115 was specific to carboxyl-terminal SH2 domain and SH3 domain of PLCγ1, and also confirmed by biochemical approaches such as co-immunoprecipitation, pull-down assay, and glycerol gradient fractionation. To further characterize the role of SH domains of PLCγ1 in the vesicle transport pathway, secreted form of alkaline phosphatase (SEAP) reporter assay was carried out. When the SH2 and/or SH3 domains of PLCγ1 were deleted, the secretion of SEAP was significantly reduced. These findings indicate that the SH2 and SH3 domains of PLCγ1 may play a role(s) in the process of the vesicle transport via interaction with other vesicle-associated proteins such as p115.

Overexpression of the ARF1 exchange factor ARNO inhibits the early secretory pathway and causes the disassembly of the Golgi complex.

The small GTPase ARF1 is a key regulator of intracellular membrane traffic. In its active, GTP-bound form, ARF1 is associated with Golgi membranes and promotes the recruitment of the cytosolic coat protein complex, which will result in membrane budding and vesicle formation. ARNO (ARF nucleotide site opener) has been shown to act in vitro as a GTP exchange factor for ARF1. Here, we have investigated the function of ARNO in vivo. By immunofluorescence and cell fractionation, ARNO was found to be mostly cytosolic in HeLa cells. Its overexpression led to a strong inhibition of the secretion of SEAP (secreted form of alkaline phosphatase). Newly synthesized SEAP failed to acquire endoglycosidase H resistance, indicating a block in the early secretory pathway. This effect on secretion was accompanied by a disassembly of the Golgi complex and a redistribution of Golgi resident proteins into the endoplasmic reticulum (ER). On the other hand, ARNO overexpression did not affect the early endocytic pathway. These results show that ARNO functions in vivo in Golgi to ER transport. Its behavior is then consistent with ARNO being an exchange factor for ARF1.

Molecular Cloning of a Novel Human CC Chemokine EBI1-ligand Chemokine That Is a Specific Functional Ligand for EBI1, CCR7

By searching the expressed sequence tag (EST) data base, we identified partial cDNA sequences encoding a novel human CC chemokine. We determined the complete cDNA sequence that encodes a highly basic polypeptide of a total 98 amino acids with 20 to 30% identity to other human CC chemokines. We termed this novel chemokine from EBI1-Ligand Chemokine as ELC (see below). The ELC mRNA was most strongly expressed in the thymus and lymph nodes. Recombinant ELC protein was expressed as a fusion protein with the Flag tag (ELC-Flag). For receptor-binding assays, recombinant ELC protein fused with the secreted form of alkaline phosphatase (SEAP) was used. By stably expressing five CC chemokine receptors (CCR1 to 5) and five orphan receptors, ELC-SEAP was found to bind specifically to an orphan receptor EBI1. Only ELC-Flag, but not MCP-1, MCP-2, MCP-3, eotaxin, MIP-1alpha, MIP-1beta, RANTES (regulated on activation normal T cell expressed and secreted), thymus and activation-regulated chemokine (TARC), or liver and activation-regulated chemokine (LARC), competed with ELC-SEAP for EBI1. ELC-Flag-induced transient calcium mobilization and chemotactic responses in EBI1-transfected cells. ELC-Flag also induced chemotaxis in HUT78 cells expressing endogenous EBI1 at high levels. By somatic hybrid and radiation hybrid analyses, the gene for ELC (SCYA19) was mapped to chromosome 9p13 instead of chromosome 17q11.2 where the genes for CC chemokines are clustered. Taken together, ELC is a highly specific ligand for EBI1, which is known to be expressed in activated B and T lymphocytes and strongly up-regulated in B cells infected with Epstein-Barr virus and T cells infected with herpesvirus 6 or 7. ELC and EBI1 may thus play roles in migration and homing of normal lymphocytes, as well as in pathophysiology of lymphocytes infected with these herpesviruses. We propose EBI1 to be designated as CCR7.

The small GTP-binding protein rab6 functions in intra-Golgi transport.

Rab6 is a ubiquitous ras-like GTP-binding protein associated with the membranes of the Golgi complex (Goud, B., A. Zahraoui, A. Tavitian, and J. Saraste. 1990. Nature (Lond.). 345:553-556; Antony, C., C. Cibert, G. Géraud, A. Santa Maria, B. Maro, V. Mayau, and B. Goud. 1992. J. Cell Sci. 103: 785-796). We have transiently overexpressed in mouse L cells and human HeLa cells wild-type rab6, GTP (rab6 Q72L), and GDP (rab6 T27N) -bound mutants of rab6 and analyzed the intracellular transport of a soluble secreted form of alkaline phosphatase (SEAP) and of a plasma membrane protein, the hemagglutinin protein (HA) of influenza virus. Over-expression of wild-type rab6 and rab6 Q72L greatly reduced transport of both markers between cis/medial (alpha-mannosidase II positive) and late (sialyl-transferase positive) Golgi compartments, without affecting transport from the endoplasmic reticulum (ER) to cis/medial-Golgi or from the trans-Golgi network (TGN) to the plasma membrane. Whereas overexpression of rab6 T27N did not affect the individual steps of transport between ER and the plasma membrane, it caused an apparent delay in secretion, most likely due to the accumulation of the transport markers in late Golgi compartments. Overexpression of both rab6 Q72L and rab6 T27N altered the morphology of the Golgi apparatus as well as that of the TGN, as assessed at the immunofluorescence level with several markers. We interpret these results as indicating that rab6 controls intra-Golgi transport, either acting as an inhibitor in anterograde transport or as a positive regulator of retrograde transport.

A fast and sensitive colorimetric assay for IL-6 in hepatoma cells based on the production of a secreted form of alkaline phosphatase (SEAP)

Structure-function studies of cytokines require that simple, sensitive and reliable biological assays are available. A well known property of interleukin-6 (IL-6) is that of being able to induce transcription from several liver-specific promoters in human hepatoma cells. However, the available assays of IL-6 in hepatoma cells, which are either based on the detection of increased expression of endogenous acute phase response genes or on the activation of reporter genes transfected under the control of IL-6 responsive promoters, are not very sensitive and are time consuming. We have established a new assay for IL-6 in hepatoma cells which is based on the transfection of an IL-6 inducible promoter/secreted alkaline phosphatase (SEAP) gene fusion and which measures the inducible production and release of SEAP in the culture medium. SEAP activity is measured with a simple colorimetric assay that requires no cell manipulation, thus allowing a large set of samples to be analysed simultaneously. The CRP/SEAP assay can be used in studies on the structure-function relationships of human IL-6.