An Efficient and Scalable Method for the Production of Immunogenic SARS-CoV-2 Virus-like Particles (VLP) from a Mammalian Suspension Cell Line

The rapid evolution of new SARS-CoV-2 variants poses a continuing threat to human health. Vaccination has become the primary therapeutic intervention. The goal of the current work was the construction of immunogenic virus-like particles (VLPs). Here, we describe a human cell line for cost-efficient and scalable production of immunogenic SARS-CoV-2 VLPs. The modular design of the VLP-production platform facilitates rapid adaptation to new variants. Methods: The N, M-, and E-protein genes were integrated into the genome of Expi293 cells (ExpiVLP_MEN). Subsequently, this cell line was further modified for the constitutive expression of the SARS-CoV-2 spike protein. The resulting cell line (ExpiVLP_SMEN) released SARS-CoV-2 VLP upon exposure to doxycycline. ExpiVLP_SMEN cells were readily adapted for VLP production in a 5 L bioreactor. Purified VLPs were quantified by Western blot, ELISA, and nanoparticle tracking analysis and visualized by electron microscopy. Immunogenicity was tested in mice. Results: The generated VLPs contained all four structural proteins, are within the size range of authentic SARS-CoV-2 virus particles, and reacted strongly and specifically with immunoserum from naturally infected individuals. The VLPs were stable in suspension at 4 °C for at least 10 weeks. Mice immunized with VLPs developed neutralizing antibodies against lentiviruses pseudotyped with the SARS-CoV-2 spike protein. The flexibility of the VLP-production platform was demonstrated by the rapid switch of the spike protein to a new variant of concern (BA.1/Omicron). The present study describes an efficient, scalable, and adaptable production method of immunogenic SARS-CoV-2 VLPs with therapeutic potential.

Towards a scalable bioprocess for rAAV production using a HeLa stable cell line

The majority of recombinant adeno-associated viruses (rAAV) approved for clinical use or in clinical trials areproduced by transient transfection using the HEK293 cell line. However, this platform has several manufacturing bottlenecks at commercial scales namely, low product quality (full to empty capsid ratio <20% in most rAAV serotypes), lower productivities obtained after scale-up and the high cost of raw materials, in particular of Good Manufacturing Practice grade plasmid DNA required for transfection. The HeLa-based stable cell line rAAV production system provides a robust and scalable alternative to transient transfection systems. Nevertheless, the time required to generate the producer cell lines combined with the complexity of rAAV production and purification processes still pose several barriers to the use of this platform as a suitable alternative to the HEK293 transient transfection. In this work we streamlined the cell line development and bioprocessing for the HeLaS3-based production of rAAV. By exploring this optimized approach, producer cell lines were generated in 3-4 months, and presented rAAV2 volumetric production (bulk) > 3 × 1011  vg/mL and full to empty capsids ratio (>70%) at 2 L bioreactor scale. Moreover, the established downstream process, based on ion exchange and affinity-based chromatography, efficiently eliminated process related impurities, including the Adenovirus 5 helper virus required for production with a log reduction value of 9. Overall, we developed a time-efficient and robust rAAV bioprocess using a stable producer cell line achieving purified rAAV2 yields > 1 × 1011  vg/mL. This optimized platform may address manufacturing challenges for rAAV based medicines.

Efficient production of bispecific antibodies-optimization of transfection strategy leads to high-level stable cell line generation of a Fabs-in-tandem immunoglobin

Bispecific antibodies (bsAbs) are often composed of more than two component chains, such as Fabs-in-tandem immunoglobin (FIT-Ig) comprising three different component chains, which bring challenges for generating a high proportion of the correctly assembled bsAbs in a stable cell line. During the CHO-K1 stable cell line construction of a FIT-Ig, we investigated the FIT-Ig component chain ratio in transfection, where two sets of expression vectors were designed. Both designs utilized two vectors for co-transfection. Multiple transfections with plasmid ratio adjustment were applied, and the resultant minipools were evaluated for expression titer and quality of produced FIT-Ig. The results suggested that abundant outer Fab short chains (twofold chain genes versus other chains) can promote complete FIT-Ig assembly and therefore reduce the fragmental impurities of FIT-Ig. This adjustment of the component chain ratios at the beginning is beneficial to FIT-Ig stable cell line generation and brings favorable clones to process development.

Complementary Cell Lines for Protease Gene-Deleted Single-Cycle Adenovirus Vectors

To increase the safety of adenovirus vector (AdV)-based therapy without reducing its efficacy, a single-cycle adenovirus vector (SC-AdV) with a deletion in the protease gene (PS) was developed in order to be used as a substitute for the replication-competent adenovirus (RC-AdV). Since no infectious viral particles are assembled, there is no risk of viral shedding. The complementary cell lines for this developed AdV proved to be suboptimal for the production of viral particles and require the presence of fetal bovine serum (FBS) to grow. In the current study, we produced both stable pools and clones using adherent and suspension cells expressing the PS gene. The best adherent cell pool can be used in the early stages for the generation of protease-deleted adenovirus, plaque purification, and titration. Using this, we produced over 3400 infectious viral particles per cell. Additionally, the best suspension subclone that was cultured in the absence of FBS yielded over 4000 infectious viral particles per cell. Harvesting time, culture media, and concentration of the inducer for the best suspension subclone were further characterized. With these two types of stable cells (pool and subclone), we successfully improved the titer of protease-deleted adenovirus in adherent and suspension cultures and eliminated the need for FBS during the scale-up production. Eight lots of SC-AdV were produced in the best suspension subclone at a scale of 2 to 8.2 L. The viral and infectious particle titers were influenced by the virus backbone and expressed transgene.

HN1 Is Enriched in the S-Phase, Phosphorylated in Mitosis, and Contributes to Cyclin B1 Degradation in Prostate Cancer Cells

HN1 has previously been shown as overexpressed in various cancers. In Prostate cancer, it regulates AR signaling and centrosome-related functions. Previously, in two different studies, HN1 expression has been observed as inversely correlated with Cyclin B1. However, HN1 interacting partners and the role of HN1 interactions in cell cycle pathways have not been completely elucidated. Therefore, we used Prostate cancer cell lines again and utilized both transient and stable inducible overexpression systems to delineate the role of HN1 in the cell cycle. HN1 characterization was performed using treatments of kinase inhibitors, western blotting, flow cytometry, immunofluorescence, cellular fractionation, and immunoprecipitation approaches. Our findings suggest that HN1 overexpression before mitosis (post-G2), using both transient and stable expression systems, leads to S-phase accumulation and causes early mitotic exit after post-G2 overexpression. Mechanistically, HN1 interacted with Cyclin B1 and increased its degradation via ubiquitination through stabilized Cdh1, which is a co-factor of the APC/C complex. Stably HN1-expressing cells exhibited a reduced Cdt1 loading onto chromatin, demonstrating an exit from a G1 to S phenotype. We found HN1 and Cdh1 interaction as a new regulator of the Cyclin B1/CDK1 axis in mitotic regulation which can be explored further to dissect the roles of HN1 in the cell cycle.

Enhanced sensitivity of neutralizing antibody detection for different AAV serotypes using HeLa cells with overexpressed AAVR

A cell-based transduction inhibition assay (TI) is widely used in clinical trials to detect neutralizing antibody (NAb) titers against recombinant adeno-associated virus (rAAV), one of the most important criteria to exclude patients in gene therapy. Different cell lines are used in cell-based TI because the rAAV transduction efficiencies vary largely among serotypes. A cell line suitable for TI for most serotypes is highly desirable, especially for those with very low transduction efficiencies in vitro such as rAAV8 and rAAV9. Herein, we report an AAVR-HeLa, a stable cell line with overexpressed AAVR, a newly identified receptor for rAAVs, was established for cell-based TIs. The AAVR expression level in AAVR-HeLa cells was approximately 10-fold higher than in HeLa cells, and was stably transfected after twenty three passages. For all AAV serotypes (AAV1-10), except for AAV4, the transduction efficiencies increased significantly in AAVR-HeLa cells. It was demonstrated that the AAVR enhancement of transduction efficiency was only for rAAV and not for lentiviral and adenoviral vectors. According to the minimal multiplicity of infection (MOIs) for the assay, the NAb detection sensitivity increased at least 10 and 20 fold for AAV8 and AAV9, respectively. The seroprevalence of NAbs were investigated at the 1:30 level as a cutoff value using AAVR-HeLa cells. It was shown that the seropositive rate for AAV2 was 87% in serum samples from 99 adults, followed by lower seropositive rates for AAV5 (7%), AAV8 (7%) and AAV9 (1%). Venn diagram analysis showed the presence of cross-reactivity of NAbs to two or three serotypes in 13 samples (13.1%). However, no patient was found to possess NAbs for all the four serotypes. These results demonstrated that the AAVR-HeLa cell line may be utilized to detect the NAbs through cell-based TI assays for most of AAV serotypes.

Establishment of a High Throughput Screening System for GABAA1 Modulators in Living Cells

BACKGROUND

The incidence of sleep disorders is more than 27% in the worldwide, and the development of novel sleep drugs that target GABAA receptors is of great interest. Traditional drug screening methods restrict the discovery of lead compounds, the high-throughput screening system is a powerful means for the lead compounds discovery of sleep drug.

METHODS

The GABA_A1-CHO cell line stably expressing α₁β₂γ₂L was constituted by cotransfection of α₁, β₂ and γ₂L subunits into CHO-T-Rex cells. The high-throughput screening method of membrane potential targeting GABA_AR was established and optimized. The optimized method was used to screen the compound library, and the compounds with high activity were obtained. The active compounds were confirmed in vitro by electrophysiological detection technique, and the sleep effects of compounds in vivo were detected by pentobarbital sodium sleep model in mice.

RESULTS

A stable cell line expressing human GABA_A1 receptor in CHO-T-Rex cells was generated and used to establish a functional high-throughput screening assay based on the measurement of membrane potential changes in living cells by fluorometric imaging plate reader (FLIPR). The assay was further used to detect the dose-effect relationships of tool compounds, the EC₅₀ values of agonist GABA (137.42 ± 26.31 nM), positive allosteric modulator diazepam (3.22 ± 0.73 μM), and antagonist gabazine (0.16 ± 0.04 μM), blocking agents bicuculine (0.47 ± 0.06 μM) and PTX (6.39 ± 1.17 μM). In the meanwhile, the compounds were screened from a compound library (10000) by the membrane potential dye assay. Selected 4 active compounds were further identified for their EC50 values in vitro by electrophysiological method, the EC₅₀ values of 4 compounds were further determined as 1.37 ± 0.43 μM, 0.69 ± 0.17 μM, 0.77 ± 0.16 μM, and 1.62 ± 0.29 μM. Furthermore, the pentobarbital sleep rate and the sleep time of mice pretreated with 4 active compounds by oral administration were significantly increased compared with mice pretreated with a negative control in vivo experiment.

CONCLUSION

We successfully generated a stable CHO cell line expressing human GABA_A1 by induced expression strategy which decreased cytotoxicity. Then, developed an efficient membrane potential detection method for high-throughput screening, the assay based on the stable cell line could distinguish different types of GABA_A1 modulators, which would be an effective in vitro system to screen the GABA_AR-targeted compounds. Compared with the patch clamp electrophysiological detection method, the membrane potential detection method has higher detection flux for compounds and higher detection sensitivity for active compounds.

Development of an efficient reproducible cell-cell transmission assay for rapid quantification of SARS-CoV-2 spike interaction with hACE2

Efficient quantitative assays for measurement of viral replication and infectivity are indispensable for future endeavors to develop prophylactic or therapeutic antiviral drugs or vaccines against SARS-CoV-2. We developed a SARS-CoV-2 cell-cell transmission assay that provides a rapid and quantitative readout to assess SARS-CoV-2 spike hACE2 interaction in the absence of pseudotyped particles or live virus. We established two well-behaved stable cell lines, which demonstrated a remarkable correlation with standard cell-free viral pseudotyping for inhibition by convalescent sera, small-molecule drugs, and murine anti-spike monoclonal antibodies. The assay is rapid, reliable, and highly reproducible, without a requirement for any specialized research reagents or laboratory equipment and should be easy to adapt for use in most investigative and clinical settings. It can be effectively used or modified for high-throughput screening for compounds and biologics that interfere with virus-cell binding and entry to complement other neutralization assays currently in use.

[Construction of a stable TrxR1 knockout HCT-116 cell line using CRISPR/Cas9 gene editing system]

To investigate the cellular target selectivity of small molecules targeting thioredoxin reductase 1, we reported the construction and functional research of a stable TrxR1 gene (encode thioredoxin reductase 1) knockout HCT-116 cell line. We designed and selected TrxR1 knockout sites according to the TrxR1 gene sequence and CRISPR/Cas9 target designing principles. SgRNA oligos based on the selected TrxR1 knockout sites were obtained. Next, we constructed knockout plasmid by cloning the sgRNA into the pCasCMV-Puro-U6 vector. After transfection of the plasmid into HCT-116 cells, TrxR1 knockout HCT-116 cells were selected using puromycin resistance. The TrxR1 knockout efficiency was identified and verified by DNA sequencing, immunoblotting, TRFS-green fluorescent probe, and cellular TrxR1 enzyme activity detection. Finally, the correlation between TrxR1 expression and cellular effects of drugs specifically targeting TrxR1 was investigated by CCK-8 assay. The results demonstrated that the knockout plasmid expressing the sgRNA effectively knocked-out TrxR1 gene within HCT-116 cells, and no expression of TrxR1 protein could be observed in stable TrxR1 knockout HCT-116 (HCT116-TrxR1-KO) cells. The TrxR1-targeting inhibitor auranofin did not show any inhibitory activity against either cellular TrxR1 enzyme activity or cell proliferation. Based on these results, we conclude that a stable TrxR1 gene knockout HCT-116 cell line was obtained through CRISPR/Cas9 techniques, which may facilitate investigating the role of TrxR1 in various diseases.

Detailed Protocol for the Novel and Scalable Viral Vector Upstream Process for AAV Gene Therapy Manufacturing

Recombinant adeno-associated viral (rAAV) vector-based gene therapy has been adapted for use in more than 100 clinical trials. This is mainly because of its excellent safety profile, ability to target a wide range of tissues, stable transgene expression, and significant clinical benefit. However, the major challenge is to produce a high-titer, high-potency vector to achieve a better therapeutic effect. Even though the three plasmid-based transient transfection method is currently being used for AAV production in many clinical trials, there are complications associated with scalability and it is not cost-effective. Other methods require either large-scale production of two herpes simplex viruses, rHSV-RepCap and rHSV-GOI (gene of interest), with high titers, or a stable cell line with high titer wild-type adenovirus infection. Both of these options make the process even more complex. To address this issue, we have developed a stable cell line-based production with the use of only one rHSV-RepCap virus. Using this new methodology in small-scale production, we achieved ∼1-6 E + 04 vg/cell of AAV9 in the top producer clones. Large-scale production in 10-CS (10-Cell Stack) of one of the top producing clones resulted in ∼1-2 E + 13 vg/10-CS with 50% of full capsid ratio after purification. This method could potentially be adapted to suspension cells. The major advantage of this novel methodology is that by using the rHSV-RepCap virus, high titer AAV can be produced with any GOI containing a stable adherent or suspension producer cell line. The use of this AAV production platform could be beneficial for the treatment of many diseases.

A Stable Cell Line Expressing Clustered AChR: A Novel Cell-Based Assay for Anti-AChR Antibody Detection in Myasthenia Gravis

Cell-based assays (CBAs) and radioimmunoprecipitation assay (RIPA) are the most sensitive methods for identifying anti-acetylcholine receptor (AChR) antibody in myasthenia gravis (MG). But CBAs are limited in clinical practice by transient transfection. We established a stable cell line (KL525) expressing clustered AChR by infecting HEK 293T cells with dual lentiviral vectors expressing the genes encoding the human AChR α1, β1, δ, ϵ and the clustering protein rapsyn. We verified the stable expression of human clustered AChR by immunofluorescence, immunoblotting, and real-time PCR. Fluorescence-activated cell sorting (FACS) was used to detect anti-AChR antibodies in 103 MG patients and 58 healthy individuals. The positive results of MG patients reported by the KL525 was 80.6% (83/103), 29.1% higher than the 51.4% (53/103) of RIPA. 58 healthy individuals tested by both the KL525 CBA and RIPA were all negative. In summary, the stable expression of clustered AChR in our cell line makes it highly sensitive and advantageous for broad clinical application in CBAs.

A Simple and Efficient Method to Generate Gene-Knockout and Transgenic Cell Lines

Knockout (KO) or exogenous expression of a gene of interest in cultured cells is one of the most important ways to study the function of the gene. Compared with transient transfection, stable cell lines possess great advantages such as excellent cell homogeneity and feasibility for long-term use. However, technical challenges in generating stable cell lines still exist in many laboratories using conventional techniques like limiting dilution or cloning cylinders. In this study we describe an optimized method to efficiently create stable cell lines for functional studies. This method was successfully used to generate a PIEZO1 gene-KO cell line with the CRISPR/Cas9 technology, and TRPC5/GCaMP6f-mCherry-coexpressing cell lines without antibiotic selection. Monoclonal cell lines can be obtained in 2-4 weeks after transfection. This method does not require any special equipment or consumables and can be conducted in all laboratories with general cell-culture facility.

Development of a Multivalent Kunjin Virus Reporter Virus-Like Particle System Inducing Seroconversion for Ebola and West Nile Virus Proteins in Mice

Kunjin virus (KUNV) is an attenuated strain of the severe neurotropic West Nile virus (WNV). The virus has a single-strand positive-sense RNA genome that encodes a polyprotein. Following gene expression, the polyprotein is cleaved into structural proteins for viral packaging and nonstructural proteins for viral replication and expression. Removal of the structural genes generate subgenomic replicons that maintain replication capacity. Co-expression of these replicons with the viral structural genes produces reporter virus-like particles (RVPs) which infect cells in a single round. In this study, we aimed to develop a system to generate multivalent RVPs based on KUNV to elicit an immune response against different viruses. We selected the Ebola virus (EBOV) glycoprotein (GP) and the matrix protein (VP40) genes, as candidates to be delivered by KUNV RVPs. Initially, we enhanced the production of KUNV RVPs by generating a stable cell line expressing the KUNV packaging system comprising capsid, precursor membrane, and envelope. Transfection of the DNA-based KUNV replicon into this cell line resulted in an enhanced RVP production. The replicon was expressed in the stable cell line to produce the RVPs that allowed the delivery of EBOV GP and VP40 genes into other cells. Finally, we immunized BALB/cN mice with RVPs, resulting in seroconversion for EBOV GP, EBOV VP40, WNV nonstructural protein 1, and WNV E protein. Thus, our study shows that KUNV RVPs may function as a WNV vaccine candidate and RVPs can be used as a gene delivery system in the development of future EBOV vaccines.

[Establishment of stable cell line expressing human bocavirus type 1 non-structural protein NS1 and its trans-transcriptional activation]

Human bocavirus 1 (HBoV1) non-structural protein NS1 is a multifunctional protein important for virus replication and induction of apoptosis in host cell. To better understand the function of the NS1 protein, it is urgent to address reducing the toxicity of NS1 to host cells. In the present study, we established a stable cell line that regulates expression of NS1 of HBoV1. The recombinant lentivirus plasmid containing a regulatable promoter fused with ns1 gene was constructed and transfected into HEK 293T cells using transfection reagent. The HEK 293T cell lines stably expressing NS1-100 and NS1-70 proteins were established by screening resistant cells with puromycin and inducing NS1 expression with doxycycline. The expression of NS1 protein was determined by fluorescent labeling protein and Western blotting. HBoV1 promoter was transfected into stably expressing NS1 cell line and its trans-transcriptional activity was analyzed. The results showed that NS1 protein was expressed stably in the established cell lines and had a strong activation activity on the HBoV1 promoter driving luciferase gene. Taken together, this study provides a solid basis for further research on the function of NS1 and the pathogenesis of human bocavirus.

Efficient Development of Stable Recombinant Chinese Hamster Ovary (rCHO) Cell Lines to Produce Antibodies by Using Dimethyl Sulfoxide (DMSO) in Electroporation

Development of stable rCHO cell lines is still time consuming and labor intensive, although it is a critical step in the commercial development of recombinant antibodies. The current work demonstrates, for the first time, that electroporation of CHO cells with DMSO can enhance stable expression of recombinant antibodies in rCHO cells. Electroporation with DMSO resulted in an average 3.7-fold and 2.8-fold increases in expression levels of aflibercept and pembrolizumab, respectively, in pools of stable rCHO cells. It also resulted in an average of 2.2-fold and 2.6-fold increases in the expression of aflibercept and pembrolizumab, respectively, in single-cell derived rCHO clones. Simple batch cultures of rCHO cell clones with the highest expression produced 1.0 g/l for aflibercept and 1.4 g/l for pembrolizumab without a time-consuming gene amplification process. Electroporation with DMSO also shortened the development of rCHO cell lines to 2-3 months, allowing rapid establishment of stable rCHO cell lines with a desirable expression level antibodies.

Lentiviral transduction of mammalian cells for fast, scalable and high-level production of soluble and membrane proteins

Structural, biochemical and biophysical studies of eukaryotic soluble and membrane proteins require their production in milligram quantities. Although large-scale protein expression strategies based on transient or stable transfection of mammalian cells are well established, they are associated with high consumable costs, limited transfection efficiency or long and tedious selection of clonal cell lines. Lentiviral transduction is an efficient method for the delivery of transgenes to mammalian cells and unifies the ease of use and speed of transient transfection with the robust expression of stable cell lines. In this protocol, we describe the design and step-by-step application of a lentiviral plasmid suite, termed pHR-CMV-TetO2, for the constitutive or inducible large-scale production of soluble and membrane proteins in HEK293 cell lines. Optional features include bicistronic co-expression of fluorescent marker proteins for enrichment of co-transduced cells using cell sorting and of biotin ligase for in vivo biotinylation. We demonstrate the efficacy of the method for a set of soluble proteins and for the G-protein-coupled receptor (GPCR) Smoothened (SMO). We further compare this method with baculovirus transduction of mammalian cells (BacMam), using the type-A γ-aminobutyric acid receptor (GABAAR) β3 homopentamer as a test case. The protocols described here are optimized for simplicity, speed and affordability; lead to a stable polyclonal cell line and milligram-scale amounts of protein in 3-4 weeks; and routinely achieve an approximately three- to tenfold improvement in protein production yield per cell as compared to transient transduction or transfection.

Stable cell lines of human SH-SY5Y uniformly expressing wild-type or mutant-type FERM domain containing 7 gene

It has been reported that FERM domain containing 7 (FRMD7) may cause X-linked idiopathic congenital nystagmus (ICN). A total of >40 mutations of the FRMD7 gene have been identified, however their pathogenic role remains unclear. In the present study, enhanced green fluorescent protein-tagged wild-type (WT) and mutant (MT) FRMD7 (c. C781>G) were expressed in stably expressing human neuroblastoma SH-SY5Y cells following viral transfection and antibiotic selection. Uniform expression of the FRMD7 fusion proteins was confirmed via fluorescence microscopy and western blotting. The expression profiles of neuron-specific proteins and Rho guanine triphosphatases (GTPases) differed significantly between the wild-type and mutant cell lines. Levels of Mtap2, NF-M, nestin, GAP43 and Rac1 mRNA were significantly increased in MT-FRMD7 cells compared with controls (P<0.01). However, the expression of Rac1 protein did not differ significantly among the two cell lines. Taken together, the results of the current study suggest that MT-FRMD7 influences the expression of neuron-specific genes and Rho GTPases, which may be involved in the pathogenesis of ICN. The FRMD7 stable expression cell line may facilitate future studies investigating the role of this protein in neuronal development.

[Knocking out of human DNAH2 gene in U2OS cells by CRISPR/Cas9n double nick system]

To study the biological function of DNAH2 (Homo sapiens dynein, axonemal, heavy chain 2) gene, we constructed human stable U2OS cell line of DNAH2 gene knockout through CRISPR/Cas9n double nick system. The A, B sgRNAs (Single guide RNA) and complementary strands were designed and synthesized. The double-stranded structures were formed during annealing, and connected with BbsⅠ cohesive ends-containing pX462 linear vector to construct the recombinant eukaryotic expression plasmids, including pX462-DNAH2-A and pX462-DNAH2-B. After the co-transfection of the two plasmids into U2OS cells, the addition of puromycin and limiting dilution method were used to obtain positive monoclonal cell line. Western blotting assay was then performed to detect the expression of DNAH2 protein, and PCR-sequencing technology was finally utilized to analyze the mutation feature. The results showed that A, B sgRNAs duplex was successfully inserted into pX462 vector, and DNAH2 protein was not expressed and DNAH2 gene suffered from the frame-shift mutation in U2OS-DNAH2-KO monoclonal cell line. These demonstrated that DNAH2 knockout U2OS stable cell line was successfully constructed through CRISPR/Cas9n double nick system, which providing a useful tool for the study of DNAH2 gene.

Simultaneous evaluation of human CYP3A4 and ABCB1 induction by reporter assay in LS174T cells, stably expressing their reporter genes

The bioavailability of orally administered therapies are often significantly limited in the human intestine by the metabolic activities of cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (P-gp). Predicting whether candidate compounds induce CYP3A4 and P-gp is a crucial stage in the drug development process, as drug-drug interactions may result in the induction of intestinal CYP3A4 and P-gp. However, the assay systems needed to evaluate both CYP3A4 and P-gp induction in the intestine are yet to be established. To address this urgent requirement, LS174T cells were used to create two stable cell lines expressing the CYP3A4 or ATP-binding cassette subfamily B member 1 (ABCB1, encoding P-gp) reporter genes. First, these stable cells were tested by treatment with 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3), all-trans-retinoic acid (ATRA) and 9-cis-retinoic acid (9-cis RA) that induce CYP3A4 and P-gp in the intestines. All these compounds significantly increased both CYP3A4 and ABCB1 reporter activities in the stable cell lines. To simultaneously assess the induction of CYP3A4 and ABCB1, both stable cells were co-cultivated to measure their reporter activities. The mixed cells showed a significant increase in the CYP3A4 and ABCB1 reporter activities following treatment with 1,25(OH)2 D3, ATRA, and 9-cis RA. These activity levels were maintained after passaging more than 20 times and following multiple freeze-thaw cycles. These results demonstrate that our established cell lines can be used to evaluate simultaneously CYP3A4 and ABCB1 induction in the intestines, providing a valuable in vitro model for the evaluation of future drug candidates.

Rapid Recovery of Classical Swine Fever Virus Directly from Cloned cDNA

The reverse genetics for classical swine fever virus (CSFV) is currently based on the transfection of in vitro transcribed RNA from a viral genomic cDNA clone, which is inefficient and time-consuming. This study was aimed to develop an improved method for rapid recovery of CSFV directly from cloned cDNA. Full-length genomic cDNA from the CSFV Shimen strain, which was flanked by a T7 promoter, the hepatitis delta virus ribozyme and T7 terminator sequences, was cloned into the low-copy vector pOK12, producing pOKShimen-RzTΦ. Direct transfection of pOKShimen-RzTΦ into PK/T7 cells, a PK-15-derived cell line stably expressing bacteriophage T7 RNA polymerase, allowed CSFV to be rescued rapidly and efficiently, i.e., at least 12 h faster and 31.6-fold greater viral titer when compared with the in vitro transcription-based rescue system. Furthermore, the progeny virus rescued from PK/T7 cells was indistinguishable, both in vitro and in vivo, from its parent virus and the virus rescued from classical reverse genetics. The reverse genetics based on intracellular transcription is efficient, convenient and cost-effective. The PK/T7 cell line can be used to rescue CSFV directly from cloned cDNA and it can also be used as an intracellular transcription and expression system for studying the structure and function of viral genes.

Immunoaffinity purification of protein complexes from Mammalian cells

In this chapter, we describe a purification scheme designed to isolate multisubunit protein complexes gently and quickly from crude extracts of mammalian cells using immunoaffinity purification of epitope tagged proteins and the multisubunit complexes with which they associate. As an example we describe isolation of the mammalian Mediator complex from HeLa S3 cells.

Stable expression of FoxA1 promotes pluripotent P19 embryonal carcinoma cells to be neural stem-like cells

FoxA1 belongs to the fork head/winged-helix transcription factor family and participates in stimulating neuronal differentiation of pluripotent stem cells at early stages. To explore the biological roles of FoxA1 during this process, the stable expression of a GFP-FoxA1 fusion protein was established in P19 pluripotent embryonal carcinoma cells. Although they still express pluripotency-related transcription factors such as Oct4, Nanog, and Sox2, the generated P19 GFPFoxA1 cells exhibited a decreased activity of alkaline phosphatase and an increased expression of SSEA-3 compared with P19 cells. Elevated levels of nestin expression and prominin-1+ populations were observed in P19 GFPFoxA1 cells, implicating that the stable expression of FoxA1 promoted P19 cells to gain partial characteristics of neural stem cells. Furthermore, the promoter of nestin was confirmed to be bound and activated by FoxA1 directly. The expression of neuron-specific marker tubulin betaIII also existed in P19 GFPFoxA1 cells. P19 GFPFoxA1 cells showed an earlier onset of differentiation during RA-induced neuronal differentiation, evidenced by a more rapid change on the Nanog decrease and the tubulin betaIII increase. Thus, overexpression of FoxA1 alone may promote pluripotent P19 cells to become neural stem-like cells.

Single channel analysis of the blocking actions of BIDN and fipronil on a Drosophila melanogaster GABA receptor (RDL) stably expressed in a Drosophila cell line

Single channel recordings were obtained from a Drosophila S2 cell line stably expressing the wild-type RDL(ac) Drosophila melanogaster homomer-forming ionotropic GABA receptor subunit, a product of the resistance to dieldrin gene, RDL: GABA (50 microM) was applied by pressure ejection to outside-out patches from S2-RDL cells at a holding potential of -60 mV. The resulting inward current was completely blocked by 100 microM picrotoxin (PTX). The unitary current-voltage relationship was linear at negative potentials but showed slight inward rectification at potentials more positive than 0 mV. The reversal potential of the current (E(GABA)=-1.4 mV) was close to the calculated chloride equilibrium potential. The single channel conductance elicited by GABA was 36 pS. A 71 pS conductance channel was also observed when the duration of the pulse, used to eject GABA, was longer than 80 ms. The mean open time distribution of the unitary events was fitted best by two exponential functions suggesting two open channel states. When either 1 microM fipronil or 1 microM BIDN was present in the external saline, the GABA-gated channels were completely blocked. When BIDN or fipronil was applied at a concentration close to the IC(50) value for suppression of open probability (281 nM, BIDN; 240 nM, fipronil), the duration of channel openings was shortened. In addition, the blocking action of BIDN resulted in the appearance of a novel channel conductance (17 pS). The effects of co-application of BIDN and fipronil were examined. Co-application of BIDN (300 nM) with various concentrations (100-1000 nM) of fipronil resulted in an additional BIDN-induced dose-dependent reduction of the maximum P(o) value. Thus both BIDN and fipronil shorten the duration of wild-type RDL(ac) GABA receptor channel openings but appear to act at distinct sites.