Mammalian Expression Research Articles

Anti-DNA antibodies--structure and function.

Expression of monoclonal anti-DNA antibodies in vitro can be used to study the relationships between molecular structure, binding properties and pathogenicity. Bacterial and yeast systems can be used to produce antibody fragments such as Fab. The yields are potentially sufficient to allow structural studies such as crystallization, but purification of the anti-DNA Fab from the bacterial periplasm may be challenging. Mammalian cell expression systems produce lower yields, but the products are whole antibodies, which can be used in assays of pathogenicity. This article describes some recent experiments in which bacterial and mammalian systems were used to study human monoclonal anti-DNA antibodies. Light chain sequence motifs were found to be important both in binding to antigens and in determining pathogenicity of the antibodies in severe combined immunodeficiency mice. The distribution of B cell subpopulations is disturbed in patients with systemic lupus erythematosus (SLE). These patients, like those with infectious mononucleosis, have an overall B cell lymphopenia but an increased frequency of plasmablasts/early plasma cells in their blood. Some of these early plasma cells belong to clones that have rearranged the V(H) gene V4-34. There is a selective rise in immunoglobulins encoded by this gene in both infectious mononucleosis and SLE.

Targeted cytokine delivery to neuroblastoma.

The aim of this study was to construct a fusion protein from the cytokine granulocyte/macrophage colony-stimulating factor (GM-CSF) and a single-chain Fv fragment (scFv D29) and to investigate its potential to activate cells of the immune system against neuroblastoma cells expressing neural cell adhesion molecule (NCAM). Mammalian cell expression of the scFv D29-GM-CSF fusion protein was compared using a number of vectors, including retroviral and adenoviral vectors. The resultant fusion protein, expressed by HeLa cells, was found by ELISA to bind immobilized recombinant NCAM. Moreover, FACS analysis confirmed binding to the human neuroblastoma cell line SKNBE and a murine neuroblastoma cell line engineered to express the glycosylphosphatidylinositol form of human NCAM (N2A-rKNIE). The fusion protein was also found to stimulate the proliferation of the FDC-P1 haemopoietic cell line, which is dependent on GM-CSF (or interleukin 3) for continued growth. In vitro clonogenic assays indicated that scFv-GM-CSF could selectively induce growth inhibition of SKNBE cells by murine lymphoid cells.

Functional genomics in rat models of hypertension: using differential expression and congenic strains to identify and evaluate candidate genes.

Hypertension is a leading contributor to cardiovascular diseases such as heart attack and stroke. Genetic and environmental factors contribute to the development of hypertension. Animal models have been developed to study the genetic contributions to blood pressure (BP) regulation and to identify chromosomal regions harboring candidate genes causative of differences in BP regulation (i.e., BP quantitative trait loci [QTL]). Advances in both mammalian genome projects and global gene expression analysis present opportunities to study functional genomics in these animal models. In this article, novel approaches for designing experiments and interpreting global gene expression data using the Dahl salt-sensitive hypertension rat model are presented. We describe two-step screening protocols that can be used to identify BP QTL candidate genes. Genetically determined expression differences are identified in the target organs of inbred strains of contrasting phenotype in the first screen. Expression patterns in a panel of congenic strains or expression differences stemming from gene x environment interactions are examined in the second screen. Chromosomal locations of these genes can then be examined to determine whether they map to BP QTL-containing regions. Another approach is to study the expression of genes identified from public databases to be located within BP QTL-containing congenic regions. Several candidate genes have been identified using these strategies.

Maternal versus paternal expression of a LacZ transgene in preimplantation mouse embryos: effects of genetic background and 2-cell block.

The expression of a transgene NI-ROSA LacZ (LacZtg) trapped into the genes for two presumably untranslated, ubiquitously expressed RNAs, was studied in preimplantation mouse embryos with respect to penetrance (fraction of expressing embryos) and to localisation of beta-galactosidase activity. With maternal origin in NMRI mice beta-galactosidase was first detected within one dot in the cytoplasm of zygotes at 30 h post-hCG. The staining pattern progressed to small clusters and to dense, homogeneous staining of the entire cytoplasm during further development. Within the NMRI background, penetrance in utero was delayed by at least 6 h when the transgene was of paternal as compared with maternal origin. Paternal transgene expression increased marginally during culture to 50 h after explantation of embryos at 30-48 h post-hCG and remained low or decreased in the '2-cell block'. Expression of a paternal transgene in preimplantation embryos developing in utero was further delayed in the maternal MF1 as compared with the NMRI background. In contrast to NMRI x NMRI embryos with paternally derived transgene, expression increased with time during the 2-cell block in MF1 x NMRI embryos. Thus, in the earliest phase of mammalian development expression of this LacZtg is influenced by parental origin, maternal genetic background and environment. The spatial distribution of the gene product is developmentally controlled.

Analysis of the molecular event of ICAM‐1 interaction with LFA‐1 during leukocyte adhesion using a reconstituted mammalian cell expression model

Ligand‐receptor clustering event is the most important step in leukocyte adhesion and spreading on endothelial cells. Intercellular adhesion mole‐cule‐1 (ICAM‐1) has been shown to enhance leukocyte adhesion, but the molecular event during the process of adhesion is unclear. To visualize the dynamics of ICAM‐1 movement during adhesion, we have engineered stable Chinese hamster ovary cell lines expressing ICAM‐1 fused to a green fluorescent protein (IC1GFP/CHO) and examined them under the fluorescence microscopy. The transfection of IC1GFP alone in these cells was sufficient to support the adhesion of K562 cells that express aLβ2 (LFA‐1) integrin stimulated by CBR LFA‐1/2 mAb. This phenomenon was mediated by ICAM‐1‐LFA‐1 interactions, as an mAb that specifically inhibits ICAM‐1‐LFA‐1 interaction (RR1/1) completely abolished the adhesion of LFA‐1+ cells to IC1_GFP/CHO cells. We found that the characteristic of adhesion was followed almost immediately (∼10min) by the rapid accumulation of ICAM‐1 on CHO cells ...

Cubilin P1297L mutation associated with hereditary megaloblastic anemia 1 causes impaired recognition of intrinsic factor–vitamin B12 by cubilin

AbstractMegaloblastic anemia 1 (MGA1) is an autosomal recessive disorder caused by the selective intestinal malabsorption of intrinsic factor (IF) and vitamin B12/cobalamin (Cbl) in complex. Most Finnish patients with MGA1 carry the disease-specific P1297L mutation (FM1) in the IF-B12 receptor, cubilin. By site-directed mutagenesis, mammalian expression, and functional comparison of the purified wild-type and FM1 mutant forms of the IF–Cbl-binding cubilin region (CUB domains 5-8, amino acid 928-1386), we have investigated the functional implications of the P1297L mutation. Surface plasmon resonance analysis revealed that the P1297L substitution specifically increases the Kd for IF–Cbl binding several-fold, largely by decreasing the association rate constant. In agreement with the binding data, the wild-type protein, but not the FM1 mutant protein, potently inhibits 37°C uptake of iodine 125–IF–Cbl in cubilin-expressing epithelial cells. In conclusion, the data presented show a substantial loss in affinity of the FM1 mutant form of the IF–Cbl binding region of cubilin. This now explains the malabsorption of Cbl and Cbl-dependent anemia in MGA1 patients with the FM1 mutation.

Cubilin P1297L mutation associated with hereditary megaloblastic anemia 1 causes impaired recognition of intrinsic factor–vitamin B12 by cubilin

Megaloblastic anemia 1 (MGA1) is an autosomal recessive disorder caused by the selective intestinal malabsorption of intrinsic factor (IF) and vitamin B12/cobalamin (Cbl) in complex. Most Finnish patients with MGA1 carry the disease-specific P1297L mutation (FM1) in the IF-B12 receptor, cubilin. By site-directed mutagenesis, mammalian expression, and functional comparison of the purified wild-type and FM1 mutant forms of the IF–Cbl-binding cubilin region (CUB domains 5-8, amino acid 928-1386), we have investigated the functional implications of the P1297L mutation. Surface plasmon resonance analysis revealed that the P1297L substitution specifically increases the Kd for IF–Cbl binding several-fold, largely by decreasing the association rate constant. In agreement with the binding data, the wild-type protein, but not the FM1 mutant protein, potently inhibits 37°C uptake of iodine 125–IF–Cbl in cubilin-expressing epithelial cells. In conclusion, the data presented show a substantial loss in affinity of the FM1 mutant form of the IF–Cbl binding region of cubilin. This now explains the malabsorption of Cbl and Cbl-dependent anemia in MGA1 patients with the FM1 mutation.

Creation of polarized cells coexpressing CYP3A4, NADPH cytochrome P450 reductase and MDR1/P-glycoprotein.

To develop model polarized cell systems expressing cytochrome P4503A4. NADPH P450 reductase, and P-glycoprotein (Pgp). LLC-PK1 and derivative L-MDR1 cells stably expressing Pgp, the product of the multidrug resistance gene (MDR1), were transfected stably using either a mammalian neomycin selectable expression vector (CYP3A4-Neo) or an episomal vector based on Epstein-Barr virus (CYP3A4-Hygro). These CYP3A4 expressing cells were compared with LLC-PK1, L-MDR1, or Caco-2 cells transduced with Adenovirus-3A4 vector (Ad3A4) with or without simultaneous Adenovirus-P450 Reductase (AdRed) transduction. Cells were characterized for expression of CYP3A4 protein and CYP3A4 mediated metabolism towards midazolam and testosterone. Analysis of membrane integrity and drug transport assays were performed to determine whether infection with recombinant Ad3A4 +/- AdRed affected Pgp function. The rank order of optimal CYP3A4 expression and activities in LLC-PKI and L-MDR1 cells from highest to lowest was cells cotransduced with Ad3A4 plus AdRed >> Ad3A4 >>> CYP3A4-Hygro > CYP3A4-Neo. Similarly, coexpression of Ad3A4 plus AdRed led to enhanced CYP3A4 mediated metabolism in Caco-2 cells over cells with Ad3A4 alone. Incubation of transwell cultured cells expressing Ad3A4/AdRed with midazolam led to readily detectable metabolite in the medium. In microsomes from Caco-2 and LLC-PK1 cells, each co-transduced with Ad3A4/AdRed, Vmax values for testosterone 6beta-hydroxylase activity ranged from 414 to 1350 pmoles/min/mg, respectively. For either Caco-2 or LLC-MDR1 cells, TEER values and the rate of apical to basal and basal to apical transport of vinblastine or digoxin were similar in cells with and without Ad3A4/Red transduction. Polarized cellular systems coexpressing Ad3A4, AdRed, and the MDR1/Pgp transporter were developed and characterized. The results document the utility of these polarized model systems for simultaneous drug transport/drug metabolism studies. Since the experimental approach can be adapted to study the interplay of multiple enzyme/ transporting systems, it may find significant application as a screening tool for the pharmaceutical industry and as a more basic research tool to study the kinetics of intestinal drug bioavailability.

Regulation of mammalian gene expression.

The expression of mammalian genes is regulated primarily at the level of initiation of transcription. The regulatory structure of the mammalian genes consists of the sequence coding for a protein, a proximal upstream promoter sequence which binds the general (basal) transcription factors and a distant enhancer sequence which binds the inducible transcription factors. The general transcription factors are proteins which combine with the RNA polymerase at the promoter to form the initiation complex. Binding of the inducible transcription factors at short DNA sequences, named response elements, mostly enhances or rarely represses the formation of the initiation complex. Transcription factors share common structural motifs; the most frequent are zinc finger, leucine zipper and helix-loop-helix structures. Inducible transcription factors are activated to bind their target response elements on DNA by protein kinases, by binding of activating or removal of inhibitory factors, or by de novo protein synthesis. Inducible transcription factors are activated by hormones or growth factors addressing a number of genes which share common response elements. Steroid and thyroid hormones combine with intracellular receptors to form active transcription factors. Other transcription factors are activated by protein kinases which are themselves activated by hormones through cell membrane receptors and further cellular signaling paths. Whereas the main level of transcriptional control is the initiation of RNA synthesis, in some instances genes are also regulated by alternative splicing of the primary transcript or control of translation into proteins. Large-scale silencing of genes is mediated by the packing of DNA in highly condensed heterochromatin structures and DNA methylation at cytosines in defined guanine-cytosine (GC)-sequences.

Regulation of transgene expression in genetic immunization.

The use of mammalian gene expression vectors has become increasingly important for genetic immunization and gene therapy as well as basic research. Essential for the success of these vectors in genetic immunization is the proper choice of a promoter linked to the antigen of interest. Many genetic immunization vectors use promoter elements from pathogenic viruses including SV40 and CMV. Lymphokines produced by the immune response to proteins expressed by these vectors could inhibit further transcription initiation by viral promoters. Our objective was to determine the effect of IFN-gamma on transgene expression driven by viral SV40 or CMV promoter/enhancer and the mammalian promoter/enhancer for the major histocompatibility complex class I (MHC I) gene. We transfected the luciferase gene driven by these three promoters into 14 cell lines of many tissues and several species. Luciferase assays of transfected cells untreated or treated with IFN-gamma indicated that although the viral promoters could drive luciferase production in all cell lines tested to higher or lower levels than the MHC I promoter, treatment with IFN-gamma inhibited transgene expression in most of the cell lines and amplification of the MHC I promoter-driven transgene expression in all cell lines. These data indicate that the SV40 and CMV promoter/enhancers may not be a suitable choice for gene delivery especially for genetic immunization or cancer cytokine gene therapy. The MHC I promoter/enhancer, on the other hand, may be an ideal transgene promoter for applications involving the immune system.

A Mammalian Gene Expression Vector with Blue–White Selection for Efficient Subcloning inEscherichia coli

A Mammalian Gene Expression Vector with Blue–White Selection for Efficient Subcloning inEscherichia coli

Expression analysis of the ligand to ly‐6e.1 mouse hematopoietic stem cell antigen

Ly‐6E.1 antigen was proposed as a regulatory molecule of T lymphocyte activation, a hematopoietic stem cell marker, a memory cell marker, and an adhesion molecule. Though there were several reports suggesting the presence of Ly‐6 ligand, the characterization of the ligand was not yet performed. As an attempt to screen the expression of Ly‐6E.1 ligand, we prepared a probe for detecting Ly‐6E.1 ligand by producing a fusion protein between Ly‐6E.1 and hlgC γ1. A mammalian cell expression vector with Ly‐6E.1/hlgC γ1 chimeric cDNA was transfected in SP2/0‐Ag14 myeloma cells, and stable transfectants were selected. The fusion protein was produced as a dimer and maintained the epitopes for monoclonal antibodies specific for Ly‐6E.1 and for anti‐human IgG antibody. The purified fusion protein through Gammabind G column was used for FACS analyses for the expression of Ly‐6E.1 ligand. The fusion protein interacted with several cell lines originating from B cells, T cells, or monocytes. The fusion protein also stron...

Mammalian expression and characterization of a dimeric single chain antibody specific for integrin avβ3 : Catherine Beidler, IXSYS Incorporated, San Diego CA 92121, USA

Mammalian expression and characterization of a dimeric single chain antibody specific for integrin avβ3 : Catherine Beidler, IXSYS Incorporated, San Diego CA 92121, USA

Localization of endothelial nitric oxide synthase in the normal and failing human atrial myocardium

Nitric oxide (NO) is a potent endothelium-derived relaxing factor which also may modulate cardiomyocyte inotropism and growth via increasing cGMP. While endothelial nitric oxide synthase (eNOS) isoforms have been detected in non-human mammalian tissues, expression and localization of eNOS in the normal and failing human myocardium are poorly defined. Therefore, the present study was designed to investigate eNOS in human cardiac tissues in the presence and absence of congestive heart failure (CHF).Normal and failing atrial tissue were obtained from six cardiac donors and six end-stage heart failure patients undergoing primary cardiac transplantation. ENOS protein expression and localization was investigated utilizing Western blot analysis and immunohistochemical staining with the polyclonal rabbit antibody to eNOS (Transduction Laboratories, Lexington, Kentucky).

Mammalian cell expression of single-chain Fv (sFv) antibody proteins and their C-terminal fusions with interleukin-2 and other effector domains.

The production of several single-chain Fv (sFv) antibody proteins was examined by three modes of mammalian cell expression. Our primary model was the 741F8 anti-c-erbB-2 sFv, assembled as either the VH-VL or VL-VH, and expressed alone, with C-terminal cysteine for dimerization, or as fusion proteins with carboxyl-terminal effector domains, including interleukin-2, the B domain of staphylococcal protein A, the S-peptide of ribonuclease S, or hexa-histidine metal chelate peptide. Constructs were expressed and secreted transiently in 293 cells and stably in CHO or Sp2/0 cell lines, the latter yielding up to 10 mg per liter. Single-chain constructs of MOPC 315 myeloma and 26-10 monoclonal antibodies were also expressed, as were hybrids comprising unrelated VH and VL regions. Our results suggest that mammalian expression is a practical and valuable complement to the bacterial expression of single-chain antibodies.

Proacrosin gene expression in rat spermatogenic cells.

Mammalian proacrosin gene expression was considered to be exclusively postmeiotic until recent studies detected the presence of proacrosin mRNA in mouse pachytene spermatocytes. To determine if rat proacrosin gene expression was initiated during meiosis, a 314-bp proacrosin cDNA fragment was amplified from rat round spermatid RNA, using proacrosin-specific primers, for use as a probe. Sequence analysis of the round spermatid 314-bp cDNA fragment confirmed > 99% identity with the rat proacrosin cDNA sequence. This 314-bp fragment was subsequently used for Northern blot analysis of RNA isolated from testicular germ cells. A 1.6-kb transcript was detected in pachytene spermatocytes, round spermatids, and a mixed population of condensing spermatids/residual bodies, with the highest level of expression in round spermatids. Northern blot analysis of testicular RNA during development revealed the earliest timepoint of expression to be at 24 days of age, further demonstrating the association of proacrosin mRNA with spermatocytes. These data demonstrate diploid expression of the rat proacrosin gene, in agreement with mouse proacrosin gene expression but in contrast to the apparent haploid expression of proacrosin described for the bull and the boar. These studies provide evidence that, in the rat, the process of acrosome biogenesis begins during meiosis.

Functional analysis of the cysteine residues of activin A.

Site-directed mutagenesis and mammalian cell expression was used to analyze the function of each of the 13 cysteine residues in the human activin A beta-subunit precursor. Substitution of the four cysteine residues in the proregion with alanine residues did not affect the function of the proregion in facilitating the dimerization and secretion of activin A homodimers. A series of activin mutants were constructed in which the nine cysteine residues (amino acids 4, 11, 12, 40, 44, 80, 81, 113, and 115) in the mature 116-amino acid beta-subunit were individually altered to alanine residues. Alanine substitution at either cysteine residues 4 or 12 did not interfere with homodimer formation, but the mutant activin A molecules had reduced biological and receptor binding activity (2- to 3-fold). Activin A monomers were produced when cysteine mutants 44, 80, and 113 were expressed in tissue culture cells. Monomers of cys mutants 44 and 80 had approximately 2% of the biological and receptor binding activity of wild type activin A. Cys 113 monomers had undetectable levels of biological activity. No detectable activin monomers or dimers were secreted from cells transfected with plasmids containing cys mutants 11, 40, 81, and 115. The data presented here suggest that a low level of noncovalent dimer formation of cysteine mutant monomers 44 and 80 may explain their low level of biological activity. Therefore, dimer formation is suggested to be an essential prerequisite for high affinity receptor binding and biological potency.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning and functional expression of a Talaromyces emersonii derived alpha-amylase encoding genetic determinant in a human cell line

A cDNA fragment encoding a Talaromyces emersonii acid stable alpha-amylase has been cloned into a mammalian cell expression vector system. When human HeLa cells were transformed with this DNA, functional enzyme could be detected in extracellular media and cell lysates derived from stable transformants. Expression of the T. emersonii derived cDNA was verified by northern dot blotting hybridisation analysis of mRNA extracted from transformants, using the labelled amylase encoding cDNA determinant as a probe. Results obtained suggest that expression of the fungus derived alpha-amylase in the transformed HeLa cells is glucocorticoid dependent.

Use of mammalian cell expression cloning systems to identify genes for cytokines, receptors, and regulatory proteins

Use of mammalian cell expression cloning systems to identify genes for cytokines, receptors, and regulatory proteins

Use of mammalian cell expression cloning systems to identify genes for cytokines, receptors, and regulatory proteins

Mammalian cell expression cloning has become a standard technique for the isolation of mammalian genes or cDNAs. Its advantage is that the biological functions of the gene of interest are used for cloning. Therefore, the identified cDNAs or genes should be functional in vivo, and there is no need for physical or chemical information about the gene products, so that protein purification in sufficient quantity to raise antibodies or to obtain amino acid sequences is not necessary. Here, we summarize recent progress in mammalian cell cloning systems, and discuss the possible directions in which this technique will lead.