High-frequency transfer of cloned herpes simplex virus type 1 sequences to mammalian cells by protoplast fusion

Analysis of cell-cell contact mediated by Ig superfamily cell adhesion molecules

Cell-cell adhesion is a fundamental requirement for all multicellular organisms. The calcium-independent cell adhesion molecules of the immunoglobulin superfamily (IgSF-CAMs) represent a major subgroup. They consist of immunoglobulin folds alone or in combination with other protein modules, often fibronectin type-III folds. More than 100 IgSF-CAMs have been identified in vertebrates and invertebrates. Most of the IgSF-CAMs are cell surface molecules that are membrane-anchored either by a single transmembrane segment or by a glycosylphosphatidylinositol (GPI) anchor. Some of the IgSF-CAMs also occur in soluble form, e.g., in the cerebrospinal fluid or in the vitreous fluid of the eye, due to naturally occurring cleavage of the GPI anchor or the membrane-proximal peptide segment. Some IgSF-CAMs, such as NCAM, occur in various forms that are generated by alternative splicing. This unit contains a series of protocols that have been used to study the function of IgSF-CAMs in vitro and in vivo.

A cell-based method for screening RNA-protein interactions: identification of constitutive transport element-interacting proteins

We have developed a mammalian cell-based screening platform to identify proteins that assemble into RNA-protein complexes. Based on Tat-mediated activation of the HIV LTR, proteins that interact with an RNA target elicit expression of a GFP reporter and are captured by fluorescence activated cell sorting. This "Tat-hybrid" screening platform was used to identify proteins that interact with the Mason Pfizer monkey virus (MPMV) constitutive transport element (CTE), a structured RNA hairpin that mediates the transport of unspliced viral mRNAs from the nucleus to the cytoplasm. Several hnRNP-like proteins, including hnRNP A1, were identified and shown to interact with the CTE with selectivity in the reporter system comparable to Tap, a known CTE-binding protein. In vitro gel shift and pull-down assays showed that hnRNP A1 is able to form a complex with the CTE and Tap and that the RGG domain of hnRNP A1 mediates binding to Tap. These results suggest that hnRNP-like proteins may be part of larger export-competent RNA-protein complexes and that the RGG domains of these proteins play an important role in directing these binding events. The results also demonstrate the utility of the screening platform for identifying and characterizing new components of RNA-protein complexes.

Use of monoclonal antibodies for expression cloning

This unit details the use of transient expression in mammalian cells to screen cDNA libraries with monoclonal antibodies (MAb) to isolate cDNA clones encoding cell-surface and intracellular proteins. The first protocol describes the cloning of cDNAs encoding cell-surface antigens. The second protocol is a modification that facilitates isolation of cDNAs encoding antigens that are expressed intracellularly. Both protocols are designed for use with the expression vector CDM8, which contains a polylinker for subcloning double-stranded cDNA.

Use of monoclonal antibodies for expression cloning

This unit details the use of transient expression in mammalian cells to screen cDNA libraries with monoclonal antibodies (MAb) to isolate cDNA clones encoding cell-surface and intracellular proteins. The first protocol in this unit describes the cloning of cDNAs encoding cell-surface antigens. Several steps in this protocol involve transfection procedures that are described in greater detail elsewhere in this volume. The second protocol is a modification that facilitates isolation of cDNAs encoding antigens that are expressed intracellularly. Both protocols are designed for use with the expression vector CDM8, which contains a polylinker for subcloning double-stranded cDNA.

Transfection of lymphoid cells

Using available vectors, a single immunoglobulin chain or both heavy (H) and light (L) chains can be simultaneously transferred to recipient myeloma cells. Several methods can be used to prepare stable transfected lymphoid cells. The Basic Protocol in this unit describes protoplast fusion, which is suitable for certain lymphoid cells but tends to be more cumbersome than electroporation or liposome-mediated transfection, which are described in the two alternate protocols. All three techniques may be adapted for stable transfection of other eukaryotic cell lines.

A simple procedure for expression and purification of selected non-structural (alpha and beta) herpes simplex virus 1 (HSV-1) proteins

The expression and isolation of herpes simplex virus 1 (HSV-1) immediate early (alpha) IE63 (ICP27) and of the early (beta) thymidine kinase (Tk) polypeptides in Escherichia coli JM 109 cells transformed with the PinPoint Xa-1 (Promega) plasmid construct carrying either the HSV-1 UL54 or UL23 genes are described. The resulting biotinylated fusion protein(s) could be easily induced and were purified in appropriate amounts by means of a monomeric avidin-conjugated resin (SoftLink Soft Release Avidin Resin, Promega) provided that: (1) the exponential growth of the selected transformed cells was monitored carefully; (2) the post-induction harvest interval was properly chosen; and (3) the period for adsorption to the avidin resin suitably adjusted. The isolated protein(s), although partially digested in the case of the IE63 polypeptide, were suitable antigen(s) for immunization of various animal species. Co-purification of trace amounts of endogenous biotinylated protein(s) produced in E. coli was eliminated by shortening the duration of adsorption to the avidin resin.

Soluble complement receptor 1 (CD35) delivered by retrovirally infected syngeneic cells or by naked DNA injection prevents the progression of collagen-induced arthritis

OBJECTIVE

The complement system is important in the development of autoimmune inflammation, including rheumatoid arthritis (RA) and collagen-induced arthritis (CIA). Complement receptor 1 (CR1) is involved in regulation of complement activity. Studies on models of autoimmunity have demonstrated that soluble CR1 (sCR1) is a potent therapeutic agent. The present study was thus undertaken to investigate the feasibility of antiinflammatory gene therapy to prevent CIA by delivery of genes encoding truncated sCR1 (tsCR1) and dimeric tsCR1-Ig.

METHODS

Syngeneic fibroblasts or arthritogenic splenocytes, engineered to express tsCR1 using retrovirus-mediated gene transfer, were injected into DBA/1 recipients that had been immunized with bovine type II collagen (CII). In separate experiments, naked DNA containing tsCR1 and tsCR1-Ig genes was injected intramuscularly into the immunized animals. The clinical development of arthritis was monitored, anti-CII levels measured, and antigenic T cell response studied. Affinity-purified tsCR1-Ig was assayed for its inhibitory effect on the alternative complement pathway in mouse serum.

RESULTS

Treatment of CII-immunized mice with the tsCR1-expressing cells inhibited development of CIA, reduced anti-CII antibody levels, and inhibited T cell response to CII in vitro. Intramuscular injections of DNA encoding the CR1 genes prevented the progression of disease. Furthermore, compared with full-length sCR1, purified tsCR1-Ig was more active in inhibiting the murine alternative complement pathway.

CONCLUSION

Our findings demonstrated that tsCR1 and tsCR1-Ig, when delivered via gene therapy, had a beneficial effect on autoimmune inflammation. These results indicate that targeting the complement system in RA patients may be of clinical importance.

Gene structure of the murine NK cell receptor 2B4: presence of two alternatively spliced isoforms with distinct cytoplasmic domains

The NK cell receptor 2B4 is expressed on the surface of all murine NK cells and a subset of T cells. Ligation of 2B4 with monoclonal antibodies increases target cell lysis and IFN-gamma production. 2B4 is the high-affinity counter-receptor for CD48 in mice and humans. 2B4-L is a member of the CD2 subgroup of the immunoglobulin supergene family, which includes CD48, LFA-3, CD84, Ly9 and SLAM. Here we describe 2B4-S, a second 2B4 isoform, and the genomic structure of the 2B4 gene. 2B4-S is identical to the 5' end of 2B4-L, differing only at the 3' end, corresponding to a portion of the cytoplasmic domain and the 3' untranslated sequence. Both 2B4-L and 2B4-S are expressed on IL-2-activated NK cells. The genomic clone of 2B4 reveals that the two cDNA clones are products of alternative splicing. Since they differ only in a portion of the cytoplasmic domain, it is likely that they transduce different signals.

Sensitization of the HIV-1-LTR upon long term low dose oxidative stress

Human lymphoid cell lines were transfected with HIV-1-LTR-CAT DNA and permanently transformed cell lines were obtained. These transformed cell lines were treated with 0.01 mM H2O2 for 25 days and the chloramphenicol acetyltransferase (CAT) activities of these cell lines were measured. The CAT activities of transformed cell lines were latent in normal culture conditions, but were activated by retreatment with 0.2 mM H2O2 for 1 h. On treatment with 0.05 mM H2O2 for 1 h, the CAT activity of these cell lines maintained in normal conditions remained latent, whereas cell lines pretreated with 0.01 mM H2O2 for 25 days were greatly activated by this treatment. Here, the HIV-1 promoter seemed latent in normal culture conditions, but it could be activated by a comparatively low concentration (0.05 mM) of H2O2 after treatment with a dilute H2O2 (0.01 mM) for about 1 month. Many patients infected with human immunodeficiency virus 1 (HIV-1) show a long latent period before development of AIDS. During this latent period, their infected cells may be subjected to oxidative stress due to metabolism and physical movement. The present results indicate that oxidative stress may cause activation of the HIV-1 promoter in patients with latent HIV-1.

Bacterial lipopolysaccharide copurifies with plasmid DNA: implications for animal models and human gene therapy

During the course of gene therapy experiments in rodents, using intramuscular injections of plasmid DNA derived from Escherichia coli, we noted dose-related toxicity. This observation prompted a search for possible contaminants of DNA samples. We used the highly specific and sensitive limulus amoebocyte lysate assay (LAL), to monitor endotoxin bioactivity in DNA samples, and found plasmid DNA derived from standard E. coli bacterial strains, using traditional DNA isolation protocols, to be heavily contaminated with endotoxin, or lipopolysaccharide (LPA). Standard DNA isolation procedures resulted in the copurification of up to 500 micrograms/ml of LPS. LPS is a potent inducer of cytokines and other inflammatory mediators, and may complicate the use of naked DNA in gene therapy. The copurification of endotoxin with plasmid DNA also has important implications for in vitro transfection studies and microinjection of DNA into embryos. A simple and efficient protocol to reduce LPS contamination of plasmid DNA was developed. The conversion of intact bacteria to spheroplasts prior to the isolation of plasmid DNA, incubation with lysozyme, treatment with the detergent n-octyl-beta-D-thioglucopyranoside (OSPG) and polymyxin-B (PMB) chromatography, allowed the isolation of plasmid DNA containing less than 50 ng/ml LPS. This represents a 10,000-fold reduction in LPS contamination, compared to conventional methods of plasmid DNA purification, avoids potentially toxic reagents such as ethidium bromide, and produces a higher yield of plasmid DNA.

Production of an immunoglobulin gene product by the plasmid expression vector L factor in mouse myeloma cells

L factor, originally discovered in a subclone of mouse L cells, is a multicopy mammalian plasmid whose structure is related to that of polyoma. When a composite DNA consisting of L factor, pBR, bacterial neo, and an immunoglobulin (kappa) gene was introduced into mouse myeloma cells, the DNA was established as plasmids in the cells without rearrangement or integration into the chromosomes. The plasmid-bearing myeloma cells produced kappa mRNA and the gene product, kappa immunoglobulin, which were apparently derived from the gene located on plasmid L factor. These results suggest that L factor can be used as a plasmid expression vector for studies on gene expression and production of biologically active substances in mammalian cells.

The second century of the antibody. Molecular perspectives in regulation, pathophysiology, and therapeutic applications

The modern age of immunology began in 1890 with the discovery of antibodies as a major component of protective immunity. The 2nd century of the antibody begins with a focus on the molecular physiology and pathophysiology of immunoglobulin production. Numerous human variable-region antibody genes have been identified through advances in molecular cloning and anti-variable-region monoclonal antibodies. Some of these variable-region genes are now known to be involved in specific stages of B-lymphocyte differentiation and immune development. This connection has yielded new insights into the pathogenesis of immune dyscrasias and lymphoid neoplasia; common variable immunodeficiency and cryoglobulinemia are highlighted here. The molecular regulation of immunoglobulin expression suggests new targets for pathogenesis and clinical intervention. Finally, genetically engineered antibodies offer novel opportunities for diagnostic and therapeutic applications.

Short-term assays for detection of conditional cancerogens. I. Construction of DR-CAT Raji cells and some of their characteristics as tester cells

A number of agents including the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) (TPA) can induce an abortive virus cycle in the EBV-non-producer Burkitt's-lymphoma line Raji. Two distant regions, DL and DR, of the EBV genome with almost complete homology carry strong promoters which are induced in an abortive or lytic cycle and additionally function as lytic origins of viral DNA replication. To set up a system in which the activity of EBV-inducing agents can be measured in a quantitative and reproducible fashion, we generated a cell line which carries multiple copies of a DR-promoter chloramphenicol-acetyltransferase (CAT) construct on an episomal vector. CAT activity is low in untreated cells, but high upon treatment of the cells with various EBV-inducing agents. Combinations of different agents can produce an over-additive effect. The Raji-DR-CAT cell line may provide a simple quantitative and reproducible test system for EBV-inducing agents, especially for tumor promoters which activate protein kinases C.

The polypeptide encoded by the cDNA for human cell surface antigen Fas can mediate apoptosis

Mouse anti-Fas monoclonal antibody has a cytolytic activity on human cells that express the antigen. Complementary DNAs encoding the cell surface antigen Fas were isolated from a cDNA library of human T cell lymphoma KT-3 cells. The nucleotide sequence of the cDNAs revealed that the molecule coding for the Fas antigen determinant is a 319 amino acid polypeptide (Mr 36,000) with a single transmembrane domain. The extracellular domain is rich in cysteine residue, and shows a similarity to that of human tumor necrosis factor receptors, human nerve growth factor receptor, and human B cell antigen CD40. Murine WR19L cells or L929 cells transformed with the human Fas antigen cDNA were killed by the anti-Fas antibody in the process known as apoptosis.

Transfection of wild-type and 'Fanconi anemia-like' mouse lymphoma mutant cells by electroporation

An electroporation protocol for the successful transfection of mouse lymphoblastoid cells has been developed. Two cell lines, a normal and a mutant sensitive to DNA cross-linking agents, were used. The optimum conditions of electroporation in terms of uptake of the fluorescent dye lucifer yellow coupled with low toxicity were established. Subsequently, these conditions were used to achieve stable transfection by a plasmid expression vector. The plasmid integration patterns were determined by Southern blot analysis.

High level expression of human proteins in murine hybridoma cells: induction by methotrexate in the absence of gene amplification

We have developed an inducible system for high level expression of heterologous genes in murine hybridoma cells. The rapid induction by methotrexate (MTX) does not involve gene amplification and is controlled at the level of mRNA accumulation. Transfection was achieved by protoplast fusion with an expression vector containing the cDNA of interest and a marker gene encoding dihydrofolate reductase. The initial clones, selected at 100 nM MTX, produced high levels of the protein of interest and contained about 100-400 copies of the integrated plasmid DNA. They could adapt to a 100- to 1000-fold stepwise increase in MTX concentration in a few weeks, during which the expression of the gene of interest but not its copy number, increased several-fold. Furthermore, the induction is freely reversible. If cells were propagated in MTX-free media, the expression level decreased, but the cells could be reinduced to their original high level of expression by adding MTX back to the media. A several-fold increase in the mRNA levels of the dihydrofolate reductase and the gene of interest could be detected after induction for 18 h.

Measurement of transient cDNA expression in mammalian cells using flow cytometric cell analysis and sorting

Generalized methods for quantitative and sensitive measurement of transient cDNA expression in mammalian cells using flow cytometry (FCM) are described. The techniques are applicable to a wide variety of cDNAs encoding intracellular or cell surface protein products through the use of immunofluorescence- or nonimmunofluorescence-based detection methods. The methods illustrated have been optimized for sensitive detection of transfectants and efficient recovery of the encoding plasmids from the sorted cells. Expression levels and heterogeneities were compared using four methods of DNA transfer in addition to description of a novel method to optimize single copy transfer probabilities by multiparameter analysis. The overall sensitivities are compared by reconstruction and molecular cloning experiments to other methods of selection, such as immunoselection by panning. Through the measurement of multiple heterologous products per cell, or the measurement of multiple epitopes or binding sites per heterologous protein, expression levels on a single cell basis can be measured and correlated with other endpoints for various purposes. The ability to detect and recover rare clones based on a number of single and multiparameter selection criteria should significantly extend the use of transient mammalian cDNA expression methods for applications involving novel FCM-based reporter cDNA assays and for cloning certain rare surface-bound or secreted proteins using FCM.

Transient expression of the angiotensin II receptor: a rapid and functional analysis of a calcium-mobilizing seven-transmembrane domain receptor in COS-7 cells

The mas oncogene/angiotensin II receptor was subcloned into a mammalian expression vector pCDM8 and used to transiently transfect monkey kidney derived COS-7 cells. As a result, the mas transfected COS-7 cells expressed a functional angiotensin II receptor capable of transducing an increase in intracellular Ca2+ following stimulation with angiotensin II. The angiotensin II stimulated changes in Ca2+ could be measured 24 hours after transfection in both a fluorimeter and a fluorescence activated cell sorter. These results describe a rapid method for the functional analysis of the 7-transmembrane domain receptor genes.

A vector that expresses secreted proteins on the cell surface

A new vector, CDM8PI, has been constructed. It was derived from the plasmid expression vector CDM8, which has been used in the epitope-loss mutant isolation technique to map the epitopes on cell-surface proteins. The new vector allows the production of fusion proteins between normally secreted proteins and the membrane anchor moiety from a cell-surface protein, LFA-3, thereby expressing the fusion proteins on the cell surface. The vector extends the application of the epitope-loss mutant isolation technique to secreted proteins. The vector also allows the easy recovery of mutated proteins in unfused forms after the immunoselection and characterization.

Mapping of murine IgE epitopes involved in IgE-Fc epsilon receptor interactions

The generation of anti-IgE monoclonal antibodies has permitted the identification of various serological epitopes on the IgE molecule. The relationship of the sites on IgE recognized by such antibodies to the Fc epsilon receptor (Fc epsilon R) interaction site has been determined using cross-inhibition studies. However, interpretation of this type of experiment is limited by problems of steric hindrance. Thus, to accomplish precise mapping on the IgE molecule of the Fc epsilon R interaction site and the binding sites of various anti-IgE mAb, we employed site-directed mutagenesis of the IgE heavy chain gene. To this end we have constructed and expressed a recombinant murine constant epsilon heavy chain (C epsilon) gene bearing a (4-hydroxy-3-nitrophenyl)acetic acid (NP)-binding VH region. Several site-specific mutants in the C epsilon 3 and C epsilon 4 domains of this recombinant C epsilon gene were prepared and expressed by transfection into the light chain-producing J558L myeloma cell line. The resulting IgE antibodies were tested for binding to mast cells and to various anti-IgE mAb. The mutants produced include a proline to histidine point mutant at amino acid residue 404 in the C epsilon 3 domain, a mutant with a truncated C epsilon 4 domain, a mutant with a 45 amino acid deletion in the carboxy end of C epsilon 3, and a chimeric human C epsilon in which the human C epsilon 3 was replaced by the homologous mouse C epsilon 3 domain. These mutants have permitted the localization, to the C epsilon 3 domain, of the epitopes recognized by the 84.1C and 95.3 anti-IgE mAb. The 84.1C mAb recognizes a site on IgE which is identical or very close to the Fc epsilon R binding site, and 95.3 recognizes a site on IgE which is related, but not identical to the Fc epsilon R binding site. The antigenic determinant recognized by the 51.3 mAb, which is inefficient at blocking the IgE-Fc epsilon R interaction, has been mapped to the C epsilon 4 domain. When tested for binding to the Fc epsilon R on RBL-2H3 cells, the point mutant bound to the Fc epsilon R with twofold reduced affinity, while the C epsilon 3 deletion mutant and the mutant truncated in C epsilon 4 lost all receptor binding activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Mutation of glycine 49 to valine in the alpha subunit of GS results in the constitutive elevation of cyclic AMP synthesis

The G-protein GS couples hormone-activated receptors with adenylyl cyclase and stimulates increased cyclic AMP synthesis. Transient expression in COS-1 cells of cDNAs coding for the GS alpha-subunit (alpha S) or alpha S cDNAs having single amino acid mutations Gly49----Val or Gly225----Thr elevated cyclic AMP levels, resulting in the activation of cyclic AMP dependent protein kinase. Stable expression in Chinese hamster ovary cells of alpha S Val49 cDNA resulted in a small constitutive elevation of cyclic AMP that was sufficient to persistently activate cyclic AMP dependent protein kinase activity 1.5-2-fold over basal activity. Stable expression of wild-type alpha S or alpha S Thr225 in Chinese hamster ovary cells was less effective in sustaining elevated cyclic AMP synthesis and kinase activation compared to alpha SVal49.

Detection by flow cytometry of protoplast fusion and transient expression of transferred heterologous CD4 sequences in COS-7 cells

Transfer and expression of a plasmid containing the gene encoding the human T-cell antigen CD4 by protoplast fusion was measured by flow cytometry (FCM). Protoplasts were prelabeled with fluorescein isothiocyanate (FITC) and fused to COS-7 cells. Nonspecific protoplast adsorption to the plasma membrane was differentiated from successful protoplast fusion by the addition of an antibody directed against fluorescein to quench extracellular protoplast fluorescence. Transfection efficiencies were defined as both percent CD4 expressing cells and CD4 expression levels on a single cell basis in the transient immunofluorescence assay. Cell sorting studies indicated that intracellular protoplast-associated fluorescence immediately after fusion exhibited a good correlation with transient CD4 transfection efficiencies as measured by indirect immunofluorescence. Reconstruction experiments comparing CD4 transfer efficiencies of protoplast fusion and calcium phosphate transfection showed that fusion resulted in a higher percentage of CD4 expressing transfectants, while calcium phosphate transfection yielded higher CD4 expression levels on a single cell basis. Thus, FCM appears to be useful as a new tool for sensitive detection of transient expression of heterologous reporter genes in COS-7 cells.

Structure and expression of the Lyt-3a gene of C.AKR mice

The mouse Lyt-3a gene, which encodes the Lyt-3.1 T-cell surface alloantigen of the C.AKR strain, has been cloned, and the nucleotide sequence of its exons and more than 2 kb of 5' flanking sequence have been determined. The gene extends over approximately 16 kb of DNA and consists of six exons encoding leader, leader plus V-like domain, membrane-proximal, transmembrane, and cytoplasmic domains. The only difference between the coding region of the Lyt-3a gene and the cDNA sequences reported for Lyt-3b (Nakauchi et al. 1987. Panaccio et al. 1987) is at position 77 of the mature protein where Lyt-3a encodes serine and Lyt-3b encodes arginine. This substitution must therefore be the basis for the serological distinction between the Lyt-3.1 and Lyt-3.2 alloantigens. Potential TATA and CAAT sequences, two Sp1 protein binding sites, two extended repeats of the dinucleotide, CA, a number of short inverted repeats, and an inverted segment of the mouse B1 repetitive sequence are found 5' to the Lyt-3a gene. Two consensus poly-A addition signals and a complete copy of the mouse B1 sequence are found 3' to the gene. Both B1-related regions are flanked by short direct repeats suggesting that they arose by an insertional mechanism. Cotransfection of the Lyt-3a gene together with a cloned Lyt-2a gene resulted in expression of both Lyt-2 and Lyt-3.1 on the surface of Ltk- and BW5147 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Retroviral-mediated gene transfer. Applications in neurobiology

There are now many examples of the successful expression of genes transduced by retroviruses in studies from outside the field of neuroscience. Retroviruses will undoubtedly also prove to be effective tools for neuro-scientists interested in expressing cloned neurotransmitter and receptor genes. There are also other less obvious applications of retroviruses, such as their insertional mutagenic effects, which may be useful in studies of the genetic factors and biochemical mechanisms involved in, for example, neurotoxicity. Strong cellular promoters have been identified by retroviral infection and subsequent rescue of the flanking genomic DNA. Retroviruses can be employed again to reintroduce these regulatory sequences back into cells. In this way the complexities of gene expression in the many subpopulations of neurons may be unraveled. Retroviruses can also serve as very useful genetic markers in studies of development and lineage relationships. Retroviruses may be used to efficiently transfer oncogenes into neuronal cells to create new cell lines. This application exploits one of the natural traits of retroviruses--oncogenesis--which led to their original discovery. Finally, there are neurotropic retroviruses that could serve as important vectors for delivering genes into neurons. Studying these retroviruses may lead to an understanding of how they cause neuropathologic changes in the CNS.

Introduction of macromolecules into mammalian cells by cell fusion

Proteins with molecular weights of up to 500K can be enclosed in erythrocyte ghosts by exposing the ghosts to hypotonic solution containing these proteins. The proteins can then be introduced into recipient cells by fusing the ghosts with the cells using HVJ, PEG, or influenza virus. Some applications of this method are described. By an improved method, 15 kbp DNA and IgM (900 kDa) can be entrapped in erythrocyte membranes and these are then treated with liposomes containing gangliosides and HVJ. These treated membranes containing large macromolecules fuse with almost 100% of the recipient cells used. Naked liposomes infrequently fuse with cultured cells, so introduction of their contents into cells is very inefficient. However, liposomes constituted from lipid and glycoproteins (HN and F) of HVJ (Sendai virus), by removing a nonionic detergent, fuse with cells about 200 times more efficiently than naked liposomes. Naked liposomes can fuse with specific cells, such as cells infected with subacute sclerosing panencephalitis virus or with human immunodeficiency virus. Plasmid DNA and mRNA of up to about 40 kbp can be entrapped efficiently in liposomes associated with gangliosides formed by reverse-phase evaporation, and then reacted with HVJ. The contents of the resulting liposomes with HVJ can be introduced efficiently into cultured cells in a suspended or plated state, and nearly all the cells then express the gene transiently. This procedure is also effective for obtaining stable transformants of many kinds of cultured cells.

Exogenous delta-crystallin gene expression as probe for differentiation of teratocarcinoma stem cells

We developed an experimental system in which differentiation of teratocarcinoma stem cell is probed by expression of stably introduced exogenous genes. We used chicken delta-crystallin gene (delta gene) and its derivative (Mo delta gene) driven by long terminal repeat (LTR) promoter of Moloney murine leukemia virus (Mo-MuLV). Neither of the genes was expressed in the undifferentiated condition. Differentiation to primitive endoderm induced by retinoic acid (RA) led to expression of delta but not Mo delta, while differentiation to more advanced endodermal cells by RA plus dibutyryl cAMP elicited Mo delta expression in addition to delta. These results are interpreted as a consequence of differential activation/suppression of gene expression through enhancer elements associated with the genes.

Genetically engineered antibody molecules and their application

Immunoglobulin genes can be efficiently expressed following transfection into myeloma cells. Using protoplast fusion, transfection frequencies greater than 10(-3) can be achieved. Compatible plasmids containing two different selectible markers are used to simultaneously deliver heavy and light chain genes to the same cell. To produce molecules with differing specificities the rearranged and expressed variable regions can be cloned from the appropriate hybridoma. In some cases, variable regions from cDNAs can be inserted into the expression vectors. It is possible to manipulate the immunoglobulin genes and produce novel antibody molecules. Antibodies have been produced in which the variable regions from mouse antibodies have been joined to human constant regions. In addition, antibodies with altered constant regions have been produced. These genetically engineered antibodies provide a unique set of reagents to study structure-function relationships within the molecule. They also can potentially be used in the diagnosis and therapy of human disease.

Protoplast-mediated gene transfer into human leukemia (K562) cells

We have examined the usefulness of a protoplast fusion technique as a tool to transfer cloned genes into hematopoietic cells. Protoplasts carrying cloned plasmids, which would express specific markers when successfully transfected into human cells, were prepared and fused with human leukemic cell line K562 cells using polyethylene glycol as a fusogenic factor. As a result, K562 cells fused with protoplasts containing a plasmid pSV2-cat constructed to code for chloramphenicol acetyltransferase (CAT) expressed CAT activity efficiently. K562 cells were also readily transformed to geneticin-(G418) resistant cells following fusion with protoplasts carrying a plasmid pSV2-neo-SV-gpt, which confers the resistance of mammalian cells to G418 and mycophenolic acid. It was also demonstrated that the plasmid genome was stably integrated into the chromosomal DNA of G418-resistant K562 cells. Our results proved that protoplast fusion could be used to study the specific expression and the biologic activities of cloned genes in human hematopoietic cells.

Specific antigen-Ia activation of transfected human T cells expressing murine Ti alpha beta-human T3 receptor complexes

The genes encoding the alpha and beta chains of the T-cell receptor (Ti) of an antigen-specific, Ia-restricted murine T-cell hybridoma were introduced into T3-positive or T3-negative human T cells. The resultant transfectants express either mouse-human or mouse-mouse Ti alpha beta molecules functionally associated with the human T3 complex. Only the complete murine Ti alpha beta dimer mediates specific functional corecognition of the appropriate antigen-Ia pair.

Expression of mouse::human immunoglobulin heavy-chain cDNA in lymphoid cells

A chimeric mouse variable::human constant immunoglobulin heavy-chain gene was expressed in transfected mouse Sp2/0 cells. The chimeric immunoglobulin genes were integrated in tandem in the genome of stably transformed cells. These integrated gene copies were amplified by selection with a second drug marker. The gene amplification led to an increase in the expression of chimeric heavy-chain protein. The level of gene expression appears to be related to the site of integration; a few gene copies in one transfectant can yield as much heavy-chain protein as many copies in a second transfectant. In addition, we found that an adventitious oligo(C) sequence, introduced by our method of gene construction at a site located 8 nt residues downstream from a splice acceptor, can apparently direct splicing towards a cryptic splice acceptor downstream from the oligo(C).

Differential transient and long-term expression of DNA sequences introduced into T-lymphocyte lines

We have used a protoplast fusion protocol to introduce the genes encoding neomycin phosphotransferase (neo) and chloramphenicol acetyltransferase (CAT) into murine and human T-lymphocyte lines. Plasmid constructs containing the neo gene under the control of the promoters from the Rous sarcoma virus long terminal repeat (RSV LTR), the SV40 early region, or the herpes simplex virus thymidine kinase gene (HSV TK) can stably transform each of three T-cell lines to G-418 resistance. The characteristic frequencies for different cell lines can differ by at least two orders of magnitude, although initial DNA uptake and transient expression are similar. In the two murine cell lines, low numbers of gene copies are retained in long-term transformants. Prior to integration, transient expression assays for cat or neo gene products reveal that the differences in intrinsic promoter strength of different constructs are further influenced by the coding sequences being transcribed. Thus, while transient expression of the neo protein is similar from both the Rous LTR and the SV40 early promoter, the Rous LTR directs synthesis of CAT protein at levels two orders of magnitude higher than those from the SV40 early promoter.

Structure of pre-pro-von Willebrand factor and its expression in heterologous cells

Von Willebrand factor (vWF), a multifunctional haemostatic glycoprotein derived from endothelial cells and megakaryocytes, mediates platelet adhesion to injured subendothelium and binds coagulation factor VIII in the circulation. Native vWF is a disulphide-bonded homopolymer; the monomeric subunits, of apparent relative molecular mass (Mr) 220,000 (220K) are derived from an intracellular precursor estimated at 260-275K. Multimer assembly is preceded by the formation of dimers, linked near their C-termini, which then assemble into filamentous polymers. The importance of the removal of the large vWF pro-polypeptide during multimer assembly, and whether this or other stages of the complex post-translational processing require components specific to endothelial cells or megakaryocytes, is unknown. Here we report an analysis of the complete sequence of pre-pro-vWF and expression of the molecule in heterologous cells. The vWF precursor is composed of several repeated subdomains. When expressed in COS and CHO cells, it is cleaved and assembled into biologically active high relative molecular mass disulphide bonded multimers. This suggests that the information for assembly of this complex molecule resides largely within its primary structure.

In situ autoradiographic detection of folylpolyglutamate synthetase activity

The enzyme folylpolyglutamate synthetase (FPGS) catalyzes the conversion of folate (pteroylmonoglutamate) to the polyglutamate forms (pteroylpolyglutamates) that are required for folate retention by mammalian cells. A rapid in situ autoradiographic assay for FPGS was developed which is based on the folate cofactor requirement of thymidylate synthase. Chinese hamster AUX B1 mutant cells lack FPGS activity and are unable to accumulate folate. As a result, the conversion of [6-3H]deoxyuridine to thymidine via the thymidylate synthase reaction is impaired in AUX B1 cells and no detectable label is incorporated into DNA. In contrast, FPGS in wild-type Chinese hamster CHO cells causes folate retention and enables the incorporation of [6-3H]deoxyuridine into DNA. Incorporation may be detected by autoradiography of monolayer cultures or of colonies replica plated onto polyester discs. Introduction of Escherichia coli FPGS into AUX B1 cells restores the activity of the thymidylate synthase pathway and demonstrates that the E. coli FPGS enzyme can provide pteroylpolyglutamates which function in mammalian cells.

Recognition of exon-shuffled class II molecules by T helper cells

Exon shuffled I-A beta genes transfected into the B lymphoma cell line A20-2J were used to localize the epitope recognized by the monoclonal antibody 10.2.16 to the carboxy terminal portion of the beta 1 domain. In addition, several T helper cell hybrids were tested against these novel I-A molecules and the following observations were made: the beta 1 domain of A beta plays a dominant role in the restricted recognition by T helper cells; there appear to be multiple restriction epitopes on the I-A molecule; these epitopes can consist of conformational epitopes created by specific alpha and beta chains or consist of the polymorphic determinants encoded on the beta chain alone, and these novel I-A molecules serve as restriction elements in the antigen-specific recognition by T cells and in one case stimulate an alloreaction in the absence of antigen.