Expression of neuronal phenotypes in neuroblastoma cell hybrids

Deactivation of the antiviral state by rabies virus through targeting and accumulation of persistently phosphorylated STAT1

Antagonism of the interferon (IFN)-mediated antiviral state is critical to infection by rabies virus (RABV) and other viruses, and involves interference in the IFN induction and signaling pathways in infected cells, as well as deactivation of the antiviral state in cells previously activated by IFN. The latter is required for viral spread in the host, but the precise mechanisms involved and roles in RABV pathogenesis are poorly defined. Here, we examined the capacity of attenuated and pathogenic strains of RABV that differ only in the IFN-antagonist P protein to overcome an established antiviral state. Importantly, P protein selectively targets IFN-activated phosphorylated STAT1 (pY-STAT1), providing a molecular tool to elucidate specific roles of pY-STAT1. We find that the extended antiviral state is dependent on a low level of pY-STAT1 that appears to persist at a steady state through ongoing phosphorylation/dephosphorylation cycles, following an initial IFN-induced peak. P protein of pathogenic RABV binds and progressively accumulates pY-STAT1 in inactive cytoplasmic complexes, enabling recovery of efficient viral replication over time. Thus, P protein-pY-STAT1 interaction contributes to ‘disarming’ of the antiviral state. P protein of the attenuated RABV is defective in this respect, such that replication remains suppressed over extended periods in cells pre-activated by IFN. These data provide new insights into the nature of the antiviral state, indicating key roles for residual pY-STAT1 signaling. They also elucidate mechanisms of viral deactivation of antiviral responses, including specialized functions of P protein in selective targeting and accumulation of pY-STAT1.

Following viral infection, the host activates multiple antiviral defenses. The ability of viruses to overcome these defenses is critical to disease. The earliest antiviral response involves the production of interferon messenger molecules. Interferons act on infected cells to inhibit viral proliferation, as well as on non-infected cells to establish an antiviral state before infection and so limit viral spread through the host organism. Many strategies used by viruses to overcome the former are well understood, but mechanisms important to the latter, and their importance to disease, are less well defined. In this study, we investigated how rabies virus overcomes a pre-established antiviral state in target cells. We found that the capacity to disable the antiviral state correlates with the ability to cause disease, and involves binding of a viral protein to cellular signaling proteins, which our data indicate are responsible for the maintenance of a prolonged antiviral state. This advances our understanding of antiviral responses, and identifies a key step in lethal infection by rabies virus that causes approximately 60,000 human deaths per year. The findings may contribute to new approaches for the development of vaccines or antivirals.

Genetic and Phenotypic Characterization of a Rabies Virus Strain Isolated from a Dog in Tokyo, Japan in the 1940s

The rabies virus strain Komatsugawa (Koma), which was isolated from a dog in Tokyo in the 1940s before eradication of rabies in Japan in 1957, is known as the only existent Japanese field strain (street strain). Although this strain potentially provides a useful model to study rabies pathogenesis, little is known about its genetic and phenotypic properties. Notably, this strain underwent serial passages in rodents after isolation, indicating the possibility that it may have lost biological characteristics as a street strain. In this study, to evaluate the utility of the Koma strain for studying rabies pathogenesis, we examined the genetic properties and in vitro and in vivo phenotypes. Genome-wide genetic analyses showed that, consistent with previous findings from partial sequence analyses, the Koma strain is closely related to a Russian street strain within the Arctic-related phylogenetic clade. Phenotypic examinations in vitro revealed that the Koma strain and the representative street strains are less neurotropic than the laboratory strains. Examination by using a mouse model demonstrated that the Koma strain and the street strains are more neuroinvasive than the laboratory strains. These findings indicate that the Koma strain retains phenotypes similar to those of street strains, and is therefore useful for studying rabies pathogenesis.

A ligand-based system for receptor-specific delivery of proteins

Gene delivery using vector or viral-based methods is often limited by technical and safety barriers. A promising alternative that circumvents these shortcomings is the direct delivery of proteins into cells. Here we introduce a non-viral, ligand-mediated protein delivery system capable of selectively targeting primary skin cells in-vivo. Using orthologous self-labelling tags and chemical cross-linkers, we conjugate large proteins to ligands that bind their natural receptors on the surface of keratinocytes. Targeted CRE-mediated recombination was achieved by delivery of ligand cross-linked CRE protein to the skin of transgenic reporter mice, but was absent in mice lacking the ligand's cell surface receptor. We further show that ligands mediate the intracellular delivery of Cas9 allowing for CRISPR-mediated gene editing in the skin more efficiently than adeno-associated viral gene delivery. Thus, a ligand-based system enables the effective and receptor-specific delivery of large proteins and may be applied to the treatment of skin-related genetic diseases.

Efficacy of Favipiravir (T-705) in Rabies Postexposure Prophylaxis

Rabies is a fatal encephalitis caused by rabies virus (RABV), and no antiviral drugs for RABV are currently available. We report for the first time the efficacy of favipiravir (T-705) against RABV in vitro and in vivo. T-705 produced a significant, 3–4 log₁₀ reduction in the multiplication of street and fixed RABV strains in mouse neuroblastoma Neuro-2a cells, with half-maximal inhibitory concentrations of 32.4 µM and 44.3 µM, respectively. T-705 significantly improved morbidity and mortality among RABV-infected mice when orally administered at a dose of 300 mg/kg/day for 7 days, beginning 1 hour after inoculation. T-705 significantly reduced the rate of virus positivity in the brain. Furthermore, the effectiveness of T-705 was comparable to that of equine rabies virus immunoglobulin for postexposure prophylaxis. Collectively, our results suggest that T-705 is active against RABV and may serve as a potential alternative to rabies immunoglobulin in rabies postexposure prophylaxis.

Presence of cross-reactions with other viral encephalitides in the indirect fluorescent-antibody test for diagnosis of rabies

The antemortem diagnosis of rabies in humans employs techniques that require accuracy, speed, and sensitivity. A combination of histochemical analysis, in vitro virus isolation, immunological methods, and molecular amplification procedures are utilized in efforts to diagnose the disease. Modern medicine now offers potentially life-saving treatment for a disease that was considered invariably fatal once clinical signs develop. However, medical intervention efforts require a rapid and accurate diagnosis as early in the course of clinical disease as possible. Indirect fluorescent-antibody (IFA) testing on cerebrospinal fluid and serum specimens provides rapid results, but the specificity of the assay has not been well studied. Because false-positive IFA results could significantly affect patient treatment and outcomes, it is critical to understand the specificity of this assay. In this study, IFA testing was performed on 135 cerebrospinal fluid and serum specimens taken from patients with viral encephalitis or a presumed viral infection involving an agent other than rabies virus. Results indicate that false-positive results can occur in interpreting the rabies IFA test. Staining patterns morphologically similar to antirabies staining were observed in 7 of the 135 cerebrospinal fluid specimens examined. In addition, a majority of the cerebrospinal fluid specimens tested from patients with encephalitis presented immunoglobulin that bound to antigens present in the cell culture substrate. Of marked concern was the frequent presence of cross-reactive antibodies in encephalitis cases associated with West Nile and Powassan flaviviruses. Because IFA testing for rabies on human specimens may result in false-positive results, it should not be used as the sole basis for initiating antirabies treatment.

Efficient propagation of betanodavirus in a murine astrocytoma cell line

Betanodavirus, a bipartite RNA virus of fishes and a member of Nodaviridae family, targets nervous tissues and is the causative agent of viral nervous necrosis in marine farmed fish. Betanodavirus is thought to be propagated only in fish cells because betanodavirus has only been isolated in fish and it is not well propagated in mammalian culture cells. However, the host specificity of betanodavirus has not yet been well analyzed. To analyze the host specificity of betanodavirus, various mammalian cells were screened for their permissiveness to betanodavirus. As a result, redspotted grouper nervous necrosis virus can be propagated efficiently in the murine astrocytoma cell line, DBT. The level of viral production in DBT was 10-fold-higher than in the fish cell line, E-11. This result is the first to demonstrate the efficient propagation of betanodavirus in mammalian cells and may help to elucidate the mechanism of the host specificity of betanodavirus.

Further characterization of a CD99-related 21-kDa transmembrane protein (VAP21) expressed in Syrian hamster cells and its possible involvement in vesicular stomatitis virus production

The VAP21, a CD99-related 21-kDa transmembrane protein, was first detected in the enveloped virions that were grown in a Syrian hamster-derived cell line, BHK-21 (Sagara et al., 1997; Yamamoto et al., 1999). We further tried to elucidate the nature and properties of VAP21. The VAP21 was detected in various organs of the Syrian hamster as well as in the Syrian hamster-derived cell lines (BHK-21 and HmLu-1). We could not detect the VAP21 antigen in other cell lines derived from other animal species we examined, including a Chinese hamster (CHO-K1), mouse (neuroblastoma C1300, clone NA), dog (MDCK), monkey (COS-7), and human (HeLa, HepG2). We tried to introduce the VAP21 gene into VAP21-negative cell lines using a tetracycline-regulated gene expression system. All of our trials, however, resulted in failure to establish stably positive inducible cell lines. To the contrary, we could easily establish the VAP21-overexpressing cell lines from the Syrian hamster cell lines, which were successfully grown and maintained without any loss of VAP21 expression even under the induced culture conditions. In such VAP21-overexpressing cells, production of the vesicular stomatitis virus (VSV) was increased several-fold, while suppression of the VAP21 expression resulted in reducing the VSV yields. From these results, we conclude that the VAP21 is a physiologically active cell membrane component of some animal species including the Syrian hamster, and might positively be involved in the VSV replication.

Modification of membrane currents in mouse neuroblastoma cells following infection with rabies virus

1. The effect on membrane currents of infection of mouse neuroblastoma NA cells with rabies virus was studied by using the whole-cell patch clamp technique. 2. Three types of membrane currents, namely voltage-dependent Na+ current (I(Na)), delayed rectifier K+ current (I(K-DR)) and inward rectifier K+ current (I(K-IR)) were elicited in uninfected cells. 3. In cells 3 days after infection with the virus, no detectable change was observed in morphology and membrane capacitance, but I(Na) and I(K-IR) were significantly decreased in amplitude without any appreciable difference in the time course of current activation and inactivation. The voltage-dependence of I(Na) activation was significantly shifted in the positive direction along the voltage axis with a decreased slope. I(K-DR) remained almost unaltered after the viral infection. 4. The resting membrane potential, measured with a physiological K+ gradient across the cell membrane, was decreased (depolarized) after the viral infection. The depolarization was associated with the decreased amplitude of I(K-IR). 5. These results suggest that infection of mouse neuroblastoma NA cells with rabies virus causes reduction of functional expression of ion channels responsible for I(Na) and I(K-IR), and provide evidence for possible involvement of the change in membrane properties in the pathogenesis of rabies disease.

Herpes simplex virus type 1 latency-associated transcripts suppress viral replication and reduce immediate-early gene mRNA levels in a neuronal cell line

During herpes simplex virus type 1 (HSV-1) latent infection in human dorsal root ganglia, limited viral transcription, which has been linked to HSV-1 reactivation ability, takes place. To study the involvement of this transcription in HSV-1 replication in neuronal cells and consequently in viral latency, we constructed stably transfected neuronal cell lines containing (i) the entire HSV-1 latency transcriptionally active DNA fragment, (ii) the same DNA sequence with deletions of the latency-associated transcript (LAT) promoters, or (iii) the DNA coding sequence of the LAT domain. Replication of HSV-1 or a LAT-negative mutant was markedly repressed in the LAT-expressing cells, a phenomenon mediated by the LATs. To study the mechanism responsible for this effect, we examined LAT influence upon expression of HSV-1 immediate-early (IE) genes ICP0, ICP4, and ICP27, by Northern blot analysis. Following infection of a LAT-expressing neuronal cell line with a LAT-negative mutant, the steady-state levels of all three IE mRNAs were reduced compared to those for control cells. Transient transfections into a neuronal cell line indicated that the LAT suppressive effect upon ICP0 mRNA was mediated directly and was not due to the LAT effect upon the ICP0 promoter. We therefore propose that the LATs may repress viral replication in neuronal cells by reducing IE gene mRNA levels and thus facilitate the establishment of HSV-1 latency in nervous tissue.

Atypical splicing of the latency-associated transcripts of herpes simplex type 1

We previously have shown that two latency-associated transcripts (LATs) of herpes simplex type 1 (HSV-1) are probably lariats, produced during splicing. By RNaseH digestion analysis, we now show that the major branchpoint of the 2.0-kb LAT was within 46 nt 5' of the splice acceptor site. A more detailed mapping by primer extension revealed the branchpoint as an adenosine 29 nt 5' of the splice acceptor site. Introduction of two branchpoint sequences with good matches to the consensus at position -25 had no effect on the splicing efficiency but reduced the accumulation of the 2.0-kb LATs at least 90-fold. The second focus of our studies was the 1.5-kb LAT. It was not detected by Northern analyses in either productively infected or transfected cultured cells or even in cells of neuronal origin. However, it was detected in the trigeminal ganglia of mice experimentally infected with HSV-1 after 10 days. Moreover, its abundance relative to that of the 2.0-kb species increased 4-fold from 10 to 30 days after infection, consistent with an interpretation that the 1.5-kb species, once formed, was more stable than the 2.0-kb species.

The abundant latency-associated transcripts of herpes simplex virus type 1 are bound to polyribosomes in cultured neuronal cells and during latent infection in mouse trigeminal ganglia

During herpes simplex virus type 1 (HSV-1) latency, limited viral transcription takes place. This transcription has been linked to the ability of the HSV-1 genome to reactivate and consists of abundant 2.0- and 1.5-kb collinear latency-associated transcripts (LATs), spanned by minor hybridizing RNA (mLAT). The 1.5-kb LAT is derived from the 2.0-kb LAT by splicing, and both transcripts contain two large overlapping open reading frames. The molecular action mechanisms of the latency-associated gene expression are unknown, and no HSV-1 latency-encoded proteins have been convincingly demonstrated. We have cloned the entire latency-associated transcriptionally active HSV-1 DNA fragment (10.4 kb) under control of a constitutive promoter and generated a neuronal cell line (NA4) stably transfected with the viral LAT's region. NA4 cells produced the 2.0- and the 1.5-kb LATs. Northern blotting and reverse transcription-PCR analysis of RNA from NA4 cells and from trigeminal ganglia of mice latently infected with HSV-1 revealed that the two abundant LAT species were present in the polyribosomal RNA fractions. After addition of EDTA, which causes dissociation of mRNA-ribosome complexes, both LATs could be detected only in subpolyribosomal, but not in polyribosomal fractions. These results show that (i) HSV-1 LATs are bound to polyribosomes during latency in vivo, as well as in neuronal cells in vitro, and therefore might be translated, and that (ii) the NA4 cell line is a suitable tool with which to look for HSV-1 latency-encoded gene products.

In vivo production and release of acetylcholine from primary fibroblasts genetically modified to express choline acetyltransferase

Primary rat fibroblasts genetically modified to express Drosophila choline acetyltransferase (dChAT) synthesize and release acetylcholine (ACh) in vitro. The ACh produced from the transduced fibroblasts was found to be enhanced by increasing amounts of choline chloride in the culture media. These dChAT-expressing cells were then implanted into the intact hippocampus of adult rats and in vivo microdialysis was performed 7-10 days after grafting to assess the ability of the cells to produce ACh and respond to exogenous choline in vivo. Samples collected from anesthetized rats revealed fourfold higher levels of ACh around dChAT grafts than from either non-grafted or control-grafted hippocampi. Localized choline infusion (200 microM) through the dialysis probes was found to induce a selective twofold increase in ACh release only from the dChAT-expressing fibroblasts. These results indicate not only that dChAT-expressing fibroblasts continue to synthesize and secrete ACh for at least 10 days after intracerebral grafting, but that the levels of ACh can be manipulated in vivo. The ability to regulate products within genetically modified cells in vivo may provide a powerful avenue for exploring the role of discrete substances within the CNS.

Syncytium formation is induced in the murine neuroblastoma cell cultures which produce pathogenic type G proteins of the rabies virus

We investigated comparatively the interactions of host cells with two types of rabies virus G protein, an avirulent type G (Gln) and a virulent type G (Arg) protein, having glutamine and arginine at position 333, respectively. For this purpose, we established four types of cell lines (referred to as G(Gln)-NA, G(Arg)-NA, G(Gln)-BHK, and G(Arg)-BHK cells, respectively) by transfecting either the G(Gln)-cDNA or G(Arg)-cDNA into two kinds of cells, murine neuroblastoma C1300 (clone NA) and nonneuronal BHK-21. Both G(Gln)-NA and G(Arg)-NA cells produced G proteins when they were treated with 5 mM sodium butyrate, but only G(Arg)-NA cells formed syncytia at the neutral pH, which was suppressed by anti-G antiserum. The sodium butyrate-treated G(Arg)-NA cells fused also with sodium butyrate-treated NA cells under coculture conditions, but neither with untreated NA cells nor with BHK-21 cells. On the other hand, both G(Gln)-BHK and G(Arg)-BHK cells constitutively produced G proteins, but no syncytium was produced at the neutral pH. G(Arg)-BHK cells, however, formed syncytia with the sodium butyrate-treated NA cells when they were cocultured. These results suggest that only G(Arg) has a potential ability to produce syncytia of NA cells regardless of cell types by which G(Arg) protein was produced and also suggest that a certain cellular factor(s) is required for the syncytium formation, the factor(s) which is lacking in BHK-21 and untreated NA cells but is produced by the sodium butyrate-treated NA cells.

Neuroattenuation of an avirulent bunyavirus variant maps to the L RNA segment

The derivation and characterization of a neuroattenuated reassortant clone (RFC 25/B.5) of California serogroup bunyavirus was described previously (M. J. Endres, A. Valsamakis, F. Gonzalez-Scarano, and N. Nathanson, J. Virol. 64:1927-1933, 1990). To map the RNA segment responsible for this attenuation, a panel of reassortants was constructed between the attenuated clone B.5 (genotype TLL) and a virulent clone (B1-1a) of reciprocal genotype (LTT). Parent viruses and clones representing all of the six possible reassortants were examined for neurovirulence by intracerebral injection in adult mice. Reassortants bearing the large RNA segment from the virulent parent were almost as virulent as the virulent parent virus, while reassortants bearing the large RNA segment from the avirulent parent virus exhibited low or intermediate virulence. These results indicate that the large RNA segment is the major determinant of neuroattenuation of clone B.5. In addition to its neuroattenuation, clone B.5 was temperature sensitive and exhibited an altered plaque morphology. These phenotypes also segregated with the large RNA segment. The importance of the large RNA segment (which encodes the viral polymerase) in neurovirulence contrasts with prior studies which indicate that the ability to cause lethal encephalitis after peripheral injection of suckling mice (neuroinvasiveness) is primarily determined by the middle-sized RNA segment, which encodes the viral glycoproteins.

A reduced panel of anti-nucleocapsid monoclonal antibodies for bat rabies virus identification in Europe

A reduced panel of 4 anti-nucleocapsid monoclonal antibodies (mAb) was set up to distinguish viruses of terrestrial mammal origin from viruses of bat origin in Europe. Four additional mAb were necessary to identify each one of the four serotypes of lyssavirus. These 8 mAb were selected out of 25 mAb secreted by hybridomas obtained from mice immunized with either serotype 1 lyssavirus (rabies virus PV4) or serotype 3 lyssavirus (Mokola). They were screened with 32 viruses representative of the four lyssavirus serotypes and the two types of European bat lyssavirus. The panel was tested by immunofluorescence assay with 25 cell-culture-adapted European wildlife isolates and in routine rabies identification with 65 rabid animal brain smears. Two isolates from Eptesicus serotinus in France were identified as European bat lyssavirus 1 with the reduced panel.

Neuroattenuated bunyavirus variant: derivation, characterization, and revertant clones

A neuroattenuated variant bunyavirus, designated RFC/25B.5 (B.5), was selected by serial passage of a reassortant clone (RFC virus) of a California serogroup virus in BHK-21 cells, followed by plaque purification of that passaged stock. Based on its virulence index (ratio of PFU/50% lethal dose), clone B5 was over 40,000-fold less virulent than its unpassaged RFC parent after intracerebral (i.c.) inoculation into adult mice. Clone B.5 also exhibited markedly reduced neuroinvasiveness after subcutaneous injection into neonatal mice, although it retained its ability to replicate and kill suckling mice after i.c. injection. A murine neuroblastoma line (NA cells) can be used as an in vitro surrogate for the adult mouse brain, since clone B.5 replicated to at least 1,000-fold-lower titers in NA cells than did several neurovirulent California serogroup viruses. Clone B.5 replicated in BHK-21 cells at 37 degrees C to titers similar to those achieved by other California serogroup viruses but was temperature sensitive (ts) since its replication was markedly restricted at 38.9 degrees C. Ten ts revertant clones of B.5 virus were selected at 38.9 degrees C, and all of them lost their ts phenotype and regained the ability to replicate to high titer in NA cells and to kill adult mice after i.c. injection. Clone B.5 is the first described California serogroup virus which is truly attenuated after i.c. inoculation, and its availability will permit genetic analysis of bunyavirus neurovirulence.

Immortalized young adult neurons from the septal region: generation and characterization

Studies of the development of the central nervous system would be greatly facilitated by the ability to immortalize neuronal tissue from a broad range of ages. We have previously used somatic cell fusion techniques to generate neuronal cell lines from embryonic mice. To immortalize older neuronal cells, a cell isolation technique was developed to obtain viable septal cells from postnatal day 21 mice. The septal cells were fused to N18TG2 neuroblastoma cells and then cultured in selective medium to isolate septum x neuroblastoma cell lines. The hybrid nature of the lines was verified by chromosome analysis and electrophoretic analysis of glucosephosphate isomerase isozymes. The lines express phenotypes typical of differentiated septal neurons. Many lines morphologically resemble neurons and express the high molecular weight neurofilament protein. Several lines express high levels of choline acetyltransferase activity; others synthesize nerve growth factor. These results demonstrate that young adult neuronal tissue can be immortalized and that hybrid cells express properties of the neuronal parent.

Development and evaluation of an in vitro virus isolation procedure as a replacement for the mouse inoculation test in rabies diagnosis

A tissue culture virus isolation procedure for rabies street strain virus on mouse neuroblastoma cells is described. Parameters for the optimum sensitivity of the procedure were determined to include a minimum 4-day incubation of virus in tissue culture and the use of diethylaminoethyl-dextran for increased cell susceptibility. The in vitro procedure performed well in a comparison with the fluorescent-antibody test and the mouse inoculation test (MIT) on weakly positive brain tissue. Decomposed specimens and virus inhibitors present in brain suspensions were found to interfere with the in vitro procedure. A Formalin-methanol fixative was found to be superior on plastic 96-well plates to previously used fixatives. A 2-year clinical trial of the procedure in parallel with the MIT demonstrated the practicality of the procedure. Accordingly, the New York State rabies diagnostic laboratory has replaced the MIT with the in vitro procedure as a backup for the fluorescent-antibody test in the routine diagnosis of rabies.

Neurotoxic activity in HTLV-I carrier lymphocyte culture

A close association between human T-lymphotropic virus type I (HTLV-I) infection and a group of chronic myelopathies of unknown etiology has recently been established and the name "HTLV-I associated myelopathy" (HAM) has been coined. Although the mechanism of neural tissue damage in HAM remains virtually unknown, several lines of evidence suggest the involvement of a soluble factor(s) including cytokines and viral proteins in the disease process. In this study, we examined cytopathic effects of the supernatants from 6 HTLV-I carrier human T lymphocyte cell lines on 4 human and one murine neuroblastoma cell lines, and 2 human glioma cell lines. Among 6 lymphocyte cell culture supernatants, only 1 from MT-2 cell culture repeatedly exerted cytopathic effects on human neuroblastoma cells, particularly on IMR-32 cells: marked retraction of neurites leading to cellular clumping. This activity was neither abolished by treatment of the medium at 80 degrees C for 30 min or by UV-irradiation, nor was it neutralized by anti-HTLV-I antibodies. The MT-2 supernatant also induced mild cytopathic changes in 2 other human neuroblastoma cell lines and 2 human glioma cell lines. This activity was abolished by treatment of the medium at 80 degrees C for 30 min but not at 56 degrees C for 30 min. Myelinated murine cerebellum explants and other cell lines showed no morphological changes when incubated with the MT-2 supernatant. In addition, the growth of THP-1 cells, a monocyte/macrophage lineage cell line, was remarkably suppressed when maintained in the MT-2 conditioned medium, accompanied by enhancement of phagocytic activity. The THP-1 conditioned medium, on the other hand, suppressed tumor necrosis factor (TNF) activity detected in the MT-2 culture. These observations suggest that HTLV-I induced cytokines may directly act on neural cells, but their action appears to be regulated by the intricate interactions of lymphocytic and monocytic cells.

Novobiocin and coumermycin A1 inhibit viral replication and the reactivation of herpes simplex virus type 1 from the trigeminal ganglia of latently infected mice

Herpes simplex virus type 1 was reactivated from the trigeminal ganglia of latently infected mice in a quantitative and time-dependent manner. Novobiocin and coumermycin A1 reversibly inhibited the reactivation of herpes simplex virus type 1. They did not inhibit viral replication in permissive cells (CV-1) but did inhibit replication in cells of neuronal origin (C1300) and acutely infected trigeminal ganglia.

Comparison of sensitivity of BHK-21 and murine neuroblastoma cells in the isolation of a street strain rabies virus

The sensitivities of BHK-21 (C-13) and murine neuroblastoma (C-1300; clone NA) cells for the isolation of small quantities of a street strain rabies virus were compared. Suspensions of brain from mice sacrificed prior to the onset of clinical signs of rabies were used to stimulate weakly positive diagnostic specimens. The results of cell culture isolation were compared with those of the direct fluorescent-antibody test and virus isolation in weanling mice. Neuroblastoma cells were more sensitive to the street strain rabies virus than were BHK-21 cells. Neuroblastoma cell virus isolation, the mouse inoculation test, and the fluorescent-antibody test all showed comparable sensitivity.

Chromosomal organization of the herpes simplex virus genome during acute infection of the mouse central nervous system

After corneal inoculation, herpes simplex virus type 1 replicates in the mouse eye, trigeminal ganglia, and brainstem, producing first an acute and then a latent infection. Previous work from this laboratory focused on the structure of the viral DNA in this system. We have now examined the structure of the viral genome at the chromosome level by using micrococcal nuclease digestion. Studies with disaggregated cell preparations made from the brainstems of acutely infected mice show that the majority of the viral DNA is in a nonnucleosomal form; however, a nucleosomelike fraction was also consistently detected. A similar result was obtained for viral DNA in herpes simplex virus type 1-infected C1300 (clone NA) neuroblastoma cells (a neuronal cell line).

Differences in cell-to-cell spread of pathogenic and apathogenic rabies virus in vivo and in vitro

Pathogenic parental rabies virus and apathogenic variant virus were shown to differ in their ability to infect neurons in vivo and neuroblastoma cells in vitro. After intracerebral inoculation, the distribution of infected neurons in the brain was similar for both viruses, but the rate of spread throughout the brain, the number of infected neurons, and the degree of cellular necrosis were much lower in the case of apathogenic virus. After adsorption to mouse neuroblastoma cells, apathogenic virus was less rapidly internalized than pathogenic virus, and cell-to-cell spread of apathogenic variant virus was completely prevented by the addition of rabies virus-neutralizing antibody, whereas the spread of pathogenic virus was not affected.

Differential expression of 2':3'-cyclic nucleotide 3'-phosphodiesterase in cultured central, peripheral, and extraneural cells

The relative levels of the central nervous system myelin marker enzyme 2':3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37, CNPase) were determined in neuroblastoma, astrocyte, oligodendrocyte and Schwann cell cultures and in freshly isolated human lymphocytes and platelets. The highest specific activities were associated with the cells that elaborate myelin membrane in the central and peripheral nervous system, oligodendrocytes and Schwann cells, respectively. Antiserum to bovine CNPase recognized both CNP1 and CNP2 in CNS myelin and human oligodendroglioma. In addition, a 53,000 dalton protein was evident on autoradiographs of immunoblotted PNS myelin and human oligodendroglioma proteins. Cultured rat oligodendrocyte, C6 and mouse NA neuroblastoma CNPase appear to share common determinants with the corresponding normal rat CNS enzyme.

Production of interspecies T cell hybrids which retain differentiation specific surface antigens

Genetic mapping of differentiation specific surface antigens has been hampered by difficulty in preparation of interspecies hybrid cells which continue to express differentiated functions. A method has been developed for production of interspecies T cell hybrids which continue to express T cell specific cell surface molecules. Hybrids were constructed from either the human leukemic cell line MOLT-4 or freshly isolated human peripheral blood T cells and the mouse T lymphoma line BW5147. Optimal fusion efficiency resulted with pre-treatment of the human parental line with phytohemagglutinin followed by hybridization with 40% polyethylene glycol and plating without thymocyte feeder layers. Immortalization of hybrid lines was accomplished through addition of rat T cell growth factor to cultures.

Scanning and freeze-fracture electron microscopy of rabies virus infection in murine neuroblastoma cells

A persistent infection of CVS strain of rabies virus was established in murine neuroblastoma cells, C-1300, by a serial passage of the cells infected with a low input multiplicity. Little cytopathic effects were seen in the infected cultures and the cell growth was not interfered, although 90-100% of the cells were bearing intracytoplasmic inclusions and the infectious virus was constantly recovered from the supernatant. Scanning electron microscopy disclosed preferential budding of the virus from fine cellular processes with a relative sparing of the cell body. Freeze-fracture of the infected cells revealed that the intracytoplasmic inclusion (matrix) was composed of an aggregate of fine particles with a diameter of approximately 200 A. Intramembrane particles were distributed sparsely and randomly in the viral envelope.

High-affinity [3H]choline accumulation in cultured human skin fibroblasts

[3H]Choline can be transported across cell membranes by high-affinity (KT less than 5 microM) and low-affinity (KT much greater than 5 microM) systems. High-affinity choline accumulation (HACA) has been demonstrated in synaptosomes made from cholinergic brain regions such as the hippocampus and caudate-putamen. In cell culture, HACA has been demonstrated in glia and avian telencephalon, dissociated spinal cord, and muscle fibroblasts. We examined [3H]choline accumulation in a single normal human fibroblast line cultured from skin biopsy. [3H]Choline accumulation was temperature-dependent and linear with incubation time up to 6 min at 0.125 microM-choline. The apparent KT for [3H]choline was 5 microM, which is similar to that observed in avian fibroblasts. Isoosmotic replacement of Na+ with either Li+ (144 mM) or sucrose (288 mM) severely reduced [3H]choline accumulation (by 70-90%). Pre-incubation with ouabain (100 microM), sodium orthovanadate (100 microM), or 2,4-dinitrophenol (100 microM), or replacement of Ca2+ by Mg2+ had little or no effect on subsequent [3H]choline accumulation. [3H]Choline accumulation was inhibited by hemicholinium-3 (HC-3); after pre-incubation in HC-3 at 37 degrees C for 10 min, the IC50 (at 0.125 microM-choline) was 5.6 microM. The HC-3 sensitivity, Na+ dependence, and low KT suggest that human skin fibroblasts have a high-affinity transport system for choline.

Modulation of the distribution of acetylcholinesterase molecular forms in a murine neuroblastoma x sympathetic ganglion cell hybrid cell line

Studies were carried out on the polymorphism of acetylcholinesterase (AChE, EC 3.1.1.7) in a neuroblastoma x sympathetic ganglion cell hybrid cell line (T28) and its parental clone (N18TG2). These cells contain the tetrameric (G4, 10S), dimeric (G2, 6.5S) and monomeric (G1, 4S) forms of AchE, but not the collagen-tailed A12(16S) form of the sympathetic ganglion. Three variants of these forms could be distinguished on the basis of their solubility properties: (i) secreted forms which do not interact with the detergent Triton X-100; (ii) cellular forms which may be solubilized in detergent-free buffer and which interact reversibly with Triton X-100; (iii) cellular forms which require detergent for solubility, and aggregate in its absence. By using a nonpenetrating inhibitor, we demonstrated that, in T28 stationary cells, the cellular G4 form is associated with the plasma membrane, whereas the G1 form is intracellular. During induction of AChE activity in T28 cells, the relative proportion of the G4 form increases, suggesting, in agreement with previous observations, that G1 is a metabolic precursor of G4. The evolution of AChE molecular forms released into the culture medium closely resembles that of the cellular forms. The preferential accumulation of the G4 molecules does not simply depend on the cellular level of G1. It is favoured by culture conditions which promote morphological differentiation, but does not require the actual extension of neurites. T28 cells as well as other neuroblastoma-derived cells appear to be useful experimental materials to investigate the regulatory mechanisms underlying the maturation of AChE globular forms.

Induction of both rat and mouse lactate dehydrogenase in hybrids between inducible rat glioma and uninducible mouse neuroblastoma cells

The specific activity of lactate dehydrogenase (LDH; EC 1.1.1.27) is induced two-fold by l-norepinephrine (NE) in C6TK- rat glioma cells, but not in NA mouse neuroblastoma cells or various other nonglial cells. Previous reports have shown that the induction is mediated by cyclic AMP (cAMP) and possibly protein phosphorylation, and that it requires RNA and protein synthesis. To study the block to LDH induction in nonglial cells, we hybridized C6TK- cells with NA cells and isolated a hybrid clone in which LDH is inducible by NE. Mouse and rat LDH from hybrid cells were separated by electrophoresis and quantitated by two independent methods, and it was found that mouse and rat LDH were induced equally when cells were exposed to NE. The results suggest that inducibility of LDH is not determined by a cis-acting control at the gene level, but rather by the presence or absence of an earlier component in the cAMP-mediated induction system, and that the induction system acts indiscriminately on all active LDH gene copies in the cell.

Rabies serogroup viruses in neuroblastoma cells: propagation, "autointerference," and apparently random back-mutation of attenuated viruses to the virulent state

Each of several strains of fixed rabies virus was found to replicate to high titers in C1300 mouse neuroblastoma (clone NA) cells, without adaptation. Rabies serogroup Lagos bat, Mokola, and Duvenhage viruses also replicated efficiently in NA cells. Kotonkan and Obodhiang viruses replicated efficiently after adaptation, to titers not previously obtained in vitro. Infection in NA cells was frequently more cytopathic than in BHK-21 cells, allowing titration of Kotonkan and Obodhiang viruses by plaque assay. Duvenhage virus caused syncytium formation. Serial propagation of rabies viruses at a high multiplicity of infection in NA cells led to a rapid decline in virus yields; similar "autointerference" has not previously been demonstrated with rabies virus in other cell systems. Rabies virus infection in NA cells exhibited extreme sensitivity to interference by experimentally added defective interfering virions. Although several strains of attenuated rabies virus consistently reverted rapidly to virulence after propagation in NA cells, other strains of attenuated rabies and rabies serogroup viruses acquired increased virulence at a more gradual rate or not at all, suggesting that diverse characters may control virulence. When attenuated Flury HEP rabies virus was serially propagated at a low multiplicity of infection in either NA cells or suckling mouse brain, virulence appeared at a very variable rate, indicating that these systems may selectively enhance replication of randomly occurring virulent virus mutants.

Evidence for a striking increase in acetylcholinesterase activity in cultured human fibroblasts which are trisomic for chromosome two

Acetylcholinesterase (AchE) is reported to have a narrowly restricted distribution among human tissues. Three strains of human fibroblasts which are trisomic for chromosome 2 had an average level of AchE activity over 28 times higher than the average level in 19 control strains of human fibroblasts. In contrast, the mean pseudocholinesterase activity of the trisomy-2 strains did not differ appreciably, or significantly, from the mean for the control strains. The 19 control strains included 10 strains trisomic for autosomes other than 2, and 9 euploid strains. Our estimate of the mean AchE activity in the control strains did not differ significantly from zero and might, in any case, have originated from a minute amount of activity contributed to the cells by an esterase in our culture medium. Despite the striking elevation of AchE activity in fibroblasts trisomic for chromosome 2, extracts of these cells had only about 1.5% of the specific AchE activity (per microgram DNA) present in extracts of human cerebral cortex. None of the 22 strains studied had detectable activity for two other enzymes which, like AchE, have a restricted distribution among human tissues: xanthine oxidase and choline acetyltransferase.

In vitro stimulation of mouse lymphoid cells by C1300 neuroblastoma cells or tumor membrane extracts

Spleen lymphoid cells from A/J mice recognize specific antigenic differences on the surface membranes of syngeneic C1300 neuroblastoma cells and incorporate 3H-thymidine into DNA in unidirectional mixed cell cultures in the absence of isologous serum. The response requires an optimal ratio of responder to stimulator cells, and is detectable after 24 h. It is specifically blocked by the presence of a papain-solubilized crude membrane extract from the same neuroblastoma cells, the extent of inhibition being dependent on the concentration of the extract and the time when it is added to the cultures. Spleen cells from mice bearing the neuroblastoma respond earlier and incorporate more 3H-thymidine than cells from unsensitized mice. The enhanced response of the primed spleen cells to the stimulator cells is similar to a secondary immune response and can be induced by soluble crude tumor extracts in the absence of stimulator cells.

Pluripotent teratocarcinoma-thymus somatic cell hybrids

We have produced a series of somatic cell hybrids by fusing pluripotent PCC4aza1 embryonal carcinoma ("teretocarcinoma") cells with thymocytes from young adult mice. When these hybrids form tumors in nu/nu or syngeneic mice, all the tumors contain a range of differentiated tissues, as well as embryonal carcinoma-like tissues. Some of the tumors produce alpha-fetoprotein. These results show that pluripotency in embryonal carcinoma cells need not to be abolished by the introduction of a complete diploid genome from a differentiated cell.