PubMed Health⌕ Search

Biomedical subjects

B Z Levi

Publications and source records attributed to B Z Levi.

48 records · Page 3Linked to original sources
PubMed1989

Genetic regulation of class I major histocompatibility complex (MHC) antigen induction on astrocytes.

Neural cells, including astrocytes, normally do not express detectable levels of class I major histocompatibility complex (MHC) molecules, unlike cells of most tissues. However, upon cultivation in vitro, astrocytes begin to express class I molecules, increasing with time after plating. This spontaneous expression was examined in the present study to characterize inducible expression on astrocytes among various strains of mice. Inducible expression, either as a consequence of cultivation or standard gamma-interferon treatment, differed markedly among the strains examined. Analysis of congenic strains on a C57BL/10 (B10) background showed that expression was controlled by genes within the MHC locus. Examination of additional congeneic animals with various recombinations within the MHC showed that high or low expression of MHC molecules correlates with the presence of particular MHC class I genes. In general, H-2a and H-2d class I products are expressed much higher on astrocytes than H-2b and H-2s products. This difference in expression is not seen on spleen cells indicating tissue specificity. Moreover, levels of expression at the cell surface are reflected by the steady-state level of RNA message within astrocytes of the different strains.

Animals↗
PubMed1989

H-2RIIBP, a member of the nuclear hormone receptor superfamily that binds to both the regulatory element of major histocompatibility class I genes and the estrogen response element.

Transcription of major histocompatibility complex (MHC) class I genes is regulated by the conserved MHC class I regulatory element (CRE). The CRE has two factor-binding sites, region I and region II, both of which elicit enhancer function. By screening a mouse lambda gt 11 library with the CRE as a probe, we isolated a cDNA clone that encodes a protein capable of binding to region II of the CRE. This protein, H-2RIIBP (H-2 region II binding protein), bound to the native region II sequence, but not to other MHC cis-acting sequences or to mutant region II sequences, similar to the naturally occurring region II factor in mouse cells. The deduced amino acid sequence of H-2RIIBP revealed two putative zinc fingers homologous to the DNA-binding domain of steroid/thyroid hormone receptors. Although sequence similarity in other regions was minimal, H-2RIIBP has apparent modular domains characteristic of the nuclear hormone receptors. Further analyses showed that both H-2RIIBP and the natural region II factor bind to the estrogen response element (ERE) of the vitellogenin A2 gene. The ERE is composed of a palindrome, and half of this palindrome resembles the region II binding site of the MHC CRE. These results indicate that H-2RIIBP (i) is a member of the superfamily of nuclear hormone receptors and (ii) may regulate not only MHC class I genes but also genes containing the ERE and related sequences. Sequences homologous to the H-2RIIBP gene are widely conserved in the animal kingdom. H-2RIIBP mRNA is expressed in many mouse tissues, in agreement with the distribution of the natural region II factor.

Amino Acid Sequence↗
PubMed1989

Neonatal induction of a nuclear protein that binds to the c-fos enhancer.

The expression of the c-fos gene is transiently induced at birth in most organs in the mouse. To study the basis of this induction we searched for a nuclear factor that binds to the 5' regulatory region of the c-fos gene. Gel mobility shift assays with tissue extracts revealed fast (band I) and slow (band III) migrating bands, which represent factor binding to the c-fos enhancer, termed the serum response element (SRE). Neonatal extracts preferentially elicited band I, with low or undetectable levels of band III, whereas fetal and adult extracts generated predominantly band III, with reduced levels of band I. These results indicate that the SRE-binding activity changes during perinatal development and that the appearance of band I, which coincides with diminution of band III, correlates with neonatal c-fos induction. Methylation interference and competition analyses showed that the neonatal factor (band I) binds to the SRE at a site different from the adult factor (band III). DNA-binding activity of the adult factor, but not the neonatal factor, was sensitive to phosphatase treatment. Furthermore, the adult factor, but not the neonatal factor, shared antigenic specificity with the human serum response factor (SRF) that is expressed in cultured cells irrespective of c-fos gene induction. We conclude that band I in neonates represents a SRE-binding factor that is distinct from the SRF, which may be responsible for the neonatal induction of the c-fos gene. The band III factor was indistinguishable from the SRF in all criteria tested.

Aging↗
PubMed1988

c-fos antisense RNA blocks expression of c-fos gene in F9 embryonal carcinoma cells.

To study the function of proto-oncogene c-fos, we prepared an antisense plasmid that expresses in mammalian cells c-fos antisense RNA which is complementary to the endogenous c-fos mRNA. Upon transfection into undifferentiated F9 EC cells, the antisense plasmid directed constitutive expression of a large amount of c-fos antisense RNA. These cells were very low in the basal level of c-fos message and were unable to induce c-fos message when stimulated with interferon or phorbol ester. The failure to induce c-fos message led to the blockade of c-fos protein expression in these cells. Thus, these cells represented a c-fos defective phenotype. The blockade of c-fos gene expression seen in antisense-cells could be caused by rapid degradation of the c-fos message, since c-fos mRNA expression was rescued in these cells when treated with protein synthesis inhibitor, cycloheximide. We found that expression of c-myc gene was down-regulated in c-fos antisense-cells: Although control undifferentiated F9 cells constitutively expressed a high level of c-myc message, the antisense cells had a much lower amount of c-myc mRNA. Since p53 and heat shock gene 70 were expressed at comparable levels in control and antisense cells, c-myc gene expression appears to be regulated by c-fos gene in F9 EC cells. Lastly, these antisense cells grew as rapidly as control F9 cells and underwent differentiation after retinoic acid treatment, indicating that c-fos expression is not a prerequisite for differentiation of F9 cells.

Animals↗
PubMed1988

Induction of c-fos gene expression by interferons.

We show that murine interferons (IFNs)-alpha/beta and -gamma induce expression of the protooncogene c-fos in F9 embryonal carcinoma cells, NIH-3T3 cells, and other tissue culture cells. The induction of c-fos mRNA is rapid and transient in that the mRNA appears within 15 min and disappears by 2 h following IFN treatment. The protein synthesis inhibitor cycloheximide (CHX) also stimulates rapid but more stable expression of c-fos mRNA in these cells. Treatment of these cells with a combination of CHX and IFNs results in superinduction of c-fos mRNA. In contrast, IFNs do not affect c-myc mRNA expression in these cells. These results suggest that c-fos gene expression plays a role in signal transduction following binding of IFNs to the receptors.

Animals↗
PubMed1988

Constitutive expression of c-fos antisense RNA blocks c-fos gene induction by interferon and by phorbol ester and reduces c-myc expression in F9 embryonal carcinoma cells.

To address the role of c-fos proto-oncogene we constructed a plasmid that allows constitutive expression of RNA complementary to c-fos mRNA, and stably introduced this plasmid into F9 embryonal carcinoma cells. Some F9 clones expressing c-fos antisense RNA had a reduced basal level of c-fos mRNA, and were unable to induce a c-fos mRNA as well as its protein when stimulated with phorbol ester or with interferon (IFN). Nevertheless, the ability to induce major histocompatibility class I genes following IFN treatment was not impaired in these clones. Clones expressing c-fos antisense RNA grew as rapidly as control F9 cells, and underwent differentiation after retinoic acid treatment. Unexpectedly, constitutive expression of c-myc mRNA was reduced on average by 10-fold in clones expressing c-fos antisense RNA. However, expression of the p53 gene and heat shock gene hsp 70 was not affected in these clones, indicating the existence of a specific regulatory linkage between c-fos and c-myc genes. Cycloheximide treatment led to induction of a large amount of c-fos mRNA in clones expressing c-fos antisense RNA as well as in control F9 clones. The amount of c-fos antisense RNA was also increased by cycloheximide treatment. We postulate that c-fos antisense RNA blocks expression of the endogenous c-fos gene by accelerating the degradation of c-fos mRNA and that cycloheximide treatment interferes with this degradation.

Cell Differentiation↗
PubMed1987

Induction of c-ets and c-fos gene expression upon antigenic stimulation of a T cell hybridoma with inducible cytolytic capacity.

Expression of cellular oncogenes was studied in a T cell hybridoma that undergoes cytolytic activation when stimulated by specific antigen or by anti-Thy-1 antibody. The activation occurs without induction of hybridoma proliferation, providing a model to examine oncogene expression during functional differentiation of lymphocytes. We found that c-fos and c-ets-1 mRNAs were transiently induced at high levels in the hybridoma 30 min and 4 h after stimulation, respectively. c-myc and c-ets-2 oncogenes were constitutively expressed in the hybridoma and their mRNA levels were unaffected during 4 h of stimulation, although c-myc expression was reduced in the later stage of stimulation. Inhibitors of T cell activation, cyclosporin A and anti-LFA-1 antibody, blocked the induction of c-fos and c-ets-1 mRNAs without reducing the levels of c-myc and c-ets-2. The results indicate that the functional activation of the CTL hybridoma is associated with induction of c-fos and c-ets-1 genes.

Animals↗
PubMed1985

The formation of genotoxic metabolites of benzo[a]pyrene by the isolated perfused rat liver, as detected by the bioluminescence test.

The kinetics of the formation of mutagenic metabolites of benzo[a]pyrene (BP) in an isolated perfused rat-liver system have been studied. No genotoxic activity was detected in the perfusate using either the Ames test or the new bioluminescence test for genotoxic agents (BLT). The bile excretion showed strong genotoxic activity especially in the presence of the deconjugation enzymes beta-glucuronidase and arylsulfatase. The BLT was 1000-fold more sensitive than the Ames test in detecting the genotoxic activity in the bile excretion.

Animals↗
PubMedDate not supplied

Failure of viral protein 3 of infectious bursal disease virus produced in prokaryotic and eukaryotic expression systems to protect chickens against the disease.

In recent years, infectious bursal disease virus (IBDV) has become a serious economic problem as a result of the emergence of new and very virulent strains. Most of the antibodies produced against IBDV are for the structural proteins viral protein (VP) 2 (VP2) and VP3. The purpose of this study was to test the potential of recombinant VP3 to induce protective antibodies. The gene for VP3 was isolated from a virulent strain of the virus and cloned into prokaryotic (Escherichia coli) and eukaryotic (baculovirus) expression systems. The protein expressed by both systems was of the expected size (32 kD) and was detected by anti-IBDV antibodies. Following partial purification, the polypeptides were injected into intact birds and induced the production of high levels of anti-IBDV antibodies, as detected by immunoblot and enzyme-linked immunosorbent assay tests. These antibodies did not prevent changes in the bursa and mortality when birds were challenged with a virulent IBDV strain after vaccination with the recombinant VP3. The results show that VP3 polypeptide cannot be used as a subunit vaccine against IBDV and raise questions concerning the nature of the neutralizing epitope on this structural protein.

Animals↗
PubMedDate not supplied

Insect cell-derived VP2 of infectious bursal disease virus confers protection against the disease in chickens.

Infectious bursal disease virus (IBDV) has become a major problem in recent years. Conventional vaccines make use of attenuated or inactivated viral strains, but these are gradually losing their effectiveness. We investigated the possibility of using purified VP2, a subunit of IBDV structural protein expressed in insect cells, as a vaccine. The VP2 gene was cloned into pAcYM1. The cloned gene was expressed in a baculovirus system, giving rise to a high quantity of recombinant VP2 (rVP2) protein. The length of the VP2 is 453 amino acids, and it contains two additional amino acids of the baculovirus at the carboxyl terminus. The molecular mass of the protein is about 48 kD. The rVP2 protein reacted with antibodies raised against viral VP2 and had a similar molecular weight. This protein was tested in a controlled vaccination experiment and compared with an inactivated commercial vaccine. High levels of antibodies were raised by the vaccinated birds. The vaccinated birds were challenged with a pathogenic viral strain. rVP2-vaccinated chickens exhibited high resistance to the virus. No mortality or weight changes in the bursa of Fabricius were observed in the vaccinated birds, whereas in the negative control birds, vaccinated with phosphate buffer, up to 50% mortality was found. Higher levels of antibodies were found by enzyme-linked immunosorbent assay in birds vaccinated with rVP2 compared with those vaccinated with the commercial vaccine. This study suggests the potential use of the isolated rVP2 as a subunit vaccine.

Animals↗
PubMedDate not supplied

Coding region of segment A sequence of a very virulent isolate of IBDV--comparison with isolates from different countries and virulence.

We determined the sequence of the coding region of segment A, coding for the viral proteins (VPs) VP2, VP4, and VP3, of a very virulent (vv) infectious bursal disease virus (IBDV) isolated in Israel and named IBDVks. We compared the deduced amino acid sequences of the proteins of the new isolate with those of the same proteins from several IBDV isolates, as published in recent years. The amino acid sequences of VP3 and VP4 of the Israeli isolate were 1.9%-2.3% different from the sequences of their counterparts from classical strains. Thus, the stable region of VP2 of IBDVks was very similar (0-0.68% difference) to the same region of VP2 from vv strains from Europe and Japan but distinct from that of proteins from classical strains from Europe, the United States, and Australia (up to 9.42% divergence), showing that IBDVks is more closely related to the vv strains from Europe and Japan. We found that viruses isolated in recent years resemble each other more than isolates from the same areas isolated a few years earlier. Hence, IBDVks can be categorized in one group with vv new isolates from Europe and Japan. This group has been found to be distinct from new isolates in the United States and strains isolated before the IBDV epidemic during the late 1980s.

Animals↗