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M Sitbon

Publications and source records attributed to M Sitbon.

At least 37 records · Page 2Linked to original sources
PubMed1994

The envelopes of two ecotropic murine leukemia viruses display distinct efficiencies in retroviral vaccination by interference.

In cell cultures infected with a retrovirus, the expression of the viral envelope interferes with superinfection by retroviruses which recognize the same receptor. We have previously demonstrated that vaccination of susceptible strains of mice (of the Mus musculus species) with the attenuated ecotropic Friend murine leukemia virus (F-MuLV) B3 efficiently protects against the early hemolytic anemia and the erythroleukemia induced by a challenge with the virulent F-MuLV 57 through a similar in vivo mechanism of interference to superinfection (A. Corbin and M. Sitbon, J. Virol. 67, 5146-5152, 1993). Vaccination with the heterologous ecotropic Moloney-MuLV (M-MuLV) efficiently protects against the early hemolytic anemia but has a weak protective effect on the F-MuLV 57-induced erythroleukemia. Furthermore, vaccination with the attenuated F-MuLV B3 had only a transient protective effect on M-MuLV-induced thymomas. These different efficiencies of F- and M-MuLV to confer protection in this model of vaccination by interference were mostly due to envelope sequences, indicative of distinct in vivo interference properties of the two ecotropic envelopes.

Animals↗
PubMed1994

A nonstructural gag-encoded glycoprotein precursor is necessary for efficient spreading and pathogenesis of murine leukemia viruses.

In addition to the Gag-Pol and Env precursors whose translation initiates at AUG codons, murine, feline, and simian type C oncoviruses also express glycosylated Gag-Pol precursors (glycoGag), glycoGag translation is initiated at CUG codons located upstream of the Gag AUG initiation codon. In contrast to Gag, glycoGag is translocated into the endoplasmic reticulum and is absent from virions. Since glycoGag has been described to be dispensable ex vivo, we investigated the in vivo effects of a glycoGag- mutation in the Friend murine leukemia virus (F-MuLV). F-MuLV induces severe early hemolytic anemia and subsequent erythroleukemia within 2 months after inoculation of newborn mice. We obtained a glycoGag- F-MuLV, strain H5, by inserting an octanucleotide linker downstream of the CUG codon leading to the reading of a stop codon in all reading frames upstream of the Gag AUG. F-MuLV H5 did not induce severe early hemolytic anemia, and latency of erythroleukemia was significantly increased most likely because of an approximately 1-week delay in the in vivo spreading. Accordingly, induction of recombinant polytropic viruses was also significantly delayed. Close examination of ex vivo spreading kinetics also showed a slower dissemination of F-MuLV H5. Western blot (immunoblot) performed after inoculation of newborn mice with this glycoGag- virus indicated the emergence of new glycoGag+ viruses. PCR analyses with F-MuLV-specific primers demonstrated in vivo pseudoreversions restoring the glycoGag reading frame. Our results demonstrated that glycoGag expression is positively selected and essential for full spreading and pathogenic abilities.

Amino Acid Sequence↗
PubMed1994

Different abilities of Friend murine leukemia virus (MuLV) and Moloney MuLV to induce promonocytic leukemia are due to determinants in both psi-gag-PR and env regions.

Moloney murine leukemia virus (M-MuLV) is capable of inducing promonocytic leukemia in 50% of adult BALB/c mice that have received peritoneal injections of pristane, but Friend MuLV strain 57 (F-MuLV) is nonleukemogenic under similar conditions. It was shown earlier that these differences could not be mapped to the U3 region of the virus long terminal repeat, indicating the probable influence of structural genes and/or R-U5 sequences. In this study, reciprocal chimeras containing exchanged structural genes and R-U5 sequences from these two closely related viruses were analyzed for differences in ability to induce disease. Results showed that two regions of F-MuLV, psi-gag-PR and env, when substituted for those of M-MuLV were dramatically disease attenuating. The 5'-most region, which is widely distributed, overlaps with the 5' end of the env intron and includes the RNA packaging region, psi, the entire gag coding region, and the viral protease coding region (PR) of pol. It was also found that reciprocal constructs having substitutions of both of these regions of M-MuLV in an F-MuLV background allowed full reestablishment of promonocytic leukemia. These leukemias were positive for c-myb rearrangements which are characteristic of M-MuLV-induced promonocytic leukemias. Neither region alone, however, was sufficient to produce disease with a greater incidence than 13%. Further studies demonstrated that the inability of viruses with psi, gag, PR, or env sequences from F-MuLV to induce leukemia in this model system was not due to their inability to replicate in hematopoietic tissue, to integrate into the c-myb locus early on after infection in vivo, or to express gag-myb mRNA characteristic of M-MuLV-induced preleukemic cells and acute leukemia.

3T3 Cells↗
PubMed1993

Sequences in the rev-responsive element responsible for premature translational arrest in the human-immunodeficiency-virus-type-1 envelope.

Cell-free translation in the presence of pancreatic microsomal membranes of the full-length envelope transcript of the human immunodeficiency virus type 1 (HIV-1) yielded the expected extensively glycosylated and immunologically reactive gp160 envelope-protein precursor. In addition to this gp160, a shorter glycoprotein, which we designated gp120*, was produced due to a premature translation arrest. Utilizing kinetic experiments, pulse-chase analyses and various gp160 envelope RNA mutants, we demonstrated that the in-vitro-produced gp120* was not formed by cleavage of the gp160 precursor or by internal initiation of translation. A gp120 produced before gp160 synthesis was completed, and, independent of the gp160 proteolytic processing, has been shown to be produced and sequestered in the endoplasmic reticulum of HIV-1-infected cells [Willey, R. L., Klimkait, T., Frucht, D. M., Bonifacino, J. S. & Martin, M. A. (1991) Virology 184, 319-329]. The specific translational arrest shown to occur in vitro was found to be dependent on the Rev-responsive element, since deletion of this highly structured sequence abolished the production of gp120*. We found that the combination of two contiguous putative stem loops of the Rev-responsive element, located at nucleotides 7494-7522 and 7525-7550 of the HIV-1 Rev-responsive-element sequence, was responsible for the production of this truncated protein. To our knowledge, these stem-loop structures, distinct from that known to bind the Rev protein, represent the first example responsible for the production of alternative products by premature translational arrest in higher eukaryotes.

Base Sequence↗
PubMed1993

Protection against retroviral diseases after vaccination is conferred by interference to superinfection with attenuated murine leukemia viruses.

Cell cultures expressing a retroviral envelope are relatively resistant to superinfection by retroviruses which bear envelopes using the same receptor. We tested whether this phenomenon, known as interference to superinfection, might confer protection against retroviral diseases. Newborn mice first inoculated with the attenuated strain B3 of Friend murine leukemia virus (F-MuLV) were protected against severe early hemolytic anemia and nonacute anemiant erythroleukemia induced by the virulent strain 57 of F-MuLV. Vaccinated animals were also protected as adults against acute polycythemic erythroleukemia induced upon inoculation with the viral complex containing the defective spleen focus-forming virus and F-MuLV 57 as helper virus. Animals were inoculated as newborns, which is known to induce immune tolerance in mice, and the rapid kinetics of protection, incompatible with the delay necessary for the immune response to develop, indicated that protection was not due to an immune mechanism but rather was due to the rapid and long-lasting phenomenon of interference. This result was confirmed by combining parental and envelope chimeric MuLV from different interference groups as vaccinal and challenge viruses. Although efficient protection could be provided by vaccination by interference, we observed that attenuated replication-competent retroviruses from heterologous interference groups might exert deleterious synergistic effects.

Aging↗
PubMed1993

Sequences responsible for the distinctive hemolytic potentials of Friend and Moloney murine leukemia viruses are dispersed but confined to the psi-gag-PR region.

Friend and Moloney murine leukemia viruses (F- and M-MuLV) induce distinct diseases in hematopoietic tissues following inoculation of newborn mice of susceptible strains. F-MuLV induces erythroleukemia preceded by severe early hemolytic anemia; M-MuLV induces thymomas and only very mild hemolysis. The major viral determinant of severe early hemolytic anemia residues in the env gene, but sequences located outside this gene can modulate this effect. By means of genetic chimeras of F- and M-MuLV, we have found that although they are confined to the 5' portion of the env gene intron, sequences that determine the distinctive hemolytic potentials of F- and M-MuLV are widely distributed over a region spanning the RNA encapsidation domain, the gag gene, and the portion of the pol gene encoding the viral protease. Within this large region, two fragments of M-MuLV, a 1.3-kb region encoding the matrix, pp12, and capsid proteins and a 0.8-kb region encoding the nucleocapsid and the viral protease, were capable, individually, of partially attenuating the capacity of F-MuLV for induction of severe early hemolytic anemia. In association, these two fragments conferred complete attenuation. Moreover, a second pair of adjacent fragments within this large region appeared to behave cooperatively to confer complete attenuation; a 0.36-kb region roughly corresponding to the encapsidation domain, although not detectably altering hemolytic potential on its own, deepened the attenuation conferred by the adjacent 1.3-kb region. Whether capable of inducing severe early hemolytic anemia or not and despite different efficiencies of induction of recombinant polytropic viruses, all chimeric viruses retained the erythroleukemogenicity of the F-MuLV parent.

3T3 Cells↗
PubMed1992

Suboptimal and optimal activation signals modulate differently the expression of HIV-1 and cytokine genes.

Expression of HIV-1 and cytokine genes was investigated in chronically infected lymphocytic and promonocytic cell lines. As in normal human peripheral blood lymphocytes (PBL), a suboptimal activation signal with phorbol myristate acetate (PMA) did not trigger significant cytokine expression, whereas optimal activation signal (PMA + ionomycin) did. In contrast, a suboptimal activation was sufficient to up-regulate expression of HIV transcripts with kinetics similar to that observed in cells infected de novo by HIV. The level of HIV RNA in the promonocytic line was very low and markedly delayed when compared to the lymphocytic lines. We concluded that HIV induction required weaker activation signals than cytokine induction and that kinetics and level of HIV expression were not modified by induction of these cytokines. However, HIV expression appeared to alter the regulation of genes involved in proliferation and functional differentiation such as a decreased expression of IL-2 and IL-2R alpha and an increased expression of IFN gamma and TNF alpha mRNA.

Antigens, CD↗
PubMed1992

Functional tolerance of the human immunodeficiency virus type 1 envelope signal peptide to mutations in the amino-terminal and hydrophobic regions.

We demonstrated that the leader sequence of the human immunodeficiency virus type 1 envelope functions as signal peptide (SP) despite low scoring in a prediction program. As expected for SP, the hydrophobic core (HC) is essential, and no other sequence could compensate for HC deletion. Contrary to other SPs, major substitutions in the HC, such as introduction of basic, polar, or alpha-helix-breaking residues, still allowed efficient translocation and glycosylation. Also, extensive deletions or substitutions of the charged residues at the N terminus had little if any inhibitory effect. This report, which is the first study of human immunodeficiency virus SP, describes the exceptional tolerance of this peptide to mutations.

Amino Acid Sequence↗
PubMed1992

Friend murine leukaemia virus is integrated at a common site in most primary spleen tumours of erythroleukaemic animals.

A common proviral integration site was identified and characterized in erythroleukaemias induced by Friend murine leukaemia virus (F-MuLV). Using inverse polymerase chain reaction, we found a proviral integration site common to at least 90% of 20 primary tumours tested. This site was identical to Fli-1, a locus recently reported by others to be rearranged in 75% (9/12) of cell lines established from spleens of erythroleukaemic mice and to code for a member of the ets gene family. Our data suggest that about half of the F-MuLV-induced erythroleukaemias contained more than one cell clone with a proviral integration in Fli-1, with different individual integration sites within Fli-1 in each cell clone. All proviruses were found to be integrated in the same transcriptional orientation with respect to flanking cellular DNA. We discuss these findings in relation to multistage models of neoplasm.

Animals↗
PubMed1991

Substitution of leucine for isoleucine in a sequence highly conserved among retroviral envelope surface glycoproteins attenuates the lytic effect of the Friend murine leukemia virus.

Friend murine leukemia virus is a replication-competent retrovirus that contains no oncogene and that exerts lytic and leukemogenic properties. Thus, newborn mice inoculated with Friend murine leukemia virus develop severe early hemolytic anemia before appearance of erythroleukemia. To identify the retroviral determinants regulating these effects, we used chimeric infectious constructions and site-directed point mutations between a virulent Friend murine leukemia virus strain and a naturally occurring variant attenuated in lytic and leukemogenic effects. We found that severe hemolytic anemia was always associated with higher numbers of blood reticulocytes with budding retroviral particles. Furthermore, a remarkably conservative leucine to isoleucine change in the extracellular SU component of the retroviral envelope was sufficient to attenuate this lytic effect. Also, this leucine at position 348 of the envelope precursor protein was located within the only stretch of five amino acids that is conserved in the extracellular SU component of all murine, feline, and primate type C and type D retroviral envelopes. This observation suggested an important structural function for this yet undescribed conserved sequence of the envelope. Lastly, we observed that lytic and leukemogenic effects were attenuated by a deletion of a second repeat in the transcriptional enhancer region of the viral long terminal repeats of the variant strain.

Amino Acid Sequence↗
PubMed1990

Isolation of a Friend recombinant polytropic virus with a T-cell-restricted leukemogenicity.

Hematopoietic malignant cells of various types were isolated from ICFW mice inoculated as newborn or adult with F-MuLV and grafted into recipient mice. After repeated in vivo cell transplants, several recombinant polytropic viruses (also termed MCF or dualtropic viruses) were isolated from tumors by limiting dilution. Two virus isolates designated RA1-17 and EA1-17 were recovered from the spleen and the omentum, respectively, of the same grafted animal. When inoculated into newborn mice, RA1-17 induced erythroblastosis similar to that induced by other Friend recombinant polytropic viruses. Remarkably, EA1-17 induced T-cell leukemia after a short latency. To our knowledge, this is the first description of a polytropic recombinant virus with a T-cell tropism isolated after inoculation of F-MuLV.

Animals↗
PubMed1990

Sequences in the U5-gag-pol region influence early and late pathogenic effects of Friend and Moloney murine leukemia viruses.

Friend replication-competent murine leukemia virus (F-MuLV), clone 57, induces a severe early hemolytic anemia and a later erythroleukemia after inoculation of newborn IRW or ICFW mice, whereas Moloney MuLV (M-MuLV) induces only lymphoid leukemia. We have shown previously that the attenuated hemolytic and erythroleukemogenic abilities of an F-MuLV variant, clone B3, were due mostly to changes in the env gene and long terminal repeat, respectively. For the present study, we derived two constructs exchanging env fragments of F-MuLV 57 and M-MuLV and compared them with two constructs described by Chatis et al. (J. Virol. 52:248-254, 1984) exchanging the U3 region of the long terminal repeat of the same parental viruses. When comparing the hemolytic effect of these constructs with those of the parent, we found that the U5-gag-pol region of F-MuLV was required for development of severe early hemolytic anemia and that, unlike the env of F-MuLV B3, the env of M-MuLV was fully competent in inducing severe early hemolytic anemia when associated with the F-MuLV U5-gag-pol and U3 regions. As expected, induction of erythroleukemia depended on the presence of the F-MuLV U3 region; however, the presence of both the U3 and U5-gag-pol regions of F-MuLV appeared to be synergistic and was associated with a more rapid appearance of erythroleukemia.

Animals↗
PubMed1988

The endogenous mink cell focus-forming (MCF) gp70 linked to the Rmcf gene restricts MCF virus replication in vivo and provides partial resistance to erythroleukemia induced by Friend murine leukemia virus.

The Rmcf locus restricts the in vitro replication of mink cell focus-forming (MCF) viruses in cell cultures derived from mice carrying the resistance allele. Previously we reported that in cell cultures from first backcross progeny, this Rmcf-linked restriction segregates with the expression of an endogenous retroviral gp70 serologically related to that of MCF viruses. The current report details the results of genetic studies designed to examine the possible association of this endogenous gp70 with resistance of mice to Friend murine leukemia virus (F-MuLV)-induced erythroleukemia. This env gene segregates as a single dominant trait in (DBA/2 X IRW) X IRW progeny, in which the expression of the gene can be detected by serological techniques. Results indicated that the gp70- progeny developed leukemia at the same rate as the susceptible IRW parent, whereas the tempo of disease among the gp70+ progeny was significantly slower. However, the resistance mediated by this gene was only partial, since most of the gp70+ offspring eventually developed erythroleukemia when followed for 6 mo. This endogenous gp70 also segregated with a restriction to the expression of recombinant MCF viruses after infection with F-MuLV. Since in this study all unlinked genes segregated independently, this is direct evidence that MCF viruses participate in the induction of erythroleukemia.

Animals↗
PubMed1986

Hemolytic anemia and erythroleukemia, two distinct pathogenic effects of Friend MuLV: mapping of the effects to different regions of the viral genome.

Two different pathogenic effects of the Friend ecotropic murine leukemia virus (F-MuLV) were distinguished by serial examinations of hematocrits and reticulocyte counts of IRW mice inoculated as newborns. F-MuLV induced hemolytic anemia with increased levels of erythropoiesis, which was detectable as early as 13 days of age, whereas blocked erythroid differentiation, associated with erythroleukemia, was apparent only after 30 days of age. Using strains of Friend-MuLV with different virulences, we constructed recombinant viruses that allowed us to map the hemolytic effect and the ability to induce rapid erythroleukemia to different regions of the viral genome. Moreover, the ability of the virus to induce rapid erythroleukemia appeared to be independent of the presence of severe early hemolytic anemia.

Anemia, Hemolytic↗
PubMed1986

Analysis of two strains of Friend murine leukemia viruses differing in ability to induce early splenomegaly: lack of relationship with generation of recombinant mink cell focus-forming viruses.

Friend murine leukemia helper viruses (F-MuLV) 57 and B3 were indistinguishable by genomic structural analyses with RNase T1-resistant oligonucleotide fingerprinting and by antigenic reactivity with a panel of 31 monoclonal antibodies directed against murine leukemia viruses. Nevertheless, F-MuLV 57 and B3 had strikingly different virulences. Approximately 2 months after inoculation, IRW and NFS/N mice inoculated as newborns with F-MuLV 57 had gross splenomegaly caused by erythroid proliferation. In contrast, an equivalent dose of F-MuLV B3 induced spleen or lymph node enlargement 4 to 13 months after inoculation. Although most cases of spleen enlargement in F-MuLV B3-inoculated mice were due to erythroid proliferation, lymphoid or myeloid proliferation was also frequently observed. The replication of both F-MuLV 57 and B3 was equally efficient, and both viruses generated recombinant dual-tropic mink cell focus-forming (MCF) viruses with the same kinetics and efficiency. Moreover, MCF viruses induced by F-MuLV 57 and B3 had the same antigenic patterns. Therefore, the ability of F-MuLV to induce early splenomegaly did not correlate with the generation of recombinant MCF viruses.

Animals↗
PubMed1985

Pseudotyping of dual-tropic recombinant viruses generated by infection of mice with different ecotropic murine leukemia viruses.

Using a new focal immunofluorescence assay (FIA) with monoclonal antibodies, dual-tropic recombinant mink cell focus-inducing (MCF) retroviruses were specifically detected directly in mouse cells. With the FIA, MCF and ecotropic murine leukemia virus (MuLV) infectious centers were quantitated in noninoculated AKR/J mice and in mice inoculated with either ecotropic Friend- or Moloney-MuLV. Comparison of the titers obtained in mouse and mink cells suggested that pseudotyping of MCF viruses with ecotropic MuLV envelopes occurred at different levels in these three mouse models. Adult and newborn IRW mice inoculated with Friend-MuLV produced MCF viruses which were mostly pseudotyped with ecotropic MuLV envelopes. Newborn IRW mice inoculated with Moloney-MuLV produced MCF viruses in both spleen and thymus. Most Moloney-MCF viruses from spleens were pseudotyped with ecotropic MuLV envelopes, whereas thymic Moloney-MCF viruses were not. Noninoculated AKR/J mice spontaneously produced MCF virus at least 2 months before the onset of organ enlargement, and the majority of MCF viruses in both spleens and thymuses of these mice did not appear to be pseudotyped.

Animals↗