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Biomedical subjects

M Barbacid

Publications and source records attributed to M Barbacid.

At least 19 recordsLinked to original sources
PubMed1992

Nerve growth factor mediates signal transduction through trk homodimer receptors.

We have investigated the molecular nature of the high affinity nerve growth factor (NGF) receptors by using cell lines expressing gp75LNGFR and gp140trk. Our results suggest that gp75LNGFR and gp140trk interact with NGF independently and that only gp140trk mediates NGF signaling. NGF binds to gp140trk with picomolar affinity and induces its phosphorylation on tyrosine residues regardless of the presence of gp75LNGFR. NGF-gp140trk complexes display the slow dissociation rate and rapid internalization characteristics of high affinity NGF receptors. Cross-linking studies reveal the existence of gp75LNGFR and gp140trk homodimers. However, we were unable to detect gp75LNGFR-gp140trk heterodimers. Coexpression in COS cells of wild-type and kinase deficient mutants reveals that gp140trk receptors can undergo intermolecular phosphorylation, indicating the formation of functional homodimers. Moreover, these kinase deficient mutants inhibit NGF-induced signaling through wild-type gp140trk receptors. These results indicate that the functional high affinity NGF receptors consist of gp140trk homodimeric (or oligomeric) complexes.

3T3 Cells↗
PubMed1979

Evolutionary relatedness of viper and primate endogenous retroviruses.

A retrovirus previously isolated from a tumored Russell's viper is shown by molecular hybridization to be an endogenous virus of this reptilian species. Radio-immunologic techniques revealed that the viper retrovirus is immunologically and, hence, evolutionarily related to endogenous type D retorviruses of Old World primates. These findings extend the number of vertebrate classes possessing endogenous retroviruses and suggest that type D retroviruses may even be more widely distributed in nature than type C retroviruses.

Animals↗
PubMed1979

Wild mouse RNA tumor viruses. A nongenetically transmitted virus group closely related to exogenous leukemia viruses of laboratory mouse strains.

Type-C RNA viruses isolated from wild mice are causative of naturally occurring neoplasia and neurologic diseases. Biochemical and immunologic characterization of this virus group revealed that amphotropic viruses isolated from wild mice trapped in separate geographical areas are indistinguishable, whereas amphotropic and ecotropic viruses naturally infecting the same animal are env gene variants. Molecular hybridization studies established that neither host range variant is endogenous to the Mus musculus genome, although each demonstrates partial nucleotide sequence homology. Wild mouse type-C viruses exhibited much closer molecular and antigenic relatedness to the exogenous virus subgroup (Friend-, Moloney-, and Rauscher-MuLV) than to prototype endogenous viruses isolated from laboratory mouse strains. The evidence indicates that exogenous mouse type-C viruses have been maintained in nature over a long period of evolution as a separate virus group, causative of tumors in mice by a mechanism solely involving their transmission as infectious agents.

Animal Population Groups↗
PubMed1979

Avian reticuloendotheliosis viruses: evolutionary linkage with mammalian type C retroviruses.

Reticuloendotheliosis viruses have been shown to be causative of tumors in a variety of avian species. The major structural protein of these non-genetically transmitted viruses is demonstrated to possess antigenic determinants common to those of all known mammalian type C viruses. These findings establish a mammalian origin for this oncogenic avian retrovirus group. None of the known mammalian type C virus groups demonstrated a closer immunological relationship to avian reticuloendotheliosis viruses. These results suggest that reticuloendotheliosis viruses have been non-genetically transmitted for a long period of evolution or that these viruses may have arisen by relatively recent infection of birds with an as yet undiscovered mammalian type C retrovirus.

Antigens, Viral↗
PubMed1978

Genetic recombination between mouse type C RNA viruses: a mechanism for endogenous viral gene amplification in mammalian cells.

A strategy based on the identification of type-specific antigenic determinants in the transitional products of gag (p15, p12, and p30 proteins), pol (reverse transcriptase), and env (gp70 glycoproteins) genes of mammalian type C viruses has been used to study genetic recombination between these RNA viruses. By this approach, recombinants involving exogenous and endogenous mouse type C viruses have been identified and genetically mapped. Analogous techniques have been applied to investigate the genetic relationships between different classes of endogenous virus that exist within the same mouse cells. Proteins of the inducible class of xenotropic virus were shown to exhibit extensive antigenic homology with the gag but not the env gene products of the ecotropic virus class. Instead, the env gene-coded glycoproteins of the inducible and noninducible xenotropic virus classes possessed striking antigenic relatedness. These results, as well as supporting findings from molecular hybridization, favor the concept that the inducible xenotropic virus of mouse cells arose by a recombinational mechanism involving the progenitors of the other two endogenous virus classes.

Animals↗
PubMed1978

Isolation and characterization of an endogenous type C RNA virus of mink (Mv1Lu) cells.

Cells of the established MvlLu mink line spontaneously released a reverse transcriptase-containing virus after long-term passage in tissue culture. By molecular hybridization, DNA of normal mink cells was found to possess extensive nucleotide sequence homology with a reverse-transcription product of the viral genome, demonstrating that the new isolate was an endogenous virus of mink origin. The mink virus shared antigenic determinants with the major structural proteins of known mammalian type C viruses. Double-antibody competition radioimmunoassays were developed by utilizing the purified major structural protein, p30, of the mink endogenous virus. The virus was shown to possess antigenic determinants unique from those of other known mammalian type C viruses. It exhibited a higher degree of immunological cross-reactivity with endogenous rat type C and horizontally transmitted feline leukemia viruses than with other mammalian type C viruses tested. The finding that mink cells can remain nonvirus producing for many cell generations argues that there normally exists some cellular restriction to endogenous virus expression in this species.

Animals↗
PubMed1978

Origin and biological properties of a new BALB/c mouse sarcoma virus.

A focus-forming virus previously isolated from a BALB/c mouse hemangiosarcoma has been shown to be replication defective. Analysis of individual BALB/c mouse sarcoma virus (BALB-MSV) nonproducer transformants for expression of helper virus-coded proteins revealed genetically stable variants that expressed two, three, or all four gag gene products in the absence of detectable helper viral env gene expression. The type-specific antigenic determinants of helper viral proteins encoded by the BALB-MSV genome and by the B-tropic virus isolated from the BALB-MSV stock were demonstrated to be indistinguishable from those of BALB:virus-1, a known endogenous virus of BALB/c cells. These findings imply that a BALB/c endogenous virus was involved in the generation of BALB-MSV. By the same immunological approach, the presence of at least a portion of the Moloney-MuLV gag gene has been identified in two other transforming viruses--Moloney-MSV and Abelson lymphosarcoma virus--previously isolated from the BALB/c strain. The tissue culture properties of cells transformed by these defective viruses were also shown to be distinguishable. These findings indicate that transforming virus isolates of the same inbred strain differ in their transforming activities as well as in the helper viral sequences stably associated with their genomes.

Animals↗
PubMed1978

Analysis of translational products of Friend strain of spleen focus-forming virus.

We have analyzed normal rat kidney cells nonproductively infected with the Friend strain of spleen focus-forming virus (SFFV) for the presence of murine leukemia virus-specific type C viral proteins. SFFV was found to code for the p15 and p12 proteins of Friend-murine leukemia virus as determined by immunological typing of their antigenic determinants. Molecular-size analysis of p15 and p12 proteins in SFFV nonproductively infected normal rat kidney cells indicated that these proteins are translated as parts of polyprotein molecules. The apparent molecular weights of the polypeptides bearing p12 antigenic determinants revealed the presence of translational products of the SFFV genome that could not be accounted for by know type C virus helper structural proteins.

Animals↗
PubMed1977

Evolutionary relationships between gag gene-coded proteins of murine and primate endogenous type C RNA viruses.

Several low molecular weight proteins of endogenous type C viruses of the RD114/baboon group are compared with the gag gene translational products of endogenous type C viruses of murine origin. The p10 proteins of each virus group are shown to be immunologically and biochemically related, while the p12 proteins of RD114/baboon viruses are demonstrated to share antigenic determinants with murine viral p15. Moreover, highly type-specific phosphoproteins, p15 of RD114/baboon viruses and p12 of murine viruses, are shown to possess very similar biochemical properties. These findings, along with previous studies indicating immunologic cross-reactivity between their major internal antigens, p30, demonstrate that each of the gag gene-coded proteins of murine type C viruses has a analogue in viruses of the RD114/baboon group. The immunologic and biochemical relatedness of their gag gene translational products supports the concept of a common progenitor in the evolution of these endogenous viruses.

Animals↗
PubMed1977

Radioimmunoassay for mammalian type C viral reverse transcriptase.

Radioimmunological techniques were applied to the analysis of reverse transcriptase of mammalian type C RNA viruses. The polymerase of Rauscher mouse leukemia virus was purified by ion exchange and sequential affinity chromatography. Radioimmunoassays that utilized the viral enzyme as a probe detected as little as 1 ng of purified polymerase. No cross-reactivity could be demonstrated between the reverse transcriptase and other known virus-coded proteins. By comparing the immunological reactivity of the purified enzyme with the reactivity of detergent-disrupted virions, Rauscher mouse leukemia virus was shown to contain the antigenic equivalent of 40 molecules of reverse transcriptase. In a homologous competition immunoassay, the Rauscher viral enzyme demonstrated type-specific antigenic determinants, which distinguish it from other mouse type C viral polymerases. In a broadly reactive interspecies immunoassay, the reverse transcriptases of a number of mammalian type C viruses were cross-reactive, indicating their shared antigenic determinants. Various treatments that inhibit or inactivated DNA polymerase activity had little or no effect on the immunological properties of the enzyme. Thus, radioimmunoassays should be useful in the search for type C viral reverse transcriptase as a marker of subviral expression.

Cross Reactions↗
PubMed1977

Differential synthesis of mammalian type C viral gene products in infected cells.

Radioimmunological techniques were applied to the quantitation of the translational products of the gag, pol, and env genes of mammalian type C viruses. Analysis of the viral proteins associated with simian sarcoma-associated virus (SSA V) and SSA V-infected cells revealed in each that the level of reverse transcriptase was less than 1% of that of the major viral structural protein, p30. The rate of intracellular degradation of reverse transcriptase in SSA V-infected cells was found to be no greater than that of several viral structural proteins, indicating that the lower levels of viral enzyme resulted from its decreased synthesis. By screening individual cells infected at limiting SSA V dilution, it was possible to isolate a clone (clone 16), which demonstrated levels of viral p12, p30, and gp70 similar to those found in wild-type SSA V-infected cells, and which released noninfectious virions in large quantity. The noninfectious virions and clone 16 cells were shown to lack immunologically or enzymologically detectable reverse transcriptase. With serial passage of clone 16 cells, reverse transcriptase activity became spontaneously detectable in tissue culture fluids, concomitant with the appearance of infectious virus. The reverse transcriptase associated with this virus was indistinguishable from SSA V polymerase, indicating that the genetic alteration restricting SSA V pol gene expression in clone 16 cells was reversible. These results further demonstrate the strict requirement of reverse transcriptase for establishment of type C virus infection. Possible mechanisms to account for the patterns of type C viral gene expression detected in SSA V-infected cells are discussed.

Cell Line↗
PubMed1976

Structural polypeptides of mammalian type C RNA viruses. Isolation and immunologic characterization of a low molecular weight polypeptide, p10.

Low molecular weight polypeptides of several mammalian type C RNA tumor viruses were purified by sequential ion exchange chromatography and molecular sizing techniques. These included a polypeptide with a molecular weight of 10,000 to 11,000, p 10, from two type C viruses of mouse origin. Rauscher- and Moloney-murine leukemia virus (MuL virus), and from an infectious type C virus isolate of the woolly monkey. The p12 structural polypeptides of these viruses as well as Rauscher-MuL virus p15 were also purified. By using radioimmunoassays developed for each polypeptide, it was possible to demonstrate that all three low molecular weight polypeptides, p15, p12, and p10, were immunologically unique. Among type C viral structural polypeptides, p10 has been least well characterized immunologically. The results of the present study indicate that p10 is virus-coded and possesses strong group-specific antigenic determinants. By use of appropriate immunoassays, broadly reactive interspecies determinants shared by mammalian type C virus isolates of murine, feline, and primate origin, were also demonstrated. The interspecies antigenic determinants of p10 were shown to be as broadly cross-reactive as those exhibited by the major type C virus structural polypeptide, p30.

Antigen-Antibody Reactions↗
PubMed1976

gag Gene of mammalian type-C RNA tumour viruses.

The translation product of the gag gene of mammalian type-c- RNA viruses is a 65,000-68,000 molecular weight precursor polypeptide (Pr65) whose cleavage leads to the formation of four virion proteins, p30, p15, p12 and p10. An immunological approach has been used to establish the arrangement of the sequences coding for these proteins within the viral genome as (5') p15-p12-p30-p10 (3').

Chromosome Mapping↗
PubMed1975

The mode of action of griseoviridin at the ribosome level.

The antibiotic griseoviridin binds to the larger subunit of Escherichia coli ribosomes blocking the interaction between the 3' terminal end of peptidyl-tRNA and the donor site of the peptidyl transferase centre. Griseoviridin inhibits binding of chloramphenicol, thiamphenicol, lincomycin, erythromycin and streptogramin A to bacterial ribosomes. Moreover griseoviridin protects the ribosomal binding site of gougerotin from the drastic conformational changes taking place in the presence of ethanol. Griseoviridin is also able to interact with eukaryotic ribosomes as shown by its effects on model systems and on anisomycin, trichodermin and gougerotin binding studies. Nevertheless, griseoviridin affinity for the 80-S type ribosomes (yeast or human) is two orders of magnitude smaller than with E. coli ribosomes. The inhibitory spectrum and mode of action of griseoviridin on ribosomes is compared to that of antibiotics of the streptogramin A group and found to be essentially the same.

Anti-Bacterial Agents↗