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Biomedical subjects

C Dickson

Publications and source records attributed to C Dickson.

At least 127 records · Page 7Linked to original sources
PubMed1984

Tumorigenesis by mouse mammary tumor virus: proviral activation of a cellular gene in the common integration region int-2.

Approximately 50% of tumors induced by mouse mammary tumor virus (MMTV) contain an acquired provirus within a limited region of chromosomal DNA, termed int-2. We have extended our previous characterization of this locus and have mapped provirus integration sites in 21 independent tumors. Although integration occurs at multiple sites, proviruses within int-2 are distributed into two oppositely oriented groups whose transcription is directed away from a central domain. Provirus insertion in int-2 is accompanied by expression of RNA derived, at least in part, from this central domain. Since the RNA is not detected in normal mammary tissue, we conclude that MMTV integration activates the expression of a cellular gene within int-2 and that this event may contribute to tumorigenesis.

Animals↗
PubMed1984

D-Baclofen: is it an antagonist at baclofen receptors?

Following intrathecal administration into the spinal subarachnoid space, baclofen produced dose related increases in tail flick latency. L-Baclofen was twice as potent as the DL-racemate and 100 times more potent than D-baclofen. When D-baclofen was injected intrathecally 15 min prior to L-baclofen, the subsequent effect of L-baclofen was markedly reduced. This reduction was dose-related for D-baclofen in doses at least 20 times the L-baclofen dose. D-baclofen administered concomitantly with L-baclofen only slightly increased the effect of L-baclofen. Pretreatment with D-baclofen (up to 10 times the dose of L-baclofen) did not inhibit the effect of L-baclofen when drugs were injected intraperitoneally. These results indicate that D-baclofen can antagonize the antinociceptive effect of L-baclofen following intrathecal administration. D-Baclofen should prove to be a useful tool for investigation of the role of stereoselective baclofen receptors in a variety of pharmacological processes.

Analgesics↗
PubMed1984

Mouse mammary tumor virus integration regions int-1 and int-2 map on different mouse chromosomes.

Two regions of mouse DNA which constitute common provirus integration sites in tumors induced by mouse mammary tumor virus have been identified and designated int-1 and int-2. By examining a series of hamster-mouse somatic cell hybrids, we mapped the int-2 locus to mouse chromosome 7 and confirmed the previous assignment of int-1 to chromosome 15. This constitutes proof that int-1 and int-2 are discrete genetic loci. It is therefore possible that proviral activation of two distinct cellular genes may result in the same neoplastic disease.

Animals↗
PubMed1983

Sequence and expression of the mouse mammary tumour virus env gene.

We have determined the DNA sequence of the envelope gene region of the GR strain of mouse mammary tumour virus. The sequence extends for 3012 nucleotides from the single EcoRI site to beyond the PstI site in the 3' long terminal repeat (LTR) of the provirus. There is a major open reading frame from nucleotides 752 to 2818 which encompasses the entire env gene. This reading frame extends through a polypurine tract and into the LTR. There is another open reading frame from the first nucleotide to position 803, presumably corresponding to the end of the pol gene. The splice acceptor site which generates env mRNA has been mapped experimentally to nucleotide 750. The env gene products, gp52 and gp36, have been positioned on the sequence using the directly determined amino acid sequences of the amino terminus of gp52; and both the amino and carboxyl termini of gp36. The start of gp52 is preceded by a series of 19 uncharged amino acids which could function as a typical signal sequence, but this sequence is only part of a much longer leader peptide. The tetrad Arg-Ala-Lys-Arg is the presumed cleavage site in the gPr73env precursor, and occurs just before the gp36 amino terminus. There are five potential asparagine-linked glycosylation sites which agrees with previous experimental results. The gp36 has two long hydrophobic regions at its amino and carboxy termini, these are suggested to act as a fusion peptide and the trans-membrane anchor, respectively.

Animals↗
PubMed1983

Tumorigenesis by mouse mammary tumor virus: evidence for a common region for provirus integration in mammary tumors.

We have prepared specific probes for unique-sequence cellular DNA adjacent to each of the newly integrated proviruses in tumors induced by mouse mammary tumor virus (MMTV). The use of such probes to screen a large number of independent mammary tumors in the BR6 strain of mouse has indicated that in at least 17 out of the 40 tumors examined so far, an MMTV provirus has integrated into a common chromosomal domain. A 10 kb Eco RI fragment of single copy DNA from this region has been isolated and partially characterized by restriction enzyme mapping. Of the proviruses located within this fragment in different tumors, all but one are complete, in the same orientation, and clustered within about 3 kb of cellular DNA. These findings are consistent with an insertional mutagenesis model for tumorigenesis by MMTV, in which the integration of a provirus in a particular region of cellular DNA may activate a neighboring oncogene. The region we describe here appears to be different from that reported for mammary tumors in the C3H strain of mouse.

Animals↗
PubMed1983

Involvement of GABA in the antinociceptive effect of gamma-acetylenic GABA (GAG), an inhibitor of GABA-transaminase.

The role of both novel GABAB and classical GABAA receptors in GAG-induced anti-nociception was investigated using the tail flick and hot plate tests. To this end, manipulations known to increase baclofen-induced antinociception (GABAB) and the receptor antagonist bicuculline (GABAA) were used. Of the modifiers of monoamine function tested, only chlorpromazine and haloperidol significantly increased GAG-induced antinociception. Theophylline antagonized antinociception produced by both GAG and GVG. Bicuculline did not antagonize antinociception produced by either GAG or muscimol. GAG-induced antinociception does not appear to result from the activation of either classical or novel GABA receptors. An interaction with dopaminergic pathways appears to be involved.

4-Aminobutyrate Transaminase↗
PubMed1982

Conservation of protein coding potential in the long terminal repeats of exogenous and endogenous mouse mammary tumor viruses.

In vitro protein synthesis and DNA sequence analysis indicate that mouse mammary tumor virus differs from other well-characterized retroviruses in that the long terminal repeat region of the provirus has the capacity to encode proteins. Different exogenously transmitted mouse mammary tumor virus strains and endogenous proviral units conserved this open reading frame feature in the long terminal repeat despite a variation in nucleotide sequence. The proteins encoded by the different long terminal repeats were clearly related, but showed minor variations in size and tryptic peptide maps. In each case, the largest in vitro product had a molecular weight of about 36,000 to 37,000, suggesting that the open reading frame sequences must extend for approximately 1,000 nucleotides beginning at the extreme 5' end of the long terminal repeat. The fact that the reading frame was conserved among these viruses argues in favor of an in vivo function for the open reading frame protein.

DNA, Recombinant↗
PubMed1981

Protein-coding potential of mouse mammary tumor virus genome RNA as examined by in vitro translation.

The protein-coding capacity of the mouse mammary tumor virus genome has been examined by in vitro translation of genome length and polyadenylated subgenomic fragments of viral RNA. Intact genome RNA of about 35S programmed synthesis of the Pr77gag, Pr110gag and Pr160gag/pol precursors seen in infected cells in vivo. Polyadenylated RNA fragments of 18 to 28S encoded products whose tryptic peptide maps resembled those of the nonglycosylated precursor to the envelope glycoproteins, confirming the gene order 5'-gag-pol-env-3'. Translation of polyadenylated RNA fragments smaller than 18S yielded a series of related proteins whose peptide maps bore no resemblance to any of the virion structural proteins. Thus, a region of the mouse mammary tumor virus genome distal to the env gene appears to have an open reading frame sufficient to encode at least 36,000 daltons of protein as of yet unknown function.

Cell-Free System↗
PubMed1980

Antibody-mediated neutralization of virus is abrogated by mycoplasma.

The ability of a mouse mammary tumor cell line to abrogate antibody neutralization of vesicular stomatitis virus was shown to be due to the presence of mycoplasma. The mycoplasma was isolated from the cell line and typed as Mycoplasma orale. Colonies of this mycoplasma were used to deliberately infect cell cultures which then gained the capacity to reactivate antibody-neutralized virus. The extent of the reactivation depended on the source of neutralizing antiserum. Other species of mycoplasma were tested and were found to reactivate neutralized virus, indicating that this may be a general phenomenon of mycoplasma contamination.

Animals↗
PubMed1980

Structure and processing of the mouse mammary tumor virus glycoprotein precursor pr73env.

The polyprotein precursor to the envelope glycoproteins of mouse mammary tumor virus was investigated by using subcellular fractionation procedures, pactomycin mapping techniques, tunicamycin inhibition of glycosylation, and endo-beta-N-acetyl glucosaminidase H-catalyzed removal of glycosylated residues in order to characterize the biosynthesis and processing of the precursor. The results suggest that the precursor (Pr73env) is synthesized on the rough endoplasmic reticulum as a transmembrane protein, with the carboxyl terminus remaining on the cytoplasmic side. The apoprotein as an estimated molecular weight of 60,000 and acquires five core oligosaccharide units during synthesis. Cleavage of the precursor precedes the secondary glycosylation steps and therefore probably occurs before transport to the plasma membrane. However, a minor population of Pr73env containing complex oligosaccharides was also found in the plasma membrane. The order of the glycoproteins in the precursor, as determined by pactomycin mapping, in NH2-gp52-gp36-COOH.

Cell Fractionation↗
PubMed1979

Morphological and biochemical characterization of viral particles produced by the tsO45 mutant of vesicular stomatitis virus at restrictive temperature.

The growth at restrictive temperature of tsO45, a group V (glycoprotein) conditional lethal mutant of vesicular stomatitis virus (VSV), was demonstrated to result in the production of large numbers of noninfectious viral particles. The infectivity of these tsO45 particles could be enhanced by procedures known to promote membrane fusion. Morphologically and biochemically these particles differed from wild-type VSV by their lack of viral glycoprotein. The other structural proteins of VSV were present and indistinguishable by size and relative proportion from those of virus grown at the permissive temperature. Examination of glycoprotein maturation at the restrictive temperature (39.5 degrees C) in tsO45-infected cells demonstrated the synthesis of normal viral glycoprotein but failed to demonstrate the presence of this glycoprotein in either the cell membrane or the envelope of free virions. The further absence of soluble viral glycoprotein from the supernatants of such cells strongly suggests that viral glycoprotein may not be necessary for the successful budding of VSV.

Cell Line↗
PubMed1979

Cell-free synthesis of mouse mammary tumor virus Pr77 from virion and intracellular mRNA.

Mouse mammary tumor virus (MuMTV) was purified from two cell lines (GR and Mm5MT/c1), and the genomic RNA was isolated and translated in vitro in cell-free systems derived from mouse L cells and rabbit reticulocytes. The major translation product in both systems was a protein with the molecular weight 77,000. Several other products were also detected, among them a 110,000-dalton and in minor amounts a 160,000-dalton protein. All three polypeptides were specifically immunoprecipitated by antiserum raised against the major core protein of MuMTV (p27), but they were not precipitated by antiserum against the virion glycoprotein gp52. Analysis of the in vitro products by tryptic peptide mapping established their relationship to the virion non-glycosylated structural proteins. The 77,000-dalton polypeptide was found to be similar, if not identical, to an analogous precursor isolated from MuMTV-producing cells. Peptide mapping of the 110,000-dalton protein shows that it contains all of the methionine-labeled peptides found in the 77,000-dalton protein plus some additional peptides. We conclude that the products synthesized in vitro from the genomic MuMTV RNA are related to the non-glycosylated virion structural proteins. Polyadenylic acid-containing RNA from MuMTV-producing cells also directed the synthesis of the 77,000-dalton polypeptide in the L-cell system. If this RNA preparation was first fractionated by sucrose gradient centrifugation the 77,000-dalton protein appeared to be synthesized from mRNA with a sedimentation coefficient between 25 and 35S.

Cell Line↗
PubMed1978

Polyproteins related to the major core protein of mouse mammary tumor virus.

The mouse mammary tumor virus (MuMTV) contains several low-molecular-weight proteins which, together with the genomic RNA, constitute the core structure of the virion. The most abundant protein in the core is the 27,000-dalton protein (p27), and, by analogy to the type C viruses, this protein probably forms the core shell. In mouse mammary tumor cell lines (GR and Mm5MT) producing MuMTV the major p57 antigenic specificity resides in a large protein, which migrates in polyacrylamide gels as a doublet of 77,000 and 75,000 daltons (p 77/75). A series of lower-molecular-weight proteins, p61, p48, p38, and p34, is also present in small amounts and is probably derived by proteolytic cleavage of the p 77/75. These proteins have been identified by immunoprecipitation with monospecific antiserum, and their sequence relatedness to p27 has been determined by an analysis of the peptides after trypsin digestion. After a 15-min pulse with [35S]-methionine, all of the p27-related proteins in these cell lines were labelled and, during a subsequent chase, progressively disappeared. The p27 was labeled poorly during the pulse, but the amount of label in this protein increased during the chase. A quantitation of these experiments suggested that the majority of the p27-related proteins were quite rapidly turned over in these cell lines. Hence, if p27 is derived by a progressive proteolytic cleavage mechanism, then the process is inefficient in the GR cells and only moderately efficient in the Mm5MT cells. When MuMTV was isolated from the culture medium of these cells harvested at 5-min intervals, the major p27-related protein was p34. The p27 accounted for only 29% of the anti-p27 serum immunoprecipitable proteins compared to 95% in virus isolated from an 18-h harvest. Incubation of the rapid-harvest virus at 37 degrees C for 2 h resulted in some conversion of p34 to p27. These results suggest that some of the p27 in MuMTV is formed in the virions by proteolytic cleavage of p34.

Animals↗