Autoreactive T lymphocytes are clonally deleted during maturation in the thymus. Deletion of T cells expressing particular receptor V beta elements is controlled by poorly defined autosomal dominant genes. A gene has now been identified by expression of transgenes in mice which causes deletion of V beta 14+ T cells. The gene lies in the open reading frame of the long terminal repeat of the mouse mammary tumour virus.
The gag membrane protein gP85gag, encoded by Moloney murine leukemia virus (M-MLV), was identified as a target molecule recognized by Moloney murine sarcoma virus--M-MLV (M-MSV--M-MLV)-specific cytolytic T lymphocyte (CTL) clones. Target cells infected with Ab-X-MLV, an M-MLV-derived mutant virus not encoding gP85gag, were not lysed by the CTL clones. The same CTL clones were shown previously to induce the destruction of M-MLV-induced tumor cells in the peritoneal cavity. We have now characterized CTL-resistant antigen-loss tumor cell variants that have lost the surface antigen, but which retain transcriptionally silent M-MLV genomes. A cloned antigen-loss variant that reverted in vitro to the CTL-susceptible phenotype reexpressed M-MLV genomes that had undergone an insertion event in the region of the viral DNA coding for the gag membrane protein. Intravenous injection of virus-specific CTL clones inhibited tumor formation in mice injected subcutaneously with M-MSV--M-MLV.
An unusual feature of the c-mos oncogene is the lack of expression in mouse tissues. Recombinant plasmids that contain the strong adenovirus late promoter and different amounts of cellular DNA 5' to c-mos(rat) were constructed and tested in transfection and transcription assays. The cellular sequences inhibit RNA accumulation in mouse but not human cells and do not inhibit in vitro transcription of the plasmid DNAs.A feature unique to the c-mos oncogene (3) is the absence of expression in tissues from adult mice or mouse embryos (8,11,16). Since methylation of v-mos, the transforming gene of Moloney murine sarcoma virus (M-MSV), reduced the transforming capacity of the gene (12), the failure to express c-mos was originally attributed to the hypermethylated state of the c-mos gene in tissues (8). Recently, evidence was published for the presence of cellular DNA sequences upstream of c-mos(mouse) which inhibited its transforming capacity (26). As the assays used by Wood et al. to detect these inhibitory mouse sequences were based on the absence of focus formation after transfection (26), it was not clear whether the inhibition was at the level of RNA transcription, RNA processing, or translation, and we decided to examine directly the effect of these DNA sequences on RNA synthesis.We previously showed a high degree of homology between the c-mos genes of mice and rats and between their 5' flanking sequences (22). Because of these similarities, we chose to investigate the effect of the putative inhibitory sequences on the expression of c-mos(rat) and constructed the vectors shown in Fig. 1. They all contain c-mos(rat). Further, they contain the adenovirus 2 major late promoter (AdMLP) on a 455-base-pair (bp) XhoI-HindIII fragment which also contains the first leader exon and the adenovirus IVa2 promoter (19). However, we were unable to detect any activity of the adenovirus IVa2 promoter in the experiments described below, in agreement with earlier observations by Fire et al. (4). All vectors also contain different amounts of rat DNA that normally precedes c-mos(rat), placed between the AdMLP and the c-mos gene. Thus clones pAL,CMR-1, -2, and -3 contain, respectively, 850, 2,100 and 3,250 bp of rat DNA flanking the c-mos(rat) gene. The sequences around the HpaI site, harboring the putative inhibitory sequences, are present in clones pAL,CMR-2 and -3 but absent from pAL1CMR-1 and were shown previously to contain extensive homology to the similar region in mouse DNA (22). In vitro transcription (2, 5) was used to test the ability of the RNA polymerase II to start at the AdMLP and transcribe efficiently through the putative inhibitory sequences to the c-mos gene. Clones pAL1CMR-1 and -2 were digested with * Corresponding author.SmaI and HpaI, whereas pAL1CMR-3 was digested with SmaI and HindIII (Fig. 1). Thus, any transcription starting at the retroviral promoter in the long terminal repeat (LTR), which might interfere with initiation of transcription at the AdMLP, would generate a 30-nucleotide run-off transcript for e...
Extremely small quantities of the product of the transforming gene v-mos of Moloney murine sarcoma virus are able to efficiently transform cells. Recent data indicate the existence of a threshold level for v-mos transformation of NIH3T3 cells. Using mouse mammary tumor virus long terminal repeat sequences or hybrid promoters consisting of mouse mammary tumor virus and Moloney murine sarcoma virus long terminal repeat elements to express v-mos in C3H10T1/2 cells, we established cell lines representing different stages of morphological transformation in vitro. The threshold level for v-mos transformation was considerably lower than that for NIH3T3 cells, because no treatment with dexamethasone or primary selection other than transformation was necessary during standard transfection procedures. Using the cell lines mentioned we established an association of the level of v-mos expression with the transformation parameters examined, but not with p53 levels. Furthermore, the characterization of the different promoters showed (i) that the distal binding site confers hormone responsiveness to Moloney murine sarcoma virus promoter elements and (ii) that artifactual transcription initiation sites can be detected in mouse mammary tumor virus-Moloney murine sarcoma virus hybrid promoters which are, however, not regulated by the hormone.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.