Oncogene mediated repression of glucocorticoid hormone response elements and glucocorticoid receptor levels (original) (raw)
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We have subjected the viral mos oncogene (v-mos), the activated human H-ras oncogene [H-ras (A)] and the normal human H-ras protooncogene [H-rms (N)] to the transcriptional regulation of glucocorticoid hormones by in vitro recombina-tion with the promoter region of the mouse mammary tumor virus long terminal repeat (MMTV LTR) and transfection into NIH 3T3 cells. Cell clones were selected which exhibit a transformed phenotype strictly dependent on the presence of hormone in the growth medium. The expression of the chimeric genes as a function of time after hormone stinula-tion was studied at the level of transcriptional rate, mRNA and protein accumulation. Oncogene expression was stimulated rapidly to high levels, after hormone addition, but declined in the continuous presence of hormone. Measurements of the transcriptional rates in nuclei from LTR v-mos and LTR H-ras (A) transfected cells showed a repression of LTR v-mos and LTR H-ras (A) transcription after the initial stimulation by hormone. LTR H-ras (N) transcription was not affected. An independently transfected LTR H-2Ld construct in LTR v-mos or LTR H-ras (A) containing cells is also transcriptionally repressed. These experiments demonstrated a transcriptional repression effect of the oncogene products on the glucocorticoid hormone-dependent MMTV LTR transcription.
Oncogenes modulate cellular gene expression and repress glucocorticoid regulated gene transcription
Journal of Steroid Biochemistry, 1988
The v-mos oncogene was subjected to the transcriptional control of the MMTV LTR and introduced by transfection into NIH 3T3 cells. The LTR v-mos gene was induced by the addition of glucocorticoid hormone to the growth medium of cells synchronized by culturing in 1.5% FCS for 36 h. The effects of p37 v-mos expression were monitored. The endogenous c-myc gene is induced as a consequence of p37 v-mos expression in a transient fashion, reaching a maximum of expression after 8 h. Induction of the c-myc gene was observed at the level of its transcriptional rate and at the level of mRNA concentration. Omithine decarboxylase (ODC) mRNA was induced constitutively and high levels were found 8 and 25 h after v-mos induction. H4 histone mRNA is elevated at 25 h after hormone addition at a time when the mitogenic stimulus of v-mos causes DNA synthesis. The expression of actin mRNA is not affected by the v-mos oncogene. We have previously described a modulation of glucocorticoid dependent gene expression by oncogenes. In an extension of these observations the consequences of expression of the v-mos and the v-ras oncogenes were also studied in retrovirally infected NIH 3T3 cells. MMTV LTR constructs transfected into the infected cells could only be transiently induced by glucocorticoid hormone. The presence of the p37 v-mos and the p21 v-ras oncoproteins causes a repression of glucocorticoid hormone dependent gene transcription.
Proceedings of the National Academy of Sciences of the United States of America, 1991
The rat hepatoma cell line M1.19 is stably infected by the mouse mammary tumor virus (MMTV), and the expression of the virus is induced by glucocorticoid treatment. However, in the 6.10.2 variant of M1.19, an increase in MMTV transcription is hardly detectable upon exposure to hormone. The mechanism of hormone-unresponsiveness in these cells has been unclear. In this study, we show that nuclear extract from 6.10.2 cells contains a specific DNA-binding activity that recognizes a sequence motif extending from positions -163 to -147 on the MMTV promoter. An oligonucleotide probe spanning this region binds a nuclear factor distinct from the glucocorticoid receptor. In vivo competition experiments, where increased amounts of a plasmid containing this element were transfected into 6.10.2 cells, showed a dose-dependent increase in hormonal inducibility of MMTV expression. Together, these results indicate that this sequence motif negatively modulates glucocorticoid-inducible activation of t...
Glucocorticoid receptors recognize DNA sequences in and around murine mammary tumour virus DNA
The EMBO journal, 1982
In several rodent cell lines, glucocorticoids increase the transcription of murine mammary tumour virus (MMTV) proviral DNA in a process mediated by the glucocorticoid receptor. To investigate whether a direct interaction between the receptor and specific sequences on the induced genes can be implicated in the hormonal regulation of transcription, filter binding studies were performed with partially purified glucocorticoid receptor of rat liver and eight cloned MMTV proviral probes. Both the 40 000 and the 90 00 mol. wt. forms of the receptor do bind preferentially to restriction fragments containing the right 400-500 nucleotides of the MMTV long terminal repeat units (LTR). Using LTR deletion mutants, we confirm that the right end of the LTR contains at least one binding site for the glucocorticoid receptor. In addition, the receptor binds preferentially to the mouse genomic sequences flanking at least three endogenous proviral copies, and to sequences within the env genes in some ...
Proceedings of the National Academy of Sciences, 1981
Activated glucocorticoid receptor protein, purified to 40-60% homogeneity from rat liver extracts, binds selectively in vitro to a cloned fragment of murine mammary tumor virus (MTV) DNA. The DNA fragment tested contains about half of the sequences present in intact MTV DNA, and its rate of transcription, like that of the intact viral element, is strongly stimulated by glucocorticoids when it is introduced into the genome of a receptor-containing cell. In contrast, the receptor fails to bind selectively to DNA restriction fragments from E. coli plasmids pBR322 and RSF2124 or from bacteriophages A and T4. Preliminary experiments to localize regions within MTV DNA responsible for selective binding have revealed thus far one subfragment that fails to bind the receptor and one selectively bound subfragment that maps far downstream from the 5' terminus ofthe normal RNA transcript. These studies are consistent with the notion that steroid receptors may modulate rates of transcription by recognizing specific DNA sequences within or near the regulated genes.