Glucocorticoid regulation of mouse mammary tumor virus: identification of a short essential DNA region.

Abstract

Transcription of mouse mammary tumor virus (MMTV) DNA is stimulated by steroid hormones. To determine the DNA sequences involved in this regulation, we constructed a plasmid containing the MMTV long terminal repeat (LTR) in front of the coding region of the herpes simplex thymidine kinase gene, from which the promoter had been removed. Portions of the LTR were removed by the nuclease Ba/31, and the deleted molecules were recloned and tested for transcriptional activity in transfections of Ltk‐aprt‐ cells. Stably transfected cell clones were selected and hormone‐dependent transcription from the MMTV promoter was studied by the S1 nuclease mapping method. The results show that DNA sequences between ‐105 and ‐204 base pairs upstream from the initiation site of viral transcription are required for glucocorticoid stimulation.

Dual function of a nuclear factor I binding site in MMTV transcription regulation

“…Several lines of evidence demonstrate the existence of a basal transcriptional activity of the MMTV promoter: 5'-deletions of the whole LTR to -105 (8) or -80 (9), and internal deletions of all glucocorticoid-responsive sequences in an otherwise complete LTR (-193/78; Fig. 2B) allowed to experimentally dissociate hormonally stimulated from basal transcriptional activity.…”

“…The hormone-responsive sequences are located in the long terminal repeat (LTR) of the provirus (4,5,6,7), in a region of approximately 200 bp upstream of the transcription start site (8,9,10). While steroids like progestins and androgens have recently been shown to also affect MMTV transcription in mammary cells (11,12,13,14,15), it is the response to glucocorticoids in cultured fibroblasts that has been studied in greatest detail (16,17,18,19).…”

“…19) are observed after addition of dexamethasone, a synthetic glucocorticoid, to cells containing the natural MMTV promoter plus the regulatory region. Stimulation occurs over a low basal promoter activity which is independent of the presence of hormone or of hormone-responsive sequences (8,9). These sequences are located relatively close to the promoter and contain several regulatory elements which act in a cooperative fashion to achieve an optimal level of transcription (18).…”

“…The other overlapped with the binding site for the so-called 'TGGCA-binding protein' (24,25,26,27), a functional equivalent of the ubiquitous nuclear factor I (NF-I; 28,29), which was shown to increase the rate of initiation (33,31,32,29). The fact that both TATA and NF-I elements map in a region that by itself does not provide any hormone response (8,9) suggests that they act in concert with receptor binding sites in the process of transcriptional stimulation by the hormone. While the role of the TATA box in promoter activity is well established (23), it was unclear from the previous studies (18,27) whether the NF-I binding site affected only the stimulation of transcription or the basal level as well.…”

Control of gene expression by glucocorticoid hormones

“…No DNA sequences specific to enhancers have been identified yet (Fried et al, 1983). Still, a 70% consensus sequence lObp long (TXAGXTCTXA) has been found in putative GRE regions for four glucocorticoid-responsive genes: MTV, somatotropin, tryptophan oxygenase, and pro-opiomelanocortin (Buetti & Diggelmann, 1983).…”