Tissue-specific and ubiquitous factors binding next to the glucocorticoid receptor modulate transcription from the mouse mammary tumor virus promoter

Abstract

Steroid hormones complexed with their receptors play an essential role in the regulation of mouse mammary tumor virus (MMTV) transcription. However, the need for additional tissue-specific regulatory factors is suggested by the lack of virus expression in liver, in which glucocorticoid receptors are highly abundant, and by the tissue-specific transcription of reporter genes linked to an MMTV long terminal repeat in transgenic mice. In this study, we characterized two distal-region regulatory elements, DRa and DRc, which, together with the distal glucocorticoid receptor binding site (DRb), increased transcription from the MMTV promoter in permissive cells. This was demonstrated by transfection of these sequences (DRa, DRb, and DRc) in different combinations with the natural MMTV promoter in mouse fibroblasts and mammary epithelial cells, followed by quantitative S1 nuclease mapping of the transcripts. We further showed by DNase I footprinting, methylation interference, and gel retardation assays with various nuclear extracts from permissive or nonpermissive tissues and cell lines that the factors binding to the DRa site are distinct and tissue-specific whereas those binding to DRc are ubiquitous.

Synergistic Action of GA-Binding Protein and Glucocorticoid Receptor in Transcription from the Mouse Mammary Tumor Virus Promoter

“…We demonstrated in a previous study that tissue-specific factors bind to a DNA sequence immediately 5Ј to the distal glucocorticoid receptor binding site (14). We also observed a correlation between the pattern of protection and the permissivity for MMTV expression of the mouse organ from which the nuclear extracts were made, e.g., spleen (permissive) versus liver (nonpermissive).…”

Structure and Dynamic Properties of a Glucocorticoid Receptor-Induced Chromatin Transition

“…In findings remarkably similar to those recently observed in vivo (15), we show that the GR-dependent chromatin remodeling extends beyond the Nuc-B region, into the Nuc-C family. Regulation of the MMTV promoter has been shown to be dependent on a variety of sequences upstream of the distal GRE (6,7,17,23,24,29). MMTV constructs containing deletion mutants in the region that includes the putative GRE5 and -6 exhibited a significant loss in hormone-dependent activation in NIH 3T3 cells (17).…”

Shared promoter elements between a viral superantigen and the major histocompatibility complex class II-associated invariant chain

“…The functional data suggest that this molecule is tightly controlled, both in terms of tissue specificity and level of expression. Three promoters linked to sag expression have been described so far; P1, the classical promoter of MMTV, located at the U3 region boundary and used for the expression of the retroviral genome and structural genes (8,44); P2, a promoter encoded within the U3 region of the 5Ј LTR (22); and Penv, a phorbol myristate acetate-inducible promoter encoded within the 5Ј end of the env gene (41). Here we provide evidence of a new promoter, Penv2, also encoded by the env gene but at the 3Ј end.…”

“…Understanding the control of superantigen expression in B cells is important, as this molecule is essential to the viral life cycle. Three promoters have previously been reported to play a role in the expression of the MMTV superantigen: the classical MMTV P1 in the U5 region of the 5Ј LTR, from which all MMTV transcripts originate (8,44); MMTV P2, a promoter mapping to the U3 region of the 5Ј LTR (22); and Penv, a T-cell-specific phorbol myristate acetate-inducible promoter encoded within the 5Ј end of the env gene (41). Here we present evidence of a new promoter, Penv2, mapping to the 3Ј region of the env gene of endogenous Mtv-7 and infectious JYG MMTV (67).…”