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J. Virol., 06 1995, 3759-3770, Vol 69, No. 6
C Cavin and E Buetti
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.
Copyright © 1995, American Society for Microbiology
Tissue-specific and ubiquitous factors binding next to the glucocorticoid receptor modulate transcription from the mouse mammary tumor virus promoter
Swiss Institute for Experimental Cancer Research, Epalinges.
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