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Mol. Cell. Biol., 07 1995, 3870-3881, Vol 15, No. 7
BM Evers, X Wang, Z Zhou, CM Townsend Jr, GP McNeil and PR Dobner
Expression of the gene encoding neurotensin/neuromedin N (NT/N) is mostly
limited to the brain and specialized enteroendocrine cells (N cells) of the
distal small intestine. We have analyzed the NT/N DNA sequences upstream of
the RNA start site that direct cell-specific expression using a novel human
endocrine cell line, BON, that resembles intestinal N cells in several
important aspects, including NT/N precursor protein processing, ratios of
different NT/N mRNA forms, and high levels of constitutive expression of
the NT/N gene. Transient transfection assays with plasmids with progressive
5' deletions of the rat NT/N promoter identified the proximal 216 bp of 5'
flanking sequences as essential for high-level constitutive NT/N expression
in BON cells. In addition, a detailed mutational analysis defined multiple
regions within the proximal 216 bp that contribute to cell-specific NT/N
expression. These elements include a proximal cyclic AMP response element
(CRE)/AP-1-like motif (TGACATCA) that binds c-Jun, JunD, CRE- binding
(CREB), and ATF proteins, a near-consensus glucocorticoid response element,
and a distal consensus AP-1 site that binds c-Fos, Fra-1, and JunD. In
addition, elements contained within two 21-bp imperfect direct repeats play
an important role in NT/N expression in BON cells and may bind novel
factors that act as positive regulators of NT/N expression. DNase I
footprinting and gel shift analyses demonstrate that the sites identified
by mutational analysis, and at least one additional site, specifically bind
BON cell nuclear proteins in vitro. We speculate that a complex pattern of
regulation requiring interaction between a proximal CRE/AP-1-like motif and
other upstream control elements play an important role in the high-level
constitutive expression of NT/N in the human endocrine cell line BON. In
addition, the BON cell line provides a unique model to further characterize
the factors regulating cell-specific NT/N expression and to better
understand the mechanisms responsible for the terminal differentiation of
the N-cell lineage in the gut.
Copyright © 1995, American Society for Microbiology
Characterization of promoter elements required for cell-specific expression of the neurotensin/neuromedin N gene in a human endocrine cell line
Department of Surgery, The University of Texas Medical Branch, Galveston 77555, USA.
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