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Mol. Cell. Biol., 12 1997, 7186-7194, Vol 17, No. 12
MA Hussain, J Lee, CP Miller and JF Habener
The proglucagon gene is expressed in a highly restricted tissue- specific
manner in the alpha cells of the pancreatic islet, the hypothalamus, and
the small and large intestines. Proglucagon is processed to glucagon and
glucagon-like peptides GLP-1 and -2. Glucagon is expressed in alpha cells
and regulates glucose homeostasis. GLP-1 is implicated in the control of
insulin secretion, food intake, and satiety signaling, and GLP-2 is
implicated in regulating small-bowel growth. Cell-specific expression of
the proglucagon gene is mediated by proteins that interact with the
proximal G1 promoter element which contains several AT-rich domains with
binding sites for homeodomain transcription factors. In an attempt to
identify major homeodomain proteins involved in pancreatic
alpha-cell-specific proglucagon expression, we found that the POU domain
transcription factor brain 4 is abundantly expressed in
proglucagon-producing islet cell lines and rat pancreatic islets. In the
latter, brain 4 and glucagon immunoreactivity colocalize in the outer
mantle of islets. Electrophoretic mobility shift assays with specific
antisera identify brain 4 as a major constituent of nuclear proteins of
glucagon- producing cells that bind to the G1 element of the proglucagon
gene proximal promoter. Transcriptional transactivation experiments reveal
that brain 4 is a major regulator of proglucagon gene expression by its
interaction with the G1 element. The finding that a neuronal transcription
factor is involved in glucagon gene transcription may explain the presence
of proglucagon in certain areas of the brain as well as in pancreatic alpha
cells. Further, this finding supports the idea that the neuronal properties
of endodermis-derived endocrine pancreatic cells may find their basis in
regulation of gene expression by neuronal transcription factors.
Copyright © 1997, American Society for Microbiology
POU domain transcription factor brain 4 confers pancreatic alpha-cell- specific expression of the proglucagon gene through interaction with a novel proximal promoter G1 element
Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Howard Hughes Medical Institute, and Harvard Medical School, Boston 02114, USA.
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