Oct-1 Binds Promoter Elements Required for Transcription of the GnRH Gene

• Published in: Molecular endocrinology (Baltimore, Md.) Vol. 12; no. 4; pp. 469 - 481
• Main Authors: Eraly, Satish A, Nelson, Shelley B, Huang, Karen M, Mellon, Pamela L
• Format: Journal Article
• Language: English
• Published: United States Endocrine Society 01-04-1998; Oxford University Press
• Subjects: Animals; Base Sequence; Binding Sites - genetics; Cell Line; DNA Footprinting; DNA-Binding Proteins - metabolism; Gonadotropin-Releasing Hormone - genetics; Host Cell Factor C1; Mice; Molecular Sequence Data; Mutagenesis, Site-Directed; Octamer Transcription Factor-1; Promoter Regions, Genetic - genetics; Promoter Regions, Genetic - physiology; Protein Binding - genetics; Rats; Transcription Factors - metabolism; Transcription, Genetic
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/mend.12.4.0092

The GnRH gene is exclusively expressed in a
discrete population of neurons in the hypothalamus. The
promoter-proximal 173 bp of the rat GnRH gene are highly conserved
through evolution and are bound by multiple nuclear proteins found in
the neuronal cell line, GT1–7, a model for the GnRH-expressing
hypothalamic neuron. To explore the protein-DNA interactions that occur
within this promoter and the role of these interactions in targeting
GnRH gene expression, we have mutagenized individual binding sites in
this region. Deoxyribonuclease I protection experiments reveal that
footprint 2, a 51-bp sequence that confers a 20-fold induction of the
GnRH gene, is comprised of at least three independent protein-binding
sites. Transfections of the GnRH promoter-reporter plasmid containing a
series of block mutations of footprint 2 into GT1–7 neurons indicate
that each of the three putative component sites contributes to
transcriptional activity. Mutations in footprint 4 also decrease GnRH
gene expression. Footprint 4 and the promoter-proximal site in
footprint 2 contain octamer-like motifs, an element that is also
present in the neuron-specific enhancer of the rat GnRH gene located
approximately 1.6 kb upstream of the promoter. Previous studies in our
laboratory have demonstrated that two enhancer octamer sites are bound
by the POU-homeodomain transcription factor Oct-1 in GT1–7 cells. We
now show that Oct-1 binds the octamer motifs within footprints 2 and 4.
Thus, Oct-1 plays a critical role in the regulation of GnRH
transcription, binding functional elements in both the distal enhancer
and the promoter-proximal conserved region.