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A common pro-opiomelanocortin-binding element mediates leukemia inhibitory factor and corticotropin-releasing hormone transcriptional synergy.
Bousquet C, Ray DW, Melmed S
J Biol Chem. 1997;272:10551-10557.
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Abstract
Using murine AtT20 pituitary cells transfected with a rat pro-opiomelanocortin (POMC) promoter (-706/+64) linked to the luciferase reporter, we showed leukemia inhibitory factor (LIF) to strongly potentiate corticotropin-releasing hormone (CRH) induction of POMC gene expression. We therefore tested mechanisms for molecular interactions between LIF and CRH. Although LIF and CRH synergized to induce an 8-fold induction of POMC transcription, CRH alone (but not LIF) induced cAMP response element-binding protein phosphorylation (5-fold) or an increase of c-fos mRNA levels (>100-fold), suggesting that these pathways are not implicated in LIF transcriptional synergistic effects. Using a DNase I footprint assay, POMC promoter regions protected by AtT20 cell nuclear extracts were identified (-121/-109, and -143/-134, and -173/-160). The protected -173/-160 element fused to a heterologous promoter conferred LIF-CRH synergy (6.5-fold induction of POMC) and formed a specific complex with AtT20 cell nuclear extracts. This complex was supershifted by an anti-phosphoserine antibody, and a serine/threonine kinase inhibitor also altered both this complex and LIF-CRH transcriptional synergy on the POMC promoter-luciferase reporter construct, indicating that these events depend on post-translational serine phosphorylations. LIF-CRH synergy on POMC transcription is therefore mediated at least in part by -173/-160 sequences conferring confluent transcriptional activity of both peptides.
Keyword(s)
Animals; Base Sequence; Cell Line; DNA Footprinting; Deoxyribonuclease I; Drug Synergism; Genes, Reporter; Interleukin-6; Leukemia Inhibitory Factor; Mice; Pituitary Gland; Pituitary Neoplasms; Promoter Regions, Genetic; Rats; Transfection; biosynthesis: Luciferases; biosynthesis: Pro-Opiomelanocortin; biosynthesis: Proto-Oncogene Proteins c-fos; biosynthesis: Recombinant Fusion Proteins; drug effects: Transcription, Genetic; genetics: Genes, fos; pharmacology: Corticotropin-Releasing Hormone; pharmacology: Growth Inhibitors; pharmacology: Lymphokines; pharmacology: Oligodeoxyribonucleotides