KLF4 positively regulates human ghrelin expression

[摘要]：Ghrelin, an endogenours ligand of the GH (growth hormone) secretagogue receptor, influences many metabolic processes including GH secretion, food intake, energy balance, insulin secretion and adipogenesis. Although ghrelin exhibits a variety of biological functions, the mechanism by which ghrelin expression is regulated is unknown. Ghrelin is expressed ill the gastrointestinal tract, predominantly in the stomach, as is KLF4 (Kruppel-like factor 4). Therefore we investigated whether ghrelin expression is associated with KLF4, and found that the tissue distribution of ghrelin corresponded with that of KLF4. Furthermore, treatment with butyrate, all inducer of KLF4 expression, stimulated ghrelin expression, and fasting, which induces ghrelin expression, also increased KLF4 expression, suggesting that ghrelin expression is associated with KLF4. Then, we investigated the effects of Kill on the human ghrelinpromoter activity and identified a KLF4-responsive region in the promoter. KLF4 expression specifically stimulated human ghrelin-promoter activity in a dose-dependent manner in human gastric-cancer AGS cells. However, this effect was not seen ill response to a mutant KLF4 construct. Transfection studies using mutant constructs containing 5'-deletions in the human ghrelin promoter revealed that the KLF4-responsive element is located between - 1228 and - 1105. Electrophoretic mobility shift assays using oligonucleotides containing - 1165/- 1146 revealed the binding of KLF4 to the human ghrelin promoter. Finally, deletion of the - 1165/- 1146 region abrogated Kill induced transactivation of the ghrelin promoter. Collectively, these results indicate that KLF4 positively regulates human ghrelin expression via binding to a KLF4-responsive region in the promoter.

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