Growth hormone induces insulin‐like growth factor‐I gene transcription by a synergistic action of STAT5 and HNF‐1α

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Abstract
Salmon insulin-like growth factor-I (sIGF-I) expression is, as in mammals, induced by growth hormone (GH). To elucidate the mechanism by which GH stimulates the transcription of the IGF-I gene, we transiently transfected Hep3B cells expressing the rat GH receptor with a sIGF-I promoter-luciferase reporter construct. Activation of the construct by GH added to the medium of the transfected cells was observed when two specific transcription factors, STAT5 and HNF-1α, were simultaneously overexpressed in these cells. This finding demonstrates for the first time a GH-dependent activation of an IGF-I promoter construct in an immortalized laboratory cell line.