Multiple Distant STAT5 Binding Sites Mediate Growth Hormone Regulation of IGF‐I Gene Expression

Abstract

Transcription factor STAT5 mediates growth hormone (GH) stimulation of insulin-like growth factor-I (IGF-I) gene expression. The objective of this study was to identify the cis-regulatory elements that bind to STAT5 to mediate GH stimulation of IGF-I gene expression in the mouse liver. A comparative genomic analysis revealed nineteen conserved STAT5 consensus binding sequences in a ~170 kb mouse chromosomal region containing the IGF-I gene and hence nineteen potential STAT5 binding sites. Chromatin immunoprecipitation assays indicated that nine of them, all located upstream or downstream from the IGF-I gene promoter, were bound by STAT5 in the mouse liver in response to GH administration and that GH-increased STAT5 binding to them preceded or coincided with GH-increased IGF-I gene transcription. In vitro DNA-protein binding assays confirmed that each of the nine STAT5 binding sites was able to bind to STAT5. Cotransfection assays demonstrated that the genomic DNA regions containing these STAT5 binding sites were able to mediate GH-induced STAT5 activation of reporter gene expression in reconstituted GH-responsive cells. These results together suggest that nine distant STAT5 binding sites mediate GH stimulation of IGF-I gene expression in the mouse liver.