Acute control of insulin-like growth factor-I gene transcription by growth hormone through Stat5b.
Many of the effects of growth hormone (GH) are mediated by insulin-like growth factor-I (IGF-I), a secreted peptide whose gene transcription is induced by GH by unknown mechanisms. Recent studies in mice have implicated Stat5b as part of a GH-regulated somatic growth pathway, because mice lacking this transcription factor show diminished growth rates and a decline in serum IGF-I levels. To test the role of Stat5b in GH-stimulated IGF-I gene expression, we have delivered modified versions of the protein to pituitary-deficient male rats by quantitative adenovirus-mediated gene transfer. In pilot studies in cell culture, both constitutively active and dominant-negative Stat5b appropriately regulated transcription from a GH-responsive Stat5-dependent reporter gene. After in vivo expression, neither protein impaired GH-induced activation of cytoplasmic signaling pathways or blocked nuclear accumulation of Stats 1 and 3 in the liver, the major site of IGF-I production. Dominant-negative Stat5b completely prevented GH-stimulated IGF-I gene transcription, whereas constitutively active Stat5b led to robust IGF-I gene expression in the absence of hormone. An adenovirus encoding enhanced green fluorescent protein was without effect. Similar results were seen with the GH-responsive Stat5b-dependent Spi 2.1 gene, whereas GH-stimulated c-fos transcription was minimally altered. These results establish Stat5b as a key component of GH-stimulated IGF-I gene transcription, and they demonstrate the feasibility of using in vivo gene transfer to target distinct components of hormone-activated signaling pathways.
Woelfle
Joachim
J
Molecular Medicine Division, Department of Medicine, Oregon Health & Science University, Portland, Oregon 97239-3098, USA.
Billiard
Julia
J
Rotwein
Peter
P
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005091:Exons; D005786:Gene Expression Regulation / Q000187:drug effects; D014644:Genetic Variation; D005822:Genetic Vectors; D013006:Growth Hormone / Q000494:pharmacology*; D007016:Hypophysectomy; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008297:Male; D008894:Milk Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050799:STAT5 Transcription Factor; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects*
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D050799:STAT5 Transcription Factor; C494097:Stat5b protein, rat; D015534:Trans-Activators; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone