In vivo regulation of growth hormone-stimulated gene transcription by STAT5b.
The long-term effects of growth hormone (GH) are mediated through coordinated changes in gene expression that are the outcome of interactions between hormone-activated signal transduction pathways and specific feedback loops. Recent studies in mice have implicated the transcription factor STAT5b as part of the GH-regulated somatic growth pathway, because mice lacking this protein showed diminished growth rates. To assess the role of Stat5b in GH-stimulated gene expression, we have delivered modified versions of the protein to the liver of pituitary-deficient male rats by quantitative adenovirus-mediated gene transfer. In pilot studies in cell culture, both constitutive-active and dominant-negative STAT5b showed appropriate binding properties toward a specific DNA response element. After in vivo expression, neither protein prevented nuclear accumulation of STATs 1 and 3 in the liver. Dominant-negative STAT5b completely inhibited GH-stimulated transcription of genes encoding the growth-promoting proteins IGF-I, IGF-binding protein-3 (IGFBP-3), and acid-labile subunit (ALS), which comprise the major circulating IGF-I complex, and blocked expression of the GH inhibitors SOCS-1, SOCS-2, and CIS, but had little effect on induction of SOCS-3. Constitutive-active STAT5b stimulated robust transcription of IGF-I, ALS, and IGFBP-3 in the absence of hormone but did little to modify GH-mediated activation of SOCS family genes. An adenovirus encoding EGFP was without effect. These results, in addition to establishing STAT5b as one of the key agents of GH-stimulated gene transcription, demonstrate the feasibility of using in vivo gene transfer to target and dissect the functions of distinct components of complex hormone-activated signal transduction pathways.
Woelfle
Joachim
J
Molecular Medicine Division, Department of Medicine, Oregon Health & Science University, Portland, Oregon 97239-3098, USA.
Rotwein
Peter
P
D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D013006:Growth Hormone / Q000378:metabolism*; D006487:Hemostasis / Q000502:physiology; D007016:Hypophysectomy; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008894:Milk Proteins; D016297:Mutagenesis, Site-Directed; D051381:Rats / Q000378:metabolism / Q000601:surgery; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology*; D015533:Transcriptional Activation / Q000502:physiology
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; C494097:Stat5b protein, rat; D015534:Trans-Activators; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone