期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 281, 期 6, 页码 3190-3197出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M510204200
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资金
- NICHD NIH HHS [K12 HD057588] Funding Source: Medline
- NIDDK NIH HHS [R01 DK069703, F32 DK70447, R01 DK67961, R01 DK063073] Funding Source: Medline
A key agent in the anabolic actions of growth hormone (GH) is insulin-like growth factor-I (IGF-I), a 70-amino acid secreted protein with direct effects on somatic growth and tissue maintenance and repair. GH rapidly and potently stimulates IGF-I gene transcription by mechanisms independent of new protein synthesis, and recent studies have linked the transcription factor Stat5b to a regulatory network connecting the activated GH receptor on the cell membrane to the IGF-I gene in the nucleus. Here we analyze two distinct conserved GH response elements in the rat IGF-I locus that contain paired Stat5b sites. Each response element binds Stat5b in vivo in a GH-dependent way, as assessed by chromatin immunoprecipitation assays, and consists of one high affinity and one lower affinity Stat5b site, as determined by both qualitative and quantitative protein-DNA binding studies. In biochemical reconstitution experiments, both response elements are able to mediate GH-stimulated and Stat5b-dependent transcription when fused to a reporter gene containing either the major IGF-I promoter or a minimal neutral promoter, although the paired Stat5b sites located in the second IGF-I intron were more than twice as effective as the response element that mapped similar to 73 kb 5' to the IGF-I exon 1. Taken together, our results define the initial molecular architecture of a complicated GH-regulated transcriptional pathway, and suggest that apparently redundant hormone response elements provide a mechanism for amplifying GH action at a physiologically important target gene.
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