Insulin-like growth factor 1 mediates negative feedback to somatotroph GH expression via POU1F1/CREB binding protein interactions.
Circulating insulin-like growth factor 1 (IGF-1) has been shown to act as a negative feedback regulator of growth hormone (GH) gene expression; however, the mechanism of this negative feedback is poorly understood. Activation and regulation of GH gene expression require the binding of the transcription factor POU1F1 to the GH promoter along with cyclic AMP (cAMP) response element binding protein (CREB) binding protein (CBP). We investigate the role of CBP as a target of IGF-1 somatotroph regulation using the MtT/S somatotroph cell line. IGF-1 significantly inhibits basal GH mRNA levels but not POU1F1 levels. Chromatin immunoprecipitation assays demonstrate inhibition of CBP binding to the GH promoter after IGF-1 treatment. We hypothesized that IGF-1 receptor (IGF-1R) signaling disrupts the POU1F1/CBP complex to inhibit gene expression. In support, the use of a mutant CBP (S436A) construct, which lacks a critical phosphorylation site, leads to the loss of IGF-1 inhibition. The studies of CBP (S436A) knock-in mice show elevated serum GH levels, a greater response to GH releasing hormone (GHRH) stimulation along with lower weight gain, and decreased body fat. Our data confirm the inhibitory effects of IGF-1 on GH expression at the level of the promoter and provide evidence of CBP's role as a target of IGF-1R signaling.
Division of Pediatric Endocrinology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. cromero5@jhmi.edu
Christopher J
CJ
Romero
Elyse
E
Pine-Twaddell
Daniela I
DI
Sima
Ryan S
RS
Miller
Ling
L
He
Fredric
F
Wondisford
Sally
S
Radovick
D000273:Adipose Tissue; D000818:Animals; D001823:Body Composition; D050882:CREB-Binding Protein / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism; D025461:Feedback, Physiological; D005419:Flavonoids / Q000494:pharmacology; D055879:Gene Knock-In Techniques; D005838:Genotype; D013006:Growth Hormone / Q000096:biosynthesis* / Q000097:blood / Q000235:genetics; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D009025:Morpholines / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D052683:Somatotrophs / Q000378:metabolism*; D050817:Transcription Factor Pit-1 / Q000235:genetics / Q000378:metabolism*; D015430:Weight Gain
D050882:CREB-Binding Protein; D002867:Chromones; D017362:Cyclic AMP Response Element-Binding Protein; D005419:Flavonoids; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D007334:Insulin-Like Growth Factor I; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger; D050817:Transcription Factor Pit-1; C494185:Pou1f1 protein, mouse; C519530:insulin-like growth factor-1, mouse; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494364:Crebbp protein, mouse; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one