Growth Hormone Corrects Proliferation and Transcription of Phosphoenolpyruvate Carboxykinase in Livers of Old Mice via Elimination of CCAAT/Enhancer-binding Protein α-Brm Complex
pmid: 17107955
Growth Hormone Corrects Proliferation and Transcription of Phosphoenolpyruvate Carboxykinase in Livers of Old Mice via Elimination of CCAAT/Enhancer-binding Protein α-Brm Complex
Growth hormone (GH), which is reduced with age, corrects the impaired proliferative capacity of livers of old animals. In this paper, we present a mechanism by which GH eliminates age-dependent negative control of proliferation and increases transcription of liver-specific genes in livers of old mice. The reduced proliferative capacities of the liver of old animals are associated with the CCAAT/enhancer-binding protein alpha (C/EBPalpha)-Brm complex, which inhibits E2F-dependent promoters. We found that a sequestration of C/EBPalpha into complexes with Brm leads to a weak interaction of C/EBPalpha with promoters of liver-specific genes, expression of which is reduced in old animals. Injection of either GH or the regulator of the amplitude of endogenous GH release, ghrelin, reduces the C/EBPalpha-Brm complex in livers of old mice, leading to a derepression of E2F targets, to increased interactions of C/EBPalpha with promoters of liver-specific genes, and to correction of their expression. GH-dependent elimination of the complex is mediated by the inhibition of cyclin D3-CDK4 activity and by elevation of a phosphatase, protein phosphatase 2A, which dephosphorylates C/EBPalpha and dissociates the complex.
- Baylor College of Medicine United States
- Hennepin County Medical Center United States
Aging, Base Sequence, Peptide Hormones, Forkhead Box Protein M1, Molecular Sequence Data, Cyclin-Dependent Kinase 4, Down-Regulation, Forkhead Transcription Factors, Cyclin-Dependent Kinase 6, Gene Expression Regulation, Enzymologic, Ghrelin, Mice, Liver, Cyclins, Growth Hormone, CCAAT-Enhancer-Binding Protein-alpha, Animals, Phosphoenolpyruvate Carboxykinase (GTP), Cyclin D3, Cell Division
Aging, Base Sequence, Peptide Hormones, Forkhead Box Protein M1, Molecular Sequence Data, Cyclin-Dependent Kinase 4, Down-Regulation, Forkhead Transcription Factors, Cyclin-Dependent Kinase 6, Gene Expression Regulation, Enzymologic, Ghrelin, Mice, Liver, Cyclins, Growth Hormone, CCAAT-Enhancer-Binding Protein-alpha, Animals, Phosphoenolpyruvate Carboxykinase (GTP), Cyclin D3, Cell Division
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