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Unlabelled: Liver cancer is the fifth most common cancer. A highly invasive surgical resection of the liver tumor is the main approach used to eliminate the tumor. Mechanisms that terminate liver regeneration when the liver reaches the original size are not known. The aims of this work were to generate an animal model that fails to stop liver regeneration after surgical resections and elucidate mechanisms that are involved in termination of liver regeneration. Because epigenetic control of liver function has been previously implicated in the regulation of liver proliferation, we generated C/EBPα-S193A knockin mice, which have alterations in formation of complexes of C/EBP family proteins with chromatin remodeling proteins. The C/EBPα-S193A mice have altered liver morphology and altered liver function leading to changes of glucose metabolism and blood parameters. Examination of the proliferative capacity of C/EBPα-S193A livers showed that livers of S193A mice have a higher rate of proliferation after birth, but stop proliferation at the age of 2 months. These animals have increased liver proliferation in response to liver surgery as well as carbon tetrachloride (CCl4 )-mediated injury. Importantly, livers of C/EBPα-S193A mice fail to stop liver regeneration after surgery when livers reach the original, preresection, size. The failure of S193A livers to stop regeneration correlates with the epigenetic repression of key regulators of liver proliferation C/EBPα, p53, FXR, SIRT1, PGC1α, and TERT by C/EBPβ-HDAC1 complexes. The C/EBPβ-HDAC1 complexes also repress promoters of enzymes of glucose synthesis PEPCK and G6Pase., Conclusion: Proper cooperation of C/EBP and chromatin remodeling proteins is essential for the termination of liver regeneration after surgery and for maintenance of liver functions., (© 2014 by the American Association for the Study of Liver Diseases.)

Unlabelled: One of the early events in the development of liver cancer is a neutralization of tumor suppressor proteins Rb, p53, hepatocyte nuclear factor 4α (HNF4α), and CCAAT/enhancer binding protein (C/EBP) α. The elimination of these proteins is mediated by a small subunit of proteasome, gankyrin, which is activated by cancer. The aim of this study was to determine the mechanisms that repress gankyrin in quiescent livers and mechanisms of activation of gankyrin in liver cancer. We found that farnesoid X receptor (FXR) inhibits expression of gankyrin in quiescent livers by silencing the gankyrin promoter through HDAC1-C/EBPβ complexes. C/EBPβ is a key transcription factor that delivers HDAC1 to gankyrin promoter and causes epigenetic silencing of the promoter. We show that down-regulation of C/EBPβ in mouse hepatoma cells and in mouse livers reduces C/EBPβ-HDAC1 complexes and activates the gankyrin promoter. Deletion of FXR signaling in mice leads to de-repression of the gankyrin promoter and to spontaneous development of liver cancer at 12 months of age. Diethylnitrosoamine (DEN)-mediated liver cancer in wild-type mice also involves the reduction of FXR and activation of gankyrin. Examination of liver cancer in old mice and liver cancer in human patients revealed that FXR is reduced, while gankyrin is elevated during spontaneous development of liver cancer. Searching for animal models with altered levels of FXR, we found that long-lived Little mice have high levels of FXR and do not develop liver cancer with age and after DEN injections due to failure to activate gankyrin and eliminate Rb, p53, HNF4α and C/EBPα proteins., Conclusion: FXR prevents liver cancer by inhibiting the gankyrin promoter via C/EBPβ-HDAC1 complexes, leading to subsequent protection of tumor suppressor proteins from degradation., (Copyright © 2012 American Association for the Study of Liver Diseases.)

Age declines liver functions, leading to the development of age-associated diseases. A member of the sirtuins family, SIRT1, is involved in the control of glucose homeostasis and fat metabolism. Because aging livers have alterations in glucose and fat metabolism, we examined a possible role of SIRT1 in these alterations. We found that aged livers have a reduced expression of SIRT1 and have lost proper control of the regulation of SIRT1 after partial hepatectomy (PH). Down-regulation of SIRT1 in the liver of old mice is mediated by CCAAT/Enhancer Binding Protein/histone deacetylase 1 (C/EBPβ-HDAC1) complexes, which bind to and repress the SIRT1 promoter. In the livers of young mice, SIRT1 is activated after PH and supports high levels of glucose and triglycerides during liver regeneration. In old mice, however, C/EBPβ-HDAC1-mediated repression of the SIRT1 promoter blocks activation of SIRT1, leading to low levels of glucose and triglycerides during liver regeneration. Down-regulation of SIRT1 in the livers of young mice resulted in alterations similar to those observed in the livers of old mice, whereas the normalization of SIRT1 in the livers of old mice corrects the levels of glucose and triglycerides after PH. The normalization of SIRT1 in old mice also improves liver regeneration via the elimination of the C/EBPα-Brm complex. These studies showed a critical role of the reduction of SIRT1 in age-associated liver dysfunctions and provide a potential tool for the correction of liver functions in old patients after surgical resections., (Copyright © 2011 American Association for the Study of Liver Diseases.)