RESUMO
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/EBPß-HDAC1 complexes. The C/EBPß-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.
Assuntos
Proteínas Estimuladoras de Ligação a CCAAT/metabolismo , Hepatócitos/fisiologia , Histona Desacetilase 1/metabolismo , Regeneração Hepática , Animais , Ciclo Celular , Doença Hepática Induzida por Substâncias e Drogas , Glucose-6-Fosfatase/metabolismo , Hepatectomia , Fígado/fisiologia , Masculino , Camundongos , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Fosfoenolpiruvato Carboxiquinase (GTP)/metabolismo , Sirtuína 1/metabolismo , Telomerase/metabolismo , Fatores de Transcrição/metabolismo , Proteína Supressora de Tumor p53/metabolismoRESUMO
The histone acetyltransferase p300 has been implicated in the regulation of liver biology; however, molecular mechanisms of this regulation are not known. In this paper, we examined these mechanisms using transgenic mice expressing a dominant negative p300 molecule (dnp300). While dnp300 mice did not show abnormal growth within 1 year, these mice have many alterations in liver biology and liver functions. We found that the inhibition of p300 leads to the accumulation of heterochromatin foci in the liver of 2-month-old mice. Transcriptome sequencing (RNA-Seq) analysis showed that this inhibition of p300 also causes alterations of gene expression in many signaling pathways, including chromatin remodeling, apoptosis, DNA damage, translation, and activation of the cell cycle. Livers of dnp300 mice have a high rate of proliferation and a much higher rate of proliferation after partial hepatectomy. We found that livers of dnp300 mice are resistant to CCl4-mediated injury and have reduced apoptosis but have increased proliferation after injury. Underlying mechanisms of resistance to liver injury and increased proliferation in dnp300 mice include ubiquitin-proteasome-mediated degradation of C/EBPα and translational repression of the p53 protein by the CUGBP1-eukaryotic initiation factor 2 (eIF2) repressor complex. Our data demonstrate that p300 regulates a number of critical signaling pathways that control liver functions.
Assuntos
Proteínas Estimuladoras de Ligação a CCAAT/metabolismo , Intoxicação por Tetracloreto de Carbono/patologia , Proteína p300 Associada a E1A/genética , Fígado/metabolismo , Proteína Supressora de Tumor p53/biossíntese , Animais , Apoptose/genética , Proteínas CELF1 , Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Proliferação de Células/genética , Dano ao DNA/genética , Fator de Iniciação 2 em Eucariotos/genética , Fígado Gorduroso/genética , Fígado Gorduroso/prevenção & controle , Perfilação da Expressão Gênica , Regulação da Expressão Gênica/genética , Hepatócitos/citologia , Heterocromatina/genética , Heterocromatina/metabolismo , Fígado/cirurgia , Camundongos , Camundongos Transgênicos , Dados de Sequência Molecular , Biossíntese de Proteínas/genética , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , Transdução de Sinais/genética , Proteína Supressora de Tumor p53/genéticaRESUMO
Molecular mechanisms underpinning nonalcoholic fatty liver disease (NAFLD) are not well understood. The earliest step of NAFLD is hepatic steatosis, which is one of the main characteristics of aging liver. Here, we present a molecular scenario of age-related liver steatosis. We show that C/EBPα-S193D knockin mice have age-associated epigenetic changes and develop hepatic steatosis at 2 months of age. The underlying mechanism of the hepatic steatosis in old wild-type (WT) mice and in young S193D mice includes increased amounts of tripartite p300-C/EBPα/ß complexes that activate promoters of five genes that drive triglyceride synthesis. Knockdown of p300 in old WT mice inhibits hepatic steatosis. Indeed, transgenic mice expressing dominant-negative p300 have fewer C/EBPα/ß-p300 complexes and do not develop age-dependent hepatic steatosis. Notably, the p300-C/EBPα/ß pathway is activated in the livers of patients with NAFLD. Thus, our results show that p300 and C/EBP proteins are essential participants in hepatic steatosis.