ABSTRACT
EZH2/H3K27me3 and polycomb group complex (PcG) play a major role in regulating global gene expression including tumor suppressor genes. EZH2 is linked to cell cycle regulated EZH2 phosphorylation by CDK1, a mitotic kinase which increases in arrested mitosis compared to S phase. CDK1 phosphorylation of EZH2 accelerates the degradation of pEZH2. Phospho-EZH2 is subjected to ubiquitination. The half-like of pEZH2 is shorter when compared to total EZH2. In the present study, pEZH2 was found concentrated together with ubiquitin in the Mallory-Denk bodies (MDB) that were formed in hepatocytes in the livers of drug primed mice refed DDC and humans with alcoholic hepatitis or hepatocellular carcinoma. The cells that formed MDBs in the mice livers studied were associated with a growth advantage and a high proliferative index. However, the livers from patients with alcoholic hepatitis showed evidence of cell cycle arrest where PCNA, cyclin D1 and p27 positive nuclei were numerous but Ki-67 positive nuclei were scarce. It is concluded that MDB formation is linked to the cell cycle and global gene expression (i.e. loss of gene silencing) through its association with the regulation of the polycomb group PRC2/EZH2/H3K27me3 complex.
Subject(s)
DNA-Binding Proteins/metabolism , Histones/metabolism , Liver/metabolism , Mallory Bodies/metabolism , Transcription Factors/metabolism , Animals , Blotting, Western , Carcinoma, Hepatocellular/genetics , Carcinoma, Hepatocellular/metabolism , Cell Cycle Checkpoints , Cell Nucleus/drug effects , Cell Nucleus/genetics , Cell Nucleus/ultrastructure , Cyclin D1/metabolism , Cyclin-Dependent Kinase Inhibitor p27/metabolism , DNA Methylation , DNA-Binding Proteins/genetics , Enhancer of Zeste Homolog 2 Protein , Hepatitis, Alcoholic/genetics , Hepatitis, Alcoholic/metabolism , Hepatocytes/drug effects , Hepatocytes/metabolism , Hepatocytes/ultrastructure , Humans , Immunohistochemistry , Liver/drug effects , Liver/pathology , Liver Neoplasms/genetics , Liver Neoplasms/metabolism , Lysine/metabolism , Mallory Bodies/drug effects , Mallory Bodies/ultrastructure , Methylation , Mice , Microscopy, Electron , Polycomb Repressive Complex 2 , Proliferating Cell Nuclear Antigen/metabolism , Pyridines/toxicity , Reverse Transcriptase Polymerase Chain Reaction , S-Adenosylmethionine/pharmacology , Transcription Factors/geneticsABSTRACT
BACKGROUND: Transforming growth factor alpha (TGF-alpha) knockout mice have increased susceptibility to dextran sodium sulphate (DSS) induced colitis. AIM: To substantiate the findings that TGF-alpha is a key mediator of colonic mucosal protection and/or repair mechanisms by evaluating the susceptibility of mice overexpressing TGF-alpha to DSS induced colitis. METHODS: TGF-alpha overexpression was induced in transgenic mice by ZnSO4 administration in drinking water (TG+). Three groups were used as controls: one transgenic group without ZnSO4 administration (TG-), and two non-transgenic littermate groups receiving ZnSO4 (Non-TG+) or only water (Non-TG-). Acute colitis was induced in all groups by administration of DSS (5%, w/v) in drinking water for six days and libitum. RESULTS: About 35-39% of the entire colonic mucosa was destroyed in Non-TG-, Non-TG+, and TG- animals compared with 9% in TG+ mice. the crypt damage score was 18.7 (0.9), 18.2 (1.0), 18.9 (0.8), and 6.8 (1.5) (means (SEM)) in Non-TG-, Non-TG+, TG-, and TG+ mice respectively. Mucin and bromodeoxyuridine staining were markedly enhanced in colons of TG+ mice compared with controls, indicating increased mucosal protection and regeneration. CONCLUSIONS: The significantly reduced susceptibility of mice overexpressing TGF-alpha to DSS further substantiates that endogenous TGF-alpha is a pivotal mediator of protection and/or healing mechanisms in the colon.
Subject(s)
Colitis/metabolism , Transforming Growth Factor alpha/physiology , Acute Disease , Animals , Body Weight , Cell Division , Colitis/chemically induced , Colitis/pathology , Colon/metabolism , Colon/pathology , Dextran Sulfate , Disease Susceptibility , Intestinal Mucosa/metabolism , Intestinal Mucosa/pathology , Male , Mice , Mice, Transgenic , Radioimmunoassay , Statistics, Nonparametric , Transforming Growth Factor alpha/analysis , Zinc/administration & dosageABSTRACT
The cell of origin of intrahepatic bile ducts during fetal development remains a subject of controversy, although there has been recent evidence that they form from hepatocytes. However, the origin of neoductules and ducts in the setting of liver disease has not been extensively investigated in humans. Using anticytokeratins characteristic of hepatocytes and bile ducts, we repeated earlier studies of fetal development to compare ductule formation in normal developing and newborn livers with the ductules formed during extrahepatic biliary atresia. We utilized an antibody to proliferating cell nuclear antigen (PCNA) staining to determine which cells were in active DNA synthesis (S phase) during fetal development and liver disease progression. The results indicated that hepatocytes undergo a phenotypic switch (metaplasia) to form ductular cells during fetal development. There was no ductular cell replication in the fetal livers. In contrast, both bile ductular metaplasia and proliferation were observed in biliary atresia. Therefore, both a limiting plate phenotypic switch to ductules and replication of ductular cells play a role in the increase in the ductules seen in the progression to biliary cirrhosis. Bile ductular proliferation in biliary atresia, however, was less than that seen in hepatocytes, whereas the number of bile ductules increased and the relative proportion of hepatocytes diminished as the accompanying periductular fibrosis progressed to cirrhosis.