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Switch from Mnt-Max to Myc-Max induces p53 and cyclin D1 expression and apoptosis during cholestasis in mouse and human hepatocytes.

ABSTRACT: Toxic bile acids induce hepatocyte apoptosis, for which p53 and cyclin D1 have been implicated as underlying mediators. Both p53 and cyclin D1 are targets of c-Myc, which is also up-regulated in cholestasis. Myc and Mnt use Max as a cofactor for DNA binding. Myc-Max typically activates transcription via E-box binding. Mnt-Max also binds the E-box sequence but serves as a repressor and inhibits the enhancer activity of Myc-Max. The current work tested the hypothesis that the switch from Mnt-Max to Myc-Max is responsible for p53 and cyclin D1 up-regulation and apoptosis during cholestasis. Following common bile duct ligation or left hepatic bile duct ligation, the expression of p53, c-Myc, and cyclin D1 increased markedly, whereas Mnt expression decreased. Nuclear binding activity of Myc to the E-box element of p53 and cyclin D1 increased, whereas that of Mnt decreased in a time-dependent fashion. Lithocholic acid (LCA) treatment of primary human hepatocytes and HuH-7 cells induced a similar switch from Mnt to Myc and increased p53 and cyclin D1 promoter activity and endogenous p53 and cyclin D1 expression and apoptosis. Blocking c-Myc induction in HuH-7 cells prevented the LCA-mediated increase in p53 and cyclin D1 expression and reduced apoptosis. Lowering Mnt expression further enhanced LCA's inductive effect on p53 and cyclin D1. Bile duct-ligated mice treated with a lentivirus harboring c-myc small interfering RNA were protected from hepatic induction of p53 and cyclin D1, a switch from Mnt to Myc nuclear binding to E-box, and hepatocyte apoptosis.The switch from Mnt to Myc during bile duct ligation and in hepatocytes treated with LCA is responsible for the induction in p53 and cyclin D1 expression and contributes to apoptosis.

SUBMITTER: Yang H

PROVIDER: S-EPMC4427513 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature

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Switch from Mnt-Max to Myc-Max induces p53 and cyclin D1 expression and apoptosis during cholestasis in mouse and human hepatocytes.

Yang Heping H Li Tony W H TW Ko Kwang Suk KS Xia Meng M Lu Shelly C SC

Hepatology (Baltimore, Md.) 20090301 3

<h4>Unlabelled</h4>Toxic bile acids induce hepatocyte apoptosis, for which p53 and cyclin D1 have been implicated as underlying mediators. Both p53 and cyclin D1 are targets of c-Myc, which is also up-regulated in cholestasis. Myc and Mnt use Max as a cofactor for DNA binding. Myc-Max typically activates transcription via E-box binding. Mnt-Max also binds the E-box sequence but serves as a repressor and inhibits the enhancer activity of Myc-Max. The current work tested the hypothesis that the sw ...[more]

PMID: 19086036

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Project description:ObjectiveOsteosarcoma is a rare primary malignant tumor of the bone characterized by poor survival rates, owing to its unclear pathogenesis. Rho GTPase-activating protein 44 (ARHGAP44), which belongs to the Rho GTPase-activating protein family, has promising applications in the targeted therapy of tumors. Therefore, this study aimed to investigate the biological function of ARHGAP44 in osteosarcoma and its possible application as a therapeutic target.MethodsThe expression level of ARHGAP44 in osteosarcoma and its relationship with tumor prognosis were detected using Gene Expression Omnibus database analysis and immunohistochemical staining of clinical specimens. The cell model of ARHGAP44 knockdown was constructed, and the effects of this gene on the malignant biological behavior of osteosarcoma cells were investigated using CCK-8, clone formation, transwell invasion, wound healing, and flow cytometry assays. Western blotting was performed to detect the expression of ARHGAP44, p53, C-myc, and Cyclin D1 in osteosarcoma.ResultsBiogenic analysis showed that ARHGAP44 was highly expressed in osteosarcoma. This result was associated with poor tumor prognosis and negatively correlated with the expression of the tumor suppressor gene p53. Immunohistochemistry and western blotting revealed significantly upregulated expression of ARHGAP44 in osteosarcoma tissues. Additionally, Kaplan-Meier analysis of clinical specimens suggested that ARHGAP44 was negatively correlated with tumor prognosis. CCK-8, clone formation, transwell invasion, wound healing, and flow cytometry assays showed that downregulation of ARHGAP44 expression significantly reduced the malignant biological behavior of osteosarcoma cells. Furthermore, western blotting showed that the expression level of p53 in osteosarcoma cells was significantly increased after the downregulation of ARHGAP44 expression, whereas the expression of C-myc and Cyclin D1 was significantly decreased compared with that in the control group.ConclusionARHGAP44 was highly expressed in osteosarcoma and was negatively correlated with its prognosis. The downregulation of ARHGAP44 expression reduced the malignant biological behavior of osteosarcoma cells. These findings suggest that the downregulation of ARHGAP44 expression inhibits the malignant progression of osteosarcoma by regulating the p53/C-myc/Cyclin D1 pathway, demonstrating the potential of ARHGAP44 as a therapeutic target for osteosarcoma.

Dataset Information

Switch from Mnt-Max to Myc-Max induces p53 and cyclin D1 expression and apoptosis during cholestasis in mouse and human hepatocytes.

Publications

Switch from Mnt-Max to Myc-Max induces p53 and cyclin D1 expression and apoptosis during cholestasis in mouse and human hepatocytes.

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