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Insulin‐like growth factor (IGF)‐II regulates CCAAT/enhancer binding protein α expression via phosphatidyl‐inositol 3 kinase in human hepatoblastoma cell lines

To reveal growth factor and its signal pathway to CCAAT/enhancer binding protein alpha (C/EBPα) in hepatocyte differentiation, we used Huh‐6 and HepG2, human hepatoblastoma (HBL) cell lines that maintain the expression of genes in hepatoblasts and remain at that stage of differentiation. Insulin‐like growth factor (IGF)‐II, hepatocyte growth factor (HGF), and dexamethasone (Dex) stimulated HBL cells for Northern blot analysis. Bromodeoxyuridine (BrdU) up‐take assay and Western blot analysis on albumin was performed to unveil proliferation and differentiation activity of IGF‐II. C/EBPα and phosphorylation of Akt were analyzed by Western blot analysis. LY294002 and wortmannin, specific inhibitors of PI3 kinase, and PD98059, a specific inhibitor of mitogen‐activated protein (MAP) kinase, were used to examine the signaling pathway of C/EBPα upregulated by IGF‐II. Luciferase assay was performed to study the promoter activity of C/EBPα. Actinomycin D was used to analyze half‐life of C/EBPα mRNA. IGF‐II up‐regualted C/EBPα by Northern blot and Western blot while HGF and Dex did not by Northern blot. IGF‐II promoted proliferation and differentiation by BrdU up‐take assay and Western blot analysis on albumin. Akt phosphorylated by IGF‐II, suggested that phosphatidyl‐inositol (PI) 3 kinase mediated the signaling pathway of IGF‐II. LY294002 and wortmannin suppressed expression of C/EBPα. IGF‐II activated the promoter activity and prolonged half‐life of mRNA, suggesting that IGF‐II activated promoter and stabilized mRNA. LY294002 and wortmannin suppressed the promoter activity of C/EBPα while PD98059 did not, suggesting that activation of the promoter was mediated by PI3 kinase. J. Cell. Biochem. 102: 161–170, 2007. © 2007 Wiley‐Liss, Inc.