title: CCAAT/enhancer binding protein alpha knock-in mice exhibit early liver glycogen storage and reduced susceptibility to hepatocellular carcinoma.
abstract: The CCAAT/enhancer binding protein alpha (C/EBPalpha) is vital for establishing normal hepatic energy homeostasis and moderating hepatocellular growth. CEBPA loss-of-function mutations identified in acute myeloid leukemia patients support a tumor suppressor role for C/EBPalpha. Recent work showed reductions of C/EBPalpha levels in human hepatocellular carcinoma with the reductions correlating to tumor size and progression. We investigated the potential of reactivating c/ebpalpha expression during hepatic carcinogenesis to prevent tumor cell growth. We have developed a c/ebpalpha knock-in mouse in which a single-copy c/ebpalpha is regulated by one allele of the alpha-fetoprotein (AFP) gene promoter. The knock-in mice are physically indistinguishable from wild-type (WT) controls. However, knock-in animals were found to deposit fetal hepatic glycogen earlier than WT animals. Quantitative real-time PCR confirmed early c/ebpalpha expression and early glycogen synthase gene activation in knock-in fetuses. We then used diethylnitrosamine to induce hepatocellular carcinoma in our animals. Diethylnitrosamine produced half the number of hepatocellular nodules in knock-in mice as in WT mice. Immunohistochemistry showed reduced C/EBPalpha content in WT nodules whereas knock-in nodules stained strongly for C/EBPalpha. The p21 protein was examined because it mediates a C/EBPalpha growth arrest pathway. Nuclear p21 was absent in WT nodules whereas cytoplasmic p21 was abundant; knock-in nodules were positive for nuclear p21. Interestingly, only C/EBPalpha-positive nodules were positive for nuclear p21, suggesting that C/EBPalpha may be required to direct p21 to the cell nucleus to inhibit growth. Our data establish that controlled C/EBPalpha production can inhibit liver tumor growth in vivo.
authors.affiliation: Department of Physiology, National University of Singapore, Singapore.
authors.forename: Ee Hong
authors.initials: EH
authors.lastname: Tan
authors.forename: Shing Chuan
authors.initials: SC
authors.lastname: Hooi
authors.forename: Mirtha
authors.initials: M
authors.lastname: Laban
authors.forename: Esther
authors.initials: E
authors.lastname: Wong
authors.forename: Sathivel
authors.initials: S
authors.lastname: Ponniah
authors.forename: Aileen
authors.initials: A
authors.lastname: Wee
authors.forename: Nai-dy
authors.initials: ND
authors.lastname: Wang
mesh_terms: D000483:Alleles; D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D048708:Cell Growth Processes / Q000235:genetics / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D020022:Genetic Predisposition to Disease; D006006:Glycogen Synthase / Q000096:biosynthesis; D008099:Liver / Q000378:metabolism; D008112:Liver Glycogen / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000517:prevention & control; D051379:Mice; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D000509:alpha-Fetoproteins / Q000235:genetics
chemical_list: D022763:CCAAT-Enhancer-Binding Protein-alpha; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D008112:Liver Glycogen; D012333:RNA, Messenger; D000509:alpha-Fetoproteins; D006006:Glycogen Synthase