CCAAT/Enhancer Binding Protein α Knock-in Mice Exhibit Early Liver Glycogen Storage and Reduced Susceptibility to Hepatocellular Carcinoma

Abstract

The CCAAT/enhancer binding protein A (C/EBPA) 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/EBPA. Recent work showed reductions of C/EBPA levels in human hepatocellular carcinoma with the reductions correlating to tumor size and progression. We investigated the potential of reactivating c/ebpa expression during hepatic carcinogenesis to prevent tumor cell growth. We have developed a c/ebpa knock-in mouse in which a single-copy c/ebpa is regulated by one allele of the A-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/ebpa 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/EBPA content in WT nodules whereas knock-in nodules stained strongly for C/EBPA. The p21 protein was examined because it mediates a C/EBPA 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/EBPA-positive nodules were positive for nuclear p21, suggesting that C/EBPA may be required to direct p21 to the cell nucleus to inhibit growth. Our data establish that controlled C/EBPA production can inhibit liver tumor growth in vivo. (Cancer Res 2005; 65(22): 10330-7)

The polymorphism rs944289 predisposes to papillary thyroid carcinoma through a large intergenic noncoding RNA gene of tumor suppressor type

“…C/EBPα is a major player in hematopoietic differentiation, and its involvement in hematologic malignancies is very well documented (37,38). It also has been described as a tumor suppressor in lung and liver tumors (39,40). The function of C/EBPβ in tumorigenesis is less investigated (41,42).…”

Elimination of C/EBPα through the ubiquitin-proteasome system promotes the development of liver cancer in mice

“…Liver tumors were induced by DEN/PB tumor liver induction protocol as described (8). 5 μg DEN/g body weight was injected into WT and S193D mice, and then mice were provided with PB (0.05%) in drinking water.…”

“…Given the strong inhibition of liver proliferation after PH in S193D knockin mice, we expected that these animals should be resistant to the development of tumors. To test this suggestion, we applied DEN/PB tumor liver induction protocol (8). We surprisingly found that the S193D mice developed tumors much earlier than WT mice ( Figure 3A).…”

“…The constitutional deletion of the C/EBPα gene causes mice to die shortly after birth due to impaired energy homeostasis (5). Numerous studies have shown that C/EBPα supports liver quiescence (3,(6)(7)(8)(9). While the energy metabolism and expression of liver-specific genes are controlled by transcriptional activity of C/EBPα, the growth inhibitory activity of C/EBPα is mediated by direct interactions of C/EBPα with cell-cycle proteins (8)(9)(10)(11).…”

“…It has been shown that C/EBPα utilizes different mechanisms in different tissues. C/EBPα growth inhibitory activity in liver of young animals is mediated through direct interactions with cdk2 (8)(9)(10)(11). In adipose and myeloid tissues, the antiproliferative effects of C/EBPα are mediated through repression of E2F-dependent transcription (12).…”