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A novel GSK‐3 beta–C/EBP alpha–miR‐122–insulin‐like growth factor 1 receptor regulatory circuitry in human hepatocellular carcinoma
Author(s) -
Zeng Chunxian,
Wang Ruizhi,
Li Daochuan,
Lin XueJia,
Wei QingKun,
Yuan Yunfei,
Wang Qing,
Chen Wen,
Zhuang ShiMei
Publication year - 2010
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.23875
Subject(s) - transactivation , chromatin immunoprecipitation , gene knockdown , mir 122 , biology , ccaat enhancer binding proteins , microbiology and biotechnology , transcription factor , microrna , nuclear receptor , carcinogenesis , cancer research , promoter , gene expression , nuclear protein , apoptosis , gene , biochemistry
miR‐122 is a highly abundant, hepatocyte‐specific microRNA. The biomedical significance and regulatory mechanisms of miR‐122 remain obscure. We explored the role of miR‐122 in tumorigenesis in the context of gene regulatory network. The miR‐122 promoter and its transactivator were identified by way of luciferase reporter system, electrophoretic mobility shift, and chromatin immunoprecipitation assays. The miR‐122 regulatory circuitry and its implication in hepatocarcinogenesis were identified using livers of different development stages, human hepatocellular carcinoma (HCC) tissues and cell lines, and aflatoxin B 1 (AFB 1 )‐transformed cells. We characterized the −5.3 to −4.8 kb region upstream of miR‐122 precursor as miR‐122 promoter. Further investigation revealed that deletion of predicted CCAAT/enhancer‐binding protein alpha (C/EBPα) binding sites C/EBPα knockdown significantly reduced miR‐122 promoter activity and endogenous miR‐122 expression; and C/EBPα directly interacted with the miR‐122 promoter in vitro and in vivo . These data suggest that C/EBPα is a transactivator for miR‐122 transcription. We further demonstrated that miR‐122 suppressed insulin‐like growth factor 1 receptor (IGF‐1R) translation and sustained glycogen synthase kinase‐3 beta (GSK‐3β) activity. The activated GSK‐3β not only repressed cell proliferation, but also activated C/EBPα, which maintained miR‐122 levels and thereby enforced IGF‐1R suppression. Interestingly, down‐regulation of miR‐122 and C/EBPα, and up‐regulation of IGF‐1R were frequently observed in HCC tissues, and decreased miR‐122 levels were associated with worse survival of HCC patients. Moreover, AFB 1 exposure resulted in decreased activity in GSK‐3β, C/EBPα, and miR‐122 and increased levels of IGF‐1R, whereas restoration of miR‐122 suppressed the tumorigenicity of HCC and AFB 1 ‐transformed cells. Conclusion : We have identified a novel GSK‐3β–C/EBPα–miR‐122–IGF‐1R regulatory circuitry whose dysfunction may contribute to the development of HCC. Our findings provide new insight into miR‐122's function and the mechanisms of hepatocarcinogenesis. (Hepatology 2010;52:1702‐1712)