Abstract
Hepatoblastomas are the most frequent malignant liver tumors of childhood. A high frequency of activating beta-catenin mutations in hepatoblastomas indicates that the Wnt signaling pathway plays an important role in the development of this embryonic neoplasm. Stabilization of beta-catenin leads to an increased formation of nuclear beta-catenin-T-cell factor complexes and altered expression of Wnt-inducible target genes. In this study, we analyzed the mRNA expression levels of nine Wnt genes, including c-JUN, c-MYC, CYCLIN D1, FRA-1, NKD-1, ITF-2, MMP-7, uPAR, and beta-TRCP, by competitive reverse transcription-PCR. We analyzed 23 hepatoblastoma biopsies for which matching liver tissue was available, 6 hepatoblastoma cell lines, and 3 human fetal liver samples. beta-TRCP and NKD-1 were highly expressed in all hepatoblastoma samples, independent of the beta-catenin mutational status, in comparison with their nontumorous counterparts. beta-TRCP mRNA overexpression was associated with accumulation of intracytoplasmic and nuclear beta-TrCP protein. In human liver tumor cells without beta-catenin mutations, Nkd-1 inhibited the Wnt-3a-activated Tcf-responsive-luciferase reporter activity, whereas Nkd-1 in hepatoblastomas with beta-catenin mutations had no antagonistic effect. Our data emphasize the inhibitory effect of beta-TrCP and Nkd-1 on the Wnt signaling pathway in a manner analogous to Conductin (AXIN2) and Dkk-1, inhibitors shown previously to be up-regulated in hepatoblastomas. Our findings indicate that overexpression of the Wnt antagonists Nkd-1 and beta-TrCP reveals an activation of the Wnt signaling pathway as a common event in hepatoblastomas. We propose that Nkd-1 and beta-TrCP may be used as possible diagnostic markers for the activated Wnt signaling pathway in hepatoblastomas.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing
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Adolescent
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Adult
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Calcium-Binding Proteins
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Carrier Proteins / genetics
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Cell Line, Tumor
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Child
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Cyclin D1 / genetics
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Cytoskeletal Proteins / genetics
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DNA-Binding Proteins / genetics
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Female
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Gene Expression Regulation, Neoplastic*
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Hepatoblastoma / genetics*
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Hepatoblastoma / metabolism
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Hepatoblastoma / pathology
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Humans
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Intercellular Signaling Peptides and Proteins / metabolism*
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Liver Neoplasms / genetics*
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Liver Neoplasms / metabolism
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Liver Neoplasms / pathology
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Male
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Matrix Metalloproteinase 7 / genetics
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Middle Aged
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Mutation
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Proto-Oncogene Proteins c-fos / genetics
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Proto-Oncogene Proteins c-jun / genetics
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Proto-Oncogene Proteins c-myc / genetics
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Receptors, Cell Surface / genetics
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Receptors, Urokinase Plasminogen Activator
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Reverse Transcriptase Polymerase Chain Reaction
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Signal Transduction
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TCF Transcription Factors
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Trans-Activators / genetics
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Transcription Factor 7-Like 2 Protein
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Transcription Factors / genetics
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Wnt Proteins
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beta Catenin
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beta-Transducin Repeat-Containing Proteins / genetics
Substances
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Adaptor Proteins, Signal Transducing
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CTNNB1 protein, human
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Calcium-Binding Proteins
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Carrier Proteins
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Cytoskeletal Proteins
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DNA-Binding Proteins
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Intercellular Signaling Peptides and Proteins
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MYC protein, human
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NKD1 protein, human
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PLAUR protein, human
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Proto-Oncogene Proteins c-fos
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Proto-Oncogene Proteins c-jun
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Proto-Oncogene Proteins c-myc
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RNA, Messenger
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Receptors, Cell Surface
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Receptors, Urokinase Plasminogen Activator
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TCF Transcription Factors
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TCF7L2 protein, human
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Trans-Activators
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Transcription Factor 7-Like 2 Protein
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Transcription Factors
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Wnt Proteins
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beta Catenin
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beta-Transducin Repeat-Containing Proteins
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fos-related antigen 1
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Cyclin D1
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Matrix Metalloproteinase 7