Elevated expression of Wnt antagonists is a common event in hepatoblastomas.
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.
Koch
Arend
A
Department of Neuropathology, University of Bonn Medical Center, Bonn, Germany.
Waha
Andreas
A
Hartmann
Wolfgang
W
Hrychyk
Aksana
A
Schüller
Ulrich
U
Waha
Anke
A
Wharton
Keith A
KA
Fuchs
Serge Y
SY
von Schweinitz
Dietrich
D
Pietsch
Torsten
T
D048868:Adaptor Proteins, Signal Transducing; D000293:Adolescent; D000328:Adult; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000235:genetics; D045744:Cell Line, Tumor; D002648:Child; D019938:Cyclin D1 / Q000235:genetics; D003598:Cytoskeletal Proteins / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D018197:Hepatoblastoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D008113:Liver Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D020783:Matrix Metalloproteinase 7 / Q000235:genetics; D008875:Middle Aged; D009154:Mutation; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics; D055293:Receptors, Urokinase Plasminogen Activator; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000235:genetics; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000235:genetics; D051153:Wnt Proteins; D051176:beta Catenin; D044844:beta-Transducin Repeat-Containing Proteins / Q000235:genetics; D000099169:Fos-Related Antigen 1
D048868:Adaptor Proteins, Signal Transducing; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D019938:Cyclin D1; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; D020783:Matrix Metalloproteinase 7; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D051820:TCF Transcription Factors; D015534:Trans-Activators; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors; D051153:Wnt Proteins; D051176:beta Catenin; D044844:beta-Transducin Repeat-Containing Proteins; D000099169:Fos-Related Antigen 1; C495270:CTNNB1 protein, human; C489427:MYC protein, human; C449091:NKD1 protein, human; C524898:PLAUR protein, human; C544894:TCF7L2 protein, human