Correlation between beta-catenin mutations and expression of Wnt-signaling target genes in hepatocellular carcinoma.
Aberrant Wnt-signaling caused by mutants of beta-catenin, a key regulator of the canonical Wnt-signaling pathway, is frequently detected in cancer. Only recently, it was suggested that in hepatocellular carcinoma (HCC) the expression of the target gene glutamine synthetase (GS) is a highly reliable marker for the identification of beta-catenin mutations. In order to prove this hypothesis, 52 samples from human hepatocellular carcinomas were analysed for the activation of beta-catenin and the expression of GS. In total, 45 samples stained positive for cytoplasmic/nuclear beta-catenin. A strong correlation between expression of GS and activated beta-catenin (100% of nuclear and 84% of cytosolic) was found. However, among 35 GS positive tumors that were analysed for beta-catenin mutations no mutations were detected in 25 GS-positive carcinomas although 24 out of the 25 carcinomas exhibited at least abnormal expression of beta-catenin. Since the mutational analysis identified 9 different point mutations of the beta-catenin gene including the rare mutation H36P and the yet unknown mutation P44A it was asked whether these mutations may differently effect beta-catenin target genes. Therefore, expression plasmids for different mutations were constructed and cotransfected with the TOP-flash luciferase reporter and a reporter carrying the GS-5'-enhancer. The experiments confirmed that there are differences between different beta-catenin target sequences and different beta-catenin mutations. In addition, the failure that the endogenous expression of GS in GS-negative cells was not induced by the transient transfection experiment indicated that the effect of beta-catenin on the GS-5'-enhancer is only one aspect of gene activation induced by beta-catenin.
Austinat
Madeleine
M
Institute for Biochemistry, Medical Faculty, University of Leipzig, Johannisallee 30, 04103 Leipzig, Germany. Austinat_M@klinik.uni-wuerzburg.de
Dunsch
Ruediger
R
Wittekind
Christian
C
Tannapfel
Andrea
A
Gebhardt
Rolf
R
Gaunitz
Frank
F
D024506:5' Flanking Region / Q000502:physiology; D019943:Amino Acid Substitution / Q000502:physiology; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008113:Liver Neoplasms / Q000235:genetics* / Q000378:metabolism; D017354:Point Mutation / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D051153:Wnt Proteins / Q000502:physiology*; D051176:beta Catenin / Q000235:genetics* / Q000378:metabolism
D051153:Wnt Proteins; D051176:beta Catenin; D005974:Glutamate-Ammonia Ligase