Diverse Basis of β-Catenin Activation in Human Hepatocellular Carcinoma: Implications in Biology and Prognosis.
OBJECTIVE
β-catenin signaling is a major oncogenic pathway in hepatocellular carcinoma (HCC). Since β-catenin phosphorylation by glycogen synthase kinase 3β (GSK3β) and casein kinase 1ε (CK1ε) results in its degradation, mutations affecting these phosphorylation sites cause β-catenin stabilization. However, the relevance of missense mutations in non-phosphorylation sites in exon 3 remains unclear. The current study explores significance of such mutations in addition to addressing the clinical and biological implications of β-catenin activation in human HCC.


METHODS
Gene alteration in exon3 of CTNNB1, gene expression of β-catenin targets such as glutamate synthetase (GS), axin2, lect2 and regucalcin (RGN), and protein expression of β-catenin were examined in 125 human HCC tissues.


RESULTS
Sixteen patients (12.8%) showed conventional missense mutations affecting codons 33, 37, 41, and 45. Fifteen additional patients (12.0%) had other missense mutations in codon 32, 34, and 35. Induction of exon3 mutation caused described β-catenin target gene upregulation in HCC cell line. Interestingly, conventional and non-phosphorylation site mutations were equally associated with upregulation of β-catenin target genes. Nuclear localization of β-catenin was associated with poor overall survival (p = 0.0461). Of these patients with nuclear β-catenin localization, loss of described β-catenin target gene upregulation showed significant poorer overall survival than others (p = 0.0001).


CONCLUSIONS
This study suggests that both conventional and other missense mutations in exon 3 of CTNNB1 lead to β-catenin activation in human HCC. Additionally, the mechanism of nuclear β-catenin localization without upregulation of described β-catenin target genes might be of clinical importance depending on distinct mechanism.
Department of Gastroenterological Surgery, Graduate School of Life Sciences, Kumamoto University, Kumamoto, Japan.|Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
Hirohisa
H
Okabe
Department of Gastroenterological Surgery, Graduate School of Life Sciences, Kumamoto University, Kumamoto, Japan.
Hiroki
H
Kinoshita
Department of Gastroenterological Surgery, Graduate School of Life Sciences, Kumamoto University, Kumamoto, Japan.
Katsunori
K
Imai
Department of Gastroenterological Surgery, Graduate School of Life Sciences, Kumamoto University, Kumamoto, Japan.
Shigeki
S
Nakagawa
Department of Gastroenterological Surgery, Graduate School of Life Sciences, Kumamoto University, Kumamoto, Japan.
Takaaki
T
Higashi
Department of Gastroenterological Surgery, Graduate School of Life Sciences, Kumamoto University, Kumamoto, Japan.
Kota
K
Arima
Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Hideaki
H
Uchiyama
Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Toru
T
Ikegami
Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Norifumi
N
Harimoto
Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Shinji
S
Itoh
Department of Gastroenterological Surgery, Graduate School of Life Sciences, Kumamoto University, Kumamoto, Japan.
Takatoshi
T
Ishiko
Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Tomoharu
T
Yoshizumi
Department of Multidisciplinary Treatment for Gastroenterological Cancer, Kumamoto University Hospital, Kumamoto, Japan.
Toru
T
Beppu
Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.|Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
Satdarshan P S
SP
Monga
Department of Gastroenterological Surgery, Graduate School of Life Sciences, Kumamoto University, Kumamoto, Japan.
Hideo
H
Baba
Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Yoshihiko
Y
Maehara
D060466:Axin Protein / Q000235:genetics; D002135:Calcium-Binding Proteins / Q000235:genetics; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000473:pathology*; D045744:Cell Line, Tumor; D005091:Exons / Q000235:genetics; D015870:Gene Expression / Q000235:genetics; D005970:Glutamate Synthase / Q000235:genetics; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D008113:Liver Neoplasms / Q000235:genetics* / Q000473:pathology*; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation / Q000235:genetics; D011379:Prognosis; D015398:Signal Transduction / Q000235:genetics; D015854:Up-Regulation / Q000235:genetics; D051176:beta Catenin / Q000235:genetics*
C491761:AXIN2 protein, human; D060466:Axin Protein; C495270:CTNNB1 protein, human; D002135:Calcium-Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; C103468:LECT2 protein, human; C513323:RGN protein, human; D051176:beta Catenin; D005970:Glutamate Synthase