Hepatitis B virus X protein shifts human hepatic transforming growth factor (TGF)-beta signaling from tumor suppression to oncogenesis in early chronic hepatitis B.
Hepatitis B virus X (HBx) protein is suspected to participate in oncogenesis during chronic hepatitis B progression. Transforming growth factor beta (TGF-beta) signaling involves both tumor suppression and oncogenesis. TGF-beta activates TGF-beta type I receptor (TbetaRI) and c-Jun N-terminal kinase (JNK), which differentially phosphorylate the mediator Smad3 to become C-terminally phosphorylated Smad3 (pSmad3C) and linker-phosphorylated Smad3 (pSmad3L). Reversible shifting of Smad3-mediated signaling between tumor suppression and oncogenesis in HBx-expressing hepatocytes indicated that TbetaRI-dependent pSmad3C transmitted a tumor-suppressive TGF-beta signal, while JNK-dependent pSmad3L promoted cell growth. We used immunostaining, immunoblotting, and in vitro kinase assay to compare pSmad3L- and pSmad3C-mediated signaling in biopsy specimens representing chronic hepatitis, cirrhosis, or hepatocellular carcinoma (HCC) from 90 patients chronically infected with hepatitis B virus (HBV) with signaling in liver specimens from HBx transgenic mice. In proportion to plasma HBV DNA levels, early chronic hepatitis B specimens showed prominence of pSmad3L in hepatocytic nuclei. HBx-activated JNK/pSmad3L/c-Myc oncogenic pathway was enhanced, while the TbetaRI/pSmad3C/p21(WAF1) tumor-suppressive pathway was impaired as human and mouse HBx-associated hepatocarcinogenesis progressed. Of 28 patients with chronic hepatitis B who showed strong oncogenic pSmad3L signaling, six developed HCC within 12 years; only one of 32 patients showing little pSmad3L developed HCC. In contrast, seven of 30 patients with little Smad3C phosphorylation developed HCC, while no patient who retained hepatocytic tumor-suppressive pSmad3C developed HCC within 12 years.


CONCLUSIONS
HBx shifts hepatocytic TGF-beta signaling from the tumor-suppressive pSmad3C pathway to the oncogenic pSmad3L pathway in early carcinogenic process. Hepatocytic pSmad3L and pSmad3C assessment in HBV-infected liver specimens should prove clinically useful for predicting risk of HCC.
Murata
Miki
M
Department of Gastroenterology and Hepatology, Kansai Medical University, Osaka, Japan.
Matsuzaki
Koichi
K
Yoshida
Katsunori
K
Sekimoto
Go
G
Tahashi
Yoshiya
Y
Mori
Shigeo
S
Uemura
Yoshiko
Y
Sakaida
Noriko
N
Fujisawa
Junichi
J
Seki
Toshihito
T
Kobayashi
Kazuki
K
Yokote
Koutaro
K
Koike
Kazuhiko
K
Okazaki
Kazuichi
K
D000328:Adult; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000821:virology; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004279:DNA, Viral / Q000097:blood; D004268:DNA-Binding Proteins / Q000378:metabolism; D005260:Female; D019694:Hepatitis B, Chronic / Q000150:complications / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008103:Liver Cirrhosis / Q000150:complications; D008113:Liver Neoplasms / Q000821:virology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008875:Middle Aged; D010766:Phosphorylation; D015398:Signal Transduction; D051900:Smad3 Protein / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D054334:Viral Regulatory and Accessory Proteins / Q000378:metabolism*; D055815:Young Adult
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004279:DNA, Viral; D004268:DNA-Binding Proteins; C116115:MYCBP protein, human; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D048031:JNK Mitogen-Activated Protein Kinases