Inhibition of c-Jun NH2-terminal kinase switches Smad3 signaling from oncogenesis to tumor- suppression in rat hepatocellular carcinoma.
Transforming growth factor beta (TGF-beta) signaling involves both tumor-suppression and oncogenesis. TGF-beta activates the TGF-beta type I receptor (TbetaRI) and c-Jun N-terminal kinase (JNK), which differentially phosphorylate the mediator Smad3 to become COOH-terminally phosphorylated Smad3 (pSmad3C) and linker-phosphorylated Smad3 (pSmad3L). TbetaRI-dependent pSmad3C transmits a tumor-suppressive TGF-beta signal, while JNK-dependent pSmad3L promotes carcinogenesis in human chronic liver disorders. The aim of this study is to elucidate how SP600125, a JNK inhibitor, affected rat hepatocellular carcinoma (HCC) development, while focusing on the domain-specific phosphorylation of Smad3. The rats received subcutaneous injections of either SP600125 or vehicle 11 times weekly together with 100 ppm N-diethylnitrosamine (DEN) administration for 56 days and were sacrificed in order to evaluate HCC development 28 days after the last DEN administration. The number of tumor nodules greater than 3 mm in diameter and the liver weight/body weight ratio were significantly lower in the SP600125-treated rats than those in the vehicle-treated rats (7.9 +/- 0.8 versus 17.7 +/- 0.9: P < 0.001; 6.3 +/- 1.2 versus 7.1 +/- 0.2%: P < 0.05). SP600125 significantly prolonged the median survival time in rats with DEN-induced HCC (113 versus 97 days: log-rank P = 0.0018). JNK/pSmad3L/c-Myc was enhanced in the rat hepatocytes exposed to DEN. However, TbetaRI/pSmad3C/p21(WAF1) was impaired as DEN-induced HCC developed and progressed. The specific inhibition of JNK activity by SP600125 suppressed pSmad3L/c-Myc in the damaged hepatocytes and enhanced pSmad3C/p21(WAF1), acting as a tumor suppressor in normal hepatocytes.


CONCLUSIONS
Administration of SP600125 to DEN-treated rats shifted hepatocytic Smad3-mediated signal from oncogenesis to tumor suppression, thus suggesting that JNK could be a therapeutic target of human HCC development and progression.
Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Hiromitsu
H
Nagata
Etsuro
E
Hatano
Masaharu
M
Tada
Miki
M
Murata
Koji
K
Kitamura
Hiroyuki
H
Asechi
Masato
M
Narita
Atsuko
A
Yanagida
Nobuyuki
N
Tamaki
Shintaro
S
Yagi
Iwao
I
Ikai
Koichi
K
Matsuzaki
Shinji
S
Uemoto
D000818:Animals; D000873:Anthracenes / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D016147:Genes, Tumor Suppressor / Q000187:drug effects*; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors*; D008113:Liver Neoplasms / Q000201:enzymology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects; D051900:Smad3 Protein / Q000187:drug effects* / Q000502:physiology*
D000873:Anthracenes; D051900:Smad3 Protein; C497787:Smad3 protein, rat; C432165:pyrazolanthrone; D048031:JNK Mitogen-Activated Protein Kinases