The TSC1 gene product hamartin interacts with NADE.

Hamartomatous brain lesions are a hallmark of brain pathology of tuberous sclerosis complex (TSC). To elucidate the mechanism of tumor development in the brain of TSC, we identified NADE (p75NTR-associated cell death executor) as an interactor for TSC1 gene product hamartin using a yeast two-hybrid system. In a pull-down assay, endogenous NADE was purified with the immobilized coiled-coil domain (CCD) of hamartin from the PC12h cell lysate. Immunofluorescence and immunoprecipitation confirmed the interaction of hamartin and NADE in cultured neurons and mouse brain lysate. Hamartin constitutively associated with NADE to prevent its proteasomal degradation. Suppression of hamartin with TSC1 small interfering RNA (siRNA) caused reduction of NADE and failed to lead to NGF-induced apoptosis in PC12h cells. These results indicate that hamartin binds to NADE to regulate neuronal cell function and loss of this association is likely to contribute to the brain pathology in TSC.

Retinoic acid receptor alpha dominant negative form causes steatohepatitis and liver tumors in transgenic mice.

Although attention has focused on the chemopreventive action of retinoic acid (RA) in hepatocarcinogenesis, the functional role of RA in the liver has yet to be clarified. To explore the role of RA in the liver, we developed transgenic mice expressing RA receptor (RAR) alpha- dominant negative form in hepatocytes using albumin promoter and enhancer. At 4 months of age, the RAR alpha- dominant negative form transgenic mice developed microvesicular steatosis and spotty focal necrosis. Mitochondrial beta-oxidation activity of fatty acids and expression of its related enzymes, including VLCAD, LCAD, and HCD, were down-regulated; on the other hand, peroxisomal beta-oxidation and its related enzymes, including AOX and BFE, were up-regulated. Expression of cytochrome p4504a10, cytochrome p4504a12, and cytochrome p4504a14 was increased, suggesting that omega-oxidation of fatty acids in microsomes was accelerated. In addition, formation of H2O2 and 8-hydroxy-2'-deoxyguanosine was increased. After 12 months of age, these mice developed hepatocellular carcinoma and adenoma of the liver. The incidence of tumor formation increased with age. Expression of beta-catenin and cyclin D1 was enhanced and the TCF-4/beta-catenin complex was increased, whereas the RAR alpha/ beta-catenin complex was decreased. Feeding on a high-RA diet reversed histological and biochemical abnormalities and inhibited the occurrence of liver tumors. These results suggest that hepatic loss of RA function leads to the development of steatohepatitis and liver tumors. In conclusion, RA plays an important role in preventing hepatocarcinogenesis in association with fatty acid metabolism and Wnt signaling.

Hepatocyte growth factor exerts a proliferative effect on oval cells through the PI3K/AKT signaling pathway.

Hepatocyte growth factor (HGF) is a potent mitogen for a variety of cells including hepatocytes. While rat oval cells are supposed to be one of hepatic stem cells, biological effects of HGF on oval cells and their relevant signal transduction pathways remain to be determined. We sought to investigate them on OC/CDE22 rat oval cells, which are established from the liver of rats fed a choline-deficient/DL-ethionine-supplemented diet. The oval cells were cultured on fibronectin-coated dishes and stimulated with recombinant HGF, transforming growth factor-alpha (TGF-alpha), and thrombopoietin (TPO) under the serum-free medium condition. HGF treatment enhanced [3H]thymidine incorporation into oval cells in a dose-dependent manner. On the contrary, treatment with TGF-alpha or TPO had no significant effects on [3H]thymidine incorporation into the oval cells. c-Met protein was phosphorylated at the tyrosine residues after the HGF treatment. AKT, extracellular signal-regulated kinase 1/2 (ERK1/2), and p70(s6k) were simultaneously activated after the HGF stimulation, peaking at 30min after the treatment. The activation of AKT, p70(s6k), and ERK1/2 induced by HGF was abolished by pre-treatment with LY294002, a phosphoinositide 3-OH kinase (PI3K) inhibitor, and U0126, a mitogen-activated protein kinase/ERK kinase (MEK) inhibitor, respectively. When the cells were pre-treated with LY294002 prior to the HGF stimulation, the proliferative action of HGF was completely abrogated, implying that the PI3K/AKT signaling pathway is responsible for the biological effect of HGF. These in vitro data indicate that HGF exerts a proliferative action on hepatic oval cells via activation of the PI3K/AKT signaling pathway.

Expression of 8-hydroxy-2'-deoxyguanosine in chronic liver disease and hepatocellular carcinoma.

Reactive oxygen species may be involved in the progression of chronic liver disease and the occurrence of hepatocellular carcinoma (HCC). To clarify whether clinicopathological findings in liver diseases are related to oxidative DNA damage, hepatic expression of the 8-hydroxy-2'-deoxyguanosine (8-OHdG) was examined in 75 liver disease patients, which included 32 chronic hepatitis (CH), 13 liver cirrhosis (LC) and 30 HCC patients. The CH patients had higher 8-OHdG-positive hepatocytes than LC (P < 0.05). In CH and LC, the number of 8-OHdG-positive hepatocytes was correlated with alanine aminotransferase and asparate aminotransferase (P < 0.01 and P < 0.05, respectively). Of 30 HCC cases, 25 cases (83%) showed stronger immunoreactivity than non-cancerous counterparts. The patients with poorly differentiated HCC had a larger tumor size and higher levels of AFP, and exhibited higher labeling indices of PCNA-, TUNEL- and 8-OHdG-positive cells than those with well and moderately differentiated HCC. Our findings suggest that oxidative DNA damage is increased in association with necroinflammation in chronic liver disease and determination of 8-OHdG is useful in assessing high-grade malignancy in HCC.