Takato Ueno

Hepatitis C virus down-regulates insulin receptor substrates 1 and 2 through up-regulation of suppressor of cytokine signaling 3

The pathogenesis of hepatitis C virus (HCV)-associated insulin resistance remains unclear. Therefore, we investigated mechanisms for HCV-associated insulin resistance. Homeostasis model assessment for insulin resistance was increased in patients with HCV infection. An increase in fasting insulin levels was associated with the presence of serum HCV core, the severity of hepatic fibrosis and a decrease in expression of insulin receptor substrate (IRS) 1 and IRS2, central molecules of the insulin-signaling cascade, in patients with HCV infection. Down-regulation of IRS1 and IRS2 was also seen in HCV core-transgenic mice livers and HCV core-transfected human hepatoma cells. Carbobenzoxy-l-leucyl-l-leucyl-l-leucinal, a potent proteosomal proteolysis inhibitor, blocked down-regulation of IRS1 and IRS2 in HCV core-transfected hepatoma cells. In human hepatoma cells, HCV core up-regulated suppressor of cytokine signaling (SOCS) 3 and caused ubiquitination of IRS1 and IRS2. HCV core-induced down-regulation of IRS1 and IRS2 was not seen in SOCS3(-/-) mouse embryonic fibroblast cells. Furthermore, HCV core suppressed insulin-induced phosphorylation of p85 subunit of phosphatidylinositol 3-kinase and Akt, activation of 6-phosphofructo-2-kinase, and glucose uptake. In conclusion, HCV infection changes a subset of hepatic molecules regulating glucose metabolism. A possible mechanism is that HCV core-induced SOCS3 promotes proteosomal degradation of IRS1 and IRS2 through ubiquitination.

Telmisartan inhibits AGE-induced C-reactive protein production through downregulation of the receptor for AGE via peroxisome proliferator-activated receptor-gamma activation

Aims/hypothesisC-reactive protein (CRP), an acute-phase reactant produced mainly by the liver, is elevated in diabetes, thus contributing to the development and progression of atherosclerosis. However, the molecular mechanism underlying the elevation of CRP in diabetes is not fully understood. Since a crosstalk between AGE and angiotensin II (Ang II) has been proposed in the pathogenesis of accelerated atherosclerosis in diabetes, we examined here whether and how telmisartan, a unique Ang II type 1 receptor blocker (ARB) with peroxisome proliferator-activated receptor-γ (PPAR-γ)-modulating activity, could inhibit AGE-induced CRP expression in a human hepatoma cell line, Hep3B cells.MethodsProtein levels of the receptor for AGE (RAGE) were analysed by western blots. Gene expression was analysed by quantitative real-time RT-PCR. CRP released into the medium was measured with ELISA. Intracellular formation of reactive oxygen species (ROS) was measured using the fluorescent probe CM-H2DCFDA.ResultsTelmisartan, but not candesartan, another ARB, downregulated RAGE mRNA levels in a dose-dependent manner. Telmisartan decreased basal as well as AGE-induced RAGE protein expression in Hep3B cells. Furthermore, telmisartan dose-dependently inhibited AGE-induced ROS generation and subsequent CRP gene and protein induction in Hep3B cells. GW9662, an inhibitor of PPAR-γ, blocked the inhibitory effects of telmisartan on RAGE expression and its downstream signalling in Hep3B cells.Conclusions/interpretationOur present study indicates a unique beneficial aspect of telmisartan: it may work as an anti-inflammatory agent against AGE by suppressing RAGE expression via PPAR-γ activation in the liver and may play a protective role in vascular injury in diabetes.

The Wilson Disease Protein ATP7B Resides in the Late Endosomes with Rab7 and the Niemann-Pick C1 Protein

Wilson disease is a genetic disorder characterized by the accumulation of copper in the body due to a defect of biliary copper excretion. Although the Wilson disease gene has been cloned, the cellular localization of the gene product (ATP7B) has not been fully clarified. Therefore, the precise physiological action of ATP7B is still unknown. We examined the distribution of ATP7B using an anti-ATP7B antibody, green fluorescent protein (GFP)-ATP7B (GFP-ATP7B) and ATP7B-DsRed in various cultured cells. Intracellular organelles were visualized by fluorescence microscopy. The distribution of ATP7B was compared with that of Rab7 and Niemann-Pick C1 (NPC1), proteins that localize in the late endosomes. U18666A, which induces the NPC phenotype, was used to modulate the intracellular vesicle traffic. GFP-ATP7B colocalized with various late endosome markers including Rab7 and NPC1 but not with Golgi or lysosome markers. U18666A induced the formation of late endosome-lysosome hybrid organelles, with GFP-ATP7B localized with NPC1 in these structures. We have confirmed that ATP7B is a late endosome-associated membrane protein. ATP7B appears to translocate copper from the cytosol to the late endosomal lumen, thus participating in biliary copper excretion via lysosomes. Thus, defective copper ATPase activity of ATP7B in the late endosomes appears to be the main defect of Wilson disease.

High expression of insulin-like growth factor binding protein-3 is correlated with lower portal invasion and better prognosis in human hepatocellular carcinoma

Insulin‐like growth factor binding protein‐3 (IGFBP‐3) modulates cell proliferation of various cancer cell types. However, it remains unclear how IGF–IGFBP‐3‐signaling is involved in growth and progression of hepatocellular carcinoma (HCC). The aim of the present study was to evaluate the role of IGFBP‐3 in HCC. Type 1 receptor for IGF (IGF‐1R) was expressed at various levels in the seven lines examined, but IGF‐2R was not expressed. Of the seven lines, the growth of HAK‐1B, KIM‐1, KYN‐2 and HepG2 cells was stimulated in a dose‐dependent manner by the exogenous addition of IGF‐I or IGF‐II, but the HAK‐1A, KYN‐1 and KYN‐3 cell lines showed no growth. Exogenous addition of IGFBP‐3 markedly blocked IGF‐I and IGF‐II‐stimulated cell growth of KYN‐2 and HepG2 cells, and moderately stimulated that of KIM‐1 and HAK‐1B cells, but no growth of the KYN‐1, KYN‐3 and HAK‐1A cell lines was observed. IGF‐I enhanced the phosphorylation of IGF‐1R, Akt and Erk1/2 in KYN‐2 cells, and coadministration of IGFBP‐3 blocked all types of activation by IGF‐I investigated here. In contrast, no such activation by IGF‐I was detected in KYN‐3 cells. IGFBP‐3 also suppressed IGF‐I‐induced cell invasion by KYN‐2 cells. Moreover, we were able to observe the apparent expression of IGFBP‐3 in KYN‐3 cells, but not in the other six cell lines. Furthermore reduced expression of IGFBP‐3, but not that of IGF‐1R, was significantly correlated with tumor size, histological differentiation, capsular invasion and portal venous invasion. Low expression of IGFBP‐3 was independently associated with poor survival. IGFBP‐3 could be a molecular target of intrinsic importance for further development of novel therapeutic strategy against HCC. (Cancer Sci 2006; 97: 1182–1190)

Pathogenesis and Significance of Restricted Diet and Exercise Therapy in Nonalcoholic Steatohepatitis (NASH)

The risk factors that are most strongly associated with nonalcoholic fatty liver disease (NAFLD) are: age greater than 40 to 50 years, and severe obesity, diabetes mellitus (DM), or hyperlipidemia (especially hypertriglyceridemia). The pathogenesis of nonalcoholic steatohepatitis (NASH) is multifactorial. Insulin resistance, fatty acids, and oxidant stress may be important pathogenic factors in NASH. Efforts are presently underway to define the role of these factors and to determine whether modifying them (for example, by improving insulin sensitivity) could be effective in the treatment of the condition. At present, lifestyle changes involving exercise and dietary restrictions appear to be an effective means of improving NASH. Physicians should actively check for the presence of NAFLD in those who are overweight and who have diabetes mellitus. The treatment is usually directed toward optimizing body weight. The role of pharmacological agents remains to be established, and much more work is necessary to define the pathogenesis of NASH and to develop effective treatments.