外源性p53诱导肝癌细胞Wnt通路抑制因子Dickkopf-1的表达

研究p53对Wnt通路抑制抑制因子Dickkopf-1(DKK-1)表达的调节作用,将携带p53基因的复制缺陷型腺病毒载体(Adp53)导入到p53缺失的人肝癌细胞株Hep3B中,以RT-PCR技术检测p53对DKK-1表达的调节作用．检测结果表明DKK-1 mRNA水平在转染p53 20h后即有明显升高,其中以32h达最高水平,随后逐渐降低,量效关系研究表明在转染剂量为0、5、5、50pfu／cell的Adp53时DKK-1mRNA表达均有显著增高,尤以50pfu／cell时表达水平最高。提示p53能明显诱导Wnt通路抑制因子DKK-1的mRNA表达。     

Differential regulation of ARE-mediated TNFalpha and IL-1beta mRNA stability by lipopolysaccharide in RAW264.7 cells

Messenger RNA degradation is a mechanism by which eukaryotic cells regulate gene expression and influence cell growth and differentiation. Many protooncogene, cytokine, and growth factor RNAs contain AU-rich element (AREs) in the 3'untranslated regions which enable them to be targeted for rapid degradation. To investigate the mechanism of ARE-mediated RNA stability, we demonstrate the expression and regulation of TNFalpha and IL-1beta mRNAs in LPS-stimulated macrophages. TNFalpha mRNA was rapidly induced by LPS and showed short half-life at 2-h induction, whereas IL-1beta mRNA was induced slowly and had longer half-life. Electrophoretic mobility shift assays showed that the LPS-induced destabilization factor tristetraprolin (TTP) could bind to TNFalpha ARE with higher affinity than to IL-1beta ARE. HuR was identified to interact with TNFalpha ARE to exert RNA stabilization activity. The expression and phosphorylation of TTP could be activated by p38 MAPK pathway during LPS stimulation. Moreover, ectopic expression with TTP and kinases in p38 pathway followed by biochemical assays showed that the activation of p38 pathway resulted in the phosphorylation of TTP and a decrease in its RNA-binding activity. The ARE-containing reporter assay presented that the p38 signal could reverse the inhibitory activity of TTP on IL-1beta ARE but not on TNFalpha ARE. The present results indicate that the heterogeneity of AREs from TNFalpha and IL-1beta could reflect distinct ARE-binding proteins to modulate their RNA expression.     

2-羟基-3-甲基蒽醌抑制结直肠癌的作用及机制研究

为观察2-羟基-3-甲基蒽醌(HMA)对结直肠癌细胞增殖的影响并探讨其作用机制,本研究采用CCK8法检测HMA对结直肠癌细胞增殖的影响;Heochst-33343/PI染色检测细胞凋亡情况;同时检测细胞内ROS及GSH含量变化并应用Western blot检测细胞凋亡相关蛋白及Keap-1/Nrf-2/ARE信号途径相关蛋白的表达。实验结果显示,HMA给予结直肠癌细胞后,细胞内ROS含量升高,GSH含量减少;HMA通过抑制Keap-1/Nrf-2/HO-1通路,诱导细胞发生凋亡。综上表明HMA具有抑制结肠癌细胞增殖的作用,其机制可能与破坏细胞内氧化还原平衡,抑制Keap-1/Nrf-2/HO-1通路有关。     

Hepatic stellate cell promoted hepatoma cell invasion via the HGF/c-Met signaling pathway regulated by p53

The biological behaviors of hepatocellular carcinoma (HCC) are complex mainly due to heterogeneity of progressive genetic and epigenetic mutations as well as tumor environment. Hepatocyte growth factor (HGF)/c-Met signaling pathway is regarded to be a prototypical example for stromal-epithelial interactions during developmental morphogenesis, wound healing, organ regeneration and cancer progression. And p53 plays as an important regulator of Met-dependent cell motility and invasion. Present study showed that 2 HCC cell lines, Hep3B and HepG2, displayed different invasive capacity when treated with HGF which was secreted by hepatic stellate cells (HSCs). We found that HGF promoted Hep3B cells invasion and migration as well as epithelial-mesenchymal transition (EMT) occurrence because Hep3B was p53 deficient, which leaded to the c-Met over-expression. Then we found that HGF/c-Met promoted Hep3B cells invasion and migration by upregulating Snail expression. In conclusion, HGF/c-Met signaling is enhanced by loss of p53 expression, resulting in increased ability of invasion and migration by upregulating the expression of Snail.     

Role of protein kinase C delta in curcumin-induced antioxidant response element-mediated gene expression in human monocytes

The Nrf2/antioxidant response element (ARE) signaling pathway plays a key role in activating cellular antioxidants, including heme oxygenase-1 (HO-1), NADPH quinone oxidoreductase-1 (NQO1), and glutathione. Protein kinase C (PKC) may also regulate these antioxidants, as PKC phosphorylates Nrf2 in vitro. This study examined the role of PKC in ARE-mediated gene regulation in human monocytes by curcumin, a potent inducer of the Nrf2/ARE pathway. Curcumin increased HO-1 and glutamyl cysteine ligase modulator (GCLM) expression and stimulated Nrf2 binding to the ARE. Curcumin also rapidly stimulated PKC phosphorylation and Ro-31-8220, a pan-PKC inhibitor, decreased curcumin-induced GCLM and HO-1 mRNA expression and ARE binding. Rottlerin (a PKC delta inhibitor) and PKC delta antisense oligonucleotides significantly inhibited curcumin-induced GCLM and HO-1 mRNA expression and ARE binding. Furthermore, a p38 MAP kinase inhibitor reduced GCLM and HO-1 expression and rottlerin inhibited curcumin-induced p38 phosphorylation. In summary, curcumin activates ARE-mediated gene expression in human monocytes via PKC delta, upstream of p38 and Nrf2.     

Epigallocatechin gallate induces expression of heme oxygenase-1 in endothelial cells via p38 MAPK and Nrf-2 that suppresses proinflammatory actions of TNF-α

Epigallocatechin gallate (EGCG), the major polyphenol in green tea, acutely stimulates production of nitric oxide (NO) from vascular endothelium to reduce hypertension and improve endothelial dysfunction in spontaneously hypertensive rats. Herein, we explored additional mechanisms whereby EGCG may mediate beneficial cardiovascular actions. When compared with vehicle-treated controls, EGCG treatment (2.5 μM, 8 h) of human aortic endothelial cells (HAEC) caused a ~three-fold increase in heme oxygenase-1 (HO-1) mRNA and protein with comparable increases in HO-1 activity. This was unaffected by pretreatment of cells with wortmannin, LY294002, PD98059 or L-NAME (PI 3-kinase, MEK and NO synthase inhibitors, respectively). Pretreatment of HAEC with SB203580 (p38 MAPK inhibitor) or siRNA knockdown of p38 MAPK completely blocked EGCG-stimulated induction of HO-1. EGCG treatment also inhibited tumor-necrosis-factor-α-stimulated expression of vascular cell adhesion molecule (VCAM)-1 and decreased adhesion of monocytes to HAEC. siRNA knockdown of HO-1, p38 MAPK or Nrf-2 blocked these inhibitory actions of EGCG. In HAEC transiently transfected with a human HO-1 promoter luciferase reporter (or an isolated Nrf-2 responsive region), luciferase activity increased in response to EGCG. This was inhibitable by SB203580 pretreatment. EGCG-stimulated expression of HO-1 and Nrf-2 was blocked by siRNA knockdown of Nrf-2 or p38 MAPK. Finally, liver from mice chronically treated with EGCG had increased HO-1 and decreased VCAM-1 expression. Thus, in vascular endothelium, EGCG requires p38 MAPK to increase expression of Nrf-2 that drives expression of HO-1, resulting in increased HO-1 activity. Increased HO-1 expression may underlie anti-inflammatory actions of EGCG in vascular endothelium that may help mediate beneficial cardiovascular actions of green tea.     

Maotai Ameliorates Diethylnitrosamine-Initiated Hepatocellular Carcinoma Formation in Mice

Consumption of alcohol is closely related to liver disease, such as hepatic fibrosis or even hepatocellular carcinoma (HCC). However, epidemiological and experimental studies indicated that consumption of Maotai, one of the famous liquors in China, exhibits no significant correlation with hepatic fibrosis or cirrhosis as other beverage sources do. This study detected the relationship of Maotai consumption and HCC development in a diethylnitrosamine (DEN)-initiated HCC animal model. DEN was given to mice at a dose of 100 mg/kg, ip, and 50 mg/kg, ip in the following week. Mice were simultaneously given Maotai or an equal amount of ethanol (53%, 5 ml/kg/day, 5days/week for up to 35weeks). At 3-week and 35- week of the experiment, serum and livers were collected for biochemical and histopathological examination of liver injury and incidence of HCC. Real-time RT-PCR, immunohistochemistry and Western blotting were used to examine the expression of metallothionein-1/2 (MT-1/2), NF-E2-related factor 2 (Nrf2), glutamate-cysteine ligase catalytic subunit (GCLC) and modified subunit (GCLM). We identified tissue damage and dysfunction of liver in ethanol + DEN-treated mice, whereas the extent of injury was reduced in Maotai+ DEN –treated mice. Significant Glypican-3(GPC3) expression and precancerous injury or HCC were seen in approximately 50% of mice with ethanol+ DEN, but barely be seen in Maotai + DEN-treated mice. A higher expression of MT-1/2, Nrf2 and GCLC could be seen in Maotai + DEN-treated mice. Thus, Maotai liquor ameliorates the formation of DEN-induced HCC in mice, and the protection mechanism is possibly related with the activation of anti-oxidation factors, such as MTs, Nrf2 and GCLC.     

Dual effects of phloretin on aflatoxin B1 metabolism: activation and detoxification of aflatoxin B1

Typically, chemopreventive agents involve either induction of phase II detoxifying enzymes and/or inhibition of cytochrome P450 enzymes (CYPs) that are required for the activation of procarcinogens. In this study, we investigated the protective effects of phloretin against aflatoxin B1 (AFB1) activation to the ultimate carcinogenic intermediate, AFB(1)-8, 9-epoxide (AFBO), and its subsequent detoxification. Phloretin markedly inhibited formation of the epoxide with human liver microsomes in a dose-dependent manner. Phloretin also inhibited the activities of nifedipine oxidation and ethoxyresorufin O-deethylase (EROD) in human liver microsomes. These data show that phloretin strongly inhibits CYP1A2 and CYP3A4 activities, which are involved in the activation of AFB1. Phloretin increased glutathione S-transferase (GST) activity of alpha mouse liver 12 (AML 12) cells in a dose-dependent manner. GST activity toward AFBO in cell lysates treated with 20 μM phloretin was 23-fold that of untreated control cell lysates. The expression of GSTA3, GSTA4, GSTM1, GSTP1 and GSTT1 was induced by phloretin in a dose-dependent manner in AML 12 cells. GSTP1, GSTM1, and GSTT1 were able to significantly increase the conjugation of AFBO with glutathione. Concurrently, induction of the GST isozyme genes was partially associated with the Nrf2/ARE pathway. Taken together, the results demonstrate that phloretin has a strong chemopreventive effect against AFB1 through its inhibitory effect on CYP1A2, CYP3A4, and its inductive effect on GST activity.