Defective insulin receptor function in down-regulated HepG2 cells

Insulin receptors on the surface of down-regulated HepG2 cells were studied, and multiple defects of receptor function were demonstrated. Insulin treatment led to a 58% decrease in cell surface receptor number, and the remaining receptors exhibited a 50% decrease in insulin internalization and degradation on a per receptor basis. Down-regulated cells internalized 36% of receptors photolabeled with 125I-NAPA-insulin vs. 56% of labeled receptors in control cells, indicating a 40% decrease in ligand-mediated receptor internalization. Total cellular receptors purified from down-regulated cells by wheat germ affinity chromatography demonstrated a 20% decrease in maximal autophosphorylation. Assessment of autophosphorylation of cell surface receptors in intact cells by restimulation of cells with insulin at 12 C (a temperature nonpermissive for receptor recycling), followed by immunoblotting with antiphosphotyrosine antibodies revealed a decrease of approximately 70% in insulin-stimulated autophosphorylation compared with controls. This method also revealed a comparable decrease in insulin-stimulable tyrosine phosphorylation of pp185, a putative endogenous substrate. When receptors were stimulated to undergo autophosphorylation with 125I-NAPA-insulin in intact cells and then solubilized, only 11% of 125I-NAPA-insulin receptor complexes from down-regulated cells were immunoprecipitated with antiphosphotyrosine antibodies compared with 35% of labeled control receptors. These results indicate that treatment with high concentrations of insulin results in the accumulation on the cell surface of a population of receptors that display multiple functional abnormalities. This probably results from preferential internalization and degradation of kinase-competent insulin receptors causing an accumulation of kinase-incompetent receptors on the cell surface. These receptors may in part be responsible for the postbinding defects in insulin action observed in down-regulated cells.     

Regulation of low-density lipoprotein receptor activity by estrogens and phytoestrogens in a HepG2 cell model

BACKGROUND/AIMS: Estrogen treatment is thought to lower low-density lipoprotein (LDL) cholesterol levels by increasing clearance through hepatic LDL receptors. This study aimed to determine the effect of estrogens and phytoestrogens on LDL receptor activity in a human hepatoma cell line, HepG2. METHODS: HepG2 cells in culture were incubated for 24 h with estrogen or phytoestrogen and LDL receptor activity was measured by examining the cellular binding of colloidal gold-labelled LDL. RESULTS: 17Beta-estradiol significantly increased LDL receptor activity whereas estriol had negligible effects. Incubation with the isoflavonoids, formononetin, biochanin A and daidzein, caused significant elevations in receptor activity at concentrations above 40 microM. Coumestrol, a coumestan with a high level of estrogenic activity, caused a 3-fold increase in receptor activity at a concentration of 50 microM. Of the phytoestrogenic mammalian lignans enterolactone and enterodiol, only enterolactone displayed the ability to significantly upregulate LDL receptor activity at 50 microM. CONCLUSION: This study suggests that the LDL receptor-stimulating effect of natural estrogens is mainly due to estradiol and that the cholesterol-lowering effect of diets high in phytoestrogens may be due in part to their ability to increase hepatic LDL receptor activity.     

雷公藤红素通过调节脂质合成及氧化降低HepG2细胞甘油三酯水平的研究

目的探讨雷公藤红素在非酒精性脂肪肝细胞模型中对TG水平的影响,并进一步研究其背后的机制。方法用CCK-8试剂盒确定细胞模型中雷公藤红素给药浓度,TG试剂盒测定HepG2细胞内TG水平。Western blot以及定量即时聚合酶链锁反应检测靶分子蛋白水平以及m RNA水平变化。结果雷公藤红素400 nmol/L组,600 nmol/L组、800 nmol/L组、1000 nmol/L组的TG水平分别为(64.55±1.92)μg/mg、(64.16±2.19)μg/mg、(60.94±2.70)μg/mg、(61.45±1.61)μg/mg,较软脂酸组水平[(69.32±1.79)μg/mg]明显下降(P均0.05)。雷公藤红素600 nmol/L组及1000 nmol/L组中,脂质合成相关的固醇调节因子结合蛋白(sterol-regulatory element-binding protein1c,SREBP-1c)及脂肪酸合成酶(fatty acid synthase,FAS)的表达显著降低,脂质氧化相关基因过氧化物酶体增殖物激活受体γ(peroxisome proliferators-activated receptor gamma,PPARγ)表达水平在600 nmol/L组以及1000 nmol/L组分别为1.11±0.09(相比正常对照组,下同)以及1.16±0.05,较软脂酸组0.86±0.07显著上调(P均0.05)。结论雷公藤红素能显著降低HepG2细胞内TG含量,该作用可能与下调SREBP1c以及FAS表达,上调PPARγ水平有关。     

Inflammatory cytokines modulate chemokine production patterns of HepG2 cells toward initially inclined direction

Aim:  Human hepatocytes are known to express an array of inflammatory cytokines and chemokines. In this study, we examined the potential roles of hepatocytes in regulating immune responses in the liver, by assessing the induction of Th1- or Th2-specific chemokines in HepG2 cells after various inflammatory stimulations.
Methods:  HepG2 cells were stimulated with IL-1α, IFN-γ, IL-4, IL-10, and/or CCL2, harvested at several time points, and served for the analyses of cytokine/chemokine mRNA expressions by semi-quantitative RT-PCR.
Results:  (i) IL-1α up-regulated mRNA levels of CXCL8, CXCL10, and CCL2. IFN-γ increased those of CXCL9, CXCL10, and CCL5, while IL-4 or IL-10 had no effect. (ii) Addition of IL-4 to the culture of IFN-γ-stimulated cells, down-regulated CXCL9 and CXCL10 mRNA levels. (iii) Addition of IFN-γ to the culture of IL-1α-stimulated cells, further up-regulated CXCL9 and CXCL10 mRNA levels. Addition of IL-4 decreased CXCL8 and CXCL10 levels, and increased CCL2 level in IL-1α-stimulated cells. (iv) CCL2 induced IL-4 mRNA expression.
Conclusions:  IFN-γ augmented mRNA expression of Th1-specific chemokines (CXCL9 and CXCL10) in HepG2 cells. IL-4 had no effect on those of Th2-spesific chemokines (CCL17 and CCL22); however, it was supposed to augment Th2 response indirectly through the induction of CCL2 under the inflammatory condition. The findings suggest that hepatocytes have ability to promote immune responses in the liver toward the direction, initially determined by the cytokine balances in the local inflammatory region.     

IL-6上调SCD1表达对HepG2细胞脂质合成功能的影响*

目的 探讨IL-6对HepG2细胞硬脂酰辅酶A去饱和酶1 （SCD1）基因的影响及其SCD1基因表达的改变对细胞脂质合成的影响。方法 应用rIL-6刺激HepG2细胞,检测细胞内脂质合成以及细胞SCD1基因水平变化。分别构建人SCD1真核表达质粒和小干扰（small interfering） RNA,转染HepG2细胞,观察改变SCD1水平后HepG2细胞脂代谢相关基因表达的变化以及细胞内脂质合成的变化。结果 rIL-6刺激HepG2细胞甘油三酯水平显著高于对照组（P<0.05）;与空质粒组比,转染真核表达质粒细胞SCD1 蛋白表达增加,细胞脂质合成相关基因SREBP1c和FASN相对水平增加1.35倍和1.27倍,脂质氧化代谢相关基因PPARα和ASCL3水平降低12.3%和13.5%;细胞甘油三酯水平显著升高（P<0.01）,而转染small interfering RNA,再用rIL-6刺激HepG2细胞SCD1蛋白表达显著降低,细胞甘油三酯水平也显著降低（P<0.05）,脂质合成相关基因SREBP1c和FASN水平显著下降了32.3%和51.9%,脂质分解相关基因PPARα相对水平也下降了80%（P<0.05）,而ASCL3水平无显著变化（P=0.832）。结论 rIL-6通过上调HepG2细胞SCD1基因表达,引起细胞内脂质合成增加,导致甘油三酯含量增多。     

Tie2 receptor expression is stimulated by hypoxia and proinflammatory cytokines in human endothelial cells

The tyrosine kinase receptor Tie2 (also known as Tek) plays an important role in the development of the embryonic vasculature and persists in adult endothelial cells (ECs). Tie2 was shown to be upregulated in tumors and skin wounds, and its ligands angiopoietin-1 and -2, although they are not directly mitogenic, modulate neovascularization. To gain further insight into the regulation of Tie2, we have studied the effect of hypoxia and inflammatory cytokines, two conditions frequently associated with neoangiogenic processes, on Tie2 expression in human ECs. Exposure to 1% O(2) led to a time-dependent significant rise of Tie2 protein levels in human coronary microvascular endothelial cells (HCMECs) and dermal microvascular ECs (HMEC-1) (3.2- and 2.5-fold within 24 hours), which was reversible after reoxygenation, and induced a less marked increase in human umbilical vein ECs (HUVECs; 1.7-fold). Hypoxia-conditioned medium and D-deoxyglucose did not change Tie2 expression, but desferrioxamine and cobalt, which are known to mimic hypoxia-sensing mechanisms, induced Tie2 at ambient oxygen tensions. Tumor necrosis factor-alpha induced Tie2 in a time- and dose-dependent fashion in all 3 EC types (HUVEC, 2.3-fold; HMEC-1, 2. 8-fold; and HCMEC, 3.0-fold; 10 ng/mL, 24 hours). Enhanced expression was also found after exposure to interleukin-1beta (1 ng/mL). Changes in Tie2 protein levels were paralleled by changes in mRNA expression. In accordance with these in vitro findings, immunohistochemistry revealed focal upregulation of Tie2 in capillaries at the border of infarcted human and rat myocardium. In conclusion, the data show that hypoxia and inflammatory cytokines upregulate Tie2, which may contribute to the angiogenic response in ischemic tissues.     

Regulation of angiotensin type 2 receptor in bovine granulosa cells

Angiotensin II (AngII) is best known for its role in blood pressure regulation, but it also has documented actions in the reproductive system. There are two AngII receptors, type 1 (AGTR1) and type 2 (AGTR2). AGTR2 mediates the noncardiovascular effects of AngII and is expressed in the granulosa cell layer in rodents and is associated with follicle atresia. In contrast, expression of AGTR2 is reported to occur only in theca cells in cattle. The objective of the present study was to determine whether AngII also plays a role in follicle atresia in cattle. RT-PCR demonstrated AGTR2 mRNA in both granulosa and theca cells of bovine follicles. The presence of AGTR2 protein was confirmed by immunofluorescence. Abundance of AGTR2 mRNA in granulosa cells was higher in healthy compared with atretic follicles, whereas in theca cells, it did not change. Granulosa cells were cultured in serum-free medium, and treatment with hormones that increase estradiol secretion (FSH, IGF-I, and bone morphogenetic protein-7) increased AGTR2 mRNA and protein levels, whereas fibroblast growth factors inhibited estradiol secretion and AGTR2 protein levels. The addition of AngII or an AGTR2-specific agonist to granulosa cells in culture did not affect estradiol secretion or cell proliferation but inhibited abundance of mRNA encoding serine protease inhibitor E2, a protein involved in tissue remodeling. Because estradiol secretion is a major marker of nonatretic granulosa cells, these data suggest that AngII is not associated with follicle atresia in cattle but may have other specific roles during follicle growth.     

Niacin accelerates intracellular ApoB degradation by inhibiting triacylglycerol synthesis in human hepatoblastoma (HepG2) cells

The mechanism by which the potent drug niacin decreases apoB-containing atherogenic lipoproteins and prevents coronary disease is unclear. Utilizing human hepatoblastoma (HepG2) cells as an in vitro model, we have examined the effect of niacin on intracellular degradation of apoB and the regulatory mechanisms involved in apoB processing. Niacin significantly increased apoB degradation in a dose- and time-dependent manner. Treatment of HepG2 cells with calpain inhibitor I [N-acetyl-leucyl-leucyl-norleucinal (ALLN), an inhibitor of certain protease-mediated apoB degradation], did not alter niacin-induced apoB degradation. Niacin decreased inhibition of oleate-mediated apoB degradation. Niacin dose-dependently inhibited the synthesis of both fatty acids and triacylglycerol (TG) by 20% to 40% as determined by the incorporation of 14C-acetate and 3H-glycerol into fatty acids and TG, respectively. Incubation of HepG2 cells with niacin significantly inhibited (by 12% to 15%) fatty acid esterification to produce TG as assessed by the incorporation of 3H-oleic acid into TG. 14C-acetate incorporation into cholesterol and phospholipids was unchanged. The activity of microsomal triglyceride transfer protein (MTP), a carrier protein for lipids, was not altered by pretreatment of cells with niacin. ApoB mRNA expression and 125I-LDL protein uptake were also unchanged. These data indicate that niacin accelerates hepatic intracellular post-translational degradation of apoB by selectively reducing triglyceride synthesis (through inhibiting both fatty acid synthesis and fatty acid esterification to produce TG) without affecting ALLN-inhibitable protease- or MTP-mediated intracellular apoB processing, resulting in decreased apoB secretion and hence lower circulating levels of the atherogenic lipoproteins.     

蜕皮甾酮对胰岛素抵抗HepG2细胞胰岛素受体表达的影响

目的 探讨蜕皮甾酮对胰岛素抵抗(IR)HepG2细胞胰岛素受体(InsR)蛋白表达的影响.方法 建立胰岛素抵抗HepG2细胞模型,培养液中加入蜕皮甾酮孵育,观察蜕皮甾酮及吡格列酮对细胞葡萄糖摄取率的影响;应用免疫组化染色法及Western blot方法观察蜕皮甾酮对IR HepG2细胞InsR蛋白表达的影响. 结果 与模型细胞比较,1×10-5 mol/L蜕皮甾酮可使IR HepG2细胞InsR蛋白的表达显著增加. 结论 蜕皮甾酮的胰岛素增敏作用可能与胰岛素信号转导分子InsR蛋白的表达增强有关.     

乙型肝炎病毒对HepG2细胞IL-17R信号通路的影响

目的:研究乙型肝炎病毒(hepatitis B virus,HBV)重组腺病毒对HepG2细胞的IL-17R和接头蛋白Act1表达的影响,以及HBV对IL-17诱导NF-B活化的影响.方法:采用实时荧光定量PCR(real-time PCR)检测HepG2细胞的IL-17、IL-17R和Act1的mRNA表达;蛋白免疫印迹法(Western blot)检测IL-17R和Act1的蛋白表达;免疫荧光检测NF-B核移位;ELISA检测上清的IL-17含量.结果:各组HepG2细胞培养上清液中均未检测到IL-17且亦未检测HepG2细胞有IL-17的mRNA表达;HBV重组腺病毒组的IL-17R mRNA和蛋白的表达明显低于相应浓度对照组(0.68±0.02vs0.89±0.03,0.33±0.06vs0.81±0.01,0.12±0.01vs0.86±0.05,P<0.05;蛋白:0.84±0.12vs1.01±0.13,0.56±0.09vs1.01±0.08,0.24±0.08vs0.98±0.05),且呈剂量和时间依赖性.但HBV重组腺病毒组与对照组比较,对HepG2细胞接头蛋白Act1的mRNA和蛋白表达水平无明显影响;同时HBV重组腺病毒能抑制IL-17R诱导Hep G2细胞的NF-B活化.但HBV重组腺病毒与对照组比较,对接头蛋白Act1在mRNA和蛋白表达水平上影响无明显变化;同时HBV重组腺病毒能抑制IL-17R诱导Hep G2细胞的NF-B活化.结论:HBV重组腺病毒可降低HepG2细胞的IL-17R mRNA和蛋白的表达,抑制IL-17R诱导Hep G2细胞的NF-B活化,对HepG2细胞的IL-17R信号通路发挥抑制作用.     

Effect of tamoxifen on cholesterol synthesis in HepG2 cells and cultured rat hepatocytes

The objective of this study was to investigate the mechanisms by which tamoxifen modifies cholesterol metabolism in cellular models of liver metabolism, HepG2 cells and rat hepatocytes. The effect of tamoxifen on cholesterol and triglyceride-palmitate synthesis was measured using isotopomer spectral analysis (ISA) and gas chromatography—mass spectrometry (GC-MS) and compared with the effects of progesterone, estradiol, the antiestrogen ICI 182,780, and an oxysterol, 25-hydroxycholesterol (25OHC). Cholesterol synthesis in cells incubated in the presence of either [1-¹³C]acetate, [U-¹³C]glucose, or [4,5-¹³C]mevalonate for 48 hours was reduced in the presence of 10 μmol/L tamoxifen and 12.4 μmol/L 25OHC in both HepG2 cells and rat hepatocytes. The ISA methodology allowed a clear distinction between effects on synthesis and effects on precursor enrichment, and indicated that these compounds did not affect enrichment of the precursors of squalene. Progesterone was effective in both cell types at 30 μmol/L and only in HepG2 cells at 10 μmol/L. Estradiol and ICI 182,780 at 10 μmol/L did not inhibit cholesterol synthesis. None of the compounds altered the synthesis of triglyceride-palmitate in either cell type. Treatment of cells with tamoxifen produced accumulation of three sterol precursors of cholesterol, zymosterol, desmosterol, and Δ⁸ cholesterol. This pattern of precursors indicates inhibition of Δ^24,25 reduction in addition to the previously described inhibition of Δ⁸ isomerase. We conclude that tamoxifen is an effective inhibitor of the conversion of lanosterol to cholesterol in cellular models at concentrations comparable to those present in the plasma of tamoxifen-treated individuals. Our findings indicate that this mechanism may contribute to the effect of tamoxifen in reducing plasma cholesterol in humans.     

Wnt信号通路在HepG2细胞株及其克隆形成细胞中表达的异质性

目的:研究Wnt信号传导通路的关键因子β-catenin和COX-2在肝癌细胞株HepG2及其克隆形成细胞中的表达,探讨Wnt信号传导通路在不同增殖能力细胞中表达的异质性.方法:以HepG2细胞为研究对象,采用软琼脂克隆形成实验筛选克隆形成细胞,应用RTPCR、免疫化学和Western blot等技术,检测Wnt信号传...     

Implication of inflammation-related cytokines in the natural history of liver cirrhosis.

BACKGROUND/AIMS: Increased serum concentrations of pro-inflammatory cytokines have been detected in patients with liver cirrhosis. However, their role in the natural history of cirrhosis and portal hypertension, in the absence of infection, and the prognostic significance of inflammation-related cytokines have not been reported. Our objective was the analysis of the prognostic value of inflammation-related cytokines in cirrhotic patients. PATIENTS AND METHODS: Serum concentrations of tumor necrosis factor (TNF-alpha) and its soluble receptors I and II and interleukin 6 (IL-6), as well as mean blood pressure, plasma renin activity, aldosterone, vasopressin and norepinephrine concentrations were determined in 72 cirrhotic patients (Child-Pugh score: A 50%, B 33.3%, C 16.7%), without any evidence of infection, and in 25 healthy controls. Patients were followed up for a median of 35.9 (range 6-60) months. RESULTS: Increased concentrations of soluble TNF receptors were detected in cirrhotic patients when compared with healthy controls. TNF receptors and IL-6 concentrations were both significantly more elevated in advanced phases of cirrhosis (Child-Pugh score C vs B and vs A). Sixteen patients died as a related consequence of liver cirrhosis. Multivariant analysis demonstrated that Child-Pugh score, mean blood pressure and serum levels of TNF receptor I were associated with mortality. CONCLUSIONS: In addition to the classic factors implicated in mortality (Child-Pugh score and hemodynamic parameters), alterations in inflammation-related components are of prognostic significance in cirrhotic patients.     

蛋白激酶B调节骨桥蛋白在肝癌HepG2细胞中的表达

目的 转移相关基因骨桥蛋白(OPN)在肝癌中的表达方式、途径尚不清楚，检测OPN在HepG2细胞中转染蛋白激酶B(Akt)前后的表达，旨在探讨磷脂酰肌醇3激酶信号途径中的关键基因Akt与OPN表达的关系。方法 用脂质体介导的基因转染法将含有Akt基因的质粒转染HepG2细胞，并用Western blot鉴定；OPN的表达用Northern blot和Western blot方法检测。结果 Akt基因成功转染HepG2细胞，Western blot能检测到HepG2细胞中外源表达的Akt基因；Northern blot和Western blot检测发现，Akt在核酸和蛋白水平调节OPN的表达；在无血清培养条件下，OPN在HepG2中结构性表达量很少或无表达,转染活性型Akt后OPN表达升高；在有血清培养条件下,HepG2细胞转染缺陷型Akt基因后OPN表达下降。结论 Akt调节转移相关基因OPN在肝癌细胞中的表达，提示可通过使Akt基因失活来阻断OPN产生，从而抑制肝癌转移。     

HepG2.2.15细胞诱导MT2淋巴细胞凋亡及其意义

观测表达Ｆａｓ抗原（Ｆａｓ）的Ｔ淋巴细胞一感染乙型肝炎病毒的ＭＴｓ细胞对表达Ｆａｓ配体（ＦａｓＬ）的实质细胞一ＨｅｐＧ２２．１５细胞的敏感性,了解乙型肝炎病毒感染对淋巴细胞和肝实质细胞交互作用的影响。方法体外培养ＭＴ２细胞,用乙型肝炎病毒诱导表达ＦａｓＬ。将表达ＦａｓＬ的ＨｅｐＧ２．２．１５细胞与其共孵育后,以Ｔｕｎｅｌ法观测ＭＴ２细胞凋亡情况。结果ＭＴ２细胞感染乙型肝炎病毒后可测到Ｆａｓ表达信号。与表达ＦａｓＬ的ＨｅＰＧ２．２．１５细胞共孵育４８～７２小时以后,出现凋亡信号。结论乙型肝炎病毒诱导表达Ｆａｓ的ＭＴｓ细胞与表达ＦａｓＬ的ＨｅｐＧ２．２．１５细胞交互作用后发生凋亡,表明通常在乙型肝炎发病中作为效应细胞的淋巴细胞,亦可成为凋亡靶细胞。