Transmembrane Lipid Transfer Is Crucial for Providing Neutral Lipids during Very Low Density Lipoprotein Assembly in Endoplasmic Reticulum

Higashi, Yusuke; Itabe, Hiroyuki; Fukase, Hironaga; Mori, Masahiro; Fujimoto, Yasuyuki; Takano, Tatsuya

doi:10.1074/jbc.m301376200

Cited by 39 publications

(40 citation statements)

References 39 publications

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“…Filters were exposed for 5-30 s. secretion of VLDL is required for HCV replication. For this purpose, we used an MTP inhibitor BMS-2101038 that blocks the secretion and accelerates the degradation of apoB by inhibiting MTP-mediated lipid transfer to apoB (25,26). Huh7-5A-GFP-6 cells were treated with various doses of the MTP inhibitor.…”

Section: Resultsmentioning

confidence: 99%

Hepatitis C virus production by human hepatocytes dependent on assembly and secretion of very low-density lipoproteins

Huang

Sun

Owen

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

491

446

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Hepatitis C virus (HCV) and triglyceride-rich very low-density lipoproteins (VLDLs) both are secreted uniquely by hepatocytes and circulate in blood in a complex. Here, we isolated from human hepatoma cells the membrane vesicles in which HCV replicates. These vesicles, which contain the HCV replication complex, are highly enriched in proteins required for VLDL assembly, including apolipoprotein B (apoB), apoE, and microsomal triglyceride transfer protein. In hepatoma cells that constitutively produce infectious HCV, HCV production is reduced by two agents that block VLDL assembly: an inhibitor of microsomal triglyceride transfer protein and siRNA directed against apoB. These results provide a possible explanation for the restriction of HCV production to the liver and suggest new cellular targets for treatment of HCV infection.apolipoprotein B ͉ microsomal triglyceride transfer protein

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Section: Resultsmentioning

confidence: 99%

Hepatitis C virus production by human hepatocytes dependent on assembly and secretion of very low-density lipoproteins

Huang

Sun

Owen

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

491

446

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“…Lipidation of apoB by triglycerides is regulated at least at three independent steps, namely the synthesis of triglycerides, the transfer of triglycerides across the ER membrane, and the delivery of triglycerides from the ER membrane to apoB by MTP (16). The process and regulation of the transfer of triglycerides across the ER membrane is not well understood (16).…”

Section: Discussionmentioning

confidence: 99%

“…The VLDLs are composed of a nonpolar core of triglycerides and cholesteryl esters surrounded by a monolayer amphipathic coating of protein, phospholipids, and cholesterol (14,15). VLDLs are formed in the luminal space within the endoplasmic reticulum (ER), whereas the lipids that are required for their formation are synthesized on the cytosolic side of the ER membrane (16). The ER is also the center of HCV translation and replication activities, resulting in the ER stress response and the induction of oxidative stress (17).…”

Section: Hepatitis C Virus (Hcv)mentioning

confidence: 99%

“…Huh-7 cells have been shown to secret lipoprotein particles that contain apoB100 (16). ApoB synthesis and secretion were determined by metabolically labeling Huh-7 cells (control) and FCA4 cells (HCV replicon-containing cells) with [ 35 S]methionine followed by immunoprecipitation with an apolipoprotein B antibody.…”

Section: Hcv Subgenomic Replicon Decreases Intact Synthesis and Secrementioning

confidence: 99%

“…The degradation of apoB due to poor lipidation occurs via the proteasome in the cytosol and by proteases in the endoplasmic reticulum (16). ALLN, a cysteinyl protease inhibitor, has been shown to help block both of these activities (43).…”

Section: Hcv Subgenomic Replicon Decreases Intact Synthesis and Secrementioning

confidence: 99%

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Hepatitis C Virus Nonstructural Proteins Inhibit Apolipoprotein B100 Secretion

Domitrovich

Felmlee

Siddiqui

2005

Journal of Biological Chemistry

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Host genes involved in lipid metabolism are differentially regulated during the early stages of hepatitis C virus (HCV) infection. The majority of lipids synthesized in the liver are exported to other tissues in the form of lipoproteins. The formation of these lipoproteins is dependent upon the association of triglycerides with apolipoprotein B100. Using the HCV subgenomic replicon expression system, we show that secretion of apoB100 is significantly reduced. Inhibition of apoB100 degradation by ALLN did not improve secretion. Triglyceride levels as well as microsomal triglyceride transfer protein mRNA and activity levels were reduced in replicon-expressing cells, indicating potential reasons for the observed decrease. Further evidence is presented for the interaction between the HCV nonstructural protein 5A and apoB100. These results provide further insight into the alteration of lipid metabolism by HCV. Hepatitis C virus (HCV)3 infection is a major health problem worldwide. HCV infection causes chronic hepatitis in up to 60 -80% of infected adults (1) and is associated with steatosis, cirrhosis, and hepatocellular carcinoma (2). The HCV viral genome consists of a positive sense single-stranded RNA 9.6 kb in length and encodes a polyprotein precursor of ϳ3000 amino acids (3). The resulting polyprotein is cleaved into at least three structural proteins (the core protein and the envelope proteins E1 and E2) and a variety of nonstructural proteins (p7 through NS5A/B) (3, 4). Many of the nonstructural proteins are essential for productive viral replication (5).The development of selectable subgenomic HCV RNA replicons has led to important advances in the field of HCV. Recently, several groups have reported the full-length infectious tissue culture system (6 -8), which is likely to further our understanding of the infectious process. The subgenomic replicons are bicistronic constructs composed of the HCV internal ribosomal entry site (IRES), the neomycin phosphotransferase (neo) gene, and the encephalomyocarditis IRES, which mediates the translation of the HCV nonstructural proteins NS3 through NS5, followed by the 3Ј-noncoding region (9).Chronic HCV is characterized by several histological features of the liver such as bile duct damage, lymphoid follicles, low serum cholesterol levels, and, in ϳ50 -60% of the cases, steatosis (10, 11). Recently, genomic analysis conducted on the livers of HCV-infected chimpanzees revealed that the transcript levels of genes involved in lipid metabolism and homeostasis are altered (12, 13).The liver is a major site of lipid synthesis. Many of the synthesized lipids are exported from the liver in the form of apolipoprotein-containing particles known as very low density lipoproteins (VLDLs), precursors of low-density lipoproteins. The VLDLs are composed of a nonpolar core of triglycerides and cholesteryl esters surrounded by a monolayer amphipathic coating of protein, phospholipids, and cholesterol (14, 15). VLDLs are formed in the luminal space within the endoplasmic reticulum (ER), ...

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Inhibition of Niemann-Pick-type C1-like1 by ezetimibe activates autophagy in human hepatocytes and reduces mutant α1-antitrypsin Z deposition

Yamamura¹,

Ohsaki²,

Suzuki³

et al. 2014

Hepatology

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Autophagy can degrade aggregate-prone proteins, but excessive autophagy can have adverse effects. It would be beneficial if autophagy could be enhanced in a cell typespecific manner, but this has been difficult because the basic mechanism of autophagy is common. In the present study we found that inhibition of Niemann-Pick-type C1-like 1 (NPC1L1) by ezetimibe activates autophagy only in hepatocytes and small intestinal epithelia, but not in other cells. Ezetimibe induced accumulation of free cholesterol in the late endosome/lysosome and increased partitioning of a Ragulator component, LAMTOR1, in rafts. The latter change led to down-regulation of mammalian target of rapamycin (mTOR)C1 activity by decreasing mTOR recruitment to the late endosome/lysosome and activated autophagy. A primary effect of ezetimibe was found to be a decrease of free cholesterol in the plasma membrane, because all the results caused by ezetimibe were suppressed by supplementation of cholesterol as a methyl-b-cyclodextrin complex. By enhancing autophagy in human primary hepatocytes with ezetimibe, insoluble mutant a1-antitrypsin Z was reduced significantly. Conclusion: Inhibition of NPC1L1 by ezetimibe activates autophagy in human hepatocytes by modulating cholesterol homeostasis. Ezetimibe may be used to ameliorate liver degeneration in a1-antitrypsin deficiency. (HEPATOLOGY 2014;59:1591-1599 M acroautophagy (hereafter referred to as autophagy) is a degradation process that is conserved in all eukaryotes, in which cytoplasmic portions are enclosed within the autophagosome and eventually digested in the lysosome. The primary role of autophagy is to maintain cellular homeostasis against various stresses, but recent studies revealed that autophagy is involved in a wider range of activities. 1 With regard to diseases, activation of autophagy was shown to reduce potentially toxic protein aggregates. 2,3 It is notable that a lack of constitutive autophagy induced the deposition of protein aggregates and caused neurodegeneration. 1 The results suggest that autophagy activators may be used to treat degenerative diseases. 4 To harness the benefit of autophagy and avoid unwanted side effects to the furthest extent possible, it would be useful if autophagy could be activated in restricted cell types. This may not be an easy task, however, because the basic molecular mechanism for autophagic induction and progression appears to be common in all mammalian cells.We supposed that cellular cholesterol may be a possible point of manipulation to induce cell type-specific autophagy. In a previous study, we found that cholesterol depletion activates autophagy, suggesting that the Abbreviations: ATZ, a1-antitrypsin Z; CBZ, carbamazepine; DeLS, delipidated serum; DMEM, Dulbecco's modified Eagle's medium; DRM, detergent-resistant membrane; FC, free cholesterol; FCS, fetal calf serum; LE/Ly, late endosomes/lysosome; LPDS, lipoprotein-deficient serum; MbCD, methyl-b-cyclodextrin; NPC1L1, Niemann-Pick-type C1-like1; S6K, p70 ribosomal S6 kinase.From the

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Transmembrane Lipid Transfer Is Crucial for Providing Neutral Lipids during Very Low Density Lipoprotein Assembly in Endoplasmic Reticulum

Cited by 39 publications

References 39 publications

Hepatitis C virus production by human hepatocytes dependent on assembly and secretion of very low-density lipoproteins

Hepatitis C virus production by human hepatocytes dependent on assembly and secretion of very low-density lipoproteins

Hepatitis C Virus Nonstructural Proteins Inhibit Apolipoprotein B100 Secretion

Inhibition of Niemann-Pick-type C1-like1 by ezetimibe activates autophagy in human hepatocytes and reduces mutant α1-antitrypsin Z deposition

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