Distribution of microsomal triglyceride transfer protein within sub-endoplasmic reticulum regions in human hepatoma cells.
Very low-density lipoprotein (VLDL) particles are formed in the endoplasmic reticulum (ER) through the association of lipids with apolipoprotein B (apoB). Microsomal triglyceride transfer protein (MTP), which transfers lipid molecules to nascent apoB, is essential for VLDL formation in ER. However, little is known of the distribution and interaction of MTP with apoB within ER. In this study, distribution patterns of apoB and MTP large subunit (lMTP) within ER were examined. Microsomes prepared from HuH-7 cells, a human hepatoma cell line, were further fractionated into rough ER (RER)-enriched subfractions (ER-I fraction) and smooth ER (SER)-enriched subfractions (ER-II fraction) by iodixanol density-gradient ultracentrifugation. ApoB was evenly distributed in the ER-I and the ER-II fractions, while 1.5 times more lMTP molecules were present in the ER-I fraction than in the ER-II fraction. lMTP and apoB were coprecipitated both in the ER-I and in the ER-II fractions by immunoprecipitation whenever anti-apoB or an anti-lMTP antibodies were used. ApoB-containing lipoprotein particles showed a lower density in the ER-II fraction than those in the ER-I fraction. From these results, it is suggested that MTP can function in both rough and smooth regions of ER in human hepatoma cells.
Higashi
Yusuke
Y
Department of Molecular Pathology, Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Tsukui, Kanagawa 199-0195, Japan.
Itabe
Hiroyuki
H
Fukase
Hironaga
H
Mori
Masahiro
M
Fujimoto
Yasuyuki
Y
Sato
Ryuichiro
R
Imanaka
Tsuneo
T
Takano
Tatsuya
T
D016632:Apolipoprotein A-I / Q000378:metabolism; D001055:Apolipoproteins B / Q000378:metabolism; D001057:Apolipoproteins E / Q000378:metabolism; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000378:metabolism; D037281:Calnexin; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008113:Liver Neoplasms / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D016632:Apolipoprotein A-I; D001055:Apolipoproteins B; D001057:Apolipoproteins E; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D008079:Lipoproteins, VLDL; C106092:microsomal triglyceride transfer protein; D037281:Calnexin