Subcellular localization of microsomal triglyceride transfer protein.
Microsomal triglyceride transfer protein (MTP) is essential for the assembly of apolipoprotein B-containing lipoproteins. Within the endoplasmic reticulum, it transfers lipid from the membrane to the forming lipoprotein. Recent evidence suggests that it may also function within the Golgi apparatus. To address this hypothesis, we developed a polyclonal antibody to MTP and used it in a series of studies on mouse liver and McArdle-RH7777 (McA) cells. Western blot analysis demonstrated the presence of MTP within mouse hepatic-Golgi apparatus-rich fractions. In addition, in vitro lipid transfer assays demonstrated the presence of triglyceride transfer activity within the Golgi fractions. Immunohistochemical studies with mouse liver demonstrated the presence of MTP within all hepatocytes, but not in nonparenchymal cells. The subcellular location of MTP in McA cells was investigated using confocal microscopy. MTP colocalized with the trans-Golgi network (TGN) 38 and Golgi SNARE (soluble N-ethylmalemide-sensitive factor attachment protein receptor) of 28 kDa (GS28), markers for the trans- and cis-Golgi apparatus, respectively. Morphometric analyses indicated that approximately 17% of the MTP signal colocalized with the TGN38, while 33% of the trans-Golgi marker colocalized with the MTP. Approximately 17% of the MTP signal colocalized with the GS28, whereas 53% of the cis-Golgi marker colocalized with the MTP. The results provide unequivocal evidence for the location of MTP within the Golgi apparatus, and further highlight the importance of this organelle in the assembly of lipoproteins.
Swift
Larry L
LL
Department of Pathology, Vanderbilt University School of Medicine, C-3321 Medical Center North, Nashville, TN 37232-2561, USA. larry.swift@vanderbilt.edu
Zhu
Mei-Ying
MY
Kakkad
Bharati
B
Jovanovska
Aneta
A
Neely
M Diana
MD
Valyi-Nagy
Klara
K
Roberts
Richard L
RL
Ong
David E
DE
Jerome
W Gray
WG
D000818:Animals; D001055:Apolipoproteins B / Q000737:chemistry / Q000378:metabolism; D002352:Carrier Proteins / Q000032:analysis / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000737:chemistry / Q000378:metabolism; D007150:Immunohistochemistry; D008074:Lipoproteins / Q000378:metabolism*; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008862:Microsomes, Liver / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport; D014280:Triglycerides / Q000378:metabolism; D021601:trans-Golgi Network / Q000378:metabolism
D001055:Apolipoproteins B; D002352:Carrier Proteins; D008074:Lipoproteins; D008079:Lipoproteins, VLDL; D008565:Membrane Proteins; D014280:Triglycerides; C106092:microsomal triglyceride transfer protein