Suppression of cytosolic triacylglycerol recruitment for very low density lipoprotein assembly by inactivation of microsomal triglyceride transfer protein results in a delayed removal of apoB-48 and apoB-100 from microsomal and Golgi membranes of primary rat hepatocytes

Cellular apoB in primary rat hepatocyte cultures was pulse-labeled with [(35)S]methionine for 1 h. Cells were then chased with excess unlabeled methionine for periods of up to 16 h in the presence or absence of BMS-200150, an inhibitor of microsomal triglyceride transfer protein (MTP). The secretion...

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Bibliographic Details
Published in:Journal of lipid research 1999-10, Vol.40 (10), p.1758-1768
Main Authors: Hebbachi, A M, Brown, A M, Gibbons, G F
Format: Article
Language:English
Subjects:
Animals
apoB-HDL
Apolipoprotein B-100
Apolipoprotein B-48
Apolipoproteins B - metabolism
Carrier Proteins - metabolism
Cells, Cultured
Cytosol - metabolism
endoplasmic reticulum
Golgi Apparatus - metabolism
Intracellular Membranes - metabolism
Kinetics
lipoprotein secretion
Lipoproteins, HDL - biosynthesis
Lipoproteins, LDL - biosynthesis
Lipoproteins, VLDL - biosynthesis
Liver - cytology
Liver - drug effects
Liver - metabolism
Male
Microsomes, Liver - metabolism
pulse-chase kinetics
Rats
Rats, Wistar
regulation
Triglycerides - metabolism
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Summary:Cellular apoB in primary rat hepatocyte cultures was pulse-labeled with [(35)S]methionine for 1 h. Cells were then chased with excess unlabeled methionine for periods of up to 16 h in the presence or absence of BMS-200150, an inhibitor of microsomal triglyceride transfer protein (MTP). The secretion of apoB-48-VLDL was more sensitive to MTP inhibition than was apoB-100-VLDL. Inhibition of MTP had no inhibitory effect on the secretion of denser particles (apoB-48 HDL and apoB-100 HDL). BMS-200150 delayed the net removal of newly synthesized apoB-48 and apoB-100 from the microsomal and Golgi membranes, but not from the corresponding lumenal compartments. Only minor proportions of the microsomal lumen apoB-48 and apoB-100 (12-16% and 17-19%, respectively) were present as VLDL irrespective of whether MTP was inactivated or not. The HDL fraction contained most of the lumenal apoB-48 (67-73%) and a somewhat smaller proportion of apoB-100 (44-47%). The remainder of the lumenal apoB was associated with the IDL/LDL fraction. These proportions were unaffected by MTP inactivation. Excess labeled apoB which accumulated in the membranes in the presence of BMS-200150 was degraded. Inhibition of MTP prevented the removal of pre-synthesized triacylglycerol (TAG) from the hepatocytes as apoB-VLDL. Under these conditions intracellular TAG accumulated mainly in the cell cytosol, but also, to a lesser extent, in the microsomal membranes. The results suggest that inactivation of MTP inhibits a pathway of VLDL assembly which does not involve the bulk lumenal compartments of the microsomes. Suppression of this pathway ultimately prevents the net transfer of cytosolic TAG into mature apoB-VLDL.
ISSN:0022-2275
DOI:10.1016/s0022-2275(20)34892-6