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 [35S]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.—Hebbachi, A-M., A-M. Brown, and G. F. Gibbons. 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. J. Lipid Res. 1999. 40: 1758–1768. Cellular apoB in primary rat hepatocyte cultures was pulse-labeled with [35S]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.—Hebbachi, A-M., A-M. Brown, and G. F. Gibbons. 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. J. Lipid Res. 1999. 40: 1758–1768. Recent studies (1Borén J. Rustaeus S. Olofsson S-O. Studies on the assembly of apolipoprotein B-100- and B-48-containing very low density lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1994; 269: 25879-25888Google Scholar, 2Rustaeus S. Lindberg K. Borén J. Olofsson S-O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1995; 270: 28879-28886Google Scholar, 3Swift L.L. Assembly of very low density lipoproteins in rat liver: a study of particles from the Lipid Res. 1995; Scholar, of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. and an that the assembly of VLDL in a which a bulk transfer of to apoB of of lipoproteins in rat Biol. The that the of VLDL assembly the of apoB into a which was with of apoB this in the pathway S. The of apolipoprotein by the pathway and protein Biol. Chem. Scholar, F. of apolipoprotein by the prevented by microsomal triglyceride transfer studies on with an inhibitor of microsomal triglyceride transfer Biol. Chem. or not the of apoB in VLDL with that this from that which the bulk transfer of TAG to apoB in the of mature particles of VLDL (1Borén J. Rustaeus S. Olofsson S-O. Studies on the assembly of apolipoprotein B-100- and B-48-containing very low density lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1994; 269: 25879-25888Google Scholar, 2Rustaeus S. Lindberg K. Borén J. Olofsson S-O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1995; 270: 28879-28886Google Scholar, 3Swift L.L. Assembly of very low density lipoproteins in rat liver: a study of particles from the Lipid Res. 1995; Scholar, of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. The intracellular which bulk TAG transfer and for and VLDL particles S. Lindberg K. Borén J. Olofsson S-O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1995; 270: 28879-28886Google Scholar, 3Swift L.L. Assembly of very low density lipoproteins in rat liver: a study of particles from the Lipid Res. 1995; triglyceride transfer protein a in or more of the in VLDL assembly and for lipoprotein assembly that microsomal triglyceride transfer protein in the of apolipoprotein lipoproteins in cells.J. Lipid Res. MTP in the lumen of the of the which with the A fraction from rat a for and Biol. Chem. 1994; 269: MTP of a and protein in MTP to transfer TAG and the the in the transfer of TAG to apoB in the pathway of the cell as to whether MTP the of apoB Olofsson S-O. Borén J. Inhibition of the microsomal triglyceride transfer protein the of apolipoprotein lipoprotein assembly but not the of bulk in the Biol. Chem. Scholar, Recent in the of the microsomal triglyceride transfer protein in apolipoprotein lipoprotein Scholar, S. Lindberg K. Olofsson S-O. The microsomal triglyceride transfer protein the assembly of apolipoprotein very low density lipoprotein in McA-RH7777 cells.J. Biol. Chem. or whether an the bulk transfer of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. that a of the of apoB a for to microsomal triglyceride transfer protein and apolipoprotein the in a Biol. Chem. Scholar, of the of apolipoprotein microsomal triglyceride transfer transfer to very low density Biol. Chem. Scholar, The of apolipoprotein but not for microsomal triglyceride transfer protein Biol. Chem. A MTP and apoB this in J. of a microsomal triglyceride transfer protein and apolipoprotein the assembly of Biol. Chem. The of MTP in the and transfer of TAG into the pathway to the of apoB and TAG the lumen and membranes of the MTP inactivated to in in of the in the assembly of and (1Borén J. Rustaeus S. Olofsson S-O. Studies on the assembly of apolipoprotein B-100- and B-48-containing very low density lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1994; 269: 25879-25888Google Scholar, 2Rustaeus S. Lindberg K. Borén J. Olofsson S-O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1995; 270: 28879-28886Google Scholar, 3Swift L.L. Assembly of very low density lipoproteins in rat liver: a study of particles from the Lipid Res. 1995; Scholar, of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. Scholar, A-M. in in rat hepatocytes in to associated with in the intracellular and secretion of apolipoprotein Lipid Res. Scholar, recruitment of apoB-48 for the assembly of VLDL in rat Biol. that this in from a for in of VLDL assembly in A of to study and lipoprotein 1994; the cell but the cell does not the bulk J. lipoprotein Biol. Chem. Scholar, of secretion of apolipoprotein from cells.J. Lipid Res. Scholar, Lipid in and Lipid Res. 1994; The rat cell McA-RH7777 this and to study of the of MTP in VLDL assembly of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. Scholar, Olofsson S-O. Borén J. Inhibition of the microsomal triglyceride transfer protein the of apolipoprotein lipoprotein assembly but not the of bulk in the Biol. Chem. Scholar, S. Lindberg K. Olofsson S-O. The microsomal triglyceride transfer protein the assembly of apolipoprotein very low density lipoprotein in McA-RH7777 cells.J. Biol. Chem. primary cultures of rat hepatocytes to study the intracellular of TAG and apoB VLDL assembly for the primary cultures of intracellular TAG for the of of VLDL A of to study and lipoprotein 1994; Scholar, The intracellular a of in hepatocytes which apolipoprotein lipoprotein and in which J. primary cultures not the presence of for as McA-RH7777 of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. primary cultures studies of the of in on of VLDL assembly A of to study and lipoprotein 1994; these this in with the MTP inhibitor BMS-200150 inhibitor of the microsomal triglyceride transfer protein inhibits apoB secretion from to the intracellular of and cytosolic TAG the of the cell MTP and were from was to the as [35S]methionine was from and were from The triacylglycerol (TAG) and were from apoB was in as recruitment of apoB-48 for the assembly of VLDL in rat Biol. was from were from and were from were conditions by of the of the conditions and of lipoprotein secretion by and in J. The were in containing methionine and The of the hepatocytes was by and was and were in which cell was than These were The cell was with G. of on membranes. and Res. the a this the cell contained to as by and in The effect of of on of and on Biol. Chem. the of intracellular TAG for into cell the was the was with and the were for h in containing the and in and to as the of this a of [35S]methionine was to for a of 1 h The was and the was with this were to into the was containing unlabeled methionine The were for periods of or 16 h in the presence or absence of BMS-200150 in of which the was and the were contained of the MTP inhibitor was present or the these the inhibitor was h the of the the which the were to the the were as and then chased for h with or the MTP inhibitor as the 16 BMS-200150 had no effect on cell as by The of was containing the inhibitor were and were from rat hepatocytes by a which was from that The of Golgi and in the and assembly of lipoprotein in rat Lipid Res. Scholar, A-M. and of apolipoprotein the and Golgi compartments of hepatocytes from and Biol. Chem. the of the was and for containing VLDL and HDL The cell was with and the were into a were by removal of were The cell was for with a containing and 1 by of an of to the cell to the to A of was to A-M. and of apolipoprotein the and Golgi compartments of hepatocytes from and Biol. Chem. of the a and were as The of Golgi and in the and assembly of lipoprotein in rat Lipid Res. of the was for the and and the were for Golgi The microsomal and Golgi were in to in a of 1 S. of intracellular membranes by of to Biol. to the and the lumenal from the membranes. These were by the were in of of the not in the of TAG in the the were not with The of the microsomal and Golgi was by of the and of the for the corresponding for and for Golgi as A-M. and of apolipoprotein the and Golgi compartments of hepatocytes from and Biol. Chem. the present the of in the microsomal fraction was of the present in the The corresponding for in the Golgi was of the of in the was that of the Golgi with was and that of the Golgi with was the of the cell was in a for 16 h The VLDL was from the denser particles in the by The density of the was to by the of and the conditions for a 16 h. The fraction containing the and was by The contained the The of the microsomal lumen were into corresponding density in an A-M. and of apolipoprotein the and Golgi compartments of hepatocytes from and Biol. Chem. apoB was from the and from the and HDL of the and microsomal a apoB in and as A-M. in in rat hepatocytes in to associated with in the intracellular and secretion of apolipoprotein Lipid Res. The was with containing of rat VLDL the containing the labeled apoB-48 and apoB-100 was to in a A-M. in in rat hepatocytes in to associated with in the intracellular and secretion of apolipoprotein Lipid Res. containing apoB-48 and apoB-100 were with and the was to for h. containing labeled and were from the and with and the with was and in a Cellular protein was by the of with the Biol. Chem. and VLDL TAG were of the fraction J. A for the and of from Biol. Chem. the from of in with an VLDL apoB was an of the with and apoB in of of lipoprotein triacylglycerol and secretion in hepatocyte cultures from J. with and were the in for was the Cellular apoB was pulse-labeled in the absence of the MTP inhibitor by periods of up to 16 in the presence or absence of Suppression of MTP the the secretion of newly synthesized apoB-48 and apoB-100 associated with VLDL A proportion of the labeled apoB the in particles of density than that of VLDL h of most of this was associated with particles in the of MTP had or no effect on the secretion of labeled apoB-48 and apoB-100 associated with these density The of secretion of the particles from of secretion of apoB associated with secretion of the for up to h the most of the labeled apoB HDL was the of the with or no secretion was into the HDL fraction of the as as the absence of BMS-200150 the of in the HDL was to that in the of apoB IDL/LDL and of lipoproteins into the cell h the were by apoB-48 and apoB-100 were by the of hepatocyte in a lipoproteins into the cell h the were by apoB-48 and apoB-100 were by the of hepatocyte the secretion of newly synthesized apoB hepatocytes to unlabeled apoB associated with VLDL for up to 16 h the of MTP the secretion of VLDL as the of this The of this that of labeled apoB-48-VLDL than that of apoB-100-VLDL. BMS-200150 the secretion of VLDL triacylglycerol (TAG) with a that was somewhat than that for VLDL 16 h of inhibition to a in the in the presence of the MTP the presence of smaller VLDL particles these conditions of MTP inactivation on the of VLDL was by of the cell was by and TAG was the of hepatocyte the the presence of BMS-200150 to a in the by in a VLDL was by of the cell was by and TAG was the of hepatocyte the the presence of BMS-200150 to a in the by Suppression of labeled VLDL apoB was by an of intracellular labeled apoB-48 and apoB-100 in the presence of the MTP inhibitor up to h of 16 this had that the excess apoB the cell h in the presence of BMS-200150 had degraded. was by of the of newly synthesized apoB present in the the of the with the of the cell and into the in the presence and absence of the MTP in the absence of BMS-200150, the 16 h was of the the The corresponding in the presence of the MTP inhibitor was apoB-48 the corresponding were and the of the and the the microsomal fraction of the was and into and lumenal compartments by with of the newly synthesized apoB-48 and apoB-100 the of the were associated with the microsomal with contained in the lumenal the absence of the MTP the of labeled apoB-100 net from the the were to for removal of the apoB from the microsomal more MTP was inactivated These were most and h of the which were The of the MTP inhibitor in this were for apoB-100 and was no effect of BMS-200150 on the net of the smaller of labeled apoB-48 and apoB-100 from the microsomal the density of labeled apoB in the microsomal lumen was by of the lumenal of the of in the more were in this for the of microsomes. the of the the of labeled apoB VLDL as a proportion of the lumenal apoB were low this proportion was somewhat for apoB-100 of to that for apoB-48 of the The of associated with the density were The HDL fraction for the proportion of the lumenal apoB and this proportion was smaller for apoB-100 HDL than for apoB-48 HDL was no in the of in these density h of the presence of BMS-200150 the these proportions the in the lumenal VLDL was than that in the VLDL to the was unaffected by the presence of of labeled apoB HDL and in lumenal of HDL were labeled for 1 h in the absence of were then for a h with methionine in the absence or presence of the of hepatocyte in a were labeled for 1 h in the absence of were then for a h with methionine in the absence or presence of the of hepatocyte the of MTP inactivation on the of newly synthesized apoB-48 and apoB-100 in the and lumenal of the to the of for of a of Golgi was not to a to that for the microsomal fraction. These studies to a the this the of MTP on microsomal apoB were this to the the of the was a excess of labeled apoB associated with the Golgi to that in the lumenal the absence of BMS-200150, was a net of labeled apoB from the Golgi of h the these were MTP was These of BMS-200150 in the Golgi were not by in the smaller of labeled apoB-100 or apoB-48 associated with the Golgi lumen of MTP removal of newly synthesized apoB from Golgi from in the absence of the MTP from in the absence of the MTP from in the absence of the MTP from in the absence of the MTP were labeled with [35S]methionine for 1 h and chased for h in the presence or absence of The Golgi were and labeled apoB-100 and apoB-48 were from and Golgi the of hepatocyte from in the absence of the MTP in a were labeled with [35S]methionine for 1 h and chased for h in the presence or absence of The Golgi were and labeled apoB-100 and apoB-48 were from and Golgi the of hepatocyte The effect of MTP inactivation on the transfer of TAG of the cell was by the cell cytosolic TAG the of the in the presence of was with and 16 h was which BMS-200150 was present or in the TAG of the microsomal and lumen were the present a of the in the of TAG these the to the TAG of of hepatocytes. The results of this in the of the in the presence of most of the TAG was associated with the cytosolic in the absence of BMS-200150 in the net removal of TAG from the cytosolic MTP was was no net in the of cytosolic Inhibition of MTP the net removal of the smaller of TAG associated with the microsomal but had no effect on the of TAG in the microsomal lumen that VLDL in and (1Borén J. Rustaeus S. Olofsson S-O. Studies on the assembly of apolipoprotein B-100- and B-48-containing very low density lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1994; 269: 25879-25888Google Scholar, 2Rustaeus S. Lindberg K. Borén J. Olofsson S-O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1995; 270: 28879-28886Google Scholar, 3Swift L.L. Assembly of very low density lipoproteins in rat liver: a study of particles from the Lipid Res. 1995; Scholar, of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. Scholar, in the assembly of lipoprotein with apolipoprotein in J. 1995; The the of newly synthesized apoB by into a the of apoB with a of and the for apoB-100 and apoB-48 (1Borén J. Rustaeus S. Olofsson S-O. Studies on the assembly of apolipoprotein B-100- and B-48-containing very low density lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1994; 269: 25879-25888Google Scholar, 2Rustaeus S. Lindberg K. Borén J. Olofsson S-O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1995; 270: 28879-28886Google Scholar, 3Swift L.L. Assembly of very low density lipoproteins in rat liver: a study of particles from the Lipid Res. 1995; The the bulk transfer of to the of apoB to mature The particles of VLDL assembly in the rat McA-RH7777 cell (1Borén J. Rustaeus S. Olofsson S-O. Studies on the assembly of apolipoprotein B-100- and B-48-containing very low density lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1994; 269: 25879-25888Google Scholar, 2Rustaeus S. Lindberg K. Borén J. Olofsson S-O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1995; 270: 28879-28886Google and in rat L.L. Assembly of very low density lipoproteins in rat liver: a study of particles from the Lipid Res. 1995; of the of apoB-48-VLDL was present in the lumen of the as a the of was associated with the S. Lindberg K. Borén J. Olofsson S-O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells.J. Biol. Chem. 1995; 270: 28879-28886Google Scholar, S. Lindberg K. Olofsson S-O. The microsomal triglyceride transfer protein the assembly of apolipoprotein very low density lipoprotein in McA-RH7777 cells.J. Biol. Chem. in the but the apoB-48 more of the lumenal The of these of assembly to of the particles by a cell which to the to the bulk transfer of to the VLDL J. lipoprotein Biol. Chem. Scholar, of secretion of apolipoprotein from cells.J. Lipid Res. Scholar, Lipid in and Lipid Res. 1994; the present primary newly synthesized apoB-100 and apoB-48 were as particles to These particles or to the 1 of VLDL assembly which the bulk of these particles a proportion of the apoB-100 and most of which from the cell as mature of the newly synthesized apoB-100 and apoB-48 HDL was the the with very secretion newly synthesized apoB to as mature VLDL for up to h of These results suggest that or of labeled apoB present the of the a that from the bulk transfer and as and a VLDL that with for h the inactivation of MTP by BMS-200150 the secretion of apoB-100 VLDL and apoB-48 VLDL in primary hepatocytes as in McA-RH7777 of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. Scholar, Olofsson S-O. Borén J. Inhibition of the microsomal triglyceride transfer protein the of apolipoprotein lipoprotein assembly but not the of bulk in the Biol. Chem. Scholar, Recent in the of the microsomal triglyceride transfer protein in apolipoprotein lipoprotein Scholar, S. Lindberg K. Olofsson S-O. The microsomal triglyceride transfer protein the assembly of apolipoprotein very low density lipoprotein in McA-RH7777 cells.J. Biol. Chem. were no on the secretion of apoB-48 HDL and apoB-100 The as that MTP not for the of VLDL that a proportion of but of newly synthesized apoB were present in the cell the of the and these were the of the irrespective of the presence or absence of that inhibition of the of apoB by BMS-200150 the as by and Olofsson S-O. Borén J. Inhibition of the microsomal triglyceride transfer protein the of apolipoprotein lipoprotein assembly but not the of bulk in the Biol. Chem. in cell cultures and by and F. of apolipoprotein by the prevented by microsomal triglyceride transfer studies on with an inhibitor of microsomal triglyceride transfer Biol. Chem. in the density of the labeled this the effect of MTP inhibition the of apoB in a on the secretion of labeled and a the was to that to study this in Olofsson S-O. Borén J. Inhibition of the microsomal triglyceride transfer protein the of apolipoprotein lipoprotein assembly but not the of bulk in the Biol. Chem. a the of associated with apoB-48 and apoB-100 in the presence of BMS-200150 were and cell of from The corresponding containing were and inhibitory effect of BMS-200150 the of apoB with the that MTP apoB F. of apolipoprotein by the prevented by microsomal triglyceride transfer studies on with an inhibitor of microsomal triglyceride transfer Biol. Chem. the the of associated with the apoB-48 and apoB-100 HDL were and cell respectively) MTP had the than MTP was this and The corresponding with apoB-48 VLDL and apoB-100 VLDL were and and and Under these inhibition of MTP apoB in a as to the secretion of the 1 transfer the assembly of VLDL in primary cultures of rat hepatocytes. The assembly of VLDL in primary cultures of rat hepatocytes not an of as the in the rat cell McA-RH7777 of microsomal triglyceride transfer protein for the secretion of very low density lipoproteins containing apolipoprotein from McA-RH7777 cells.J. Biol. Chem. VLDL secretion in primary cultures of which apoB as apoB-100 of an of The intracellular a of in hepatocytes which apolipoprotein lipoprotein and in which J. primary the VLDL TAG in the of the cell not for the of lipoprotein in primary cultures of rat J. Scholar, and secretion of cytosolic triacylglycerol in hepatocyte The of J. Scholar, of very low density lipoprotein of TAG in as to the of bulk transfer to The intracellular not MTP a protein of the microsomal does not to the cytosolic of TAG on the of the microsomal the of the inhibition of MTP and the of cytosolic TAG TAG in the in in of a for MTP in the bulk of VLDL the results suggest in inhibition of MTP ultimately to a net transfer of cytosolic TAG into mature VLDL and that this was associated with an in the of TAG with the microsomal membranes and with a of the of newly synthesized apoB transfer from microsomal and Golgi membranes into the presence of the MTP the of cytosolic TAG the secretion of TAG as in and TAG hepatocyte in the absence of of lipoprotein the of J. of this from from the of the lumenal apoB a to the of newly synthesized apoB in the microsomal most of which was associated with the A of labeled apoB in McA-RH7777 S. Lindberg K. Olofsson S-O. The microsomal triglyceride transfer protein the assembly of apolipoprotein very low density lipoprotein in McA-RH7777 cells.J. Biol. Chem. and in rat hepatocytes A-M. and of apolipoprotein the and Golgi compartments of hepatocytes from and Biol. Chem. the lumenal a proportion of apoB-100 or apoB-48 was associated with particles in the VLDL density The most labeled lumenal particles were associated with HDL A density of particles in the microsomal lumen of hepatocytes A-M. and of apolipoprotein the and Golgi compartments of hepatocytes from and Biol. Chem. in rat a proportion of lumenal apoB was present as particles of density L.L. Assembly of very low density lipoproteins in rat liver: a study of particles from the Lipid Res. 1995; Scholar, of a in the of very low density lipoprotein particles in the Golgi but not in the of rat Biol. Chem. the present was no in the proportion of lumenal VLDL apoB a was in the proportion of apoB associated with lumenal HDL this of from the lumen the of with a lumenal and The of the of lumenal apoB in rat Rustaeus S. Lindberg K. Olofsson S-O. The microsomal triglyceride transfer protein the assembly of apolipoprotein very low density lipoprotein in McA-RH7777 cells.J. Biol. Chem. that of of and from the into the of the denser of apoB from the was not for apoB-VLDL. primary rat hepatocytes in a then the present that the and that in the microsomal lumen were associated with the microsomal in the this the to MTP inhibition had effect on the of and VLDL that in the lumen were on apoB from which were present no the of newly synthesized apoB VLDL and HDL in the microsomal this by of the of the of newly synthesized lumenal results the that a of into the S. Lindberg K. Olofsson S-O. The microsomal triglyceride transfer protein the assembly of apolipoprotein very low density lipoprotein in McA-RH7777 cells.J. Biol. Chem. the Golgi apoB-48 and apoB-100 labeled as a of transfer of apoB in the BMS-200150 was present the the net removal of of apoB from the Golgi was to that which in the microsomal was an as of MTP the Golgi The of of Golgi membranes with was by of The of the apoB in the Golgi to the on the Golgi inhibition of MTP had no effect on the removal of labeled apoB from the lumen of the Golgi that the Golgi as an of the VLDL assembly Assembly of very low density lipoprotein in the of the Biol. Chem. Scholar, that very low density lipoprotein assembly in rat hepatocytes most of the triacylglycerol and with apolipoprotein in the Golgi Scholar, for into membranes or for secretion as lipoproteins by Golgi membranes of rat Lipid Res. in the of of a in the of very low density lipoprotein particles in the Golgi but not in the of rat Biol. 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