Inactivation of microsomal triglyceride transfer protein impairs the normal redistribution but not the turnover of newly synthesized glycerolipid in the cytosol, endoplasmic reticulum and Golgi of primary rat hepatocytes

The requirements for microsomal triglyceride transfer protein (MTP) during the turnover and transfer of glycerolipids from intracellular compartments into secretory very low-density lipoprotein (VLDL) were studied by pre-labe lling lipids with [H-3]glycerol and [C-14]oleate in primary cultures of rat hepatocytes. The intracellular redistribution of pre-labelled glycerolipid s was then compared at the end of subsequent chase periods during which the MTP inhibitor BMS-200150 was either present or absent in the medium. Inhib ition of MTP resulted in a decreased output of VLDL triacylglycerol (TAG) a nd a delayed removal of labelled TAG from the cytosol and from the membrane s of the smooth endoplasmic reticulum (SER), the cis- and the trans-Golgi. Inactivation of MTP did not decrease the bulk lipolytic turnover of cellula r TAG as reflected by changes in its [H-3]glycerol:[C-14]oleate ratios. How ever, a larger proportion of the resultant TAG fatty acids was re-esterifie d and remained with the membranes of the various subcellular fractions rath er than emerging as VLDL. The effects of BMS-200150 on the pattern of phosp holipid (PL) mechanism and redistribution suggested that inhibition of MTP prevented the normal lipolytic transfer of PL-derived fatty acids out of th e SER, cis- and trans-Golgi membrane pools. Finally, changes in the C-14 sp ecific radioactivities of the cytosolic and membrane pools of TAG suggested that inhibition of MTP prevented a normal influx of relatively unlabelled fatty acids into these pools during the chase period. (C) 1999 Elsevier Sci ence B.V. All rights reserved.