Synthesis and secretion of VLDL by rat hepatocytes--modulation by cholesterol and phospholipids.
The synthesis and secretion of apoB, the major protein component of very low density lipoprotein (VLDL) and low density lipoprotein (LDL), were studied using rat hepatocytes maintained in primary culture. Supplementation of hepatocytes with rat serum VLDL and LDL increased the production of apoB while delipidated lipoproteins had no significant effect, suggesting a role for lipids in the production of apoB. Addition of cholesterol to the culture medium also increased the production of apoB in a concentration-dependent manner. Pulse labelling followed by chase in presence of cholesterol indicated enhancement in apoB secretion. Mevinolin which inhibits cholesterol synthesis significantly reduced the secretion of apoB. The presence of phosphatidylcholine and phosphatidylethanolamine in the culture medium also increased the secretion of apoB into the medium. These data suggest that availability of lipids, particularly cholesterol, is an important determinant of apoB synthesis and secretion as VLDL.