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. 1995 Sep 15;310(Pt 3):897–907. doi: 10.1042/bj3100897

Intracellular events in the assembly of very-low-density-lipoprotein lipids with apolipoprotein B in isolated rabbit hepatocytes.

I J Cartwright 1, J A Higgins 1
PMCID: PMC1135981  PMID: 7575425

Abstract

Isolated rabbit hepatocytes incorporated [35S]methionine into cellular and secreted apolipoprotein B (apo-B), and [3H]glycerol into cellular and secreted triacylglycerol and phospholipids. Newly synthesized apo-B was incorporated into rough endoplasmic reticulum (RER), smooth endoplasmic reticulum (SER), cis-Golgi and trans-Golgi membranes and was preferentially transferred into the lumen of the RER with specific radioactivities ten times those in the membrane. Radiolabelled apo-B did not equilibrate with pre-existing unlabelled apo-B, and pools of different specific radioactivities were established in different subcellular fractions. Only a small fraction of the newly synthesized apo-B was transferred to the Golgi lumen. In pulse-chase experiments, most of the newly synthesized apo-B in the RER membrane and the RER lumen was degraded. [3H]Glycerol was incorporated into triacylglycerol and phospholipids in the lumen of the RER, SER, cis-Golgi and trans-Golgi. However, in contrast with apo-B, all of the radiolabelled lipids in the lumen of the RER, SER and cis-Golgi were transferred to the trans-Golgi lumen or secreted. Analysis of the lipid composition of the lumenal content fractions suggests that, although very-low-density-lipoprotein (VLDL) lipids are present in the endoplasmic reticulum lumen, a large fraction of these is not associated with apo-B. Collectively these observations suggest that assembly of apo-B into complete VLDL is not cotranslational, that most lipids become associated with apo-B late in the endoplasmic reticulum compartment and that the lipids are further modified in the Golgi lumen.

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Selected References

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