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Human plasma lipoproteins regulate apolipoprotein E secretion from a post-Golgi compartment.
S Q Ye1, L M Olson, C A Reardon
1Department of Pathology, University of Chicago, Illinois 60637.
The Journal of Biological Chemistry
|October 25, 1992
Summary
Human low-density lipoprotein (LDL) increases apolipoprotein E (apoE) protein levels in cells. This effect occurs post-translationally, specifically after the Golgi apparatus, influencing apoE secretion but not its synthesis.
Area of Science:
- Molecular biology
- Cell biology
- Biochemistry
Background:
- The regulation of apolipoprotein E (apoE) synthesis and secretion is not fully understood.
- Apolipoprotein E plays a critical role in lipid metabolism and transport.
Purpose of the Study:
- To investigate the effect of human low-density lipoprotein (LDL) on apoE mRNA and protein levels in eukaryotic cells.
- To determine the regulatory level (transcriptional, post-transcriptional, or post-translational) at which LDL influences apoE levels.
Main Methods:
- Exposure of HepG2, JeG-3, and Chinese hamster ovary (CHO) cells to human LDL.
- Measurement of apoE mRNA and protein levels using techniques like 35S labeling.
- Pulse-chase experiments and treatment with cycloheximide, brefeldin A (BFA), and protease inhibitors.
Main Results:
- LDL exposure significantly increased apoE protein accumulation in the medium by 2.2-fold without altering apoE mRNA levels.
- The LDL effect was confirmed to be post-transcriptional and specifically post-translational, occurring after the Golgi apparatus.
- LDL also increased apolipoprotein A-I (ApoA-I) accumulation but did not affect albumin levels.
Conclusions:
- LDL regulates apoE protein levels at a post-translational level, impacting its secretion.
- The cellular site of LDL's action on apoE secretion is likely a post-Golgi compartment.
- These findings provide new insights into the complex regulation of apoE metabolism by lipoproteins.