Monensin Enhances the Binding of LDL to Human Hepatocyte-Like C3A Cells without Increasing the Number of LDL Receptors at the Plasma Membrane
Abstract
The hepatic LDL receptor is the major determinant of plasma LDL levels, and as a result, a greater
understanding of the regulatory mechanisms that control LDL receptor expression and function is essential.
Herein, we optimized a biotinylation assay that was able to differentiate between cell surface (plasma membrane)
and intracellular LDL receptors. We also tested monensin, a chemical that prevents the recycling of the LDL
receptors to the cell surface and enhances the number of receptors that can bind and internalize LDL. Herein, it
was confirmed the effects of monensin on the ability of the LDL receptor to bind LDL, and demonstrated for the
first time, using the biotinylation assay, that monensin did not affect the LDL receptor expression levels at the
plasma membrane or inside the cell. This was confirmed using immunocy to chemistry and Western blotting
analysis. Monensin treatment may enhance the distribution of the LDL receptor to clathrin-coated pits explaining
the higher binding of LDL, but not of VLDL, to the cells. This effect of monensin did not require upregulation of
the LDL receptor expression. This indicates that the biotinylation assay described herein, in combination with
monensin treatment, could be used in future studies to determine the effects of different treatments/drugs on the
plasma membrane distribution/function of the hepatic LDL receptors.
