The low-density lipoprotein (LDL) receptor (LDLR) binds to and internalizes lipoproteins that contain apolipoproteinB100 (apoB100) or apolipoproteinE (apoE). Internalization of the apoB100 lipoprotein ligand, LDL, requires the FDNPVY807 sequence on the LDLR cytoplasmic domain, which binds to the endocytic machinery of coated pits. We show here that inactivation of the FDNPVY807 sequence by mutation of Y807 to cysteine prevented the uptake of LDL; however, this mutation did not prevent LDLR-dependent uptake of the apoE lipoprotein ligand, β-VLDL. Comparison of the surface localization of the LDLR-Y807C using LDLR-immunogold, LDL-gold and β-VLDL-gold probes revealed enrichment of LDLR-Y807C-bound β-VLDL in coated pits, suggesting that β-VLDL binding promoted the internalization of the LDLR-Y807C. Consistent with this possibility, treatment with monensin, which traps internalized LDLR in endosomes, resulted in the loss of surface LDLR-Y807C only when β-VLDL was present. Reconstitution experiments in which LDLR variants were introduced into LDLR-deficient cells showed that the HIC818 sequence is involved in β-VLDL uptake by the LDLR-Y807C. Together, these experiments demonstrate that the LDLR has a very low-density lipoprotein (VLDL)-induced, FDNPVY-independent internalization mechanism.
ASJC Scopus subject areas
- Molecular Biology
- Biochemistry, Genetics and Molecular Biology(all)
- Immunology and Microbiology(all)