title: Quantitative fluorescence imaging reveals point of release for lipoproteins during LDLR-dependent uptake.
abstract: The LDL receptor (LDLR) supports efficient uptake of both LDL and VLDL remnants by binding lipoprotein at the cell surface, internalizing lipoprotein through coated pits, and releasing lipoprotein in endocytic compartments before returning to the surface for further rounds of uptake. While many aspects of lipoprotein binding and receptor entry are well understood, it is less clear where, when, and how the LDLR releases lipoprotein. To address these questions, the current study employed quantitative fluorescence imaging to visualize the uptake and endosomal processing of LDL and the VLDL remnant β-VLDL. We find that lipoprotein release is rapid, with most release occurring prior to entry of lipoprotein into early endosomes. Published biochemical studies have identified two mechanisms of lipoprotein release: one that involves the β-propeller module of the LDLR and a second that is independent of this module. Quantitative imaging comparing uptake supported by the normal LDLR or by an LDLR variant incapable of β-propeller-dependent release shows that the β-propeller-independent process is sufficient for release for both lipoproteins but that the β-propeller process accelerates both LDL and β-VLDL release. Together these findings define where, when, and how lipoprotein release occurs and provide a generalizable methodology for visualizing endocytic handling in situ.
authors.affiliation: Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX.
authors.forename: Shanica
authors.initials: S
authors.lastname: Pompey
authors.affiliation: Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX.
authors.forename: Zhenze
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX.
authors.forename: Kate
authors.initials: K
authors.lastname: Luby-Phelps
authors.affiliation: Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX.
authors.forename: Peter
authors.initials: P
authors.lastname: Michaely
mesh_terms: D002478:Cells, Cultured; D011992:Endosomes / Q000378:metabolism; D005453:Fluorescence; D005455:Fluorescent Antibody Technique; D006801:Humans; D008074:Lipoproteins / Q000378:metabolism*; D053419:Lipoproteins, IDL / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D061848:Optical Imaging; D011973:Receptors, LDL / Q000378:metabolism*
chemical_list: D008074:Lipoproteins; D053419:Lipoproteins, IDL; D008077:Lipoproteins, LDL; D011973:Receptors, LDL