Endocytosis of Apolipoprotein A-V by Members of the Low Density Lipoprotein Receptor and the Vps10p Domain Receptor Families

• Published in: The Journal of biological chemistry Vol. 283; no. 38; pp. 25920 - 25927
• Main Authors: Nilsson, Stefan K., Christensen, Stine, Raarup, Merete K., Ryan, Robert O., Nielsen, Morten S., Olivecrona, Gunilla
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 19.09.2008; American Society for Biochemistry and Molecular Biology
• Subjects: Adaptor Proteins, Vesicular Transport; Animals; Apolipoprotein A-V; Apolipoproteins A - chemistry; Biochemistry; Biokemi; Chemistry; CHO Cells; Clinical Chemistry; Cricetinae; Cricetulus; Endocytosis; Golgi Apparatus - metabolism; Humans; Kemi; Kidney - embryology; klinisk kemi; LDL-Receptor Related Proteins - chemistry; MEDICIN; MEDICINE; Membrane Glycoproteins - chemistry; Membrane Transport Proteins - chemistry; Nerve Tissue Proteins - chemistry; Protein Binding; Protein Structure, Tertiary; Receptors, Cell Surface - chemistry; Receptors, LDL - chemistry
• ISSN: 0021-9258; 1083-351X; 1083-351X
• DOI: 10.1074/jbc.M802721200

Apolipoprotein A-V (apoA-V) is present in low amounts in plasma and has been found to modulate triacylglycerol levels in humans and in animal models. ApoA-V displays affinity for members of the low density lipoprotein receptor (LDL-R) gene family, known as the classical lipoprotein receptors, including LRP1 and SorLA/LR11. In addition to LDL-A binding repeats, the mosaic receptor SorLA/LR11 also possesses a Vps10p domain. Here we show that apoA-V also binds to sortilin, a receptor from the Vsp10p domain gene family that lacks LDL-A repeats. Binding of apoA-V to sortilin was competed by neurotensin, a ligand that binds specifically to the Vps10p domain. To investigate the biological fate of receptor-bound apoA-V, binding experiments were conducted with cultured human embryonic kidney cells transfected with either SorLA/LR11 or sortilin. Compared with nontransfected cells, apoA-V binding to SorLA/LR11- and sortilin-expressing cells was markedly enhanced. Internalization experiments, live imaging studies, and fluorescence resonance energy transfer analyses demonstrated that labeled apoA-V was rapidly internalized, co-localized with receptors in early endosomes, and followed the receptors through endosomes to the trans-Golgi network. The observed decrease of fluorescence signal intensity as a function of time during live imaging experiments suggested ligand uncoupling in endosomes with subsequent delivery to lysosomes for degradation. This interpretation was supported by experiments with 125I-labeled apoA-V, demonstrating clear differences in degradation between transfected and nontransfected cells. We conclude that apoA-V binds to receptors possessing LDL-A repeats and Vsp10p domains and that apoA-V is internalized into cells via these receptors. This could be a mechanism by which apoA-V modulates lipoprotein metabolism in vivo.