title: LRP6 protein regulates low density lipoprotein (LDL) receptor-mediated LDL uptake.
abstract: Genetic variations in LRP6 gene are associated with high serum LDL cholesterol levels. We have previously shown that LDL clearance in peripheral B-lymphocytes of the LRP6(R611C) mutation carriers is significantly impaired. In this study we have examined the role of wild type LRP6 (LRP6(WT)) and LRP6(R611C) in LDL receptor (LDLR)-mediated LDL uptake. LDL binding and uptake were increased when LRP6(WT) was overexpressed and modestly reduced when it was knocked down in LDLR-deficient CHO (ldlA7) cells. These findings implicated LRP6 in LDLR-independent cellular LDL binding and uptake. However, LRP6 knockdown in wild type CHO cells resulted in a much greater decline in LDL binding and uptake compared with CHO-ldlA7 cells, suggesting impaired function of the LDLR. LDLR internalization was severely diminished when LRP6 was knocked down and was restored after LRP6 was reintroduced. Further analysis revealed that LRP6(WT) forms a complex with LDLR, clathrin, and ARH and undergoes a clathrin-mediated internalization after stimulation with LDL. LDLR and LRP6 internalizations as well as LDL uptake were all impaired in CHO-k1 cells expressing LRP6(R611C). These studies identify LRP6 as a critical modulator of receptor-mediated LDL endocytosis and introduce a mechanism by which variation in LRP6 may contribute to high serum LDL levels.
authors: Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
authors: Zhi-jia
authors: ZJ
authors: Ye
authors: Gwang-Woong
authors: GW
authors: Go
authors: Rajvir
authors: R
authors: Singh
authors: Wenzhong
authors: W
authors: Liu
authors: Ali Reza
authors: AR
authors: Keramati
authors: Arya
authors: A
authors: Mani
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D016466:CHO Cells; D002966:Clathrin / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D004705:Endocytosis / Q000502:physiology*; D005347:Fibroblasts; D055785:Gene Knockdown Techniques; D006801:Humans; D008077:Lipoproteins, LDL / Q000097:blood*; D060488:Low Density Lipoprotein Receptor-Related Protein-6 / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002966:Clathrin; C469745:LDLRAP1 protein, human; C555475:LRP6 protein, human; D008077:Lipoproteins, LDL; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D011973:Receptors, LDL