title: A common polymorphism in the LDL receptor gene has multiple effects on LDL receptor function.
abstract: A common synonymous single nucleotide polymorphism in exon 12 of the low-density lipoprotein receptor (LDLR) gene, rs688, has been associated with increased plasma total and LDL cholesterol in several populations. Using immortalized lymphoblastoid cell lines from a healthy study population, we confirmed an earlier report that the minor allele of rs688 is associated with increased exon 12 alternative splicing (P < 0.05) and showed that this triggered nonsense-mediated decay (NMD) of the alternatively spliced LDLR mRNA. However, since synonymous single nucleotide polymorphisms may influence structure and function of the encoded proteins by co-translational effects, we sought to test whether rs688 was also functional in the full-length mRNA. In HepG2 cells expressing LDLR cDNA constructs engineered to contain the major or minor allele of rs688, the latter was associated with a smaller amount of LDLR protein at the cell surface (-21.8 ± 0.6%, P = 0.012), a higher amount in the lysosome fraction (+25.7 ± 0.3%, P = 0.037) and reduced uptake of fluorescently labeled LDL (-24.3 ± 0.7%, P < 0.01). Moreover, in the presence of exogenous proprotein convertase subtilisin/kexin type 9 (PCSK9), a protein that reduces cellular LDL uptake by promoting lysosomal degradation of LDLR, the minor allele resulted in reduced capacity of a PCSK9 monoclonal antibody to increase LDL uptake. These findings are consistent with the hypothesis that rs688, which is located in the β-propeller region of LDLR, has effects on LDLR activity beyond its role in alternative splicing due to impairment of LDLR endosomal recycling and/or PCSK9 binding, processes in which the β-propeller is critically involved.
authors.affiliation: Children’s Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Gao
authors.forename: Hansel E
authors.initials: HE
authors.lastname: Ihn
authors.forename: Marisa W
authors.initials: MW
authors.lastname: Medina
authors.forename: Ronald M
authors.initials: RM
authors.lastname: Krauss
mesh_terms: D000483:Alleles; D017398:Alternative Splicing; D005091:Exons; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011973:Receptors, LDL / Q000235:genetics* / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism
chemical_list: C573412:LDLR protein, human; D008077:Lipoproteins, LDL; D020033:Protein Isoforms; D012333:RNA, Messenger; D011973:Receptors, LDL; C472125:PCSK9 protein, human; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases