title: Adaptor protein disabled-2 modulates low density lipoprotein receptor synthesis in fibroblasts from patients with autosomal recessive hypercholesterolaemia.
abstract: Autosomal recessive hypercholesterolaemia (ARH), characterized clinically by severe inherited hypercholesterolaemia, is caused by recessive null mutations in LDLRAP1 (formerly ARH). Immortalized lymphocytes and monocyte-macrophages, and presumably hepatocytes, from ARH patients fail to take up and degrade plasma low density lipoproteins (LDL) because they lack LDLRAP1, a cargo-specific adaptor required for clathrin-mediated endocytosis of the LDL receptor. Surprisingly, LDL-receptor function is normal in ARH patients' skin fibroblasts in culture. Disabled-2 (Dab2) has been implicated previously in clathrin-mediated internalization of LDL-receptor family members, and we show here that Dab2 is highly expressed in skin fibroblasts, but not in lymphocytes. SiRNA-depletion of Dab2 profoundly reduced LDL-receptor activity in ARH fibroblasts as a result of profound reduction in LDL-receptor protein, but not mRNA; heterologous expression of murine Dab2 reversed this effect. In contrast, LDL-receptor protein content was unchanged in Dab-2-depleted control cells. Incorporation of 35S-labelled amino acids into LDL receptor protein revealed a corresponding apparent reduction in accumulation of newly synthesized LDL-receptor protein on depletion of Dab2 in ARH, but not in control, cells. This reduction in LDL-receptor protein in Dab2-depleted ARH cells could not be reversed by treatment of the cells with proteasomal or lysosomal inhibitors. Thus, we propose a novel role for Dab2 in ARH fibroblasts, where it is apparently required to allow normal translation of LDL receptor mRNA.
authors.affiliation: MRC Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, DuCane Road, London W12 ONN, UK.
authors.forename: Emily R
authors.initials: ER
authors.lastname: Eden
authors.forename: Xi-Ming
authors.initials: XM
authors.lastname: Sun
authors.forename: Dilipkumar D
authors.initials: DD
authors.lastname: Patel
authors.forename: Anne K
authors.initials: AK
authors.lastname: Soutar
mesh_terms: D033962:Adaptor Protein Complex 2 / Q000235:genetics / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D016022:Case-Control Studies; D006224:Cricetinae; D003412:Cricetulus; D004705:Endocytosis; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D005808:Genes, Recessive; D006801:Humans; D006938:Hyperlipoproteinemia Type II / Q000235:genetics*; D008214:Lymphocytes / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism*; D012867:Skin / Q000378:metabolism* / Q000473:pathology; D014158:Transcription, Genetic
chemical_list: D033962:Adaptor Protein Complex 2; D048868:Adaptor Proteins, Signal Transducing; C469745:LDLRAP1 protein, human; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011973:Receptors, LDL