Restoration of LDL receptor function in cells from patients with autosomal recessive hypercholesterolemia by retroviral expression of ARH1. Journal of Clinical Investigation, 110, 1695-1702

Medical Research Council, Clinical Sciences Centre, Faculty of Medicine, Imperial College, London, United Kingdom.
Journal of Clinical Investigation (Impact Factor: 13.22). 01/2003; 110(11):1695-702. DOI: 10.1172/JCI16445
Source: PubMed


Familial hypercholesterolemia is an autosomal dominant disorder with a gene-dosage effect that is usually caused by mutations in the LDL receptor gene that disrupt normal clearance of LDL. In the homozygous form, it results in a distinctive clinical phenotype, characterized by inherited hypercholesterolemia, cholesterol deposition in tendons, and severe premature coronary disease. We described previously two families with autosomal recessive hypercholesterolemia that is not due to mutations in the LDL receptor gene but is characterized by defective LDL receptor-dependent internalization and degradation of LDL by transformed lymphocytes from the patients. We mapped the defective gene to chromosome 1p36 and now show that the disorder in these and a third English family is due to novel mutations in ARH1, a newly identified gene encoding an adaptor-like protein. Cultured skin fibroblasts from affected individuals exhibit normal LDL receptor activity, but their monocyte-derived macrophages are similar to transformed lymphocytes, being unable to internalize and degrade LDL. Retroviral expression of normal human ARH1 restores LDL receptor internalization in transformed lymphocytes from an affected individual, as demonstrated by uptake and degradation of (125)I-labeled LDL and confocal microscopy of cells labeled with anti-LDL-receptor Ab.

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    • "One mutation rs5742904, located in the APOB gene, were reported to cause FH and was found in one patient (Soria et al., 1989; Taylor et al., 2010; Chatzistefanidis et al., 2013;). Another mutation (rs41291058) in LDLRAP1 gene had been linked to autosomal recessive FH (Garcia et al., 2001; Eden et al., 2002). Four mutations (rs1367117, rs679899, rs533617 and rs562556), located in the APOB and PCSK9 genes, in the HGMD database were reported to be associated with altered lipid levels or altered binding efficiency (Shioji et al., 2004; Humphries et al., 2006b; Liao et al., 2008; Makela et al., 2012; Calandra et al., 2011; Al-Waili et al., 2013). "
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    ABSTRACT: Familial hypercholesterolemia (FH) is one of the most common single gene disorders, which is mostly inherited as an autosomal dominant trait. The physical signs of FH are elevated low den- sity lipoprotein cholesterol (LDL-C), elevated total cholesterol (TC) levels and tendon xantomas. Identification and early treatment of affected individuals is desirable and in lack of physical symp- toms DNA-based diagnosis provides confirmation of diagnosis and enables early patient manage- ment. The majority of FH cases are caused by mutations in four genes (APOB, LADLR, PCSK9, and LDLRAP1). There are commercial kits available for testing of the 20 most common FH caus- ing mutations, but the spectrum of disease-causing mutations is quite diverse in various popula- tions and these tests cover only a minority of disease-causing genetic variants. There is therefore a need to determine the full spectrum of mutations in LDLR, APOB, PCSK9 and LDLRAP1 genes in each population. Here we report mutations found in 16 patients with suspected FH in a sample from the Genome Database of the Latvian population enrolled at the Latvian Centre of Cardiol- ogy. We used the next generation sequencing approach to determine the full spectrum of muta- tions in coding regions of LDLR, APOB, PCSK9, and LDLRAP1. In total we found 22 missense mutations, from which only rs5742904 (Arg3527Gln) in APOB gene had been previously de- scribed as a FH-causing mutation confirming FH in one patient. Possible FH-causing mutations however were identified in the majority of patients. The conclusion is that the most commonly em- ployed commercial mutation panel is not sufficient for diagnosis of FH patients and NGS can help to identify FH-causing mutations in the Latvian population.
    Full-text · Article · Nov 2014 · Proceedings of the Latvian Academy of Sciences Section B Natural Exact and Applied Sciences
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    • "During CME, AP-2 is known to act in the formation of clathrin-coated pits/vesicles [38], while Dab2 can either associate with AP-2 as an accessory protein [39] or act as an adaptor protein in its own right [38]. Dab2 also has numerous functions outside of CME, and so the extent of its association with clathrin-coated vesicles varies between cell types [40, 41]. In this study CLS fluorescence microscopy was used to show that AP-2α2 and Dab2 (Figure 4) are located adjacent to the periphery of both THP-1 macrophages and HMDM in a punctate staining pattern, indicative of vesicle association. "
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    ABSTRACT: Myosin VI (Myo6) functions in endocytosis in conjunction with binding partners including adaptor protein (AP)-2, disabled 2 (Dab2), and GAIP interacting protein C terminus 1 (GIPC1). This study aimed to investigate the expression and function of Myo6 in macrophages and its possible role in the endocytosis of lipoproteins during the induction of foam cell formation. Expression of Myo6, AP-2 ( α 2 subunit), and Dab2 in THP-1 macrophages and primary human monocyte-derived macrophages was demonstrated at the mRNA and protein level, but GIPC1 was only detected at the mRNA level. Immunofluorescence showed that Myo6 was distributed similarly to F-actin in both macrophage types. AP-2 α 2 was found to have a similar subcellular distribution to Myo6 and Dab2 in THP-1 cells. Myo6 was located within membrane ruffles and protrusions of the plasma membrane. These results suggest that in macrophages Myo6 is required for several functions including cell adhesion, cell progression, and macropinocytosis. Low-density lipoprotein (LDL) and oxidised LDL (oxLDL) decreased Myo6 and GIPC1 mRNA expression in THP-1 cells, but uptake of the fluorescence-labelled lipoproteins was unaffected by knockdown of the expression of Myo6 or associated proteins with siRNA. Our findings, therefore, do not support the idea that Myo6 plays a major role in foam cell formation.
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    • "AP-2 serves a general requirement in the formation of endocytic clathrin coats and is essential to internalization of myriad receptors, including LDLR, epidermal growth factor receptor (EGFR), and the transferrin receptor (Motley et al., 2003; Boucrot et al., 2010). By contrast, ARH and Dab2 are related monomeric adaptor proteins that perform more selective, tissue-specific roles in receptor endocytosis (Morris and Cooper, 2001; Eden et al., 2002; Mishra et al., 2002; Sirinian et al., 2005; Mettlen et al., 2010). ARH and Dab2 are modular scaffolding proteins containing an amino-terminal phosphotyrosine-binding (PTB) domain that engages both phospholipids and the FxNPxY internalization motif present within the cytoplasmic tail of target receptors such as LDLR (Yun et al., 2003). "
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    ABSTRACT: Low density lipoprotein receptor (LDLR) internalization clears cholesterol-laden LDL particles from circulation in humans. Defects in clathrin-dependent LDLR endocytosis promote elevated serum cholesterol levels and can lead to atherosclerosis. However, our understanding of the mechanisms that control LDLR uptake remains incomplete. To identify factors critical to LDLR uptake, we pursued a genome-wide RNAi screen using Caenorhabditis elegans LRP-1/megalin as a model for LDLR transport. In doing so, we discovered an unanticipated requirement for the clathrin-binding endocytic adaptor epsin1 in LDLR endocytosis. Epsin1 depletion reduced LDLR internalization rates in mammalian cells, similar to that observed following clathrin depletion. Genetic and biochemical analyses of epsin in C. elegans and mammalian cells uncovered a requirement for the ubiquitin-interaction motif (UIM) as critical for receptor transport. As the epsin UIM promotes the internalization of some ubiquitinated receptors, we predicted LDLR ubiquitination as necessary for endocytosis. However, engineered ubiquitination-impaired LDLR mutants showed modest internalization defects that were further enhanced with epsin1 depletion, demonstrating epsin1-mediated LDLR endocytosis is independent of receptor ubiquitination. Finally, we provide evidence that epsin1-mediated LDLR uptake occurs independently of either of the two documented internalization motifs (FxNPxY or HIC) encoded within the LDLR cytoplasmic tail, indicating an additional internalization mechanism for LDLR.
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