Identification of an apical sorting determinant in the cytoplasmic tail of megalin

2003 ◽  
Vol 284 (5) ◽  
pp. C1105-C1113 ◽  
Author(s):  
Tetsuro Takeda ◽  
Hajime Yamazaki ◽  
Marilyn G. Farquhar
Keyword(s):  
Mdck Cells ◽  
Receptor Gene ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Cytoplasmic Tail ◽  
Apical Plasma Membrane ◽  
Binding Motif ◽  
Cell Surface Biotinylation ◽  
Apical Sorting

Megalin is the main endocytic receptor of the proximal tubule and is responsible for reabsorption of many filtered proteins. In contrast to other members of the low-density lipoprotein (LDL) receptor gene family, it is expressed on the apical plasma membrane (PM) of polarized epithelial cells. To identify megalin's apical sorting signal, we generated deletion mutants and chimeric minireceptors composed of complementary regions of megalin and LDL receptor-related protein (LRP) and assessed the distribution of the mutants in Madin-Darby canine kidney (MDCK) cells by immunofluorescence and cell surface biotinylation. Megalin and LRP minireceptors are correctly targeted to the apical and basolateral PM, respectively, of MDCK cells. We found that the information that directs apical sorting is present in the cytoplasmic tail (CT) of megalin, which contains three NPXY motifs, YXXØ, SH3, and dileucine motifs, and a PDZ-binding motif at its COOH terminus. Deletion analysis established that amino acids 107–136 of the megalin-CT containing the second NPXY-like motif are critical for apical sorting and targeting, whereas the regions containing the first and third NPXY motifs are required for efficient endocytosis. We conclude that the megalin-CT contains a novel apical sorting determinant and that cytoplasmic sorting machinery exists in MDCK cells for some apical transmembrane proteins.

Characterization of a family of gamma-ray-induced CHO mutants demonstrates that the ldlA locus is diploid and encodes the low-density lipoprotein receptor

1986 ◽  
Vol 6 (9) ◽  
pp. 3268-3277
Author(s):  
R D Sege ◽  
K F Kozarsky ◽  
M Krieger
Keyword(s):  
Gamma Irradiation ◽  
Cho Cells ◽  
Gamma Ray ◽  
Receptor Gene ◽  
Low Density Lipoprotein ◽  
Chinese Hamster ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Low Density ◽  
Ldl Receptors

The ldlA locus is one of four Chinese hamster ovary (CHO) cell loci which are known to be required for the synthesis of functional low-density lipoprotein (LDL) receptors. Previous studies have suggested that the ldlA locus is diploid and encodes the LDL receptor. To confirm this assignment, we have isolated a partial genomic clone of the Chinese hamster LDL receptor gene and used this and other nucleic acid and antibody probes to study a family of ldlA mutants isolated after gamma-irradiation. Our analysis suggests that there are two LDL receptor alleles in wild-type CHO cells. Each of the three mutants isolated after gamma-irradiation had detectable deletions affecting one of the two LDL receptor alleles. One of the mutants also had a disruption of the remaining allele, resulting in the synthesis of an abnormal receptor precursor which was not subject to Golgi-associated posttranslational glycoprotein processing. The correlation of changes in the expression, structure, and function of LDL receptors with deletions in the LDL receptor genes in these mutants directly demonstrated that the ldlA locus in CHO cells is diploid and encodes the LDL receptor. In addition, our analysis suggests that CHO cells in culture may contain a partial LDL receptor pseudogene.

Flow cytometry with a monoclonal antibody to the low density lipoprotein receptor compared with gene mutation detection in diagnosis of heterozygous familial hypercholesterolemia

1998 ◽  
Vol 44 (5) ◽  
pp. 966-972 ◽  
Author(s):  
Bent Raungaard ◽  
Finn Heath ◽  
Jens Uffe Brorholt-Petersen ◽  
Henrik Kjærulf Jensen ◽  
Ole Faergeman
Keyword(s):  
Flow Cytometry ◽  
T Lymphocytes ◽  
Receptor Gene ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Receptor Expression ◽  
Low Density ◽  
Flow Cytometry Assay ◽  
Stop Mutation

Abstract We used a fluorescence flow cytometry assay with a monoclonal low density lipoprotein (LDL) receptor-specific antibody to detect LDL receptor expression on blood T lymphocytes and monocytes. We prepared peripheral blood mononuclear cells from patients with genetically verified LDL receptor-defective (Trp66-Gly mutation, n = 17) or receptor-negative (Trp23-stop mutation, n = 17) heterozygous familial hypercholesterolemia (FH) and from healthy individuals (n = 24). The cells were stimulated to express the maximum amount of LDL receptor by preincubation in lipoprotein-deficient medium. A dual-labeling technique allowed flow cytometric analysis of LDL receptor expression on cells identified by fluorescently conjugated surface marker antibodies. Knowing the LDL receptor gene mutation of the FH patients allowed us to compare the diagnostic capability of this functional assay with the DNA diagnosis and to validate the assay with molecular genetics instead of clinical indices of heterozygous FH. T lymphocytes expressed more LDL receptors and gave better diagnostic results than monocytes, and cells from patients with either the Trp66-Gly or the Trp23-stop mutation had variable but significantly reduced LDL receptor expression. The data indicate that this fluorescence flow cytometry assay is unsuitable for diagnosis of individual cases of heterozygous FH but that it may be useful for functionally characterizing mutations in the LDL receptor gene.

Control of low density lipoprotein receptor gene expression in steroidogenic cells

1989 ◽  
Vol 67 (8) ◽  
pp. 968-973 ◽  
Author(s):  
Koichiro Takagi ◽  
Jerome F. Strauss III
Keyword(s):  
Gene Expression ◽  
Cyclic Amp ◽  
Granulosa Cells ◽  
Receptor Gene ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Low Density ◽  
Steroidogenic Cells ◽  
Receptor Gene Expression

Low density lipoprotein (LDL)-carried cholesterol is a primary substrate for steroid hormone synthesis by luteinized human granulosa cells. Chorionic gonadotropin and 8-bromo-cAMP both increase LDL receptor levels in granulosa cells by stimulating accumulation of the receptor mRNA. LDL and 25-hydroxycholesterol reduce LDL receptor expression, but this suppressive effect is partially overcome by 8-bromo-cAMP. Using fusion gene constructs containing the LDL receptor gene promoter transfected into JEG-3 cells, a cyclic AMP responsive enhancer could not be identified in the LDL receptor gene upstream promoter in transfection studies. We suggest that the LDL receptor gene in human steroidogenic cells is under negative control by a sterol effector, but that a cyclic AMP triggered process overcomes, to some extent, the sterol-mediated suppression. The detailed mechanisms by which sterol and cyclic AMP modulate LDL receptor gene expression remain to be elucidated.Key words: low density lipoproteins, low density lipoprotein receptors, cholesterol, steroidogenesis, gonadotropins.

scholarly journals Overexpression of Cholesterol 7α-Hydroxylase (CYP7A) in Mice Lacking the Low Density Lipoprotein (LDL) Receptor Gene

1998 ◽  
Vol 273 (1) ◽  
pp. 126-132 ◽  
Author(s):  
David K. Spady ◽  
Jennifer A. Cuthbert ◽  
Maureen N. Willard ◽  
Robert S. Meidell
Keyword(s):  
Receptor Gene ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Low Density

scholarly journals A novel peroxisome proliferator response element modulates hepatic low-density lipoprotein receptor gene transcription in response to PPARδ activation

2015 ◽  
Vol 472 (3) ◽  
pp. 275-286 ◽  
Author(s):  
Vikram R. Shende ◽  
Amar Bahadur Singh ◽  
Jingwen Liu
Keyword(s):  
Gene Transcription ◽  
Receptor Gene ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Peroxisome Proliferator ◽  
Density Lipoprotein Receptor ◽  
Peroxisome Proliferator Response Element

PPARδ activation beneficially regulates lipid metabolism. We have now identified a novel function of PPARδ that increases LDL receptor gene transcription in hepatic cells in vitro and in vivo through direct binding to a PPRE motif on LDLR promoter.

scholarly journals Cholesterol Levels in Genetically Determined Familial Hypercholesterolaemia in Russian Karelia

Cholesterol ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
V. A. Korneva ◽  
T. Yu. Kuznetsova ◽  
T. Yu. Bogoslovskaya ◽  
D. S. Polyakov ◽  
V. B. Vasilyev ◽  
...  
Keyword(s):  
Ldl Cholesterol ◽  
Familial Hypercholesterolaemia ◽  
Receptor Gene ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Gene Mutations ◽  
Density Lipoprotein ◽  
Single Strand Conformation Polymorphism ◽  
Polymorphism Analysis ◽  
Cholesterol Levels

Familial hypercholesterolaemia (FH) is a rare disease that tends to be diagnosed lately. In Russia, the genetic and phenotypic characteristics of the disease are not well defined. We investigated 102 patients with definite FH. In 52 of these patients (50.9%) genetic analysis was performed, revealing pathogenic mutations of the low density lipoprotein (LDL) receptor gene in 22 patients. We report here five mutations of the LDL receptor gene found in the Karelian FH sample for the first time. The detection rate of mutations in definite FH patients was 42.3%. Two groups of patients with a definite diagnosis of FH according to the Dutch Lipid Clinic Network criteria were compared: the first group had putatively functionally important LDL receptor gene mutations, while in the second group LDL receptor gene mutations were excluded by single-strand conformation polymorphism analysis. Total and LDL cholesterol levels were higher in the group with LDL receptor mutations compared to the mutation-free population. The frequency of mutations in patients with LDL cholesterol > 6.5 mmol/L was more than 3 times higher than that in patients with LDL < 6.5 mmol/L. Total and LDL cholesterol levels and the frequency of coronary heart disease and myocardial infarction were higher in the group with definite FH compared to groups with probable and possible FH. Cholesterol figures in FH patients of different age and sex from the Karelian population were comparable.

Use of polymerase chain reaction to detect heterozygous familial hypercholesterolemia

1990 ◽  
Vol 36 (6) ◽  
pp. 900-903 ◽  
Author(s):  
M Keinänen ◽  
J P Ojala ◽  
E Helve ◽  
K Aalto-Setälä ◽  
K Kontula ◽  
...  
Keyword(s):  
Polymerase Chain Reaction ◽  
Familial Hypercholesterolemia ◽  
Receptor Gene ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Amplification Product ◽  
Chain Reaction ◽  
Oligonucleotide Primers ◽  
Polymerase Chain

Abstract We used a modification of the polymerase chain reaction (PCR), involving two pairs of oligonucleotide primers, to detect a mutation in the low-density lipoprotein (LDL) receptor gene, commonly occurring among patients with familial hypercholesterolemia (FH) in Finland. This mutation, called FH-Helsinki, involves a large (about 9500 base pairs, bp) deletion in the LDL receptor gene extending from intron 15 to exon 18. For the PCR, one pair of primers was designed to cover both sides of the deletion in its immediate vicinity. In the presence of the deletion, the primers were brought close enough to each other to allow the amplification and electrophoretic detection of a 300-bp amplification product. In the absence of the deletion, no amplification occurred and this band accordingly was not visible in the gel. To render the interpretation of the results unequivocal, we designed a second pair of oligonucleotide primers. This pair of primers allowed another amplification product (158 bp) to appear in samples containing a normal exon 17, i.e., in DNA specimens from healthy subjects and FH heterozygotes with or without the FH-Helsinki deletion. The technique is easy to perform, avoids the use of radioactive reagents, and is applicable to the detection of any extensive DNA deletion.

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