ABSTRACT
LR11, also known as SorLA or SORL1, is a type-I membrane protein from which a large extracellular part, soluble LR11 (sLR11), is released by proteolytic shedding on cleavage with a disintegrin and metalloproteinase 17 (ADAM17). A shedding mechanism is presumed to have a key role in the functions of LR11, but the evidence for this has not yet been demonstrated. Tetraspanin CD9 has been recently shown to regulate the ADAM17-mediated shedding of tumor necrosis factor-alpha and intercellular adhesion molecule-1 on the cell surface. Here, we investigated the role of CD9 on the shedding of LR11 in leukocytes. LR11 was not expressed in THP-1 monocytes, but it was expressed and released in phorbol 12-myristate 13-acetate (PMA)-induced THP-1 macrophages (PMA/THP-1). Confocal microscopy showed colocalization of LR11 and CD9 proteins on the cell surface of PMA/THP-1. Ectopic neo-expression of CD9 in CCRF-SB cells, which are LR11-positive and CD9-negative, reduced the amount of sLR11 released from the cells. In contrast, incubation of LR11-transfected THP-1 cells with neutralizing anti-CD9 monoclonal antibodies increased the amount of sLR11 released from the cells. Likewise, the PMA-stimulated release of sLR11 increased in THP-1 cells transfected with CD9-targeted shRNAs, which was negated by treatment with the metalloproteinase inhibitor GM6001. These results suggest that the tetraspanin CD9 modulates the ADAM17-mediated shedding of LR11 in various leukemia cell lines and that the association between LR11 and CD9 on the cell surface has an important role in the ADAM17-mediated shedding mechanism.
Subject(s)
Humans , ADAM Proteins/metabolism , Tetraspanin 29/genetics , Cell Line, Tumor , LDL-Receptor Related Proteins/genetics , Leukocytes/metabolism , Macrophages/metabolism , Membrane Transport Proteins/genetics , ProteolysisABSTRACT
In this study, we investigated the associations between single-nucleotide polymorphisms in GAB2 (rs2373115), GSK3B (rs6438552) and SORL1 (rs641120) and Alzheimer's disease (AD), both alone and in combination with the APOE*4 allele.
Subject(s)
Aged , Female , Humans , Male , Adaptor Proteins, Signal Transducing/genetics , Alzheimer Disease/genetics , /genetics , Cytoskeletal Proteins/genetics , LDL-Receptor Related Proteins/genetics , Membrane Transport Proteins/genetics , Nuclear Proteins/genetics , Polymorphism, Single Nucleotide/genetics , Age of Onset , Risk FactorsSubject(s)
Animals , Humans , Male , Mice , Middle Aged , Atherosclerosis/genetics , /genetics , Hypertension/genetics , LDL-Receptor Related Proteins/deficiency , Bone Diseases, Metabolic/genetics , Chromosome Mapping , Dyslipidemias/genetics , Genes, Dominant , Iran , LDL-Receptor Related Proteins/genetics , LDL-Receptor Related Proteins/physiology , Mice, Knockout , Models, Biological , Myocardial Ischemia/genetics , Phenotype , Signal Transduction , TCF Transcription Factors/physiology , Wnt Proteins/physiology , beta Catenin/physiologyABSTRACT
Heterozygous familial hypercholesterolemia affects one every 400 individuals, is caused by mutations in the LDL receptor gene and is associated with premature coronary artery disease. Nowadays, LDL cholesterol can be efficiently reduced with the new therapies to reduce blood lipids. We report a female patient who consulted in 1975, when she was 46 years old, for severe hypercholesterolemia. In 2003, a sample of leukocyte DNA was obtained and the uncommon 1705 + 1G >A mutation of the LDL receptor gene was detected. No mutations in the apolipoprotein B gene were found. The patient was treated successfully with simvastatin 80 mg/day and ezetimibe 10 mg/day and LDL cholesterol levels were reduced below 200 mg/dl.