ABSTRACT
Phospholipase A2 receptor 1 (PLA2R1) is a 180-kDa transmembrane protein that plays a role in inflammation and cancer and is the major autoantigen in membranous nephropathy, a rare but severe autoimmune kidney disease. A soluble form of PLA2R1 has been detected in mouse and human serum. It is likely produced by proteolytic shedding of membrane-bound PLA2R1 but the mechanism is unknown. Here, we show that human PLA2R1 is cleaved by A Disintegrin And Metalloprotease 10 (ADAM10) and ADAM17 in HEK293 cells, mouse embryonic fibroblasts, and human podocytes. By combining site-directed mutagenesis and sequencing, we determined the exact cleavage site within the extracellular juxtamembrane stalk of human PLA2R1. Orthologs and paralogs of PLA2R1 are also shed. By using pharmacological inhibitors and genetic approaches with RNA interference and knock-out cellular models, we identified a major role of ADAM10 in the constitutive shedding of PLA2R1 and a dual role of ADAM10 and ADAM17 in the stimulated shedding. We did not observe evidence for cleavage by ß- or γ-secretase, suggesting that PLA2R1 may not be a substrate for regulated intramembrane proteolysis. PLA2R1 shedding occurs constitutively and can be triggered by the calcium ionophore ionomycin, the protein kinase C activator PMA, cytokines, and lipopolysaccharides, in vitro and in vivo. Altogether, our results show that PLA2R1 is a novel substrate for ADAM10 and ADAM17, producing a soluble form that is increased in inflammatory conditions and likely exerts various functions in physiological and pathophysiological conditions including inflammation, cancer, and membranous nephropathy.
Subject(s)
ADAM10 Protein , ADAM17 Protein , Amyloid Precursor Protein Secretases , Membrane Proteins , Receptors, Phospholipase A2 , ADAM10 Protein/metabolism , ADAM10 Protein/genetics , Humans , ADAM17 Protein/metabolism , ADAM17 Protein/genetics , Amyloid Precursor Protein Secretases/metabolism , Amyloid Precursor Protein Secretases/genetics , Animals , Membrane Proteins/metabolism , Membrane Proteins/genetics , Mice , HEK293 Cells , Receptors, Phospholipase A2/metabolism , Receptors, Phospholipase A2/genetics , Podocytes/metabolism , Proteolysis , Protein Domains , Ionomycin/pharmacologyABSTRACT
Genome-wide association studies (GWAS) have associated several genetic variants with late-onset Alzheimer's disease (LOAD), a neurodegenerative disease. Among those, rs3764650 ABCA7, rs6656401 CR1, and rs744373 BIN1 were associated as risk factors for LOAD, while rs11136000 CLU and rs610932 MS4A6A were protective. Recently, several case-control studies have investigated the association of these polymorphisms with AD. However, not all meta-analyses analyzed these variants across different ethnic groups. Therefore, we performed an updated meta-analysis of rs3764650 ABCA7, rs6656401 CR1, rs744373 BIN1, rs11136000 CLU, and rs610932 MS4A6A variants associated with LOAD, considering different ethnic populations. We utilized samples from 38 articles, comprising a total of 24,771 patients and 35,324 controls obtained through the PubMed database. Odds ratios (ORs) with 95% confidence intervals (CI) for polymorphisms were calculated by allelic comparison as an additive genetic model. We validated the risk for LOAD with BIN1 (rs744373), CR1 (rs6656401), and ABCA7 (rs376465), as well as the protective association for MS4A6A (rs610932) and CLU (rs11136000) variants.
Subject(s)
ATP-Binding Cassette Transporters/genetics , Adaptor Proteins, Signal Transducing/genetics , Alzheimer Disease/genetics , Clusterin/genetics , Membrane Proteins/genetics , Nuclear Proteins/genetics , Polymorphism, Single Nucleotide , Receptors, Complement 3b/genetics , Tumor Suppressor Proteins/genetics , HumansABSTRACT
Late-onset Alzheimer's disease (LOAD) is a multifactorial neurodegenerative disorder that corresponds to most Alzheimer's disease (AD) cases. Inflammation is frequently related to AD, whereas microglial cells are the major phagocytes in the brain and mediate the removal of Aß peptides. Microglial cell dsyregulation might contribute to the formation of amyloid plaques, a hallmark of AD. Genome-wide association studies have reported genetic loci associated with the inflammatory pathway involved in AD. Among them, rs3865444 CD33, rs3764650 ABCA7, rs6656401 CR1, and rs610932 MS4A6A variants in microglial genes are associated with LOAD. These variants are proposed to participate in the clearance of Aß peptides. However, their association with LOAD was not validated in all case-control studies. Thus, the present work aimed to assess the involvement of CD33 (rs3865444), ABCA7 (rs3764650), CR1 (rs6656401), and MS4A6A (rs610932) with LOAD in a sample from southeastern Brazil. The genotype frequencies were assessed in 79 AD patients and 145 healthy elders matched for sex and age. We found that rs3865444 CD33 acts as a protective factor against LOAD. These results support a role for the inflammatory pathway in LOAD.
