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Posttranscriptional Regulation of the Human LDL Receptor by the U2-Spliceosome.

Paolo ZanoniGrigorios PanteloglouAlaa OthmanJoel T HaasRoger MeierAntoine RimbertMarta FutemaYara Abou-KhalilSimon Flyvbjerg NørrelykkeAndrzej RzepielaSzymon StomaMichael SteblerFreerk van DijkMelinde WijersJustina C WoltersNawar DalilaNicolette HuijkmanMarieke SmitAntonio GalloValerie CarreauAnne PhilippiJean-Pierre RabèsCatherine BoileauMichele VisentinLuisa VonghiaJonas WeylerSven M FrancqueAn VerrijkenAnn VerhaegenLuc F Van GaalAdriaan van der GraafBelle V van RosmalenJérôme RobertSrividya VelagapudiMustafa YalcinkayaMichaela KeelSilvija RadosavljevicAndreas GeierAnne Tybjærg-HansenMathilde VarretLucia RohrerSteve E HumphriesBart StaelsBart van de SluisJan Albert KuivenhovenArnold Von Eckardstein
Published in: Circulation research (2021)
Background: The low-density lipoprotein receptor (LDLR) in the liver is the major determinant of LDL-cholesterol levels in human plasma. The discovery of genes that regulate the activity of LDLR helps to identify pathomechanisms of hypercholesterolemia and novel therapeutic targets against atherosclerotic cardiovascular disease. Methods: We performed a genome-wide RNA interference screen for genes limiting the uptake of fluorescent LDL into Huh-7 hepatocarcinoma cells. Top hit genes were validated by in vitro experiments as well as analyses of datasets on gene expression and variants in human populations. Results: The knockdown of 54 genes significantly inhibited LDL uptake. Fifteen of them encode for components or interactors of the U2-spliceosome. Knocking down any one of 11 out of 15 genes resulted in the selective retention of intron 3 of LDLR. The translated LDLR fragment lacks 88% of the full length LDLR and is detectable neither in non-transfected cells nor in human plasma. The hepatic expression of the intron 3 retention transcript is increased in non-alcoholic fatty liver disease as well as after bariatric surgery. Its expression in blood cells correlates with LDL-cholesterol and age. Single nucleotide polymorphisms and three rare variants of one spliceosome gene, RBM25, are associated with LDL-cholesterol in the population and familial hypercholesterolemia, respectively. Compared to overexpression of wild type RBM25, overexpression of the three rare RBM25 mutants in Huh-7 cells led to lower LDL uptake. Conclusions: We identified a novel mechanism of post-transcriptional regulation of LDLR activity in humans and associations of genetic variants of RBM25 with LDL-cholesterol levels.
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