title: ABCC6 prevents ectopic mineralization seen in pseudoxanthoma elasticum by inducing cellular nucleotide release.
abstract: Pseudoxanthoma elasticum (PXE) is an autosomal recessive disease characterized by progressive ectopic mineralization of the skin, eyes, and arteries, for which no effective treatment exists. PXE is caused by inactivating mutations in the gene encoding ATP-binding cassette sub-family C member 6 (ABCC6), an ATP-dependent efflux transporter present mainly in the liver. Abcc6(-/-) mice have been instrumental in demonstrating that PXE is a metabolic disease caused by the absence of an unknown factor in the circulation, the presence of which depends on ABCC6 in the liver. Why absence of this factor results in PXE has remained a mystery. Here we report that medium from HEK293 cells overexpressing either human or rat ABCC6 potently inhibits mineralization in vitro, whereas medium from HEK293 control cells does not. Untargeted metabolomics revealed that cells expressing ABCC6 excrete large amounts of nucleoside triphosphates, even though ABCC6 itself does not transport nucleoside triphosphates. Extracellularly, ectonucleotidases hydrolyze the excreted nucleoside triphosphates to nucleoside monophosphates and inorganic pyrophosphate (PPi), a strong inhibitor of mineralization that plays a pivotal role in several mineralization disorders similar to PXE. The in vivo relevance of our data are demonstrated in Abcc6(-/-) mice, which had plasma PPi levels <40% of those found in WT mice. This study provides insight into how ABCC6 affects PXE. Our data indicate that the factor that normally prevents PXE is PPi, which is provided to the circulation in the form of nucleoside triphosphates via an as-yet unidentified but ABCC6-dependent mechanism.
authors.affiliation: Divisions of Molecular Oncology and Gene Regulation, Netherlands Cancer Institute, 1066 CX, Amsterdam, The Netherlands.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Jansen
authors.forename: Aslı
authors.initials: A
authors.lastname: Küçükosmanoglu
authors.forename: Marcel
authors.initials: M
authors.lastname: de Haas
authors.forename: Sunny
authors.initials: S
authors.lastname: Sapthu
authors.forename: Jon Andoni
authors.initials: JA
authors.lastname: Otero
authors.forename: Ilse E M
authors.initials: IE
authors.lastname: Hegman
authors.forename: Arthur A B
authors.initials: AA
authors.lastname: Bergen
authors.forename: Theo G M F
authors.initials: TG
authors.lastname: Gorgels
authors.forename: P
authors.initials: P
authors.lastname: Borst
authors.forename: Koen
authors.initials: K
authors.lastname: van de Wetering
mesh_terms: D000818:Animals; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D015226:Dinucleoside Phosphates / Q000378:metabolism; D011756:Diphosphates / Q000097:blood*; D057809:HEK293 Cells; D006801:Humans; D008659:Metabolic Diseases / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D055432:Metabolomics; D051379:Mice; D018345:Mice, Knockout; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D011561:Pseudoxanthoma Elasticum / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051381:Rats
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D015226:Dinucleoside Phosphates; D011756:Diphosphates; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C102029:ABCC6 protein, human; C107241:diphosphoric acid
keywords: ATP secretion; ENPP1; MRP6; ectopic calcification