title: An Ile-568 to Asn polymorphism prevents normal trafficking and function of the human P2X7 receptor.
abstract: The P2X(7) receptor is a ligand-gated channel that is highly expressed on mononuclear cells and that mediates ATP-induced apoptosis of these cells. Wide variations in the function of the P2X(7) receptor have been observed, in part because of a loss-of-function polymorphism that changes Glu-496 to Ala without affecting the surface expression of the receptor on lymphocytes. In this study a second polymorphism (Ile-568 to Asn) has been found in heterozygous dosage in three of 85 normal subjects and in three of 45 patients with chronic lymphocytic leukemia. P2X(7) function was measured by ATP-induced fluxes of Rb(+), Ba(2+), and ethidium(+) into various lymphocyte subsets and was decreased to values of approximately 25% of normal. The expression of the P2X(7) receptor on lymphocytes was approximately half that of normal values as measured by the binding of fluorescein-conjugated monoclonal antibody. Transfection experiments showed that P2X(7) carrying the Ile-568 to Asn mutation was non-functional because of the failure of cell surface expression. The differentiation of monocytes to macrophages with interferon-gamma up-regulated P2X(7) function in cells heterozygous for the Ile-568 to Asn mutation to a value around 50% of normal. These data identify a second loss-of-function polymorphism within the P2X(7) receptor and show that Ile-568 is critical to the trafficking domain, which we have shown to lie between residues 551 and 581.
authors.affiliation: Department of Medicine, University of Sydney at Nepean Hospital, Penrith, New South Wales 2750, Australia. wileyj@medicine.usyd.edu.au
authors.forename: James S
authors.initials: JS
authors.lastname: Wiley
authors.forename: Lan-Phuong
authors.initials: LP
authors.lastname: Dao-Ung
authors.forename: Changping
authors.initials: C
authors.lastname: Li
authors.forename: Anne N
authors.initials: AN
authors.lastname: Shemon
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Gu
authors.forename: Megan L
authors.initials: ML
authors.lastname: Smart
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Fuller
authors.forename: Julian A
authors.initials: JA
authors.lastname: Barden
authors.forename: Steven
authors.initials: S
authors.lastname: Petrou
authors.forename: Ronald
authors.initials: R
authors.lastname: Sluyter
mesh_terms: D001216:Asparagine; D002460:Cell Line; D006801:Humans; D007532:Isoleucine; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D009154:Mutation; D020641:Polymorphism, Single Nucleotide; D017434:Protein Structure, Tertiary / Q000235:genetics; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D058486:Receptors, Purinergic P2X7; D015398:Signal Transduction / Q000235:genetics
chemical_list: C546468:P2RX7 protein, human; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D007532:Isoleucine; D001216:Asparagine