Activity and specificity of toxin-related mouse T cell ecto–ADP-ribosyltransferase ART2.2 depends on its association with lipid rafts

Abstract

IntroductionART2.2 is a glycosylphosphatidylinositol (GPI)-anchored ectoenzyme expressed on the surfaces of most terminally differentiated T cells. 1 ART2.2 is related in structure and function to adenosine diphosphate (ADP)-ribosylating bacterial toxins. [2][3][4] After the release of the ADP-ribosyltransferase (ART) substrate nicotinamide adenine dinucleotide (NAD) from cells by lytic or nonlytic mechanisms, ART2.2 catalyzes the transfer of ADP-ribose from NAD onto arginine residues onto leukocyte function-associated antigen (LFA-1), the P2X7 purinoceptor, and other cell-surface proteins. 5,6 Akin to protein phosphorylation, protein ADPribosylation usually profoundly affects the function of the modified target protein. 7,8 ADP-ribosylation activates P2X7, triggering calcium flux, phosphatidylserine flashing, and nonselective pore formation in the cell membrane. 6 ADP-ribosylation of LFA-1 and other cell-surface proteins inhibits the binding of T cells to target cells and interferes with the clustering of the T-cell receptor (TCR). 5,9 Lipid rafts, also known as glycosphingolipid-enriched membranes (GEMs) or detergent-insoluble glycosphingolipid-enriched membranes (DIGs), are plasma membrane microdomains enriched in gangliosides and cholesterol that form liquid-ordered domains. [10][11][12] It is postulated that lipid rafts segregate molecules in the plasma membrane and regulate signaling through the spatial coordination of intermolecular interactions. Lipid rafts are characterized by insolubility in nonionic detergents and low buoyancy in sucrose density gradients. The posttranslational modification of proteins with saturated acyl groups can result in their localization within lipid rafts. Thus, these microdomains are enriched in many signaling molecules, such as the lck protein kinase, the adaptor protein LAT, heterotrimeric G proteins, and GPI-anchored proteins. 13 In addition, TCR and other transmembrane receptors, including interleukin-2 (IL-2) receptor and LFA-1, are inducibly recruited or stabilized in lipid rafts. [14][15][16] Activation of signaling molecules in lipid rafts is thought to facilitate signaling through the TCR and other immunoreceptors. 17 Some cell-surface proteins lack a transmembrane-spanning domain and are anchored in the outer leaflet of the plasma membrane by a GPI moiety. The physiologic significance of the GPI anchor is unknown. Despite the fact that GPI-anchored proteins are restricted to the outer leaflet of the membrane lipid bilayer and lack a cytoplasmic domain, many GPI-anchored proteins can mediate signaling events after the binding of specific antibodies. 18 With Qa-2, CD55, and CD59, it has been shown that exchange of the GPI anchor by a transmembrane anchor abrogates antibody-induced signaling. [19][20][21] The association of GPI-anchored proteins with Src family kinases in lipid rafts may explain the involvement of GPI-anchored proteins in signaling.Considering that ART2.2 and other members of the ART family carry a GPI anchor, 22,23 we hypothesized that the GPI anchor ...

Lipid metabolism modulation by the P2X7 receptor in the immune system and during the course of infection: new insights into the old view

“…3 and unpublished data), which corroborates with published findings [27,88]. P2X7R has been shown to be at least partially localized to the lipid raft fraction in T cells, and the authors suggested that lipid raft localization facilitated ADP-ribosylation of P2X7R [89]. Much evidence has indicated that rafts play an important role in T cell activation in immunological synapses between T cells and antigen-presenting cells.…”

NAD+ and ATP Released from Injured Cells Induce P2X7-Dependent Shedding of CD62L and Externalization of Phosphatidylserine by Murine T Cells

“…ART2.2 is known to ADP-ribosylate several distinct T cell surface proteins (14,29,56). ADP-ribosylation sites on cell surface proteins already occupied during cell preparation would not be available to subsequent ADP-ribosylation, e.g., upon addition of exogenously added NAD ϩ .…”

“…This is the mechanism by which several bacterial toxins, like cholera-and pertussis-toxin, cause pathology after translocating into mammalian host cells (11). ART2.2 is a GPI-anchored, raft-associated ecto-enzyme prominently expressed by murine T cells (12)(13)(14). ART2.2 catalyzes ADP-ribosylation of CD8, the integrin LFA-1, the P2X 7 receptor, and several other target proteins (12)(13)(14)(15).…”

“…ART2.2 is a GPI-anchored, raft-associated ecto-enzyme prominently expressed by murine T cells (12)(13)(14). ART2.2 catalyzes ADP-ribosylation of CD8, the integrin LFA-1, the P2X 7 receptor, and several other target proteins (12)(13)(14)(15). T cell activation induces the metalloprotease-mediated shedding of a soluble, enzymatically active isoform of ART2.2 (16).…”

Emerging Functions of Extracellular Pyridine Nucleotides

“…The ART2-encoding gene has been duplicated into 2 functional copies in the murine lineage, but has been inactivated by premature stop codons in humans and other primates (17). ART2 is expressed on murine T cells in association with lipid rafts (18). Exposure of ART2-expressing cells to NAD results in ADP-ribosylation of the P2X 7 purinoceptor, CD38, the LFA-1 integrin (CD11a/ CD18), and other raft-associated signal- -releasing CD38 metabolites cADPR and NAADP are transported across the plasma membrane to reach their intracellular sites of action while NAD can be released or transported out of the cell.…”