title: CysLT1 receptor is a target for extracellular nucleotide-induced heterologous desensitization: a possible feedback mechanism in inflammation.
abstract: Both cysteinyl-leukotrienes and extracellular nucleotides mediate inflammatory responses via specific G-protein-coupled receptors, the CysLT and the P2Y receptors, respectively. Since these mediators accumulate at sites of inflammation, and inflammatory cells express both classes of receptors, their responses are likely to be crossregulated. We investigated the molecular basis of desensitization and trafficking of the CysLT1 receptor constitutively and transiently expressed in the human monocyte/macrophage-like U937 or COS-7 cells in response to LTD4 or nucleotides. Exposure to agonist induced a rapid homologous desensitization of the CysLT1 receptor [as measured by the reduction in the maximal agonist-induced intracellular cytosolic Ca2+ ([Ca2+]i) transient], followed by receptor internalization (as assessed by equilibrium binding and confocal microscopy). Activation of P2Y receptors with ATP or UDP induced heterologous desensitization of the CysLT1 receptor. Conversely, LTD4-induced CysLT1 receptor activation had no effect on P2Y receptor responses, which suggests that the latter have a hierarchy in producing desensitizing signals. Furthermore, ATP/UDP-induced CysLT1 receptor desensitization was unable to cause receptor internalization, induced a faster recovery of CysLT1 functionality and was dependent upon protein kinase C. By contrast, homologous desensitization, which is probably dependent upon G-protein-receptor kinase 2 activation, induced a fast receptor downregulation and, accordingly, a slower recovery of CysLT1 functionality. Hence, CysLT1 receptor desensitization and trafficking are differentially regulated by the CysLT1 cognate ligand or by extracellular nucleotides. This crosstalk may have a profound physiological implication in the regulation of responses at sites of inflammation, and may represent just an example of a feedback mechanism used by cells to fine-tune their responses.
authors.affiliation: Laboratory of Molecular Pharmacology, Section of Eicosanoid Pharmacology, Department of Pharmacological Sciences, University of Milan, Via Balzaretti 9, 20133 Milan, Italy.
authors.forename: Valérie
authors.initials: V
authors.lastname: Capra
authors.forename: Saula
authors.initials: S
authors.lastname: Ravasi
authors.forename: Maria Rosa
authors.initials: MR
authors.lastname: Accomazzo
authors.forename: Simona
authors.initials: S
authors.lastname: Citro
authors.forename: Monica
authors.initials: M
authors.lastname: Grimoldi
authors.forename: Maria P
authors.initials: MP
authors.lastname: Abbracchio
authors.forename: G Enrico
authors.initials: GE
authors.lastname: Rovati
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D002522:Chlorocebus aethiops; D004305:Dose-Response Relationship, Drug; D045604:Extracellular Fluid / Q000378:metabolism; D025461:Feedback, Physiological / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D007249:Inflammation / Q000378:metabolism*; D017998:Leukotriene D4 / Q000494:pharmacology; D008565:Membrane Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism*; D017239:Paclitaxel / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D018077:Receptors, Leukotriene / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D015290:Second Messenger Systems / Q000502:physiology; D020298:U937 Cells; D014530:Uridine Diphosphate / Q000494:pharmacology
chemical_list: D008565:Membrane Proteins; D009711:Nucleotides; D010456:Peptides, Cyclic; D018077:Receptors, Leukotriene; D018048:Receptors, Purinergic P2; C475455:YM-254890; D014530:Uridine Diphosphate; D017998:Leukotriene D4; D000255:Adenosine Triphosphate; D011494:Protein Kinases; C083169:leukotriene D4 receptor; D017239:Paclitaxel; D002118:Calcium