title: Natural, proteolytic release of a soluble form of human IL-15 receptor alpha-chain that behaves as a specific, high affinity IL-15 antagonist.
abstract: IL-15 and IL-2 are two structurally and functionally related cytokines whose high affinity receptors share the IL-2R beta-chain and gamma-chain in association with IL-15R alpha-chain (IL-15R alpha) or IL-2R alpha-chain, respectively. Whereas IL-2 action seems restricted to the adaptative T cells, IL-15 appears to be crucial for the function of the innate immune responses, and the pleiotropic expression of IL-15 and IL-15R alpha hints at a much broader role for the IL-15 system in multiple cell types and tissues. In this report, using a highly sensitive radioimmunoassay, we show the existence of a soluble form of human IL-15R alpha (sIL-15R alpha) that arises from proteolytic shedding of the membrane-anchored receptor. This soluble receptor is spontaneously released from IL-15R alpha-expressing human cell lines as well as from IL-15R alpha transfected COS-7 cells. This release is strongly induced by PMA and ionomycin, and to a lesser extent by IL-1 beta and TNF-alpha. The size of sIL-15R alpha (42 kDa), together with the analysis of deletion mutants in the ectodomain of IL-15R alpha, indicates the existence of cleavage sites that are proximal to the plasma membrane. Whereas shedding induced by PMA was abrogated by the synthetic matrix metalloproteinases inhibitor GM6001, the spontaneous shedding was not, indicating the occurrence of at least two distinct proteolytic mechanisms. The sIL-15R alpha displayed high affinity for IL-15 and behaved as a potent and specific inhibitor of IL-15 binding to the membrane receptor, and of IL-15-induced cell proliferation (IC(50) in the range from 3 to 20 pM). These results suggest that IL-15R alpha shedding may play important immunoregulatory functions.
authors.affiliation: Groupe de Recherche Cytokines et Récepteurs en Immunologie et Cancérologie, Département de Cancérologie, Institut National de la Santé et de la Recherche Médicale Unité 601, Institut de Biologie, Nantes, France.
authors.forename: Erwan
authors.initials: E
authors.lastname: Mortier
authors.forename: Jérôme
authors.initials: J
authors.lastname: Bernard
authors.forename: Ariane
authors.initials: A
authors.lastname: Plet
authors.forename: Yannick
authors.initials: Y
authors.lastname: Jacques
mesh_terms: D000818:Animals; D019556:COS Cells; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism; D002522:Chlorocebus aethiops; D017077:Culture Media, Conditioned / Q000032:analysis; D018076:DNA, Complementary / Q000235:genetics; D004151:Dipeptides / Q000494:pharmacology; D005909:Glioblastoma / Q000473:pathology; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D019409:Interleukin-15 / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D016399:Lymphoma, T-Cell / Q000473:pathology; D008970:Molecular Weight; D011480:Protease Inhibitors / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D021122:Protein Subunits; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012995:Solubility; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D020298:U937 Cells / Q000187:drug effects / Q000378:metabolism
chemical_list: D017077:Culture Media, Conditioned; D018076:DNA, Complementary; D004151:Dipeptides; D017261:Glycosylphosphatidylinositols; C508024:IL15RA protein, human; D007375:Interleukin-1; D019409:Interleukin-15; C078131:N-(2(R)-2-(hydroxamidocarbonylmethyl)-4-methylpentanoyl)-L-tryptophan methylamide; D011480:Protease Inhibitors; D021122:Protein Subunits; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2; D014409:Tumor Necrosis Factor-alpha; D015759:Ionomycin; D013755:Tetradecanoylphorbol Acetate