title: Dexamethasone enhances interaction of endogenous annexin 1 with L-selectin and triggers shedding of L-selectin in the monocytic cell line U-937.
abstract: (1) L-selectin, constitutively expressed by leukocytes, is involved in the initial binding of leukocytes to activated endothelium. Anti-inflammatory drugs like glucocorticoids can induce shedding of L-selectin, but the mechanism is still unknown. Annexin 1, a protein whose synthesis and externalization/secretion are induced during the inflammatory response, has been proposed as a mediator of the anti-inflammatory actions of glucocorticoids. (2) The monocytic cell line U-937 strongly expresses Annexin 1 after 24 h of phorbol 12-myristate 13-acetate (PMA, 1 nm) treatment and externalizes/releases the protein after additional 16 h of dexamethasone (1 microm) treatment. (3) This study investigated the possible regulation of cell surface L-selectin shedding by endogenous Annexin 1, and its role in glucocorticoid-induced L-selectin shedding in the U-937 cell line. (4) PMA- and dexamethasone treatment-induced L-selectin shedding was potentially mediated by Annexin 1, since neutralizing antibodies against Annexin 1 reduced dexamethasone- and Annexin 1-induced shedding. (5) Immunoprecipitation and binding assays provided support for the suggestion that this effect could be mediated by an interaction between externalized Annexin 1 and L-selectin. Such interaction involved the N-terminal domain of Annexin 1 and was calcium-dependent. Confocal microscopy studies demonstrated increased colocalization of Annexin 1 and L-selectin on the cell surface. (6) Overall, our study provides new insights into the potential role of endogenous ANXA1 as a mediator of dexamethasone-induced L-selectin shedding, which may contribute to the anti-inflammatory activity of glucocorticoids.
authors.affiliation: Department of Medicine and Oral and Maxillofacial Surgery, NIH Pain Center, Box 0440, University of California at San Francisco, 521 Parnassus Avenue, San Francisco, CA 94143, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: de Coupade
authors.forename: Egle
authors.initials: E
authors.lastname: Solito
authors.forename: Jon D
authors.initials: JD
authors.lastname: Levine
mesh_terms: D017305:Annexin A1 / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D019041:L-Selectin / Q000378:metabolism*; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism*; D020298:U937 Cells
chemical_list: D017305:Annexin A1; D019041:L-Selectin; D003907:Dexamethasone