title: Evidence for a role of the adenosine 5'-triphosphate-binding cassette transporter A1 in the externalization of annexin I from pituitary folliculo-stellate cells.
abstract: Annexin 1 (ANXA1) has a well-demonstrated role in early delayed inhibitory feedback of glucocorticoids in the pituitary. ANXA1 is located in folliculo-stellate (FS) cells, and glucocorticoids act on these cells to externalize and stimulate the synthesis of ANXA1. However, ANXA1 lacks a signal sequence so the mechanism by which ANXA1 is externalized from FS cells was unknown and has been investigated. The ATP-binding cassette (ABC) transporters are a large group of transporters with varied roles that include the externalization of proteins. Glucocorticoid-induced externalization of ANXA1 from an FS cell line (TtT/GF) and rat anterior pituitary was blocked by glyburide, which inhibits ABC transporters. Glyburide also blocked the glucocorticoid inhibition of forskolin-stimulated ACTH release from pituitary tissue in vitro. RT-PCR revealed mRNA and Western blotting demonstrated protein for the ATP binding cassette A1 (ABCA1) transporter in mouse FS, TtT/GF, and A549 lung adenocarcinoma cells from which glucocorticoids also induce externalization of ANXA1. In TtT/GF cells, immunofluorescence labeling revealed a near total colocalization of cell surface ANXA1 and ABCA1. We conclude that ANXA1, which mediates the early delayed feedback of glucocorticoids in the anterior pituitary, is externalized from FS cells by an ABC transporter and that the ABCA1 transporter is a likely candidate.
authors.affiliation: Department of Human Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, United Kingdom.
authors.forename: Lee P
authors.initials: LP
authors.lastname: Chapman
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Epton
authors.forename: Julia C
authors.initials: JC
authors.lastname: Buckingham
authors.forename: John F
authors.initials: JF
authors.lastname: Morris
authors.forename: Helen C
authors.initials: HC
authors.lastname: Christian
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D000230:Adenocarcinoma; D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000818:Animals; D017305:Annexin A1 / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D015153:Blotting, Western; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D005938:Glucocorticoids / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D008175:Lung Neoplasms; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D017305:Annexin A1; D005938:Glucocorticoids; D012333:RNA, Messenger; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D005905:Glyburide