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.

Cross-inhibition of SR-BI- and ABCA1-mediated cholesterol transport by the small molecules BLT-4 and glyburide

“…The inhibition of ABCA1-mediated cholesterol efflux by BLT-4 prompted us to determine if the ABCA1 inhibitor glyburide (29,31,(46)(47)(48)(49)(50)(51) (Fig. 1A) As expected from previous studies (29,31,(48)(49)(50), glyburide inhibited ABCA1-mediated [ 3 H]cholesterol efflux from HEK[ABCA1] cells to apoA-I (10 g protein/ml) with an IC 50 of ‫003ف‬ M (Fig.…”

“…However, their common abilities to mediate cholesterol efflux from cells led us to probe their activities using small molecules that had previously been shown to inhibit their lipid transport activities. These included small molecules that block lipid transport (BLTs) mediated by SR-BI (45) and the drug glyburide (29,31,(46)(47)(48)(49)(50)(51), which blocks ABCA1-mediated cholesterol efflux.…”

“…Glyburide also inhibits the activities of other ABC proteins (54)(55)(56), including ABCA1. Inhibition of ABCA1 by glyburide has been reported to occur in the concentration range of 100-1,000 M (29,31,(46)(47)(48)(49)(50)(51).…”

Annexin 1: a paracrine/juxtacrine mediator of glucorticoid action in the neuroendocrine system

“…19 Further studies have shown that the initial steroid-induced exportation of the native protein is effected via a novel, GCreceptor mediated, non-genomic signalling mechanism involving PI3-kinase, MAP-kinase and PKC. 18 In addition, they have provided functional and histological evidence that the translocation of the protein across the plasma membrane is effected via a member of the ATP binding cassette family of proteins (ABC A1 20 ). In particular, confocal imaging has demonstrated co-localization of annexin 1 and the ABC A1 annexin 1 and neuroendocrine function 219 transport protein at junctions of follicostellate cells and corticotrophs, suggesting that annexin 1 may subserve a juxtacrine role.…”

Folliculo-stellate Cells: Paracrine Communicators in the Anterior Pituitary

“…Glucocorticoids cause the export of Anx A1 which is evident after 30 mins and maximal at 90 mins. The ATP-binding cassette (ABC) transporter family is known to export a number of proteins, including bFGF [67] and Anx A1 in inflamed gut mucosa [69]. Glyburide, an ABC transporter inhibitor, markedly inhibits glucocorticoidstimulated (but not potassium-stimulated) export of Anx A1from TtT/GF cells and from pituitary tissue [69].…”