Endocrine Abstracts

Acknowledgements: This work was generously supported by the Wellcome Trust

Annexin 1 (ANXA1) plays an important role in mediating the negative feedback effects of glucocorticoids on the HPA axis. It is released from non-secretory folliculostellate (FS) cells by glucocorticoids and acts locally to suppress ACTH release from corticotrophs. Previous studies suggest that the steroid-induced translocation of ANXA1 across the FS cell membrane is effected via membrane ABCA1 transport protein following activation of a kinase cascade. However, some drugs which block ABCA1 (e.g. the sulphonylurea glyburide), and hence ANXA1 release from FS cells, also block SUR2B/Kir6.1 ATP-sensitive K⁺ channels (K⁺_ATP channels). These channels are expressed in FS cells and our studies suggest that they also contribute to the mechanisms effecting ANXA1 release¹. To explore further the roles of ABCA1 and K⁺_ATP channels in the regulation of ANXA1 release we have used a murine FS cell line (TtT/GF) as a model and compared the effects a sulphonylurea (glipizide) on ANXA1 release with those of two drugs (geranylgeranylpyrophosphate, GGPP and bromosulphopthalein, BSP) which block ABCA1 but have no reported actions on K⁺_ATP channels. Cells were incubated as described previously and cell surface ANXA1 was measured by flow cytometry and western blot analysis. Minoxidil, cromakalim (K⁺_ATP channels openers, 1-100μM) and dexamethasone (10nM) each induced concentration-dependent increases in cell surface ANXA1. Their effects were abolished by glipizide (5-100μM). The effects of dexamethasone were also inhibited by BSP (10-50μM) but those of cromakalim were not. GGPP (10μM) on the other hand failed to affect the responses to dexamethasone or cromakalim. While these results do not exclude a role for ABCA1 in the dexamethasone-induced translocation of ANXA1 to the cell membrane, they suggest that the translocation induced by K⁺_ATP channel openers is independent of this transport protein.