Evidence From Studies on Co‐Cultures of TtT/GF and AtT20 Cells That Annexin 1 Acts as a Paracrine or Juxtacrine Mediator of the Early Inhibitory Effects of Glucocorticoids on ACTH Release

Abstract

Annexin 1 (ANXA1) is a key mediator of the inhibitory effects of glucocorticoids on adrenocorticotropic hormone (ACTH) release, which develop within 1-2 h of a steroid challenge. Our previous studies, which showed that (i) ANXA1 is expressed principally by the nonsecretory folliculo-stellate cells in the pituitary gland; (ii) glucocorticoids cause the exportation of ANXA1 from these cells; and (iii) corticotrophs express specific ANXA1 binding sites, led us to propose that ANXA1 serves as a paracrine or juxtacrine mediator of glucocorticoids. To address this hypothesis, we examined ANXA1-dependent glucocorticoid actions in co-cultures of murine corticotroph (AtT20 clone D1) and folliculo-stellate (TtT/GF) cell lines. ANXA1 mRNA and protein were found in abundance in TtT/GF cells but neither was detectable in the AtT20 cells. AtT20 cells (alone and in co-culture with TtT/GF cells) responded to corticotropin-releasing hormone (CRH) (0.1-1 micro m) with increased ACTH release. The CRH-stimulated release of ACTH from AtT20 cells cultured alone was unaffected by preincubation with dexamethasone (Dex, 100 nm); by contrast, in co-cultures of AtT20 and TtT/GF cells, the steroid readily inhibited the secretory response to CRH. The effects of Dex on ACTH release were mimicked by N-terminal ANXA1 fragments (ANXA1Ac2-26, 2 micro g/ml and ANXA11-188, 0.1 ng/ml) and reversed by mifepristone (1 micro m) and by an antisense oligodeoxynucleotide (ODN) to ANXA1 (50 nm) but not by control ODNs. The antisense ODN also specifically blocked the Dex-induced externalization of ANXA1 from TtT/GF cells. Immunofluorescence imaging of the co-cultures localized the exported protein to the vicinity of the AtT20 cells and identified ANXA1 binding sites on these cells. These results provide functional and histological evidence to support our premise that the early inhibitory effects of glucocorticoids on ACTH release are dependent upon paracrine/juxtacrine actions of ANXA1 derived from folliculo-stellate cells.

Differential gene expression in ACTH -secreting and non-functioning pituitary tumors

“…It has been reported that ANXA1 acts as a paracrine or juxtacrine mediator of the early inhibitory effects of glucocorticoids on ACTH secretion in the rat anterior pituitary (30,31). However, our data showed variable gene expressions of ANXA1 in NFT when compared with its stable expression in ACTH-secreting pituitary tumors.…”

History and perspectives of pituitary folliculo-stellate cell research

“…Annexins are a group of proteins that share the property of interacting with membranes in a Ca 2þ -dependent manner. Tierney et al (59) demonstrated that glucocorticoids cause the exportation of ANXA1 from FS cells and that corticotrophs express ANXA1-binding sites. These observations led to the conclusion that ANXA1 acts as a paracrine or juxtacrine mediator of the early inhibitory effects of glucocorticoids on ACTH release (59).…”

“…Also in the amphibian Xenopus laevis, FS cells as well as endocrine (58). It was recently shown that annexin-1 (ANXA1) in the pituitary is principally expressed in FS cells (59). Annexins are a group of proteins that share the property of interacting with membranes in a Ca 2þ -dependent manner.…”

Novel Aspects of Glucocorticoids Actions on Energy Homeostasis and Hydromineral Balance

“…In pituitaryderived cells, the use of a GR antagonist prevented the dexamethasone-induced translocation of annexin-1, which was implicated in the rapid inhibition of adrenocorticotrophic hormone (ACTH) release Solito et al, 2003;Tierney et al, 2003). Nevertheless, a GR-independent pathway has been also reported in the fast feedback mechanism at the pituitary level in vivo (Hinz & Hirschelmann, 2000).…”