Annexin 1, glucocorticoids, and the neuroendocrine-immune interface

Abstract

Annexin 1 (ANXA1) was originally identified as a mediator of the anti-inflammatory actions of glucocorticoids (GCs) in the host defense system. Subsequent work confirmed and extended these findings and also showed that the protein fulfills a wider brief and serves as a signaling intermediate in a number of systems. ANXA1 thus contributes to the regulation of processes as diverse as cell migration, cell growth and differentiation, apoptosis, vesicle fusion, lipid metabolism, and cytokine expression. Here we consider the role of ANXA1 in the neuroendocrine system, particularly the hypothalamo-pituitary-adrenocortical (HPA) axis. Evidence is presented that ANXA1 plays a critical role in effecting the negative feedback effects of GCs on the release of corticotrophin (ACTH) and its hypothalamic-releasing hormones and that it is particularly pertinent to the early-onset actions of the steroids that are mediated via a nongenomic mechanism. The paracrine/juxtacrine mode of ANXA1 action is discussed in detail, with particular reference to the significance of the secondary processing of ANXA1, the processes that control the intracellular and transmembrane trafficking of the protein of the molecule and the mechanism of ANXA1 action on its target cells. In addition, the role of ANXA1 in the perinatal programming of the HPA axis is discussed.

FIGURE 1

Schematic diagram to show the structure of the human annexin 1 gene and protein. Note that the N-terminal includes potential sites for phosphorylation (*) and that each of the four repeats in the core domain includes a 17–amino acid consensus sequence, which is critical to Ca²⁺ binding. Differences in the N-terminal amino acid sequence of the rat and mouse proteins are indicated in italics. (Reprinted by permission from Endocrinology).

FIGURE 2

Reversal of the inhibitory effects of corticosterone on the IL-1β-stimulated release of ACTH in adult male rats by administration of an antiannexin 1 polyclonal antiserum raised in sheep against ANXA1_Ac2–26. Corticosterone 500 μg/kg, i.p in a volume of 1 mL/kg; IL-1β 10 ng/rat in a volume of 3 μL, i.c.v. Controls received equivalent volumes of the sterile saline (Sal) vehicle. Antiannexin 1 antiserum (anti-ANXA1 pAb) 1mL/kg, s.c. or nonimmune sheep serum (NSS, control) 1mL/kg, s.c. was administered 15 min before the steroid. Values represent mean ± SEM (n = 6–7). **P < 0.01 versus Sal–Sal treated control; †† P < 0.01 versus Sal–IL-1-β treated group; NS = not significant (P > 0.05). (ANOVA plus Scheffé's test).

FIGURE 3

Electron micrograph showing immunogold detection of annexin 1 in a folliculostellate cell adjacent to three endocrine (E) cells in freeze-substituted mouse anterior pituitary tissue. Gold particles (15 nm) are scattered over the cytoplasm and adjacent to the plasma membrane of the cell; they are also localized on the FS cell surface at the ends of the processes contacting endocrine cells (see enlarged inset). Arrows indicate intercellular junctions. Scale bar: 1 μm. (Reprinted by permission from Endocrinology).

FIGURE 4

Effects of corticotrophin-releasing hormone (CRH 1 μm) and dexamethasone (Dex 100 nm) on the secretion of adrenocorticotrophic hormone (ACTH) by AtT20 D1 cells (200,000 per well) cultured alone and in the presence of increasing numbers of TtT/GF cells (5,000–50,000 cells per well). (A) basal and CRH-stimulated release of ACTH. ***P < 0.001 basal versus CRH. †P < 0.05, ^††P < 0.01 co-cultures versus AtT20 D1 cells alone. (B) The effects of Dex on CRH-stimulated ACTH release; Dex had no effect on basal ACTH release (data not shown). ***P < 0.001 Basal versus CRH. ^†††P < 0.001 CRH + Dex versus corresponding group treated with CRH alone. Data shown are mean ± SEM of six wells per group. Statistical analysis was carried out by ANOVA and Tukey's post hoc test. The data shown are representative of three separate experiments. (Reprinted by permission from the Journal of Neuroendocrinology).

FIGURE 5

Comparison of the biological activity of full-length human recombinant annexin 1 (hrANXA1_1–346), a truncated protein (ANXA1_1–188), and an N-terminal peptide (ANXA1_Ac2–26) on (a) pituitary function and (b) in a model of inflammation. (A) demonstrates the inhibitory effects of graded concentrations of (i) ANXA1_1–346, (ii) ANXA1_1–188, and (iii) ANXA1_Ac2–26 on the release of ir-ACTH from rat anterior pituitary segments in in vitro data. Mean ± SEM (n = 6) are expressed as percentage of the secretory response to forskolin alone (100 μM). *P < 0.05, **P < 0.01 versus forskolin alone group (ANOVA and Duncan's multiple range test). (B) demonstrates the effects of the peptides in vivo on the IL-1 β-induced migration of neutrophils into a mouse air pouch migration (elicited by in vivo injection of IL-1-β into a small air pouch in the mouse). ANXA1 protein/peptides were co-injected with IL-1-β; the data are expressed as the mean ± SEM, n-4–10. Note (a) that in the pituitary gland, ANXA1_1–364 and ANXA1_1–188 are roughly equipotent, whereas in the air pouch model ANXA1_1–346 is approximately two orders of magnitude more potent than ANXA1_1–188, (b) that ANXA1_Ac2–26 shows the full efficacy of the parent protein in the air pouch model but not in the pituitary gland, where at best it produces a 60% inhibition of peptide release and (c) that while ANXA1_Ac2–26 is less potent than the parent protein in both models, the potency difference is considerably greater in the pituitary gland. (Reprinted by permission from Trends in Endocrinology and Metabolism).

FIGURE 6

Schematic diagram illustrating the proposed mechanism by which ANXA1 produced and stored in folliculostellate cells acts as paracrine/juxtacrine mediator of the early inhibitory effects of GCs on the release of ACTH from the corticotrophs. CRH = corticotrophin-releasing hormone; CRH-R = corticotrophin-releasing hormone receptor; PKA = protein kinase A; GC = glucocorticoid; GR = glucocorticoid receptor; ANXA1 = annexin 1; ANXA1–P = serine-phosphorylated ANXA1; ABC A1–ATP binding cassette protein A1, the putative ANXA1 transporter; FPR-like = formyl peptide receptor like, the putative ANXA1 receptor. (Reprinted by permission from Trends in Endocrinology and Metabolism).