Annexin 1 (ANXA1) is a Ca 2+ and phospholipid binding protein that plays an important role as a mediator of glucocorticoid (GC) action in the host-defence and neuroendocrine-systems. Our previous studies (Christian et al., 1998) in ovarietomised rats +/- oestradiol (E2) replacement suggested oestrogen may exert an inhibitory influence on ANXA1 expression in the pituitary gland. Our more recent finding that ANXA1 knockout mice exhibit unexpected sexual dimorphisms in HPA function and inflammatory responses suggest that the effects of E2 are more complex (Hannon et al., 2003) and have led us to hypothesise that E2 exerts tissue-specific effects on the regulation of ANXA1 and, in some instances, opposes the positive effects of GCs. To address this hypothesis we have used a reporter gene (luciferase) driven by the human (882 bp) and murine (709 bp) ANXA1 promoter to examine the influence of oestrogen (E2, 1 microM, 18 hrs), +/- dexamethasone (DEX, 1 microM, 18 hours) on the expression of ANXA1 in three cell lines, viz. TtT/GF and PDFS (murine pituitary folliculostellate), Raw-1 (murine macrophage) and MhAT2 (murine hepatocyte). Western blot analysis confirmed that these cell lines express the glucocorticoid receptor (GR), oestrogen receptor alpha (ER alpha) and ANXA1. In all three cell lines dexamethasone increased luciferase expression driven by the murine or human promoter (P<0.01 n=3). E2 also increased luciferase expression in TtT/GF and Raw-1 cells (P<0.01, n=3); however, when given in combination with DEX, luciferase expression was reduced (p<0.005, n=3). By constrast, E2 alone had little effect on luciferase expression in MhAT2 cells and, while it reduced the effects of DEX on the murine promoter. These findings support our hypothesis that oestrogens exert complex, tissue-specific effects on ANXA1 expression, which may contribute to the aetiology of the sexual dimorphisms in neuroendocrine and host-defence function.
This work was supported by the Wellcome Trust.