Kinase‐Dependent Regulation of the Secretion of Thyrotrophin and Luteinizing Hormone By Glucocorticoids and Annexin 1 Peptides

Abstract

Our previous studies have identified a role for annexin 1 (ANXA1), a protein produced by the pituitary folliculostellate cells, as a paracrine/juxtacrine mediator of the acute regulatory effects of glucocorticoids on the release of adrenocorticotropic hormone and other pituitary hormones. In the present study, we focused on the secretion of thyroid stimulating hormone (TSH) and luteinizing hormone (LH) and used a battery of ANXA1-derived peptides to identify the key domains in the ANXA1 molecule that are critical to the inhibition of peptide release. In addition, as ANXA1 is a substrate for protein kinase C (PKC) and tyrosine kinase, we examined the roles of these kinases in the manifestation of the ANXA1-dependent inhibitory actions of dexamethasone on TSH and LH release. Dexamethasone suppressed the forskolin-induced release of TSH and LH from rat anterior pituitary tissue in vitro. Its effects were mimicked by human recombinant ANXA1 (hrANXA1) and a truncated protein, ANXA1(1-188). ANXA1(Ac2-26), also suppressed stimulated peptide release but it lacked both the potency and the efficacy of the parent protein. Shorter N-terminal ANXA1 sequences were without effect. The PKC inhibitor PKC(19-36) abolished the inhibitory actions of dexamethasone on the forskolin-evoked release of TSH and LH; it also attenuated the inhibitory actions of ANXA1(Ac2-26). Similar effects were produced by annexin 5 (ANXA5) which sequesters PKC in other systems. By contrast, the tyrosine kinase inhibitors, p60v-src (137-157) and genistein, had no effect on the secretion of TSH or LH alone or in the presence of forskolin and/or dexamethasone. Dexamethasone caused the translocation of a tyrosine-phosphorylated species of ANXA1 to the surface of pituitary cells. The total amount of ANXA1 exported from the cells in response to the steroid was unaffected by tyrosine kinase blockade. However, the degree of tyrosine-phosphorylation of the exported protein was markedly reduced by genistein. These results suggest that (i) the ANXA1-dependent inhibitory actions of dexamethasone on the release of TSH and LH require PKC and sequences in the N-terminal domain of ANXA1, but are independent of tyrosine kinase, and (ii) while dexamethasone induces the cellular exportation of a tyrosine-phosphorylated species of ANXA1, tyrosine phosphorylation per se is not critical to the steroid-induced passage of ANXA1 across the membrane.

Diminished and irregular TSH secretion with delayed acrophase in patients with Cushing's syndrome

“…Several in vitro studies in the last decades have suggested that part of the inhibitory effect of glucocorticoids on TSH secretion may be mediated via a direct effect on the pituitary gland (12,23). Subsequent studies have identified a role for annexin 1 (lipocortin 1), a protein produced by the pituitary folliculostellate cell, which acts as a paracrine mediator of acute regulatory effects of glucocorticoids, not only for TSH secretion but also for the secretion of ACTH, prolactin, and luteotropic hormone (24)(25)(26)(27). Glucocorticoid-suppressive effects on TSH secretion in the human, either in acute experiments in volunteers or in patients suffering from chronic glucocorticoid excess, are fully in agreement with these experimental studies, particularly because a direct pituitary-inhibitory effect would not necessarily change the pulse frequency or half-life of TSH.…”

Involvement of Phospholipase C-Related Inactive Protein in the Mouse Reproductive System Through the Regulation of Gonadotropin Levels1

“…Anterior lobes of the pituitary glands were carefully isolated free from intermediate and posterior lobes under a stereoscopic microscope (Olympus) from 3-mo-old female mice of each genotype immediately after decapitation, followed by cultivation according to the method described by John et al [22]. After dividing the isolated anterior pituitary gland into four segments of equal size, the segments were incubated with 100 ll of Eagle balanced salt solution (Sigma) in a 96-well culture plate for 3 h at 378C, with medium changes every hour.…”

CAF-Secreted Annexin A1 Induces Prostate Cancer Cells to Gain Stem Cell–like Features

“…In both leukocytes and pituitary cells phosphorylation on Ser 27 is necessary for protein export and secretion. This action is directed by Ca 2+ -dependent isoforms of PKC, and subsequent translocation of the serine 27 -phosphorylated species of AnxA1 to the plasma membrane occurs at specific lipid domains that allow for secretion [18–20]. Extracellular Ser 27 -AnxA1 undergoes a conformational change in the presence of ≥ 1 mM Ca 2+ causing exposure of the N-terminal domain from inside the pore created by the four repeated motifs of the core domain and, thereby, binding to its receptor [19, 21].…”