Steroid effects on secretion from subsets of lactotrophs: role of folliculo-stellate cells and annexin 1

Gold nanoparticle uptake is enhanced by estradiol in MCF-7 breast cancer cells

Purpose: In the present study, we investigated the effects of 17β-estradiol (E₂) on membrane roughness and gold nanoparticle (AuNP) uptake in MCF-7 breast cancer cells. Methods: Estrogen receptor (ER)-positive breast cancer cells (MCF-7) were exposed to bare 20 nm AuNPs in the presence and absence of 1×10^-9 M E₂ for different time intervals for up to 24 hrs. The effects of AuNP incorporation and E₂ incubation on the MCF-7 cell surface roughness were measured using atomic force microscopy (AFM). Endocytic vesicle formation was studied using confocal laser scanning microscopy (CLSM). Finally, the results were confirmed by hyperspectral optical microscopy. Results: High-resolution AFM images of the surfaces of MCF-7 membranes (up to 250 nm²) were obtained. The incubation of cells for 12 hrs with AuNP and E₂ increased the cell membrane roughness by 95% and 30% compared with the groups treated with vehicle (ethanol) or AuNPs only, respectively. This effect was blocked by an ER antagonist (7α,17β-[9-[(4,4,5,5,5-Pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol [ICI] 182,780). Higher amounts of AuNPs were localized inside MCF-7 cells around the nucleus, even after 6 hrs of E₂ incubation, compared with vehicle-treated cells. Endolysosome formation was induced by E₂, which may be associated with an increase in AuNP-uptake. Conclusions: E₂ enhances AuNP incorporation in MCF-7 cells by modulating of plasma membrane roughness and inducing lysosomal endocytosis. These findings provide new insights into combined nanotherapies and hormone therapies for breast cancer.

Cardioprotective potential of annexin-A1 mimetics in myocardial infarction

Myocardial infarction (MI) and its resultant heart failure remains a major cause of death in the world. The current treatments for patients with MI are revascularization with thrombolytic agents or interventional procedures. These treatments have focused on restoring blood flow to the ischemic tissue to prevent tissue necrosis and preserve organ function. The restoration of blood flow after a period of ischemia, however, may elicit further myocardial damage, called reperfusion injury. Pharmacological interventions, such as antioxidant and Ca(2+) channel blockers, have shown premises in experimental settings; however, clinical studies have shown limited success. Thus, there is a need for the development of novel therapies to treat reperfusion injury. The therapeutic potential of glucocorticoid-regulated anti-inflammatory mediator annexin-A1 (ANX-A1) has recently been recognized in a range of systemic inflammatory disorders. ANX-A1 binds to and activates the family of formyl peptide receptors (G protein-coupled receptor family) to inhibit neutrophil activation, migration and infiltration. Until recently, studies on the cardioprotective actions of ANX-A1 and its peptide mimetics (Ac2-26, CGEN-855A) have largely focused on its anti-inflammatory effects as a mechanism of preserving myocardial viability following I-R injury. Our laboratory provided the first evidence of the direct protective action of ANX-A1 on myocardium, independent of inflammatory cells in vitro. We now review the potential for ANX-A1 based therapeutics to be seen as a "triple shield" therapy against myocardial I-R injury, limiting neutrophil infiltration and preserving both cardiomyocyte viability and contractile function. This novel therapy may thus represent a valuable clinical approach to improve outcome after MI.

CAF-secreted annexin A1 induces prostate cancer cells to gain stem cell-like features

Annexin A1 (AnxA1), a phospholipid-binding protein and regulator of glucocorticoid-induced inflammatory signaling, has implications in cancer. Here, a role for AnxA1 in prostate adenocarcinoma was determined using primary cultures and a tumor cell line (cE1), all derived from the conditional Pten deletion mouse model of prostate cancer. AnxA1 secretion by prostate-derived cancer-associated fibroblasts (CAF) was significantly higher than by normal prostate fibroblasts (NPF). Prostate tumor cells were sorted to enrich for epithelial subpopulations based on nonhematopoietic lineage, high SCA-1, and high or medium levels of CD49f. Compared with controls, AnxA1 enhanced stem cell-like properties in high- and medium-expression subpopulations of sorted cE1 and primary cells, in vitro, through formation of greater number of spheroids with increased complexity, and in vivo, through generation of more, larger, and histologically complex glandular structures, along with increased expression of p63, a basal/progenitor marker. The differentiated medium-expression subpopulations from cE1 and primary cells were most susceptible to gain stem cell-like properties as shown by increased spheroid and glandular formation. Further supporting this increased plasticity, AnxA1 was shown to regulate epithelial-to-mesenchymal transition in cE1 cells. These results suggest that CAF-secreted AnxA1 contributes to tumor stem cell dynamics via two separate but complementary pathways: induction of a dedifferentiation process leading to generation of stem-like cells from a subpopulation of cancer epithelial cells and stimulation of proliferation and differentiation of the cancer stem-like cells.

IMPLICATIONS

AnxA1 participates in a paradigm in which malignant prostate epithelial cells that are not cancer stem cells are induced to gain cancer stem cell-like properties.

Gastric estrogen increases pituitary estrogen receptor α and prolactin mRNAs during the different pathological conditions of the liver

Mammalian liver is an estrogen-responsive tissue mediated by hepatic estrogen receptors. Although Ueyama et al. (Endocrinology 143:3162-3170, 2002) have reported the presence of aromatase and active production of gastric 17β-estradiol in parietal cells, there are a few studies on gastric 17β-estradiol exploring the relationship between gastro-hepato function and the gastro-pituitary-gonadal axis. The alteration of gastric 17β-estradiol flow into the systemic circulation by portal vein ligation (PVL) or partial hepatectomy (PH), and the effect of gastric 17β-estradiol on the pituitary function was investigated. In the PVL rats, arterial 17β-estradiol increased 9.5 times that of controls on day 3, and gradually decreased near to control levels in the portal vein by 4 weeks, which was still 5 times higher than those in the arteries of the control rats. In the PH rats, arterial 17β-estradiol increased 2 times that of controls on day 3, and gradually decreased to the control levels. Regeneration and growth of the liver remnants were observed about 2 weeks after PH. In the PVL and PH animals, pituitary ERα and prolactin mRNAs levels increased, positively correlating with an increase of arterial 17β-estradiol levels. Both reduced LHβ mRNA. It is apparent that hepatic dysfunction causes changes in gastric 17β-estradiol levels in the systemic circulation; and that elevated gastric 17β-estradiol affects pituitary function(s). This data suggest that gastric 17β-estradiol has a pivotal role in the regulation of the gastro-hepato-pituitary axis.

Cromoglycate drugs suppress eicosanoid generation in U937 cells by promoting the release of Anx-A1

Using biochemical, epifluorescence and electron microscopic techniques in a U937 model system, we investigated the effect of anti-allergic drugs di-sodium cromoglycate and sodium nedocromil on the trafficking and release of the anti-inflammatory protein Annexin-A1 (Anx-A1) when this was triggered by glucocorticoid (GC) treatment. GCs alone produced a rapid (within 5 min) concentration-dependent activation of PKCα/β (Protein Kinase C; EC 2.7.11.13) and phosphorylation of Anx-A1 on Ser²⁷. Both phosphoproteins accumulated at the plasma membrane and Anx-A1 was subsequently externalised thereby inhibiting thromboxane (Tx) B₂ generation. When administered alone, cromoglycate or nedocromil had little effect on this pathway however, in the presence of a fixed sub-maximal concentration of GCs, increasing amounts of the cromoglycate-like drugs caused a striking concentration-dependent enhancement of Anx-A1 and PKCα/β phosphorylation, membrane recruitment and Anx-A1 release from cells resulting in greatly enhanced inhibition of TxB₂ generation. GCs also stimulated phosphatase accumulation at the plasma membrane of U937 cells. Both cromoglycate and nedocromil inhibited this enzymatic activity as well as that of a highly purified PP2A phosphatase preparation. We conclude that stimulation by the cromoglycate-like drugs of intracellular Anx-A1 trafficking and release (hence inhibition of eicosanoid release) is secondary to inhibition of a phosphatase PP2A (phosphoprotein phosphatase; EC 3.1.3.16), which probably forms part of a control loop to limit Anx-A1 release. These experiments provide a basis for a novel mechanism of action for the cromolyns, a group of drugs that have long puzzled investigators.

Functional maturation of growth hormone cells in the anterior pituitary gland of the fetus

Recent studies have disclosed the molecular mechanisms responsible for the phenotype determination of the anterior pituitary cell types. However, as far as growth hormone (GH) cells are concerned, particular extra-cellular cues are required for the initiation of GH and GH-releasing hormone (GHRH)-receptor gene production in addition to the expression of the cell type specific transcription factor, pit-1. The glucocorticoids play a principal role in the functional maturation of nascent GH cells in the fetal pituitary glands in rodents, inducing GH and GHRH-receptor gene expression, and establish the GH secretory system regulated by the brain in late gestation. Research supporting this role for glucocorticoid in the development of GH cells is discussed.

Perinatal glucocorticoid treatment disrupts the hypothalamo-lactotroph axis in adult female, but not male, rats

This study aimed to test the hypothesis that the tuberoinfundibular dopaminergic neurons of the arcuate nucleus and/or the lactotroph cells of the anterior pituitary gland are key targets for the programming effects of perinatal glucocorticoids (GCs). Dexamethasone was administered noninvasively to fetal or neonatal rats via the mothers' drinking water (1 mug/ml) on embryonic d 16-19 or neonatal d 1-7, and control animals received normal drinking water. At 68 d of age, the numbers of tyrosine hydroxylase-positive (TH+) cells in the arcuate nucleus and morphometric parameters of pituitary lactotrophs were analyzed. In control animals, striking sex differences in TH+ cell numbers, lactotroph cell size, and pituitary prolactin content were observed. Both pre- and neonatal GC treatment regimens were without effect in adult male rats, but in females, the overriding effect was to abolish the sex differences by reducing arcuate TH+ cell numbers (pre- and neonatal treatments) and reducing lactotroph cell size and pituitary prolactin content (prenatal treatment only) without changing lactotroph cell numbers. Changes in circulating prolactin levels represented a net effect of hypothalamic and pituitary alterations that exhibited independent critical windows of susceptibility to perinatal GC treatments. The dopaminergic neurons of the hypothalamic periventricular nucleus and the pituitary somatotroph populations were not significantly affected by either treatment regimen in either sex. These data show that the adult female hypothalamo-lactotroph axis is profoundly affected by perinatal exposure to GCs, which disrupts the tonic inhibitory tuberoinfundibular dopaminergic pathway and changes lactotroph morphology and prolactin levels in the pituitary and circulation. These findings provide new evidence for a long-term disruption in prolactin-dependent homeostasis in females, but not males, after inappropriate GC exposure in perinatal life.

Steroid Hormones, their Receptors and Neuroendocrine System

The brain is an important target organ for circulating steroid hormones secreted from peripheral organs such as the adrenal cortex, testis and/or ovary. In other words, these peripheral organs control the central nervous system. Steroid hormones substantially influence brain development, reproduction, sexual differentiation, cognition, memory, behavior, and so on. These effects are mediated by steroid hormone receptors, which directly regulate gene expression. The steroid hormone receptor superfamily is an intracellular ligand-regulated transcription factor. All members, including the glucocorticoid receptors (GR), mineralocoroticoid receptors (MR), estrogen receptors (ER), progesterone receptors (PR) and androgen receptor (AR), mediate the expression of a gene by binding to hormone responsive elements (HREs) as dimmers in a ligand-dependent manner. In particular, steroid hormones have an important role for the regulating neurons and cells, which are associated with the neuroendocrine and endocrine regulation system, because many neuroendocrine neurons and cells express the steroid hormone receptors, such as estrogen receptor (ER), androgen receptor (AR) and corticosteroid receptors. In this review, first the localization of GR and MR immunoreactivities in the brain is introduced, and secondly, the effects of change of GR expression in neurons are examined by several morphological approaches. Third, the interaction of GR expression and pituitary cell function is introduced. Finally, the recent topics on the control system of feeding regulation in the central nervous system, which also closely involves steroid hormone action, are discussed.

Pituitary cell lines and their endocrine applications

The pituitary gland is an important component of the endocrine system, and together with the hypothalamus, exerts considerable influence over the functions of other endocrine glands. The hypothalamus either positively or negatively regulates hormonal productions in the pituitary through its release of various trophic hormones which act on specific cell types in the pituitary to secrete a variety of pituitary hormones that are important for growth and development, metabolism, reproductive and nervous system functions. The pituitary is divided into three sections-the anterior lobe which constitute the majority of the pituitary mass and is composed primarily of five hormone-producing cell types (thyrotropes, lactotropes, corticotropes, somatotropes and gonadotropes) each secreting thyrotropin, prolactin, ACTH, growth hormone and gonadotropins (FSH and LH) respectively. There is also a sixth cell type in the anterior lobe-the non-endocrine, agranular, folliculostellate cells. The intermediate lobe produces melanocyte-stimulating hormone and endorphins, whereas the posterior lobe secretes anti-diuretic hormone (vasopressin) and oxytocin. Representative cell lines of all the six cell types of the anterior pituitary have been established and have provided valuable information on genealogy of the various cell lineages, endocrine feedback control of hormone synthesis and secretions, intrapituitary interactions between the various cell types, as well as the role of specific transcription factors that determine each differentiated cell phenotype. In this review, we will discuss the morphology and function of the cell types that make up the anterior pituitary, and the characteristics of the various functional anterior pituitary cell systems that have been established to be representative of each anterior pituitary cell lineage.

In vitro effects of cortisol on the release and gene expression of prolactin and growth hormone in the tilapia, Oreochromis mossambicus

Exposure to cortisol inhibits prolactin (PRL) release from the tilapia pituitary within 10-20min through a plasma membrane-associated, non-genomic pathway. In the present study, in vitro effects of cortisol on the release and mRNA levels of two PRLs (PRL(188) and PRL(177)) and growth hormone (GH) were examined in the organ-cultured pituitary of the Mozambique tilapia, Oreochromis mossambicus. The PRL release was significantly greater in hyposmotic (300mOsmolal) than in hyperosmotic (350mOsmolal) medium during the 2-8h of incubation. The mRNA levels of two PRLs, as estimated by RNase protection assay, were increased after 8h in hyposmotic medium. Cortisol (200nM) inhibited the release of two PRLs under hyposmotic conditions within 1h, and the inhibitory effects lasted for 24h. Cortisol also reduced the gene transcription of both PRLs during 2-8h of incubation but not after 24h. No effect of cortisol was observed on PRL release or on its mRNA levels under hyperosmotic condition. There was no significant effect of medium osmolality on the release or mRNA levels of GH during 8h of incubation. However, GH release was significantly stimulated by cortisol after 4h, and the effect lasted for 24h under both hyposmotic and hyperosmotic conditions. Cortisol also caused a significant increase in GH mRNA levels at 8 and 24h. These results suggest that cortisol inhibits PRL release from the tilapia pituitary through non-genomic and also through transcriptional pathways, while stimulating GH release through classical genomically mediated glucocorticoid actions.

Kinase-dependent regulation of the secretion of thyrotrophin and luteinizing hormone by glucocorticoids and annexin 1 peptides

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.

Dexamethasone induces rapid serine-phosphorylation and membrane translocation of annexin 1 in a human folliculostellate cell line via a novel nongenomic mechanism involving the glucocorticoid receptor, protein kinase C, phosphatidylinositol 3-kinase, and mitogen-activated protein kinase

Our recent studies on rat pituitary tissue suggest that the annexin 1 (ANXA1)-dependent inhibitory actions of glucocorticoids on ACTH secretion are effected via a paracrine mechanism that involves protein kinase C (PKC)-dependent translocation of a serine-phosphorylated species of ANXA1 (Ser-P-ANXA1) to the plasma membrane of the nonsecretory folliculostellate cells. In the present study, we have used a human folliculostellate cell line (PDFS) to explore the signaling mechanisms that cause the translocation of Ser-P-ANXA1 to the membrane together with Western blot analysis and flow cytometry to detect the phosphorylated protein. Exposure of PDFS cells to dexamethasone caused time-dependent increases in the expression of ANXA1 mRNA and protein, which were first detected within 2 h of steroid contact. This genomic response was preceded by the appearance within 30 min of substantially increased amounts of Ser-P-ANXA1 and by translocation of the phosphorylated protein to the cell surface. The prompt membrane translocation of Ser-P-ANXA1 provoked by dexamethasone was inhibited by the glucocorticoid receptor, antagonist, mifepristone, but not by actinomycin D or cycloheximide, which effectively inhibit mRNA and protein synthesis respectively in our preparation. It was also inhibited by a nonselective PKC inhibitor (PKC(9-31)), by a selective inhibitor of Ca(2+)-dependent PKCs (Go 6976) and by annexin 5 (which sequesters PKC in other systems). In addition, blockade of phosphatidylinositiol 3-kinase (wortmannin) or MAPK pathways with PD 98059 or UO 126 (selective for MAPK kinse 1 and 2) prevented the steroid-induced translocation of Ser-P-ANXA1 to the cell surface. These results suggest that glucocorticoids induce rapid serine phosphorylation and membrane translocation of ANXA1 via a novel nongenomic, glucocorticoid receptor-dependent mechanism that requires MAPK, phosphatidylinositiol 3-kinase, and Ca(2+)-dependent PKC pathways.