N-Terminal Prolactin-Derived Fragments, Vasoinhibins, Are Proapoptoptic and Antiproliferative in the Anterior Pituitary (original) (raw)
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Proceedings of the National Academy of Sciences, 1979
Male rats received acute or chronic primary or acute secondary stimulation with estradiol, and the effects on pituitary prolactin synthesis and its mRNA accumulation were examined. Prolactin synthesis was determined by the in vitro incorporation of [ 3 H]leucine into prolactin over a period of 1 hr. Prolactin mRNA was measured both by cell-free translation in a nuclease-treated rabbit reticulocyte lysate and by hybridization to the complementary DNA. The latter two methods gave similar results under all experimental conditions. Acute primary stimulation with estradiol produced a significant increase in pituitary prolactin mRNA accumulation at 12 hr, which further increased by 2- to 3-fold over the next 48 hr. In contrast, no increase in prolactin synthesis was observed during the first 24 hr. Chronic stimulation with estradiol induced increases of both prolactin synthesis and prolactin mRNA that were quantitatively indistinguishable over the period of 1-4 weeks, reaching a plateau a...
Biochemical and Biophysical Research Communications, 1980
A new form of prolactin which has a cleavage in its large disulphide loop and is synthesised and secreted by rat pituitary glands radioactively labelled in vitro has been detected on sodium dodecyl sulphate polyacrylamide gel analysis and identified by tryptic fingerprinting; this form of prolactin was also found in fresh pituitary glands. The molecule is a 2-chain structure; the 2 component polypeptide chains are separable into an N-terminal 16,000 dalton and a C-terminal 8,000 dalton fragment by the reduction of the intervening disulphide bridge. The cleaved prolactin is a post-translationally modified form of the hormone whose production is regulated by physiological and pharmacological stimuli. ergic inhibitory control of the hypothalamus; and suggested that it could be expected to be synthesised and secreted by the pituitary gland in vitro.
2004 Estrogens sensitize anterior pituitary gland to apoptosis
homeostasis results from a balance between cell proliferation and cell death by apoptosis. Estradiol affects proliferation as well as apoptosis in hormone-dependent tissues. In the present study, we investigated the apoptotic response of the anterior pituitary gland to lipopolysaccharide (LPS) in cycling female rats, and the influence of estradiol in this response in ovariectomized (OVX) rats. The OVX rats were chronically estrogenized with implanted Silastic capsules containing 1 mg of 17-estradiol (E2). Cycling or OVX and E2-treated rats were injected with LPS (250 g/rat ip). Apoptosis was determined by the terminal deoxynucleotidyl-mediated dUTP nickend labeling (TUNEL) method in sections of the anterior pituitary gland and spleen. Chronic estrogenization induced apoptosis in the anterior pituitary gland. Acute endotoxemia triggered apoptosis of cells in the anterior pituitary gland of E2-treated rats but not of OVX rats. No differences were observed in the apoptotic response to LPS in spleen between OVX and E2-treated rats. The apoptotic response of the anterior pituitary to LPS was variable along the estrous cycle, being higher at proestrus than at estrus or diestrus I. Approximately 75% of the apoptotic cells were identified as lactotropes by immunofluorescence. In conclusion, our results indicate that estradiol induces apoptosis and enables the proapoptotic action of LPS in the anterior pituitary gland. Also, our study suggests that estrogens may be involved in anterior pituitary cell renewal during the estrous cycle, sensitizing lactotropes to proapoptotic stimuli.
Journal of Endocrinological Investigation, 1995
Pituitary glands of rats, injected with estrogen to increase the prolactin (PRL) storage in secretory granules, were submitted to various extraction procedures for prolactin. Homogenization and centrifugation of pituitary tissue, in Tris-HCI buffer, pH 7.3, yielded a small amount of radioimmunoassayable prolactin, which increased remarkably after extraction in alkaline pH, disruption of granular membranes with Lubrol and specially after treatment with 2.5 molll urea. Nb2 lymphoma cell and pigeon crop sac bioassay (BA) revealed higher levels
Estrogens exert a rapid apoptotic action in anterior pituitary cells
AJP: Endocrinology and Metabolism, 2009
It is now accepted that estrogens not only stimulate lactotrope proliferation but also sensitize anterior pituitary cells to proapoptotic stimuli. In addition to their classical mechanism of action through binding to intracellular estrogen receptors (ERs), there is increasing evidence that estrogens exert rapid actions mediated by cell membrane-localized ERs (mERs). In the present study, we examined the involvement of membrane-initiated steroid signaling in the proapoptotic action of estradiol in primary cultures of anterior pituitary cells from ovariectomized rats by using estren, a synthetic estrogen with no effect on classical transcription and a cell-impermeable 17-estradiol conjugate (E 2-BSA). Both compounds induced cell death of anterior pituitary cells after 60 min of incubation as assessed by flow cytometry and the [3-(4,5dimethylthiazol-2-yl)]-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. Estren, E 2, and E2-BSA induced apoptosis of lactotropes and somatotropes as evaluated by the deoxynucleotidyltransferase-mediated dUTP nick end-labeling assay and immunodetection of prolactin (PRL) and growth hormone (GH). The proapoptotic effect of E 2-BSA was abrogated by ICI-182,780, an antagonist of ERs. The expression of membrane-associated ER␣ was observed in PRL-and GH-bearing cells. Our results indicate that estradiol is able to exert a rapid apoptotic action in anterior pituitary cells, especially lactotropes and somatotropes, by a mechanism triggered by mERs. This mechanism could be involved in anterior pituitary cell turnover.
Mechanisms in progestin antagonism of pituitary tumorigenesis
Journal of Steroid Biochemistry and Molecular Biology, 1998
Chronic exposure of F344 rats to diethylstilbestrol (DES) induces pituitary tumors (DES-T) composed of proliferating lactotrophs. Presently, we studied the effect of progestins on parameters related to tumor growth and function, due to previous evidences of progesterone antagonism of pituitary tumorigenesis acting at pituitary and hypothalamic levels [Piroli, G., Grillo, C., Ferrini, M., Lux-Lantos, V. and De Nicola, A. F., Antagonism by progesterone of diethylstilbestrol-induced pituitary tumorigenesis in Fischer 344 rats: Effects on sex steroid receptors and tyrosine hydroxylase mRNA, Neuroendocrinology, 1996, 63, 530±539]. In search of a quantitatively more important effect, animals bearing DES-T were treated with synthetic progestins. Competition assays using DES-T as source of progestin receptors indicated that levonorgestrel (LNG), gestodene and R5020 showed higher af®nities (IC 50 1±2 nM) than progesterone, norethisterone and medroxyprogesterone (IC 50 10±25 nM). Treatment with LNG reduced DES-T weight by 45%, and serum PRL by one half. Small (monomeric) and big (polymeric) PRL increased 5-and 2.5-fold, respectively, in DES-T in comparison with pituitaries of ovariectomized (OVX) rats. However, LNG produced no changes indicating that synthesis and storage of PRL was conserved in rats receiving both hormonal treatments. DES induced a 15-fold increase in cell proliferation, measured as bromodeoxyuridine incorporation into cell nuclei, in comparison to OVX rats, while LNG treatment of DES-T bearing rats reduced this index by 72%. Electron microscopic images showed that LNG markedly reduced hypertrophy and hyperplasia of lactotropes, increasing the proportions of degenerating cells and cells of high electronic density with alterations of cytoplasmic organelles. However, histopathological signs of apoptosis were absent. Therefore, reduced cell proliferation and non-apoptotic cell death are part of the mechanisms employed by progestins to antagonize tumorigenesis at the pituitary level. The results may open a new therapeutic strategy for treatment of PRL secreting adenoma in humans. #
Prolactin Induces Apoptosis of Lactotropes in Female Rodents
PLoS ONE, 2014
bstract Anterior pituitary cell turnover occurring during female sexual cycle is a poorly understood process that involves complex regulation of cell proliferation and apoptosis by multiple hormones. In rats, the prolactin (PRL) surge that occurs at proestrus coincides with the highest apoptotic rate. Since anterior pituitary cells express the prolactin receptor (PRLR), we aimed to address the actual role of PRL in the regulation of pituitary cell turnover in cycling females. We showed that acute hyperprolactinemia induced in ovariectomized rats using PRL injection or dopamine antagonist treatment rapidly increased apoptosis and decreased proliferation specifically of PRL producing cells (lactotropes), suggesting a direct regulation of these cell responses by PRL. To demonstrate that apoptosis naturally occurring at proestrus was regulated by transient elevation of endogenous PRL levels, we used PRLR-deficient female mice (PRLRKO) in which PRL signaling is totally abolished. According to our hypothesis, no increase in lactotrope apoptotic rate was observed at proestrus, which likely contributes to pituitary tumorigenesis observed in these animals. To decipher the molecular mechanisms underlying PRL effects, we explored the isoform-specific pattern of PRLR expression in cycling wild type females. This analysis revealed dramatic changes of long versus short PRLR ratio during the estrous cycle, which is particularly relevant since these isoforms exhibit distinct signaling properties. This pattern was markedly altered in a model of chronic PRLR signaling blockade involving transgenic mice expressing a pure PRLR antagonist (TG D1-9-G129R-hPRL ), providing evidence that PRL regulates the expression of its own receptor in an isoform-specific manner. Taken together, these results demonstrate that i) the PRL surge occurring during proestrus is a major proapoptotic signal for lactotropes, and ii) partial or total deficiencies in PRLR signaling in the anterior pituitary may result in pituitary hyperplasia and eventual prolactinoma development, as observed in TG D1-9-G129R-hPRL and PRLRKO mice, respectively.
Regulated expression of the prolactin gene in rat pituitary tumor cells
Journal of Cell Biology, 1980
Prolactin (PRL) gene expression in three strains of GH cells (rat pituitary tumor cells) has been quantitated by measurement of: (a) intracellular and extracellular PRL, (b) cytoplasmic translatable PRL-specific mRNA (mRNAPRL), and (c) molecular hybridization of cytoplasmic poly(A) RNA to cDNAPRL (DNA complementary to mRNAPRL). Three GH cell lines utilized in this investigation were a PRL-producing (PRL+) strain, GH4C1, a PRL nonproducing 5-bromo-deoxyuridine resistnat (PRL- BrdUrdr) strain, F1BGH12C1, and a new strain, 928-9b, derived by fusion of PRL+ cells with a nuclear monolayer of the PRL-, BrdUrdr GH cell strain. PRL production is a characteristic of 928-9b cells, but the level of PRL production (2-4 micrograms/mg protein/24 h) is much lower than that of the PRL+ strain, GH4C1 (15-25 micrograms/mg protein/24 h). Levels of cytoplasmic translatable mRNAPRL and cytoplasmic PRL-RNA sequences quantitated with a cDNAPRL probe were also much lower in 928-9b as compared to the PRL+ p...