Expression of c-myc and c-fos protooncogenes in the anterior pituitary gland of the rat. Effect of estrogen

Ept7, a quantitative trait locus that controls estrogen-induced pituitary lactotroph hyperplasia in rat, is orthologous to a locus in humans that has been associated with numerous cancer types and common diseases

Pituitary adenoma is a common intracranial neoplasm that is observed in approximately 10% of unselected individuals at autopsy. Prolactin-producing adenomas, i.e., prolactinomas, comprise approximately 50% of all pituitary adenomas and represent the most common class of pituitary tumor. Multiple observations suggest that estrogens may contribute to development of prolactinoma; however, direct evidence for a causal role of estrogens in prolactinoma etiology is lacking. Rat models of estrogen-induced prolactinoma have been utilized extensively to identify the factors, pathways and processes that are involved in pituitary tumor development. The objective of this study was to localize to high resolution Ept7 (Estrogen-induced pituitary tumor), a quantitative trait locus (QTL) that controls lactotroph responsiveness to estrogens and was mapped to rat chromosome 7 (RNO7) in an intercross between BN and ACI rats. Data presented and discussed herein localize the Ept7 causal variant(s) to a 1.91 Mb interval of RNO7 that contains two protein coding genes, A1bg and Myc, and Pvt1, which yields multiple non-protein coding transcripts of unknown function. The Ept7 orthologous region in humans is located at 8q24.21 and has been linked in genome wide association studies to risk of 8 distinct epithelial cancers, including breast, ovarian, and endometrial cancers; 3 distinct types of B cell lymphoma; multiple inflammatory and autoimmune diseases; and orofacial cleft defects. In addition, the Ept7 locus in humans has been associated with variation in normal hematologic and development phenotypes, including height. Functional characterization of Ept7 should ultimately enhance our understanding of the genetic etiology of prolactinoma and these other diseases.

Comparison of different separation technologies for proteome analyses: Isoform resolution as a prerequisite for the definition of protein biomarkers on the level of posttranslational modifications

In this article we evaluate methods used to reveal the molecular complexity, which is generated in biological samples by posttranslational modifications (PTM) of proteins. We show how distinct molecular differences on the level of phosphorylation sites in a single protein (ovalbumin) can be resolved with different success using 1D and 2D gel-electrophoresis and reversed-phase liquid chromatography (LC) with monolithic polystyrol-divinylbenzol (PS-DVB) columns for protein separation, and matrix-assisted laser desorption ionisation-time of flight mass spectrometry (MALDI-TOF MS) for protein identification. Phosphorylation site analysis was performed using enzymatic dephosphorylation in combination with differential peptide mass mapping. Liquid chromatography-MALDI-TOF MS coupling with subsequent on-target tryptic protein digestion turned out to be the fastest method tested but yielded low resolution for the analysis of PTM, whereas 2D gel-electrophoresis, due to its unique capability of resolving highly complex isoform pattern, turned out to be the most suitable method for this purpose. The evaluated methods complement one another and in connection with efficient technologies for differential and quantitative analysis, these approaches have the potential to reveal novel molecular details of protein biomarkers.

Effects of changing gonadotropin-releasing hormone pulse frequency and estrogen treatment on levels of estradiol receptor-alpha and induction of Fos and phosphorylated cyclic adenosine monophosphate response element binding protein in pituitary gonadotropes: studies in hypothalamo-pituitary disconnected ewes

Estrogen receptor-alpha (ER alpha) levels in gonadotropes are increased during the follicular phase of the ovine estrous cycle, a time of increased frequency of pulsatile secretion of GnRH and elevated plasma estrogen levels. In the present study, our first aim was to determine which of these factors causes the rise in the number of gonadotropes with ER alpha. Ovariectomized hypothalamo-pituitary disconnected ewes (n = 4-6) received the following treatments: 1) no treatment, 2) injection (im) of 50 microg estradiol benzoate (EB), 3) pulses (300 ng iv) of GnRH every 3 h, 4) GnRH treatment as in group 3 and EB treatment as in group 2, 5) increased frequency of GnRH pulses commencing 20 h before termination, and 6) GnRH treatment as in group 5 with EB treatment. These treatments had predictable effects on plasma LH levels. The number of gonadotropes in which ER alpha was present (by immunohistochemistry) was increased by either GnRH treatment or EB injection, but combined treatment had the greatest effect. Immunohistochemistry was also performed to detect phosphorylated cAMP response element binding protein (pCREB) and Fos protein in gonadotropes. The number of gonadotropes with Fos and with pCREB was increased only in group 6. We conclude that either estrogen or GnRH can up-regulate ER alpha in pituitary gonadotropes. On the other hand, during the period of positive feedback action of estrogen, the appearance of pCREB and Fos in gonadotropes requires the combined action of estrogen and increased frequency of GnRH input. This suggests convergence of signaling for GnRH and estrogen.

Possible mechanisms of gender bias in SLE: a new hypothesis involving a comparison of SLE with atopy

The prevalence of systemic lupus erythematosus (SLE) is far higher in females than in males, and numerous investigations of this gender bias have been performed from several perspectives. Sex hormones, particularly estrogens, may be significant in causing the gender discrepancy. This article discusses the possible importance of estrogens in regulating the expression of and responsivity to autoantigens in SLE and in atopic disorders, which are associated with hyperreactivity to exogenous antigens. Estrogens seem to play an important role in the overexpression of endogenous autoantigens, such as human endogenous retroviruses (HERV), and this may be related to the existence of a gender bias in the incidence of SLE but not atopy.

Identification of estrogen-responsive genes in the GH3 cell line by cDNA microarray analysis

To identify estrogen-responsive genes in somatolactotrophic cells of the pituitary gland, a rat pituitary cell line GH3 was subjected to cDNA microarray analysis. GH3 cells respond to estrogen by growth as well as prolactin synthesis. RNAs extracted from GH3 cells treated with 17beta-estradiol (E2) at 10(-9) M for 24 h were compared with the control samples. The effect of an antiestrogen ICI182780 was also examined. The array analysis indicated 26 genes to be up-regulated and only seven genes down-regulated by E2. Fourteen genes were further examined by real-time RT-PCR quantification and 10 were confirmed to be regulated by the hormone in a dose-dependent manner. Expression and regulation of these genes were then examined in the anterior pituitary glands of female F344 rats ovariectomized and/or treated with E2 and 8 out of 10 were again found to be up-regulated. Interestingly, two of the most estrogen-responsive genes in GH3 cells were strongly dependent on E2 in vivo. #1 was identified as calbindin-D9k mRNA, with 80- and 118-fold induction over the ovariectomized controls at 3 and 24 h, respectively, after E2 administration. #2 was found to be parvalbumin mRNA, with 30-fold increase at 24 h. Third was c-myc mRNA, with 4.5 times induction at 24 h. The levels were maintained after one month of chronic E2 treatment. Identification of these estrogen-responsive genes should contribute to understating of estrogen actions in the pituitary gland.

Role of transcription factors in the pathogenesis of pituitary adenomas: a review

The diversity inherent in every organ has its roots in gene-expression variation and is revealed through distinctions in the molecular profile and hence the identity of individual cell type. Study into the molecular mechanisms of the development of individual cell type within the pituitary, which is under the control of transcription factors, has provided a basis for a deeper insight into the molecular mechanisms underlying the pathogenesis of a variety of hormone-producing pituitary tumors. Identification of some of these transcription factors in pituitary adenomas further supports their role in the pathogenesis of pituitary adenomas. Understanding the molecular mechanisms of regulation of proliferation of pituitary cell types by transcription factors offers a basis for hope that rational genetic or pharmacologic therapies for pituitary tumors can be designed in the future.

Fos expression in female hamsters after various stimuli associated with mating

Detection of the expression of c-fos mRNA or its protein product, Fos, has been used to indicate differences in neuronal response to exogenous stimuli. Factors contributing to differences in Fos expression as a result of various stimuli associated with mating have been extensively studied in the female rat. Less is known about the factors that contribute to Fos expression in female hamsters. Female hamsters differ from female rats in several aspects of sexual behavior; therefore, it seems likely that Fos expression may also differ. The purpose of this study was to determine which factors associated with mating selectively affect Fos expression in the female hamster. Animals were ovariectomized, hormone treated, and then exposed to several behavioral conditions. Fos expression in several brain areas was then assessed via immunocytochemistry (ICC). As has been found by others, mating increases Fos immunoreactivity in a number of brain regions. Specifically, vaginal-cervical stimulation (VCS) was determined to be the salient factor contributing to Fos expression in the preoptic area (POA) and bed nucleus of the stria terminalis (BNST) of ovariectomized hormone primed female hamsters that received a mating interaction.

Changes in estrogen receptor expression and cell activity of lactotropes in female mink (Mustela vison) pituitary in response to variations in the gonadal steroid environment

This study was undertaken to get new information on the role played by estrogen (E) on the activity of mink lactotropes. Immunocytochemistry for estrogen receptor (ER) and prolactin (PRL) was applied to assess modifications in the protein production that occur as a result of in vivo changes in the gonadal steroid environment. Variations in the functional activity of lactotropes were demonstrated from the ultrastructural characteristics and morphometric parameters (cellular area, numerical density, and secretory granular size). The present study documents the presence of ER in mink lactotropes revealing the ability of E to regulate the expression of ER in the mink pituitary. Furthermore, all morphological and morphometric parameters of lactotropes activity appeared significantly increased in intact females, killed during the mating period, compared with castrated females under the same photoperiodic conditions. Castration thus blocks the stimulatory effect of photoperiod on metabolic activity of mink lactotropes suggesting that E may participate in the photoperiodic regulation of PRL.

Sex difference and testosterone modulation of pheromone-induced NeuronalFos in the Ferret's main olfactory bulb and hypothalamus

A carnivore, the ferret possesses a vomeronasal organ--accessory olfactory bulb (VNO-AOB) projection to the hypothalamus; however, little is known about its function. Pheromones in soiled bedding from estrous female ferrets or an artificial peppermint odor significantly augmented nuclear Fos protein immunoreactivity (Fos-IR), a marker of neural activation, in several main olfactory bulb (MOB) sites but not in the AOB of gonadectomized male and females. Testosterone propionate (TP) significantly augmented the MOB's neuronal Fos responses to estrous females' pheromones, but not to peppermint. Estrous odors, but not peppermint, also augmented neuronal Fos-IR in the medial preoptic area (mPOA) of female, but not male, subjects. Pheromones in soiled bedding from breeding male ferrets significantly augmented neuronal Fos-IR in the MOB and in the medial amygdala of gonadectomized, TP-treated male and female subjects. Again, male pheromones failed to influence neuronal Fos-IR in the AOB of either sex, and only females showed significant increases in neuronal Fos-IR in the lateral aspect of the ventromedial nucleus and mPOA. These results point to an essential role among higher mammals of the main olfactory epithelium-MOB projection to the hypothalamus in detecting and processing pheromones. Gonadectomized ferrets showed significant increases in sniffing behavior when placed on either female or male bedding. This occurred regardless of whether they had received TP or oil vehicle, suggesting that testosterone's facilitation of neuronal Fos responses to estrous females' odors in the MOB of both sexes cannot be attributed to increased scent gathering. Androgen receptor-IR was present in the MOB granule cell layer of male and female ferrets, raising the possibility that testosterone acts directly on these cells to augment their responsiveness to pheromones.

Female cats have lower rates of apoptosis in peripheral blood lymphocytes than male cats: correlation with estradiol-17beta, but not with progesterone blood levels

During earlier study, we quantified by flow cytometry the rate of apoptotic feline lymphocytes after overnight culture. We found evidence that the sex of the animals influences the rate of apoptosis, intact females showed lower rates of apoptosis in lymphocytes cultured overnight than castrated male cats. This observation was also confirmed for cats that were previously experimentally infected with the feline immunodeficiency virus (FIV). In an attempt to find an explanation for these sexually determined differences, plasma estradiol-17beta and progesterone levels were measured by radio-immuno assay in the blood of these cats. The hormone levels were analyzed with respect to the rate of lymphocyte apoptosis. As expected, castrated males had lower blood levels of estradiol and progesterone than females. However, no overall correlation was found between hormone blood levels and rate of apoptosis under non-stimulating conditions. Interestingly, the rate of apoptosis found in lymphocytes collected from females and stimulated overnight in phytohaemaglutinin-containing medium, showed a strong negative correlation with the estradiol levels in the blood of these cats. To our knowledge, this is the first confirmation that estradiol in physiological concentrations may protect peripheral lymphocytes from apoptosis after stimulation. No correlation was found in male cats. In conclusion, these observations broaden the list of sexually determined differences of the immune system, sex and sex hormones predispose males and females for certain immune responses and dysfunctions. The present observations have to be taken into account when designing or interpreting experiments on apoptosis and, for example, evaluating the influence of a preexisting FIV infection on the rate of apoptosis. It would be highly advisable to include only spayed cats in studies on the immune system so as to minimize the influence of sex hormones.

Differential regulation of AP-1 DNA binding activity in rat hypothalamus and pituitary by estrogen

Ap-1 proteins such as Fos and Jun are nuclear transcription factors that have been postulated to function as third messengers in signal transduction pathways to regulate target gene expression. Using electrophoretic mobility shift assays (EMSA), we have studied estrogen (E) effects on regulation of AP-1 DNA binding activity in the rat hypothalamus and pituitary. AP-1 binding is defined herein as the specific association with a consensus AP-1 site during EMSA. Specific AP-1 binding activity was observed in nuclear extracts from the hypothalamus and pituitary of ovariectomized (OVX) female and castrated (CAS) male rats. Treatment with E increased the levels of AP-1 binding activity in the pituitary and uterus, whereas E decreased the levels of AP-1 binding in the hypothalamus, of OVX females. These effects were observed within 60 min and maintained for at least 72 h after a single dose of estrogen. Estrogen-induced changes in AP-1 binding were much more prominent in OVX females than in CAS males. Treatment with progesterone in OVX females had no significant effects on AP-1 binding activity in either pituitary or hypothalamus. Analysis of AP-1 binding activity in both hypothalamus and pituitary by supershift, immunodepletion and shift-Western blot indicated that part of the AP-1 binding was due to the presence of Fos and Jun proteins. However, Western blot analysis shows that the levels of Fos and Jun proteins in the hypothalamic nuclear extracts were not altered by E treatment. We conclude that E produced tissue and sex-differentiated alterations in AP-1 DNA binding activity in the hypothalamus and pituitary of female rats, which may be related to differential estrogenic actions on gene regulation.

Transcription factors in normal and neoplastic pituitary tissues

Transcription factors are proteins that bind to regulatory elements in DNA and have critical roles in gene regulation during development, in cellular growth and differentiation. The four major groups of transcription factors have been classified according to the motif in the DNA-binding domains and include: (1) the helix-turn-helix group, which includes the Pit-1/GHF-1 (Pit-1) transcription factor; (2) the zing finger group, which includes estrogen and other steroid hormone receptors; (3) the leucine zipper group, which includes c-fos protooncogene, and (4) the helix-loop-helix group, which includes the c-myc oncogene. Members of all four groups have been described in normal and neoplastic anterior pituitary gland tissues. Pit-1 has been shown to regulate prolactin (PRL), growth hormone (GH), and thyroid-stimulating hormone (TSH) cells during development and differentiation. Genetic defects in this transcription factor have led to specific diseases in rodents and humans such as dwarfism and cretinism. Estrogen receptor (ER) protein plays a critical role in the regulation of gene expression in some anterior pituitary cells. There is a differential distribution of ER in anterior pituitary cells and tumors; PRL, gonadotroph, and null cell tumors are the principal adenomas expressing ER. The protooncogene c-fos is regulated by estrogen in various tissues, linking the regulation of one transcription factor by another transcription factor with a different motif. The c-myc oncogene has been detected in the pituitary gland and in some pituitary tumors, although the exact role of this oncogene in pituitary tumor development is uncertain. Because of the critical role that transcription factors play in pituitary cell development and differentiation, we can anticipate many more studies to elucidate their many functions in normal and neoplastic pituitary tissues.

Cell-specific induction of c-fos expression in the pituitary gland by estrogen

Estrogens regulate many functions of pituitary lactotrophs, including PRL gene expression, release, storage, and cellular proliferation. The mechanism by which estrogens exert such a variety of functions is poorly understood. In the uterus, estrogens rapidly and transiently induce the expression of the immediate early genes c-fos and c-jun in specific cell types. The Fos/Jun proteins form the activating protein-1 (AP1) transcription factor that mediates ligand-activated cell proliferation, differentiation, and secretion. Here we used Fischer 344 (F344) rats that develop hyperprolactinemia and prolactinomas in response to estrogens. The objectives were to: 1) determine whether estrogen induces c-fos expression in the pituitary gland and identify the responsive cells; 2) compare the dynamics of c-fos induction in the pituitary and uterus; and 3) examine the temporal relationship between c-fos expression and PRL release. Ovariectomized F344 rats were injected with 1 microg estradiol and killed at different times thereafter. Pituitaries were subjected to in situ hybridization for c-fos and immunostaining for selected pituitary cells. Estradiol stimulated c-fos expression in lactotrophs and folliculo-stellate cells within the anterior lobe without affecting either the intermediate or neural lobes. In a second experiment, c-fos messenger RNA levels were measured by solution hybridization in anterior pituitaries and uteri from estradiol-treated rats. Trunk blood was analyzed for PRL by RIA. The estrogen-induced c-fos rise in the uterus was rapid, robust, and transient, whereas that in the anterior pituitary was delayed, lower, and sustained. The profile of serum PRL levels resembles that of c-fos induction in the anterior pituitary. We conclude that: 1) both lactotrophs and folliculo-stellate cells increase c-fos expression in response to estrogens; 2) induction of c-fos expression may mediate some estrogenic effects on PRL synthesis and release and lactotroph proliferation in F344 rats; and 3) the atypical dynamics of c-fos induction in the pituitary could be due to indirect effects of estrogens on PRL-regulating factors within the hypothalamo-pituitary complex as well as to pituitary-specific estrogen receptor isoforms, coactivators, or repressors.

Pituitary Sex Steroid Receptors: Localization and Function

The pituitary contains estrogen receptor (ER), progesterone receptor (PR), and androgen receptor (AR). In accordance with immunocytochemistry, it is agreed that sex hormone receptors reside into the nucleus. All three receptors are found predominantly in gonadotrophs and lactotrophs, and less frequently in other cell types. ER plays a major role in prolactin (PRL) production and lactotroph proliferation, and protracted estrogen administration induces lactotroph hyperplasia and adenoma in rodents. Most research on PR and AR is focused on their role in the fine-tuning of gonadotropin secretion during estrous cycle. Contrary to the effect in nontumorous pituitary, estrogens can inhibit the proliferation of transplantable rat pituitary tumors and of cell lines derived from them. In humans, despite the presence of ER in all types of adenohypophysial tumors, the role of estrogen in tumor cell proliferation is still unclear. Few results indicate that tumor growth is stimulated by estrogen, and inhibited by progesterone and androgen. Novel data reveal that steroid hormones can act directly on plasma membrane or via other receptors, and interact with growth factors, oncogenes, and other transcription factors. The mechanisms by which steroid hormones control cell proliferation remain a major challenge for future research.

Division of labor among gonadotropes

This chapter has presented a somewhat complex view of the gonadotrope population, indicating that it consists of independent subsets. There may be regulatory cells that influence development and other ancillary processes needed for normal reproduction. For example, normal differentiation of PRL cells requires a functioning population of gonadotropes (Kendall et al., 1991). In addition, gonadotropes appear to be autoregulatory; subsets may produce inhibin or activin (in rats) and follistatin. Production of GnRH itself may serve as another regulatory tool. The gonadotrope population appears to be quite dynamic and convertible in the female rat. Cytological and cytochemical changes with the stage of the cycle are obvious. Increases in the numbers of immunoreactive gonadotropes parallel increases in GnRH target cells and culminate in peak expression of LH and FSH beta subunit mRNAs. The immunoreactive gonadotropes are greatly reduced after the surge activity, as though the cells had disappeared from the population. However, gonadotropes can still be detected by their content of gonadotropin mRNAs. This finding has led to the hypothesis that the gonadotropes recycle themselves. However, do they go through a resting phase? Is there a normal cycle of cell death and turnover? These are basic questions that must be answered in order to understand how the population is organized and renewed. Finally, we have returned to one of our original problems. Whereas it is clear that nonparallel release can be brought about by granules or cells with only one gonadotropin, the exact mechanisms that sort the gonadotropin molecules or turn off bihormonal expression are not known. A combination of autoregulatory events involving follistatin, activin, inhibin, and possibly steroids may play a role in modulating expression by a given subset. Delays in maturation may also prevent secretion of FSH and, hence, effect the delayed rise seen during late proestrus. The nonsecretory FSH cells seen in the studies by Lloyd and Childs (1988a) may be delayed maturers, requiring additional receptor types or changes in the calcium flux pattern to secrete their product. We also have a new question to address. What is the significance of the presence of GH in proestrous gonadotropes? Is GH a regulatory hormone, bound to receptors inside gonadotropes, or do subsets of somatotropes augment the population, producing a cocktail of GH and gonadotropins to aid ovulation? Either hypothesis is intriguing. Co-storage of GH and gonadotropins would be an efficient way of providing the hormones needed by the ovary. However, further work with in situ hybridization is needed to detect GH mRNA in such cells.(ABSTRACT TRUNCATED AT 400 WORDS)