scholarly journals Novel Aspects of Growth Hormone (GH) Autoregulation: GH-Induced GH Gene Expression in Grass Carp Pituitary Cells through Autocrine/Paracrine Mechanisms

Endocrinology ◽  
2004 ◽  
Vol 145 (10) ◽  
pp. 4615-4628 ◽  
Author(s):  
Hong Zhou ◽  
Wendy K. W. Ko ◽  
Walter K. K. Ho ◽  
Stanko S. Stojilkovic ◽  
Anderson O. L. Wong
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Grass Carp ◽  
Pituitary Cells ◽  
Gh Gene

Signaling mechanisms for α2-adrenergic inhibition of PACAP-induced growth hormone secretion and gene expression grass carp pituitary cells

2007 ◽  
Vol 292 (6) ◽  
pp. E1750-E1762 ◽  
Author(s):  
Xinyan Wang ◽  
Mable M. S. Chu ◽  
Anderson O. L. Wong
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Adenylate Cyclase ◽  
Grass Carp ◽  
Promoter Activity ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Pituitary Cells ◽  
Gh Secretion ◽  
Gh Gene

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a potent growth hormone (GH)-releasing factor in lower vertebrates. However, its functional interactions with other GH regulators have not been fully characterized. In fish models, norepinephrine (NE) inhibits GH release at the pituitary cell level, but its effects on GH synthesis have yet to be determined. We examined adrenergic inhibition of PACAP-induced GH secretion and GH gene expression using grass carp pituitary cells as a cell model. Through activation of pituitary α2-adrenoreceptors, NE or the α2-agonist clonidine reduced both basal and PACAP-induced GH release and GH mRNA expression. In carp pituitary cells, clonidine also suppressed cAMP production and intracellular Ca2+ levels and blocked PACAP induction of these two second messenger signals. In GH3 cells transfected with a reporter carrying the grass carp GH promoter, PACAP stimulation increased GH promoter activity, and this stimulatory effect could be abolished by NE treatment. In parallel experiments, clonidine reduced GH primary transcript and GH promoter activity without affecting GH mRNA stability, and these inhibitory actions were mimicked by inhibiting adenylate cyclase (AC), blocking protein kinase A (PKA), removing extracellular Ca2+ in the culture medium, or inactivating L-type voltage-sensitive Ca2+ channels (VSCC). Since our recent studies have shown that PACAP can induce GH secretion in carp pituitary cells through cAMP/PKA- and Ca2+/calmodulin-dependent mechanisms, these results, taken together, suggest that α2-adrenergic stimulation in the carp pituitary may inhibit PACAP-induced GH release and GH gene transcription by blocking the AC/cAMP/PKA pathway and Ca2+ entry through L-type VSCC.

scholarly journals Paracrine regulation of growth hormone gene expression by gonadotrophin release in grass carp pituitary cells: functional implications, molecular mechanisms and signal transduction

2005 ◽  
Vol 34 (2) ◽  
pp. 415-432 ◽  
Author(s):  
Hong Zhou ◽  
Yonghua Jiang ◽  
Wendy K W Ko ◽  
Wensheng Li ◽  
Anderson O L Wong
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Adenylate Cyclase ◽  
Mrna Expression ◽  
Grass Carp ◽  
Janus Kinase ◽  
Growth Hormone Gene ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Gh Gene

Growth hormone (GH) is known to stimulate luteinizing hormone (LH) release via paracrine interactions between somatotrophs and gonadotrophs. However, it is unclear if LH can exert a reciprocal effect to modulate somatotroph functions. Here we examined the paracrine effects of LH on GH gene expression using grass carp pituitary cells as a cell model. LH receptors were identified in grass carp somatotrophs and their activation by human chorionic gonadotropin (hCG) increased ‘steady-state’ GH mRNA levels. Removal of endogenous LH by immunoneutralization using LH antiserum inhibited GH release and GH mRNA expression. GH secretagogues, including gonadotrophin releasing hormone (GnRH), pituitary adenylate cyclase-activating polypeptide (PACAP) and apomorphine, were effective in elevating GH mRNA levels but these stimulatory actions were blocked by LH antiserum. In pituitary cells pretreated with actinomycin D, the half-life of GH mRNA was not affected by hCG but was enhanced by LH immunoneutralization. Treatment with LH antiserum also suppressed basal levels of mature GH mRNA and primary transcripts. hCG increased cAMP synthesis in carp pituitary cells and hCG-induced GH mRNA expression was mimicked by forskolin but suppressed by inhibiting adenylate cyclase and protein kinase A. Similarly, the stimulatory actions of hCG and forskolin on GH mRNA expression were blocked by inhibiting Janus kinase 2 (JAK2) and MAP kinase (MAPK), including P42/44MAPK and P38 MAPK. These results suggest that LH is essential for the maintenance of GH release, GH gene expression, and somatotroph responsiveness to GH-releasing factors. The paracrine actions of LH on GH mRNA expression are mediated by a concurrent increase in GH gene transcription and GH mRNA turnover, probably through JAK2/MAPK coupled to the cAMP-dependent pathway.

172 IN VITRO EXPOSURE TO XENOESTROGENS INDUCES GROWTH HORMONE TRANSCRIPTION AND RELEASE VIA AN ESTROGEN RECEPTOR-DEPENDENT PATHWAY IN RAT PITUITARY GH3 CELLS

2008 ◽  
Vol 20 (1) ◽  
pp. 166
Author(s):  
V.-H. Dang ◽  
E.-B. Jeung
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Estrogen Receptor ◽  
Gene Transcription ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Rat Pituitary ◽  
In Vitro Exposure ◽  
Gh Gene

The term endocrine disruptor (ED) has been used widely to characterize natural and synthetic environmental compounds that may interfere with the endocrine system(s) of humans and wildlife. In previous studies, we demonstrated that in vitro single exposure to EDs induces CaBP-9k expression, a useful biomarker for detecting the estrogenic activities of EDs in rat pituitary GH3 cells. Here we employ the identical model to examine the effects of EDs in the regulation of growth hormone (GH) gene expression, an important hormone in growth, development, and body composition. We measured levels of GH mRNA transcription and GH release using semi-quantitative RT-PCR and EIA kit, respectively. GH3 cells were treated with alkyphenols (APs), i.e., octyl-phenol (OP), nonyl-phenol (NP), and bisphenol A (BPA), in a dose-dependent manner (10–5, 10–6, and 10–7 M) and harvested following 24 h of treatment. Cells were also exposed to a high concentration (10–5 M) of OP, NP, or BPA and harvested at various time points (1, 3, 6, 12, and 24 h). An anti-estrogen, ICI 182780 (10–7 M) was used to examine the potential involvement of estrogen receptor (ER) in the induction of GH by EDs through an ER-mediated pathway. The data were analyzed by one-way ANOVA, followed by Tukey's multiple comparison. OP, NP, and BPA induced a significant increase in GH gene expression at high (10–5 M) and medium (10–6 M) doses at 24 h. ED-exposure induced a marked increase in GH gene transcription as early as 6 h and peaked at 12 h. Co-treatment with ICI 182780 significantly attenuated ED-induced GH expression in GH3 cells. Interestingly, the level of in vitro GH release was increased significantly at 24 h in response to OP, NP, or BPA, whereas co-treatment with ICI 182780 significantly diminished ED-induced GH secretion in GH3 cells, indicating that ER may play a part in both GH gene transcription and GH release in these cells. Here we demonstrate for the first time that single in vitro exposure to OP, NP, or BPA results in an increase in GH expression at 24 h in GH3 rat pituitary cells. These results may provide new insight into the mode of ED action in GH gene regulation as well as the biological pathway underlying these molecular events. Furthermore, data showing GH responsiveness evoked by EDs supports the aim to develop an assay for use in predicting adverse health effects of EDs in humans and wildlife.

PKC and ERK are differentially involved in gonadotropin-releasing hormone-induced growth hormone gene expression in the goldfish pituitary

2005 ◽  
Vol 289 (6) ◽  
pp. R1625-R1633 ◽  
Author(s):  
Christian Klausen ◽  
Takeshi Tsuchiya ◽  
John P. Chang ◽  
Hamid R. Habibi
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Primary Cultures ◽  
Gonadotropin Releasing Hormone ◽  
Growth Hormone Gene ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Releasing Hormone ◽  
Gh Secretion ◽  
Gh Gene

Gonadotropin-releasing hormone (GnRH) is produced by the hypothalamus and stimulates the synthesis and secretion of gonadotropin hormones. In addition, GnRH also stimulates the production and secretion of growth hormone (GH) in some fish species and in humans with certain clinical disorders. In the goldfish pituitary, GH secretion and gene expression are regulated by two endogenous forms of GnRH known as salmon GnRH and chicken GnRH-II. It is well established that PKC mediates GnRH-stimulated GH secretion in the goldfish pituitary. In contrast, the signal transduction of GnRH-induced GH gene expression has not been elucidated in any model system. In this study, we demonstrate, for the first time, the presence of novel and atypical PKC isoforms in the pituitary of a fish. Moreover, our results indicate that conventional PKCα is present selectively in GH-producing cells. Treatment of primary cultures of dispersed goldfish pituitary cells with PKC activators (phorbol ester or diacylglycerol analog) did not affect basal or GnRH-induced GH mRNA levels, and two different inhibitors of PKC (calphostin C and GF109203X) did not reduce the effects of GnRH on GH gene expression. Together, these results suggest that, in contrast to secretion, conventional and novel PKCs are not involved in GnRH-stimulated increases in GH mRNA levels in the goldfish pituitary. Instead, PD98059 inhibited GnRH-induced GH gene expression, suggesting that the ERK signaling pathway is involved. The results presented here provide novel insights into the functional specificity of GnRH-induced signaling and the regulation of GH gene expression.

scholarly journals Modulation of Calmodulin Gene Expression as a Novel Mechanism for Growth Hormone Feedback Control by Insulin-like Growth Factor in Grass Carp Pituitary Cells

Endocrinology ◽  
2005 ◽  
Vol 146 (9) ◽  
pp. 3821-3835 ◽  
Author(s):  
Longfei Huo ◽  
Guodong Fu ◽  
Xinyan Wang ◽  
Wendy K. W. Ko ◽  
Anderson O. L. Wong
Keyword(s):  
Gene Expression ◽  
Feedback Control ◽  
Grass Carp ◽  
Cell Model ◽  
Pituitary Hormone ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Hormone Synthesis ◽  
Igf I ◽  
Gh Gene

Abstract Calmodulin (CaM), the Ca2+ sensor in living cells, is essential for biological functions mediated by Ca2+-dependent mechanisms. However, modulation of CaM gene expression at the pituitary level as a means to regulate pituitary hormone synthesis has not been characterized. In this study we examined the functional role of CaM in the feedback control of GH by IGF using grass carp pituitary cells as a cell model. To establish the structural identity of CaM expressed in the grass carp, a CaM cDNA, CaM-L, was isolated from the carp pituitary using 3′/5′ rapid amplification of cDNA ends. The open reading frame of this cDNA encodes a 149-amino acid protein sharing the same primary structure with CaMs reported in mammals, birds, and amphibians. This CaM cDNA is phylogenetically related to the CaM I gene family, and its transcripts are ubiquitously expressed in the grass carp. In carp pituitary cells, IGF-I and IGF-II induced CaM mRNA expression with a concurrent drop in GH transcript levels. These stimulatory effects on CaM mRNA levels were not mimicked by insulin and appeared to be a direct consequence of IGF activation of CaM gene transcription without altering CaM transcript stability. CaM antagonism and inactivation of calcineurin blocked the inhibitory effects of IGF-I and IGF-II on GH gene expression, and CaM overexpression also suppressed the 5′ promoter activity of the grass carp GH gene. These results, as a whole, provide evidence for the first time that IGF feedback on GH gene expression is mediated by activation of CaM gene expression at the pituitary level.

scholarly journals Somatotroph recruitment by glucocorticoids involves induction of growth hormone gene expression and secretagogue responsiveness

2001 ◽  
Vol 169 (3) ◽  
pp. 499-509 ◽  
Author(s):  
TE Porter ◽  
CE Dean ◽  
MM Piper ◽  
KL Medvedev ◽  
S Ghavam ◽  
...  
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Anterior Pituitary ◽  
Precursor Cells ◽  
Pituitary Cells ◽  
Caudal Lobe ◽  
Releasing Hormone ◽  
Gh Secretagogues ◽  
Gh Cells ◽  
Gh Gene

Prior research indicates that growth hormone (GH) cell differentiation can be induced prematurely by treatment with glucocorticoids in vitro and in vivo. However, the nature of these responses has not been fully characterized. In this study, the time course of corticosterone induction of GH-secreting cells in cultures of chicken embryonic pituitary cells, responsiveness of differentiated somatotrophs to GH secretagogues, localization of somatotroph precursor cells within the pituitary gland, and the effect of corticosterone on GH gene expression were determined to better define the involvement of glucocorticoids in somatotroph recruitment during development. Anterior pituitary cells from embryonic day 12 chicken embryos were cultured in 10(-9) M corticosterone for 4 to 48 h and were then subjected to reverse haemolytic plaque assays (RHPAs) for GH. Corticosterone treatment for as short as 16 h increased the percentage of GH cells compared with the control. When corticosterone was removed after 48 h and cells were cultured for an additional 3 days in medium alone, the percentage of GH secretors decreased but remained greater than the proportion of somatotrophs among cells that were never treated with corticosterone. To determine if prematurely differentiated somatotrophs were responsive to GH secretagogues, cells were exposed to corticosterone for 48 h and then subjected to GH RHPAs in the presence or absence of GH-releasing hormone (GHRH) or thyrotropin-releasing hormone (TRH). Approximately half of the somatotrophs induced to differentiate with corticosterone subsequently released more GH in response to GHRH and TRH than in their absence. The somatotroph precursor cells were localized within the anterior pituitary by culturing cells from the caudal lobe and cephalic lobe of the anterior pituitary separately. Corticosterone induction of GH cells was substantially greater in cultures derived from the caudal lobe of the anterior pituitary, where somatotroph differentiation normally occurs. GH gene expression was evaluated by ribonuclease protection assay and by in situ hybridization. Corticosterone increased GH mRNA in cultured cells by greater than fourfold. Moreover, corticosterone-induced somatotroph differentiation involved GH gene expression in cells not expressing GH mRNA previously, and the extent of somatotroph differentiation was augmented by treatment with GHRH in combination with corticosterone. We conclude that corticosterone increases the number of GH-secreting cells within 16 h, increases GH gene expression in cells formerly not expressing this gene, confers somatotroph sensitivity to GHRH and TRH, and induces GH production in a precursor population found primarily in the caudal lobe of the anterior pituitary, a site consistent with GH localization in adults. These findings support the hypothesis that glucocorticoids function to induce the final stages in the differentiation of fully functional somatotrophs from cells previously committed to this lineage.

Human growth hormone as a reporter gene in regulation studies employing transient gene expression

1986 ◽  
Vol 6 (9) ◽  
pp. 3173-3179 ◽  
Author(s):  
R F Selden ◽  
K B Howie ◽  
M E Rowe ◽  
H M Goodman ◽  
D D Moore
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Transient Expression ◽  
Human Growth Hormone ◽  
Expression System ◽  
Simian Virus 40 ◽  
Human Growth ◽  
Assay System ◽  
Transient Assay ◽  
Pituitary Cells

The human growth hormone (hGH) transient assay system described here is based on the expression of hGH directed by cells transfected with hGH fusion genes. Levels of secreted hGH in the medium, measured by a simple radioimmunoassay, are proportional to both levels of cytoplasmic hGH mRNA and the amount of transfected DNA. The system is extremely sensitive, easy to perform, and is qualitatively different from other transient expression systems in that the medium is assayed and the cells themselves are not destroyed. The hGH transient assay system is appropriate for analyses of regulation of gene expression and was utilized here to investigate the effect of the simian virus 40 enhancer on the herpes simplex virus thymidine kinase promoter and the effect of zinc on the mouse metallothionein-I promoter. The expression of hGH can also be used as an internal control to monitor transfection efficiency along with any other transient expression system. All cell types tested thus far (including AtT-20, CV-1, GC, GH4, JEG, L, and primary pituitary cells) were able to secrete hGH into the medium.

Growth hormone in the nervous system: autocrine or paracrine roles in retinal function?

2003 ◽  
Vol 81 (4) ◽  
pp. 371-384 ◽  
Author(s):  
S Harvey ◽  
M Kakebeeke ◽  
A E Murphy ◽  
E J Sanders
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Nervous System ◽  
Pituitary Gland ◽  
Neural Development ◽  
Growth Hormone Receptor ◽  
Neural Retina ◽  
Full Length ◽  
Chick Embryos ◽  
Gh Gene

Growth hormone (GH) is primarily produced in the pituitary gland, although GH gene expression also occurs in the central and autonomic nervous systems. GH-immunoreactive proteins are abundant in the brain, spinal cord, and peripheral nerves. The appearance of GH in these tissues occurs prior to the ontogenic differentiation of the pituitary gland and prior to the presence of GH in systemic circulation. Neural GH is also present in neonates, juveniles, and adults and is independent of changes in pituitary GH secretion. Neural GH is therefore likely to have local roles in neural development or neural function, especially as GH receptors (GHRs) are widespread in the nervous system. In recent studies, GH mRNA and GH immunoreactive proteins have been identified in the neural retina of embryonic chicks. GH immunoreactivity is present in the optic cup of chick embryos at embryonic day (ED) 3 of the 21-d incubation period. It is widespread in the neural retina by ED 7 but also present in the nonpigmented retina, choroid, sclera, and cornea. This immunoreactivity is associated with proteins in the neural retina comparable in size with those in the adult pituitary gland, although it is primarily associated with 15–16 kDa moieties rather than with the full-length molecule of approximately 22 kDa. These small GH moieties may reflect proteolytic fragments of "monomer" GH and (or) the presence of different GH gene transcripts, since full-length and truncated GH cDNAs are present in retinal tissue extracts. The GH immunoreactivity in the retina persists throughout embryonic development but is not present in juvenile birds (after 6 weeks of age). This immunoreactivity is also associated with the presence of GH receptor (GHR) immunoreactivity and GHR mRNA in ocular tissues of chick embryos. The retina is thus an extrapituitary site of GH gene expression during early development and is probably an autocrine or paracrine site of GH action. The marked ontogenic pattern of GH immunoreactivity in the retina suggests hitherto unsuspected roles for GH in neurogenesis or ocular development.Key words: growth hormone, growth hormone receptor, nervous system, retina, autocrine, paracrine.

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