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.

Insulin-like growth factor as a novel stimulator for somatolactin secretion and synthesis in carp pituitary cells via activation of MAPK cascades

2011 ◽  
Vol 301 (6) ◽  
pp. E1208-E1219 ◽  
Author(s):  
Quan Jiang ◽  
Wendy K. W. Ko ◽  
Anderson O. L. Wong
Keyword(s):  
Growth Factor ◽  
P38 Mapk ◽  
Grass Carp ◽  
Pituitary Hormone ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Insulin Like Growth Factor ◽  
Cell Content ◽  
Mapk Cascades ◽  
Igf I

Somatolactin (SL), a member of the growth hormone/prolactin family, is a pituitary hormone unique to fish models. Although SL is known to have diverse functions in fish, the mechanisms regulating its secretion and synthesis have not been fully characterized. Using grass carp pituitary cells as a model, here we examined the role of insulin-like growth factor (IGF) in SL regulation at the pituitary level. As a first step, the antisera for the two SL isoforms expressed in the carp pituitary, SLα and SLβ, were produced, and their specificity was confirmed by antiserum preabsorption and immunohistochemical staining in the carp pituitary. Western blot using these antisera revealed that grass carp SLα and SLβ could be N-linked glycosylated and their basal secretion and cell content in carp pituitary cells could be elevated by IGF-I and -II treatment. These stimulatory effects occurred with parallel rises in SLα and SLβ mRNA levels, and these SL gene expression responses were not mimicked by insulin but blocked by IGF-I receptor inactivation. In carp pituitary cells, IGF-I and -II could induce rapid phosphorylation of IGF-I receptor, MEK1/2, ERK1/2, MKK3/6, and p38 MAPK; and SLα and SLβ secretion, protein production, and mRNA expression caused by IGF-I and -II stimulation were negated by inactivating MEK1/2 and p38 MAPK. Parallel inhibition of PI3K and Akt, however, were not effective in these regards. These results, taken together, provide evidence that IGF can upregulate SL secretion and synthesis at the pituitary level via stimulation of MAPK- but not PI3K/Akt-dependent pathways.

Grass carp somatolactin: II. Pharmacological study on postreceptor signaling mechanisms for PACAP-induced somatolactin-α and -β gene expression

2008 ◽  
Vol 295 (2) ◽  
pp. E477-E490 ◽  
Author(s):  
Quan Jiang ◽  
Mulan He ◽  
Xinyan Wang ◽  
Anderson O. L. Wong
Keyword(s):  
Gene Expression ◽  
Mrna Expression ◽  
Grass Carp ◽  
Pharmacological Study ◽  
Primary Cultures ◽  
Pituitary Hormone ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Fish Model ◽  
Subsequent Activation

Somatolactin (SL), the latest member of the growth hormone/prolactin family, is a novel pituitary hormone with diverse functions. However, the signal transduction mechanisms responsible for SL expression are still largely unknown. Using grass carp as an animal model, we examined the direct effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on SL gene expression at the pituitary level. In primary cultures of grass carp pituitary cells, SLα and SLβ mRNA levels could be elevated by PACAP via activation of PAC-I receptors. With the use of a pharmacological approach, the AC/cAMP/PKA and PLC/inositol 1,4,5-trisphosphate (IP3)/PKC pathways and subsequent activation of the Ca2+/calmodulin (CaM)/CaMK-II cascades were shown to be involved in PACAP-induced SLα mRNA expression. Apparently, the downstream Ca2+/CaM-dependent cascades were triggered by extracellular Ca2+ ([Ca2+]e) entry via L-type voltage-sensitive Ca2+ channels (VSCC) and Ca2+ release from IP3-sensitive intracellular Ca2+ stores. In addition, the VSCC component could be activated by cAMP/PKA- and PLC/PKC-dependent mechanisms. Similar postreceptor signaling cascades were also observed for PACAP-induced SLβ mRNA expression, except that [Ca2+]e entry through VSCC, PKC coupling to PLC, and subsequent activation of CaMK-II were not involved. These findings, taken together, provide evidence for the first time that PACAP can induce SLα and SLβ gene expression in fish model via PAC-I receptors through differential coupling to overlapping and yet distinct signaling pathways.

Grass carp somatolactin: I. Evidence for PACAP induction of somatolactin-α and -β gene expression via activation of pituitary PAC-I receptors

2008 ◽  
Vol 295 (2) ◽  
pp. E463-E476 ◽  
Author(s):  
Quan Jiang ◽  
Wendy K. W. Ko ◽  
Ethan A. Lerner ◽  
K. M. Chan ◽  
Anderson O. L. Wong
Keyword(s):  
Gene Expression ◽  
Grass Carp ◽  
Primary Cultures ◽  
Single Copy ◽  
Nerve Fibers ◽  
Pars Intermedia ◽  
Pituitary Hormone ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Rapid Amplification

Somatolactin (SL), the latest member of the growth hormone/prolactin family, is a novel pituitary hormone with diverse functions. At present, SL can be identified only in fish but not in tetrapods and its regulation at the pituitary level has not been fully characterized. Using grass carp as a model, we examined the direct effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on SL secretion and synthesis at the pituitary cell level. As a first step, the structural identity of grass carp SL, SLα and SLβ, was established by 5′/3′-rapid amplification of cDNA ends. These two SL isoforms are single-copy genes and are expressed in two separate populations of pituitary cells located in the pars intermedia. In the carp pituitary, PACAP nerve fibers were detected in the nerve tracts of the neurohypophysis and extended into the vicinity of pituitary cells forming the pars intermedia. In primary cultures of grass carp pituitary cells, PACAP was effective in stimulating SL release, cellular SL content, and total SL production. The increase in SL production also occurred with parallel rises in SLα and SLβ mRNA levels. With the use of a combination of molecular and pharmacological approaches, PACAP-induced SL release and SL gene expression were shown to be mediated by pituitary PAC-I receptors. These findings, as a whole, suggest that PACAP may serve as a hypophysiotropic factor in fish stimulating SL secretion and synthesis at the pituitary level. Apparently, PACAP-induced SL production is mediated by upregulation of SLα and SLβ gene expression through activation of PAC-I receptors.

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.

scholarly journals Evidence for a Novel Intrapituitary Autocrine/Paracrine Feedback Loop Regulating Growth Hormone Synthesis and Secretion in Grass Carp Pituitary Cells by Functional Interactions between Gonadotrophs and Somatotrophs

Endocrinology ◽  
2004 ◽  
Vol 145 (12) ◽  
pp. 5548-5559 ◽  
Author(s):  
Hong Zhou ◽  
Xinyan Wang ◽  
Wendy K. W. Ko ◽  
Anderson O. L. Wong
Keyword(s):  
Mrna Expression ◽  
Grass Carp ◽  
Feedback Loop ◽  
Cell Model ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Local Interactions ◽  
Hormone Synthesis ◽  
A Cell ◽  
High Doses

Abstract Gonadotropin (GTH) and GH released from the pituitary are known to interact at multiple levels to modulate the functions of the gonadotrophic and somatotrophic axes. However, their interactions at the pituitary level have not been fully characterized. In this study, autocrine/paracrine regulation of GH synthesis and secretion by local interactions between gonadotrophs and somatotrophs was examined using grass carp pituitary cells as a cell model. Exogenous GTH and GH induced GH release and GH mRNA expression in carp pituitary cells. Removal of endogenous GTH and GH by immunoneutralization with GTH and GH antisera, respectively, suppressed GH release, GH production, and GH mRNA levels. GH antiserum also blocked the stimulatory effects of exogenous GTH on GH release and GH mRNA levels. In reciprocal experiments, GH release and GH mRNA expression induced by exogenous GH was significantly reduced by GTH antiserum. In addition, exogenous GH was found to be inhibitory to basal GTH release and treatment with GH antiserum elevated GTH secretion at low doses but suppressed GTH production at high doses. These results suggest that local interactions between gonadotrophs and somatotrophs may form an intrapituitary feedback loop to regulate GH release and synthesis. In this model, GTH released from gonadotrophs induces GH release and GH production in neighboring somatotrophs. GH secreted maintains somatotroph sensitivity to GTH stimulation, and at the same time, inhibits basal GTH release in gonadotrophs. This feedback loop may represent a novel mechanism regulating GH release and synthesis in lower vertebrates.

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 Signal Transduction Mechanisms for Glucagon-Induced Somatolactin Secretion and Gene Expression in Nile Tilapia (Oreochromis niloticus) Pituitary Cells

2021 ◽  
Vol 11 ◽  
Author(s):  
Chaoyi Zhang ◽  
Anji Lian ◽  
Yue Xu ◽  
Quan Jiang
Keyword(s):  
Gene Expression ◽  
Oreochromis Niloticus ◽  
Nile Tilapia ◽  
Primary Cultures ◽  
Hormone Secretion ◽  
Hek293 Cells ◽  
Luciferase Reporter ◽  
Pituitary Hormone ◽  
Pituitary Cells ◽  
Mrna Levels

Glucagon (GCG) plays a stimulatory role in pituitary hormone regulation, although previous studies have not defined the molecular mechanism whereby GCG affects pituitary hormone secretion. To this end, we identified two distinct proglucagons, Gcga and Gcgb, as well as GCG receptors, Gcgra and Gcgrb, in Nile tilapia (Oreochromis niloticus). Using the cAMP response element (CRE)-luciferase reporter system, tilapia GCGa and GCGb could reciprocally activate the two GCG receptors expressed in human embryonic kidney 293 (HEK293) cells. Quantitative real-time PCR analysis revealed that differential expression of the Gcga and Gcgb and their cognate receptors Gcgra and Gcgrb was found in the various tissues of tilapia. In particular, the Gcgrb is abundantly expressed in the neurointermediate lobe (NIL) of the pituitary gland. In primary cultures of tilapia NIL cells, GCGb effectively stimulated SL release, with parallel rises in the mRNA levels, and co-incubation with the GCG antagonist prevented GCGb-stimulated SL release. In parallel experiments, GCGb treatment dose-dependently enhanced intracellular cyclic adenosine monophosphate (cAMP) accumulation with increasing inositol 1,4,5-trisphosphate (IP3) concentration and the resulting in transient increases of Ca2+ signals in the primary NIL cell culture. Using selective pharmacological approaches, the adenylyl cyclase (AC)/cAMP/protein kinase A (PKA) and phospholipase C (PLC)/IP3/Ca2+/calmodulin (CaM)/CaMK-II pathways were shown to be involved in GCGb-induced SL release and mRNA expression. Together, these results provide evidence for the first time that GCGb can act at the pituitary level to stimulate SL release and gene expression via GCGRb through the activation of the AC/cAMP/PKA and PLC/IP3/Ca2+/CaM/CaMK-II cascades.

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 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

scholarly journals Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) as a Growth Hormone (GH)-Releasing Factor in Grass Carp. I. Functional Coupling of Cyclic Adenosine 3′,5′-Monophosphate and Ca2+/Calmodulin-Dependent Signaling Pathways in PACAP-Induced GH Secretion and GH Gene Expression in Grass Carp Pituitary Cells

Endocrinology ◽  
2005 ◽  
Vol 146 (12) ◽  
pp. 5407-5424 ◽  
Author(s):  
Anderson O. L. Wong ◽  
Wensheng Li ◽  
Ching Yu Leung ◽  
Longfei Huo ◽  
Hong Zhou
Keyword(s):  
Protein Kinase ◽  
Adenylate Cyclase ◽  
Grass Carp ◽  
Pituitary Cells ◽  
Cam Kinase Ii ◽  
Mrna Levels ◽  
Cam Kinase ◽  
Gh Secretion ◽  
Pituitary Adenylate Cyclase ◽  
Gh Gene

Pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the glucagon/secretin peptide family, has been recently proposed to be the ancestral GH-releasing factor. Using grass carp as a model for bony fish, we examined the mechanisms for PACAP regulation of GH synthesis and secretion at the pituitary level. Nerve fibers with PACAP immunoreactivity were identified in the grass carp pituitary overlapping with the distribution of somatotrophs. At the somatotroph level, PACAP was shown to induce cAMP synthesis and Ca2+ entry through voltage-sensitive Ca2+ channels (VSCC). In carp pituitary cells, PACAP but not vasoactive intestinal polypeptide increased GH release, GH content, total GH production, and steady-state GH mRNA levels. PACAP also enhanced GH mRNA stability, GH promoter activity, and nuclear expression of GH primary transcripts. Increasing cAMP levels, induction of Ca2+ entry, and activation of VSCC were all effective in elevating GH secretion and GH mRNA levels. PACAP-induced GH secretion and GH mRNA expression, however, were abolished by inhibiting adenylate cyclase and protein kinase A, removing extracellular Ca2+ or VSCC blockade, or inactivating calmodulin (CaM)-dependent protein kinase II (CaM kinase II). Similar sensitivity to VSCC and CaM kinase II blockade was also observed by activating cAMP production as a trigger for GH release and GH gene expression. These results suggest that PACAP stimulates GH synthesis and secretion in grass carp pituitary cells through PAC1 receptors. These stimulatory actions probably are mediated by the adenylate cyclase/cAMP/protein kinase A pathway coupled to Ca2+ entry via VSCC and subsequent activation of CaM/CaM kinase II cascades.

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