Role of PKC in the regulation of gonadotropin subunit mRNA levels: interaction with two native forms of gonadotropin-releasing hormone

2005 ◽  
Vol 289 (6) ◽  
pp. R1634-R1643 ◽  
Author(s):  
Christian Klausen ◽  
David L. Severson ◽  
John P. Chang ◽  
Hamid R. Habibi
Keyword(s):  
Primary Cultures ◽  
Gonadotropin Releasing Hormone ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Dependent Manner ◽  
Releasing Hormone ◽  
Subunit Mrna ◽  
Important Regulator ◽  
Lh Secretion

Gonadotropin-releasing hormone (GnRH) is an important regulator of reproduction in all vertebrates through its actions on the production and secretion of pituitary gonadotropin hormones (GtHs). Most vertebrate species express at least two GnRHs, including one form, designated chicken (c)GnRH-II or type II GnRH, which has been well conserved throughout evolution. The goldfish brain and pituitary contain salmon GnRH and cGnRH-II. In goldfish, GnRH-induced luteinizing hormone (LH) secretion involves PKC; however, whether PKC mediates GnRH stimulation of GtH subunit mRNA levels is unknown. In this study, we used inhibitors and activators of PKC to examine its possible involvement in GnRH-induced increases in GtH-α, follicle-stimulating hormone (FSH)-β and LH-β mRNA levels in primary cultures of dispersed goldfish pituitary cells. Treatment with PKC inhibitors calphostin C and GF109203X unmasked a basal repression of GtH subunit mRNA levels by PKC; both inhibitors increased GtH subunit mRNA levels in a dose-dependent manner. PKC activators, 12- O-tetradecanoylphorbol 13-acetate (TPA), and 1,2-dioctanoyl- sn-glycerol, stimulated GtH subunit mRNA levels, whereas an inactive phorbol ester (4-α-TPA) was without effect. Thus, a dual, inhibitory and stimulatory, influence for PKC in the regulation of GtH subunit mRNA levels is suggested. In contrast, PKC inhibitor- and activator-induced effects were, for the most part, additive to those of GnRH, suggesting that conventional and novel PKCs are unlikely to be involved in GnRH-stimulated increases in GtH subunit mRNA levels. Our data illustrate major differences in the signal transduction of GnRH effects on GtH secretion and gene expression in the goldfish pituitary.

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.

Effects of crude and highly purified bovine inhibin (Mr 32 000 form) on gonadotrophin production by ovine pituitary cells in vitro: inhibin enhances gonadotrophin-releasing hormone-induced release of LH

1990 ◽  
Vol 127 (1) ◽  
pp. 149-159 ◽  
Author(s):  
S. Muttukrishna ◽  
P. G. Knight
Keyword(s):  
Primary Cultures ◽  
Suppressive Effect ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Α Subunit ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone

ABSTRACT Primary cultures of ovine pituitary cells (from adult ewes) were used to investigate the actions of steroid-free bovine follicular fluid (bFF) and highly-purified Mr 32 000 bovine inhibin on basal and gonadotrophin-releasing hormone (GnRH)-induced release of FSH and LH. Residual cellular contents of each hormone were also determined allowing total gonadotrophin content/well to be calculated. As in rats, both crude and highly purified inhibin preparations promoted a dose (P < 0·001)- and time (P < 0·001)-dependent suppression of basal and GnRH-induced release of FSH as well as an inhibition of FSH synthesis, reflected by a fall in total FSH content/well. However, while neither inhibin preparation affected basal release of LH or total LH content/well, GnRH-induced LH release was significantly (P< 0·001) increased by the presence of either bFF (+ 75%) or highly-purified inhibin (+ 64%) in a dose- and time-dependent manner. This unexpected action of bFF on GnRH-induced LH release was abolished in the presence of 5 μl specific anti-inhibin serum, confirming that the response was indeed mediated by inhibin. Furthermore, neither oestradiol-17β (1 pmol/l–10 nmol/l) nor monomeric α-subunit of bovine inhibin (2·5–40 ng/ml) significantly affected basal or GnRH-induced release of LH. These in-vitro findings for the ewe lend support to a number of recent in-vivo observations and indicate that, in addition to its well-documented suppressive effect on the synthesis and secretion of FSH, inhibin may actually facilitate LH release in this species, in marked contrast to its action in the rat. Journal of Endocrinology (1990) 127, 149–159

Time- and dose-related effects of gonadotropin-releasing hormone on growth hormone and gonadotropin subunit gene expression in the goldfish pituitary

2002 ◽  
Vol 80 (9) ◽  
pp. 915-924 ◽  
Author(s):  
Christian Klausen ◽  
John P Chang ◽  
Hamid R Habibi
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Gonadotropin Releasing Hormone ◽  
Molecular Forms ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Induced Responses ◽  
Releasing Hormone ◽  
Significant Difference

The goldfish brain contains two molecular forms of gonadotropin-releasing hormone (GnRH): salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II). In a preliminary report, we demonstrated the stimulation of gonadotropin hormone (GtH) subunit and growth hormone (GH) mRNA levels by a single dose of GnRH at a single time point in the goldfish pituitary. Here we extend the work and demonstrate time- and dose-related effects of sGnRH and cGnRH-II on GtH subunit and GH gene expression in vivo and in vitro. The present study demonstrates important differences between the time- and dose-related effects of sGnRH and cGnRH-II on GtH subunit and GH mRNA levels. Using primary cultures of dispersed pituitary cells, the minimal effective dose of cGnRH-II required to stimulate GtH subunit mRNA levels was found to be 10-fold lower than that of sGnRH. In addition, the magnitudes of the increases in GtH subunit and GH mRNA levels stimulated by cGnRH-II were found to be higher than the sGnRH-induced responses. However, no significant difference was observed between sGnRH and cGnRH-II-induced responses in vivo. Time-related studies also revealed significant differences between sGnRH- and cGnRH-II-induced production of GtH subunit and GH mRNA in the goldfish pituitary. In general, the present study provides novel information on time- and dose-related effects of sGnRH and cGnRH-II on GtH subunit and GH mRNA levels and provides a framework for further investigation of GnRH mechanisms of action in the goldfish pituitary.Key words: gonadotropin-releasing hormone, gonadotropin hormone, growth hormone, gene expression, goldfish.

scholarly journals Differential expression and regulation of progesterone receptor isoforms in rat and mouse pituitary cells and LβT2 gonadotropes

2006 ◽  
Vol 190 (3) ◽  
pp. 837-846 ◽  
Author(s):  
Judith L Turgeon ◽  
Dennis W Waring
Keyword(s):  
Progesterone Receptor ◽  
Mrna Level ◽  
Primary Cultures ◽  
Ovariectomized Rats ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Mouse Cells ◽  
Isoform Expression ◽  
Mouse Pituitary ◽  
Lh Secretion

Manipulation of endogenous progesterone receptor (PR) does not produce equivalent physiological effects in mouse and rat pituitary cells. To test whether this may be due in part to difference in PR isoform expression, we examined hormonally regulated pituitary PR-A and PR-B mRNA levels using quantitative real-time PCR. The LβT2 mouse gonadotrope line or pituitary cells from adult, ovariectomized rats or mice were cultured with or without 0.2 nM 17β-estradiol (E2) for 3 days. PR-A was the predominant form expressed for all groups. For mouse cells, E2 led to an increase in both isoforms without a change in the A:B ratio; for rat cells, the PR-B response to E2 was more robust resulting in a decrease in the A:B ratio. Exposure of E2-treated pituitary cells to 200 nM progesterone for 6 h decreased both PR-A and PR-B levels in rat cells, but had no effect on PR isoform expression in mouse cells even when exposure was extended to 12 h. The low level of PR expression found in LβT2 gonadotropes was unaffected by E2, alone or with progesterone. The weak PR expression and lack of responsiveness of LβT2 cells cannot be explained by a male phenotype as was shown by the more than tenfold higher PR mRNA level in primary cultures of male mouse pituitary cells, which responded to E2 stimulation with a proportional increase in PR isoforms similar to female cells. Functionally, E2-stimulated changes in PR mRNA isoform ratios in rat, mouse or LβT2 cells correlated with the degree of progesterone augmentation of GnRH-stimulated LH secretion in these models. These results are consistent with the hypothesis that robust GnRH priming and progesterone augmentation of LH secretion in the rat compared to these events in the mouse are a consequence, in part, of differences in the E2-modulated ratio of PR isoforms.

scholarly journals Mechanism of action of gonadotropin-releasing hormone upon gonadotropin α-subunit mRNA levels in the α T3-1 cell line: role of Ca2+ and protein kinase C

1995 ◽  
Vol 309 (1) ◽  
pp. 325-329 ◽  
Author(s):  
D Ben-Menahem ◽  
Z Shraga-Levine ◽  
P L Mellon ◽  
Z Naor
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Gonadotropin Releasing Hormone ◽  
Alpha Subunit ◽  
Similar Response ◽  
Mrna Levels ◽  
Α Subunit ◽  
Releasing Hormone ◽  
Subunit Mrna ◽  
Kinase C

Addition of [D-Trp6]gonadotropin-releasing hormone (GnRHa) to alpha T3-1 cells induced a very rapid response upon gonadotropin alpha-subunit mRNA which was detected after 30-60 min and was abolished by pretreatment with actinomycin D. A similar response was obtained with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA), or the Ca2+ ionophore, ionomycin. GnRHa (10 nM) also stimulated a secondary rise in alpha-subunit mRNA levels between 12 and 24 h of incubation. No additivity was obtained (at 60 min) upon the combined addition of GnRHa and PMA, GnRHa and ionomycin, or PMA and ionomycin. The effect of GnRHa upon alpha-subunit mRNA was blocked by the PKC inhibitors staurosporine or GF 109203X. Down-regulation of endogenous PKC activity resulted in inhibition of the stimulatory effect of gonadotropin-releasing hormone (GnRH), PMA and ionomycin. Removal of extra-cellular Ca2+ abolished the effect of GnRHa and PMA upon alpha-subunit mRNA levels. Interestingly PMA and ionomycin had no effect on alpha-subunit mRNA levels at 24 h of incubation; however, the combined addition of the drugs mimicked the late phase of GnRHa (10 nM) action. The data provide evidence that PKC and Ca2+ are involved in mediating the early and the late responses of GnRHa upon alpha-subunit mRNA elevation and that differential cross-talk exists between the messengers.

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