Thyroid hormone disrupting potentials of benzisothiazolinone in embryo-larval zebrafish and rat pituitary GH3 cell line.

Benzisothiazolinone (BIT), one of the most widely used antimicrobial agents in consumer products, has frequently been detected in the water environment. The present study was conducted to determine the adverse effects of BIT on the thyroid neuroendocrine system of zebrafish embryos/larvae. Rat pituitary (GH3) cell line was employed to support the underlying mechanism of thyroid hormone disrupting effects. Significant coagulation and hatching delay were observed in embryos exposed to 30 µg/L of BIT, which in turn remarkably decreased hatchability and larval survival. In BIT-exposed larvae, tshß, tshr, and trh genes were significantly upregulated along with a decrease in thyroxine and triiodothyronine content, indicating that BIT decreased thyroid hormones and increased thyrotropin-releasing hormone and thyroid stimulating hormone secretion through a feedback circuit. The downregulation of trα and deio2 genes in the zebrafish larvae suggests the inhibition of thyroid hormone receptors and deiodination. Similar to the results in zebrafish, upregulation of tshß and downregulation of trα, trß, deio1, and deio2 genes were observed in GH3 cells. Our observations suggest that BIT can decrease the level of thyroid hormones by influencing central regulation, receptor binding, and deiodination.

TRH Regulates the Synthesis and Secretion of Prolactin in Rats with Adenohypophysis through the Differential Expression of miR-126a-5p.

Prolactin (PRL) is an important hormone that is secreted by the pituitary gland and plays an important role in the growth, development and reproduction of organisms. Thyrotropin-releasing hormone (TRH) is a common prolactin-releasing factor that regulates the synthesis and secretion of prolactin. In recent studies, microRNAs (miRNAs) have been found to play a key role in the regulation of pituitary hormones. However, there is a lack of systematic studies on the regulatory role that TRH plays on the pituitary transcriptome, and the role of miRNAs in the regulation of PRL synthesis and secretion by TRH lacks experimental evidence. In this study, we first investigated the changes in PRL synthesis and secretion in the rat pituitary gland after TRH administration. The results of transcriptomic analysis after TRH treatment showed that 102 genes, including those that encode Nppc, Fgf1, PRL, Cd63, Npw, and Il23a, were upregulated, and 488 genes, including those that encode Lats1, Cacna2d1, Top2a, and Tfap2a, were downregulated. These genes are all involved in the regulation of prolactin expression. The gene expression of miR-126a-5p, which regulates the level of PRL in the pituitary gland, was screened by analysis prediction software and by a dual luciferase reporter system. The data presented in this study demonstrate that TRH can regulate prolactin synthesis and secretion through miR-126a-5p, thereby improving our understanding of the molecular mechanism of TRH-mediated PRL secretion and providing a theoretical basis for the role of miRNAs in regulating the secretion of pituitary hormones.

Maltol total alkaloid inhibits expression and secretion of prolactin by upregulating dopamine D2 receptor / 中草药

Objective: To study the role of dopamine D2 receptor (D2R) on the regulation of prolactin (PRL) secretion by malt total alkaloids. Methods: MMQ and GH3 cells of pituitary adenoma were divided into control group, bromocriptine (5 μg/mL), malt total alkaloids (4.4, 8.8, 35.2, 70.4 μg/mL), haloperidol (10, 20, 40 μg/mL), and combined administration group of total malt alkaloids and haloperidol. Cell viability was detected by CCK-8; The expressions of PRL and D2R were detected by western blotting; The level of PRL was detected by ELISA; The level of PRL and D2R mRNA were detected by qRT-PCR. Results: Compared with control group, malt alkaloids (35.2, 70.4 μg/mL) significantly reduced the expression levels of PRL protein and mRNA, and the level of PRL in the supernatant of MMQ cells (P < 0.05). Malt alkaloids (35.2, 70.4 μg/mL) significantly increased the expression levels of D2R protein and mRNA in MMQ cells. Haloperidol significantly inhibited the downregulation of malt alkaloids on the expression levels of PRL protein and mRNA, and the expression level of PRL in supernatant of MMQ cells (P < 0.05). Haloperidol significantly inhibited the upregulation of malt alkaloids on the levels of D2R protein and mRNA (P < 0.05). The level of PRL in GH3 cells had no change by malt alkaloids. Conclusion: Malt alkaloids could inhibit the expression and secretion of PRL in MMQ cell by upregulating D2R.

Effects of bisphenol analogs on thyroid endocrine system and possible interaction with 17ß-estradiol using GH3 cells.

This study was conducted using a rat pituitary (GH3) cell line to understand the effects of bisphenol analogs (BPs) on the thyroid endocrine system, in the presence of 17ß-estradiol (E2). In the first series of experiments, changes in cell proliferation were examined after exposure to each of ten BPs, in the absence or presence of a median effective concentration (6.4 × 10-10 M) of triiodothyronine (T3). All tested BPs significantly increased cell proliferation, suggesting thyroid hormone (TH) agonistic effects of BPs. BPs did not potentiate the T3-induced cell proliferation at 48 h exposure, while several tested BPs including BPA, BPAF, BPB, BPF, BPS, and BPZ elicited a potentiating effect on the T3-induced cell proliferation at 96 h exposure. These results indicate that TH-antagonistic effects of BPs depend on the tested dose and exposure time. In the second set of experiments, one of the most potent BPs, i.e., BPAF, was selected, and its possible interaction with E2 on the thyroid endocrine system was evaluated. Co-exposure of GH3 cells to 10-12 M E2 showed an additive-like effect. The extent of increase in cell proliferation was more pronounced with a combination of BPAF and E2 than with that of BPA and E2. Significant down-regulation of Trα, Trß, and Dio2 genes and up-regulation of the Tshß gene were observed in GH3 cells following co-exposure to BPAF and E2. Our results showed that some BP analogs might influence the thyroid endocrine system, and such perturbation appeared to be enhanced in the presence of E2.

Induction of the Estrogenic Marker Calbindn-D9k by Octamethylcyclotetrasiloxane.

Interrupting the hormonal balance of an organism by interfering with hormones and their target receptors gives rise to various problems such as developmental disorders. Collectively, these reagents are known as endocrine disruptors (EDs). Cyclic volatile methyl siloxanes (cVMSs) are a group of silicone polymers that including octamethylcyclotetrasiloxane (D4). In the present study, we examined the estrogenicity of D4 through in vitro and in vivo assays that employed calcium-binding protein 9K (calbindin-D9k; CaBP-9K) as a biomarker. For in vitro investigation, GH3 rat pituitary cells were exposed to vehicle, 17ß-estradiol (E2), or D4 with/without ICI 182 780 (ICI). CaBP-9K and progesterone receptor (PR) both were up-regulated by E2 and D4 which were completely blocked by ICI. Transcription of estrogen receptor α (ER α) was decreased by E2 and D4 but increased by ICI. D4 was also administered to immature female rats for an uterotrophic (UT) assay and detection of CaBP-9K. Ethinyl estradiol (EE) or D4 was administered subcutaneously with or without ICI. Although uterine weight was not significant altered by D4, an effect thought to be due to cytochrome P450 (CYP), it induced CaBP-9K and PR gene expression. Based on these results we reveal that D4 has estrogenic potential proven under in vitro and in vivo experimental conditions.

Mechanisms for luteinizing hormone induction of growth hormone gene transcription in fish model: crosstalk of the cAMP/PKA pathway with MAPK-and PI3K-dependent cascades.

In our previous studies in grass carp pituitary cells, local production of luteinizing hormone (LH) was shown to induce growth hormone (GH) production and gene expression, which constitutes a major component of the "intrapituitary feedback loop" regulating GH secretion and synthesis via autocrine/paracrine interactions between gonadotrophs and somatotrophs in the carp pituitary. To further investigate the signaling mechanisms mediating LH action at the transcriptional level, promoter studies were performed in GH3 cells co-transfected with the expression vector for carp LH receptor and luciferase-expressing reporter constructs with grass carp GH promoter. In this cell model, treatment with human chorionic gonadotropin (hCG) was effective in increasing GH promoter activity and the responsive sequence was mapped to position -616 and -572 of the grass carp GH promoter. GH promoter activation induced by hCG occurred with concurrent rise in cAMP production, CREB phosphorylation, and could be inhibited by inactivation of adenylate cyclase (AC), PKA, MEK1/2, P(38) MAPK, PI3K and mTOR. AC activation, presumably via cAMP production, could mimic hCG-induced CREB phosphorylation and GH promoter activity, and these stimulatory effects were also sensitive to the blockade of PKA-, MAPK- and PI3K- dependent cascades. These results, as a whole, suggest that LH receptor activation in the carp pituitary may trigger GH gene transcription through CREB phosphorylation as a result of the functional crosstalk of the cAMP/PKA pathway with MAPK-and PI3K-dependent cascades.

Dopamine receptor D2S gene transfer improves the sensitivity of GH3 rat pituitary adenoma cells to bromocriptine.

Bromocriptine, a dopamine agonist (DA), has been used in the treatment of prolactinomas. Recent studies have indicated that dopamine 2 receptor short isoform (D2S) may play an important role in suppressing PRL synthesis and prolactinoma cell growth under DA treatment. In the current study, we investigated the role of D2S in the therapeutic action of bromocriptine in GH3 using both in vitro and in vivo approaches. Infection of adenovirus-D2S increased D2S expression in GH3 cells (P<0.05). D2S expression significantly decreased the GH3 cell viability subjected to bromocriptine treatment in vitro (P<0.05). In nude mice, adenovirus-D2S transfection sensitized GH3 xenograft to bromocriptine treatment evidenced by the significant inhibition of D2S expressed tumor growth as compared with vector control. Furthermore, decrease of Bcl-2 expression, increase of Bax, and active Caspase-3 were found in D2S expressed GH3 xenograft subjected to bromocriptine treatment. In summary, our study indicates that D2S expression plays a critical role in the therapeutic action of bromocriptine in pituitary adenomas and that adenovirus-mediated D2S gene transfer combined with bromocriptine may provide a novel treatment for DA-resistant prolactinomas.

Effects of fulvestrant on biological activity and Wnt expression in rat GH3 cells.

The present study investigated the influence of anti-estrogen treatment (fulvestrant) on pituitary adenoma cell line GH3 biological activity, the estrogen receptor α pathway, the WnT pathway, and mechanisms of decreased Wnt inhibitory factor-1 expression in GH3 cells. Results showed that fulvestrant suppressed GH3 cell proliferation and reduced hormone secretion in a dose-dependent manner. Estrogen receptor α and Wnt4 expression decreased, but Wnt inhibitory factor-1 expression increased in a dose-dependent manner following fulvestrant treatment, and ß-catenin expression remained unchanged. Inhibitors of DNA methylation and histone modification upregulated Wnt inhibitory factor-1 expression. Results suggested that fulvestrant suppressed biological activity of GH3 cells via the estrogen receptor α and Wnt pathways. These results suggested that decreased Wnt inhibitory factor-1 expression in GH3 cells played a role in epigenetic mechanisms. Anti-estrogen therapies could provide novel treatments for growth hormone adenomas.

Troglitazone inhibits proliferation of GH3 cell in vitro / 第二军医大学学报

Objective: To study the anti-proliferation effects of thiazolidinedione compounds-troglitazone, which is a high affinity ligand of PPAR-γ, on rat pituitary adenoma GH3 cell line and explore the related mechanisms. Methods: GH3 cells were separately treated with troglitazone (10-7, 10-6 and 10-5 mol/L), dimethyl sulfoxide (DMSO) (DMSO control group) and phenol red- and serum-free F-12 medium (blank group). MTT was used to examine the cell growth in each group and FACS was used to detect the distribution of cell cycle. Semi-quantitative RT-PCR method was utilized to determine the expression of CyclinDi mRNA. ANOVA was used for statistical analysis. Results: The 72 h treatment with troglitazone inhibited GH3 cell proliferation in a dose-dependent manner. The treatment also induced cell cycle arrest in G1/S phase and significantly decreased the expression of CyclinD1 mRNA as compared to the other 2 groups (P< 0.05). Conclusion: Troglitazone can obviously inhibit the proliferation of GH3 cells; the molecular mechanism may be the decrease of CyclinD1 mRNA due to binding to PPAR-γ.

Intracellular trafficking and metabolic turnover of yeast prepro-alpha-factor-SRIF precursors in GH3 cells

Chimeric genes coding for prepro region of yeast alpha-factor and anglerfish SRIF were expressed in rat GH3 cells to determine whether yeast signals could regulate hormone processing in mammalian cells. We report that nascent hybrid polypeptides were efficiently targeted to ER, where cleavage of signal peptides and core glycosylation occurred, and were localized mainly in Golgi. These data indicate that prepro region of yeast alpha-factor functions in sorting molecules to secretory pathway in mammalian cells. A hybrid construct with a mutated signal peptide underwent similar ER translocation, whereas such a mutation resulted in defective translocation in yeast (Cheong et al., 1997). This difference may be due to the differences in ER translocation between yeast and mammalian cells, i.e., posttranslational versus cotranslational translocation. Processing and secretion of metabolically labeled hybrid propeptides to mature SRIF peptides were assessed by HPLC. When pulse-labeled cells were chased for up to 2 h, intracellular propeptides disappeared with a half-life of approximately 25 min, showing that -68% of initially synthesized propeptides were secreted constitutively. About 22% of SRIF-related products were proteolytically processed to mature SRIF, of which 38.7% were stored intracellularly with a half-life of - 2 h. In addition, immunocytochemical localization showed that a small proportion of SRIF molecules accumulated in secretory vesicles. All these results suggest that yeast prepropeptide could direct hybrid precursors to translocate into ER lumen and transit through secretory pathway to the distal elements of Golgi compartment, but could process and target it less efficiently to downstream in rat endocrine cells.

Intracellular trafficking and metabolic turnover of yeast prepro-alpha-factor-SRIF precursors in GH3 cells

Chimeric genes coding for prepro region of yeast alpha-factor and anglerfish SRIF were expressed in rat GH3 cells to determine whether yeast signals could regulate hormone processing in mammalian cells. We report that nascent hybrid polypeptides were efficiently targeted to ER, where cleavage of signal peptides and core glycosylation occurred, and were localized mainly in Golgi. These data indicate that prepro region of yeast alpha-factor functions in sorting molecules to secretory pathway in mammalian cells. A hybrid construct with a mutated signal peptide underwent similar ER translocation, whereas such a mutation resulted in defective translocation in yeast (Cheong et al., 1997). This difference may be due to the differences in ER translocation between yeast and mammalian cells, i.e., posttranslational versus cotranslational translocation. Processing and secretion of metabolically labeled hybrid propeptides to mature SRIF peptides were assessed by HPLC. When pulse-labeled cells were chased for up to 2 h, intracellular propeptides disappeared with a half-life of approximately 25 min, showing that -68% of initially synthesized propeptides were secreted constitutively. About 22% of SRIF-related products were proteolytically processed to mature SRIF, of which 38.7% were stored intracellularly with a half-life of - 2 h. In addition, immunocytochemical localization showed that a small proportion of SRIF molecules accumulated in secretory vesicles. All these results suggest that yeast prepropeptide could direct hybrid precursors to translocate into ER lumen and transit through secretory pathway to the distal elements of Golgi compartment, but could process and target it less efficiently to downstream in rat endocrine cells.

Effect of TRH on Phospholipase D Activity in GH3 Cell / 대한내분비학회지

BACKGROUND: GH3 cells are a well characterized and widely used model used for the in vitro study of growth hormone (GH) secretion. Thyrotropin releasing hormone (TRH) binds to receptors belonging to the family of G protein-coupled receptors, and secrets both GH & prolactin. Phospholipase D (PLD) is an enzyme that hydrolyses phosphatidylcholine to yield phosphatidic acid and choline, and plays important roles in cellular proliferation and hormonal secretion. To elucidate the pathway of the action of TRH in GH3 cells, we investigated the activities of PLC and PLD in GH3 cells treated with TRH or phorbor 12-myristate 13-acetate (PMA). METHODS: GH3 cells were labeled with [3H] myristate, followed by incubation of with 0.3% ethanol, prior to before the addition of the agonists. The total lipids were extracted from the harvested cells following treatment with the agonists. The PLD activity was assessed by measuring [3H] phosphatidylethanol from the [3H] phospholipid using thin layer chromatography. RESULTS: TRH (1 muM) stimulated the PLC activity by 44-fold over that of the control values. TRH (1 microM), mastoparan (5 muM), and PMA (500 muM) for 30 minutes increased PLD activity by 1.9, 1.5 and 2.2 fold, respectively, in comparison to the controls. The PLD activities after 15, 30, 60, 120 and 240 min treatments of TRH (1 microM) were 142%, 170%, 172%, 160% and 115%, respectively. CONCLUSION: These results suggest that TRH stimulates not only the PLC activity, but also the PLD activity in GH3 cells.

Modulation of L-type Ca2+ channel currents by various protein kinase activators and inhibitors in rat clonal pituitary GH3 cell line

L-type Ca2+ channels play an important role in regulating cytosolic Ca2+ and thereby regulating hormone secretions in neuroendocrine cells. Since hormone secretions are also regulated by various kinds of protein kinases, we investigated the role of some kinase activators and inhibitors in the regulation of the L-type Ca2+ channel currents in rat pituitary GH3 cells using the patch-clamp technique. Phorbol 12,13-dibutyrate (PDBu), a protein kinase C (PKC) activator, and vanadate, a protein tyrosine phosphatase (PTP) inhibitor, increased the Ba2+ current through the L-type Ca2+ channels. In contrast, bisindolylmaleimide I (BIM I), a PKC inhibitor, and genistein, a protein tyrosine kinase (PTK) inhibitor, suppressed the Ba2+ currents. Forskolin, an adenylate cyclase activator, and isobutyl methylxanthine (IBMX), a non-specific phosphodiesterase inhibitor, reduced Ba2+ currents. The above results show that the L-type Ca2+ channels are activated by PKC and PTK, and inhibited by elevation of cyclic nucleotides such as cAMP. From these results, it is suggested that the regulation of hormone secretion by various kinase activity in GH3 cells may be attributable, at least in part, to their effect on L-type Ca2+ channels.

Troglitazone inhibits proliferation of GH3 cell in vitro / 第二军医大学学报

Objective:To study the anti-proliferation effects of thiazolidinedione compounds-troglitazone, which is a high affinity ligand of PPAR-? , on rat pituitary adenoma GH3 cell line and explore the related mechanisms.Methods: GH3 cells were separately treated with troglitazone (10-7,10-6 and 10-5 mol/L), dimethyl sulfoxide (DMSO) (DMSO control group) and phenol red- and serum-free F-12 medium (blank group). MTT was used to examine the cell growth in each group and FACS was used to detect the distribution of cell cycle. Semi-quantitative RT-PCR method was utilized to determine the expression of CyclinD1 mRNA. ANOVA was used for statistical analysis.Results:The 72 h treatment with troglitazone inhibited GH3 cell proliferation in a dose-Dependent manner. The treatment also induced cell cycle arrest in G1/S phase and significantly decreased the expression of CyclinD1 mRNA as compared to the other 2 groups (P

Effects of Epidermal growth factor (EGF) on the suppression of GH3 cell growth / 대한해부학회지

Some of the pituitary prolactinomas were reported that they don't have active dopamine receptors and do not respond to bromocriptine which is a dopamine agonist. GH3 cell line which is derived from the rat pituitary tumor cells lacks affinity of dopamine receptors and secrete prolactin as well as small amount of growth hormone. Although it has been reported that epidermal growth factor (EGF) induces functional expression of dopamine receptors on GH3 cells in vitro, there has been a contradictory result. In the present study, EGF effect on the GH3 cell response to the bromocriptine was observed in order to investigate whether EGF induces dopamine receptor expression on dopamine resistant tumors in the absence of serum. GH3 cells were cultured for 4 days in the serum-supplemented medium (SSM) followed by culture in serum-free medium (SFM) with or without EGF. Additionally, effect of tamoxifen was also observed. EGF decreased the cell number and the ratio of cell division of GH3 cells while the ratio of prolactin-immunoreac-tive cells was increased. However, EGF did not show any significant effect on the GH3 cell response to bromocriptine treatment. Although tamoxifen decreased the GH3 cell number by increasing apoptosis, it did not influence GH3 cell response to bromocriptine. Our results indicate that EGF does not increase the affinity of dopamine receptors on GH3 cells and is not useful for the treatment of the dopamine-resistant prolactinoma.

EGF Enhances the Differentiation Effect of the Extracellular Matrix Components on the GH3 Pituitary Tumor Cell / 대한해부학회지

This study was performed in order to establish the culture system optimal for the study on pituitary prolactin cells using growth factor and extra cellular matrix components as the culture substrate. The effect of epidermal growth factor (EGF) alone or along with extracellular marix components on GH3 cell growth and PRL expression was assessed using cell count, BrdU-immunocytochemistry and PRL-immunocytochemistry in in vitro cultures on plastic, laminin and Matrigel. EGF decreased the cell growth, BrdU-labeling and increased the PRL-immunoreactive cells regardless of the culture substrate by day 3 of the culture. Matrigel was the best culture substrate to decrease the cell growth and to increase the PRL expression. EGF treatment in the Matrigel culture showed about 80.5% of PRL-immunoreactive cells by day 6 of the culture. These results indicated that Matrigel is the better culture substrate than plastic or laminin to inhibit the overgrowth and to increase the prolactin expression of the GH3 cell and that EGF and Matrigel causes very effective culture environment for the long-term culture of the GH3 cell by synergistic mechanism.

Thyrotropin-releasing Hormone(TRH) Receptor Gene Expression in GH3 Cells Permanently Transfected with a Mutant Gs alpha Gene / 대한내분비학회지

BACKGROUND: Gs alpha gene mutation, that constitutively increases intracellular cAMP, is found in some acromegalic patients. It was demonstrated that increased intracellular cAMP levels suppress the expression of rat TRH receptor (TRH-R) mRNA. We previously demonstrated that transient expression of a mutant Gs alpha gene suppress the rat TRH-R gene expression in the cultured rat growth hormone-secreting tumor cell line (GH3), whereas TRH-R gene expression in adenomas with Gs alpha gene mutation (gsp oncogene) did not differ from that in tumors without the mutation. The discrepancy suggests the possibilities that the effect of permanent expression of mutant Gs alpha gene on TRH-R gene expression is different from that of transient expression of the mutant gene and hypothalamic hormones including TRH regulate the gene expression. METHODS: We investigated whether permanent expression of the mutant-type Gs alpha does not suppress the TRH receptor gene expression in GH3 cells, and whether TRH suppresses the gene expression by using reverse transcription-polymerase chain reaction (RT-PCR) and in vitro transcription. RESULTS: Permanent expression of a mutant-type Gs alpha increased basal cAMP levels up to 1.7-fold relative to the controls, whereas the wild-type cell line did not show increased cAMP levels. Permanent expression of a mutant-type Gs alpha increased TRH receptor mRNA level up to 2.8 fold compared with the controls. Treatment of the permanently transfected GH3 cells with TRH suppressed TRH-R gene expression more prominently compared to the wild type GH3 cells. CONCLUSION: These results suggest that permanent expression of mutant Gs alpha enhances the expression of TRH-R in GH-secreting pituitary tumors with gsp oncogene, but the gene expression may also be regulated by other factors including TRH.