Rapid induction of the Growth Hormone Gene Transcription by Glucocorticoids In Vitro: Possible Involvement of Membrane Glucocorticoid Receptors and Phosphatidylinositol 3‐Kinase Activation

Abstract

The regulation of transcription of the growth hormone (GH) gene by glucocorticoids was studied in MtT/S cells, a cell line derived from an oestrogen-induced mammotrophic tumour in the rat, and in the primary culture of the anterior pituitary gland of adult mice. The levels of the GH heteronuclear RNA (GH hnRNA), which are mainly determined by the transcription rate, increased by 25-fold during 24 h in response to dexamethasone (DEX; 1 μM) in MtT/S cells that were cultured in the medium containing charcoal-stripped serum for 7 days. The stimulatory effect of DEX on the GH hnRNA levels was detectable as early as 30 min. This rapid effect of DEX did not require on-going protein synthesis, whereas it was considered that DEX requires the presence of unknown cellular proteins produced independently of DEX stimulation. By contrast, on-going protein synthesis was required for DEX action when incubated for 6 h, as has been observed in the previous studies. The specific inhibitor of glucocorticoid receptor, RU486, inhibited both rapid (30 min) and delayed (6 h) the effects of glucocorticoids on GH hnRNA levels. Membrane impermeable glucocorticoid, corticosterone-bovine serum albumin conjugate (CSBSA), was found to have effects similar to those of DEX and free corticosterone (CS), suggesting that glucocorticoids regulate GH gene transcription at least in part through the membrane bound receptors. From pharmacological studies, it was suggested that phosphatidylinositol 3-kinase (PI3K) activation is involved in the rapid effects but not in the delayed effects of glucocorticoids. This also suggests that the delayed effects of glucocorticoids depend on mechanisms other than the activation of PI3-kinase. Finally, both rapid and delayed effects of CS and CSBSA were observed not only in MtT/S cells, but also in the mouse pituitary cells in primary culture. Therefore, it is possible that the membrane initiated action of glucocorticoids is involved in the regulation of GH transcription in normal pituitary cells, as well as in pituitary tumour cells.

Corticosterone induces growth hormone expression in pituitary somatotrophs during goose embryonic development

“…The activated GR translocate into the nucleus, binds glucocorticoid, and controls specific gene transcription [ 18 ]. In somatotrophs of a normal pituitary gland, GR is possibly involved in the rapid induction of the GH gene transcription by CORT [ 19 ]. Our results show that in ovo administration of exogenous CORT brought about correspondingly identical changes in the expression of membrane GR and GH.…”

“…In vitro , protein synthesis inhibitors completely inhibited the glucocorticoid-induced GH mRNA expression in both, mice and chick embryonic pituitary cells, suggesting the absence of a direct involvement of glucocorticoid in this process [ 20 , 21 ]. Studies have proved that in vitro , phosphatidylinositol 3-kinase might possibly be involved in the rapid induction of gene transcription of GH by glucocorticoids [ 19 ]. A recent study has demonstrated the involvement of Ras- and ERK 1/2-mediated transcriptional events requiring histone deacetylase activity in the glucocorticoid mediated induction of pituitary GH during chicken embryonic development [ 22 ].…”

Inhibition of epidermal growth factor receptor stimulates prolactin expression in primary culture of the mouse pituitary gland

“…The assessments of the embryonic day were based on the plug date, defined as embryonic day (E)0. The preparation of the monolayer culture of pituitary cells was carried out as described previously with slight modifications. Adult mice were killed by cervical dislocation, and the anterior pituitary glands were removed.…”

Targeting cyclophilin-D by compound 19 protects neuronal cells from oxygen glucose deprivation/re-oxygenation

“…Glyceraldehyde-3-phosphatedehydrogenase ( GAPDH ) mRNA was chosen as the reference gene, and the 2 −ΔΔ C t method was applied to quantify Cyp-D mRNA expression change. The murine Cyp-D mRNA primers were 5’-AGGTGGCGAAAGTATTTATG-3’ and 5’-GGAGTCGGAACTGTTGTGAT-3’ [ 52 ].…”