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Characterization of Basal and Stimulated Gnrhr Expression in Pituitary Cells
Author(s) -
Janjic Marija M,
Bjelobaba Ivana,
Tavcar Jovana,
Kucka Marek,
Tomic Melanija,
Stojilkovic Stanko
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1248.5
Subject(s) - gnrhr , medicine , endocrinology , gonadotropin releasing hormone receptor , gonadotropic cell , biology , anterior pituitary , somatotropic cell , gene expression , gonadotropin releasing hormone , signal transduction , protein kinase a , receptor , corticotropic cell , pituitary gland , hormone , kinase , microbiology and biotechnology , gene , luteinizing hormone , genetics
Gonadotropin‐releasing hormone (GnRH) is a potent stimulus for expression of multiple genes in pituitary gonadotrophs, including the gene encoding GnRH receptor (Gnrhr). Here we examined the signaling pathways accounting for Gnrhr expression in vitro, using primary cultures of rat and mice anterior pituitary cells and mouse immortalized LβT2 gonadotrophs. After removal of anterior pituitary glands and cell dispersion, there was decay in Gnrhr expression, which progressed in cultured cells, with the rates not affected by substitution of horse or fetal calf serum with BSA and by application of a GnRHR antagonist. The decay in gene expression reached a steady state level during 40–50 h incubation to about 20% of that observed in vivo and the residual expression was termed basal. Pulsatile as well as continuous application of GnRH restored, at least partially, Gnrhr expression in a time‐dependent manner, with a peak in expression after about 6 h of application. In pituitaries from neonatal and infantile animals, the profiles of GnRH‐induced responses were similar in females and males and the amplitudes of responses were low. During juvenile to postpubertal period, the profiles of GnRH‐induced gene expression were also comparable in cells from both sexes, but the amplitudes of responses were several‐fold higher in female cells. GnRH‐stimulated Gnrhr expression was independent of cAMP‐PKA signaling pathway and was mediated by calcium and protein kinase C signaling pathways; downstream elements of protein kinase C pathways included ERK1/2 but not JNK, p38, or big MAPK. In naïve LβT2 cells (never previously stimulated with GnRH), there was also a substantial basal Gnrhr expression not affected by removal of fetal calf serum for 24 h and by application of a GnRHR antagonist; these cells also expressed functional GnRHR, as indicated by GnRH‐induced calcium signaling. However, application of GnRH was unable to elevate gene expression in LβT2 cells. Pharmacological activation of cAMP‐protein kinase A, calcium, and protein kinase C signaling pathways were also ineffective. On the other hand, basal Gnrhr expression was reduced by inhibition or depletion of classic protein kinase C isozymes in both normal and immortalized pituitary cells. These results indicate that Gnrhr expression is operative in the absence of any hormonal stimulation, probably reflecting intrinsic protein kinase C activity. Physiologically, such activity secures the presence of sufficient number of functional GnRHR needed to up‐regulate Gnrhr expression and initiate the expression of signature and other genes once GnRH is available. Support or Funding Information This work was supported by the Intramural Research Program of the National Institute of Child Health and Human Development (ZIA DH000195‐22).