ABSTRACT
Considering that the role of ERß in the growth of pituitary cells is not well known, the aim of this work was to determine the expression of ERß in normal and tumoral cells and to investigate its implications in the proliferative control of this endocrine gland, by analyzing the participation of cyclin D1, Cdk4 and p21. Our results showed that the expression of ERß decreased during pituitary tumoral development induced by chronic E2 stimulation. The 20 ± 1.6% of normal adenohypophyseal cells expressed ERß, with this protein being reduced in the hyperplastic/adenomatous pituitary: at 20 days the ERß+ population was 10.7 ± 2.2%, while after 40 and 60 days of treatment an almost complete loss in the ERß expression was observed (40 d: 1 ± 0.6%; 60 d: 2 ± 0.6%). The ERα/ß ratio increased starting from tumors at 40 days, mainly due to the loss of ERß expression. The cell proliferation was analyzed in normal and hyperplastic pituitary and also in GH3ß- and GH3ß+ which contained different levels of ERß expression, and therefore different ERα/ß ratios. The over-expression of ERß inhibited the GH3 cell proliferation and expression of cyclin D1 and ERα. Also, the ERß activation by its agonist DPN changed the subcellular localization of p21, inducing an increase in the p21 nuclear expression, where it acts as a tumoral suppressor. These results show that ERß exerts an inhibitory role on pituitary cell proliferation, and that this effect may be partially due to the modulation of some key regulators of the cell cycle, such as cyclin D1 and p21. These data contribute significantly to the understanding of the ER effects in the proliferative control of pituitary gland, specifically related to the ERß function in the E2 actions on this endocrine gland.
Subject(s)
Cell Cycle/drug effects , Estradiol/adverse effects , Estrogen Receptor beta/metabolism , Pituitary Gland, Anterior/cytology , Pituitary Neoplasms/metabolism , Animals , Cell Line, Tumor , Cell Proliferation/drug effects , Cells, Cultured , Cyclin D1/metabolism , Cyclin-Dependent Kinase 4/metabolism , Cyclin-Dependent Kinase Inhibitor p21/metabolism , Female , Gene Expression Regulation/drug effects , NAD/pharmacology , Pituitary Gland, Anterior/metabolism , Pituitary Neoplasms/chemically induced , Pituitary Neoplasms/pathology , RatsABSTRACT
Lactotroph cells display morphological and functional heterogeneity, a feature which is closely related to the oestrogenic environment. In this study, we focused on sex-related differences linked to the proliferative and secretory responses of lactotrophs exposed to EGF in vitro. Furthermore, we addressed the involvement of the PKCε/ERK1/2 signalling pathway and the contribution of Pit-1 in the EGF actions in primary pituitary cultures from male and female rats. EGF promoted a differential proliferative activity on PRL cells, which was closely associated to the sex, as revealed by the uptake of bromodeoxyuridine (BrdU). In females, the mitogenic activity was up to nine times greater, whereas in males, the number of BrdU-labelled PRL cells was only doubled compared to control. However, in both models, EGF had a similar effectiveness in promoting PRL secretion. EGF also induced a significant increase in the PKCε, P -ERK 1/2, and Pit-1 protein levels, which were higher in females than in males. Pre-incubation with BIM blocked EGF-induced ERK 1/2 activation and Pit-1 expression. These results suggest a sexually dimorphic response of lactotroph cells to the proliferative effects of EGF, with the PKCε/ERK1/2 Pit-1 pathway being involved in this action.
