Pro-oxidant effects induced by 17β-estradiol promote p53 and p21 activation in normal and tumoral pituitary cells

Abstract

Abstract: 

The estrogenic action on pituitary cell growth is widely known. We have previously demonstrated the activation of the antioxidant pathway of phosphorylated erythroid 2-derived nuclear factor 2 (p-Nrf2) in response to DNA damage by 17β-estradiol (E2). In this study we analyzed the impact of E2 on the tumoral suppressor p53 and cell cycle regulator p21 activation, as well as the damage response in pituitary cells in vitro.

Pituitary tumour development was induced in adult male Wistar rats by subcutaneous implantation of silastic capsules containing estradiol benzoate (30mg) for 10 days (E10; n = 5). The control group was implanted with empty capsules (n=5). Subsequently, pituitary glands were collected, with cells being cultured and exposed to E2 (1-10-100nM) for 15, 30 and 60 min. The p53 and p21 protein levels were determined by western blot. By immunofluorescence, the co-expression of prolactin (PRL)/p-Nrf2 and growth hormone (GH)/p-Nrf2 was evaluated to determinate the cell type involved in the activation of the oxidative damage response. Statistical analysis: ANOVA-Fischer (p <0.05).

Under tumoral contexts, a significant increase in p53 protein at the cytoplasmic level was detected after 15 and 30 min of treatment with E2 (1nM). After supraphysiological concentrations (10-100nM), this response was observed after 30 and 60 min. At nuclear level, we only detected an increase in p53 at 15 min, regardless of the dose. The p2 expression showed a similar profile in both subcellular compartments, with significant increases after 15 and 30 min of exposure with 1nM E2 and 30 and 60 min with supraphysiological doses. In normal cells cultures we did not observe significant changes in the expression of both markers. The number of lactotroph tumoral cells co-expressing PRL/p-Nrf2 increased significantly at 30 min compared to supraphysiological doses of E2. No changes were detected in the expression of GH/p-Nrf2 in GH cells.

In tumoral pituitary cells, the pro-oxidant action induced by E2 triggers the activation of p53 and p21 in order to repair DNA damage, through the stabilization of Nrf2. This response would mainly have an impact on PRL tumoral cells. These mechanisms could guarantee the cell viability, thus regulating pituitary tumor development.