In the present work we propose to analyze the expression of estrogen receptor (ER) β and cell cycle regulators in normal and tumoral pituitary cells using a specific agonist of ERβ.

Normal anterior pituitary cells from female rats and hyperplastic/adenomatous pituitary glands were used. Normal cells were stimulated with 17β-estradiol (E2) or ERβ agonist (DPN). The expression of ERα and β was analyzed by confocal microscopy (CM), Western Blot (WB) and flow cytometry (FC). Cell cycle progression was quantified by FC. The expression of p21, cyclin D1, CDK4 and PTEN were analyzed by WB and CM. Statistical analysis: ANOVA-Tukey.

As expected, normal anterior pituitary cells expressed ERα and β. A remarkable decrease in ERβ expression was observed during the development of the hyperplastic/adenomatous model (16.6±2.2% of normal anterior pituitary cells expressed ERβ, 10.7±2.2% in hyperplastic glands of 20days, 1±0.6 in gland of 40days and 2± 0.6% in gland of 60days). No variations were found in ERα expression. The cell cycle progression analysis revealed that 1.57±0.1% of the normal pituitary cells were at S/G2M phase; this percentage was doubled for hyperplastic glands of 20days and maintained at 40 and 60days. In normal pituitary cells, E2 treatment increased cyclin D1, CDK4, PTEN and p21, while DPN inhibited PTEN and p21 without changing in CDK4 and cyclin D1 levels. By CM p21 was observed in the cytoplasm, meanwhile DPN was able to induce nuclear localization. During the development of the hyperplastic/adenomatous model, a gradual decrease in PTEN expression was observed, while cyclin D1, CDK4 and cytoplasmatic p21 increased in correlation with the number of cells in the S/G2M phase.

The ERβ expression decrease during pituitary tumor development suggests that this ER subtype may be an inhibitor of the cell cycle, likely through p21, regulating the cell proliferation in the pituitary gland.