Efecto estimulador del calcitriol a través del receptor de la vitamina D en la expresión génica y secreción de la prolactina de origen linfocitario

Abstract

Prolactin is a protein hormone that is produced by the pituitary lactotrophs and also by extrapituitary sites such as decidua and lymphocytes. Calcitriol, the active form of vitamin D3, is a secosteroid with immunomodulatory actions that exerts its effects through vitamin D receptor (VDR). It is known that calcitriol stimulates PRL expression in pituitary cells in culture as well as in decidua. However, regulators of lymphocyte prolactin synthesis are less known. The aim of this study was to evaluate the effect of calcitriol on the mRNA expression and secretion of PRL in cultured peripheral blood mononuclear cells (PBMNC) from healthy subjects. PBMNC were cultured with different concentrations of calcitriol in the absence or presence of a VDR antagonist. The presence of VDR was evaluated by Westernblot. PRL, and highly responsive genes for calcitriol such as VDR, CYP24A1 and CYP27B1 mRNA expression were evaluated by RT and real time PCR. PRL secretion was quantified by ELISA and protein-VDRE binding was assessed by EMSA. Immunoblots showed the presence of a 48-kDa VDR form in PHA treated PBMNC and Jurkat cells, while a 75-kDa form was recognized in both, nonactivated and activated cells. Treatment with calcitriol increased both, PRL and CYP24A1 mRNA expression only in non-activated cells, in a dose-dependent manner. Incubation with VDR antagonist reverted the stimulatory effect of calcitriol upon PRL expression. In activated cells, calcitriol increased CYP27B1 and VDR expression. EMSA analysis showed that lysates of non-activated cells contained a protein that binds to VDRE. In conclusion, calcitriol stimulates PRL and CYP24A1 gene expression in non-activated lymphocytes through a VDR-mediated mechanism. This study provides evidence that calcitriol exerts differential effects depending on activation cellular state which could be related to the presence of functional VDR isoforms in lymphocytes.