Regulation of 25-hydroxyvitamin D3 1alpha-hydroxylase, 1,25-dihydroxyvitamin D3 24-hydroxylase and vitamin D receptor gene expression by 8-bromo cyclic AMP in cultured human syncytiotrophoblast cells

Abstract

In vitro differentiation of human trophoblast cells is a dynamic process accompanied by increasing intracellular levels of cyclic AMP (cAMP). Signaling through cAMP in this tissue is central to hormone expression and cytodifferentiation. In the present study, we analyzed transcriptional regulation of key enzymes involved in vitamin D endocrine system during in vitro syncytiotrophoblast formation. Total RNA was isolated from human trophoblast cells and subjected to reverse transcription, polymerase chain reaction and Southern blot analysis using specific primers and radiolabeled probes. During syncytium formation 25-hydroxyvitamin D(3) 1alpha-hydroxylase (CYP27B1) was decreased while vitamin D receptor (VDR) gene remained unaffected. No 1,25-dihydroxyvitamin D(3) 24-hydroxylase (CYP24) transcription signal was detected. Nevertheless, incubations in the presence of 8-bromo cAMP (1.5mM) resulted in CYP24 induction and CYP27B1 inhibition, respectively. The overall data showed that cultured human syncytiotrophoblasts express key enzymes involved in vitamin D metabolism, as well as VDR. The results support previous findings that human placenta is a source of 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)), which synthesis is regulated by common growth and developmental factors. The data also suggest a tissue-dependant differential regulation of CYP27B1 gene expression by cAMP.