Regulation of human placental lactogen expression by 1,25-dihydroxyvitamin D3

The human placenta synthesizes 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and expresses the vitamin D receptor (VDR), but the roles of 1,25-(OH)2D3 and the VDR in placental physiology are poorly understood. In this study, we have demonstrated that 1,25-(OH)2D3 stimulates the synthesis and release of human placental lactogen (hPL), one of the major secretory products of syncytiotrophoblast cells. Enzymatically dispersed trophoblast cells from term placentas exposed continuously to 1,25-(OH)2D3 (0.1, 6, and 37 microM) for 5 days released significantly more hPL than control cells after the third day of exposure. On days 4 and 5, the amounts of hPL released by cells exposed to 1,25-(OH)2D3 were 2.54- and 4.14-fold that of control cells (P < 0.001 in each instance). The stimulation by 1,25-(OH)2D3 was dose dependent and was accompanied by stimulation of hPL messenger RNA levels. Transient transfection studies of BeWo choriocarcinoma cells transfected with hPL promoter constructs coupled to the chloramphenicol acetyltransferase reporter gene indicated that the stimulation of hPL expression is due at least in part to stimulation of hPL gene expression. Deletion analysis studies of the hPL promoter indicated that a region between -500 to -1200 basepairs is necessary for 1,25-(OH)2D3 responsiveness. Analysis of this region shows a consensus vitamin D response element (VDRE) DNA-binding site of a direct repeat motif separated by three bases. Ligation of this placental VDRE site into a heterologous chloramphenicol acetyltransferase vector caused 1,25-(OH)2D3 responsiveness. Moreover, mobility shift assays demonstrated binding of VDR to placental VDRE. These results indicate that 1,25-(OH)2D3 stimulates the synthesis and release of hPL by a mechanism involving hPL gene transcription and support a role for vitamin D and the VDR in placental function.