Identification of a composite steroid hormone response element on the human placental lactogen promoter

Three regions of the human placental lactogen (hPL) promoter that contain several half-site motifs that closely resemble the responsive elements for thyroid hormone (TR), all trans retinoic acid (RAR) and 1,25 dihydroxyvitamin D3 (VDR) have been identified and characterized. Transfection studies in BeWo choriocarcinoma cells indicate that site A (nt -979 to -954) is responsive to RAR alpha but not TR beta. Site B (nt -1140 to -1170) is responsive to both RAR alpha and TR beta, and site C (nt -550 to -580) is not responsive to either RAR alpha or TR. These findings, together with the observation that placental cells express retinoid receptors and TRs, strongly suggest a role for these receptors in the regulation of the hPL gene. Site B on the hPL promoter is able to integrate the responses to RA and T3 through a single element.