Cloning and characterization of the type I inositol 1,4,5-trisphosphate receptor gene promoter. Regulation by 17β-estradiol in osteoblasts

The inositol 1,4,5-trisphosphate (InsP₃) receptor is essential for signal Ca²⁺ release from intracellular stores and for capacitative Ca²⁺ entry. We have isolated the promoter and proximal DNA segments of the human type I InsP₃ receptor gene. Transcription initiation in human G-292 osteosarcoma and HL-60 promyelocytic leukemia cells was shown to occur predominantly from an adenine residue located 39 base pairs downstream of a consensus TATA box element. Upstream DNA including the TATA box promoted directional transcription of a chloramphenicol acetyltransferase reporter gene when transfected into G-292 cells. A negative regulatory element in the distal promoter and a positive element in the proximal region were identified by deletion mapping and transcription assays. The proximal region enhanced transcription in response to 12-O-tetradecanoyl-phorbol-13-acetate or serum, but conferred transcriptional repression in response to 1,25-dihydroxyvitamin D₃ or 17β-estradiol. The repressive effect of 17β-estradiol was mediated by the nuclear estrogen receptor, as estrogen-dependent transcriptional repression was inhibited by the antiestrogen tamoxifen and the estrogen receptor antagonist ICI 182,780. This is the first study of the type I InsP₃ receptor gene promoter, and the results suggest a mechanism by which chronic estrogen treatment of osteoblasts affects type I InsP₃ receptor gene expression, signal transduction, and secretion.