CLONING AND CHARACTERIZATION OF THE TYPE-I INOSITOL 1,4,5-TRISPHOSPHATE RECEPTOR GENE PROMOTER - REGULATION BY 17-BETA-ESTRADIOL IN OSTEOBLASTS

The inositol 1,4,5-trisphosphate (InsP(3)) receptor is essential for s ignal Ca2+ release from intracellular stores and for capacitative Ca2 entry, We have isolated the promoter and proximal DNA segments of the human type I InsP(3) receptor gene, Transcription initiation in human 6-292 osteosarcoma and HL-60 promyelocytic leukemia cells was shown t o occur predominantly from an adenine residue located 39 base pairs do wnstream of a consensus TATA box element, Upstream DNA including the T ATA box promoted directional transcription of a chloramphenicol acetyl transferase reporter gene when transfected into 6-292 cells, A negativ e regulatory element in the distal promoter and a positive element in the proximal region were identified by deletion mapping and transcript ion assays, The proximal region enhanced transcription in response to 12-O-tetradecanoylphorbol-13-acetate or serum, but conferred transcrip tional repression in response to 1,25-dihydroxyvitamin D-3 or 17 beta- estradiol. The repressive effect of 17 beta-estradiol was mediated by the nuclear estrogen receptor, as estrogen-dependent transcriptional r epression was inhibited by the antiestrogen tamoxifen and the estrogen receptor antagonist ICI 182,780. This is the first study of the type I InsP(3) receptor gene promoter, and the results suggest a mechanism by which chronic estrogen treatment of osteoblasts affects type I InsP (3) receptor gene expression, signal transduction, and secretion.