title: Transcriptional control of the osteocalcin gene by 1,25-dihydroxyvitamin D-2 and its 24-epimer in rat osteosarcoma cells.
abstract: The effects of two vitamin D analogs, 1,25-dihydroxyvitamin D-2 and 24-epi-1,25-dihydroxyvitamin D-2, were examined on osteocalcin gene expression in the rat osteosarcoma cell line ROS 17/28. Our results indicate that these analogs are more transcriptionally active than 1,25-dihydroxyvitamin D-3, particularly the 24-epimer. Assessment of reporter gene chloramphenicol acetyltransferase (CAT) activity, using the vitamin D responsive element (VDRE) derived from the human osteocalcin gene promoter. revealed that both analogs stimulated CAT activity 5- to 10-fold. 1,25-Dihydroxyvitamin D-2 was slightly more active than 1,25-dihydroxyvitamin D-3, while the 24-epimer was twice as effective. 1,25-Dihydroxyvitamin D-3 also stimulated osteocalcin mRNA accumulation by 2-fold over vehicle-treated cells, 1,25-dihydroxyvitamin D-2 by 2.5-fold, and 24-epi-1,25-dihydroxyvitamin D-2 by 4-fold. Electrophoretic mobility shift assays using the osteocalcin vitamin D responsive element revealed no increase in DNA binding with either analog when compared to 1,25-(OH)2D3. Examination of CAT activity using the rat 24-hydroxylase VDRE indicated no significant difference in transcription with these compounds, suggesting that the vitamin D-2 analogs preferentially activate osteocalcin gene expression.
authors.affiliation: Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison 53706, USA.
authors.forename: N C
authors.initials: NC
authors.lastname: Arbour
authors.forename: H M
authors.initials: HM
authors.lastname: Darwish
authors.forename: H F
authors.initials: HF
authors.lastname: DeLuca
mesh_terms: D000818:Animals; D001483:Base Sequence; D002117:Calcitriol / Q000494:pharmacology; D002478:Cells, Cultured; D004872:Ergocalciferols / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D008969:Molecular Sequence Data; D015675:Osteocalcin / Q000235:genetics* / Q000378:metabolism; D012516:Osteosarcoma / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D018167:Receptors, Calcitriol / Q000502:physiology; D014158:Transcription, Genetic
chemical_list: D004872:Ergocalciferols; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D015675:Osteocalcin; C063087:1,24-dihydroxyvitamin D2; C003564:1,25-dihydroxyergocalciferol; D002117:Calcitriol