Upregulation of PTH receptor mRNA expression by dexamethasone in UMR-106 osteoblast-like cells.
OBJECTIVE
Glucocorticoids influence receptor interactions of the parathyroid hormone (PTH) that are crucial for osteoblast function. As mechanisms linking receptor mRNA with glucocorticoids are incompletely understood, we investigated regulation of PTH receptor (PTH1R) mRNA expression in rat osteoblast-like UMR-106 cells by using dexamethasone (Dex), a synthetic glucocorticoid.


METHODS
UMR-106 cells were exposed to 10(-8) to 10(-5) M Dex, while some cells were also exposed to a transcriptional inhibitor (DRB) for 24 h with or without Dex. PTH-stimulated cyclicAMP activities were measured by an enzyme-linked immunosorbent assay. PTH1R mRNA was determined by Northern analysis. Transcriptional activities were measured as heretogeneous nuclear PTH1R RNA and also as luciferase activity in constructs, including the PTH1R gene promoter.


RESULTS
Dexamethasone dose-dependently increased PTH-stimulated adenylyl cyclase activity at 72 h. Dex markedly increased PTH1R mRNA accumulation, but did not change transcriptional activity. PTH1R mRNA stability was significantly increased by Dex in transcriptionally arrested cells.


CONCLUSIONS
In osteoblast-like cells, Dex induced upregulation of PTH1R mRNA followed by increased functional PTH receptor expression. This was caused by posttranscriptional mechanisms increasing mRNA stability.
Haramoto
N
N
Section of Biochemistry, Department of Oral Function and Molecular Biology, Ohu University School of Dentistry, Koriyama, Japan.
Kawane
T
T
Horiuchi
N
N
D000262:Adenylyl Cyclases / Q000187:drug effects; D000818:Animals; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000032:analysis; D003907:Dexamethasone / Q000008:administration & dosage / Q000494:pharmacology*; D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects; D005938:Glucocorticoids / Q000008:administration & dosage / Q000494:pharmacology*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects*; D012516:Osteosarcoma / Q000473:pathology; D011401:Promoter Regions, Genetic / Q000187:drug effects; D012333:RNA, Messenger / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects*
D005938:Glucocorticoids; D019384:Nucleic Acid Synthesis Inhibitors; D012333:RNA, Messenger; D044168:Receptor, Parathyroid Hormone, Type 1; D004004:Dichlororibofuranosylbenzimidazole; D003907:Dexamethasone; D000242:Cyclic AMP; D000262:Adenylyl Cyclases