title: Down-regulation of the receptor for parathyroid hormone (PTH) and PTH-related peptide by PTH in primary fetal rat osteoblasts.
abstract: We studied the effects of parathyroid hormone (PTH) on PTH parathyroid hormone related peptide (PTHrP) receptor mRNA level, PTHrP binding and PTH-stimulated cyclic adenosine monophosphate (cAMP) accumulation in osteoblasts, derived from fetal rat calvariae (ROB). Cells isolated during 10-70 minutes of collagenase treatment were seeded at a density of 25,000 cells/cm2 and cultured for 4 days. These cells show a fast increase in cAMP production after stimulation for 5 minutes with 20 nM bovine parathyroid hormone(1-34) (bPTH(1-34)). When ROB are incubated with bPTH(1-34) (0.04-40nM) for 24 h, a dose-dependent decrease of the PTH/PTHrP receptor mRNA level, PTHrP binding, and PTH-stimulated cAMP accumulation can be observed. Pretreatment of ROB with a high concentration of bPTH(1-34) (40 nM) leads within 15 minutes to a decrease in PTH-stimulated cAMP accumulation. However, it takes > or = 3 h before a significant decrease in PTH/PTHrP receptor mRNA level can be observed. Also a significant decrease in PTHrP binding is observed after only 4 h of incubation with bPTH(1-34). Compared with bPTH(1-34), pretreatment of ROB with bPTH(3-34) (40 and 100 nM) for 24 h causes smaller decreases in PTH-stimulated cAMP accumulation, PTHrP binding, and in the PTH/PTHrP receptor mRNA level. We investigated the possible involvement of the protein kinase A signaling pathway in the regulation of the PTH/PTHrP receptor mRNA expression. Both forskolin and (Bu)2cAMP decreased PTHrP binding and PTH/PTHrP mRNA levels. These observations suggest that chronic activation of the PKA signaling pathway may down-regulate PTH/PTHrP receptor expression and thus hormone responsiveness in "normal" osteoblasts. In short, we found that the decrease of the PTH-stimulated cAMP accumulation after long-term pretreatment with bPTH(1-34) is correlated with both PTH/PTHrP receptor mRNA level and PTHrP binding. These data also suggest that the initial desensitization (< 30 minutes) of PTH-stimulated cAMP responsiveness by pretreatment with a high concentration of bPTH(1-34) (40 nM) is not dependent on the number of available PTH/PTHrP receptors. The protein kinase A signaling pathway is involved in the regulation of the PTH/PTHrP receptor, but, regarding the effect of bPTH(3-34), other signaling systems are also involved.
authors.affiliation: Laboratory of Cell Biology and Histology, University of Leiden, The Netherlands.
authors.forename: J W
authors.initials: JW
authors.lastname: Jongen
authors.forename: E C
authors.initials: EC
authors.lastname: Willemstein-van Hove
authors.forename: J M
authors.initials: JM
authors.lastname: van der Meer
authors.forename: M P
authors.initials: MP
authors.lastname: Bos
authors.forename: H
authors.initials: H
authors.lastname: Jüppner
authors.forename: G V
authors.initials: GV
authors.lastname: Segre
authors.forename: A B
authors.initials: AB
authors.lastname: Abou-Samra
authors.forename: J H
authors.initials: JH
authors.lastname: Feyen
authors.forename: M P
authors.initials: MP
authors.lastname: Herrmann-Erlee
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D003994:Bucladesine / Q000494:pharmacology; D002417:Cattle; D002452:Cell Count; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D044162:Parathyroid Hormone-Related Protein; D011485:Protein Binding; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D018016:Receptors, Parathyroid Hormone / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D019379:Teriparatide / Q000378:metabolism / Q000494:pharmacology
chemical_list: D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D018016:Receptors, Parathyroid Hormone; D019379:Teriparatide; D005576:Colforsin; D003994:Bucladesine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases