Differential Regulation of RGS-2 by Constant and Oscillating PTH Concentrations

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Abstract

PTH has diverse effects on bone metabolism: anabolic when given intermittently, catabolic when given continuously. The cellular mechanisms underlying the varying target cell response are not clear yet. PTH induces RGS-2, a member of the Regulator of G-protein Signaling protein family, via cAMP/PKA, and inactivates PKC-mediated signaling. To investigate intracellular signaling pathways with different PTH concentration-time patterns, we treated UMR 106-01 osteoblast-like cells in a perfusion system. PTH was administered intermittently (4 min/h, 10−7 M) or continuously at an equivalent cumulative dose (6.6 × 10−9 M). cAMP was measured using radioimmunoassay, mRNA levels using real-time rtPCR and ribonuclease protection assay, and protein levels using Western immunoblotting. A single PTH pulse transiently increased cAMP levels by 2000% ± 1200%. In contrast to continuous PTH exposure, cAMP induction remained unchanged with intermittent PTH, ruling out desensitization of the PTH receptor. In continuously perfused cells, RGS-2 abundance was three to five times higher than in cells intermittently exposed to PTH for up to 12 h. MKP-1 and -3 were significantly less induced with pulsatile PTH; exposure-mode-dependent differences in MMP-13 and IGFBP-5 were small. Pulsatile but not continuous PTH administration prevents PTHrP receptor desensitization and accumulation of RGS-2 in osteoblasts, which should preserve PKC-dependent signaling.

Keywords

Peptide hormones Parathyroid hormone/PTHrP Osteoblasts Gene transcription regulation 
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Notes

Acknowledgments

We thank Bärbel Phillipin for excellent technical support. Meike Hömme received grants from the Young Investigator Award Programme of the medical faculty of Heidelberg and the Else Kröner Fresenius Foundation.

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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • M. Hömme
    • 1
  • F. Schaefer
    • 1
  • O. Mehls
    • 1
  • C. P. Schmitt
    • 1
  1. 1.Division of Pediatric NephrologyUniversity Hospital for Pediatric and Adolescent MedicineHeidelbergGermany

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