Differential regulation of RGS-2 by constant and oscillating PTH concentrations.
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 x 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.
Hömme
M
M
Division of Pediatric Nephrology, University Hospital for Pediatric and Adolescent Medicine, Im Neuenheimer Feld 153, 69120, Heidelberg, Germany. Meike.Hoemme@med.uni-heidelberg.de
Schaefer
F
F
Mehls
O
O
Schmitt
C P
CP
D000818:Animals; D001842:Bone and Bones / Q000187:drug effects* / Q000378:metabolism; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D054638:Dual Specificity Phosphatase 1 / Q000378:metabolism; D054642:Dual Specificity Phosphatase 6 / Q000378:metabolism; D005786:Gene Expression Regulation; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D020710:RGS Proteins / Q000378:metabolism*; D051381:Rats; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
D018975:Insulin-Like Growth Factor Binding Protein 5; D010281:Parathyroid Hormone; D020710:RGS Proteins; C087182:RGS2 protein, human; D044168:Receptor, Parathyroid Hormone, Type 1; D017868:Cyclic AMP-Dependent Protein Kinases; D054638:Dual Specificity Phosphatase 1; D054642:Dual Specificity Phosphatase 6; D053509:Matrix Metalloproteinase 13