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Submitted on October 8, 2007
Accepted on January 8, 2008
Department of Pharmacology, University of Pittsburgh School of Medicine, and the Medical Scientist Training Program, University of Pittsburgh School of Medicine
* To whom correspondence should be addressed. E-mail: ggr{at}pitt.edu.
The effects of the expression of the Na+/H+ exchanger regulatory factor-1 (NHERF1) on the distribution, dynamics, and signaling properties of the parathyroid hormone receptor (PTH1R) were studied in rat osteosarcoma cells ROS 17/2.8. NHERF1 had a dramatic effect on the subcellular distribution of PTH1R, promoting a substantial relocation of the receptor to regions of the plasma membrane located in very close proximity to cytoskeletal fibers. Direct interactions of NHERF1 with the PTH1R and the cytoskeleton were required for these effects, since they were abolished by 1) PTH1R mutations that impair NHERF1 binding, and 2) NHERF1 mutations that impair binding to the PTH1R or the cytoskeleton. NHERF1 reduced significantly the diffusion of the PTH1R by a mechanism that was also dependent on a direct association of NHERF1 with the PTH1R and the cytoskeleton. NHERF1 increased ligand-dependent production of cAMP and induced ligand-dependent rises in intracellular calcium. These effects on calcium were due to increased calcium uptake, as they were blocked by calcium channel inhibitors and by the addition of EGTA to the medium. These calcium effects were abolished by PKA inhibition, but PLC inhibition was without effect. Based on these analyses, we propose that, in ROS cells, the presence of NHERF1 induces PTH-dependent calcium signaling by a cAMP-mediated mechanism that involves local PKA-dependent activation of calcium channels.
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