The long-term goal of this project is to elucidate the cellular mechanisms of parathyroid hormone receptor (PTHR) action in bone. It has generally been assumed that internalized receptors are constitutively recycled. We discovered that intact PTH peptides promote receptor recycling, whereas amino-truncated PTH peptides, which accumulate in renal failure, lead to PTHR ubiquitination and downregulation. This is the first demonstration of PTHR ubiquitination, a reversible post-translational modification. The mechanism underlying ligand-regulated ubiquitination and deubiquitination is unknown. This gap in our understanding is a major focus of the proposed studies. PTHR recycling begins soon after its sequestration but is not complete for some time. Preliminary studies now show that a cytoplasmic PDZ protein, SNX27, accelerates receptor recycling without affecting signaling or internalization. The proposed studies are designed to define the sustainability of the parathyroid hormone receptor, which after activation and internalization is destined either for degradation or recycling. The actions and mechanism by which PTH receptor salvage is regulated are poorly understood. The unifying hypothesis of this proposal is that post-translational modifications and cytoplasmic adapter chaperones determine PTHR degradation and recycling. Two interrelated aims are developed to test this theory.
Aim 1 will characterize novel PTHR post-translational modifications, their mechanism of action, and effect on receptor fate and function.
Aim 2 addresses the mechanism by which cytoplasmic chaperone proteins facilitate PTHR recycling. The planned studies use an array of complementary biophysical, molecular and biochemical, and cell biological tools. These studies will characterize a novel mechanism to explain regulated PTHR recycling. The results will generate new information that is relevant to understanding bone turnover. The outcomes will help define potential therapeutic targets for treating PTH resistance, osteoporosis and other metabolic bone diseases.

Public Health Relevance

The proposed studies are designed to define the sustainability of the parathyroid hormone receptor, which after activation and internalization is destined either for degradation or recycling. The actions and mechanism by which PTH receptor salvage is regulated is poorly understood. The planned experiments will fill this gap. We identified novel PTH receptor partners that determine its fate. The outcome of the experiments is highly relevant to our understanding of osteoporosis and will define potential therapeutic targets for improved treatment of osteoporosis and other metabolic bone diseases. The results of our studies are highly relevant to understanding bone biology and the factors that cause PTH resistance. The results will help define potential therapeutic targets for improved treatment of osteoporosis and other metabolic bone diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK054171-28
Application #
8452051
Study Section
Skeletal Biology Development and Disease Study Section (SBDD)
Program Officer
Malozowski, Saul N
Project Start
1998-09-01
Project End
2016-03-31
Budget Start
2013-04-01
Budget End
2014-03-31
Support Year
28
Fiscal Year
2013
Total Cost
$387,429
Indirect Cost
$119,119
Name
University of Pittsburgh
Department
Pharmacology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15213
Pavlos, Nathan J; Friedman, Peter A (2016) GPCR Signaling and Trafficking: The Long and Short of It. Trends Endocrinol Metab :
McGarvey, Jennifer C; Xiao, Kunhong; Bowman, Shanna L et al. (2016) Actin-Sorting Nexin 27 (SNX27)-Retromer Complex Mediates Rapid Parathyroid Hormone Receptor Recycling. J Biol Chem 291:10986-1002
Pereira, Renata C; Andersen, Thomas L; Friedman, Peter A et al. (2016) Bone Canopies in Pediatric Renal Osteodystrophy. PLoS One 11:e0152871
Walsh, Dustin R; Nolin, Thomas D; Friedman, Peter A (2015) Drug Transporters and Na+/H+ Exchange Regulatory Factor PSD-95/Drosophila Discs Large/ZO-1 Proteins. Pharmacol Rev 67:656-80
Stubbs, Jason R; Zhang, Shiqin; Friedman, Peter A et al. (2014) Decreased conversion of 25-hydroxyvitamin D3 to 24,25-dihydroxyvitamin D3 following cholecalciferol therapy in patients with CKD. Clin J Am Soc Nephrol 9:1965-73
Alonso, Veronica; Friedman, Peter A (2013) Minireview: ubiquitination-regulated G protein-coupled receptor signaling and trafficking. Mol Endocrinol 27:558-72
Liu, Li; Schlesinger, Paul H; Slack, Nicole M et al. (2011) High capacity Na+/H+ exchange activity in mineralizing osteoblasts. J Cell Physiol 226:1702-12
Blair, Harry C; Robinson, Lisa J; Huang, Christopher L-H et al. (2011) Calcium and bone disease. Biofactors 37:159-67
Vilardaga, Jean-Pierre; Romero, Guillermo; Friedman, Peter A et al. (2011) Molecular basis of parathyroid hormone receptor signaling and trafficking: a family B GPCR paradigm. Cell Mol Life Sci 68:1-13
Ardura, Juan A; Wang, Bin; Watkins, Simon C et al. (2011) Dynamic Na+-H+ exchanger regulatory factor-1 association and dissociation regulate parathyroid hormone receptor trafficking at membrane microdomains. J Biol Chem 286:35020-9

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