title: Critical role of parathyroid hormone (PTH) receptor-1 phosphorylation in regulating acute responses to PTH.
abstract: Agonist-induced phosphorylation of the parathyroid hormone (PTH) receptor 1 (PTHR1) regulates receptor signaling in vitro, but the role of this phosphorylation in vivo is uncertain. We investigated this role by injecting "knock-in" mice expressing a phosphorylation-deficient (PD) PTHR1 with PTH ligands and assessing acute biologic responses. Following injection with PTH (1-34), or with a unique, long-acting PTH analog, PD mice, compared with WT mice, exhibited enhanced increases in cAMP levels in the blood, as well as enhanced cAMP production and gene expression responses in bone and kidney tissue. Surprisingly, however, the hallmark hypercalcemic and hypophosphatemic responses were markedly absent in the PD mice, such that paradoxical hypocalcemic and hyperphosphatemic responses were observed, quite strikingly with the long-acting PTH analog. Spot urine analyses revealed a marked defect in the capacity of the PD mice to excrete phosphate, as well as cAMP, into the urine in response to PTH injection. This defect in renal excretion was associated with a severe, PTH-induced impairment in glomerular filtration, as assessed by the rate of FITC-inulin clearance from the blood, which, in turn, was explainable by an overly exuberant systemic hypotensive response. The overall findings demonstrate the importance in vivo of PTH-induced phosphorylation of the PTHR1 in regulating acute ligand responses, and they serve to focus attention on mechanisms that underlie the acute calcemic response to PTH and factors, such as blood phosphate levels, that influence it.
authors.affiliation: Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Akira
authors.initials: A
authors.lastname: Maeda
authors.forename: Makoto
authors.initials: M
authors.lastname: Okazaki
authors.forename: David M
authors.initials: DM
authors.lastname: Baron
authors.forename: Thomas
authors.initials: T
authors.lastname: Dean
authors.forename: Ashok
authors.initials: A
authors.lastname: Khatri
authors.forename: Mathew
authors.initials: M
authors.lastname: Mahon
authors.forename: Hiroko
authors.initials: H
authors.lastname: Segawa
authors.forename: Abdul B
authors.initials: AB
authors.lastname: Abou-Samra
authors.forename: Harald
authors.initials: H
authors.lastname: Jüppner
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Bloch
authors.forename: John T
authors.initials: JT
authors.lastname: Potts
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Gardella
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000097:blood / Q000652:urine; D000242:Cyclic AMP / Q000097:blood / Q000652:urine; D004305:Dose-Response Relationship, Drug; D020869:Gene Expression Profiling; D055879:Gene Knock-In Techniques; D006706:Homeostasis; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008024:Ligands; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010281:Parathyroid Hormone / Q000031:analogs & derivatives*; D010710:Phosphates / Q000097:blood / Q000652:urine; D010766:Phosphorylation; D051381:Rats; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000502:physiology*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D013997:Time Factors
chemical_list: D008024:Ligands; D010281:Parathyroid Hormone; D010710:Phosphates; D044168:Receptor, Parathyroid Hormone, Type 1; D043562:Receptors, G-Protein-Coupled; D000242:Cyclic AMP; D002118:Calcium