Parathyroid Hormone-Related Peptide Transiently Increases Cytosolic Calcium in Osteoblast-Like Cells: Comparison with Parathyroid Hormone*

Abstract

PTH-related protein (PTHrP), similarly to PTH, stimulates cAMP production in target tissues. However, different potencies have been observed for the two peptides in some biological assays, suggesting that cAMP-independent second messenger pathways might be involved in PTHrP signal transduction. This hypothesis was tested in the osteogenic sarcoma cell line UMR 106-01. Addition of PTHrP-(1-34) to cell suspensions loaded with the Ca2+ indicator indo-1 produced a transient dose-dependent increase in intracellular calcium ([Ca2+]i), with a maximal effect at 2 x 10(-7) M and an ED0.5 at about 4 x 10(-8) M. The amplitude and duration of the transients were similar to those induced by equimolar concentrations of bovine PTH-(1-34) (bPTH), and the dose-responses of the two peptides completely overlapped. Both full-length peptides, PTHrP-(1-141) and bPTH-(1-84), produced effects identical to those observed with the 1-34 fragments. Homologous and heterologous desensitization to both PTHrP-(1-34) and PTHrP-(1-141) occurred when the cells were prestimulated with equimolar or 10-fold lower doses of either PTHrP-(1-34) or bPTH-(1-34). Desensitization to bPTH-(1-34) was also observed when cells were prestimulated with PTHrP-(1-34). Furthermore, pretreatment with either bPTH-(3-34) or [Nle8,18, Tyr34]bPTH-(3-34) amide did not affect [Ca2+]i, but reduced the response to PTHrP-(1-34) by 55 +/- 10% (n = 3) and 67 +/- 8% (n = 3), respectively. The PTHrP-(1-34)-induced [Ca2+]i transient was not substantially affected by either extracellular Ca2+ chelation by EGTA or pretreatment with diltiazem, and nitrendipine only partially inhibited the [Ca2+]i response to PTHrP-(1-34) by about 10%. These results indicate that in osteoblastic cells PTHrP mobilizes Ca2+ from an intracellular storage pool with potency equal to that of PTH, and that the two hormones interact with the same receptor.

Parathyroid Hormone-Receptor Interactions Identified Directly by Photocross-linking and Molecular Modeling Studies

“…PTH and PTH-related protein exert their actions via a seven-transmembrane (TM) domain-containing receptor (PTH1-Rc) (3) belonging to a subfamily of related G proteincoupled receptors (4 -11). The PTH1-Rc is coupled to both adenylyl cyclase/cyclic AMP and phospholipase C/inositol 1,4,5-trisphosphate/cytosolic calcium intracellular signaling pathways (12)(13)(14)(15).…”

“…PTH and PTH-related protein exert their actions via a seven-transmembrane (TM) domain-containing receptor (PTH1-Rc) (3) belonging to a subfamily of related G proteincoupled receptors (4 -11). The PTH1-Rc is coupled to both adenylyl cyclase/cyclic AMP and phospholipase C/inositol 1,4,5-trisphosphate/cytosolic calcium intracellular signaling pathways (12)(13)(14)(15).Understanding the molecular mechanism of ligand recognition and signal transduction by the PTH1-Rc may identify new directions for the design of novel hormone analogs for the treatment of diseases such as osteoporosis, hypercalcemia of malignancy and hyperparathyroidism (16). In order to directly identify the structural elements involved in PTH-PTH1-Rc interactions, we employed a photoaffinity scanning approach (17).…”

Endocytosis of Ligand-Human Parathyroid Hormone Receptor 1 Complexes Is Protein Kinase C-dependent and Involves β-Arrestin2

“…PTH is the major regulator of calcium and phosphate homeostasis and plays a central role in bone metabolism (24). Activation of the parathyroid hormone receptor subtype 1 (PTH1-Rc) by PTH stimulates both adenylyl cyclase/cAMP/protein kinase A (PKA) and the phospholipase C/inositol 1,4,5-trisphosphate/cytosolic Ca 2ϩ and diacylglycerol/PKC pathways (25)(26)(27). In addition, PTH activates G protein-coupled receptor kinases, such as GPCR kinase 2 (28 -30).…”

Deletion of the nuclear localization sequence and C-terminus of parathyroid hormone–related protein decreases osteogenesis and chondrogenesis but increases adipogenesis and myogenesis in murine bone marrow stromal cells

“…More specifically, the effects of N-terminal PTHrP 1-34, PTHrP 1-108, and full-length PTHrP 1-141 on AC and PLC signaling are equivalent, as noted in many studies by their equivalent biological effects in increasing (1) intracellular cAMP (AC/PKA pathway activation) and (2) intracellular calcium (PLC/PKC stimulation). [23][24][25][26][27][28] However, administration of PTHrP analogs containing only the NLS or C-terminus has no effect on intracellular cAMP or calcium, indicating no effects on PTH1R signaling by the NLS or C-terminus of PTHrP. 25,28 Considering this, the absence of a decrease in Pka and Pkc expression in Pthrp Δ/Δ BMSCs, and historical data on the effects of different lengths of PTHrP on PTH1R signaling, we believe that our findings in Pthrp Δ/Δ mice result from (1) the lack of the intracellular intracrine effects of the protein or (2) PTH1R-independent effects due to the absence of the NLS and C-terminus of PTHrP and are not due to differences in PTHrP expression, production, or decreased signaling through PTH1R.…”