1. Proliferative effect of parathyroid hormone-related protein on the hypercalcemic Walker 256 carcinoma cell line
J Benítez-Verguizas, P Esbrit Biochem Biophys Res Commun. 1994 Feb 15;198(3):1281-9. doi: 10.1006/bbrc.1994.1181.
The rat Walker 256 carcinoma is an animal model for humoral hypercalcemia of malignancy. This tumor produces and secretes parathyroid hormone (PTH)-related protein (PTHrP), a likely mediator for this syndrome. In this study, we investigated the effect of PTHrP on Walker 256 tumor cell proliferation. We found that [Tyr36]human (h)PTHrP (1-36)NH2 and hPTHrP (1-86), unlike hPTHrP (38-64)NH2, stimulate DNA synthesis dose-dependently in these cells. A similar mitogenic effect was also observed with bovine (b)PTH (1-34) or (Nle8.18, Tyr34)bPTH (3-34)NH2. Moreover, addition of anti-hPTHrP (1-34) neutralizing antibodies decreased tumor cell growth. Conversely, 10(-4)M dibutyryl cAMP or Sp-cDBIMPS (a cAMP analogue) inhibited DNA synthesis in these cells, being incompetent at lower doses. PTHrP or PTH failed to stimulate cAMP production, but they induced a cytosolic calcium transient increase in these cells. These findings support an autocrine role of PTHrP in the regulation of this tumor growth.
2. Functional properties of the PTH/PTHrP receptor
H Jüppner Bone. 1995 Aug;17(2 Suppl):39S-42S. doi: 10.1016/8756-3282(95)00206-s.
The PTH/PTHrP receptor belongs to a novel family of G-protein-coupled receptors which also includes an insect receptor for a diuretic hormone and the protein encoded by a genomic DNA clone from Caenorhabditis elegans. Despite significant structural conservation, rat, opossum, and human PTH/PTHrP receptor homologs display distinct functional characteristics when tested with either [Arg2, Tyr34]hPTH(1-34)amide or [Nle8.18, Tyr34]bPTH(7-34)-amide. These PTH analogs, and chimeras between rat/opossum and between rat/human PTH/PTHrP receptors, led to the identification of receptor residues that appear to be involved in ligand/receptor interaction and receptor activation, respectively. The search for mutations in the PTH/PTHrP receptor gene in genomic DNA of patients with pseudohypoparathyroidism type Ib (PHP-Ib) revealed several silent polymorphisms and a missense mutation in the receptor's tail region which did not affect receptor function. Mutations in the PTH/PTHrP receptor are therefore rarely, if at all, responsible for PHP-Ib. A mutation in the PTH/PTHrP receptor is, however, the most likely cause of Jansen-type metaphyseal chondrodysplasia, a rare form of short-limbed dwarfism which is associated with severe hypercalcemia despite normal or low levels of circulating PTH and PTHrP. A missense mutation was identified which causes constitutive, ligand-independent receptor activation, and thus explains the laboratory and the growth-plate abnormalities in affected individuals.
3. Evidence for adenylyl cyclase-dependent receptors for parathyroid hormone (PTH)-related protein in rabbit kidney glomeruli
T Massfelder, C Saussine, U Simeoni, B Enanga, C Judes, J J Helwig Life Sci. 1993;53(11):875-81. doi: 10.1016/0024-3205(93)90439-a.
Studies were conducted to test whether parathyroid hormone-related protein (PTHrP) is able to stimulate adenylate cyclase activity in isolated rabbit glomeruli. Maximal stimulations were reached at 10(-7) M of human PTHrP-(1-34) or rat PTH-(1-34) and showed a 3-3.3 fold increase over basal activity. The potency (EC50) values were close to 10(-9) M. The guanyl nucleotide GTP, at 10(-5) M, potentiated the effect of PTH and PTHrP but reduced their potency. The combined effect of maximal concentrations of PTHrP and PTH was not additive, and the PTH antagonist [Nle8.18, Tyr34]-bPTH-(3-34)amide inhibited both PTHrP- and PTH-stimulated adenylate cyclase activities. These findings suggest that PTHrP could affect glomerular function through changes in glomerular cAMP content by interaction with PTH receptors.
