Cell-specific signal transduction of parathyroid hormone (PTH)-related protein through stably expressed recombinant PTH/PTHrP receptors in vascular smooth muscle cells

• Published in: Endocrinology (Philadelphia) 1996-08, Vol.137 (8), p.3154-3162
• Main Authors: Maeda, S, Wu, S, Jüppner, H, Green, J, Aragay, A M, Fagin, J A, Clemens, T L
• Format: Article
• Language: English
• Subjects: Aorta; Binding; Biological activity; Biological effects; Calcium; Calcium (intracellular); Calcium phosphates; Cell activation; Cyclic AMP; DNA biosynthesis; G protein-coupled receptors; Gene expression; Inositol phosphate; Inositol phosphates; Inositols; Intracellular; Ligands; Muscles; Osteopontin; Parathyroid hormone; Parathyroid hormone-related protein; Parathyroid hormone-related protein receptors; Proteins; Receptors; Signal transduction; Smooth muscle; Transcription
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/endo.137.8.8754733

PTH-related protein activates a G protein-coupled PTH/PTHrP receptor in many cell types and produces diverse biological actions. To study the signal transduction events associated with biological activity of the PTH/PTHrP receptor in vascular smooth muscle, a principal PTHrP-responsive tissue, rat aortic smooth muscle cells (A10) were stably transfected with a plasmid encoding a PTH/PTHrP receptor and tested for ligand binding, PTHrP-(1-34)-induced cAMP levels, inositol phosphate production, and cytosolic calcium transients. Of nineteen G418-resistant lines recovered, all exhibited high affinity binding [approximately dissociation constant (Kd) > 10(-10)) of iodinated [Tyr36]hPTHrP(1-36)NH2 and ligand-induced cAMP accumulation (2- to 100-fold), which was directly proportional to PTH/PTHrP receptor number (range 4 x 10(3) to 7 x 10(7) sites/cell]. PTHrP had no effect on intracellular calcium or inositol phosphate formation in any cell line regardless of receptor number despite the presence of detectable G alpha q). Transient overexpression of individual G alpha q proteins (G alpha q, G alpha 11 or G alpha 14) into PTH/PTHrP receptor-expressing A10 cells conferred the ability of PTHrP to increase intracellular calcium and inositol phosphate formation. Ligand activation of the recombinant PTH/PTHrP receptor elicited appropriate downstream biological effects in A10 cells including inhibition of DNA synthesis and osteopontin messenger RNA (mRNA) expression. Thus, a single PTH/PTHrP receptor, though capable of coupling to different G proteins, signals exclusively through a cAMP-dependent pathway in vascular smooth muscle.