CELL-SPECIFIC SIGNAL-TRANSDUCTION OF PARATHYROID-HORMONE (PTH)-RELATED PROTEIN THROUGH STABLY EXPRESSED RECOMBINANT PTH PTHRP RECEPTORS IN VASCULAR SMOOTH-MUSCLE CELLS/

PTH-related protein activates a G protein-coupled PTH/pTHrP receptor i n many cell types and produces diverse biological actions. To study th e signal transduction events associated with biological activity of th e PTH/PTHrP receptor in vascular smooth muscle, a principal PTHrP-resp onsive tissue, rat aortic smooth muscle cells (A10) were stably transf ected with a plasmid encoding a PTH/PTHrP receptor and tested for liga nd binding, PTHrP-(1-34)-induced cAMP levels, inositol phosphate produ ction, and cytosolic calcium transients. Of nineteen G418-resistant 18 -resistant lines recovered, all exhibited high affinity binding [simil ar to dissociation constant (K-d) > 10(-10)) of iodinated [Tyr(36)]hPT HrP(1-36)NR(2) 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 o f receptor number despite the presence of detectable G alpha(q). Trans ient overexpression of individual G alpha(q) proteins (G alpha(q), G a lpha(11) or G alpha(14)) into PTH/PTHrP receptor-expressing A10 cells conferred the ability of PTHrP to increase intracellular calcium and i nositol phosphate formation. Ligand activation of the recombinant PTH/ PTHrP receptor elicited appropriate downstream biological effects in A 10 cells including inhibition of DNA synthesis and osteopontin messeng er RNA (mRNA) expression. Thus, a single PTH/PTHrP receptor, though ca pable of coupling to different G proteins, signals exclusively through a cAMP-dependent pathway in vascular smooth muscle.