STIMULATION OF CAMP PRODUCTION IN CULTURED OSTEOBLASTS BY A CARBOXY-TERMINAL FRAGMENT OF PARATHYROID HORMONE-RELATED PEPTIDE (PTHRP107-139)

Synthetic N- and C-terminal fragments of parathyroid hormone-related p eptide (PTHrP) were compared for their ability to enhance cAMP product ion in cultured osteoblasts, Both PTHrP(107-139) and PTHrP(1-34) produ ced comparable large (5-80-fold) increases in cAMP in cultured rat (RO S 17/2.8) and human (SaOs-2) osteosarcoma cell lines. Both peptides al so increased cAMP in freshly isolated osteoblast-enriched cell fractio ns from neonatal rat calvaria. Dose-response studies in ROS 17/2.8 cel ls showed that the ED(50) for PTHrP(107-139), greater than or equal to 100-200 nM, was higher than that for PTHrP 1-34 (6-12 nM). No cAMP st imulation was observed in ROS 17/2.8 cells exposed to 1-10 mu M [Asn(1 0), Leu(11), d-Trp(12)]PTHrP(7-34), PTHrP(107-138), PTHrP(107-111), or PTHrP(109-141). However, the PTHrP(7-34) analog inhibited the increas e in cAMP in ROS 17/2.8 cells caused by both PTHrP(1-34) and PTHrP(107 -139). Related studies in rat renal plasma membranes and cultured colo n or breast myoepithelial cells revealed that PTHrP(1-34) stimulated a denylate cyclase activity or cAMP production, but PTHrP(107-139) did n ot. The findings show that a C-terminal portion of the PTHrP molecule, PTHrP(107-139), can stimulate cAMP production in osteoblasts, presuma bly by activating a unique receptor.