Parathyroid hormone-induced calcium efflux from cultured bone is mediated by protein kinase C translocation.
Activation of adenylate cyclase is believed to be the major intracellular mediator of bone resorption induced by parathyroid hormone (PTH), prostaglandins, and various bone resorbing cytokines. Studies have demonstrated a dissociation between PTH-induced bone resorption and adenosine 3',5'-cyclic monophosphate (cAMP) formation, as well as suggested a role of protein kinase C (PKC) in mediating in part the actions of PTH. We therefore investigated the relative contribution of the adenylate cyclase or PKC signal transduction pathways in mediating the PTH-induced net calcium release from cultured neonatal calvariae, an in vitro model of bone resorption. PTH (10(-11) to 10(-7) M) caused a dose-dependent increase in calcium efflux from cultured bone and activated both cAMP and PKC. To determine the role of each of these second messengers in mediating PTH-induced calcium release from bone, calvariae were preincubated with either the adenylate cyclase inhibitor SQ-22536 (10(-5) to 10(-4) M) or the PKC inhibitor staurosporine (10(-7) M) before coincubation with PTH. Compared with control, PTH caused a significant calcium efflux, whereas preincubation with SQ-22536 had no effect on basal calcium efflux and partially inhibited the calcium efflux caused by PTH. In contrast preincubation with staurosporine completely obliterated the PTH-induced calcium efflux. PTH is a potent stimulator of calcium release and activates both the cAMP and PKC signal transduction pathways in cultured bone. Inhibition of PTH-stimulated PKC activity completely abolished the PTH-induced calcium efflux from calvariae, whereas PTH-induced calcium efflux persisted despite adenylate cyclase inhibition. Thus the bone resorbing effect of PTH appears to be dependent predominantly on activation of PKC.
Sprague
S M
SM
Section of Nephrology and Hypertension, Hadassah University Hospital, Hebrew University, Jerusalem, Israel.
Popovtzer
M M
MM
Dranitzki-Elhalel
M
M
Wald
H
H
D000818:Animals; D001692:Biological Transport; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000096:biosynthesis; D004789:Enzyme Activation; D009924:Organ Culture Techniques; D010281:Parathyroid Hormone / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014178:Translocation, Genetic
D010281:Parathyroid Hormone; D000242:Cyclic AMP; D011493:Protein Kinase C; D002118:Calcium