DIRECT INVOLVEMENT OF CAMP-DEPENDENT PROTEIN-KINASE IN THE REGULATIONOF ALKALINE-PHOSPHATASE ACTIVITY BY PARATHYROID-HORMONE (PTH) AND PTH-RELATED PEPTIDE IN OSTEOBLASTIC UMR-106 CELLS

The present study was performed to characterize the participation of p arathyroid hormone (PTH)- and PTH-related peptide (PTHrP)-responsive d ual signal transduction systems [cAMP-dependent protein kinase (PKA) a nd Calcium/protein kinase C (Ca/PKC)] in the regulation of alkaline ph osphatase (ALP) activity in osteoblastic osteosarcoma cells (UMR-106). Both human (h) PTH-(1-34) and hPTHrP-(1-34) at 10(-8)M stimulated ALP activity to the similar degree. Dibutyryl cAMP (dbcAMP) (10(-5), 10(- 4)M) and Sp-diastereoisomer of adenosine cyclic 3', 5'-phosphorothioat e (Sp-cAMPS), a direct stimulator of PKA (10(-4)M) also stimulated its activity. Phorbor 12-myristate 13-acetate (PMA), an activator of PKC, (10(-7), 10(-6)M) did not affect its activity, while calcium ionophor es, A23187 and ionomycin (10(-7), 10(-6)M) inhibited it. Although Rp-d iastereoisomer of adenosine cyclic 3', 5'-phosphorothioate (Rp-cAMPS), a direct inhibitor of PKA, (10(-4)M) did not affect ALP activity by i tself, it significantly antagonized not only Sp-cAMPS-induced increase in ALP activity, but also PTH- and PTHrP-induced one. The present stu dy first indicated that the activation of PKA was directly involved an d acted as a main pathway in the regulation of ALP activity by PTH and PTHrP in osteoblasts. (C) 1994 Academic Press, Inc.