Direct Involvement of cAMP-Dependent Protein Kinase in the Regulation of Alkaline Phosphatase Activity by Parathyroid Hormone (PTH) and PTH-Related Peptide in Osteoblastic UMR-106 Cells

Abstract

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