Role of calcium/protein kinase C in the regulation of DNA synthesis by parathyroid hormone-related peptide in osteoblastic osteosarcoma cells.

Our recent study demonstrated the direct involvement of cAMP-dependent protein kinase (PKA) in the regulation of DNA synthesis by PTH-related peptide (PTHrP) in osteoblastic osteosarcoma cells, UMR-106. Since PTHrP has been reported to possess dual signal transduction systems [PKA and calcium/protein kinase C (Ca/PKC]), present study was performed to characterize the involvement of Ca/PKC signal transduction system in the regulation of DNA synthesis by PTHrP in these cells. Human PTHrP-(1-34) (10(-7) M) caused a rapid increase in intracellular Ca ([Ca2+]i), followed by return to the basal level within 1 min. Pretreatment with 10(-4) M TMB-8 or 10(-5) M dantrolene, inhibitors of calcium release from intracellular calcium store, significantly blocked the PTHrP-induced increase in [Ca2+]i, but did not affect the PTHrP-induced inhibition of DNA synthesis. Pretreatment with 50 uM H-7 or 1 nM staurosporine, inhibitors of PKC, significantly blocked the PTHrP (10(-9) to 10(-7) M)-induced inhibition of DNA synthesis. Pretreatment with 10(-6) M phorbol 12-myristate 13-acetate, which downregulated PKC, significantly blocked the inhibition of DNA synthesis by PTHrP. Present study indicates that in addition to PKA activation, PKC activation is coupled to the regulation of DNA synthesis by PTHrP in osteoblasts.