Prostaglandin-Induced changes in calcium uptake and cAMP production in osteoblast-like cells: Role of protein kinase C

Phorbol esters were used to evaluate the putative effect of protein kinase C (PKC) activation on prostaglandin E₂ (PGE₂)-induced increases in calcium uptake and cAMP production in the human osteoblastic osteosarcoma cell line, Saos-2. The cells were pretreated for 15 min with phorbol myristate acetate (PMA) followed by a 5 min incubation with PGE₂. Calcium uptake was measured with⁴⁵Ca and cAMP by radioimmunoassay. A significant increase in calcium uptake was noted in the PGE-treated cells compared with controls and preincubation with the PMA caused a significant decrease in this response. Preincubation with PMA also inhibited the PGE₂-induced increase in cAMP under identical conditions. The effect of PMA on the cAMP response was not influenced by the addition of a phosphodiesterase inhibitor. PMA had no effect on the basal levels of either calcium uptake or cAMP production. Likewise, the inactive phorbol esters, phorbol 12,13-didecanoate (PDD) and 4 α-phorbol 12-myristate, 13-acetate (4alpha), had no effect on either basal levels of these parameters or on the PGE₂-induced increases. These results suggest that PKC is involved in the down-regulation of PGE₂-induced increases in calcium uptake and cAMP production in the Saos-2 osteoblastic cell line.