Protein Kinase C Does Not Mediate the Inhibitory Action of Lead on Vitamin D sub(3)-Dependent Production of Osteocalcin in Osteoblastic Bone Cells

The level of osteocalcin in serum is lower in lead-intoxicated children than in their normal counterparts. To explain this clinical observation, we investigated the mechanism of action of lead on vitamin D sub(3)-dependent osteocalcin production. Lead (5-20 mu M) blocked the stimulating effects of vitamin D sub(3) on osteocalcin production in cultured rat osteosarcoma cells (ROS 17 /2.8). It is often suggested that activation of protein kinase C (PKC) is a critical mediator of the toxic actions of lead. Treatment of ROS cells with Goe6976, an inhibitor of PKC alpha and beta isozymes, produced similar effects as lead on vitamin D sub(3)-dependent osteocalcin production, while activation of PKC by phorbol-12-myristate-13-acetate (TPA) did not reverse or mimic this effect of lead. Thus activation of PKC is not consistent with the actions of lead on vitamin D sub(3)-dependent osteocalcin production. Measurement of PKC enzyme activity showed that 10 mu M lead treatment does not activate or inhibit the activity of PKC in ROS cells. Western blot analysis indicated that lead treatment does not translocate PKC alpha , beta , or zeta from cytosol to membrane. Therefore, we concluded that PKC does not mediate the cellular toxicity of lead on vitamin D sub(3)-dependent osteocalcin production. [copy ]2002 Elsevier Science (USA).