Protein kinase C does not mediate the inhibitory action of lead on vitamin D3-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 D3-dependent osteocalcin production. Lead (5-20 microM) blocked the stimulating effects of vitamin D3 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 Gö6976, an inhibitor of PKC alpha and beta isozymes, produced similar effects as lead on vitamin D3-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 D3-dependent osteocalcin production. Measurement of PKC enzyme activity showed that 10 microM 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 D3-dependent osteocalcin production.
Guity
Partow
P
Institute of Chemical Toxicology, Wayne State University, Detroit, Michigan 48201, USA.
McCabe
Michael J
MJ
Pitts
David K
DK
Santini
Ronald P
RP
Pounds
Joel G
JG
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D001846:Bone Development / Q000187:drug effects; D001859:Bone Neoplasms / Q000201:enzymology / Q000378:metabolism; D001842:Bone and Bones / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002458:Cell Fractionation; D002762:Cholecalciferol / Q000037:antagonists & inhibitors / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D007854:Lead / Q000633:toxicity*; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D015675:Osteocalcin / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D012516:Osteosarcoma / Q000201:enzymology / Q000378:metabolism; D010281:Parathyroid Hormone / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000187:drug effects; D014407:Tumor Cells, Cultured
D010281:Parathyroid Hormone; D011965:Receptors, Glucocorticoid; D015675:Osteocalcin; D002762:Cholecalciferol; D007854:Lead; D011493:Protein Kinase C; D000469:Alkaline Phosphatase