The effect of cadmium on cytosolic free calcium, protein kinase C, and collagen synthesis in rat osteosarcoma (ROS 17/2.8) cells.
Cadmium affects normal bone growth but the mechanisms of Cd2+ toxicity are not fully understood. Calcium is an integral component of bone growth and a second messenger necessary for the actions of calciotropic hormones. Ca2+ activates protein kinase C (PKC), and PKC is a mediator of [Ca2+]1 and mediator of collagen synthesis in osteoblastic cells. Therefore, PKC is a possible loci of Cd2+ effects on Ca2+ metabolism and Ca(2+)-regulated processes. This work was conducted to determine the effect of Cd2+ on cytosolic free Ca2+ ([Ca2+]i) levels, characterize the activation and/or inhibition of PKC by Cd2+ and Ca2+, and measure the effect of Cd2+ on collagen synthesis in ROS 17/2.8 cells. Cells were treated for 120 min with Cd2+ (0 to 30 microM) and [Ca2+]i was measured. Basal [Ca2+]i was 132 nM and the maximal increase to 268 nM occurred in the presence of 5 microM Cd2+. Treatment with 1 or 5 microM Cd2+ caused an increase in [Ca2+]i at 40 min with return to basal levels at 120 min of treatment. Pretreatment (24 hr) with 0.1 microM calphostin C (CC), a PKC inhibitor, produced no change in [Ca2+]i and prevented any rise in [Ca2+]i in response to Cd2+. Free Cd2+ activates PKC with an activation constant of 7.5 X 10(-11) M, while Ca2+ activates PKC with an activation constant of 3.6 X 10(-7) M. Cd2+ also caused a dose-dependent decrease in collagen synthesis, a PKC-mediated process. These data suggest that Cd2+ affects Ca2+ metabolism and Ca(2+)-mediated processes via unwarranted PKC activation as demonstrated by Cd2+ perturbation of collagen synthesis.
Long
G J
GJ
Department of Biology, Olivet Nazarene University, Kankakee, Illinois 60901, USA.
D000818:Animals; D001859:Bone Neoplasms / Q000378:metabolism*; D002104:Cadmium / Q000633:toxicity*; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D003094:Collagen / Q000096:biosynthesis / Q000187:drug effects*; D003600:Cytosol / Q000187:drug effects* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D012516:Osteosarcoma / Q000378:metabolism*; D011493:Protein Kinase C / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D014407:Tumor Cells, Cultured
D002104:Cadmium; D003094:Collagen; D011493:Protein Kinase C; D002118:Calcium