ucn-1028-c and Osteosarcoma

The mechanism of the toxic effects of Cd2+ on bone cell function is not completely understood at this time. This study was designed to characterize the effect of Cd2+ on Ca2+ metabolism in ROS 17/2.8 cells. Cells were labeled with (45)Ca (1.87 mM Ca) for 20 h in the presence of 0.01, 0.1, or 1.0 microM Cd2+ and kinetic parameters were determined from (45)Ca efflux curves. Three kinetic compartments described the intracellular metabolism of (45)Ca. Cd2+ (0.01 microM) caused an approximate 9 x increase in Ca2+ flux across the plasma membrane and a decrease in the most rapidly exchanging intracellular Ca2+ compartment (S1). However, there was no change in total cell Ca2+, indicating an increased cycling of Ca2+ across the plasma membrane. Flux between S1 and the intermediate Ca2+ compartment (S2) was also increased and S2 increased significantly. All Cd2+ induced changes in Ca2+ homeostasis were obliterated by concurrent treatment with 0.1 microM calphostin C (CC), a potent protein kinase C (PKC) inhibitor. This data suggests that Cd2+ perturbs Ca2+ metabolism via a PKC dependent process.

Topics: Animals; Cadmium; Calcium; Enzyme Inhibitors; Homeostasis; Intracellular Fluid; Kinetics; Naphthalenes; Osteosarcoma; Protein Kinase C; Rats; Tumor Cells, Cultured

In this study, the effect of 24,25(OH)2 vitamin D3 (24,25D3), on the L-type Ca2+ channel current (L-channel current) in UMR 106 cells was investigated using the whole cell version of the patch clamp technique. It was found that 24,25D3 had a dual effect on the L-channel current: a low concentration of 24,25D3 (1 x 10(-8) M) increased the amplitude of the L-channel current by 49 +/- 11%, whereas a high concentration of 24,25D3 (1 x 10(-5) M) reduced the amplitude of the current by 55 +/- 7%. The effect of a low concentration of 24,25D3 was mimicked by 8-bromo-cAMP and inhibited by Rp-cAMPs, indicating the involvement of the cAMP/protein kinase A pathway. In contrast, the effect of a high concentration of 24,25D3 was mimicked by 4 beta-phorbol 12-myristate 13-acetate and inhibited by calphostin C, indicating the involvement of protein kinase C. In comparison, a high concentration of 1,25(OH)2 vitamin D3 (1,25D3) (1 x 10(-6) M) increased the L-channel current in UMR 106 cells. Therefore, 24,25D3 appears to have an action on the L-channel current that is distinct from that of 1,25D3. This demonstration of a non-genomic effect of 24,25D3 on calcium channels suggests that 24,25D3 is an active metabolite of vitamin D3 and may play an important role in regulating the function of bone cells.

Topics: 24,25-Dihydroxyvitamin D 3; 8-Bromo Cyclic Adenosine Monophosphate; Animals; Calcium Channels; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Electric Conductivity; Enzyme Inhibitors; Naphthalenes; Osteoblasts; Osteosarcoma; Patch-Clamp Techniques; Protein Kinase C; Rats; Signal Transduction; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured

The effect of the tumor promoter 4 beta-phorbol 12-myristate 13-acetate and of the phosphatases inhibitor okadaic acid on the binding of tumor necrosis factor-alpha (TNF-alpha) to a human osteogenic sarcoma cell line (Saos-2) was investigated. Both substances prevented almost completely TNF binding to its receptors. The effect of 4 beta-phorbol 12-myristate 13-acetate was reversed by the protein kinase C inhibitors staurosporine and calphostin C or by protein kinase C depletion. Vinblastine, under conditions causing full microtubule disassembly, produced only a 50% decrease of TNF binding. Vinblastine plus PMA was additive in fully preventing TNF binding. It is suggested that the degree of binding of TNF-alpha to its receptors in Saos-2 cells is under the control of a microtubule-dependent and of a microtubule-independent regulatory pathway.

Topics: Alkaloids; Cell Membrane; Cycloheximide; Ethers, Cyclic; Humans; Kinetics; Microtubules; Naphthalenes; Okadaic Acid; Osteosarcoma; Phosphoprotein Phosphatases; Polycyclic Compounds; Protein Kinase C; Receptors, Cell Surface; Receptors, Tumor Necrosis Factor; Staurosporine; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha; Vinblastine