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A pleiotropic effect of fluoride on signal transduction in macrophages: is it mediated by GPT-binding proteins?
1Department of Membrane Research & Biophysics, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
The activation of GTP-binding proteins (G-proteins) by sodium fluoride + aluminum (AlF4-) was shown in several cell free systems. In the intact cell, NaF +/- aluminum was shown to activate various signal transduction pathways and indirect evidence is in line with effector mechanisms involving regulation of G-protein activity. We have explored the effect of NaF on several components of signal transduction pathways in macrophages. NaF was shown to reduce intracellular ATP levels and to suppress agonist-induced protein tyrosine phosphorylation and reactive oxygen species formation. NaF led to in situ activation of nitrogen activated protein kinase, phospholipase A2 and PtdIns-phospholipase C. Addition of AlCl(3) or deferoxamine, a chelator of aluminum, had little or no effect on NaF mediated enzyme activation. The results suggest that at least some of the pleiotropic effects of NaF in intact cells may not be mediated by G-protein activation but rather by depletion of ATP which is essential for protein phosphorylation reactions.
Insights
Sodium fluoride (NaF) affects cell signaling in macrophages. While previously thought to activate G-proteins, this study suggests NaF primarily depletes ATP, impacting protein phosphorylation, not G-protein pathways.
Area of Science:
- Cellular signaling
- Biochemistry
- Immunology
Background:
- Sodium fluoride (NaF) with aluminum (AlF4-) activates GTP-binding proteins (G-proteins) in cell-free systems.
- In intact cells, NaF influences signal transduction pathways, with indirect evidence suggesting G-protein regulation.
Purpose of the Study:
- To investigate the effects of NaF on signal transduction pathways in macrophages.
- To determine if NaF-induced effects in intact cells are mediated by G-protein activation or other mechanisms.
Main Methods:
- Macrophages were treated with NaF to assess its impact on intracellular ATP levels.
- Agonist-induced protein tyrosine phosphorylation and reactive oxygen species (ROS) formation were measured.
- Activation of specific enzymes, including nitrogen-activated protein kinase, phospholipase A2, and PtdIns-phospholipase C, was evaluated.
- The influence of aluminum chloride (AlCl3) and deferoxamine on NaF effects was examined.
Main Results:
- NaF reduced intracellular ATP levels in macrophages.
- NaF suppressed agonist-induced protein tyrosine phosphorylation and ROS formation.
- In situ activation of nitrogen-activated protein kinase, phospholipase A2, and PtdIns-phospholipase C was observed with NaF.
- Aluminum chloride and deferoxamine showed minimal impact on NaF-mediated enzyme activation.
Conclusions:
- NaF's effects in intact cells may be primarily due to ATP depletion rather than G-protein activation.
- ATP depletion by NaF can inhibit essential protein phosphorylation reactions, explaining some observed cellular responses.