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Regulation of the phosphoinositide cascade by polyamines in brain
S Periyasamy1, M R Kothapalli, W Hoss
1Department of Medicinal and Biological Chemistry, College of Pharmacy, University of Toledo, Ohio 43606.
Journal of Neurochemistry
|October 1, 1994
Summary
Polyamines like spermidine enhance phosphoinositide turnover by affecting multiple steps in the signaling cascade. This occurs through interactions with GTP-gamma-S and calcium, independent of NMDA receptor sites.
Area of Science:
- Biochemistry
- Cell Signaling
- Molecular Pharmacology
Background:
- Polyamines are crucial for cellular processes.
- Phosphoinositide turnover is a key signaling pathway.
- The precise mechanisms of polyamine action on this pathway require further elucidation.
Purpose of the Study:
- To investigate the effects of endogenous and synthetic polyamines on phosphoinositide turnover.
- To elucidate the mechanism by which spermidine modulates this signaling pathway.
- To determine if spermidine's effects are mediated through NMDA receptor polyamine sites.
Main Methods:
- Assessing GTP-gamma-S-stimulated phosphoinositide turnover in the presence of various polyamines.
- Performing kinetic analysis of GTP-gamma-S-stimulated phosphoinositide turnover with spermidine.
- Evaluating spermidine's impact on Ca(2+)-stimulated phosphoinositide turnover.
- Testing the effect of polyamine antagonists (arcaine, agmatine) on spermidine's actions.
- Measuring the levels of different phosphatidylinositol phosphates ([3H]phosphatidylinositol, [3H]phosphatidylinositol 4-phosphate, [3H]phosphatidylinositol 4,5-bis-phosphate).
Main Results:
- Endogenous spermidine and spermine enhanced GTP-gamma-S-stimulated phosphoinositide turnover, while synthetic analogs inhibited it.
- Spermidine increased the Vmax of GTP-gamma-S-stimulated turnover, indicating interaction at a different site than GTP-gamma-S.
- Spermidine enhanced Ca(2+)-stimulated turnover by reducing the calcium requirement for phospholipase C.
- Spermidine's effects were not blocked by NMDA receptor polyamine antagonists.
- Spermidine selectively increased phosphatidylinositol 4-phosphate levels.
Conclusions:
- Spermidine enhances phosphoinositide turnover through interactions with both GTP-gamma-S and Ca(2+) signaling pathways.
- The mechanism involves modulation at multiple levels of the phosphoinositide cascade, not solely through NMDA receptor sites.
- Spermidine's specific effect on phosphatidylinositol 4-phosphate suggests a targeted regulatory role.