Aluminium impacts elements of the phosphoinositide signalling pathway in neuroblastoma cells.
Inositol phosphate formation was examined in aluminium-treated murine neuroblastoma cells labelled with [3H]-myoinositol. Employing fluoride-stimulated intact cells, aluminium (0.2 microM to 1 mM) reduced inositol phosphate formation in a dose-dependent manner. In digitonin-permeabilized cells, stimulated with nonhydrolyzable GTP[S], inositol phosphate formation was also inhibited by increasing aluminium doses; the IC50 value was about 20 microM aluminium, while the inositol phosphate level was reduced 2.5 to 3 fold by 50 microM aluminium. The inhibitory effect of aluminium (50 microM) could not be reversed by increasing GTP[S] concentrations up to 500 microM. Prechelation of aluminium to citrate or EGTA completely abolished the aluminium-triggered inhibition of fluoride-stimulated inositol phosphate formation in intact cells, but had little effect on the inhibition of permeabilized cells stimulated with GTP[S]. In neuroblastoma cells phosphoinositide hydrolysis could be evoked either through a pathway involving the Mg2+/guanine nucleotide binding (Gp) protein, or via a pathway operative in the presence of high intracellular Ca2+ concentrations. In the Mg2+/Gp protein-mediated pathway, formation of inositol triphosphate, IP3, inositol diphosphate, IP2, and inositol monophosphate, IP, was apparently inhibited by aluminium in an interdependent manner. As to the Ca(2+)-mediated pathway, aluminium application mainly diminished the release of IP3. Following interiorization, aluminium thus acts upon elements critical for phosphoinositide-associated signal transduction. An aluminium target apparently resides on the Gp protein. Phosphatidylinositol-4,5-diphosphate-specific phospholipase C probably harbours a second aluminium target.
Department of Microbiology, Michigan State University, East Lansing 48824.
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Shi
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Chou
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Haug
D000535:Aluminum / Q000633:toxicity*; D000818:Animals; D019204:GTP-Binding Proteins / Q000187:drug effects*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000037:antagonists & inhibitors; D006868:Hydrolysis; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D012969:Sodium Fluoride / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000187:drug effects*
D010716:Phosphatidylinositols; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D012969:Sodium Fluoride; D000535:Aluminum; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins