ALUMINUM IMPACTS ELEMENTS OF THE PHOSPHOINOSITIDE SIGNALING PATHWAY IN NEUROBLASTOMA-CELLS

Inositol phosphate formation was examined in aluminium-treated murine neuroblastoma cells labelled with [H-3]-myoinositol. Employing fluorid e-stimulated intact cells, aluminium (0.2 muM to 1 mM) reduced inosito l phosphate formation in a dose-dependent manner. In digitonin-permeab ilized cells, stimulated with nonhydrolyzable GTP[S], inositol phospha te formation was also inhibited by increasing aluminium doses; the IC5 0 value was about 20muM aluminium, while the inositol phosphate level was reduced 2.5 to 3 fold by 50muM aluminium. The inhibitory effect of aluminium (50muM) could not be reversed by increasing GTP[S] concentr ations up to 500muM. Prechelation of aluminium to citrate or EGTA comp letely abolished the aluminium-triggered inhibition of fluoride-stimul ated inositol phosphate formation in intact cells, but had little effe ct on the inhibition of permeabilized cells stimulated with GTP[S]. In neuroblastoma cells phosphoinositide hydrolysis could be evoked eithe r through a pathway involving the Mg2+/guanine nucleotide binding (G(p )) protein, or via a pathway operative in the presence of high intrace llular Ca2+ concentrations. In the Mg2+/G(p) protein-mediated pathway, formation of inositol triphosphate, IP3, inositol diphosphate, IP2, a nd inositol monophosphate, IP, was apparently inhibited by aluminium i n an interdependent manner. As to the Ca2+-mediated pathway, aluminium application mainly diminished the release of IP3. Following interiori zation, aluminium thus acts upon elements critical for phosphoinositid e-associated signal transduction. An aluminium target apparently resid es on the G(p) protein. Phosphatidylinositol-4,5-diphosphate-specific phospholipase C probably harbours a second aluminium target.