RT Journal Article SR Electronic T1 Mastoparan Changes the Cellular Localization of Gαq/11 and Gβ through Its Binding to Ganglioside in Lipid Rafts JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 1466 OP 1474 DO 10.1124/mol.105.013524 VO 68 IS 5 A1 Sugama, Jun A1 Ohkubo, Satoko A1 Atsumi, Masanori A1 Nakahata, Norimichi YR 2005 UL http://molpharm.aspetjournals.org/content/68/5/1466.abstract AB Although it is known that mastoparan, a wasp venom toxin, directly activates Gi/o, mastoparan-induced biological responses are not always explained by this mechanism. For instance, we have demonstrated previously that mastoparan suppressed phosphoinositide hydrolysis induced by carbachol in human astrocytoma cells (FEBS Lett 206:91–94, 1990). In the present study, we examined whether mastoparan affected phosphoinositide hydrolysis by interacting with lipid rafts in PC-12 cells. Mastoparan inhibited UTP-induced increase in [Ca2+]i and phosphoinositide hydrolysis in a concentration-dependent manner. UTP-induced phosphoinositide hydrolysis occurred in lipid rafts, because methyl-β-cyclodextrin, a disrupting regent of lipid rafts, inhibited the hydrolysis. Mastoparan changed the localization of Gαq/11 and Gβ together with cholesterol from lipid rafts to nonraft fractions or cytosol. These changes were inhibited by ganglioside mixtures, suggesting that mastoparan interacts with gangliosides in lipid rafts. In fact, ganglioside mixtures and neuraminidase, but not sialic acid, attenuated the inhibitory effect of mastoparan on phosphoinositide hydrolysis. Furthermore, fluorescence intensity of tyrosine residue of [Tyr3]mastoparan was potentiated by ganglioside mixtures, suggesting the direct binding of mastoparan to gangliosides. Mastoparan caused cytotoxicity of PC-12 cells in a concentration-dependent manner, determined by LDH release. The mastoparan-induced cytotoxicity was significantly inhibited by neuraminidase or gangliosides. The order of inhibitory potency of gangliosides was GT1b ≈ GD1b > GD1a > GM1 >> GQ1b, but asialo-GM1 and sialic acid were inactive. These results suggest that mastoparan initially binds to gangliosides in lipid rafts and then it inhibits phosphoinositide hydrolysis by changing the localization of Gαq/11 and Gβ in lipid rafts.