Mastoparan, a
wasp venom toxin, has various pharmacological activities, the mechanisms of which are still unknown. To clarify the action of
mastoparan on
G protein-coupled receptor-mediated signaling, we previously examined the effect of
mastoparan on G(q)-mediated signaling and demonstrated that
mastoparan binds to
gangliosides causing a decrease in Galpha(q/11) content in
lipid rafts, and resulting in the inhibition of G(q)-mediated
phosphoinositide hydrolysis (Sugama et al., Mol. Pharmacol., 68, 1466, 2005). In the present study, we examined the effect of
mastoparan on beta-
adrenoceptor-G(s) signaling in 1321N1 human
astrocytoma cells.
Mastoparan inhibited
isoproterenol-induced elevation of
cyclic AMP in a concentration-dependent manner. Although
mastoparan is known to be an activator of G(i),
pertussis toxin only slightly attenuated
mastoparan-induced inhibition of
cyclic AMP elevation, suggesting that a major part of the inhibition of
cyclic AMP elevation induced by
mastoparan is not mediated by Galpha(i). By contrast,
mastoparan-induced inhibition of
cyclic AMP elevation was clearly attenuated by preincubation of the cells with
ganglioside mixtures. Moreover,
mastoparan changed the localization of Galpha(s) in
lipid rafts without disrupting the structure of
lipid rafts. Fluorescent staining analysis showed that
mastoparan released GFP-Galpha(s) from plasma membranes into the cytosol. These results suggest that the
mastoparan-induced suppression of
cyclic AMP elevation is mainly caused by changing the localization of Galpha(s) in
lipid rafts into a compartment in the cellular interior where it is not available to activate
adenylyl cyclase.