Agonist-induced translocation of Gq/11α immunoreactivity directly from plasma membrane in MDCK cells

Both G(s)alpha and G(q)alpha are palmitoylated and both can move from a crude membrane fraction to a soluble fraction in response to stimulation with agonists. This response may be mediated through depalmitoylation. Previous studies have not demonstrated that endogenous guanine nucleotide-binding regulatory protein (G protein) alpha-subunits are released directly from the plasma membrane. We have examined the effect of agonist stimulation on the location of G(q/11)alpha immunoreactivity in Madin-Darby canine kidney (MDCK) cells. Bradykinin (BK; 0.1 mu M) caused G(q/11)alpha, but not G(i)alpha, to rapidly translocate from purified plasma membranes to the supernatant. AlF and GTP also caused translocation of G(q/11)alpha immunoreactivity from purified plasma membranes. BK caused translocation of G(q/11)alpha immunoreactivity in intact cells from the basal and lateral plasma membranes to an intracellular compartment as assessed by confocal microscopy. Thus G(q/11)alpha is released directly from the plasma membrane to an intracellular location in response to activation by an agonist and direct activation of G proteins. G protein translocation may be a mechanism for desensitization or for signaling specificity.