Action of Pasteurella multocida toxin on Gαq is persistent and independent of interaction with G-protein-coupled receptors

Pasteurella multocida toxin (PMT) activates G alpha(q) and facilitates stimulation of inositol phosphate accumulation induced by agonists via G(q)-coupled membrane receptors. Here, we studied the effects of PMT on agonist-induced GTP gamma S binding to G(q) in cell membranes and a role of G-protein-coupled receptors in the action of PMT. Pre-treatment of Swiss 3T3 cells with PMT increased bombesin or vasopressin-induced GTP gamma S-binding in cell membranes by about 50 to 150%. Increase in agonist-stimulated GTP gamma S-binding caused by PMT pretreatment was specific for G alpha(q), and not observed with G alpha(11). PMT-induced effects on GTP gamma S-binding were persistent after removing the toxin or in the presence of anti-PMT antibody. Stimulation of agonist-induced GTP gamma S-binding by PMT was independent of phosphorylation of the C-terminal tyrosine356 of Got,. Activation of phospholipase C by PMT occurred via G alpha(q) which was fused to the alpha(1b)-adrenoceptor and also with a C-terminally deleted G alpha(q), which is not able to interact with G protein-coupled membrane receptors. The data indicate that activation of G alpha(q) by PMT is persistent and independent of a functional interaction of G(q) with G-protein-coupled receptors. (c) 2007 Elsevier Inc. All rights reserved.