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

Pasteurella multocida toxin (PMT) activates Gαq and facilitates stimulation of inositol phosphate accumulation induced by agonists via Gq-coupled membrane receptors. Here, we studied the effects of PMT on agonist-induced GTPγS binding to Gq 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 GTPγS-binding in cell membranes by about 50 to 150%. Increase in agonist-stimulated GTPγS-binding caused by PMT pretreatment was specific for Gαq and not observed with Gα11. PMT-induced effects on GTPγS-binding were persistent after removing the toxin or in the presence of anti-PMT antibody. Stimulation of agonist-induced GTPγS-binding by PMT was independent of phosphorylation of the C-terminal tyrosine356 of Gαq. Activation of phospholipase C by PMT occurred via Gαq which was fused to the α1b-adrenoceptor and also with a C-terminally deleted Gαq, which is not able to interact with G protein-coupled membrane receptors. The data indicate that activation of Gαq by PMT is persistent and independent of a functional interaction of Gq with G-protein-coupled receptors.