Activation of Gαiand Subsequent Uncoupling of Receptor-GαiSignaling byPasteurella multocidaToxin

Joachim H. C. Orth, Ines Fester, Inga Preuss, Laura Agnoletto, Brenda A. Wilson, Klaus Aktories
2008 Journal of Biological Chemistry  
Bacterial protein toxins are powerful tools for elucidating signaling mechanisms in eukaryotic cells. A number of bacterial protein toxins, e.g. cholera toxin, pertussis toxin (PTx), or Pasteurella multocida toxin (PMT), target heterotrimeric G proteins and have been used to stimulate or block specific signaling pathways or to demonstrate the contribution of their target proteins in cellular effects. PMT is a major virulence factor of P. multocida causing pasteurellosis in man and animals and
more » ... n and animals and is responsible for atrophic rhinitis in pigs. PMT modulates various signaling pathways, including phospholipase C␤ and RhoA, by acting on the heterotrimeric G proteins G␣ q and G␣ 12/13 , respectively. Here we report that PMT is a powerful activator of G i protein. We show that PMT decreases basal isoproterenol and forskolin-stimulated cAMP accumulation in intact Swiss 3T3 cells, inhibits adenylyl cyclase activity in cell membrane preparations, and enhances the inhibition of cAMP accumulation caused by lysophosphatidic acid via endothelial differentiation gene receptors. PMT-mediated inhibition of cAMP production is independent of toxin activation of G␣ q and/or G␣ 12/13 . Although the effects of PMT are not inhibited by PTx, PMT blocks PTx-catalyzed ADP-ribosylation of G i . PMT also inhibits steadystate GTPase activity and GTP binding of G i in Swiss 3T3 cell membranes stimulated by lysophosphatidic acid. The data indicate that PMT is a novel activator of G i , modulating its GTPase activity and converting it into a PTx-insensitive state.
doi:10.1074/jbc.m803435200 pmid:18583341 fatcat:ru2r3dxm6zatbkhb7fmrzuq5oy