Pasteurella multocida Toxin Stimulates Mitogen-activated Protein Kinase via G_q/11-dependent Transactivation of the Epidermal Growth Factor Receptor*

Abstract

The dermatonecrotic toxin produced byPasteurella multocida is one of the most potent mitogenic substances known for fibroblasts in vitro. Exposure to recombinant P. multocida toxin (rPMT) causes phospholipase C-mediated hydrolysis of inositol phospholipids, calcium mobilization, and activation of protein kinase C via a poorly characterized mechanism involving G_q/11 family heterotrimeric G proteins. To determine whether the regulation of G protein pathways contributes to the mitogenic effects of rPMT, we have examined the mechanism whereby rPMT stimulates the Erk mitogen-activated protein kinase cascade in cultured HEK-293 cells. Treatment with rPMT resulted in a dose and time-dependent increase in Erk 1/2 phosphorylation that paralleled its stimulation of inositol phospholipid hydrolysis. Both rPMT- and α-thrombin receptor- stimulated Erk phosphorylation were selectively blocked by cellular expression of two peptide inhibitors of G_q/11 signaling, the dominant negative mutant G protein-coupled receptor kinase, GRK2(K220R), and the Gα_qcarboxyl-terminal peptide, Gα_q-(305–359). Like α-thrombin receptor-mediated Erk activation, the effect of rPMT was insensitive to the protein kinase C inhibitor GF109203X, but was blocked by the epidermal growth factor receptor-specific tyrphostin, AG1478 and by dominant negative mutants of mSos1 and Ha-Ras. These data indicate that rPMT employs G_q/11 family heterotrimeric G proteins to induce Ras-dependent Erk activation via protein kinase C-independent “transactivation” of the epidermal growth factor receptor.