Pasteurella multocida toxin stimulates mitogen-activated protein kinase via G(q)/(11)-dependent transactivation of the epidermal growth factor receptor

The dermatonecrotic toxin produced by Pasteurella multocida is one of the m ost potent mitogenic substances known for fibroblasts in vitro. Exposure to recombinant P. multocida toxin (rPMT) causes phospholipase C-mediated hydr olysis of inositol phospholipids, calcium mobilization, and activation of p rotein kinase C via a poorly characterized mechanism involving G(q/11) fami ly heterotrimeric G proteins. To determine whether the regulation of G prot ein pathways contributes to the mitogenic effects of rPMT, we have examined the mechanism whereby rPMT stimulates the Erk mitogen-activated protein ki nase cascade in cultured HEK-293 cells. Treatment with rPMT resulted in a d ose and time-dependent increase in Erk 1/2 phosphorylation that paralleled its stimulation of inositol phospholipid hydrolysis. Both rPMT- and alpha-t hrombin receptor- stimulated Erk phosphorylation were selectively blocked b y cellular expression of two peptide inhibitors of G(q/11) signaling, the d ominant negative mutant G protein-coupled receptor kinase, GRK2(K220R), and the G alpha(q) carboxyl-terminal peptide, G alpha(q)-(305359). Like alpha- thrombin receptor-mediated Erk activation, the effect of rPMT was insensiti ve to the protein kinase C inhibitor GF109203X, but was blocked by the epid ermal growth factor receptor-specific tyrphostin, AG1478 and by dominant ne gative mutants of mSos1 and Ha-Ras, These data indicate that rPMT employs G (q/11) family heterotrimeric G proteins to induce Ras-dependent Erk activat ion via protein kinase C-independent "transactivation" of the epidermal gro wth factor receptor.