Pasteurella multocida toxin, a potent intracellularly acting mitogen, induces p125FAK and paxillin tyrosine phosphorylation, actin stress fiber formation, and focal contact assembly in Swiss 3T3 cells

Abstract

Treatment of Swiss 3T3 cells with recombinant Pasteurella multocida toxin (rPMT), a potent intracellularly acting mitogen, stimulated tyrosine phosphorylation of multiple substrates including bands of Mr 110,000-130,000 and Mr 70,000-80,000. Tyrosine phosphorylation induced by rPMT occurred after a pronounced lag period (1 h) and was blocked by either lysosomotrophic agents or incubation at 22 °C. Focal adhesion kinase (p125FAK) and paxillin are prominent substrates for rPMT-stimulated tyrosine phosphorylation. Tyrosine phosphorylation by rPMT could be dissociated from both protein kinase C activation and the mobilization of calcium from intracellular stores. rPMT stimulated striking actin stress fiber formation and focal adhesion assembly in Swiss 3T3 cells. Cytochalasin D, which disrupts the actin cytoskeleton, completely inhibited rPMT-induced tyrosine phosphorylation. In addition, tyrosine phosphorylation of p125FAK and paxillin in response to rPMT was completely abolished when cells were subsequently treated with platelet-derived growth factor at a concentration (30 ng/ml) that disrupted the actin cytoskeleton. Our results demonstrate for the first time that rPMT, a bacterial toxin, induces tyrosine phosphorylation of p125FAK and paxillin and promotes actin stress fiber formation and focal adhesion assembly in Swiss 3T3 cells.