Crotoxin induces actin reorganization and inhibits tyrosine phosphorylation and activity of small GTPases in rat macrophages

Crotoxin is the main neurotoxic component of Crotalus durissus terrificus snake venom. Previous work of our group demonstrated that this toxin or its phospholipase A2 subunit inhibits macrophage spreading and phagocytosis. The phagocytic activity of macrophages is controlled by the rearrangement of actin cytoskeleton and activity of the small Rho GTPases. The effect of crotoxin and its subunit on actin reorganization and tyrosine phosphorylation in rat peritoneal macrophages, during phagocytosis of opsonized zymosan, was presently investigated. The crude venom was used as positive control. In addition, the effect of crotoxin on the activity of Rho and Rac1 small GTPases was examined. Transmission electron studies showed that the venom or crotoxin decreased the extent of spread cells and increased microprojections often extended from macrophage surface. Immunocytochemical assays demosntrated that the venom or toxins increased F-actin content in the cytoplasm of these cells, but induced a marked decrease of phosphotyrosine. These effects were abolished by treatment with zileuton, a 5-lipoxygenase inhibitor. Furthermore, crotoxin decreased membrane-associated RhoA and Rac1 in translocation assays. The present results indicate that the crotalid venom and crotoxin are able to induce cytoskeleton rearrangement in macrophages. This effect is associated with inhibition of tyrosine phosphorylation and of the activity of proteins involved in intracellular signalling pathways important for the complete phagocytic activity of these cells.