EFFECT OF CYTOTOXIC NECROTIZING FACTOR-I ON ACTIN CYTOSKELETON IN HUMAN MONOCYTES - ROLE IN THE REGULATION OF INTEGRIN-DEPENDENT PHAGOCYTOSIS

Cytotoxic necrotizing factor-1 (CNF1) is isolated from pathogenic stra ins of Escherichia coli and catalyzes the activation of Rho GTPases by the deamidation of a glutamine residue, This toxin induces stress fib er formation, cell spreading, and membrane folding and promotes phagoc ytosis competence in epithelial cells. We show that CNF1 induces morph ologic changes in monocytic cells: polarized-like shape in THP I cells , lamellipodia, and cell spreading in adherent monocytes. CNF1 also in creased filamentous actin (F-actin) content in a time- and dose-depend ent manner. In addition, the toxin profoundly reorganized the actin cy toskeleton: redistribution of F-actin in polarized deformations of THP -1 cells and disorganization of microfilament network in monocytes, We also studied the effects of CNF1 on phagocytosis. It markedly impaire d the ingestion of unopsonized zymosan involving CR type 3, However, C NF1 had no effect on the uptake of iC3b-coated zymosan or IgG-mediated phagocytosis of SRBC. In addition, CNF1 induced clustering of CR3 and Fc gamma RII (CD32) but selectively impaired the colocalization of CR 3 with F-actin, It is likely that CNF1-induced reorganization of actin cytoskeleton down-modulates integrin activation-dependent phagocytosi s by preventing the codistribution of CR3 with F-actin, CNF1 mag contr ol some features of integrin-dependent phagocytosis in myeloid cells t hrough its action on Rho GTP binding proteins and cytoskeletal organiz ation.