Activation of Rho GTPases by cytotoxic necrotizing factor 1 induces macropinocytosis and scavenging activity in epithelial cells

Macropinocytosis, a ruffling-driven process that allows the capture of larg e material, is an essential aspect of normal cell function. It can be eithe r constitutive, as in professional phagocytes where it ends with the digest ion of captured material, or induced, as in epithelial cells stimulated by growth factors. In this case, the internalized material recycles back to th e cell surface. We herein show that activation of Rho GTPases by a bacteria l protein toxin, the Escherichia coli cytotoxic necrotizing factor 1 (CNF1) , allowed epithelial cells to engulf and digest apoptotic cells in a manner similar to that of professional phagocytes. In particular, we have demonst rated that 1) the activation of all Rho, Rac, and Cdc42 by CNF1 was essenti al for the capture and internalization of apoptotic cells; and 2) such acti vation allowed the discharge of macropinosomal content into Rab7 and lysoso mal associated membrane protein-1 acidic lysosomal vesicles where the inges ted particles underwent degradation. Taken together, these findings indicat e that CNF1-induced "switching on" of Rho GTPases may induce in epithelial cells a scavenging activity, comparable to that exerted by professional pha gocytes. The activation of such activity in epithelial cells may be relevan t, in mucosal tissues, in supporting or integrating the scavenging activity of resident macrophages.