Rho-dependent cell spreading activated by E.coli cytotoxic necrotizing factor 1 hinders apoptosis in epithelial cells

Cell-cell and cell-matrix interactions play a pivotal role in numerous cell functions including cell survival and death. In this work, we report evidence that the Rho-dependent cell spreading activated by a protein toxin from E. coli, the cytotoxic necrotizing factor 1 (CNF1), is capable of hindering apoptosis in HEp-2 cells. In addition to the promotion of cell spreading, CNF1 protects cells from the experimentally-induced rounding up and detachment and improves the ability of cells to adhere to each other and to the extracellular matrix by modulating the expression of proteins related to cell adhesion. In particular, the expression of integrins such as alpha 5, alpha 6 and alpha v, as well as of some heterotypic and homotypic adhesion-related proteins such as the Focal Adhesion Kinase, E-cadherin, alpha and beta catenins were significantly increased in cells exposed to CNF1. Our results suggest, however, that the promotion of Rho-dependent cell spreading is the key mechanism in protecting cells against apoptosis rather than cell adhesion per se. A toxin inducing cell spreading without activating Rho, such as Cytochalasin B, was in fact ineffective in favouring cell survival. These data are of relevance (i) for the understanding of the role of the actin-dependent and especially Rho-dependent cellular activities involved in apoptosis regulation and (ii) in providing some clues to understanding the mechanisms by which bacteria, by controlling cell fate, might exert their pathogenic activity.