Listeria monocytogenesantagonizes the human GTPase Cdc42 to promote bacterial spread

Abstract

Summary The bacterial pathogen Listeria monocytogenes uses actin-based motility to spread from infected human cells to surrounding healthy cells. Cell-cell spread involves the formation of thin extensions of the host plasma membrane (‘protrusions’) containing motile bacteria. In cultured enterocytes, the Listeria protein InlC promotes protrusion formation by binding and antagonizing the human scaffolding protein Tuba. Tuba is a known activator of the GTPase Cdc42. In this work, we demonstrate an important role for Cdc42 in controlling Listeria spread. Infection of the enterocyte cell line Caco-2 BBE1 induced a decrease in the level of Cdc42-GTP, indicating that Listeria downregulates this GTPase. Genetic data involving RNA interference indicated that bacterial impairment of Cdc42 may involve inhibition of Tuba. Experiments with dominant negative and constitutively activated alleles of Cdc42 demonstrated that the ability to inactivate Cdc42 is required for efficient protrusion formation by Listeria. Taken together, these findings indicate a novel mechanism of bacterial spread involving pathogen-induced downregulation of host Cdc42.

Host endoplasmic reticulum COPII proteins control cell-to-cell spread of the bacterial pathogenListeria monocytogenes

“…In addition to assessing bacterial protrusions, we also determined the effect of Sec31A on the final event of spreading. Cell‐to‐cell spread of wild‐type and Δ inlC strains was evaluated by quantifying the surface area of foci resulting from infection of a monolayer of Caco‐2 BBE1 cells as previously described (Polle et al ., ; Rigano et al ., ). Consistent with the protrusion formation results, we found that siRNA‐mediated depletion of Sec31A restored normal spreading to the Δ inlC mutant, without significantly affecting spread of wild‐type Listeria (Fig.…”

“…How COPII affects cell junctions is not known, but may involve the exocytic delivery of one or more membrane protein involved in generating tension. Importantly, previous results demonstrate that depletion of Tuba or infection with wild‐type, but not inlC mutant, Listeria increases junctional curvature (Rajabian et al ., ; Polle et al ., ; Rigano et al ., ). In combination with these established findings, the results in the present study indicate that InlC likely perturbs apical junctions through inhibition of Tuba and COPII.…”

“…By contrast, in the polarized enterocyte cell line Caco‐2 BBE1, the secreted Listeria protein InlC acts in conjunction with ActA to promote bacterial spread (Rajabian et al ., ). InlC acts after F‐actin tail formation to enhance the formation of bacterial protrusions (Rajabian et al ., ; Rigano et al ., ).…”

“…In uninfected cells, Cdc42 is activated by a Dbl homology (DH) in Tuba (Salazar et al ., ; Otani et al ., ; Kodani et al ., ; Rigano et al ., ). During infection, wild‐type Listeria inhibits Cdc42, an event critical for bacterial protrusion formation (Rigano et al ., ). Impairment of host Cdc42 involves an incompletely characterized mechanism that is independent of InlC.…”

Bacterial spread from cell to cell: beyond actin-based motility

“…For instance, the bacterial factor OspE2 contributes to the maintenance of integrin-dependent cell adhesion during S. flexneri infection [21,22]. Conversely, cell-cell contacts may represent a physical barrier that needs to be manipulated in order to facilitate protrusion formation, as exemplified by the role of the bacterial factors internalin C (InlC) in relieving Tuba/N-WASP-dependent cortical tension in polarized epithelial cells infected with L. monocytogenes [23,24,25,26]. …”