ARS | Publication request: IDENTIFICATION OF CYTOKERATINS AS ACCESSORY MEDIATORS OF SALMONELLA ENTRY INTO EUKARYOTIC CELLS

Submitted to: Life Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 2001
Publication Date: N/A

Interpretive Summary: Disease-causing Salmonella initiate intestinal infection of a host by inducing their own uptake into specialized intestinal cells. During this uptake process, the bacteria activate an intrinsic secretion system that allows them to release proteins into host cells. The secreted proteins subsequently interact with unknown host cell components that induce disruptions in the actin network that is responsible for the regulation of the supportive architecture of the host cell. This disruptive process allows the bacteria to gain entrance to the cell and thus subsequently cause disease. To identify mechanisms underlying this process, we attempted to identify what host cell protein is being influenced by SipC, one of the major secreted Salmonella invasion proteins. Using the yeast-two hybrid system, a genetic assay that enables the blind identification of protein-protein interactions, we found that SipC could physically interact with a group of proteins called cytokeratins. Cytokeratins are the supportive components of the cell as they form a spherical network that gives the cell its shape, provides a scaffold for other proteins to lie upon and forms a protective barrier. Further studies revealed an inhibition of Salmonella infection in cells in which the presence of cytokeratin-18 was perturbed. Also, an enhanced ability to internalize Salmonella was found in cells in which cytokeratin-18 production was enhanced. Microscopy studies identified a co-condensation of actin and cytokeratins at the site of Salmonella entry into cells. These results suggest that Salmonella invasion may occur consequent to the interaction between SipC and cytokeratin-18.

Technical Abstract: Pathogenic Salmonella species initiate infection of a mammalian host by inducing their own uptake into intestinal M-cells. During the uptake process, the bacteria utilize an intrinsic secretion system to release proteins that enter host cells. The secreted invasion-mediating proteins subsequently interact with host cell components that induce alterations in the actin cytoskeleton. To identify potential cellular determinants of invasion, we employed a yeast two-hybrid system using the secreted Salmonella invasion protein SipC as the bait protein. This system identified cytokeratins, supportive components of the cytoskeletal matrix, as proteins that may physically interact with SipC. Transfection-based studies revealed an inhibition of Salmonella invasion when a dominant negative cytokeratin-18 was expressed. Immunofluorescent microscopy studies identified a co-condensation of actin and cytokeratins at the site of Salmonella entry into HEp-2 cells. These results suggest that an interaction between SipC and cytokeratin-18 may occur as part of Salmonella invasion.