The role of clathrin-dependent endocytosis in bacterial internalization

Abstract

Internalization of bacteria into mammalian host cells has been studied extensively in the past two decades. These studies have highlighted the amazingly diverse strategies used by bacterial pathogens to induce their entry in non-phagocytic cells. The roles of actin and of the whole cytoskeletal machinery have been investigated in great detail for several invasive organisms, such as Salmonella, Shigella, Yersinia and Listeria. Recent results using Listeria highlight a role for the endocytosis machinery in bacterial entry, suggesting that clathrin-dependent endocytic mechanisms are also involved in internalization of large particles. This contrasts with the generally accepted dogma but agrees with previous studies of bacterial and viral infections and also of phagocytosis.

Figure I

(a) A scanning electron microscopy image (top) of a L. monocytogenes bacterium entering an epithelial cell. Reproduced with permission from . The diagram below shows a model of the signalling produced by the interaction of listerial protein InlB with Met. (b) A scanning electron micrograph (top) of a Shigella bacterium entering into an epithelial cell. The diagram below is a representation of the signalling cascades produced during Shigella invasion. Green circles represent actin.

Figure 1

Localization of clathrin and dynamin at L. monocytogenes entry sites into HeLa cells. (a) Extracellular bacteria are in blue, total bacteria in green and clathrin in red. (b) Extracellular bacteria are in blue, total bacteria and the cellular nucleus in green and dynamin in red. The merged images clearly show clathrin and dynamin surrounding bacteria that are entering the cell. Reproduced with permission from Ref. .

Figure 2

Image of a bead being phagocytosed revealing a large clathrin basketwork immediately below the advancing lip of a nascent phagosome. The scale bar represents 0.2 μm. Reproduced with permission from Ref. .