Salmonella interact with eucaryotic membranes to trigger internalization into non-phagocytic cells. In this study we examined the distribution of host plasma membrane proteins during S. typhimurium invasion of epithelial cells. Entry of S. typhimurium into HeLa epithelial cells produced extensive aggregation of cell surface class I MHC heavy chain, beta 2-microglobulin, fibronectin-receptor (alpha 5 beta 1 integrin), and hyaluronate receptor (CD-44). Other cell surface proteins such as transferrin-receptor or Thy-1 were aggregated by S. typhimurium to a much lesser extent. Capping of these plasma membrane proteins was observed in membrane ruffles localized to invading S. typhimurium and in the area surrounding these structures. In contrast, membrane ruffling induced by epidermal growth factor only produced minor aggregations of surface proteins, localized exclusively in the membrane ruffle. This result suggests that extensive redistribution of these proteins requires a signal related to bacterial invasion. This bacteria-induced process was associated with rearrangement of polymerized actin but not microtubules, since preincubation of epithelial cells with cytochalasin D blocked aggregation of these proteins while nocodazole treatment did not. Of the host surface proteins aggregated by S. typhimurium, only class I MHC heavy chain was predominantly present in the bacteria-containing vacuoles. No extensive aggregation of host plasma membrane proteins was detected when HeLa epithelial cells were infected with invasive bacteria that do not induce membrane ruffling, including Yersinia enterocolitica, a bacterium that triggers internalization via binding to beta 1 integrin, and a S. typhimurium invasion mutant that utilizes the Yersinia-internalization route. In contrast to the situation with S. typhimurium, class I MHC heavy chain was not selectively internalized into vacuoles containing these other bacteria. Extensive aggregation of host plasma membrane proteins was also not observed when other S. typhimurium mutants that are defective for invasion were used. The amount of internalized host plasma membrane proteins in the bacteria-containing vacuoles decreased over time with all invasive bacteria examined, indicating that modification of the composition of these vacuoles occurs. Therefore, our data show that S. typhimurium induces selective aggregation and internalization of host plasma membrane proteins, processes associated with the specific invasion strategy used by this bacterium to enter into epithelial cells.
Microtubule perturbation retards both the direct and the indirect apical pathway but does not affect sorting of plasma membrane proteins in intestinal epithelial cells (Caco-2).
