CYTOSKELETAL REARRANGEMENTS AND THE FUNCTIONAL-ROLE OF T-PLASTIN DURING ENTRY OF SHIGELLA-FLEXNERI INTO HELA-CELLS

Shigella flexneri is an enteroinvasive bacterium which causes bacillar y dysentery in humans. A major feature of its pathogenic potential is the capacity to invade epithelial cells. Shigella entry into epithelia l cells is considered a parasite-induced internalization process requi ring polymerization of actin. Here we describe the cytoskeletal rearra ngements during S. flexneri invasion of HeLa cells. After an initial c ontact of the bacterium with the cell surface, distinct nucleation zon es of heavy actin polymerization appear in close proximity to the cont act site underneath the parasite with long filaments being polymerized . These structures then push cellular protrusions that rise beside the entering bacterium, being sustained by tightly bundled long actin fil aments organized in parallel orientation with their positive ends poin ting to the cytoplasmic membrane. Finally, the cellular projections co alesce above the bacterial body, leading to its internalization. In ad dition, we found the actin-bundling protein plastin to be concentrated in these protrusions. Since plastin is known to bundle actin filament s in parallel orientation, colocalization of parallel actin filaments and plastin in the cellular protrusions strongly suggested a functiona l role of this protein in the architecture of parasite-induced cellula r projections. Using transfection experiments, we show the differentia l recruitment of the two plastin isoforms (T- and L-) into Shigella en try zones. By transient expression of a truncated T-plastin which is d eprived of one of its actin-binding sites, we also demonstrate the fun ctional role of T-plastin in Shigella entry into HeLa cells.