Shiga toxins 1 and 2 translocate differently across polarized intestinal epithelial cells

Shiga toxin-producing Escherichia coli (STEC) is an important food-borne pa thogen that causes hemolyticuremic syndrome. Following ingestion, STEC cell s colonize the intestine and produce Shiga toxins (Stx), which appear to tr anslocate across the intestinal epithelium and subsequently reach sensitive endothelial cell beds. STEC cells produce one or both of two major toxins, Stx1 and Stx2, Stx2-producing STEC is more often associated with disease f or reasons as yet undetermined. In this study, we used polarized intestinal epithelial cells grown on permeable filters as a model to compare Stx1 and Stx2 movement across the intestinal epithelium. We have previously shown t hat biologically active Stx1 is able to translocate across cell monolayers in an energy-dependent, saturable manner. This study demonstrates that biol ogically active Stx2 is also capable of movement across the epithelium with out affecting barrier function, but significantly less Stx2 crossed monolay ers than Stx1. Chilling the monolayers to 4 degrees C reduced the amount of Stx1 and Stx2 movement by 200-fold and 20-fold respectively, Stx1 movement was clearly directional, favoring an apical-to-basolateral translocation, whereas Stx2 movement was not. Colchicine reduced Stx1, but not Stx2, trans location, Monensin reduced the translocation of both toxins, but the effect was more pronounced with Stx1. Brefeldin A. had no effect on either toxin. Excess unlabeled Stx1 blocks the movement of I-125-Stx1. Excess Stx2 faile d to have any effect on Stx1 movement. Our data suggests that, despite the many common physical and biochemical properties of the two toxins, they app ear to be crossing the epithelial cell barrier by different pathway.