Surfing on a retrograde wave: how does Shiga toxin reach the endoplasmic reticulum?

Bacterial Shiga toxin and related toxins are endocytosed by higher eukaryotic cells. The toxin protein is then transported via the Golgi apparatus to the endoplasmic reticulum (ER) and into the cytosol, where it exerts its toxic effect. This review discusses current understanding of this retrograde transport pathway and how newly developed modified toxins that allow detection and quantification of specific transport steps might prove useful tools in the future.