Riccardo Vago and Catherine J. Marsden contributed equally to this work.
Saporin and ricin A chain follow different intracellular routes to enter the cytosol of intoxicated cells
Article first published online: 7 SEP 2005
Volume 272, Issue 19, pages 4983–4995, October 2005
How to Cite
Vago, R., Marsden, C. J., Lord, J. M., Ippoliti, R., Flavell, D. J., Flavell, S.-U., Ceriotti, A. and Fabbrini, M. S. (2005), Saporin and ricin A chain follow different intracellular routes to enter the cytosol of intoxicated cells. FEBS Journal, 272: 4983–4995. doi: 10.1111/j.1742-4658.2005.04908.x
- Issue published online: 7 SEP 2005
- Article first published online: 7 SEP 2005
- (Received 18 May 2005, revised 11 July 2005, accepted 9 August 2005)
- anticancer therapy;
- bacterial toxins;
- intracellular trafficking;
- KDEL retrieval sequence;
- plant ribosome-inactivating proteins
Several protein toxins, such as the potent plant toxin ricin, enter mammalian cells by endocytosis and undergo retrograde transport via the Golgi complex to reach the endoplasmic reticulum (ER). In this compartment the catalytic moieties exploit the ER-associated degradation (ERAD) pathway to reach their cytosolic targets. Bacterial toxins such as cholera toxin or Pseudomonas exotoxin A carry KDEL or KDEL-like C-terminal tetrapeptides for efficient delivery to the ER. Chimeric toxins containing monomeric plant ribosome-inactivating proteins linked to various targeting moieties are highly cytotoxic, but it remains unclear how these molecules travel within the target cell to reach cytosolic ribosomes. We investigated the intracellular pathways of saporin, a monomeric plant ribosome-inactivating protein that can enter cells by receptor-mediated endocytosis. Saporin toxicity was not affected by treatment with Brefeldin A or chloroquine, indicating that this toxin follows a Golgi-independent pathway to the cytosol and does not require a low pH for membrane translocation. In intoxicated Vero or HeLa cells, ricin but not saporin could be clearly visualized in the Golgi complex using immunofluorescence. The saporin signal was not evident in the Golgi, but was found to partially overlap with that of a late endosome/lysosome marker. Consistently, the toxicities of saporin or saporin-based targeted chimeric polypeptides were not enhanced by the addition of ER retrieval sequences. Thus, the intracellular movement of saporin differs from that followed by ricin and other protein toxins that rely on Golgi-mediated retrograde transport to reach their retrotranslocation site.