Internalized Pseudomonas exotoxin A can exploit multiple pathways to reach the endoplasmic reticulum.
Receptor-mediated internalization to the endoplasmic reticulum (ER) and subsequent retro-translocation to the cytosol are essential sequential processes required for the intoxication of mammalian cells by Pseudomonas exotoxin A (PEx). The toxin binds the alpha2-macroglobulin receptor/low-density lipoprotein receptor-related protein. Here, we show that in HeLa cells, PEx recruits a proportion of this receptor to detergent-resistant microdomains (DRMs). Uptake of receptor-bound PEx involves transport steps both directly from early endosomes to the trans-Golgi network (TGN) independently of Rab9 function and from late endosomes to the TGN in a Rab9-dependent manner. Furthermore, treatments that simultaneously perturb both Arf1-dependent and Rab6-dependent retrograde pathways show that PEx can use multiple routes to reach the ER. The Rab6-dependent route has only been described previously for cargo with lipid-sorting signals. These findings suggest that partial localization of PEx within DRM permits a choice of trafficking routes consistent with a model that DRM-associated toxins reach the ER on a lipid-dependent sorting pathway whilst non-DRM-associated PEx exploits the previously characterized KDEL receptor-mediated uptake pathway. Thus, unexpectedly, an ER-directed toxin with a proteinaceous receptor shows promiscuity in its intracellular trafficking pathways, exploiting routes controlled by both lipid- and protein-sorting signals.
Molecular Cell Biology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
Daniel C
DC
Smith
Robert A
RA
Spooner
Peter D
PD
Watson
James L
JL
Murray
Thomas W
TW
Hodge
Mohamed
M
Amessou
Ludger
L
Johannes
J Michael
JM
Lord
Lynne M
LM
Roberts
D016475:3T3 Cells; D036002:ADP Ribose Transferases / Q000378:metabolism*; D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005098:Exotoxins / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism; D051379:Mice; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D018000:Receptors, Peptide / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051438:Syntaxin 16 / Q000235:genetics / Q000378:metabolism; D014709:Vero Cells; D037521:Virulence Factors / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D001427:Bacterial Toxins; D005098:Exotoxins; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D034741:RNA, Small Interfering; D018000:Receptors, Peptide; D051438:Syntaxin 16; D037521:Virulence Factors; D020691:rab GTP-Binding Proteins; D000097668:Pseudomonas aeruginosa Exotoxin A; C064459:KDEL receptor; C079856:RAB9A protein, human