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J. Cell Biol.,
Volume 143, Number 4, November 16, 1998 973-990
Institut Curie, Centre National de la Recherche Scientifique UMR 144, Laboratoire Mécanismes Moléculaires du Transport
Intracellulaire, F-75248 Paris Cedex 05, France
Shiga toxin and other toxins of this family
can escape the endocytic pathway and reach the Golgi
apparatus. To synchronize endosome to Golgi transport, Shiga toxin B-fragment was internalized into
HeLa cells at low temperatures. Under these conditions, the protein partitioned away from markers destined for the late endocytic pathway and colocalized extensively with cointernalized transferrin. Upon
subsequent incubation at 37°C, ultrastructural studies
on cryosections failed to detect B-fragment-specific label in multivesicular or multilamellar late endosomes,
suggesting that the protein bypassed the late endocytic
pathway on its way to the Golgi apparatus. This hypothesis was further supported by the rapid kinetics of B-fragment transport, as determined by quantitative
confocal microscopy on living cells and by B-fragment
sulfation analysis, and by the observation that actin-
depolymerizing and pH-neutralizing drugs that modulate vesicular transport in the late endocytic pathway had no effect on B-fragment accumulation in the Golgi
apparatus. B-fragment sorting at the level of early/recycling endosomes seemed to involve vesicular coats,
since brefeldin A treatment led to B-fragment accumulation in transferrin receptor-containing membrane tubules, and since B-fragment colocalized with adaptor
protein type 1 clathrin coat components on early/recycling endosomes. Thus, we hypothesize that Shiga toxin
B-fragment is transported directly from early/recycling
endosomes to the Golgi apparatus. This pathway may
also be used by cellular proteins, as deduced from our
finding that TGN38 colocalized with the B-fragment on its transport from the plasma membrane to the TGN.
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