Khine AA, Tam P, Nutikka A, Lingwood
CA.Brefeldin A and filipin distinguish two globotriaosyl
ceramide/verotoxin-1 intracellular trafficking pathways involved
in Vero cell cytotoxicity.
Glycobiology. 2004 Apr 21
In verotoxin 1 (VT1)-sensitive cells, globotriaosyl ceramide
(Gb3) bound VT1 is endocytosed and transported retrogradely to
the Golgi/endoplasmic reticulum (ER). The importance of the
Golgi-dependent retrograde transport of VT1 is now shown to vary
as a function of both VT1 exposure time and concentration.
Following 3 h exposure to < 50 ng/ml VT1, Vero cell cytotoxicity
and protein synthesis inhibition is absolutely dependent on
intact Golgi structure. However, after 24 h incubation with
concentrations of VT1 above 50 ng/ml, a filipin-sensitive
(caveolae-dependent) route for cytotoxicity becomes significant.
Brefeldin A , which prevents Golgi-dependent retrograde traffic,
protects cells from low VT1 concentrations but not following
prolonged toxin exposure at higher VT1 concentrations. Under
these conditions, only a combination of Brefeldin A and
filipin is sufficient to fully protect cells. Intracellular VT1
trafficking monitored using the nontoxic B subunit showed
accumulation within Brefeldin A -collapsed TGN/endosomes.
Considerable VT1 B was retained at the surface of
filipin-treated cells, but Golgi targeting was still apparent.
Filipin-sensitive VT1 cytotoxicity does not require Golgi access
and may involve direct transmembrane signaling. Although cell
surface VT1 does not colocalize with caveolin 1, a small
fraction of endocytosed VT1 is found within caveolin
1-containing vesicles. These studies indicate both a
caveolae-dependent and independent pathway for VT1 access to the
TGN/Golgi from the cell surface and two noninterconverting pools
of membrane Gb3.
PMID: 15102715 |
