hide
Free keywords:
-
Abstract:
Glycosphingolipids are controlled by the spatial
organization of their metabolism and by trans port
specifi city. Using immunoelectron microscopy,
we localize to the Golgi stack the glycosyltransferases that
produce glucosylceramide (GlcCer), lactosylceramide
(LacCer), and GM3. GlcCer is synthesized on the cytosolic
side and must translocate across to the Golgi lumen for
LacCer synthesis. However, only very little natural GlcCer
translocates across the Golgi in vitro. As GlcCer reaches
the cell surface when Golgi vesicular traffi cking is inhibited,
it must translocate across a post-Golgi membrane.
Concanamycin, a vacuolar proton pump inhibitor, blocks
translocation independently of multidrug transporters that
are known to translocate short-chain GlcCer. Concanamycin
did not reduce LacCer and GM3 synthesis. Thus, GlcCer
destined for glycolipid synthesis follows a different pathway
and transports back into the endoplasmic reticulum
(ER) via the late Golgi protein FAPP2. FAPP2 knockdown
strongly reduces GM3 synthesis. Overall, we show that
newly synthesized GlcCer enters two pathways: one toward
the noncytosolic surface of a post-Golgi membrane and
one via the ER toward the Golgi lumen LacCer synthase.
