De. Warnock et al., TRANSPORT OF NEWLY SYNTHESIZED GLUCOSYLCERAMIDE TO THE PLASMA-MEMBRANE BY A NON-GOLGI PATHWAY, Proceedings of the National Academy of Sciences of the United Statesof America, 91(7), 1994, pp. 2708-2712
High-gradient magnetic affinity chromatography (HIMAC) has been used t
o obtain highly enriched plasma membranes, free of intracellular membr
ane contaminants, from cultured Chinese hamster ovary (CHO) cells in y
ields of greater-than-or-equal-to 80%. Using this procedure we have ch
aracterized the transport of glucosylceramide (GlcCer) and the ganglio
side GM3 to the plasma membrane. Newly synthesized GlcCer reaches the
plasma membrane in 7.2 min, whereas GM3 requires 21.5 min to reach the
plasma membrane. Brefeldin A prevents transport of newly synthesized
GM3 and sphingomyelin to the plasma membrane but has no effect on the
transport of GlcCer. Similarly, incubation of CHO cells at 15-degrees-
C blocks transport of GM3 and sphingomyelin to the plasma membrane but
has no effect on GlcCer movement. We propose that carrier-mediated tr
ansport accounts for a major fraction of the plasma membrane GlcCer. P
ulse-chase studies with either [H-3]glucose or [H-3]palmitate indicate
that newly synthesized GlcCer which has reached the plasma membrane i
s not utilized for the synthesis of GM3 but is instead rapidly either
degraded or converted into an as yet unidentified product. Our results
indicate that in addition to serving as a precursor for higher glycos
ylation in the Golgi, a major fraction of newly synthesized GlcCer is
rapidly transported to the plasma membrane by a non-Golgi pathway and
then rapidly turned over.