The Journal of Neuroscience, November 15, 2001, 21(22):8915-8930
Sorting of Internalized Neurotrophins into an Endocytic
Transcytosis Pathway via the Golgi System: Ultrastructural Analysis in
Retinal Ganglion Cells
Rafal
Butowt and
Christopher S.
von Bartheld
Department of Physiology and Cell Biology, University of Nevada
School of Medicine, Reno, Nevada 89557
Subcellular pathways and accumulation of internalized
radiolabeled neurotrophins NGF, BDNF, and NT-3 were examined in retinal ganglion cells (RGCs) of chick embryos by using quantitative electron microscopic autoradiography. All three neurotrophins accumulated in
endosomes and multivesicular bodies. BDNF and NGF also concentrated at
the plasma membrane, whereas NT-3 accumulated transiently in the Golgi
system. The enhanced targeting of NT-3 to the Golgi system correlated
with the anterograde axonal transport of this neurotrophin. Anterograde
transport of NT-3, but not its internalization, was significantly
attenuated by the tyrosine kinase (trk) inhibitor K252a.
Abolishment of trk activity with K252a shifted NT-3 (and BDNF) away
from the Golgi system and into a lysosomal pathway, indicating that trk
activity regulated sorting of the ligand-receptor complex.
Cross-linking of neurotrophins and immunoprecipitation with antibodies
to the neurotrophin receptors p75, trkA, trkB, and trkC showed that the
large majority of exogenous, receptor-bound NT-3 was bound to trkC in
RGC somata, but during anterograde transport in the optic nerve most
receptor-bound NT-3 was associated with p75, and after arrival and
release in the optic tectum transferred to presumably postsynaptic
trkC. These results reveal remarkable and unexpected differences in the
intracellular pathways and fates of different neurotrophins within the
same cell type. They provide first evidence for an endocytic pathway of
internalized neurotrophic factors via the Golgi system before
anterograde transport and transcytosis. The results challenge the
belief that after internalization all neurotrophins are rapidly
degraded in lysosomes.
Key words:
anterograde transport; BDNF; NT-3; NGF; trkB; trkC; p75
neurotrophin receptor; neurotrophic factor; visual system; internalization; degradation; K252a; Golgi; lysosome; sorting; retina
Copyright © 2001 Society for Neuroscience 0270-6474/01/21228915-16$05.00/0
Previous Article | Next Article
