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J. Cell Biol.,
Volume 142, Number 6, September 21, 1998 1413-1427
European Molecular Biology Laboratory, Cell Biology and Biophysics Programme, D-69012 Heidelberg, Germany; and Max
Planck Institute for Molecular Cell Biology and Genetics, Dresden, Germany
A member of the annexin XIII sub-family,
annexin XIIIb, has been implicated in the apical exocytosis of epithelial kidney cells. Annexins are phospholipid-binding proteins that have been suggested to be
involved in membrane trafficking events although their
actual physiological function remains open. Unlike the
other annexins, annexin XIIIs are myristoylated. Here,
we show by immunoelectron microscopy that annexin
XIIIb is localized to the trans-Golgi network (TGN),
vesicular carriers and the apical cell surface. Polarized
apical sorting involves clustering of apical proteins into
dynamic sphingolipid-cholesterol rafts. We now provide evidence for the raft association of annexin XIIIb.
Using in vitro assays and either myristoylated or unmyristoylated recombinant annexin XIIIb, we demonstrate that annexin XIIIb in its native myristoylated form stimulates specifically apical transport whereas
the unmyristoylated form inhibits this route. Moreover,
we show that formation of apical carriers from the
TGN is inhibited by an anti-annexin XIIIb antibody
whereas it is stimulated by myristoylated recombinant annexin XIIIb. These results suggest that annexin
XIIIb directly participates in apical delivery.
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