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© The Rockefeller University Press, 0021-9525/1998//1413 $5.00
The Journal of Cell Biology, Volume 142, Number 6, , 1998 1413-1427


Regular Articles

Annexin XIIIb Associates with Lipid Microdomains to Function in Apical Delivery



Frank Lafont, Sandra Lecat, Paul Verkade, and Kai Simons

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.

Key Words: cholesterol • exocytosis • MDCK • polarity • raft



Abbreviations used in this paper: CLAP, chymostatin, leupeptin, antipain, pepstatin A; DIG, detergent-insoluble glycosphingolipid complex; GPI, glycosylphosphatidylinositol; his6-GST, his6-glutathione-S-transferase; HA, hemagglutinin; MeβCD, methyl-β-cyclodextrin; NSF, N-ethyl maleimide-sensitive factor; PIP2, phosphatidylinositol (4,5) biphosphate; SLO, streptolysin-O; SNAP, soluble NSF-associated protein; SNARE, SNAP receptor; TfR, transferrin receptor; VIP, vesicular integral protein; VSV, vesicular stomatitis virus.

Address all correspondence to Frank Lafont, European Molecular Biology Laboratory, Cell Biology and Biophysics Programme, Meyerhofstrasse 1, Postfach 10 2209, D-69012 Heidelberg, Germany. Tel: (49) 6221 387390. Fax: (49) 6221 387512. E-mail: lafont{at}embl-heidelberg.de



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