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© The Rockefeller University Press, 0021-9525/2000/6/1473/ $5.00
The Journal of Cell Biology, Volume 149, Number 7, June 26, 2000 1473-1484

Original Article

Apical Membrane Targeting of Nedd4 Is Mediated by an Association of Its C2 Domain with Annexin XIIIb

Pamela J. Planta, Frank Lafontb,c, Sandra Lecatb,c, Paul Verkadeb,c, Kai Simonsb,c, and Daniela Rotina
a Program in Cell Biology, The Hospital for Sick Children and Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada, M5G 1X8
b Cell Biology and Biophysics Programme, European Molecular Biology Laboratory, Heidelberg, Germany
c Max Planck Institute for Molecular Biology and Genetics, Dresden 69012, Germany

Correspondence to: Daniela Rotin, Program in Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8. Tel:(416) 813-5098 Fax:(416) 813-5771 E-mail:drotin{at}sickkids.on.ca.

Nedd4 is a ubiquitin protein ligase (E3) containing a C2 domain, three or four WW domains, and a ubiquitin ligase HECT domain. We have shown previously that the C2 domain of Nedd4 is responsible for its Ca2+-dependent targeting to the plasma membrane, particularly the apical region of epithelial MDCK cells. To investigate this apical preference, we searched for Nedd4-C2 domain-interacting proteins that might be involved in targeting Nedd4 to the apical surface. Using immobilized Nedd4-C2 domain to trap interacting proteins from MDCK cell lysate, we isolated, in the presence of Ca2+, a ~35–40-kD protein that we identified as annexin XIII using mass spectrometry. Annexin XIII has two known isoforms, a and b, that are apically localized, although XIIIa is also found in the basolateral compartment. In vitro binding and coprecipitation experiments showed that the Nedd4-C2 domain interacts with both annexin XIIIa and b in the presence of Ca2+, and the interaction is direct and optimal at 1 µM Ca2+. Immunofluorescence and immunogold electron microscopy revealed colocalization of Nedd4 and annexin XIIIb in apical carriers and at the apical plasma membrane. Moreover, we show that Nedd4 associates with raft lipid microdomains in a Ca2+-dependent manner, as determined by detergent extraction and floatation assays. These results suggest that the apical membrane localization of Nedd4 is mediated by an association of its C2 domain with the apically targeted annexin XIIIb.

Key Words: apical rafts, polarized epithelia, protein trafficking, ubiquitin protein ligase


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