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MBC in Press, published online ahead of print March 26, 2004
Mol. Biol. Cell 10.1091/mbc.E04-02-0163

A more recent version of this article appeared on June 1, 2004
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Submitted on February 29, 2004
Accepted on March 15, 2004

Role for Actin Filament Turnover and a Myosin II Motor in Cytoskeleton-Driven Disassembly of the Epithelial Apical Junctional Complex

Andrei I. Ivanov1*, Ingrid C. McCall1, Charles A. Parkos1, and Asma Nusrat1

1 Epithelial Pathobiology Research Unit, Department of Pathology and Laboratory Medicine, Emory University, Atlanta, Georgia 30322

* Corresponding author. E-mail address: aiivano{at}emory.edu.

Disassembly of the epithelial apical junctional complex (AJC) composed of the tight junction (TJ) and adherens junction (AJ), is important for normal tissue remodeling and pathogen-induced disruption of epithelial barriers. Using a calcium depletion model in T84 epithelial cells, we previously found that disassembly of the AJC results in endocytosis of AJ/TJ proteins. In the present study, we investigated the role of the actin cytoskeleton in disassembly and internalization of the AJC. Calcium depletion induced reorganization of apical F-actin into contractile rings. Internalized AJ/TJ proteins colocalized with these rings. Both depolymerization and stabilization of F-actin inhibited ring formation and disassembly of the AJC, suggesting a role for actin filament turnover. Actin reorganization was accompanied by activation (dephosphorylation) of cofilin-1 and its translocation to the F-actin rings. In addition, Arp3 and cortactin colocalized with these rings. F-actin reorganization and disassembly of the AJC were blocked by blebbistatin, an inhibitor of nonmuscle myosin II. Myosin IIA was expressed in T84 cells and colocalized with F-actin rings. We conclude that disassembly of the AJC in calcium-depleted cells is driven by reorganization of apical F-actin. Mechanisms of such reorganization involve cofilin-1-dependent depolymerization and Arp2/3-assisted repolymerization of actin filaments as well as myosin IIA-mediated contraction.






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