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Journal of Biomedicine and Biotechnology
Volume 2010 (2010), Article ID 402593, 11 pages
Review Article

The Dual Role of Zonula Occludens (ZO) Proteins

1Department of Organismic Biology, University of Salzburg, Hellbrunner Strasse 34, 5020 Salzburg, Austria
2Unit for Applied Cell Biology, Paracelsus Private Medical University, Salzburg, Austria

Received 14 July 2009; Accepted 6 January 2010

Academic Editor: Amanda McCann

Copyright © 2010 H. Bauer et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


ZO (zonula occludens) proteins are scaffolding proteins providing the structural basis for the assembly of multiprotein complexes at the cytoplasmic surface of intercellular junctions. In addition, they provide a link between the integral membrane proteins and the filamentous cytoskeleton. ZO proteins belong to the large family of membrane-associated guanylate kinase (MAGUK)-like proteins comprising a number of subfamilies based on domain content and sequence similarity. Besides their structural function at cell-cell contacts, ZO proteins appear to participate in the regulation of cell growth and proliferation. Detailed molecular studies have shown that ZO proteins exhibit conserved functional nuclear localization and nuclear export motifs within their amino acid sequence. Further, ZO proteins interact with dual residency proteins localizing to the plasma membrane and the nucleus. Although the nuclear targeting of ZO proteins has well been described, many questions concerning the biological significance of this process have remained open. This review focuses on the dual role of ZO proteins, being indispensable structural components at the junctional site and functioning in signal transduction pathways related to gene expression and cell behavior.