The PDZ2 domain of zonula occludens-1 and -2 is a phosphoinositide binding domain
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Zonula occludens proteins (ZO) are postsynaptic density protein-95 discs large-zonula occludens (PDZ) domain-containing proteins that play a fundamental role in the assembly of tight junctions and establishment of cell polarity. Here, we show that the second PDZ domain of ZO-1 and ZO-2 binds phosphoinositides (PtdInsP) and we identified critical residues involved in the interaction. Furthermore, peptide and PtdInsP binding of ZO PDZ2 domains are mutually exclusive. Although lipid binding does not seem to be required for plasma membrane localisation of ZO-1, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P 2) binding to the PDZ2 domain of ZO-2 regulates ZO-2 recruitment to nuclear speckles. Knockdown of ZO-2 expression disrupts speckle morphology, indicating that ZO-2 might play an active role in formation and stabilisation of these subnuclear structures. This study shows for the first time that ZO isoforms bind PtdInsPs and offers an alternative regulatory mechanism for the formation and stabilisation of protein complexes in the nucleus.
KeywordsTight junction Phospholipid Post synaptic density-discs large-zonula occludens Nucleus Cell polarity
We thank Dr. E. Mortier for helpful discussions during the course of this project and Dr. L. Van Troys and Dr. G. Hammond for useful advice on the lipid stainings. This work was supported by the Fund for Scientific Research-Flanders (FWO-Vlaanderen), the Concerted Actions Programme of Ghent University (GOA), the Interuniversity attraction poles (IUAP06), the Human Frontier Science Program (HFSP), a NIH grant (GM68849) (for W.C.), and the Catalyst Award from Chicago Biomedical Consortium (for W.C. and H.L.). K.M. was supported by a Postdoctoral Fellowship of the Fund for Scientific Research-Flanders (Belgium) (FWO-Vlaanderen). E.R. is supported by a fellowship from the research council of Ghent University (BOF).
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