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A distinct PAR complex associates physically with VE-cadherin in vertebrate endothelial cells.

ABSTRACT: A cell polarity complex consisting of partitioning defective 3 (PAR-3), atypical protein kinase C (aPKC) and PAR-6 has a central role in the development of cell polarity in epithelial cells. In vertebrate epithelial cells, this complex localizes to tight junctions. Here, we provide evidence for the existence of a distinct PAR protein complex in endothelial cells. Both PAR-3 and PAR-6 associate directly with the adherens junction protein vascular endothelial cadherin (VE-cadherin). This association is direct and mediated through non-overlapping domains in VE-cadherin. PAR-3 and PAR-6 are recruited independently to cell-cell contacts. Surprisingly, the VE-cadherin-associated PAR protein complex lacks aPKC. Ectopic expression of VE-cadherin in epithelial cells affects tight junction formation. Our findings suggest that in endothelial cells, another PAR protein complex exists that localizes to adherens junctions and does not promote cellular polarization through aPKC activity. They also point to a direct role of a cadherin in the regulation of cell polarity in vertebrates.

SUBMITTER: Iden S

PROVIDER: S-EPMC1794700 | biostudies-literature | 2006 Dec

REPOSITORIES: biostudies-literature

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A distinct PAR complex associates physically with VE-cadherin in vertebrate endothelial cells.

Iden Sandra S Rehder Daniela D August Benjamin B Suzuki Atsushi A Wolburg-Buchholz Karen K Wolburg Hartwig H Ohno Shigeo S Behrens Jürgen J Vestweber Dietmar D Ebnet Klaus K

EMBO reports 20061020 12

A cell polarity complex consisting of partitioning defective 3 (PAR-3), atypical protein kinase C (aPKC) and PAR-6 has a central role in the development of cell polarity in epithelial cells. In vertebrate epithelial cells, this complex localizes to tight junctions. Here, we provide evidence for the existence of a distinct PAR protein complex in endothelial cells. Both PAR-3 and PAR-6 associate directly with the adherens junction protein vascular endothelial cadherin (VE-cadherin). This associati ...[more]

PMID: 17057644

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Project description:RATIONALE:The mechanistic foundation of vascular maturation is still largely unknown. Several human pathologies are characterized by deregulated angiogenesis and unstable blood vessels. Solid tumors, for instance, get their nourishment from newly formed structurally abnormal vessels which present wide and irregular interendothelial junctions. Expression and clustering of the main endothelial-specific adherens junction protein, VEC (vascular endothelial cadherin), upregulate genes with key roles in endothelial differentiation and stability. OBJECTIVE:We aim at understanding the molecular mechanisms through which VEC triggers the expression of a set of genes involved in endothelial differentiation and vascular stabilization. METHODS AND RESULTS:We compared a VEC-null cell line with the same line reconstituted with VEC wild-type cDNA. VEC expression and clustering upregulated endothelial-specific genes with key roles in vascular stabilization including claudin-5, vascular endothelial-protein tyrosine phosphatase (VE-PTP), and von Willebrand factor (vWf). Mechanistically, VEC exerts this effect by inhibiting polycomb protein activity on the specific gene promoters. This is achieved by preventing nuclear translocation of FoxO1 (Forkhead box protein O1) and ?-catenin, which contribute to PRC2 (polycomb repressive complex-2) binding to promoter regions of claudin-5, VE-PTP, and vWf. VEC/?-catenin complex also sequesters a core subunit of PRC2 (Ezh2 [enhancer of zeste homolog 2]) at the cell membrane, preventing its nuclear translocation. Inhibition of Ezh2/VEC association increases Ezh2 recruitment to claudin-5, VE-PTP, and vWf promoters, causing gene downregulation. RNA sequencing comparison of VEC-null and VEC-positive cells suggested a more general role of VEC in activating endothelial genes and triggering a vascular stability-related gene expression program. In pathological angiogenesis of human ovarian carcinomas, reduced VEC expression paralleled decreased levels of claudin-5 and VE-PTP. CONCLUSIONS:These data extend the knowledge of polycomb-mediated regulation of gene expression to endothelial cell differentiation and vessel maturation. The identified mechanism opens novel therapeutic opportunities to modulate endothelial gene expression and induce vascular normalization through pharmacological inhibition of the polycomb-mediated repression system.

Project description:par3 is a multiple-PDZ-containing scaffold protein that is central to the organization of an evolutionarily conserved cell polarity complex consisting of par3, par6, and aPKC. The ability of par3 PDZ domains to target various adhesion molecules and enzymes at the plasma membrane leads to the controlled localization of par6 and aPKC, which has firmly established its role in epithelial cell polarity. Of the numerous PDZ ligands associated with par3, interaction of its third PDZ domain with the class II ligand found within the C-terminal tail of vascular endothelial cadherin (VE-Cad) suggests a role in endothelial cell polarity as well, but the molecular details of the interaction are unknown. Previously determined structures of par3-PDZ3 bound to the class I ligand found within the C-terminal tail of the phosphoinositide phosphatase PTEN revealed two discrete binding sites: a canonical PDZ-ligand interaction site and a distal site involving charge-charge complements. Currently, it is unclear if par3-PDZ3 employs both canonical and distal binding modes in its association with VE-Cad or if these modes are unique to the PTEN interaction, suggesting a possible mechanism for ligand specificity within the polarity network. The structure of par3-PDZ3 bound to the C-terminal tail of VE-Cad presented in this work shows that both canonical and distal interactions are utilized in binding. Biophysical measurements using fluorescence polarization and two-dimensional NMR implicate the intermolecular charge pairing of aspartic acid 777 (VE-Cad) and arginine 609 (par3-PDZ3) as a crucial modulator of complex formation. Phosphorylation of VE-Cad at serine 776 increases its affinity for par3, demonstrating that post-translational modifications outside of the canonical carboxylate binding site can enhance PDZ-ligand interactions. Comparison of the VE-Cad and PTEN complexes highlights how the unique molecular architecture of par3-PDZ3 can accommodate both canonical and distal interaction modes that allow dual-class specificity for these two ligand types.

Dataset Information

A distinct PAR complex associates physically with VE-cadherin in vertebrate endothelial cells.

Publications

A distinct PAR complex associates physically with VE-cadherin in vertebrate endothelial cells.

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