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Par-3 controls tight junction assembly through the Rac exchange factor Tiam1



The par (partitioning-defective) genes express a set of conserved proteins that function in polarization and asymmetric cell division1,2. Par-3 has multiple protein-interaction domains, and associates with Par-6 and atypical protein kinase C (aPKC)3,4,5. In Drosophila, Par-3 is essential for epithelial cell polarization6. However, its function in mammals is unclear. Here we show that depletion of Par-3 in mammalian epithelial cells profoundly disrupts tight junction assembly. Expression of a carboxy-terminal fragment plus the third PDZ domain of Par-3 partially rescues junction assembly, but neither Par-6 nor aPKC binding is required. Unexpectedly, Rac is constitutively activated in cells lacking Par-3, and the assembly of tight junctions is efficiently restored by a dominant-negative Rac mutant. The Rac exchange factor Tiam1 (ref. 7) binds directly to the carboxy-terminal region of Par-3, and knockdown of Tiam1 enhances tight junction formation in cells lacking Par-3. These results define a critical function for Par-3 in tight junction assembly, and reveal a novel mechanism through which Par-3 engages in the spatial regulation of Rac activity and establishment of epithelial polarity.

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We thank J. G. Collard for providing Tiam1 C1199 plasmid and anti-Tiam1 antibody, M. A. Schwartz for pGEX-RBD and pGEX-PBD plasmids, and A. Spang (Tübingen) and members of the Macara laboratory for helpful comments. This work was supported by grants GM070902 and CA40042 from the National Institutes of Health, DHHS.

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The authors declare no competing financial interests.

Correspondence to Xinyu Chen.

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  1. Supplementary information

    Supplementary figures S1, S2 and S3 (PDF 554 kb)

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Further reading

Figure 1: Par-3 loss severely disrupts tight junction formation in MDCK II cells.
Figure 2: Rescue of tight junction assembly in Par-3-knockdown cells.
Figure 3: Inhibition of the Rho pathway rescues junction assembly.
Figure 4: Constitutive activation of Rac in Par-3-knockdown cells.
Figure 5: Par-3 regulates tight junction formation through interaction with Tiam1.