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

Nat Cell Biol. 2005 Mar;7(3):262-9. doi: 10.1038/ncb1226. Epub 2005 Feb 20.


The par (partitioning-defective) genes express a set of conserved proteins that function in polarization and asymmetric cell division. Par-3 has multiple protein-interaction domains, and associates with Par-6 and atypical protein kinase C (aPKC). In Drosophila, Par-3 is essential for epithelial cell polarization. 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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actins / chemistry
  • Adaptor Proteins, Signal Transducing
  • Animals
  • Blotting, Western
  • Cell Adhesion Molecules / metabolism
  • Cell Adhesion Molecules / physiology*
  • Cell Cycle Proteins
  • Cell Line
  • Dogs
  • Electroporation
  • Epithelial Cells / cytology
  • Epithelium / metabolism
  • Genes, Dominant
  • Guanine Nucleotide Exchange Factors
  • Humans
  • Immunoprecipitation
  • Membrane Proteins / chemistry
  • Microscopy, Fluorescence
  • Occludin
  • Protein Kinase C / metabolism
  • Protein Structure, Tertiary
  • Proteins / metabolism
  • Proteins / physiology*
  • RNA, Messenger / metabolism
  • T-Lymphoma Invasion and Metastasis-inducing Protein 1
  • Time Factors
  • Transfection
  • cdc42 GTP-Binding Protein / metabolism


  • Actins
  • Adaptor Proteins, Signal Transducing
  • Cell Adhesion Molecules
  • Cell Cycle Proteins
  • Guanine Nucleotide Exchange Factors
  • Membrane Proteins
  • OCLN protein, human
  • Occludin
  • Ocln protein, mouse
  • Pard3 protein, mouse
  • Proteins
  • RNA, Messenger
  • T-Lymphoma Invasion and Metastasis-inducing Protein 1
  • TIAM1 protein, human
  • Tiam1 protein, mouse
  • Protein Kinase C
  • cdc42 GTP-Binding Protein