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 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.
Chen
Xinyu
X
Center for Cell Signaling, Department of Microbiology, HSC, University of Virginia, Charlottesville, Virginia 22908, USA. xc2d@virginia.edu
Macara
Ian G
IG
D000199:Actins / Q000737:chemistry; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015153:Blotting, Western; D015815:Cell Adhesion Molecules / Q000378:metabolism / Q000502:physiology*; D018797:Cell Cycle Proteins; D002460:Cell Line; D004285:Dogs; D018274:Electroporation; D004847:Epithelial Cells / Q000166:cytology; D004848:Epithelium / Q000378:metabolism; D005799:Genes, Dominant; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000737:chemistry; D008856:Microscopy, Fluorescence; D062793:Occludin; D011493:Protein Kinase C / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D013997:Time Factors; D014162:Transfection; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism
D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D015815:Cell Adhesion Molecules; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; C568986:Ocln protein, mouse; C115084:Pard3 protein, mouse; D011506:Proteins; D012333:RNA, Messenger; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C087334:TIAM1 protein, human; C513260:Tiam1 protein, mouse; D011493:Protein Kinase C; D020764:cdc42 GTP-Binding Protein