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1 Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States
2 Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, 90095, California, United States
3 Department of Pathology, Molecular Pathology, Massachusetts General Hospital, Charlestown, Massachusetts, United States
4 Pathology & Laboratory Medicine, University of California, Los Angeles, 10833 Le Conte Ave, Los Angeles, California, 90095, United States; Molecular Biology Institute, Los Angeles, California, United States; Jonsson Comprehensive Cancer Center, Los Angeles, California, United States
* To whom correspondence should be addressed. E-mail: arajasekaran{at}mednet.ucla.edu.
Tight junctions are crucial for maintaining the polarity and vectorial transport functions of epithelial cells. We and others have shown that Na,K-ATPase plays a key role in the organization and permeability of tight junctions in mammalian cells, and analogous septate junctions in Drosophila. However, the mechanism by which Na,K-ATPase modulates tight junctions is not known. In this study, using a well-differentiated human pancreatic epithelial cell line HPAF-II, we demonstrate that Na,K-ATPase is present at the apical junctions and forms a complex with protein phosphatase (PP)-2A, a protein known to be present at tight junctions. Inhibition of Na,K-ATPase ion transport function reduced PP2A activity, hyper-phosphorylated occludin, induced rearrangement of tight junction strands, and increased permeability of tight junctions to ionic and non-ionic solutes. These data suggest that Na,K-ATPase is required for controlling the tight junction gate function.
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