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EDITORIAL FOCUS

Compromised E-cadherin adhesion and epithelial barrier function with activation of G protein-coupled receptors is rescued by Y-to-F mutations in β-catenin

Department of Internal Medicine, University of Iowa, Iowa City, Iowa

Submitted 28 September 2007 ; accepted in final form 10 December 2007

Activation of the type 1 histamine (H1) or the type 2 protease-activated (PAR-2) G protein-coupled receptors interrupts E-cadherin adhesion and decreases the transepithelial resistance (TER) of epithelium. Several reports suggest that cadherin adhesive function depends on the association of cadherin with β-catenin and that this association is regulated by phosphorylation of tyrosines in β-catenin. We tested the hypothesis that loss of cadherin adhesion and compromise of TER on activation of the H1 or PAR-2 receptor is due to phosphorylation of tyrosines in β-catenin. L cells were stably transfected to express E-cadherin (L-E-cad cells) and H1 (L-H1-E-cad cells). L cells and Madin-Darby canine kidney (MDCK) cells constitutively express PAR-2. Stably transfected L-E-cad, L-H1-E-cad, and MDCK cells were also stably transfected with FLAG-tagged wild-type (WT) or mutant β-catenin, converting tyrosine 142, 489, or 654 to the nonphosphorylatable mimetic, phenylalanine (WT, Y142F, Y489F, or Y654F). Activation of H1 or PAR-2 interrupted adhesion to an immobilized E-cadherin-Fc fusion protein of L-H1-E-cad, L-E-cad, and MDCK cells expressing WT or Y142F β-catenin but did not interrupt adhesion of L-H1-E-cad, L-E-cad, and MDCK cells expressing the Y489F or Y654F mutant β-catenins. PAR-2 activation decreased the TER of monolayers of MDCK cells expressing WT or Y142F β-catenin 40–45%. However, PAR-2 activation did not decrease the TER of monolayers of MDCK cells expressing Y489F or Y654F β-catenin. The protein tyrosine phosphatase PTP1B binds to the cadherin cytoplasmic domain and dephosphorylates β-catenin. Inhibition of PTP1B interrupted adhesion to E-cadherin-Fc of MDCK cells expressing WT β-catenin but did not affect the adhesion of MDCK cells expressing Y489F or Y654F β-catenin. Similarly, inhibition of PTP1B compromised the TER of MDCK cells expressing WT β-catenin but did not affect the TER of MDCK cells expressing Y489F or Y654F β-catenin. We conclude that phosphorylation of tyrosines 489 and 654 in β-catenin is a necessary step in the process by which G protein-coupled H1 and PAR-2 receptors interrupt E-cadherin adhesion. We also conclude that activation of PAR-2 has no effect on the TER without first interrupting E-cadherin adhesion.

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