title: MEK/ERK regulates adherens junctions and migration through Rac1.
abstract: Polyamine depletion with the ornithine decarboxylase inhibitor alpha-difluoromethyl ornithine (DFMO), prevents Rac1 activation causing the formation of a thick actin cortex at the cell periphery and inhibits migration of intestinal epithelial cells. In the present study, we demonstrate that MEK activation by EGF increased Rac1 activation, dissociation of intercellular contacts, and migration in both control and polyamine-depleted cells, while U0126, a specific inhibitor of MEK1, prevented disruption of junctions as well as EGF-induced Rac1 activation. Constitutively active MEK1 (CA-MEK) expression altered cell-cell contacts in control and polyamine depleted cells. The expression of constitutively active Rac1 (CA-Rac1) restored beta-catenin to the cell periphery and prevented the formation of actin cortex and caused the appearance of F-actin stress fibers in polyamine-depleted cells. Inhibition of Rac activation by NSC23766, a specific inhibitor of Tiam1, an upstream guanidine nucleotide exchange factor for Rac1, reproduced the beta-catenin localization and actin structure of polyamine-depleted cells. Tiam1 localized more extensively with beta-catenin at the cell periphery in CA-Rac1 cells compared to vector cells. Polyamine depletion decreased the expression of E-cadherin to a greater extent compared to beta-catenin. Subcellular fractionation further confirmed our immuno-localization and western blotting observations. These data suggest that EGF acting through MEK1/ERK to activate Rac1 regulates cell-cell contacts. Thus, decreased migration in polyamine depleted cells may be due to the inhibition of Tiam1 activation of Rac1 and the subsequent decreased expression of beta-catenin and E-cadherin leading to reduced cell-cell contacts.
authors.affiliation: Department of Physiology, The University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA. rray@physiol.utmem.edu
authors.forename: Ramesh M
authors.initials: RM
authors.lastname: Ray
authors.forename: Rajiv J
authors.initials: RJ
authors.lastname: Vaidya
authors.forename: Leonard R
authors.initials: LR
authors.lastname: Johnson
mesh_terms: D000199:Actins / Q000378:metabolism; D022005:Adherens Junctions / Q000187:drug effects / Q000201:enzymology*; D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D015820:Cadherins / Q000378:metabolism; D002448:Cell Adhesion / Q000187:drug effects; D002450:Cell Communication / Q000187:drug effects; D002465:Cell Movement / Q000187:drug effects; D003599:Cytoskeleton / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D011073:Polyamines; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D051176:beta Catenin / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000199:Actins; D002070:Butadienes; D015820:Cadherins; D020662:Guanine Nucleotide Exchange Factors; D009363:Neoplasm Proteins; D009570:Nitriles; D011073:Polyamines; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513259:Tiam1 protein, rat; C113580:U 0126; D051176:beta Catenin; D004815:Epidermal Growth Factor; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1; D020830:rac1 GTP-Binding Protein