MEK/ERK regulates adherens junctions and migration through Rac1

Abstract

Polyamine depletion with the ornithine decarboxylase inhibitor a-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 b-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 b-catenin localization and actin structure of polyamine-depleted cells. Tiam1 localized more extensively with b-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 b-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 b-catenin and E-cadherin leading to reduced cell-cell contacts. Cell Motil.

Radixin regulates cell migration and cell-cell adhesion through Rac1

“…The changes induced by radixin depletion are dependent on Rac1 since Rac1 knockdown inhibits the radixin knockdown-induced increase of cell area, and expression of constitutively active Rac1 induces cell spreading and N-cadherin accumulation at cell-cell contacts. The role of Rac1 in inducing and maintaining adherens junctions is well established (Hage et al, 2009;Ray et al, 2007), and thus increased Rac1 activity could explain the high level of adherens junctions in radixin-depleted cells. Several RacGEFs have been implicated in adherens junction assembly.…”

Polyamine-dependent activation of Rac1 is stimulated by focal adhesion-mediated Tiam1 activation

“…Rac1 activity was determined by pull down assay as described previously. 36,37 GST-PAK fusion protein bound with the glutathione agarose beads was mixed with cell lysate (200 µg). The binding was allowed to proceed for 1.5 h at 4°C, the beads were washed with lysis buffer and the amount of GTP-Rac1 bound was analyzed by SDS-PAGE and western blot using Rac1 specific antibody.…”

Role of the Guanine Nucleotide Exchange Factor Ost in Negative Regulation of Receptor Endocytosis by the Small GTPase Rac1

“…EGF is known to induce Rac1 activation in various cell types including HeLa cells (25,26), and thus, we examined the effect of EGF pretreatment on transferrin receptor endocytosis. Transferrin receptor endocytosis was in fact inhibited by 30-min pretreatment with EGF ( Fig.…”