MEK/ERK regulates adherens junctions and migration through Rac1

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Polyamine depletion using alpha-difluoromethyl ornithine (DFMO) inhibits intestinal epithelial cell migration by preventing Rac1 activation and actin cortex formation.
• Epidermal Growth Factor (EGF) signaling is crucial for cell migration and junction dynamics.

Purpose of the Study:

• To investigate the role of MEK1/ERK and Rac1 in regulating cell-cell contacts and migration during polyamine depletion.
• To elucidate the upstream regulators of Rac1 activation in intestinal epithelial cells.

Main Methods:

• Utilized DFMO for polyamine depletion.
• Employed MEK inhibitors (U0126) and constitutively active MEK1 (CA-MEK) and Rac1 (CA-Rac1) expression.
• Assessed cell-cell contacts, actin cytoskeleton organization, and protein expression (E-cadherin, beta-catenin) via immunolocalization, western blotting, and subcellular fractionation.
• Investigated the role of Tiam1 using a specific inhibitor (NSC23766).

Main Results:

• EGF-induced Rac1 activation, cell dissociation, and migration were observed in both control and polyamine-depleted cells.
• MEK inhibition prevented EGF-induced Rac1 activation and junction disruption.
• CA-MEK expression altered cell-cell contacts in both conditions.
• CA-Rac1 expression restored beta-catenin localization, prevented actin cortex formation, and induced stress fibers in polyamine-depleted cells.
• Tiam1 inhibition mimicked the effects of polyamine depletion on beta-catenin and actin.
• Polyamine depletion reduced E-cadherin and beta-catenin expression.

Conclusions:

• EGF signaling through MEK1/ERK activates Rac1, regulating cell-cell contacts.
• Polyamine depletion decreases intestinal cell migration by inhibiting Tiam1-mediated Rac1 activation, leading to reduced beta-catenin and E-cadherin expression and impaired cell-cell contacts.