PKC delta and cofilin activation affects peripheral actin reorganization and cell-cell contact in cells expressing integrin alpha 5 but not its tailless mutant

Abstract

Integrin-mediated cell adhesion transduces signaling activities for actin reorganization, which is crucially involved in cellular function and architectural integrity. In this study, we explored the possibility of whether cell-cell contacts might be regulated via integrin-alpha 5 beta 1-mediated actin reorganization. Ectopic expression of integrin alpha 5 in integrin-alpha 5-null intestinal epithelial cells resulted in facilitated retraction, cell-cell contact loss, and wound healing depending on Src and PI3K ( phosphoinositide 3-kinase) activities by a reagent that affects actin organization. However, cytoplasmic tailless integrin alpha 5 (hereafter referred to as alpha 5/1) expression caused no such effects but rather sustained peripheral actin fibers, regardless of Src and PI3K signaling activities. Furthermore, integrin alpha 5 engagement with fibronectin phosphorylated Ser643 of PKC delta, upstream of FAK and Src and at a transmodulatory loop with PI3K/Akt. Pharmacological PKC delta inactivation, dominant-negative PKC delta adenovirus or inactive cofilin phosphatase (SSH1L mutant) retrovirus infection of alpha 5-expressing cells sustained peripheral actin organization and blocked the actin reorganizing-mediated loss of cell-cell contacts. Meanwhile, wild-type PKC delta expression sensitized alpha 5/1-expressing cells to the actin disruptor to induce cell scattering. Altogether, these observations indicate that integrin alpha 5, but not alpha 5/1, mediates PKC delta phosphorylation and cofilin dephosphorylation, which in turn modulate peripheral actin organization presumably leading to an efficient regulation of cell-cell contact and migration.