PKCɛ Regulation of an α 5 Integrin–ZO-1 Complex Controls Lamellae Formation in Migrating Cancer Cells

Phosphorylated ZO-1 relocalizes from tight junctions to lamellae to associate with α 5 integrin and control migration. The tight junction protein ZO-1 (zonula occludens-1) is involved in cell-cell adhesion, whereas integrins containing the α 5 integrin subunit mediate both cell-cell and cell-matrix adhesion. Alterations in the abundance of ZO-1 and α 5 are correlated with increased invasiveness in lung cancer cells. Through biochemical, RNA interference, and imaging techniques, Tuomi et al. found that ZO-1 and α 5 interacted at the leading edge of migrating lung cancer cells, where the complex promoted lamellae formation and motility. Protein kinase Cɛ (PKCɛ) promoted the phosphorylation of ZO-1 at Ser 168 , which triggered the relocalization of ZO-1 from tight junctions to lamellae. The ZO-1–α 5 complex was detected only in migrating cells in vitro and, intriguingly, was also present only in a subset of cells in metastatic lung tumors, suggesting that ZO-1 and α 5 integrin may be involved in motility and invasion in vivo. Disruption of intercellular adhesions, increased abundance of α 5 β 1 integrin, and activation of protein kinase Cɛ (PKCɛ) correlate with invasion and unfavorable prognosis in lung cancer. However, it remains elusive how these distinct factors contribute to the invasive behavior of cancer cells. Persistent cell motility requires the formation of stable lamellae at the leading edge of a migrating cell. Here, we report that the tight junction protein zonula occludens-1 (ZO-1) preferentially interacts with α 5 β 1 integrin at the lamellae of migrating cells. Disruption of ZO-1 binding to an internal PDZ-binding motif in the α 5 cytoplasmic tail prevented the polarized localization of ZO-1 and α 5 at the leading edge. Furthermore, silencing of α 5 integrin inhibited migration and invasion of lung cancer cells, and silencing of ZO-1 resulted in increased Rac activity and reduced directional cell motility. The formation of the α 5 –ZO-1 complex was dependent on PKCɛ: Phosphorylation of ZO-1 at serine-168 regulated the subcellular localization of ZO-1 and thus controlled its association with α 5 integrin. In conclusion, PKCɛ activation drives the formation of a spatially restricted, promigratory α 5 –ZO-1 complex at the leading edge of lung cancer cells.