Myosin-Ie drives ruffle-edge lamellipodia formation and motility in A549 invasive lung cancer cells.

Lamellipodia are generally defined as thin, sheet-like cell protrusions that constitute the actin cytoskeleton-based motile apparatus, which promotes the movement of migrating cells. Recently, we identified a novel type of lamellipodia, termed ruffle-edge lamellipodia, which have α-actinin-4 (ACTN4)-enriched multilayer membrane folds at their leading edges in certain invasive cancer cell lines. In this study, the role of unconventional myosin-Ie (Myo1E) in ACTN4-enriched ruffle-edge lamellipodia was analyzed using live-cell, immunofluorescence, and scanning electron microscopy. Immunofluorescence microscopy for endogenous Myo1E and live-cell imaging of mApple-Myo1E expressing cells showed that Myo1E was localized to ACTN4-rich lamellipodia tips in A549 cells. The wound healing assay and live-cell movies showed that Myo1E siRNA knockdown significantly suppressed cell migration and ruffle-edge lamellipodia formation. Furthermore, scanning electron microscopy demonstrated that Myo1E knockdown significantly reduced ruffle-edge structures. These results suggest that Myo1E may play an important role not only in the motility of ruffle-edge lamellipodia but also in the construction of ruffle-edge structures, which are probably associated with cancer cell invasion and metastasis.