Expression of functional integrin α_E(CD103)β₇ influences the cellular shape and induces filopodia formation in a ligand-dependent fashion in vitro. (A) Wild-type or mutant α_E(CD103) subunits were fused to YFP as outlined in “Plasmids.” K562 cells were cotransfected with the wild-type β₇ subunit and either wild-type α_E(CD103)/YFP, α_E-open/YFP, α_E-closed/YFP, or YFP alone as indicated. Adhesion experiments (determined as bound cells/20× field, n = 3 experiments) performed on E-cadherin– or FCS-coated surfaces demonstrate the functionality of the integrin α_E-YFP-fusion-proteins. (B) K562 cells cotransfected with wild-type α_E(CD103)/YFP and β₇ subunits were plated on E-cadherin in the presence of a control mAb or a mAb directed against α_E(CD103). Images were taken by confocal microscopy in z-stacks (top panels) and phase contrast microscopy (bottom panels). Arrows indicate examples of protrusions/filipodia in the E-cadherin contact zone. (C) The indicated transfectants were seeded on E-cadherin, and the formation of filopodia was monitored by confocal microscopy. The E-cadherin contact zone of a representative cell for each condition is shown. Scale bar = 10 μm. (D) The indicated transfectants were mixed and cocultured with PAM212 keratinocytes. Analysis was performed by confocal microscopy in z-steps of 0.2 to 0.5 μm. One section within the contact zone between the K562 and PAM212 is depicted, in the top row the fluorescence and in the bottom row the phase contrast image of the cells. Arrows indicate examples of protrusions/filopodia extended toward the keratinocytes. Scale bar = 10 μm.