English: Supplementary Movie 2 Pk1 is required for lateral polarity of migrating cells. MDA-MB-231 cells stably expressing YFP-actin were transfected with siRNA targeting Pk1. Three days later, the cells were treated with ACM and time-lapse image acquisition was initiated at 4 hours after treatment using spinning-disc confocal microscopy (6 sec intervals, 70 frames, 5 fps).