PM blebbing triggers nuclear accumulation of MRTF-A. (A) Live MCF10A cells stably expressing MRTF-A–GFP together with LifeAct-mCherry were plated on poly-HEMA, and MRTF-A–GFP subcellular localization was monitored over time. LifeAct-mCherry is shown for each frame to visualize PM blebbing. Arrows highlight a cell showing dynamic oscillations of nuclear redistribution of MRTF-A–GFP in response to PM blebbing. Bars, 5 µm. (B) Quantification of MRTF-A–GFP subcellular localization in blebbing versus nonblebbing cells as in A. 180 cells from at least six experiments. (C) Live cells were imaged as in A. To interfere with cortical contractility and PM blebbing, cells were treated with 100 µM blebbistatin at 0 min, and MRTF-A–GFP subcellular localization was monitored over time. Coexpression of the actin marker LifeAct-mCherry reveals inhibition of membrane bleb activity. Asterisks indicate cytosolic redistribution of MRTF-A–GFP. Bars, 5 µm. (D) Quantification of MRTF-A–GFP subcellular localization in MCF10A cells treated with or without blebbistatin as indicated. (B and D) Localization was scored as predominantly cytoplasmic (C), pancellular (N/C), or predominantly nuclear (N). 200 cells from at least six experiments. Error bars indicate SD.