Switching between blebbing and lamellipodia depends on the degree of Nonmuscle Myosin II activity.

Cells can adopt both mesenchymal and amoeboid mode of migration through membrane protrusive activities, namely lamellipodia and blebbing. How the molecular players control the transition between lamellipodia and blebbing is yet to be explored. Here, we show that addition of ROCK inhibitor, Y27632 or lower doses of (-) blebbistatin, an inhibitor of NMII ATPase activity and filament partitioning, induces blebbing to lamellipodia conversion (BLC), whereas addition of lower doses of ML7, an inhibitor of MLCK, induces lamellipodia to blebbing conversion (LBC) in human MDA-MB-231 cells. Similarly, siRNA mediated knockdown of ROCK and MLCK induces BLC and LBC, respectively. Interestingly, both blebbing and lamellipodia membrane protrusion are able to maintain pRLC/RLC ratio at cortices when MLCK and ROCK are inhibited, respectively, either pharmacologically or genetically, suggesting that they are interlinked in BLC and LBC. Such BLC and LBC are also inducible in other cells like MCF7 and MCF10A. These studies reveal that relative activity of ROCK and MLCK, which controls both NMII's ATPase activity and filamentous property is a determining factor for a cell to exhibit blebbing or lamellipodia.