Differential Role of Nonmuscle Myosin II Isoforms in Bleb Formation in MCF‐7 Cells

Abstract

Previous reports suggest that cortical tension plays an important role in bleb formation. Bleb formation has been correlated with Nonmuscle myosin II (NM‐II) activity as inhibition of NM‐II activity leads to decrease in cortical tension and thereby inhibits bleb formation. Whether, three isoforms of NM‐II (NM‐IIA, ‐IIB, and ‐IIC) have same or differential role in bleb formation is not well understood. Here, we report that ectopically expressed GFP‐tagged NM‐II isoforms exhibit different types of membrane protrusions such as multiple blebs, lamellipodia, and combination of both or without having any protrusions in a human breast tumor cell line MCF‐7 as revealed by time lapse video microscopy. Quantification suggests that 49% of GFP‐NM‐IIA, 26% of GFP‐NM‐IIB and 19% of GFP‐NM‐IIC1 expressing MCF‐7 cells show multiple bleb formation. Interestingly, expression of phospho‐dead mutant of regulatory light chain (RLC), but not the phospho‐mimic or wild‐type, could reduce the multiple bleb formation to 8% in MCF‐7 cells. When we induce the bleb formation by disruption of cortex using 405 nm laser light, we find that all the three GFP‐tagged NM‐II isoforms can re‐appear and form filaments at different degree into the growing bleb. GFP‐NM‐IIB can form filament into the blebs in 48 % of GFP‐NM‐IIB expressing cells compared with GFP‐NM‐IIA and ‐IIC1 which form filament only in 10 % and 3 % of GFP‐NM‐IIA and GFP‐NM‐IIC1 expressing cells, respectively. These studies suggest that myosin IIs have differential role in bleb dynamics.Source of research support:Indian Association for the Cultivation of Science, India