One of the identified hallmarks of cancer is the evasion of apoptosis (65). Glioma cells have been observed to exhibit reversible membrane blebbing, a phenomenon in which increased hydrostatic pressure drives cytoplasm through local ruptures in the actin cortex (66). It has recently been reported that blebbing cells exist in a state of simultaneous hypercontractility and reduced actin polymerization, but when corrected through the use of various cytoskeletal drugs, these same cells can revert to pseudopodial/lamellipodial protrusions (67). Previous work in our group has shown that blebbing ceases when the cell takes on a spread area >1400 mm2 (38). Taken together, these works suggest that blebbing can be reduced in the absence of drugs via prolonged subfailure stretch.
Thus, a step strain was applied to single-blebbing Denver Brain Tumor Research Group (DBTRG-05MG) cells and was held constant while cells transitioned from blebbing to lamellipodia (Movie S8; Fig. 6 b). Onset of transition, evidenced by the first observed force decrease, required ~5–10 min to take place. Upon initializing transition, blebbing ceased and lamellipodia were observed after another 200–400 s. This transition was marked by decreased cell contractility wherein the average force reduced by ~20 nN (40% of blebbing force; n ¼ 11). These tests confirm that hypercontractility is partially responsible for producing blebs, and we believe that this demonstrates the mechanical stretch-based quantification of forces involved in this
reversal for the first time.