Protrusions observed in MCF10A cells at different concentrations of the Arp2/3 inhibitor, CK-869.

(A) Phase contrast images of the protrusion phenotypes observed. A broad lamellipodia that remains stable for ∼1 hr drives persistent migration in wild type cells (Stable LP). Small (1 µm) and dynamic blebs drive local protrusions in cell treated with 50 µM CK-869. Unstable, lamellipodia-like protrusions (Unstable LP) drive local protrusion in cell treated with 50 µM CK-869 over ∼10 min time periods. Protrusions are unstable and appear as a travelling wave along the cell periphery. Large pseudopodial protrusions rapidly extend ∼30 µm over ∼30 min but are unstable and retract shortly thereafter. Red line indicates protrusion of interest for each phenotype. Scale bar is 25 µm. (B) Percentage of cells exhibiting the protrusion phenotype described in A for untreated cells, cells treated with 12.5, 25 and 50 µM of CK-869, 50 µM CK-312 or cells transfected with Arp3 siRNA n = 39, 30, 24, 21 and 27 cells respectively, (C) Box plot of protrusion rate for untreated cells, cells treated with 12.5, 25 and 50 µM of CK 312, and cells treated with 12.5, 25 and 50 µM of CK-869 and imaged for 16 hours. Square  =  mean, X = 1% and 99% quantile. Box is median and SD. n = 39, 13, 14, 17, 30, 24 and 21 cells respectively; NS, not significant; **, P<0.01; ***, P<0.001 with respect to WT or control.