Monensin treatment enhances mutant EGFR-Src colocalization in endocytic vesicles. (A) Cells were either growth factor-deprived or left in regular growth medium for 48 hr and incubated with DMSO or 10 μM monensin for 3 hr. Cells were fixed, permeabilized, and immunostained with anti-EGFR antibody 528 (green) followed by anti-Src antibody SRC2 (red) staining. Images were acquired under a confocal microscope at the medial plane. Bars represent 20 μm. (B) Colocalization coefficients for the red channel (anti-Src staining) were obtained using LSM510 Image Examiner software and normalized to the colocalization coefficient from DMSO controls.