Figure 2. Oncogenic K-Ras-induced macropinocytosis in NIH 3T3 cells mediates the internalization of extracellular albumin that is subsequently targeted for proteolytic degradation.

a, TMR-dextran (red) is internalized at higher levels in NIH 3T3 [K-Ras^V12] cells (K-Ras^V12, top panel) compared to untransformed control cells (CTL, bottom panel). b, Quantification of macropinocytic uptake in control cells and NIH 3T3 [K-RasV12] cells incubated with vehicle (DMSO) or with 75 μM EIPA. Data are presented relative to the values obtained for the untransformed control cells. Error bars indicate mean +/− SEM for n=3 independent experiments with at least 300 cells scored per experiment. Statistical significance was determined via t-test; **p<0.01, ***p<0.001. c, FITC-BSA (green) is internalized into discrete puncta that co-localize (white arrowheads) with TMR-dextran (red). d, FITC-BSA uptake is abrogated by treatment with 75 μM EIPA. e, Analysis of DQ-BSA fluorescence in NIH 3T3 [K-Ras^V12] cells that were co-incubated with DQ-BSA (green) and TMR-dextran (red) and fixed either immediately (T=0) or following a 1 hour chase. The fluorescent signal emanating from DQ-BSA (T=1 HOUR) is an indication of albumin degradation. Insets represent a higher magnification of the boxed areas. Images shown in c, d and e are representative of at least 3 independent experiments.