Fig. 3.
Loss of function of the tumor suppressors Axin or APC trigger macropinocytosis of high molecular weight TMR-dextran 70 kDa, GSK3 and PRMT1 translocation to vesicles, and increased degradation of extracellular BSA protein in lysosomes. (A–D) Depletion of Axin or APC with siRNA triggered an increase in macropinocytosis marked by TMR-dextran 70 kDa in NIH 3T3 cells. Note that although Axin and APC are components of the β-catenin destruction complex, they also function as repressors of macropinocytosis. (E–J) APC induces localization of PRMT1 and GSK3 in vesicles in HeLa cells; GSK3 and PRMT1 sequestration are essential steps in canonical Wnt signaling. (K–N) Still images from Movie S2 showing that the colon cancer cell line SW480 had high BSA-DQ utilization within 30 min of addition, which was greatly reduced when full-length APC was restored in an isogenic cell line (SW480APC). (O–R) Similar experiment using the macropinocytosis tracer TMR-dextran 70 kDa. (S) Quantification of BSA-DQ digestion per SW480 or SW480APC cell. (T) Quantification of macropinocytosis of TMR-dextran 70 kDa in SW480 cells and its inhibition by restoration of APC. **P < 0.01. (Scale bars, 10 μm.)