APC-M2 pAb immunofluorescence signal reduced by APC-shRNA. (A) U2OS cells transfected for 48 hours with negative control shRNA or one of two individual shRNA plasmids specific for APC were probed using APC-M2 pAb. GFP (green) expression from the shRNA vector marks transfected cells. Expression of either shRNA-APC number 5 or 6 resulted in reduction of the majority of the nuclear and cytoplasmic APC-M2 pAb signal. Scale bar, 5 μm. (B) Immunofluorescence microscopy using APC-M2 pAb to probe HCA46 cells, null for APC (upper panel), or purified rabbit IgG to probe HCT116βw cells (lower panel) reveals only minimal signal. Scale bars, 5 μm.