Inhibition of clathrin-mediated endocytosis reduces PFN- and GzmB-mediated apoptosis, but does not alter the extent of CTL-mediated death. (A-B) Chemical inhibitors of clathrin-mediated endocytosis decrease PFN- and GzmB-induced apoptosis. HeLa cells were preincubated with or without hypertonic sucrose or Dynasore before treatment with buffer or sublytic rPFN and/or GzmB. Apoptosis was measured 2 hours later by caspase activation by labeling with M30 monoclonal antibody. Representative flow cytometric histogram (A) and mean ± SD from 3 independent experiments (B) are depicted. **P < .005 relative to control siRNA–treated cells. (C-D) Specific inhibition of Dyn/clathrin-mediated endocytosis with siRNAs decreases PFN- and GzmB-induced apoptosis. HeLa cells were transfected with indicated siRNAs before treatment with rPFN and/or GzmB and apoptosis was measured as in panels A and B. Representative flow cytometric histogram (C) and mean ± SD from 3 independent experiments (D) are shown. **P < .005 relative to control siRNA–transfected cells. (E) Inhibition of Dyn/clathrin-mediated endocytosis does not interfere with overall CTL-induced cell death evaluated by ⁵¹Cr release assay. HeLa cells transfected with indicated siRNAs were incubated for 4 hours with specific CTLs. The data (mean ± SD) were obtained from 2 independent experiments performed in triplicate.