Figure 3.

Cortactin is necessary for IL-2Rβ and for transferrin endocytosis. (A) Hep2β cells transfected with a dominant-negative mutant of cortactin, Flag-Cort^SH3 (green). (B) Cells treated with control small interfering RNA (siRNAC). (C) Cells treated with siRNA against cortactin (siRNACort). (A–C) Endocytosis and immunofluorescence were carried out as described in Fig 1A (asterisks indicate the cells expressing Cort^SH3). Nuclei were stained with Hoechst (purple). (D) Quantification of IL-2Rβ and Tf endocytosis was carried out as described in Fig 2C. (E) Western blots of siRNA-transfected cells were probed with antibodies against cortactin or flotillin 2 (Flot2) as a control; quantification by Storm FluoroImager. IL-2Rβ, interleukin-2 receptor β; Pak, p21-activated kinase; Rac1, Ras-related C3 botulinum toxin substrate 1; Tf, transferrin.