Internalization of Aα17-83 requires caveolin-1. (A-F) Intracellular localization of α2-macroglobulin/α2–M with FITC-labeled α2-M–antibody, FITC-labeled Aα17-83, and caveolin-1 with Cy3-conjugated anti-cav1–antibody in MEF (A-E) and JEG3 cells (F) by confocal fluorescence microscopy. Aα17-83 colocalizes with caveolin-1. (G-H) MEF prepared from cav1−/− embryos were cultured for 48 hours in the presence of 2 μM Aα17-83 (G) or 20 μM 17-37–TAT, followed by TUNEL staining. Cav1-deficient MEFs are resistant to apoptosis induced by Aα17-83; but not Aα17-37–TAT. Bars represent 20 (A-E), 50 (F), or 200 μm (G,H).