Munc13-4 KD strongly impairs exosome release. (A) SDS-PAGE Western blot of indicated proteins in MDA-MB-231 cells after stable expression of shRNA for Munc13-4 or Rab27a or a scrambled control (Ctrl). (B) Culture medium from MDA-MB-231 cells either untreated or stimulated with 1.25 µM ionomycin for 30 min was centrifuged at 1,000 g to remove cellular debris and 10,000 g to remove large extracellular vesicles. (C) The resulting 10,000-g supernatant was filtered onto a nitrocellulose membrane and analyzed for CD63, CD9, ALIX, and GM130 content by antibody blotting. (D) Quantification of CD63, CD9, and ALIX blots in C are shown as exosome release as a percentage of total cellular material with mean values ± standard error (SE) for n ≥ 3. *, P < 0.05 for comparison with corresponding control samples. (E) Panc-1 or A549 cells were left untreated or were treated with TGFβ-1 for 24 h. Indicated proteins were detected by SDS-PAGE Western blot. (F) Panc-1 cells were left untreated or were treated with TGFβ-1 for 24 h, and Munc13-4 levels were determined by immunofluorescence. TGFβ-1–treated cells exhibited a mesenchymal morphology. Bars, 5 μm. (G) A549 cells stably expressing control shRNA (Ctrl) or Munc13-4 shRNA were left untreated (Untr) or were treated with TGFβ-1 for 24 h, and SDS-PAGE Western blotting for indicated proteins was conducted. (H) Culture media supernatants (as in B) from A549 cells that were either untreated or were stimulated with 1.25 µM ionomycin for 30 min were filtered onto nitrocellulose membrane and analyzed for CD63 and GM130. (I) Quantification of CD63⁺ exosome release shown as a percentage of total cellular material with mean values ± SE for n = 5. *, P < 0.05; **, P < 0.01 for comparison with corresponding control samples.