SEPT9 promotes perinuclear clustering of lysosomes in HeLa cells under oxidative stress. (A) Images show SEPT9-stained HeLa cells after transfection with plasmids that coexpress GFP (magenta) and scramble or SEPT9 shRNAs. Scale bars, 20 µm. (B) Bar graph shows mean (± SEM; Mann–Whitney U test) fluorescence intensity of SEPT9 per shRNA-expressing cell (n = 65–66). ***, P < 0.001. A.U., arbitrary units. (C) HeLa cells were transfected with plasmids that coexpress shRNAs (scramble control or SEPT9) and GFP or shRNA-resistant SEPT9-GFP (wild type or T339G mutant; magenta). After treatment with NaAsO₂ (400 µM) for 1 h, cells were stained with antibodies against LAMP1 (green). Representative images show LAMP1 (green) and GFP or SEPT9-GFP (magenta). Arrows point to lysosomes that localize to the periphery of SEPT9-depleted and SEPT9(T339G)-GFP–expressing cells. Quantifications of lysosome localization are shown in Fig. 5, F and G. Scale bars, 20 µm.