Figure 6.

Internalized LDL and the acidotropic probe LysoTracker Red accumulate in perinuclear EGFP-Rab7 wt–associated lysosomes in live cells. Live HeLa cultures with EGFP-Rab7 wt–expressing cells were incubated for 2 h at 37°C in the presence of fluorescent DiI-LDL (A–C) or for 30 min at 37°C with LysoTracker Red (D–I). Green corresponds to EGFP (A, D, and G), whereas red is DiI-LDL in B and LysoTracker Red in E and H. C, F, and I represent the merged images, where yellow shows colocalization. It is seen that the perinuclear lysosome aggregate associated with EGFP-Rab7 wt is acidic and accumulates endocytosed LDL. J is a higher magnification of the merged image shown in I. In particular, the larger vesicular structures are distinctly double labeled for EGFP and LysoTracker Red, with the EGFP signal appearing as a ring corresponding to the lysosome perimeter surrounding the acidic, lumenal LysoTracker Red signal. Bars, 20 μm.