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Châtenay-Malabry, France

Yue W.,INSE RM U984 | Yue W.,University Paris - Sud | Hamai A.,INSE RM U984 | Hamai A.,University Paris - Sud | And 10 more authors.
Autophagy | Year: 2013

Breast cancer tissue contains a small population of cells that have the ability to self-renew; these cells are known as cancer stem-like cells (CSC s). We have recently shown that autophagy is essential for the tumorigenicity of these CSC s. Salinomycin (Sal), a K+/H+ ionophore, has recently been shown to be at least 100 times more effective than paclitaxel in reducing the proportion of breast CSC s. However, its mechanisms of action are still unclear. We show here that Sal blocked both autophagy flux and lysosomal proteolytic activity in both CSC s and non-CSC s derived from breast cancer cells. GFPLC3 staining combined with fluorescent dextran uptake and LysoTracker-Red staining showed that autophagosome/ lysosome fusion was not altered by Sal treatment. Acridine orange staining provided evidence that lysosomes display the characteristics of acidic compartments in Sal-treated cells. However, tandem mCherry-GFP-LC3 assay indicated that the degradation of mCherry-GFP-LC3 is blocked by Sal. Furthermore, the protein degradation activity of lysosomes was inhibited, as demonstrated by the rate of long-lived protein degradation, DQ-BSA assay and measurement of cathepsin activity. Our data indicated that Sal has a relatively greater suppressant effect on autophagic flux in the ALDH+ population in HMLER cells than in the ALDH- population; moreover, this differential effect on autophagic flux correlated with an increase in apoptosis in the ALDH+ population. ATG7 depletion accelerated the proapoptotic capacity of Sal in the ALDH+ population. Our findings provide new insights into how the autophagy-lysosomal pathway contributes to the ability of Sal to target CSC s in vitro. © 2013 Landes Bioscience.

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