Lysosomal protein turnover contributes to the acquisition of TGF?-1 induced invasive properties of mammary cancer cells
15.02.2015
Kern U, Wischnewski V, Biniossek ML, Schilling O, Reinheckel T.
Mol Cancer. 2015 Feb 15;14(1):39
Epithelial-to-mesenchymal transition (EMT) is a process of considerable cellular reorganization by which normal epithelial cells and carcinoma cells can acquire motility. In cellular remodeling processes the endosomal/lysosomal compartment is a principal site of intracellular protein degradation. We hypothesized that the largest group of lysosomal proteases, the cysteine cathepsins, whose role in cancer cell dissemination has been established, affect transforming growth factor ?-1 (TGF?-1)-induced EMT of normal and malignant murine mammary epithelial cells. Addition of the general cysteine cathepsin inhibitor E64d had no effect on the induction of the TGF?-1-induced EMT program on transcriptional level. Protease inhibition did not affect invasion of TGF?-1 treated normal mammary epithelial cells, but reduced the invasion of murine breast cancer cells. Remarkably, the reduced invasion was also evident if E64d was removed 24h before the invasion assay in order to allow for recovery of cathepsin activity. Proteome analyses by stable isotopic labeling with amino acids in culture (SILAC) revealed a high abundance of lysosomal enzymes and lysosome-associated proteins in cancer cells treated with TGF?-1 and E64d. An accumulation of those proteins and of lysosomal vesicles was further confirmed by independent methods. Interestingly, E64d caused lysosomal accumulation of the junctional adhesion molecule A (Jam-a), a tight junction component facilitating epithelial cell-cell adhesion. In summary our results demonstrate an important role of lysosomal proteolysis in cellular remodeling during EMT and the acquisition of an invasive phenotype of breast cancer cells.
