Lysosomal proteases and their role in signaling pathways

Lysosomes contain more than 50 acid hydrolases and are the major location for degradation of both intracellular and extracellular macromolecules. However, lysosomes also play a key role in cell signaling processes, for example, trafficking via the endosomal/lysosomal pathway, regulation of autophagy, growth factor degradation, and through their involvement in antigen presentation. In this chapter, we summarize the classification of lysosomal proteases and their roles in cell signaling, with particular focus on the cysteine, serine, and aspartic cathepsins. In addition, we summarize how disruption of these processes may be linked to specific diseases, including neurodegenerative disease, cardiovascular disease, cancer, and inflammation.