Proteasomes are protease complexes which are responsible for degrading endogenous proteins. Proteins to be destroyed are recognized by proteasomes because of the presence of ubiquitin conjugated to the targeted protein. The ubiquitin-proteasome pathway plays an essential role in regulating the intracellular concentration of specific proteins, thereby maintaining homeostasis within cells. Proteasome inhibitors prevent this targeted decomposition of protein, which can affect multiple signaling cascades within the cell. This disruption of normal homeostatic mechanisms can lead to cell death. Proteasome inhibitors may be used to treat multiple myeloma and certain types of lymphoma.