Abstract
Intracellular protein breakdown plays a pivotal role in cell biology. This process is involved in the control of essential cellular functions such as progression through the cell cycle, differentiation, apoptosis and the production of antigenic peptides. Thereby, proteolysis influences the organism's physiology, particularly at the level of organogenesis, morphogenesis, vascularization and the immune response. It is thus not surprising that intracellular proteolysis impairment contributes to oncogenesis. Recent literature has shown that the degradation of various proto-oncogenic and onco-suppressive proteins is altered in many cancer situations, and that some components of the intracellular proteolytic systems are also proto-oncoproteins or onco-suppressive proteins. The diversity of the proteolytic mechanisms affected in tumors can be illustrated through several examples involving the ubiquitin/proteasome system, which constitutes the main intracellular protein destruction pathway.