Proteolysis, the ubiquitin-proteasome system, and renal diseases

Protein degradation is a critical process for the growth and function of cells. Proteolysis eliminates abnormal proteins, controls many cellular regulatory processes, and supplies amino acids for cellular remodeling. When substrates of proteolytic pathways are poorly recognized or there is mistiming of proteolysis, profound changes in cell function can occur. Based on these potential problems, it is not surprising that alterations in proteolytic enzymes/cofactors or in the structure of protein substrates that render them more or less susceptible to degradation are responsible for disorders associated with kidney cell malfunctions. Multiple pathways exist for protein degradation. The best-described proteolytic system is the ubiquitin-proteasome pathway, which requires ATP and degrades the bulk of cellular and some membrane proteins. This review will survey examples of renal abnormalities that are associated with defective protein degradation involving the ubiquitin- proteasome pathway. Loss of muscle mass associated with chronic renal failure, von Hippel-Lindau disease, Liddle syndrome, and ischemic acute renal failure will be discussed. These examples are indicative of the diverse roles of the ubiquitin-proteasome system in renal-associated pathological conditions.