Immunologic aspects of protein degradation by the ubiquitin-proteasome system.

The ubiquitin-proteasome pathway has a central role in selective degradation of intracellular proteins. Among the key proteins degraded by the system are those involved in the control of inflammation, cell cycle regulation and gene expression. With numerous important cellular pathways affected, derangements in the ubiquitin system were shown to result in a variety of human diseases including malignancies, neurodegenerative diseases and hereditary syndromes, and proteasome inhibition was implicated as a potential treatment for cancer and inflammatory conditions. Two proteasome inhibitors are currently under clinical evaluation for multiple myeloma and acute ischemic stroke. The ubiquitin system also has an important function in the immune and inflammatory response. It is involved in antigen processing and presentation to cytotoxic T cells, and the activation of nuclear factor-kappa B--the central transcription factor of the immune system. Since the proteasome is the central source of antigenic peptides that are presented to the immune system, some viruses, such as the Epstein-Barr virus, developed escape mechanisms that manipulate the ubiquitin-proteasome system in order to persist in the infected host. Understanding the mechanisms underlying the production of viral antigens by the ubiquitin-proteasome system may have therapeutic applications such as future development of vaccines.