Ubiquitin-Independent Proteasomal Degradation Mediated by Antizyme

Most of the proteins in eukaryotic cells are degraded by the proteasome in an ubiquitin-dependent manner. However, ubiquitin-independent protein degradation pathway by the 26S proteasome exists in the cells. Ornithine decarboxylase (ODC) is a well-known protein that is degraded by the 26S proteasome without ubiquitination. Degradation of ODC requires the protein, “antizyme (AZ),” that is induced by polyamine and binds to the ODC monomer to inhibit ODC activity and target it to the 26S proteasome for proteolytic degradation. Namely, AZ contributes the feedback regulation of intracellular polyamine level. ODC has been considered to be the only protein that AZ binds and accelerates its degradation. However, recently AZ-mediated proteasomal protein degradation will gradually increase. Most recently, we found that one of the antizyme families, AZ2, accelerates c-Myc degradation by the proteasome without ubiquitination. In this chapter, we introduce latest several ubiquitin-independent proteasomal degradation mediated by antizyme